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ANNUAL REPORT 2015

Aalto University School of Science Low Temperature Laboratory http://ltl.aalto.fi/

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Table of Contents PREFACE ...... 3 THE NEW GOALS AND RESTRUCTURING OF LTL ...... 4 PERSONNEL, LOCATIONS, FACILITIES ...... 5 SUB MK RESEARCH FACILITIES ...... 5 Rotating cryostat with 0.1 mK base temperature ...... 6 Stationary cryostat with 50 µK base temperature ...... 6 Dry Demagnetization cryostat with 160 µK base temperature ...... 7 SUB 0.1 K RESEARCH FACILITIES AND THERMOMETRY ...... 8 Liquid helium refrigerators ...... 8 Plastic dilution refrigerators ...... 8 Dry dilution refrigerators ...... 8 High-frequency measurements ...... 8 MICRO- AND NANOFABRICATION FACILITIES ...... 9 SAMPLE CHARACTERIZATION FACILITIES ...... 9 DEVELOPMENT OF INFRASTRUCTURE ...... 9 New liquefaction system ...... 9 Dry sub mK cryostat ...... 10 Dry cryostat for quantum nanomechanics ...... 11 FinCryo cryostat ...... 11 Rotating cryostat ...... 12 Wide-band measurement capabilities ...... 12 New cooling principles ...... 12 ACHIEVEMENTS ...... 13 SCIENTIFIC PUBLICATIONS IN INTERNATIONAL JOURNALS ...... 13 OTHER SCIENTIFIC PUBLICATIONS ...... 27 Book chapters ...... 27 Oral presentations, invited talks and posters ...... 27 Patents ...... 35 Other publications ...... 35 SPECIAL ASSIGNMENTS ...... 35 THESES ...... 35 Doctoral theses ...... 35 Masters theses ...... 36 Bachelors theses ...... 36 TECHNICAL SERVICES ...... 37 MACHINE SHOP ...... 37 CRYOGENIC LIQUIDS ...... 38 EQUIPMENT USE AND INFRASTRUCTURE FUNDING ...... 39 TEACHING ...... 40 VISITORS ...... 41 EXPERIMENTAL COWORKERS ...... 41 THEORETICAL COLLABORATION AND SUPPORT ...... 41 OTHER VISITORS ...... 42 PERSONNEL ...... 42 USERS AND COLLABORATORS OF LTL ...... 42

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PREFACE Low Temperature Laboratory (LTL), founded in 1965 by Academician Olli V. Lounasmaa, is one of the world centres in ultra-low-temperature physics and technology, and a state-of-the-art working environment for internationally recognized research fields, such as quantum technology and nano- electronics. Its leading position is based on vigorous in-house development and construction of uniquely designed refrigerators, leveraging visionary research with strong international collabora- tions. The year 2015 started a new era in the history of the laboratory. LTL was merged as one of the constituents in the Department of Applied Physics. In parallel, the collaboration as part of the national Otaniemi Research Infrastructure (RI) for Micro- and Nanotechnologies (OtaNano, http://www.otanano.fi) took another step forward, as the three large-scale RIs of Aalto University (Aalto); LTL, Micronova Nanofabrication Centre, and Nanomicroscopy Center, were internally integrated as one OtaNano of Aalto. In the spirit of these organizational changes, we decided to simplify the annual reporting compared to previous years. In the present report, meticulously assembled by Minna Günes and Alexander Savin, we focus on the development and achievements of the LTL infrastructure, while scientific progress is covered by the activity report of the national Centre of Excellence in Low Temperature Quantum Phenomena and Devices (CoE-LTQ). The majority of the users and developers of the LTL infrastructure are part of CoE-LTQ. I truly hope and believe, that the organizational changes we have been going through, provide a fertile ground for the development of our infrastructure and the research it nurtures. They force us to step back from our established positions and to reconsider our pathways to new achievements in science and technology. I am grateful to all members of our staff for patience and persistence at these times of organizational turbulence. Without a committed personnel, it would be impossible to maintain the prominent position in the research fields for which LTL has been so well known.

Pertti Hakonen

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THE NEW GOALS AND RESTRUCTURING OF LTL The pioneering ultra-low-temperature cryostat, which eventually became the trademark of LTL, was the first cryostat ever built to combine 3He/4He dilution refrigeration and adiabatic nuclear demag- netization of metallic copper in 1970. Today essentially all sub-mK cryostats are based on these same operating principles. Our first rotating nuclear refrigerator, a forerunner as well, became operational in early 1982, when 0.3 mK was reached in rotating superfluid 3He and the first quantized vortices were discovered in unconventional superfluid/superconductor pairing states. In 1983, antiferromag- netic spin order at 58 nK was observed in copper metal, using a cascade of two thermally series coupled, but operationally independent nuclear refrigeration units. A much improved version of this cryostat started working in 1998 and provided a platform for many types of experiments down to 50 µK electronic temperatures. These qualities, a measuring environment with the lowest base temperatures, the lowest heat leaks, and the lowest electrical interference in the sample region, are still today offered by the equipment in LTL. Our work has several times resulted in new world records of refrigeration. Since the year 2000, the lowest and “highest” nuclear spin temperatures are 100 pK and –750 pK on the positive and negative sides of the absolute zero, respectively. In 2005 LTL started to develop new cryogen free dilution refrigerators and a few years later a spin-off company BlueFors Cryogenics Ltd was estab- lished for their world-wide marketing. Today more than one third of the annual world production of such refrigerators is provided by BlueFors. LTL provides today a selection of 14 ultra-low temperature refrigerators with versatile capabilities for electronic transport and high-frequency measurement. Three of the refrigerators are equipped with nuclear demagnetization stages, providing sub-mK base temperatures, while the rest of the devices allow studies down to below 0.1 K. Much of the apparatus is home built and can be modified accord- ing to the specific research needs. LTL has a selection of facilities for the characterization and fabri- cation of micro- and nano-size samples, operated in a semi-clean-room environment. These facilities supplement the top-of-the-line nano-fabrication facilities of OtaNano in the sense that cleanliness requirements are not as strict, some non-standard operations are allowed, and even modifications of the equipment have been accommodated, to reach special research goals. Organizationally LTL is part of the national OtaNano research infrastructure, operated by Aalto University (Aalto) and a section of the government-run State Technical Research Centre of Finland (VTT) in Otaniemi. OtaNano was established in its present form in 2013 to bring together and to reinforce the benefits of the two large national RIs, LTL and Micronova, complemented with the Nanomicroscopy Center (NMC). It builds on longstanding experience and collaboration in RI development, and demonstrates the commitment and vision of its host organizations. OtaNano is included in the Finnish Strategy and Roadmap for Research Infrastructures (RI) 2014-2020 and it provides open access for academic and commercial users world-wide. LTL and OtaNano are participating in the current work plan of the European Microkelvin Platform (http://www.emplatfor.eu/), which is a consortium of 20 leading low temperature physics and technology partners in Europe. Very recently, a similar initiative has emerged in the field of quantum technology, with the goal to create a European Research Infrastructure for Quantum Engineering (ERIQE). Its first joint effort was to submit a proposal (H2020 proposal coordinated by AALTO) to the European Commission (EC) in March 2016. ERIQE focuses on transforming the most promising quantum technologies and devices to real products and applications, and the project relies on strong collaboration within national nodes (which in Finland are OtaNano and LTL). The OtaNano steering group is comprised of four members who come from the Aalto University (Dean Keijo Nikoskinen/Jyri Hämäläinen, Aalto School of Electrical Engineering, Dean Risto Nieminen, Aalto School of Science, Dean Janne Laine, Aalto School of Chemical Technology, Prof.

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Mauri Airila, Associate Vice President), one from VTT (Arto Maaninen, VP Operations, Knowledge- intensive Products and Services), and one from the University of Helsinki (Prof. Keijo Hämäläinen, Vice Rector). The chair appointed of the Steering group for the years 2014-2015 was the Dean of the School of Electrical Engineering, in 2015 first Prof. Keijo Nikoskinen and later Prof. Jyri Hämä- läinen. In addition there is an assisting group of expert members who come from Aalto (Prof. Jukka Pekola, Prof. Pertti Hakonen, Prof. Janne Ruokolainen, Dr. Mika Koskenvuori, Prof. Harri Lipsanen, Ms. Katariina Toivonen, and Dr. Minna Günes) and from VTT (Res. Manager Jyrki Kiihamäki). LTL’s leading position is based on vigorous in-house development and construction of sub-mK re- frigerators plus their utilization for different types of measurement. These measurements are conducted by in-house research groups, whilst supported by external research grants, as well as by external users pursuing their own research agenda. In addition, partnership with the new Aalto Centre for Quantum Engineering has demanded a thorough restructuring of the goals and requirements for the LTL infrastructure. Our long tradition in pioneering new research has led to multiple tech- nological and methodological innovations and to the emergence of spin-off companies. With their line of products, these companies have demonstrated the power and practicality of low-temperature refrigeration and instrumentation for today’s research needs.

PERSONNEL, LOCATIONS, FACILITIES As an Aalto research infrastructure LTL has an annual budget and permanent staff, most of whom have part-time responsibilities in maintaining LTL. The director is Prof. Pertti Hakonen. The strategic development and management is supported by the coordinator Dr. Minna Günes and our controller Ms. Katariina Toivonen. Technical operations and developments are maintained by staff scientists. Dr. Alexander Savin is responsible for the use and development of the RI, in particular for the ad- vanced research equipment in the facilities of the Nano building, while the Senior Scientist Doc. Matthias Meschke oversees the facilities at Micronova. Doc. Vladimir Eltsov holds a Senior Scien- tist’s position leading the research of the rotating cryostat (see Sec. 2.1). The LTL infrastructure is situated on the campus of the Aalto University in Otaniemi, in two different locations. The sub-mK facilities, the majority of the sub 0.1 K equipment, and the semi-clean-room with associated room-temperature characterization facilities are all located in the Nano building (Puu- miehenkuja 2, Espoo, Finland). The small 3He/4He dilution refrigerators and one dry dilution refri- gerator are located in the immediate vicinity of the major nanofabrication facilities of OtaNano in Micronova (Tietotie 3). The total floor space of the LTL facilities is close to 950 m2, including the semi-clean-room, 5 shielded rooms (80 m2) and six vibration isolated platforms (50 m2). The LTL equipment is upheld with the help of a centralized booking system, which sport fixed user fees, and is accessible on the LTL website.

SUB mK RESEARCH FACILITIES Two nuclear demagnetization cryostats, in particular, are the flagships for work at µK temperatures. One of them is designed for studies of superfluid 3He in rotation, with a base temperature below ~140 µK for a large superfluid sample of ~1 mole of 3He. The second is a stationary cryostat designed for cooling metallic samples down to a 50 µK base temperature, with long operating time at the base temperature in the presence of external heat leaks on the level of ~10 pW. In 2015, the construction of a new dry demagnetization cryostat was finished in collaboration with BlueFors Cryogenics. It now offers easy fully automated operation, with a base temperature of ~160 µK.

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ROTATING CRYOSTAT WITH 0.1 mK BASE TEMPERATURE Rotation is an essential component in the investigation of superfluids. Studying superfluids without access to rotation would be analogous to studying superconductors without the possibility to apply magnetic fields – many important features would be missed. In the experiments of the so-called ROTA group rotation is applied by rotating the whole cryostat on air bearings using a belt drive with a digitally controlled stepper motor. The cryostat is currently capable of rotation up to 3.5 rad/s while maintaining the heat leak to the sample below 25 pW and the sample temperature below 140 µK. These are world-wide the lowest values for 3He experiments in rotation. They have made it possible to explore the superfluid properties of the unconventional 3He condensate states in the zero-temper- ature limit during the past decade.

STATIONARY CRYOSTAT WITH 50 µK BASE TEMPERATURE The so-called µKI cryostat is designed for cooling macroscopic condensed matter specimens to the lowest possible temperatures. The achievable lowest temperature depends on the nature of the system under study: pure metals can be cooled to low µK temperatures, while dielectric materials decouple thermally from the cooling system already at mK temperatures. Impure metals, metal compounds and alloys can often be refrigerated only just below 1 mK due to limitations in thermal conductivity. For cooling helium fluids the practical limit is about 0.1 mK. Nuclear spin ensembles in suitably chosen and carefully prepared samples can be cooled to nK and even pK temperatures.

These record low temperatures are achieved in cryostats where several cooling stages are operated in series. A helium bath or a pulse tube refrigerator is needed to maintain a base temperature of 3-4 K for the cryostat. Next a helium liquid-to-gas evaporator can be used to get a second step downward in temperature to 1-1.5 K. The third major leap is obtained by appending these stages to a dilution refrigerator capable of producing 5-10 mK. The final series coupled refrigeration stage is based on nuclear demagnetization cooling. While the previous stages are usually operated to maintain their base temperature in a continuous fashion, the demagnetization stage is a single shot refrigerator - it must be recharged periodically using the dilution refrigerator for precooling.

The µKI cryostat is equipped with a massive nuclear stage with about 100 moles of pure copper in order to achieve long hold times at the lowest temperatures. When properly precooled over a weekend and slowly demagnetized over 10-12 hours, we maintain and control temperatures below 0.1 mK continuously for more than one month. This makes complicated experiments possible at these low temperatures, although care has to be exercised to reduce all possible heat leaks to a minimum. In general, experiments in such environment work at low signal and noise levels, to avoid self-heating of the sample. For these reasons sub-mK measurements require dedicated experienced personnel.

The main characteristics of the µKI cryostat can be summarized as follows:

- Nuclear stage base temperature: 50 µK (conduction electron temperature in metal samples), 100 pK (nuclear spin temperature in a series coupled second nuclear cooling stage) - Hold time of nuclear cooling stage: below 100 µK over 1 month (heat leak < 10 nW) - Cooldown time to base temperature: about 1 week from room temperature - Dilution refrigerator base temperature: 3 mK in continuous operation - Cooling power at 10 mK: 15 µW - He boil-off 25-30 liters/day in total, liquid He refill transfer required after 3-4 days

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The following kinds of experiments are currently available on solid samples or helium fluids:

- Low temperature NMR - Capacitance and susceptibility measurements - SQUID measurements - Liquid and solid helium samples (pure 4He, pure 3He, isotope mixtures) - Moderate magnetic fields or magnetic shielding can be applied to the sample space

DRY DEMAGNETIZATION CRYOSTAT WITH 160 µK BASE TEMPERATURE At present time cryogen-free refrigeration solutions are rapidly replacing refrigerators with liquid nitrogen and helium baths. In particular the commercially built dilution refrigerator with pulse-tube precooling has become a standard piece of equipment of physics laboratories around the world. These fully automated platforms offer cheaper easy operation, provide a base temperature below 10 mK, and can be equipped with large superconducting magnets for different types of experimental pur- poses. Combined with their flexibility with respect to design and construction, all these improvements have meant that the dilution refrigerator has found numerous new applications in microscopy, imaging, medicine, astronomy and satellite-based measurements, security, to name a few of the new areas.

