DOCSLIB.ORG

Measurement-Enhanced Determination of BEC Phase Transitions

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Measurement-Enhanced Determination of BEC Phase Transitions View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Sussex Research Online Journal of Physics B: Atomic, Molecular and Optical Physics PAPER Related content - Sub-atom shot noise Faraday imaging of Measurement-enhanced determination of BEC ultracold atom clouds M A Kristensen, M Gajdacz, P L Pedersen phase transitions et al. - Two-terminal transport measurements with cold atoms To cite this article: Mark G Bason et al 2018 J. Phys. B: At. Mol. Opt. Phys. 51 175301 Sebastian Krinner, Tilman Esslinger and Jean-Philippe Brantut - PhD Tutorial Axel Griesmaier View the article online for updates and enhancements. This content was downloaded from IP address 139.184.246.34 on 08/08/2018 at 12:10 Journal of Physics B: Atomic, Molecular and Optical Physics J. Phys. B: At. Mol. Opt. Phys. 51 (2018) 175301 (9pp) https://doi.org/10.1088/1361-6455/aad447 Measurement-enhanced determination of BEC phase transitions Mark G Bason1,3 , Robert Heck3 , Mario Napolitano, Ottó Elíasson , Romain Müller, Aske Thorsen, Wen-Zhuo Zhang2, Jan J Arlt and Jacob F Sherson Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark E-mail: [email protected] Received 17 May 2018, revised 2 July 2018 Accepted for publication 18 July 2018 Published 6 August 2018 Abstract We demonstrate how dispersive atom number measurements during evaporative cooling can be used for enhanced determination of the parameter dependence of the transition to a Bose– Einstein condensate (BEC). In this way shot-to-shot fluctuations in initial conditions are detected and the information extracted per experimental realization is increased. We furthermore calibrate in situ images from dispersive probing of a BEC with corresponding absorption images in time- of-flight. This allows for the determination of the transition point in a single experimental realization by applying multiple dispersive measurements. Finally, we explore the continuous probing of several consecutive phase transition crossings using the periodic addition of a focused ‘dimple’ potential. Keywords: Bose–Einstein condensates, Faraday effect, phase transitions, quantum simulation, ultracold quantum gases, phase diagrams, dispersive probing (Some figures may appear in colour only in the online journal) Quantum effects have become increasingly important in the during forced evaporative cooling can be used to enhance the development of modern technologies and have led to the need accuracy in determining the critical point, at which the for accurate quantum simulation [1, 2]. Various approaches, transition to a Bose–Einstein condensate (BEC) occurs. Sec- including cold atoms [3–5] and ions [6], superconducting ond, we investigate multiple, in situ probing of BECs during circuits [7], and photons [8] are used to perform such simu- evaporation as a means of single-shot mapping of a phase lations. In particular, many quantum simulators aim to pin transition. down the boundaries between discrete phases of many-body Since the pioneering work on dispersive probing systems, such as Ising spin transition points [4, 6] or magnetic [10, 11], it has been employed to investigate the relative phases [5], with the highest possible accuracy. Current repulsion of BECs and thermal clouds [12] and to monitor the simulations focus on providing tight experimental bounds for formation of a BEC [13, 14] as well as the appearance and fi benchmarking theoretical models, such as nite temperature dynamics of solitons [15, 16]. In-sequence benchmark mea- fl [ ] bosonic super uids in optical lattices 9 . surements of cold atomic clouds have recently been applied as In this article we investigate the potential for using dis- a tool to moderately reduce classical fluctuations in atom persive probing of ultracold atom clouds in two distinct toy- number [17]. Using active feedback, atom number stabiliza- model settings to enhance future quantum simulations. First, −3 tion of cold clouds to the 10 level was demonstrated in we demonstrate that benchmark probes of thermal clouds [18]. However, to date no experiments have explored 1 Present address: Department of Physics and Astronomy, University of benchmark-measurement-enhanced evaluation of the BEC Sussex, Falmer, Brighton BN1 9QH, United Kingdom. atom number. Efficient suppression of classical fluctuations 2 Present address: Innovation Center of Quantum Information and Quantum could enable the settlement of long-standing theoretical dis- Physics, Chinese Academy of Sciences, University of Science and fl Technology, Shanghai, People’s Republic of China. putes concerning the nature of fundamental uctuations 3 Contributed equally to this work. arising at the BEC phase transition [19]. 