However, many novel quantum experiments require a further reduction of temperature into the sub- mK regime. To meet this demand, the dry dilution refrigerator can be used to precool a nuclear cooling stage. This solution allows to make use of the advantages of modern dilution refrigeration in nuclear cooling, but because of the presence of the pulse-tube cooler, higher levels of vibration, heat leaks, and electrical interference come as a disadvantage.

Our dry demagnetization cryostat uses the BF-LD400 dry dilution refrigerator from BlueFors Cryogenics as its precooling platform. It has a two-stage pulse tube refrigerator with a base temperature of 3 K for the second stage. For the condensation of the 3He-4He mixture, the system employs a 2 bar compressor, which can be switched off during continuous circulation. The dilution unit cools down to 7 mK and provides 550 µW of cooling power at 100 mK. The cryostat is equipped with a 9 T magnet from American Magnetics which is thermally anchored to the 2nd stage of the pulse tube cooler.

In our BF-LD400, the still pumping line and the thermal contacts to the pulse tube cooling stages were mounted with damper systems, to decouple mechanically both the turbo pump and the pulse tube from the cryostat as much as possible. The central design principle was to eliminate relative vibrations between the high-field magnet and the nuclear refrigeration stage. These precautions were found to work well and a heat leak of Q = 4.4 nW to the nuclear stage was measured in a magnetic field of 35 mT. In a liquid 3He sample with immersed quartz tuning fork thermometry, the lowest temperature was determined to be 0.16 mK.

During the year 2015 the cryostat was equipped with two experimental sample containers which can be filled with liquid 3He or 4He and into which nano-mechanical devices can be immersed. One of the cells is embedded in the top flange of the copper nuclear coolant and includes a sintered silver powder heat exchanger with an effective surface area of 20 m2. The second container is moveable and can be mounted on the different cooling stages of the cryostat.

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SUB 0.1 K RESEARCH FACILITIES AND THERMOMETRY Altogether twelve dilution refrigerators form the backbone of LTL: • two dilution refrigerators with liquid He baths and 20 mK base temperature • four small 3He/4He dilution refrigerators with 20-50 mK base temperature • five dry dilution refrigerators with 10-20 mK base temperature and 24 hour cool down time from room temperature to 100 mK; one of them equipped with a 9T superconducting magnet • one dry dilution refrigerator with 30 mK base temperature for noise cross-correlation measurements at microwave frequencies

Their measurement capabilities range from simple DC electrical measurements to microwave meas- urements for noise, cross-correlations, and vibrations in NEMS resonators.

LIQUID HELIUM REFRIGERATORS LTL operates two traditional liquid-helium based dilution refrigerators with base temperatures close to 20 mK. Their cooldown time is approximately 8 hours. One of the refrigerators is a small machine with fast turn-around time and a liquid He consumption which is ¼ of the usual values, being around 6 liters/day in continuous operation. This setup allows the simultaneous cooldown of two different experiments. Both cryostats have been utilized for experiments involving Josephson junction qubits and mechanical NEMS resonators.

PLASTIC DILUTION REFRIGERATORS The four plastic dilution refrigerators (PDR) have been developed and assembled locally. These cryo- stats are characterized by ease of operation, flexibility of sample mounting, small He consumption (about 5 l/day), short cool down time of less than 5 hours, and a low level of electromagnetic noise. Their base temperature varies between 20 and 50 mK, depending on the particular sample stage design and wiring. These cryostats are used for sample testing and for DC or low frequency measure- ments of nano-electronic devices.

DRY DILUTION REFRIGERATORS Altogether six dry dilution refrigerators are available at LTL. All of these devices have slightly different base temperatures and cool down times, depending on the particular experimental setup. Their base temperatures vary between 10-20 mK and their cooldown times from room temperature between18-26 hours. For noise cross-correlation measurements at microwave frequencies, two of the cryostats are equipped with a 9 T superconducting magnet.

One of the dry dilution refrigerators (called FinCryo) is specifically designed for multi-user service. The cryostat is equipped with a variety of measurement equipment and wiring for both DC and RF measurements: 24+12 twisted pairs to the mixing chamber, 12 twisted pairs to the 4K plate, 14 filtered thermocoax DC lines to the sample holder, 8 RF coaxial lines (18 GHz) with different attenuation levels, and 2 RF output lines with cold RF amplifiers.

HIGH-FREQUENCY MEASUREMENTS LTL has extensive expertise in high-frequency measurements. The two liquid He based dilution cryostats, as well as two of the dry dilution refrigerators with enhanced vibration isolation, are installed in electromagnetically shielded rooms (manufactured by Euroshield from Al, with 100dB@12GHz). These cryostats are configured not only for DC measurements, but for low noise microwave measurements at 0.5-15 GHz with control and excitation cables up to 40 GHz. In the standard rf configuration each cryostat is equipped with a couple of 4K-cooled low-noise amplifiers

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– 9 – and 1-3 circulators are available for measurements with high-performance network analyzers and spectrum analyzers. Also Josephson junction based microwave amplifiers can be employed with nearly quantum limited performance characteristics.

MICRO- AND NANOFABRICATION FACILITIES The facilities for the fabrication of planar devices include a production line for e-beam lithography down to 60 nm resolution, operated in a semi-clean-room (100 m2) environment. These facilities are sufficient for basic manufacturing and testing of mesoscopic or nano-carbon devices and are recommended to users who need facilities for non-standard operations or with lower cleanliness requirements. These fabrication facilities also include equipment for heat treatment, critical point drying, and annealing, to guarantee the best quality of samples before cool down to mK temperatures.

SAMPLE CHARACTERIZATION FACILITIES Room temperature research facilities are available to characterize samples after fabrication. Their equipment includes a micro-Raman setup for local Raman measurements and an atomic force microscope (AFM) for surface enhanced Raman spectroscopy. In addition, there are setups to measure the susceptibility of novel materials at microwave frequencies. This equipment supplements the more versatile sample characterization facilities of OtaNano, by providing flexible and easy on- site access to the most common characterization measurements.

DEVELOPMENT OF INFRASTRUCTURE The rapid and significant increase of our cryo-liquid expenses during last decade has accelerated the development of new cryogenic equipment. This has had profound consequences on the LTL long- term strategy for equipment renewal and replacement. Another driver are the large savings in man power which can be gained in the maintenance of the equipment, owing to automation and increased flexibility in its use. The central principle in the current economic environment is to speed up the transition from cryo-liquid-based systems to user-friendly closed cycle ‘dry’ systems whose turn- around times are faster and whose usage might be shared by more research groups. Regarding the LTL dilution refrigerator arsenal, this renewal is carried out in cooperation with BlueFors Cryogenics Ltd. During 2015, one new dry dilution refrigerator was installed in LTL and two recent dry systems (multipurpose dilution refrigerator FinCryo and sub-mK demagnetization cryostat) were upgraded and modified for use allowing a wider range of applications. Nevertheless, there also exist refrigeration applications where a liquid helium bath is still the most convenient overall alternative. The rotating cryostat for superfluid 3He work is one example where continuous maintenance-free 4 K precooling is difficult to incorporate. Thus it was deemed useful to continue upgrading the existing machinery, to invest more work in upgrading its cooling power and in reducing heat leaks and electrical interference from external sources. Similarly, the low level of disturbance from external sources in the µKI cryostat reinforces its position as a test bed for the planned experiments with a novel cooling principle for refrigerating liquid 3He/4He mixtures to record low temperatures. This development work was continued also in 2015.

NEW LIQUEFACTION SYSTEM In spite of the on-going transition towards cryogen-free cooling, there is a continuous permanent need for a reliable and affordable source of liquid He (LHe). The consumption of LHe by these users is more or less uniformly distributed over the year, or perhaps at a slightly reduced rate in the summer months. In the wake of a sudden appreciable price increase of our commercial LHe deliveries, the

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– 10 – decision was finally made to purchase a distributed helium liquefaction system that is able to re- condense the evaporated and collected He gas. This decision was facilitated by the fact that LTL already has a well-developed infrastructure for maintaining and distributing LHe, consisting of a He gas collecting network and a storage system in Nanotalo plus a large arsenal of different sizes of transport dewars. The new investment includes two pulse-tube-cooler-based liquefiers (of model LHP60) and smaller re-liquefier (of model PT410), all three from Cryomech. The two independent liquefier units with purification systems were installed in Nanotalo, while the smaller PT410 re- liquefier was set up in Micronova. The liquefiers started operation in September 2015 and produced 9000 l of LHe during September-December 2015. The investment was mostly covered by the FIRI funding granted by the Academy of Finland.

Figure 1 Cryoliquid center in Nanotalo: Two identical PT based He liquefiers (left) with purifiers (right).

DRY SUB mK CRYOSTAT The dry demagnetization refrigerator with a base temperature below 200 µK was adapted for measurements on micromechanical systems which are immersed in liquid 3He or 4He. Two new experimental cells were prepared for this purpose and tested to yield the first results. In parallel with the development of these new experimental platforms, measurements on quantum surfaces were carried out in the main experimental cell which is incorporated in the top flange of the nuclear demagnetization stage. Waves on quantum liquid surfaces and crystallization waves in solids are usually excited electrostatically, by applying a high AC voltage to a capacitor placed on the cell wall. Too high voltages easily lead to intolerable heat release due to dielectric losses in the capacitor, which restricts the accessible temperatures to tens of mK. To enable experiments in the sub-mK regime, we developed a novel measurement scheme, where the sensor element is an oscillating quartz tuning fork placed in the vicinity of the surface to be probed. A change in the location of the surface or interface alters the velocity field around the oscillating fork, causing a change in the associated hydrodynamic mass and correspondingly in the resonance fre- quency of the fork. The sensitivity of this scheme is of the order of nanometers in the interface position, compared to tens of micrometers with traditional optical detection methods. The high sensitivity allows us to apply tiny drives to the excitation capacitor and thus temperatures well below 1 mK can be reached. By now crystallization wave resonances have been recorded down to a record low temperature of 0.38 mK.

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In these measurements the temperature is also determined with an oscillating quartz tuning fork which is immersed in the 3He superfluid. Its calibration is fixed by means of the onset of the ballistic regime in the propagation of thermal quasiparticle excitations. This method has been checked against simul- taneous measurements of the 3He melting pressure and was found to be accurate within 5%. In addition, a noise thermometer was installed on the top flange of the nuclear stage for monitoring the precooling. It was found to work correctly down to 0.4 mK and thus also provides overlap with the tuning fork thermometer in the regime of the calibration point. DRY CRYOSTAT FOR QUANTUM NANOMECHANICS A new BF-LD250 cryogen-free dilution refrigerator system from BlueFors was installed and reached operational status in April 2015. The cryostat is used for studies of micromechanical resonators. Such measurements can be seriously disturbed by vibrations from the pulse tube precooling system. In fact, we observed that samples mounted in the traditional way on a rigid metallic cold finger, which is fixed to the mixing chamber of the refrigerator, did not cool below about 50 mK because of the interference from the pulse tube cooler. The resonators also displayed spurious resonant excitation at certain frequencies, which stopped when the pulse tube compressor was switched off. To remove this interference, we explored the possibility of using a mechanical low-pass filtering for isolating the sample stage from the vibrations. The pulse tube noise consists mainly of bursts of about 5 kHz sound. Hence it should be straightforward to filter it out, although it is not known what frequency range is the most harmful. The sample holder was suspended with a 15 cm long copper braid which one would normally use for electrical grounding. In addition, the high-frequency cables to the sample were prepared from 40 cm long 0.86 mm diameter Nb coax, which was twisted into a spiral with 1 cm radius, as shown in Fig. 2. With these precautions no difference was detected whether the pulse tube cooler is switched on or not. Nor any amount of gentle knocking of the cryostat frame was found to excite the sample. Currently two suspension setups of this type have been installed in the cryostat (Fig 2).

Figure 2 A mechanical low-pass filter isolating the sample stage from the vibrations caused by the pulse tube precooling system.

FinCryo CRYOSTAT This cryostat is also originally a BlueFors BF-LD250 series dilution refrigerator, but it has been developed together with Bluefors Ltd. to incorporate a top-loading insert for changing samples at

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– 12 – mixing chamber temperatures while the cryostat is running. At present the insert is still undergoing testing at the company’s research facilities. The development of the cryostat in 2015 has concentrated on adding versatile and user friendly wiring for measurement purposes. By the end of 2015, the cryostat was equipped with 48 DC lines from which 12 are technical lines to the 4 K regime while the remaining 36 continue down to the mixing chamber. The sample stage for DC measurements contains high frequency filtering with 7 twisted pairs of thermocoax lines from which 4 pairs have additional low frequency RC-filtering. The cryostat is also equipped with eight rigid high-frequency (18 GHz) input lines with SMA connectors. Four of them are superconducting from the 4 K flange to the mixing chamber and four are resistive stainless steel lines. The input lines are thermalized with cryogenic attenuators at all temperature stages. Two high frequency output lines have NbTi coaxial cables running directly from the mixing chamber to the 4K flange where the low noise amplifiers are located. These are Low Noise Factory LNF-LNC1_12A and LNF-LNC4_8C and have bandwidths of 1-12 GHz and 4-8GHz with noise temperatures of 5.5 K and 2.1 K, respectively.

ROTATING CRYOSTAT In February 2015 the ROTA cryostat was refurbished with a new higher-capacity demagnetization magnet, replacing the previous 35-years-old defective superconducting magnet. This way a more effective working routine could be secured: the nuclear stage can be kept sufficiently cold to run superfluid 3He measurements in the zero temperature limit for almost one entire week, while the weekend is used for precooling. Furthermore, the higher fields after demagnetization provide extra stability for temperature control and hence enhance measurement quality.

WIDE-BAND MEASUREMENT CAPABILITIES Two Caltech CITLF3 cryogenic low-noise amplifiers were purchased in the autumn of 2015. They are based on cutting-edge SiGe technology and combine low noise temperature and a wide bandwidth of 10 MHz - 2 GHz (useable up to 5 GHz). The ability to perform experiments using relatively low wide-band frequencies is particularly useful for the users of LTL. Since Caltech (California Institute of Technology) is a research organization, one of the conditions tied to the purchase is a collaboration agreement which requires that Caltech will be acknowledged in all future research publications in which the amplifiers have been used.

NEW COOLIN PRINCIPLES When the thermal energy of a physical system is reduced, it will eventually collapse to its thermodynamic ground state, which sometimes may happen via a series of phase transitions. The investigation of phase-transition processes, is both theoretically and experimentally a prime source of new physics and provides strong motivation for pursuing ever lower temperatures. An example is the investigation of nuclear spin ensembles in pure metals, which undergo spontaneous nuclear magnetic ordering at nano- and picokelvin temperatures. The methods to achieve the required low temperatures were originally developed in LTL, using cascade adiabatic nuclear demagnetization. More recently, we have focused on attempts to cool mixtures of helium isotopes to record low tem- peratures. He mixtures consist of the bosonic superfluid 4He component and of fermionic 3He. At the currently lowest temperatures the 3He component is in a degenerate Fermi liquid state, but eventually at still lower temperatures it is expected to experience a superfluid transition to a Cooper paired BCS state. We are experimenting with a novel method to cool the mixture, by manipulating the system between liquid and solid state, while it is phase separated to a pure 3He phase and a dilute 3He/4He mixture phase, in which cooling can be produced in the liquid state by the process of dilution. This process is expected to bring about the lowest possible temperatures in the mixture phase and the transition to the long sought doubly superfluid state of intermixed Bose-Fermi superfluids. Promising

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– 13 – first results have been obtained, but more work is needed to overcome some remaining technical difficulties.

ACHIEVEMENTS LTL provides state-of-the-art measurement facilities for several Aalto internal and external research teams, and it is the core RI of the national Centre of Excellence in Low Temperature Quantum Phenomena and Devices. The achievements of LTL reflect the leading research directions of the users, strongly bound to the development of the RI.

SCIENTIFIC PUBLICATIONS IN INTERNATIONAL JOURNALS (with affiliation and/or acknowledgement to the Low Temperature Laboratory or its predecessor OVLL) 1. Arpaia, R., Ejrnaes, M., Parlato, L., Tafuri, F., Cristiano, R., Golubev, D., Sobolewski, R., Bauch, T., Lombardi, F., and Pepe, G.P., High-temperature superconducting nanowires for photon detection, Physica C 509, p. 16–21 (2015). (DOI)

The possible use of high-temperature superconductors (HTS) for realizing superconducting nanowire single-photon detectors is a challenging, but also promising, aim because of their ultrafast electron relaxation times and high operating temperatures. The state-of-the-art HTS nanowires with a 50-nm thickness and widths down to 130 nm have been fabricated and tested under a 1550-nm wavelength laser irradiation. Experimental results presenting both the amplitude and rise times of the photoresponse signals as a function of the normalized detector bias current, measured in a wide temperature range, are discussed. The presence of two distinct regimes in the photoresponse temperature dependence is clearly evidenced, indicating that there are two different response mechanisms responsible for the HTS photoresponse mechanisms.

2. Baghdadi, R., Arpaia, R., Charpentier, S., Golubev, D., Bauch, T., Lombardi, F., Fabricating Nanogaps in YBa2Cu3O7−δ for Hybrid Proximity-Based Josephson Junctions, Physical Review Applied 4, p. 014002 (2015). (DOI)

The advances of nanotechnologies applied to high-critical-temperature superconductors (HTSs) have recently given a huge boost to the field, opening new prospectives for their integration in hybrid devices. The feasibility of this research goes through the realization of HTS nanogaps with superconductive properties close to the as-grown bulk material at the nanoscale. Here we present a fabrication approach allowing the realization of YBa2Cu3O7−δ (YBCO) nanogaps with dimensions as small as 35 nm. To assess the quality of the nanogaps, we measure, before and after an ozone treatment, the current-voltage characteristics and the resistance versus temperature of YBCO nanowires with various widths and lengths, fabricated by using different lithographic processes. The analysis of the superconducting transition with a thermally activated vortex-entry model allows us to determine the maximum damage the nanowires undergo during the patterning which relates to the upper bound for the dimension of the nanogap. We find that the effective width of the nanogap is of the order of 100 nm at the superconducting transition temperature while retaining the geometrical value of about 35 nm at lower temperatures. The feasibility of the nanogaps for hybrid Josephson devices is demonstrated by bridging them with thin Au films. We detect a Josephson coupling up to 85 K with an almost ideal magnetic-field response of the Josephson current. These results pave the way for the realization of complex hybrid devices, where tiny HTS nanogaps can be instrumental to study the Josephson effect through barriers such as topological insulators or graphene.

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3. Borrelli, M., Koski, J.V., Maniscalco, S., and Pekola, J.P., Fluctuation relations for driven coupled classical two-level systems with incomplete measurements, Physical Review E 91, p. 012145 (2015). (DOI) We theoretically investigate fluctuation relations in a classical incomplete measurement process where only partial information is available. The scenario we consider consists of two coupled single-electron boxes where one or both devices can undergo a nonequilibrium transformation according to a chosen protocol. The entropy production of only one of the two boxes is recorded and fluctuation relations for this quantity are put to a test, showing strong modifications whose nature depends upon the specific case study.

4. Campisi, M., Pekola, J., and Fazio, R., Nonequilibrium fluctuations in quantum heat engines: Theory, example, and possible solid state experiments, New Journal of Physics 17, p. 035012 (2015). (DOI) We study stochastic energetic exchanges in quantum heat engines. Due to microreversibility, these obey a fluctuation relation, called the heat engine fluctuation relation, which implies the Carnot bound: no machine can have an efficiency greater than Carnot's efficiency. The stochastic thermodynamics of a quantum heat engine (including the joint statistics of heat and work and the statistics of efficiency) are illustrated by means of an optimal two-qubit heat engine, where each qubit is coupled to a thermal bath and a two-qubit gate determines energy exchanges between the two qubits. We discuss possible solid-state implementations with Cooper-pair boxes and flux qubits, quantum gate operations, and fast calorimetric on-chip measurements of single stochastic events.

5. Faivre, T., Golubev, D.S., and Pekola, J.P., Andreev current for low temperature thermometry, Applied Physics Letters, 106 p. 182602 (2015). (DOI) We demonstrate experimentally that disorder enhanced Andreev current in a tunnel junction between a normal metal and a superconductor provides a method to measure electronic temperature, specifically at temperatures below 200 mK when aluminum is used. This Andreev thermometer has some advantages over conventional quasiparticle thermometers: For instance, it does not conduct heat and its reading does not saturate until at lower temperatures. Another merit is that the responsivity is constant over a wide temperature range.

6. Ferrari, A.C., Bonaccorso, F., Fal'ko, V., Novoselov, K.S., Roche, S., Bøggild, P., Borini, S., Koppens, F.H.L., Palermo, V., Pugno, N., Garrido, J.A., Sordan, R., Bianco, A., Ballerini, L., Prato, M., Lidorikis, E., Kivioja, J., Marinelli, C., Ryhänen, T., Morpurgo, A., Coleman, J.N., Nicolosi, V., Colombo, L., Fert, A., Garcia-Hernandez, M., Bachtold, A., Schneider, G.F., Guinea, F., Dekker, C., Barbone, M., Sun, Z., Galiotis, C., Grigorenko, A.N., Konstantatos, G., Kis, A., Katsnelson, M., Vandersypen, L., Loiseau, A., Morandi, V., Neumaier, D., Treossi, E., Pellegrini, V., Polini, M., Tredicucci, A., Williams, G.M., Hee Hong, B., Ahn, J.-H., Kim, J.M., Zirath, H., van Wees, B.J., van der Zant, H., Occhipinti, L., Di Matteo, A., Kinloch, I.A., Seyller, T., Quesnel, E., Feng, X., Teo, K., Rupesinghe, N., Hakonen, P., Neil, S.R.T., Tannock, Q., Löfwanderaq, T., and Kinaret, J., Science and technology roadmap for graphene, related two- dimensional crystals, and hybrid systems, Nanoscale 7, p. 4598-4810 (2015). (DOI) (No official affiliation to LTL – Aalto author the director of LTL.)

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We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

7. Feshchenko, A.V., Casparis, L., Khaymovich, I.M., Maradan, D., Saira, O.-P., Palma, M., Meschke, M., Pekola, J.P., Zumbühl, D.M., Tunnel junction thermometry down to millikelvin temperatures, Physical Review Applied 4, p. 034001 (2015). (DOI) We present a simple on-chip electronic thermometer with the potential to operate down to 1 mK. It is based on transport through a single normal-metal–superconductor tunnel junction with rapidly widening leads. The current through the junction is determined by the temperature of the normal electrode that is efficiently thermalized to the phonon bath, and it is virtually insensitive to the temperature of the superconductor, even when the latter is relatively far from equilibrium. We demonstrate here the operation of the device down to 7 mK and present a systematic thermal analysis.

8. Gasparinetti, S., Viisanen, K. L., Saira, O.-P., Faivre, T., Arzeo, M., Meschke, M. and Pekola, J. P., Fast Electron Thermometry for Ultrasensitive Calorimetric Detection, Physical Review Applied 3, p. 014007 (2015). (DOI) We demonstrate radio-frequency thermometry on a micrometer-sized metallic island below 100 mK. Our device is based on a normal-metal–insulator–superconductor tunnel junction coupled to a resonator with transmission readout. In the first generation of the device, we achieve 90 �K/ Hz noise-equivalent temperature with 10 MHz bandwidth. We measure the thermal relaxation time of the electron gas in the island, which we find to be of the order of 100 µs. Such a calorimetric detector, upon optimization, can be seamlessly integrated into superconducting circuits, with immediate applications in quantum-thermodynamics experiments down to single quanta of energy.

9. Di Marco, A., Maisi, V.F., Hekking, F.W.J., Pekola, J.P., Effect of photon-assisted Andreev reflection in the accuracy of a SINIS turnstile, Physical Review B 92, p. 094514-12 (2015). (DOI) We consider a hybrid single-electron transistor constituted by a gate-controlled normal-metal island (N) connected to two voltage-biased superconducting leads (S) by means of two tunnel junctions (SINIS), operated as a turnstile. We show that the exchange of photons between this system and the high-temperature electromagnetic environment where it is embedded enhances Andreev reflection, thereby limiting the single-electron tunneling accuracy.

10. Giazotto, F., Heikkila, T.T., Bergeret, F. S., Very Large Thermophase in Ferromagnetic Josephson Junctions, Physical Review Letters 114, p. 067001/1-5 (2015). (DOI) The concept of thermophase refers to the appearance of a phase gradient inside a superconductor originating from the presence of an applied temperature bias across it. The resulting supercurrent flow may, in suitable conditions, fully counterbalance the temperature-bias-induced quasiparticle current therefore preventing the formation of any voltage drop, i.e., a thermovoltage, across the superconductor. Yet, the appearance of a thermophase is expected to occur in Josephson-coupled superconductors as well. Here, we theoretically investigate the thermoelectric response of a

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thermally biased Josephson junction based on a ferromagnetic insulator. In particular, we predict the occurrence of a very large thermophase that can reach π/2 across the contact for suitable temperatures and structure parameters; i.e., the quasiparticle thermal current can reach the critical current. Such a thermophase can be several orders of magnitude larger than that predicted to occur in conventional Josephson tunnel junctions. In order to assess experimentally the predicted very large thermophase, we propose a realistic setup realizable with state-of-the-art nanofabrication techniques and well-established materials, based on a superconducting quantum interference device. This effect could be of strong relevance in several low-temperature applications, for example, for revealing tiny temperature differences generated by coupling the electromagnetic radiation to one of the superconductors forming the junction.

11. Golubev, D.S., and Pekola, J.P., Statistics of heat exchange between two resistors, Physical Review B 92, p. 085412 (2015). (DOI) We study energy flow between two resistors coupled by an arbitrary linear and lossless electric circuit. We show that the fluctuations of energy transferred between the resistors are determined by random scattering of photons on an effective barrier with frequency dependent transmission probability τ(ω). We express the latter in terms of the circuit parameters. Our results are valid in both quantum and classical regimes and for nonequilibrium electron distribution functions in the resistors. Our theory is in good agreement with recent experiment performed in the classical regime.

12. Gunnarsson, D., Richardson-Bullock, J.S., Prest, M.J., Nguyen, H.Q., Timofeev, A.V., Shah, V.A., Whall, T.E., Parker, E.H.C., Leadley, D.R., Myronov, M., Prunnila, M., Interfacial Engineering of Semiconductor-Superconductor Junctions for High Performance Micro-Coolers, Scientific Reports 5, p. 1-10 (2015). (DOI) The control of electronic and thermal transport through material interfaces is crucial for numerous micro and nanoelectronics applications and quantum devices. Here we report on the engineering of the electro-thermal properties of semiconductor-superconductor (Sm-S) electronic cooler junctions by a nanoscale insulating tunnel barrier introduced between the Sm and S electrodes. Unexpectedly, such an interface barrier does not increase the junction resistance but strongly reduces the detrimental sub-gap leakage current. These features are key to achieving high cooling power tunnel junction refrigerators, and we demonstrate unparalleled performance in silicon- based Sm-S electron cooler devices with orders of magnitudes improvement in the cooling power in comparison to previous works. By adapting the junctions in strain-engineered silicon coolers we also demonstrate efficient electron temperature reduction from 300 mK to below 100 mK. Investigations on junctions with different interface quality indicate that the previously unexplained sub-gap leakage current is strongly influenced by the Sm-S interface states. These states often dictate the junction electrical resistance through the well-known Fermi level pinning effect and, therefore, superconductivity could be generally used to probe and optimize metal- semiconductor contact behaviour.

13. Häkkinen, P., Fay, A., Golubev, D., Lähteenmäki, P., and Hakonen, P., Wideband superconducting nanotube electrometer, Applied Physics Letters 107, p. 012601 (2015). (DOI) We have investigated the microwave response of nanotube Josephson junctions at 600–900 MHz at microwave powers corresponding to currents from 0 to 2 × IC in the junction. Compared with theoretical modeling, the response of the junctions corresponds well to the lumped element model of resistively and capacitively shunted junction. We demonstrate the operation of these superconducting FETs as charge detectors at high frequencies without any matching circuits. Gate-voltage-induced charge QG modifies the critical current IC, which changes the effective

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impedance of the junction under microwave irradiation. This change, dependent on the transfer characteristics dIC/dQG, modifies the reflected signal and it can be used for wide band electrometry. We measure a sensitivity of 3.1×10-5 e/ �� from a sample which has a maximum switching current of 2.6 nA.