0953-4075/18/175301+09$33.00 1 © 2018 IOP Publishing Ltd Printed in the UK J. Phys. B: At. Mol. Opt. Phys. 51 (2018) 175301 M G Bason et al In recent years, theoretical studies on dispersive light– matter interaction based quantum non-demolition (QND) measurements have demonstrated these as a useful tool for the detection and control of quantum many-body systems. Quantum-noise-limited probing and feedback may enable the line-width reduction of atom lasers [20], the stabilization of BECs against spontaneous emission [21], and to squeeze and entangle Bogoliubov excitations [22]. If extended to optical lattices, it may allow for QND detection of quantum phase transitions [23, 24] as well as Schrödinger cat state generation [25, 26] and arbitrary quantum state engineering using tun- neling [25] and pinned [27] atoms. To realize its full potential, however, careful studies of the fundamental information-dis- turbance trade-off [14, 28–31] associated with dispersive Figure 1. (a)Experimental setup showing the crossed dipole trap imaging are required. (red) at a wavelength of 1064 nm and the imaging lens. Detuned This article is structured as follows: in section 1, we show light (blue) is used to dispersively probe the BEC. A dimple ( ) that minimally destructive measurements of the atom number potential orange arrow at a wavelength of 912 nm allows for repeated phase transition crossings. The probing light and the early in the experimental sequence can be used to predict the trapping light are separated by dichroic mirrors. A polarizing beam BEC atom number. Based on the results of these dispersive splitter (not depicted) filters the rotated component of the probing measurements of the intermediate phase-space density (PSD) light. (b)Evaporation scheme showing the evaporation power as a we group the BEC data and demonstrate a clear shift in the function of time. Illustrated are the dispersive benchmark pulse at ( ) BEC transition versus initial conditions. We use this addi- evaporation power Po yellow line and the probing around the phase transition (red lines) realized either with destructive absorption tional information for a high-resolution investigation of the imaging or with multiple dispersive probe pulses. The inset transition point in our toy-model. The purpose of this schematically shows the toy-model critical curve describing the investigation is not to obtain parameters of this well-studied power, Pc, at which the transition to a BEC occurs as a function of transition at high precision but rather to demonstrate a novel the phase-space density, PSDo, measured dispersively at Po. The methodology to increase the available information per arrows illustrate the paths of individual experimental realizations for different PSD . experimental run. This methodology may also find applica- o tions for fluctuating magnetic fields in the determination of – ≈( – ) × 6 magnetic order phase transitions in Ising spin chains [4], N0 N» 0 0.6 and total atom numbers N 2.1 0.8 10 impurity doping concentrations for the quantum simulation of are produced. the doped Hubbard Hamiltonian [32, 33], or the chemical Non-destructive, dispersive measurements of the cloud fi ( ) potential in the realization of both Bose- and Fermi–Hubbard are recorded using dark eld Faraday imaging DFFI .An models. Recently, post-selection of data conditioned on in- introduction to this method as well as a comparison with other [ ] sequence in situ measurements of magnetic field values was non-destructive imaging techniques is given in 29 . In brief, used to enhance Rabi oscillation contrast [34]. the Faraday effect leads to a rotation of the incoming linear In section 2 of this article, we perform a detailed com- light polarization proportional to the column density of an parison of images obtained by dispersively probing BECs atomic cloud. To implement DFFI, probing light blue detuned Δ = in situ and equivalent absorption images after a time-of-flight. by 1.5 GHz from the ∣FF=ñ¢=ñ23∣ transition propagates along the same axis as one of the dipole trap This allows for the observation of the phase transition in a −2 single experimental realization using multiple dispersive beams. Intensities of 10 mW cm are used, corresponding to μ –2 μ –1 fi probe pulses as well as the quantification of the deterministic around 400 photons m s . A small bias magnetic eld of shift of the critical point due to probe induced heating. around 1 G along the light propagation direction preserves the ’ Finally, we take first steps to dispersively probe several atomic sample s spin polarization. By inserting a polarizing -4 consecutive phase transitions using the periodic addition of a beam splitter cube with a suppression factor of 3 ´ 10 in focused dimple potential in a single experimental realization. the imaging path, only the rotated component of the light is imaged onto an electron multiplying charge coupled device (EMCCD) camera with an effective spatial resolution of – μ 1. Faraday imaging as dispersive benchmark probe 3 4 m. In each realization of the experiment, a DFFI pulse of 20 μs duration probes the thermal cloud at a trapping 4 ( fi ( )) Our experimental setup is shown in figure 1(a). Atoms are power Po = 1.1 W see gure 1 b and thus realizes a dis- 87 persive benchmark (DB) measurement.