14. Häkkinen, P., Isacsson, A., Savin, A., Sulkko, J., and Hakonen, P., Charge Sensitivity Enhancement via Mechanical Oscillation in Suspended Carbon Nanotube Devices, Nano Letters 15, p. 1667–1672 (2015). (DOI) Single electron transistors (SETs) fabricated from single-walled carbon nanotubes (SWNTs) can be operated as highly sensitive charge detectors reaching sensitivity levels comparable to metallic radio frequency SETs (rf-SETs). Here, we demonstrate how the charge sensitivity of the device can be improved by using the mechanical oscillations of a single-walled carbon nanotube quantum dot. To optimize the charge sensitivity δQ, we drive the mechanical resonator far into the nonlinear regime and bias it to an operating point where the mechanical third order nonlinearity is canceled out. This way we enhance δQ, from 6 µe/(Hz)1/2 for the static case to 0.97 µe/(Hz)1/2 at a probe frequency of ∼1.3 kHz.

15. Hänninen, R., Comment on "Reconnection of quantized vortex filaments and the Kolmogorov spectrum", Physical Review B 91, p. 106501 (2015). (DOI) In this Comment we would like to emphasize that in Phys. Rev. B 90, 104506 (2014) the calculated energy spectrum takes into account only the small interaction (cross) term and, additionally, this term is only calculated at the instant when the two vortices reconnect. The majority of the kinetic energy is contained in the self-energy term which has a characteristic spectrum of 1/k. If this, and the additional average over time, is taken into account the suggested Kolmogorov-type k−5/3 spectrum is likely not visible in the kinetic energy spectrum which contains both terms. Therefore, we find the suggestion misleading that the Kolmogorov spectrum in superfluids arises from the reconnection of vortices.

16. Hänninen, R., Kelvin waves from vortex reconnection in superfluid helium at low temperatures, Physical Review B 92, p. 184508 (2015). (DOI) We report on the analysis of the root mean square curvature as a function of the numerical resolution for a single reconnection of two quantized vortex rings in superfluid helium. We find a similar scaling relation as reported in the case of decaying thermal counterflow simulations by L. Kondaurova et al. There the scaling was related to the existence of a Kelvin-wave cascade which was suggested to support the L'vov-Nazarenko spectrum. Here we provide an alternative explanation that does not involve the Kelvin-wave cascade but is due to the sharp cusp generated by a reconnection event in a situation where the maximum curvature is limited by the computational resolution. We also suggest a method for identifying the Kelvin spectrum based on the decay of the rms curvature by mutual friction. Our vortex filament simulation calculations show that the spectrum of Kelvin waves after the reconnection is not simply n(k)∝ k−η with constant η. At large scales the spectrum seems to be close to the Vinen prediction with η=3 but becomes steeper at smaller scales.

17. Heikkilä, T.T. and Volovik, G.E., Nexus and Dirac lines in topological materials, New Journal of Physics 17, p. 093019 (2015). (DOI)

We consider the Z2 topology of the Dirac lines, i.e., lines of band contacts, on an example of graphite. Four lines – three with topological charge � = −1 each and one with � = −1 – merge together near the H-point and annihilate due to summation law1 + 1 + 1 − 1 = 0. The merging

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point is similar to the real-space nexus, an analog of the Dirac monopole at which the Z2 strings terminate.

18. Jannes, G. and Volovik, G.E., Emergent physics on Mach's principle and the rotating vacuum, JETP Letters 102, p. 82-88 (2015). (DOI) Mach’s principle applied to rotation can be correct if one takes into account the rotation of the quantum vacuum together with the Universe. Whether one can detect the rotation of the vacuum or not depends on its properties. If the vacuum is fully relativistic at all scales, Mach’s principle should work and one cannot distinguish the rotation: in the rotating Universe + vacuum, the co- rotating bucket will have a flat surface (not concave). However, if there are “quantum gravity” effects, which violate Lorentz invariance at high energy, then the rotation will become observable. This is demonstrated by analogy in condensed-matter systems, which consist of two subsystems: superfluid background (analog of vacuum) and “relativistic” excitations (analog of matter). For the low-energy (long-wavelength) observer the rotation of the vacuum is not observable. In the rotating frame, the “relativistic” quasiparticles feel the background as a Minkowski vacuum; i.e., they do not feel the rotation. Mach’s idea of the relativity of rotational motion does indeed work for them. However, rotation becomes observable by high-energy observers, who can see the quantum gravity effects.

19. Khan, R., Massel, F., And Heikkilä, T.T., Cross-Kerr nonlinearity in optomechanical systems, Physical Review A 91, p. 043822 (2015). (DOI) We consider the response of a nanomechanical resonator interacting with an electromagnetic cavity via a radiation-pressure coupling and a cross-Kerr coupling. Using a mean-field approach we solve the dynamics of the system and show the different corrections coming from the radiation pressure and the cross-Kerr effect on the usually considered linearized dynamics.

20. Khaymovich, I.M., Koski, J.V., Saira, O.-P., Kravtsov, V.E. and Pekola, J.P., Multifractality of random eigenfunctions and generalization of Jarzynski equality, Nature Communications 6, p. 7010 (2015). (DOI) Systems driven out of equilibrium experience large fluctuations of the dissipated work. The same is true for wavefunction amplitudes in disordered systems close to the Anderson localization transition. In both cases, the probability distribution function is given by the large-deviation ansatz. Here we exploit the analogy between the statistics of work dissipated in a driven single- electron box and that of random multifractal wavefunction amplitudes, and uncover new relations that generalize the Jarzynski equality. We checked the new relations theoretically using the rate equations for sequential tunnelling of electrons and experimentally by measuring the dissipated work in a driven single-electron box and found a remarkable correspondence. The results represent an important universal feature of the work statistics in systems out of equilibrium and help to understand the nature of the symmetry of multifractal exponents in the theory of Anderson localization.

21. Khaymovich, I.M., Maisi, V.F., Pekola, J.P., Mel'nikov, A.S., Charge-vortex interplay in a superconducting Coulomb-blockaded island, Physical Review B 92, p. 020501 (2015). (DOI) We show that charge transfer through a small superconducting (S) island of a single-electron transistor is strongly affected by vorticity. This interplay of charge and rotational degrees of

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freedom in a mesoscopic superconductor occurs through the effect of vorticity on the quantum mechanical spectrum of electron-hole excitations. The subgap quasiparticle levels in vortices can host an extra electron, thus suppressing the so-called parity effect in the S island. We propose to measure the collective dynamics of vorticity and electric charge via the charge pumping effect caused by alternating vortex entry and exit controlled by a periodic magnetic field.

22. Koski, J. V., Kutvonen, A. Khaymovich, I. M., Ala-Nissila, T., Pekola, J. P., On-Chip Maxwell’s Demon as an Information-Powered Refrigerator, Physical Review Letters 115, p. 260602 (2015). (DOI) We present an experimental realization of an autonomous Maxwell’s demon, which extracts microscopic information from a system and reduces its entropy by applying feedback. It is based on two capacitively coupled single-electron devices, both integrated on the same electronic circuit. This setup allows a detailed analysis of the thermodynamics of both the demon and the system as well as their mutual information exchange. The operation of the demon is directly observed as a temperature drop in the system. We also observe a simultaneous temperature rise in the demon arising from the thermodynamic cost of generating the mutual information.

23. Kravtsov, V.E., Khaymovich, I.M., Cuevas, E., Amini, M., A random matrix model with localization and ergodic transitions, New Journal of Physics 17, p. 122002 (2015). (DOI) Motivated by the problem of many-body localization and the recent numerical results for the level and eigenfunction statistics on the random regular graphs, a generalization of the Rosenzweig– Porter random matrix model is suggested that possesses two transitions. One of them is the Anderson localization transition from the localized to the extended states. The other one is the ergodic transition from the extended non-ergodic (multifractal) states to the extended ergodic states. We confirm the existence of both transitions by computing the two-level spectral correlation function, the spectrum of multifractality �(�) and the wave function overlap which consistently demonstrate these two transitions.

24. Kumar, M., Laitinen, A., Cox, D., and Hakonen, P.J., Ultra low 1/f noise in suspended bilayer graphene, Applied Physics Letters 106, p. 263505 (2015). (DOI)

We have studied 1/f noise power SI in suspended bilayer graphene devices. Around the Dirac point, we observe ultra low noise amplitude on the order of � ∗ �/� = 10 . The low frequency noise level is barely sensitive to intrinsic carrier density, but temperature and external doping are found to influence the noise power. In our current-annealed samples, the 1/f noise is dominated by resistance fluctuations at the contacts. Temperature dependence of the 1/f noise suggests the presence of trap states in the contact regions, with a nearly exponential distribution function displaying a characteristic energy of 0.12 eV. At 80 K, the noise displays an air pressure sensitivity that corresponds to ∼0.3 ppm gas detection sensitivity; this indicates the potential of suspended graphene as a platform for gas sensing applications.

25. Kutvonen, A., Ala-Nissila, T., and Pekola, J., Entropy production in a non-Markovian environment, Physical Review E 92, p. 012107 (2015). (DOI) Stochastic thermodynamics and the associated fluctuation relations provide the means to extend the fundamental laws of thermodynamics to small scales and systems out of equilibrium. The fluctuating thermodynamic variables are usually treated in the context of either isolated Hamiltonian evolution, or Markovian dynamics in open systems. However, there is no reason a priori why the Markovian approximation should be valid in driven systems under nonequilibrium

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conditions. In this work, we introduce an explicitly non-Markovian model of dynamics of an open system, where the correlations between the system and the environment drive a subset of the environment out of equilibrium. Such an environment gives rise to a new type of non-Markovian entropy production term. Such non-Markovian components must be taken into account in order to recover the fluctuation relations for entropy. As a concrete example, we explicitly derive such modified fluctuation relations for the case of an overheated single electron box.

26. Laitinen, A., Kumar, M., Oksanen, M., Plaçais, B., Virtanen, P., and Hakonen, P., Coupling between electrons and optical phonons in suspended bilayer graphene, Physical Review B 91, p. 121414(R) (2015). (DOI) Using electrical transport experiments and shot noise thermometry, we investigate electron- phonon heat transfer rate in a suspended bilayer graphene. Contrary to monolayer graphene with heat flow via three-body supercollision scattering, we find that regular electron–optical-phonon scattering in bilayer graphene provides the dominant scattering process at electron energies ≳ 0.15 eV. We determine the strength of these intrinsic heat flow processes of bilayer graphene and find good agreement with theoretical estimates when both zone edge and zone center optical phonons are taken into account.

27. Marthaler, M., Utsumi, Y., Golubev, D.S., Lasing in circuit quantum electrodynamics with strong noise, Physical Review B 91, p. 184515 (2015). (DOI) We study a model which can describe a superconducting single-electron transistor or a double quantum dot coupled to a transmission-line oscillator. In both cases the degree of freedom is given by a charged particle, which couples strongly to the electromagnetic environment or phonons. We consider the case where a lasing condition is established and study the dependence of the average photon number in the resonator on the spectral function of the electromagnetic environment. We focus on three important cases: a strongly coupled environment with a small cutoff frequency, a structured environment peaked at a specific frequency, and 1/f noise. We find that the electromagnetic environment can have a substantial impact on the photon creation. Resonance peaks are in general broadened and additional resonances can appear.

28. Nguyen, H.Q., Meschke, M. and Pekola, J.P., A robust platform cooled by superconducting electronic refrigerators, Applied Physics Letters 106, p. 012601 (2015). (DOI) A biased tunnel junction between a superconductor and a normal metal can cool the latter electrode. Based on a recently developed cooler with high power and superior performance, we have integrated it with a dielectric silicon nitride membrane, and cooled phonons from 305 mK down to 200 mK. Without perforation and covered under a thin alumina layer, the membrane is rigorously transformed into a cooling platform that is robust and versatile for multiple practical purposes. We discussed our results and possibilities to further improve the device.

29. Pekola, J.P., Towards quantum thermodynamics in electronic circuits, Nature Physics 11, p. 118- 123 (2015). (DOI) Electronic circuits operating at sub-kelvin temperatures are attractive candidates for studying classical and quantum thermodynamics: their temperature can be controlled and measured locally with exquisite precision, and they allow experiments with large statistical samples. The availability and rapid development of devices such as quantum dots, single-electron boxes and superconducting qubits only enhance their appeal. But although these systems provide fertile ground for studying heat transport, entropy production and work in the context of quantum mechanics, the field remains in its infancy experimentally. Here, we review some recent experiments on quantum heat transport, fluctuation relations and implementations of Maxwell’s

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demon, revealing the rich physics yet to be fully probed in these systems.

30. Pekola, J.P., Masuyama, Y., Nakamura, Y., Bergli, J., and Galperin, Y.M., Dephasing and dissipation in qubit thermodynamics, Physical Review E 91, p. 062109 (2015). (DOI) We analyze the stochastic evolution and dephasing of a qubit within the quantum jump approach. It allows one to treat individual realizations of inelastic processes, and in this way it provides solutions, for instance, to problems in quantum thermodynamics and distributions in statistical mechanics. We demonstrate that dephasing and relaxation of the qubit render the Jarzynski and Crooks fluctuation relations (FRs) of nonequilibrium thermodynamics intact. On the contrary, the standard two-measurement protocol, taking into account only the fluctuations of the internal energy U, leads to deviations in FRs under the same conditions. We relate the average � (where β is the inverse temperature) with the qubit's relaxation and dephasing rates in the weak dissipation limit and discuss this relationship for different mechanisms of decoherence.

31. Pepe, G.P., Parlato, L., Ejrnaes, M., Cristiano, R., Arpaia, R., Tafuri, F., Golubev, D., Bauch, T., Lombardi, F., Sobolewski, R., Y-Ba-Cu-O Nanostripes for Optical Photon Detection, SPIE - Photon Counting Applications I 9504, p. 950406/1-4 (2015). (DOI) Nanowires of Y-Ba-Cu-O, with the thickness of 50 nm and the width ranging from 90 nm to 500 nm have been successfully grown on lanthanum aluminate substrates for photon detection experiments. The nanowires were up to 10- µm long and formed a meander structure, covering the area of up to 30×10 µm2 with a fill factor of 50%. The samples were excited using optical laser pulses at a 1550 nm wavelength and resulting photoresponse signals were measured as a function of both temperature and normalized bias current. Presence of two, distinct regimes in the photoresponse temperature dependence has been clearly evidenced, suggesting different physical mechanisms of the signal formation. Presented experimental results shed new light on prospects of implementation of high-temperature superconducting oxides in photon detection and counting.

32. Pirkkalainen, J.-M., Cho, S.U., Massel, F., Tuorila, J., Heikkilä, T.T., Hakonen, P.J., and Sillanpää, M.A., Cavity optomechanics mediated by a quantum two-level system, Nature Communications 6, p. 6981 (2015). (DOI) Coupling electromagnetic waves in a cavity and mechanical vibrations via the radiation pressure of photons is a promising platform for investigations of quantum–mechanical properties of motion. A drawback is that the effect of one photon tends to be tiny, and hence one of the pressing challenges is to substantially increase the interaction strength. A novel scenario is to introduce into the setup a quantum two-level system (qubit), which, besides strengthening the coupling, allows for rich physics via strongly enhanced nonlinearities. Here we present a design of cavity optomechanics in the microwave frequency regime involving a Josephson junction qubit. We demonstrate boosting of the radiation–pressure interaction by six orders of magnitude, allowing to approach the strong coupling regime. We observe nonlinear phenomena at single-photon energies, such as an enhanced damping attributed to the qubit. This work opens up nonlinear cavity optomechanics as a plausible tool for the study of quantum properties of motion.

33. Pirkkalainen, J.-M., Damskägg, E., Brandt, M., Massel, F., and Sillanpää, M.A., Squeezing of Quantum Noise of Motion in a Micromechanical Resonator, Physical Review Letters 115, p. 243601 (2015). (DOI) A pair of conjugate observables, such as the quadrature amplitudes of harmonic motion, have fundamental fluctuations that are bound by the Heisenberg uncertainty relation. However, in a squeezed quantum state, fluctuations of a quantity can be reduced below the standard quantum

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limit, at the cost of increased fluctuations of the conjugate variable. Here we prepare a nearly macroscopic moving body, realized as a micromechanical resonator, in a squeezed quantum state. We obtain squeezing of one quadrature amplitude 1.1±0.4 dB below the standard quantum limit, thus achieving a long-standing goal of obtaining motional squeezing in a macroscopic object.

34. Probst, B., Virtanen, P., and Recher, P., Controlling spin polarization of a quantum dot via a helical edge state, Physical Review B 92, p. 045430 (2015). (DOI) We investigate a Zeeman-split quantum dot (QD) containing a single spin ½ weakly coupled to a helical Luttinger liquid (HLL) within a generalized master equation approach. The HLL induces a tunable magnetization direction on the QD controlled by an applied bias voltage when the quantization axes of the QD and the HLL are noncollinear. The backscattering conductance (BSC) in the HLL is finite and shows a resonance feature when the bias voltage equals the Zeeman energy in magnitude. The observed BSC asymmetry in bias voltage directly reflects the quantization axis of the HLL spin.

35. Reivinen, M., Salonen, E.-M., Todoshchenko, I., and Vaskelainen, V.P., Equilibrium Crystal Shapes by Virtual Work in 3D, Journal of Low Temperature Physics 180, p. 394-415 (2015). (DOI) A formulation on equilibrium crystal shape determination based on the principle of virtual work is presented. The treatment is an extension of the two-dimensional study presented in Reivinen et al. (J Low Temp Phys 170:75–90, 2013) to three dimensions. A corresponding discrete solution method is described and applied in four example cases. The first two examples deal with a “bubble” having constant surface energy density. In the latter case also gravity is included. In the third example, the surface energy depends on one direction angle with the γ-plot containing cusps where the second derivative of energy density with respect to the direction angle thus becomes infinite. The solution is an axisymmetric surface giving accurately a facet and two “facet-like” curved parts. In the fourth example case, the surface energy depends on two direction angles and the γ-plot contains again cusps. The discrete model can produce the corresponding facets with reasonable accuracy. The ability of the discrete formulation to detect automatically facets is considered as an important property.

36. Röntynen, J., and Ojanen, T., Topological Superconductivity and High Chern Numbers in 2D Ferromagnetic Shiba Lattices, Physical Review Letters 114, p. 236803 (2015). (DOI) Inspired by the recent experimental observation of topological superconductivity in ferromagnetic chains, we consider a dilute 2D lattice of magnetic atoms deposited on top of a superconducting surface with a Rashba spin-orbit coupling. We show that the studied system supports a generalization of � + �� superconductivity and that its topological phase diagram contains Chern numbers higher than ξ/a(≫1), where ξ is the superconducting coherence length and a is the distance between the magnetic atoms. The signatures of nontrivial topology can be observed by STM spectroscopy in finite-size islands.

37. Schmidt, R., Carusela, M.F., Pekola, J.P., Suomela, S., and Ankerhold, J., Work and heat for two-level systems in dissipative environments: Strong driving and non-Markovian dynamics, Physical Review B 91, p. 224303 (2015). (DOI) Work, moments of work, and heat flux are studied for the generic case of a strongly driven two- level system immersed in a bosonic heat bath in domains of parameter space where perturbative treatments fail. This includes in particular the interplay between non-Markovian dynamics and

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moderate to strong external driving. Exact data are compared with predictions from weak- coupling approaches. Further, the role of system-bath correlations in the initial thermal state and their impact on the heat flux are addressed. The relevance of these results for current experimental activities on solid-state devices is discussed.

38. Schoepe, W., Hänninen, R., and Niemetz, M., Breakdown of Potential Flow to Turbulence Around a Sphere Oscillating in Superfluid 4He Above the Critical Velocity, Journal of Low Temperature Physics 178, p. 383-391 (2015). (DOI) The onset of turbulent flow around an oscillating sphere in superfluid 4He is known to occur at a

critical velocity �~ �� where � is the circulation quantum and ω is the oscillation frequency. But it is also well known that initially in a first up-sweep of the oscillation amplitude, � can be considerably exceeded before the transition occurs, thus leading to a strong hysteresis in the ∗ velocity sweeps. The velocity amplitude � > � where the transition finally occurs is related to the density L0 of the remanent vortices in the superfluid. Moreover, at temperatures below ca. 0.5 K and in a small interval of velocity amplitudes between � and a velocity that is about 2 % larger, the flow pattern is found to be unstable, switching intermittently between potential flow and turbulence. From time series recorded at constant temperature and driving force, the distribution ∗ of the excess velocities Δ� = � − � is obtained and from that the failure rate. Below 0.1 K we also can determine the distribution of the lifetimes of the phases of potential flow. Finally, the frequency dependence of these results is discussed.

39. Silaev, M., Virtanen, P., Bergeret, F.S., and Heikkilä, T.T., Long-Range Spin Accumulation from Heat Injection in Mesoscopic Superconductors with Zeeman Splitting, Physical Review Letters 114, p. 167002 (2015). (DOI) We describe far-from-equilibrium nonlocal transport in a diffusive superconducting wire with a Zeeman splitting, taking into account different spin relaxation mechanisms. We demonstrate that due to the Zeeman splitting, an injection of current in a superconducting wire creates spin accumulation that can only relax via thermalization. This effect leads to a long-range spin accumulation detectable in the nonlocal signal. Our model gives a qualitative explanation and provides accurate fits of recent experimental results in terms of realistic parameters.

40. Silaev, M., Virtanen, P., Heikkilä, T.T., and Bergeret, F.S., Spin Hanle effect in mesoscopic superconductors, Physical Review B 91, p. 024506 (2015). (DOI) We present a theoretical study of spin transport in a superconducting mesoscopic spin valve under the action of a magnetic field misaligned with respect to the injected spin. We demonstrate that superconductivity can either strongly enhance or suppress the coherent spin rotation, depending on the type of spin relaxation mechanism being dominated either by spin-orbit coupling or spin- flip scattering at impurities. We also predict a subgap contribution to the nonlocal conductance in multiterminal superconducting hybrid structures which completely eliminates the effect of spin rotation at sufficiently low temperatures.

41. Silveri, M.P., Kumar, K.S., Tuorila, J., Li, J., Vepsäläinen, A., Thuneberg, E.V., and Paraoanu, G.S., Stückelberg interference in a superconducting qubit under periodic latching modulation, New Journal of Physics 17, p. 045058 (2015). (DOI) When the level separation of a qubit is modulated periodically across an avoided crossing, tunneling to the excited state – and consequently Landau–Zener–Stückelberg interference – can occur. The types of modulation studied so far correspond to a continuous change of the level

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separation. Here we study periodic latching modulation, in which the level separation is switched abruptly between two values and is kept constant otherwise. In this case, the conventional approach based on the asymptotic Landau–Zener formula for transition probabilities is not applicable. We develop a novel adiabatic-impulse model for the evolution of the system and derive the resonance conditions. Additionally, we derive analytical results based on the rotating- wave approximation (RWA). The adiabatic-impulse model and the RWA results are compared with those of a full numerical simulation. These theoretical predictions are tested in an experimental setup consisting of a transmon whose flux bias is modulated with a square wave form. A rich spectrum is observed, with distinctive features correspoding to two regimes: slow- modulation and fast-modulation. These experimental results are shown to be in very good agreement with the theoretical models. Also, differences with respect to the well-known case of sinusoidal modulation are discussed, both theoretically and experimentally.

42. Solinas, P., Gasparinetti, S., Golubev, D., and Giazotto, F., A Josephson radiation comb generator, Scientific Reports 5, p. 12260 (2015). (DOI) We propose the implementation of a Josephson Radiation Comb Generator (JRCG) based on a dc superconducting quantum interference device (SQUID) driven by an external magnetic field. When the magnetic flux crosses a diffraction node of the critical current interference pattern, the superconducting phase undergoes a jump of π and a voltage pulse is generated at the extremes of the SQUID. Under periodic drive this allows one to generate a sequence of sharp, evenly spaced voltage pulses. In the frequency domain, this corresponds to a comb-like structure similar to the one exploited in optics and metrology. With this device it is possible to generate up to several hundreds of harmonics of the driving frequency. For example, a chain of 50 identical high-critical- temperature SQUIDs driven at 1 GHz can deliver up to a 0.5 nW at 200 GHz. The availability of a fully solid-state radiation comb generator such as the JRCG, easily integrable on chip, may pave the way to a number of technological applications, from metrology to sub-millimeter wave generation.

43. Tan, Z.B., Cox, D., Nieminen, T., Lähteenmäki, P., Golubev, D., Lesovik, G.B., Hakonen, P.J., Cooper Pair Splitting by Means of Graphene Quantum Dots, Physical Review Letters 114, p. 096602 (2015). (DOI) A split Cooper pair is a natural source for entangled electrons which is a basic ingredient for quantum information in the solid state. We report an experiment on a superconductor-graphene double quantum dot (QD) system, in which we observe Cooper pair splitting (CPS) up to a CPS efficiency of ∼10%. With bias on both QDs, we are able to detect a positive conductance correlation across the two distinctly decoupled QDs. Furthermore, with bias only on one QD, CPS and elastic cotunneling can be distinguished by tuning the energy levels of the QDs to be asymmetric or symmetric with respect to the Fermi level in the superconductor.

44. Tomi, M., Isacsson, A., Oksanen, M., Lyashenko, D., Kaikkonen, J.-P., Tervakangas, S., Kolehmainen, J., and Hakonen, P.J., Buckled diamond-like carbon nanomechanical resonators, Nanoscale 7, p. 14747-14751 (2015). (DOI) We have developed capacitively-transduced nanomechanical resonators using sp2-rich diamond- like carbon (DLC) thin films as conducting membranes. The electrically conducting DLC films were grown by physical vapor deposition at a temperature of 500 °C. Characterizing the resonant response, we find a larger than expected frequency tuning that we attribute to the membrane being buckled upwards, away from the bottom electrode. The possibility of using buckled resonators to increase frequency tuning can be of advantage in rf applications such as tunable GHz filters and voltage-controlled oscillators.

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45. Viisanen, K.L., Suomela, S., Gasparinetti, S., Saira, O-P., Ankerhold, J., and Pekola, J.P., Incomplete measurement of work in a dissipative two level system, New Journal of Physics 17, p. 055014 (2015). (DOI) We discuss work performed on a quantum two-level system coupled to multiple thermal baths. To evaluate the work, a measurement of photon exchange between the system and the baths is envisioned. In a realistic scenario, some photons remain unrecorded as they are exchanged with baths that are not accessible to the measurement, and thus only partial information on work and heat is available. The incompleteness of the measurement leads to substantial deviations from standard fluctuation relations. We propose a recovery of these relations, based on including the mutual information given by the counting efficiency of the partial measurement. We further present the experimental status of a possible implementation of the proposed scheme, i.e. a calorimetric measurement of work, currently with nearly single-photon sensitivity.

46. Virtanen, P., and Giazotto, F., Fluctuation of heat current in Josephson junctions, AIP Advances 5, p. 027140 (2015). (DOI) We discuss the statistics of heat current between two superconductors at different temperatures connected by a generic weak link. As the electronic heat in superconductors is carried by Bogoliubov quasiparticles, the heat transport fluctuations follow the Levitov–Lesovik relation. We identify the energy-dependent quasiparticle transmission probabilities and discuss the resulting probability density and fluctuation relations of the heat current. We consider multichannel junctions, and find that heat transport in diffusive junctions is unique in that its statistics is independent of the phase difference between the superconductors.

47. Volovik, G.E. and Zubkov, M.A., Scalar excitation with Leggett frequency in 3He-B and the 125 GeV Higgs particle in top quark condensation models as pseudo-Goldstone bosons, Physical Review D 92, p. 055004 (2015). (DOI) We consider the scenario in which the light Higgs scalar boson appears as the pseudo-Goldstone boson. We discuss examples in both condensed matter and relativistic field theory. In 3He−B the symmetry breaking gives rise to four Nambu-Goldstone (NG) modes and 14 Higgs modes. At lower energy one of the four NG modes becomes the Higgs boson with a small mass. This is the mode measured in experiments with the longitudinal NMR, and the Higgs mass corresponds to the Leggett frequency � = ℏΩ. The formation of the Higgs mass is the result of the violation of the hidden spin-orbit symmetry at low energy. In this scenario the symmetry-breaking energy scale Δ (the gap in the fermionic spectrum) and the Higgs mass scale � are highly separated: � ≪ Δ. On the particle physics side we consider the model inspired by the models of Refs. Cheng et al. [J. High Energy Phys. 08 (014) 095] and Fukano et al. [Phys. Rev. D 90, 055009 (2014)]. At high energies the SU(3) symmetry is assumed which relates the left-handed top and bottom quarks to the additional fermion χL. This symmetry is softly broken at low energies. As a result the only CP-even Goldstone boson acquires a mass and may be considered as a candidate for the 125 GeV scalar boson. We consider a condensation pattern different from that typically used in top-seesaw models, where the condensate ⟨�LχR⟩ is off-diagonal. In our case the condensates are mostly diagonal. Unlike the work of Cheng et al. [J. High Energy Phys. 08 (014) 095] and Fukano et al. [Phys. Rev. D 90, 055009 (2014)], the explicit mass terms are absent and the soft breaking of SU(3) symmetry is given solely by the four-fermion terms. This reveals a complete analogy with 3He, where there is no explicit mass term and the spin-orbit interaction has the form of the four-fermion interaction.