Load more

Recommended publications
  • Condensed Matter Physics with Light and Atoms: Strongly Correlated Cold Fermions in Optical Lattices
    Condensed Matter Physics With Light And Atoms: Strongly Correlated Cold Fermions in Optical Lattices. Antoine Georges Centre de Physique Th´eorique, Ecole Polytechnique, 91128 Palaiseau Cedex, France Lectures given at the Enrico Fermi Summer School on ”Ultracold Fermi Gases” organized by M. Inguscio, W. Ketterle and C. Salomon (Varenna, Italy, June 2006) Summary. — Various topics at the interface between condensed matter physics and the physics of ultra-cold fermionic atoms in optical lattices are discussed. The lec- tures start with basic considerations on energy scales, and on the regimes in which a description by an effective Hubbard model is valid. Qualitative ideas about the Mott transition are then presented, both for bosons and fermions, as well as mean-field theories of this phenomenon. Antiferromagnetism of the fermionic Hubbard model at half-filling is briefly reviewed. The possibility that interaction effects facilitate adiabatic cooling is discussed, and the importance of using entropy as a thermometer is emphasized. Geometrical frustration of the lattice, by suppressing spin long-range order, helps revealing genuine Mott physics and exploring unconventional quantum magnetism. The importance of measurement techniques to probe quasiparticle ex- arXiv:cond-mat/0702122v1 [cond-mat.str-el] 5 Feb 2007 citations in cold fermionic systems is emphasized, and a recent proposal based on stimulated Raman scattering briefly reviewed. The unconventional nature of these excitations in cuprate superconductors is emphasized. c Societ`aItaliana di Fisica 1 2 A. Georges 1. – Introduction: a novel condensed matter physics. The remarkable recent advances in handling ultra-cold atomic gases have given birth to a new field: condensed matter physics with light and atoms.
    [Show full text]
  • Arxiv:2106.03883V2 [Cond-Mat.Quant-Gas] 21 Jun 2021
    Cooling and state preparation in an optical lattice via Markovian feedback control Ling-Na Wu∗ and Andr´eEckardty Institut f¨urTheoretische Physik, Technische Universit¨atBerlin, Hardenbergstraße 36, Berlin 10623, Germany (Dated: 22nd June 2021) We propose and investigate a scheme for in-situ cooling a system of interacting bosonic atoms in a one-dimensional optical lattice without particle loss. It is based on Markovian feedback control. The system is assumed to be probed weakly via the homodyne detection of photons that are scattered off-resonantly by the atoms from a structured probe beam into a cavity mode. By applying an inertial force to the system that is proportional to the measured signal, the system can be guided into a pure target state. Cooling is achieved by preparing the system's ground state, but also excited states can be prepared. While the approach always works for weak interactions, for integer filling the ground state can be prepared with high fidelity for arbitrary interaction strengths. The scheme is found to be robust against reduced measurement efficiencies. Introduction.| Atomic quantum gases in optical lat- kHz scale is sufficient, which can be achieved easily us- tices constitute a unique experimental platform for ing digital signal processors. The Markovian feedback studying quantum many-body systems under extremely method has been applied to various control problems, in- clean and flexible conditions [1]. An important property cluding the stabilization of arbitrary one-qubit quantum of atomic quantum gases is their extremely high degree states [43, 44], the manipulation of quantum entangle- of isolation from the environment, which is provided by ment between two qubits [45{48] as well as optical and the optical trapping of atoms inside ultrahigh vacuum.