48. Volovik, G.E., and Zubkov, M.A., Emergent geometry experienced by fermions in graphene in the presence of dislocations, Ann.Phys. (Leipzig) 356, p. 255–268 (2015). (DOI)

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In graphene in the presence of strain the elasticity theory metric naturally appears. However, this is not the one experienced by fermionic quasiparticles. Fermions propagate in curved space, whose metric is defined by expansion of the effective Hamiltonian near the topologically protected Fermi point. We discuss relation between both types of metric for different parametrizations of graphene surface. Next, we extend our consideration to the case, when the dislocations are present. We consider the situation, when the deformation is described by elasticity theory and calculate both torsion and emergent magnetic field carried by the dislocation. The dislocation carries singular torsion in addition to the quantized flux of emergent magnetic field. Both may be observed in the scattering of quasiparticles on the dislocation. Emergent magnetic field flux manifests itself in the Aharonov–Bohm effect while the torsion singularity results in Stodolsky effect.

49. Volovik, G.E., From Standard Model of particle physics to room-temperature superconductivity, Physica Scripta T164, p. 014014 (2015). (DOI) Topological media are gapped or gapless fermionic systems, whose properties are protected by topology, and thus are robust to deformations of the parameters of the system and generic. We discuss here the class of gapless topological media, which contains the quantum vacuum of the Standard Model in its symmetric phase, and also the condensed matter systems with zeroes in the fermionic energy spectrum, which form Fermi surfaces, Weyl and Dirac points, Dirac lines, Khodel–Shaginyan flat bands, etc. Some zeroes are topologically protected, being characterized by topological invariants, expressed in terms of Green's function. For the stability of the others the p-space topology must be accompanied by symmetry. Vacua with Weyl points serve as a source of effective relativistic quantum fields emerging at low energy: chiral fermions, effective gauge fields and tetrad gravity emerge together in the vicinity of a Weyl point. The accompanying effects, such as chiral anomaly, electroweak baryo-production and chiral vortical effect, are expressed via the symmetry protected p-space invariants. The gapless topological media exhibit the bulk-surface and bulk-vortex correspondence: which in particular may lead to the flat band on the surface of the system or in the core of topological defects. The materials with flat band in bulk, on the surface or within the dislocations have singular density of states, which crucially influences the critical temperature of the superconducting transition in such media. While in all the known superconductors the transition temperature is exponentially suppressed as a function of the pairing interaction, in the flat band the transition temperature is proportional to the pairing interaction, and thus can be essentially higher. So the p-space topology may give us the general recipe for the search or artificial fabrication of room-temperature superconductors.

50. Volovik, G.E., Orbital momentum of chiral superfluids and the spectral asymmetry of edge states (First online: 27 February 2015), JETP Letters 100, p. 742-745 (2015). (DOI) This is comment to preprint Y. Tada, W. Nie, and M. Oshikawa, Orbital Angular Momentum and Spectral Flow in Two Dimensional Chiral Superfluids, arXiv:1409.7459, where the effect of spectral flow along the edge states on the magnitude of the orbital angular momentum is discussed. The general conclusion of the preprint on the essential reduction of the angular momentum for the higher values of chirality, |ν| > 1, is confirmed. However, we show that if parity is violated, the reduction of the angular momentum takes place also for the p-wave superfluids with |ν| = 1.

51. Volovik, G.E., Superfluids in rotation: Landau-Lifshitz vortex sheets vs Onsager-Feynman vortices, (Sverkhtekuchie zhidkosti vo vrashchenii. Vikhrevye listy Landau—Lifshitsa i vikhri Onzagera—Feinmana), Uspekhi Fizicheskii Nauk 185, p. 970-979 (2015). (DOI) Landau's and Lifshitz's 1955 paper on vortex sheets in a rotating superfluid came out almost

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simultaneously with Feynman's paper on quantized vortices in superfluid 4He and was long considered incorrect. Forty years later, in what was a triumph for the authors' theory, experiments at the Olli Lounasmaa Low Temperature Laboratory (Otaniemi, Finland) detected vortex sheets in chiral superfluid 3He-A in a rotating cryostat, validating Landau's and Lifshitz's equation relating the vortex sheet separation and the angular velocity of rotation. This paper discusses vortex sheet configurations that have been or can be observed in superfluid 3He.

52. Westström, A., Pöyhönen, K., and Ojanen, T., Topological properties of helical Shiba chains with general impurity strength and hybridization, Physical Review B 91, p. 064502 (2015). (DOI) Recent experiments announced an observation of topological superconductivity and Majorana quasiparticles in Shiba chains, consisting of an array of magnetic atoms deposited on top of a superconductor. In this work we study helical Shiba chains and generalize the microscopic theory of subgap energy bands to a regime where the decoupled magnetic impurity energy and the hybridization of different impurity states can be significant compared to the superconducting gap of the host material. From exact solutions of the Bogoliubov-de Gennes equation we extract expressions for the topological phase boundaries for arbitrary values of the superconducting coherence length. The subgap spectral problem can be formulated as a nonlinear matrix eigenvalue problem from which we obtain an analytical solution for energy bands in the long coherence length limit. Physical consequences and departures from the previously obtained results in the deep dilute impurity limit are discussed in detail.

53. Zavjalov, V.V., Autti, S., Eltsov, V.B., Heikkinen, P.J., Measurements of anisotropic mass of magnons confined in a harmonic trap in superfluid 3He-B, JETP Letters 101, p. 802-807 (2015). (DOI) We pump magnons to a nearly harmonic magneto-textural trap in superfluid 3He-B. Using NMR spectroscopy of the energy levels in the trap, we have measured the anisotropic magnon mass and related values of the spin-wave velocities. From the measurements we extract values for the Fermi-liquid parameter � . 54. Zubkov, M.A. and Volovik, G.E., Emergent gravity in graphene, Journal of Physics: Conference Series 607, p. 012020 (2015). (DOI) We reconsider monolayer graphene in the presence of elastic deformations. It is described by the tight - binding model with varying hopping parameters. We demonstrate, that the fermionic quasiparticles propagate in the emergent 2D Weitzenbock geometry and in the presence of the emergent U(1) gauge field. Both emergent geometry and the gauge field are defined by the elastic deformation of graphene.

OTHER SCIENTIFIC PUBLICATIONS

BOOK CHAPTERS 1. Paraoanu, G.S., Book Title: The quantum vacuum, Boston Studies in the Philosophy and History of Science, 313, p. 181-198 (2015). (DOI)

ORAL PRESENTATIONS, INVITED TALKS AND POSTERS

Nearly 100 oral presentations, invited talks and posters in international and national scientific conferences and meetings were recorded by the groups that are users of LTL infrastructure and by those theorists that support the work at LTL. The reader is recommended to take into consideration that the

Annual Report 2015

– 28 – achievements in this category are based solely on notifications from our users and the true number is likely different, yet very difficult to report accurately.

Antunes Dos Santos, J. poster, Coupling macroscopic quartz resonators to nanoelectronics, Physics Days 2015, Helsinki, Finland (17. - 19.3.)

Autti, S. invited talk, Relaxation of Magnon BECs in Superfluid 3He via Light Higgs Bosons and Majorana Fermions, Quantum Fluids and Solids QFS2015, Niagara Falls, NY, USA (8. - 17.8.) poster, Observation of Half Quantum Vortices in Polar Phase of Superfluid 3He, Quantum Fluids and Solids QFS2015, Niagara Falls, NY, USA (8. - 17.8.) oral presentation, Magnon Bose-Einstein Condesates in Superfluid 3He, Centre of Excellence in Low Temperature Quantum Phenomena and Devices (LTQ) Workshop 2015, Naantali, Finland (11.9.)

Brandner, K. poster, Strong bounds on Onsager coefficients and efficiency for three terminal thermoelectric transport, LTQ SAB 2015, Naantali, Finland (10.9.)

Damskägg, E. poster, Squeezing of quantum noise of motion in a micromechanical resonator, LTQ SAB 2015, Naantali, Finland (10.9.)

Danilin, S. poster, Stimulated Raman adiabatic passage in a superconducting circuit, LTQ SAB 2015, Naantali, Finland (10.9.)

Eltsov, V. invited talk, Trapped Bose-Einstein condensates of magnons in superfluid 3He-B, Landau Days 2015, Chernogolovka, Russia (22. - 25.6.) invited talk, Observation of turbulence of inertial and Kelvin waves in superfluid 3He-B, International Quantum Fluids and Solids QFS2015, Niagara Falls, USA (9. - 15.8.) invited talk, Quantum turbulence at ultra-low temperatures, Workshop on Grand Challenges in Quantum Fluids and Solids, Buffalo, USA (7. - 9.8.) invited talk, Observation of turbulence of inertial and Kelvin waves in superfluid 3He-B, Workshop on interpretation of measurements in superfluid turbulence, Saclay, France (14. - 18.9.)

Feshchenko, A. invited talk, Experimental realization of a Coulomb blockade refrigerator, 2nd Quantum

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Thermodynamics Conference, Palma de Mallorca, Spain (20. - 24.4.)

Flindt, C. invited talk, Bistable photon emission in hybrid circuit-QED, Charge Transfer meets Circuit Quantum Electrodynamics, Dresden, Germany (29.6. - 3.7.)

Golubev, D. invited talk, Tunneling and relaxation of single quasiparticles in a normal-superconducting-normal single electron transistor, International Symposium on Nanophysics and Electronics, Nizhnij Novgorod, Russia (10. - 14.3.) invited talk, Statistics of heat exchange between two coupled resistors, seminar, Karlsruhe, Germany (19.1.) invited talk, Tunneling and relaxation of single quasiparticles in a normal-superconducting-normal single electron transistor, seminar, Osaka, Japan (2.2.) invited talk, Josephson junction based thermometer and its application in bolometry, seminar, Tsu, Japan (5.2.) oral presentation, Maxwell's Demon Based on a Single Qubit, Meeting within the framework of the European project INFERNOS, Oslo, Norway (27. - 28.11.)

Hakonen, P. invited talk, Dynamical Casimir photons with multifrequency interference effects, Quantum metamaterials 2015, Spetses, Greece (1. - 5.6.) oral presentation, Electron-phonon coupling in suspended mono- and bilayer graphene, Graphene Week 2015, Manchester, UK (22. - 26.6.) poster, Klein tunneling, contact doping, and pn-interfaces in gated suspended graphene, Graphene Week 2015, Manchester, UK (22. - 26.6.) poster, 1/f-Noise in Suspended Bilayer Graphene, GSS15, Graphene satellite symposium of NT15, Nagoya, Japan (28.6.) poster, Cooper Pair Splitting by means of Graphene Quantum Dots, GSS15, Graphene satellite symposium of NT15, Nagoya, Japan (28.6.) invited talk, Dynamical Casimir photons with interference effects: Microwave cavities with multi- frequency correlations, Charge Transfer meets Circuit Quantum Electrodynamics, Dresden, Germany (29.6. - 3.7.) lecture, Electrical and mechanical resonance modes in suspended graphene systems, Cambridge Graphene Center lecture series, Cambridge, UK (23.10.)

Annual Report 2015

– 30 – lecture, Coherence from vacuum fluctuations under double parametric pumping, Visit to Saclay, discussions on the coming FET Proactive call, Paris, France (17.11.) lecture, Coherence from vacuum fluctuations, Visit to MC2, Gothenburg, Sweden (16.12.) oral presentation, Modeling of metal to graphene contacts and electron-phonon coupling in suspended graphene bilayers, 3rd Graphene Flagship WP7 workshop, Delft, The Netherlands (30. - 31.3.) lecture, Graphene, Summer school on Nanostructured materials, Helsinki, Finland (24. - 28.8.) invited talk, Graphene and the Graphene Flagship, Graphene: The platform for future technology and the economy, Turku, Abo Akademi University, Finland (4.9.) invited comment, review on WP sensors in Graphene Flagship, Science and Technology Forum, Graphene Flagship, Paris, France (18. - 20.11.)

Heikkinen, P.J. poster, Probing properties of 3He-B with trapped magnons, International Symposium on Quantum Fluids and Solids, Niagara Falls, United States (9. - 15.8.)

Hietala, N. oral presentation, Wave excitations in adjacent vortex filaments, 15th European Turbulence Conference 2015 (ETC15), Delft, Netherlands (25. - 28.8.)

Häkkinen, P. poster, Exploiting nonlinear mechanics in charge sensing with carbon nanotubes, LTQ SAB 2015, Naantali, Finland (10.9.)

Kauppila, V. oral presentation, Flat band superconductivity, LTQ Workshop 2015, Naantali, Finland (11.9.)

Khaymovich, I. oral presentation, Analogy between work statistics in supercon-ducting single-electron box and multifractality of random eigenfunctions in disordered metal, XIX Symposium “Nanophysics & Nanoelectronics”, Nizhniy Novgorod, Russia (10. - 14.3.) invited plenary talk, Stochastic thermodynamics in single electron circuits, Frontiers of Quantum and Mesoscopic Thermodynamics, Prague, Czech Republic (26.7. - 1.8.) oral presentation, Charge pumping in a single electron transistor mediated by the parity – effect modulation, School-Conference “Ideas and Methods of Condensed Matter Physics” (XIV School- Confrerence for young researchers “Problems of Solid State and High-Pressure Physics”), Sochi region, Russia (11. - 20.9.) poster, Analogy between work statstics in superconducting singleelectron box and multifractality of random eigenfunctions in disordered metal, International Workshop on Non-equlibrium Dynamics

Annual Report 2015

– 31 – of Low-dimensional Electronic Systems, Leipzig, Germany (12. - 15.1.)

Koski, J. oral presentation, Maxwell's Demon, LTQ Workshop 2015, Naantali, Finland (11.9.) invited talk, Information to energy conversion with electronic Maxwell's demons, Third Conference on Quantum Thermodynamics, Porquerolles, France (11. - 17.10.)

Laitinen, A. poster, Electron-Phonon Coupling in Suspended Graphene, Graphene Study 2015, Kaprun, Austria (23. - 28.3.) poster, Ultra Low 1/f Noise in Suspended Bilayer Graphene, Graphene Week 2015, Manchester, UK (22. - 26.6.)

Lähteenmäki, P. poster, Coherence from vacuum fluctuations by double parametric pumping, LTQ SAB 2015, Naantali, Finland (10.9.)

Meschke, M. oral presentation, Nanofabrication of Coulomb Blockade Thermometers (CBT), DPG- Frühjahrstagung 2015, Berlin, 15.03.2015, Berlin, Germany (15. - 21.3.) oral presentation, Coulomb Blockade Thermometers (CBT) for InK=> status of High T CBT (up to 40 K and beyond), InK final meeting, London, UK (20.5.)

Mi, S. poster, Fake Majorana zero-modes in a trivial superconducting quantum dot, LTQ SAB 2015, Naantali, Finland (10.9.)

Mäkinen, J. oral presentation, Wave turbulence of a rotating array of quantized vortices in T → 0 limit, 15th European Turbulence Conference 2015 (ETC15), Delft, The Netherlands (25. - 28.8.) poster, Wave turbulence on vortices in 3He-B, Centre of Excellence in Low Temperature Quantum Phenomena and Devices SAB 2015, Naantali, Finland (10.9.) oral presentation, Vortex-core-bound fermions in 3He, Vortex IX, Rhodos, Greece (12. - 17.9.)

Nguyen, H. oral presentation, Electronic refrigeration using superconducting junctions in the sub kelvin regime, Quantum Fluids and Solids, Niagara Falls, NY, USA (8. - 17.8.)

Annual Report 2015

– 32 – poster, Manipulation of quasiparticle trapping and electron cooling in Meissner and vortex states of mesoscopic superconductors, Quantum Fluids and Solids, Niagara Falls, NY, USA (8. - 17.8.)

Nieminen, T. poster, Shot Noise Correlations in Graphene Box, Physics Days 2015, Helsinki, Finland (17. - 19.3.)

Ojanen, T. oral presentation, Topological superconductivity and high Chern numbers in 2D Shiba lattices, APS march meeting 2015, San Antonio, USA (2. - 6.3.) invited talk, Topological superconductivity and high Chern numbers in 2D Shiba lattices, Condensed matter physics seminar, University of St Andrews, St Andrews, Great Britain (17.2.) oral presentation, Topological superconductivity and high Chern numbers magnetic lattices, Physics of Interfaces and Layered Structures, Stockholm, Sweden (24.8. - 11.9.)

Oksanen, M. oral presentation, Graphene Optomechanics at Microwave Frequencies, Physics Days 2015, Helsinki, Finland (17. - 19.3.)

Padurariu, C. poster, Closing the proximity gap in three terminal superconducting junctions, LTQ SAB 2015, Naantali, Finland (10.9.)

Paraoanu, S. invited talk, Quantum simulations with superconducting circuits, Quantum metamaterials 2015, Spetses, Greece (1. - 5.6.) invited talk, Experimental realization of the STIRAP protocol in a superconducting qubit, Stimulated Raman adiabatic passage in physics, chemistry, and technology, Kaiserslautern, Germany (22. - 25.9.) invited talk, Modulation effects and quantum control in superconducting circuits, Seminar at Department of Physics, University of Palermo, Palermo, Italy (25.3.)

Pekola, J. invited talk, Experiments on non-equilibrium quasiparticles in superconducting aluminium: generation and relaxation, International Workshop on Non-equilibrium Dynamics of Low- dimensional Electronic Systems, Leipzig, Germany (12. - 15.1.) invited talk, Maxwell's Demon in a single-electron circuit, Yukawa International Seminar 2015 (YKIS2015), Kioto, Japan (17. - 19.8.) invited talk, Towards Quantum Thermodynamics in Electronic Circuits, International Symposium on Fluctuation and Structure out of Equilibrium 2015, Kioto, Japan (20. - 23.8.)

Annual Report 2015

– 33 – invited talk, Maxwell's Demon in a single-electron circuit, Community building activity, Göteborg, Sweden (24. - 26.8.) lecture, Les Houches session "Frontiers of Condensed Matter", Grenoble, France (30.8. - 4.12.) invited talk, Maxwell's demons with electrons in a circuit, New Horizons in Nonequilibrium Thermodynamics, Erice, Italy (26. - 30.10.)

Riekki, T. poster, Coupling between first sound and second sound in 3He - superfluid 4He mixtures, LTQ SAB 2015, Naantali, Finland (10.9.)

Röntynen, J. poster, Chiral topological superconductivity and high Chern numbers in 2D ferromagnetic Shiba lattices, LTQ SAB 2015, Naantali, Finland (10.9.)

Saira, O.-P. poster, Thermal phenomena in microwave-coupled NIS devices, LTQ SAB 2015, Naantali, Finland (10.9.)

Sillanpää, M. invited talk, Optomechanics at microwave frequencies: mechanical resonators coupled to microwave cavities and superconducting qubits, Charge Transfer meets Circuit Quantum Electrodynamics, Dresden, Germany (29.6. - 3.7.) invited talk, Squeezing of quantum noise of motion in a micromechanical resonator, Progress In Electromagnetics Research Symposium PIERS 2015 in Prague, Prague, Czech Republic (6. - 9.7.) invited talk, Squeezing of quantum noise of motion in a micromechanical resonator, NIM Conference on Resonator QED, Munich, Germany (3. - 7.8.) invited talk, Squeezing of quantum noise of motion in a micromechanical resonator, International Symposium on Nanoscale Transport and Technology (ISNTT2015), Tokyo, Japan (17. - 20.11.) invited talk, Squeezing of quantum noise of motion in a micromechanical resonator, Nano- and Quantum Physics Seminar, Basel, Switzerland (19.10.)

Singh, S. poster, Distribution of the time-integrated current in a single-electron transistor, European School On Nanosciences & Nanotechnologies (ESONN2015), Grenoble, France (23.8. - 12.9.)

Song, X. oral presentation, Graphene optomechanics at microwave frequencies, Diavolezza Workshop, Diavolezza, Switzerland (1. - 5.2.)

Tan, Z.

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Taupin, M. poster, Manipulation of quasiparticle trapping and electron cooling in Meissner and vortex states of mesoscopic superconductors, Conference M2S, Geneva, Switzerland (23. - 28.8.) oral presentation, Manipulation of quasiparticle trapping and electron cooling in Meissner and vortex states of a mesoscopic superconductor, LTQ Workshop 2015, Naantali, Finland (11.9.)

Todoshchenko, I. oral presentation, Oscillations on helium surfaces, LTQ Workshop 2015, Naantali, Finland (11.9.)

Vepsäläinen, A. poster, Stimulated Raman adiabatic passage using a three-level superconducting circuit, The 10th Principles and Applications of Control in Quantum Systems (PRACQSYS), Sydney, Australia (20. - 24.7.) oral presentation, Realization of a STIRAP protocol with a transmon, LTQ Workshop 2015, Naantali, Finland (11.9.)

Viisanen, K. poster, Fast electron thermometry towards ultra-sensitive single shot energy detection, LTQ SAB 2015, Naantali, Finland (10.9.)

Volovik, G. invited talk, Topology in Physics: From Standard Model of particle physics to room-T superconductivity, colloquium at Leipzig University, Leipzig, Germany (20.1.) invited talk, Flat bands and their superconductivity, Mini symposium for the dissertation of Dmitry Yudin, Uppsala, Sweden (12.2.) invited talk, Superfluids in rotation: Landau-Lifshitz vortex sheets vs Onsager-Feynman vortices, session of the division of general physics of Russian Academy, Moscow, Russia (26.3.) invited talk, Heavy Higgs modes and little Higgs sector in superfluid 3He, Landau Days 2015 conference, Chernogolovka, Russia (22. - 25.6.) invited talk, From Standard Model of particle physics to room-temperature superconductivity, Third International Conference on Quantum Technologies, Moscow, Russia (13. - 18.7.) invited talk, 3He topological materials, program: Physics of Interfaces and Layered Structures, Stockholm, Sweden (24.8. - 11.9.) invited talk, Flat band and room-T superconductivity, International Conference "Fundamental

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Problems of High-Temperature Superconductivity" (FPS'15), Malakhovka, Russia (5. - 9.10.) invited talk, Topological defects and anomalies in topological superfluids, Topology and Superconductivity, Grenoble, France (27.11.) invited talk, Topology in physics: From Standard Model of particle physics to room-T superconductivity, seminar at NORDITA, Stockholm, Sweden (11.2.) invited talk, Topology of Dirac lines and nexus in graphite, Landau Institute seminar, Chernogolovka, Russia (8.5.) invited talk, Observation of half-quantum vortices in superfluid 3He, seminar at Landau Institute, Chernogolovka, Russia (18.9.) invited talk, From condensed matter to high energy physics: Weyl fermions and Higgs bosons, 4th V.N. Gribov Memorial Workshop, Chernogolovka, Russia (17. - 20.6.)

Zavyalov, V.V. poster, Acoustic magnons in superfluid 2He-B, Quantum Fluids and Solids, QFS2015, Niagara Falls, NY, USA (8. - 17.8.)

PATENTS

Ermolov, V.A., Oksanen, M.A., Chalapat, K., and Paraoanu, G.S., Composite for providing electromagnetic shielding US8980137.

OTHER PUBLICATIONS

Ojanen, T., Revolution of topological materials, Pan European Networks: Science & Technology, 16, p. 64-65 (2015). (URL)

SPECIAL ASSIGNMENTS

Moisio, Antti, Test of fluctuation relations with a single-electron box. Instructor: Prof. Jukka Pekola.

Taavitsainen, Aapo, Designing and fabricating samples for studying the dynamical Casimir effect. Instructor: Prof. Jukka Pekola.

THESES

DOCTORAL THESES

Kumar, Karthikeyan Sampath, Quantum state control with a superconducting qubit. Supervisor: Prof. Jukka Pekola, Instructor: Doc. Sorin Paraoanu, Opponent: Dr. Olivier Buisson.

Järvinen, Päivi, Molecular self-assembly and local electronic properties of graphene probed by scanning tunnelling microscopy. Supervisor: Prof. Peter Liljeroth, Opponent: Prof. Brian LeRoy.

Faivre, Timothé, Low dissipation thermometry using superconducting tunnel junctions. Supervisor: Prof. Jukka Pekola, Opponent: Dr. Valery. V. Ryazanov.

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Manninen, Matti, Oscillations on helium surfaces. Supervisor: Prof. Pertti Hakonen, Instructor: Doc. Juha Tuoriniemi, Opponent: Dr. Peter Skyba.

Vesterinen, Visa, Microwave-coupled superconducting devices for sensing and quantum information processing. Supervisor: Prof. Pertti Hakonen, Opponent: Prof. Vitaly Shumeiko.

Sarkar, Jayanta, Microwave Experiments and Noise in Mesoscopic Devices. Supervisor: Prof. Pertti Hakonen, Opponent: Dr. Alexander Zorin.

MASTERS THESES

Nieminen, Teemu, High-sensitivity correlation spectrometer for shot noise measurements. Supervisor: Prof. Pertti Hakonen. Instructor: Mr. Pasi Lähteenmäki.

Räisänen, Ilmo, Development of a lumped element Josephson parametric amplifier for frequencies below 1 GHz. Supervisor: Prof. Jukka Pekola. Instructor: Dr. Olli-Pentti Saira.

Mäkinen, Jere, Wave turbulence in superfluid helium in the zero temperature limit. Supervisor: Prof. Pertti Hakonen. Instructor: Doc. Vladimir Eltsov.

Damskägg, Erno, Collective Dynamics of Multimode Circuit Optomechanical Systems. Supervisor: Prof. Mika Sillanpää.

BACHELORS THESES

Paananen, Topi, Fabrication of Suspended Graphene Josephson Junctions. Supervisor: Prof. Pertti Hakonen. Instructor: Mr. Mika Oksanen.

Soikkeli, Ari-Pekka, Measurements of shot noise in superconducting tunnel junction. Supervisor: Prof. Pertti Hakonen. Instructor: Mr. Pasi Lähteenmäki.

Taavitsainen, Aapo, Design, fabrication and characterization of transmon circuits. Supervisor: Prof. Jukka Pekola. Instructor: Doc. Sorin Paraoanu.

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TECHNICAL SERVICES

MACHINE SHOP Markku Korhonen, and Joel Salminen

PICO BECS NANO BRAIN NEW ENERGY uKI ROTA MEG CORE KVANTTI MOL.MAT. STM POSITRON LAB NANOSPIN NIMEG AALTO TMS NANOMAT NEMS SOFT MAT. AMI CENTER NANOMIC.CENTER DEMAG MECH. ENG.

Figure 3 Distribution of workshop usage per group.

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CRYOGENIC LIQUIDS Jari Isomäki and Joel Salminen

Liquid nitrogen The total amount of liquid nitrogen purchased in 2015 was 50 800 kg. A significant part of the liquid nitrogen was used for running the compressed nitrogen gas system in Nanotalo.

Liquid helium The amount of liquid helium purchased from AGA during the year 2015 was 25 988 l, while 11 229 l were produced onsite by re-liquefaction of the collected He gas. In total 31 602 l of liquid He were delivered to the research groups. The recycling He gas losses were 15 %.

The in-house pulse-tube-based liquefiers started operation in September 2015 and produced 8 969 l of liquid He during September - December 2015. This amount was enough for running all liquid He based installations in Nanotalo during that period. The re-liquefier in Micronova was running during all of the year 2015 and produced 2 260 l of liquid He. This amount covered 37% of the He consumption of the PICO group located in Micronova.

ROTA

NEMS

BRAIN

PICO

QCD

LT-STM

VTT

NANO

uKI

MICROSCOPY CENTER

DEMAG

Figure 4 Liquid helium consumption per group.

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EQUIPMENT USE AND INFRASTRUCTURE FUNDING

The total use of the LTL facilities in 2015 was 35 704 hours, of which 372,5 hours was used by external academic users, and 8 hours by companies.

The total funding of LTL in 2015 was approximately 1 470 000 €, of which nearly 550 000 € was covered by user fees. The rest of the funding was university basic funding.

Table 1: grants that have supported research in LTL during 2015 (non-exclusive list): Title of the grant Funding source Aalto doctoral training network in condensed matter Budgetary funding and materials physics (CMMP) Aalto School of Science Visiting Professor Funding Budgetary funding Approaching the thermal motion and quantum limit Academy of Finland: Academy with graphene nano-mechanical resonators Postdoctoral Researcher European Research Council: Consolidator Cavity quantum phonon dynamics (CAVITYQPD) grant Centre of Excellence in Low Temperature Quantum Academy of Finland: Centres of Phenomena and Devices (LTQ) Excellence (2012 – 2017) Development of Otaniemi Micro- and Academy of Finland: Research Nanotechnology Infrastructure (DOMAN) Infrastructure funding 2013 Development of Otaniemi Micro- and Nano- Academy of Finland: Research technology Infrastructure – phase II (DOMAN II) Infrastructure funding 2014 Electromechanical quantum coherent systems European Research Council: Starting grant (NEMSQED) Foundational Questions Institute grant FACE-OFF (FQXi) Fast and sensitive thermometry for low-temperature Academy of Finland: Academy Research nanoelectronic circuits Fellow Graphene Flagship European Union: FET Flagships European Association of National Metrology Institutes (EURAMET)/ Implementing the new Kelvin (InK) European Metrology Research Programme (EMRP): Individual research grant Information, fluctuations, and energy control in small European Union/ FP7: FET Open systems (INFERNOS) Interfacing Quantum Optical, Electrical, and European Union/ FP7: ICT programme Mechanical Systems (iQUOEMS) Academy of Finland: Bilateral research Low Temperature Physics mobility funding Mesoscopic heattronics: thermal and nonequilibrium European Research Council: Starting grant

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effects and fluctuations in nanoelectronics (HEATTRONICS) Nonequilibrium and quantum effects in topological Academy of Finland: Academy Research insulators and superconducting nanostructures Fellow StationQ Industry Academy of Finland: Programmable Tunable quantum metamaterials materials, OMA (2012-2016) program Quantum devices in topological matter: carbon European Research Council: Advanced nanotubes, graphene, and novel superfluids (QuDeT) grant Academy of Finland: Academy Quantum Entanglement in Graphene Postdoctoral Researcher Academy of Finland: Academy Quantum nanoelectronics Professorship funding European Union/ FP7: Marie-Curie Initial Quantum Nano-Electronics Training (Q-NET) Training Network for young researchers Quantum phenomena in novel topological insulator Academy of Finland: Academy Research and superconductor materials and theoretical Fellow nanoelectronics Quantum technology and materials for parallel Academy of Finland: ICT 2023 program sensor-actuator units in ICT

The number of active LTL users in 2015 was 76, of which 40 were external users.

TEACHING

Courses in low temperature and nanophysics

Special Course in Physics V: Experimental methods in Low Temperature Nanophysics (PHYS- E0541) Lecturers: Prof. Pertti Hakonen, Dr. Alexander Savin Special Course in Theoretical Physics V: Introduction to Open Quantum Systems (PHYS-E0542) Lecturers: Prof. Erik Aurell, Prof. Jukka Pekola, Dr. Paolo Muratore-Ginanneschi (University of Helsinki), Dr. Ivan Khaymovich Individual Studies in Physics: LTL Quantum Physics Seminar (PHYS-E0544) Coordinators: Doc. Vladimir Eltsov, Doc. Sorin Paraoanu Low Temperature Physics: Theory of Superconductivity (PHYS-E0551) Lecturer: Doc. Vladimir Eltsov Low Temperature Physics: Basics of Cryoengineering (PHYS-E0551) Lecturer: Doc. Juha Tuoriniemi

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VISITORS EXPERIMENTAL COWORKERS Buisson, Olivier, Dr., 2. – 5.12., Institut NÉEL, CNRS & UJF, Université Grenoble Alpes, France Chidambaram, Vivek, Mr., 25. – 27.11., University of Cambridge, UK Cleland, Andrew, Prof., 9. – 12.9. University of Chicago, USA Connolly, Malcolm, Dr., 25. – 27.11., University of Cambridge, UK Dmitriev, Vladimir, Prof., 9. – 19.6., Kapitza Institute, Russia Dumur, Étienne, Dr., 8. – 10.11., Institut NÉEL, France George, Richard, Dr., 20.9. – 3.10., Lancaster University, UK Halperin, William, Prof., 9. – 12.9., Northwestern University, IL, USA Lebedev, Mikhail, Dr., 20. – 24.4. Institute of Solid State Physics, RAS, Russi Marcus, Charles, Prof., 22. – 23.4., Niels Bohr Institute, Copenhagen University, Denmark Nakamura, Shuji, Dr., 11.11.2014 – 2.5.2015, National Metrology Institute, Japan Nguyen, Hung, Dr., 15.1. – 14.5., 28.9.2015 – 10.1.2016, Vietnam National University, Vietnam Pudalov, Vladimir, Dr., 9. – 11.12., P.N. Lebedev Institute, RAS, Russia Ritort, Felix, Dr., 24. – 25.9., University of Barcelona, Spain Ryazanov, Valery, Dr., 19. – 23.11., RAS, Russia Senior, Jorden, Mr., 11. – 14.3., Lancaster University, UK Simonsen, Anders, Mr., 12. – 13.2., 30.8. – 30.11., Niels Bohr Institute, Copenhagen University, Denmark Skyba, Peter, Dr., 27. – 29.8., Slovak Academy of Sciences, Slovak Republic Wiesner, Maciej, Prof., 30.8. – 30.10., Adam Mickiewicz University, Poland Ying, Liu, Mr., 22.-31.12., National University of Defense Technology, China Yudin, Alexey, Dr., 7.4. – 7.5., P.L. Kapitza Institute for Physical Problems, RAS, Russia Zgirski, Maciej, Prof., 6. – 11.7., Institute of Physics, Polish Academy of Sciences, Poland

THEORETICAL COLLABORATION AND SUPPORT Akashdeep, Karma, Ph.D., 23. – 25.2., Delft University of Technology, The Netherlands Braggio, Alessandro, Prof., 7. – 11.1., University of Genoa, Italy Brandner, Kay, Dr., 11. – 13.3., University of Stuttgart, Germany Catelani, Gianluigi, Dr., 20. – 23.12., Institute for Theoretical Nanoelectronics, Peter Grünberg Institute, Germany Dasenbrook, David, Mr., 7.4. – 7.6., University of Geneva, Switzerland Falko, Vladimir, Prof., 4. – 5.2., Lancaster University, UK Fazio, Rosario, Prof., 31.3. – 2.4., Scuola Normale Superiore, Italy Ford, Ian, Prof., 22.1., University College London, UK Galperine, Yuri, Prof., 18. – 25.1., University of Oslo, Norway Grifoni, Milena, Prof., 9. – 12.9., University of Regensburg, Germany Ioselevich, Alexey, Prof., 19. – 31.1., Landau Institute for Theoretical Physics, RAS, Russia Isacsson, Andreas, Prof., 22. – 27.3., Chalmers University of Technology, Sweden Jonson, Mats, Prof., 15. – 17.10., University of Gothenburg, Sweden Kravtsov, Vladimir, Prof., 15. – 27.3., ICTP, Italy L’vov, Victor, Prof., 13. – 22.1., Weizmann Institute of Science, Israel Lesovik, Gordey, Dr. Sci. ,15. – 25.4. Landau Institute for Theoretical Physics, RAS, Russia Makhlin, Yuriy, Prof., 30.11. – 4.12., Landau Institute for Theoretical Physics, RAS, Russia Maniscalco, Sabrina, Prof., 22. – 23.4., University of Turku, Finland Mel’nikov, Alexander, Prof., 21.3. – 22.4., 15.11. – 12.12., Institute for Physics od Microstructures, RAS, Russia

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Mi, Shuo, Dr., 24. – 28.3., Lorentz Institute for theoretical physics, University of Leiden, The Netherlands Nagaev, Kirill, Prof., 18. – 22.5., Kotelnikov Institute of Radioengineering and Electronics, Russia Padurariu, Ciprian, Dr., 16. – 18.3., Institut NÉEL, France Ponomarenko, Vadim, Prof., 26. – 30.8., University of Minho, Portugal Samuelsson, Peter, Prof., 4. – 5.8., Lund University, Sweden Sanchez, Rafael, Dr., 27. – 30.9., Instituto de Ciencia de Materiales de Madrid, Spain Schön, Gerd, Prof., 9. – 12.9., Karlsruhe Institute of Technology, Germany Shumeiko, Vitaly, Prof., 17. – 19.6., Chalmers University of Technology, Sweden Solinas, Paolo, Dr., 9. – 15.8., SPIN-CNR, Italy Ueda, Akiko, Prof., 15. – 17.3., University of Tsukuba, Japan Utsumi, Yasuhiro, Assoc. Prof., 18. – 26.7., Mie University, Japan

OTHER VISITORS Williams, Colin, P., Mr., 22. – 23.4., D-Wave Systems Inc., Canada

PERSONNEL The personnel listed below was responsible for the development and maintenance of the LTL research infrastructure in 2015. In addition, a pool of post-doctoral and graduate student researchers had the responsibility to maintain certain parts of the equipment arsenal.

Pertti Hakonen, Prof., scientific director Vladimir Eltsov, Doc., senior scientist Minna Günes, Ph.D., coordinator Jari Isomäki, technician Markku Korhonen, technician Matthias Meschke, Doc., senior scientist Joel Salminen, technician Alexander Savin, Ph.D., staff scientist Katariina Toivonen, controller

USERS AND COLLABORATORS OF LTL

The persons listed below are authors in scientific publications and theses where LTL is acknowledged or indicated in the byline, or where data measured at LTL was used in 2015, and/or they are members of research teams collecting data or carrying out research on data measured at LTL. The total number of users and collaborators of LTL in 2015 was 113, of which nearly 60 % were international users. Abbreviations:

CHEM = Department of Chemistry, School of Chemical Technology, Aalto University, Finland FOREST = Department of Forest Products Technology, School of Chemical Technology, Aalto University, Finland MATER = Department of Materials Science and Engineering, School of Chemical Technology, Aalto University, Finland MICRO = Department of Micro- and Nanosciences, School of Electrical Engineering, Aalto University, Finland PHYS = Department of Applied Physics, School of Science, Aalto University, Finland

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Markus Aapro, PHYS, NanoMaterials group Mariko Ago, FOREST, Bio-based Colloids and Materials group Saima Ali, FOREST, Wood Material Technology group Jorge Antunes Dos Santos, PHYS, NEMS group Samuli Autti, PHYS, ROTA group Kaustuv Banerjee, PHYS, STM group Abhijit Bera, PHYS, NanoSpin group Maryam Borghei, FOREST, Bio-based Colloids and Materials group Shirong Bu, PHYS, KVANTTI group/ University of Electronic Science and Technology of China Matthias Brandt, PHYS, NEMS group Arianna Casiraghi, PHYS, NanoSpin group Binbin Chen, PHYS, NanoSpin group Vivek Chidambaram, University of Cambridge, UK Malcolm Connolly, University of Cambridge, UK Daniel Cox, PHYS, NANO group Erno Damskägg, PHYS, NEMS group Sergey Danilin, PHYS, KVANTTI group Vladimir Dmitriev, Kapitza Institute for Physical Problems, RAS, Russia Vladimir Eltsov, PHYS, ROTA group Timothé Faivre, PHYS, PICO group Anna Feshchenko, PHYS, PICO group Kévin Franke, PHYS, NanoSpin group Simone Gasparinetti, PHYS, PICO group Richard George, Lancaster University, UK Mélany Gouëllo, VTT, Finland Henrika Granbohm, MATER, Advanced and Functional Materials group Miika Haataja, PHYS, µKI group Pertti Hakonen, PHYS, NANO group Maoshuai He, PHYS, NanoMaterials group Petri Heikkinen, PHYS, ROTA group Niklas Hietala, PHYS, ROTA group Aqeel Hussain, PHYS, NanoMaterials group Pasi Häkkinen, PHYS, NANO group Vsevolod Iakovlev, PHYS, NanoMaterials group Jesper Ilves, PHYS, NEMS group Ajai Iyer, MATER, PCS group Robab Najafi Jabdaraghi, PHYS, PICO group Susoma Jannatul, MICRO, Nanotechnology group Antti Jokiluoma, PHYS, PICO group Jukka-Pekka Kaikkonen, PHYS, NANO group Timo Kamppinen, PHYS, ROTA group Mikael Kervinen, PHYS, NEMS group Jonne Koski, PHYS, PICO group Janne Kotilahti, PHYS, NANO group Matti Krusius, PHYS, ROTA group Manohar Kumar, PHYS, NANO group Patrik Laiho, PHYS, NanoMaterials group Antti Laitinen, PHYS, NANO group Yongping Liao, PHYS, NanoMaterials group Markus Lilja, PHYS, NANO group

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Diego López Gonzáles, PHYS, NanoSpin group Victor L’vov, Weizmann Institute of Science, Rehovot, Israel Pasi Lähteenmäki, PHYS, NANO group Elsa Mannila, PHYS, PICO group Matti Manninen, PHYS, µKI group Matthias Meschke, PHYS, PICO group Bulota Mindaugas, FOREST, Wood Material Technology group Antti Moisio, PHYS, PICO group Jesse Muhojoki, PHYS, PICO group Kimmo Mustonen, PHYS, NanoMaterials group Jere Mäkinen, PHYS, ROTA group Shuji Nakamura, National Metrology Institute, Japan Irina Nefedova, Department of Radio Science and Engineering, School of Electrical Engineering, Aalto, Finland Nguyen Ngan, PHYS, NanoMaterials group Hung Nguyen, PHYS, PICO group and Niels Bohr Institute, University of Copenhagen, Denmark Teemu Nieminen, PHYS, NANO group Magdalena Nosek, CHEM, Physical Chemistry group Caspar Ockeloen, PHYS, NEMS group Mika Oksanen, PHYS, NANO group Topi Paananen, PHYS, NANO group Sorin Paraoanu, PHYS, KVANTTI group Nicolas Paillet, PHYS, PICO group Joonas Peltonen, PHYS, PICO group Juha-Matti Pirkkalainen, PHYS, NEMS group Ilona Pohjavirta, PHYS, STM group Taneli Prittinen, PHYS, ROTA group Vera Protopova, MATER, Microfabrication group Antti Ranni, PHYS, µKI group Tapio Riekki, PHYS, µKI group Ilmo Räisänen, PHYS, PICO group Qihang Qin, PHYS, NanoSpin group Sakari Saarenpää, PHYS, NEMS group Olli-Pentti Saira, PHYS, PICO group Karthikeyan Sampath Kumar, PHYS, KVANTTI group Alexander Savin, PHYS, LTL Alexander Sebedash, PHYS, µKI group Jorden Senior, PHYS, PICO group Mika Sillanpää, PHYS, NEMS group Shilpi Singh, PHYS, PICO group Anders Simonsen, Niels Bohr Institute, Copenhagen University, Denmark Peter Skyba, Slovak Academy of Sciences, Slovakia Vivek Kumar Singh, FOREST, Wood Material Technology group Ari-Pekka Soikkeli, PHYS, NANO group Xuefeng Song, PHYS, NANO group Jelle Stumpel, PHYS, MolMat group Jaakko Sulkko, PHYS, NEMS group Zhenbing Tan, PHYS, NANO group Mathieu Taupin, PHYS, PICO group Mohammad Tavakkoli, CHEM, Physical Chemistry group

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Ying Tian, PHYS, NanoMaterials group Igor Todoshchenko, PHYS, µKI group Matti Tomi, PHYS, NANO group Juha Tuoriniemi, PHYS, µKI group Antti Vepsäläinen, PHYS, KVANTTI group Klaara Viisanen, PHYS, PICO group Libin Wang, PHYS, PICO group Maciej Wiesner, Adam Mickiewicz University, Poland He Yang, MICRO, Photonics group Liu Ying, National University of Defense Technology, China Alexey Yudin, Kapitza Institute for Physical Problems, RAS, Russia Vladislav Zavyalov, PHYS, ROTA group Maciej Zgirski, Institute of Physics, Polish Academy of Sciences, Poland

Annual Report 2015