    [Show full text]
  • Experimentally Exploring the Dicke Phase Transition
    Diss. ETH No. 19943 Experimental Realization of the Dicke Quantum Phase Transition A dissertation submitted to the ETH Zurich¨ for the degree of Doctor of Sciences presented by Kristian Gotthold Baumann Dipl.-Phys., Technische Universit¨at Munchen,¨ Germany born 7.4.1983 in Leipzig, Germany citizen of Germany accepted on the recommendation of Prof. Dr. Tilman Esslinger, examiner Prof. Dr. Johann Blatter, co-examiner 2011 Zusammenfassung In dieser Arbeit wird die erste experimentelle Realisierung des Quantenphasenuberganges¨ im Dicke Modell vorgestellt. Wir betrachten die Quantenbewegung eines Bose-Einstein Konden- sates die an einen optischen Resonator gekoppelt ist. Konzeptionell ist der Phasenubergang¨ durch langreichweitige Wechselwirkungen induziert, die zum Entstehen eines selbstorgani- sierten suprasoliden Zustandes fuhren.¨ Der Quantenphasenubergang¨ im Dicke Modell wurde bereits 1973 vorhergesagt. Vor dieser Arbeit konnte dieser aber wegen grundlegenden und technologischen Grunden¨ experimentell nicht nachgewiesen werden. Durch die Verwendung von atomaren Impulszust¨anden konnten wir diese Herausforderung nun bew¨altigen. Die Impulszust¨ande werden durch Zweiphotonen- Uberg¨ ¨ange miteinander gekoppelt, wobei je ein Photon aus dem Resonator und ein Photon aus einer transversalen Lichtwelle gebraucht werden. Diese offene Implementierung des Di- cke Modells erlaubt es alle relevanten Parameter einzustellen und bietet eine einzigartige Detektionsmethode in Echtzeit. Wir zeigen in dieser Doktorarbeit, dass der Phasenubergang¨ von einem
    [Show full text]
  • Creating, Moving and Merging Dirac Points with a Fermi Gas in a Tunable Honeycomb Lattice
    Creating, moving and merging Dirac points with a Fermi gas in a tunable honeycomb lattice Leticia Tarruell, Daniel Greif, Thomas Uehlinger, Gregor Jotzu and Tilman Esslinger Institute for Quantum Electronics, ETH Zurich, 8093 Zurich, Switzerland PACS numbers: 03.75.Ss, 05.30.Fk, 67.85.Lm, 71.10.Fd, 73.22.Pr Dirac points lie at the heart of many fascinat- space { the Dirac points { leads to extraordinary trans- ing phenomena in condensed matter physics, from port properties, even in the absence of interactions [1]. In massless electrons in graphene to the emergence of conducting edge states in topological insulators [1, 2]. At a Dirac point, two energy bands inter- a b Chequerboard Triangular Dimer sect linearly and the particles behave as relativis- tic Dirac fermions. In solids, the rigid structure X of the material sets the mass and velocity of the δ particles, as well as their interactions. A differ- X ent, highly flexible approach is to create model Y systems using fermionic atoms trapped in the λ/2 periodic potential of interfering laser beams, a Honeycomb 1D chains Square c method which so far has only been applied to ex- 1 a2 plore simple lattice structures [3, 4]. Here we T. A B ] report on the creation of Dirac points with ad- a R 1 E D. [ X justable properties in a tunable honeycomb opti- V H.c. cal lattice. Using momentum-resolved interband y Chequerboard 1D c. 0 transitions, we observe a minimum band gap in- 0 Square 8 x side the Brillouin zone at the position of the Dirac VX ̅ [ER ] VY = 2 ER points.
    [Show full text]
  • Novel, Retroreflective, Magneto-Optical Trap Near a Surface
    Novel, Retroreflective, Magneto-Optical Trap Near a Surface Jonathan Trossman,1, ∗ Zigeng Liu,1 Ming-Feng Tu,1 Selim Shariar,2 Brian Odom,1 and J.B. Ketterson2, y 1Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60209 2Department of Physics and Astronomy, Department of Electrical and Computer Engineering, Northwestern University, Evanston, Illinois 60209 We report on a novel Magneto-Optical Trap (MOT) geometry involving the retroreflection of one of the six MOT beams in order to create an atom cloud close to the surface of a prism which does not have optical access along one axis. A MOT of Rb85 with ∼ 4 × 107 atoms can be created 700 µm from the surface. The MOT lies close to the minimum of an evanescent Gravito-Optical Surface Trap (GOST) allowing for transfer into the GOST with potentially minimal losses. The study of optical lattices has been an area of great and is proportional to the light intensity and inversely interest in recent years [1][2][3][4][5]. Surface traps are a proportional to the detuning of the frequency of light prospective method for surpassing the diffraction limit for the lattice constants [6][7]. Here we will describe 2 a technique for trapping cold Rubidium atoms close to 3πc Γ I(r) Udip(r) = 3 (3) a surface. In the simple case we are considering, a 2!0 δ boundary is generated by the evanescent field created by total internal reflection of a blue detuned laser beam, Where Γ is the spontaneous decay rate, !0 is the reso- which with gravity creates a Gravito-Optical Surface nant transition frequency, and δ is the difference between Trap (GOST).
    [Show full text]
  • Matter-Wave Diffraction from a Quasicrystalline Optical Lattice
    Matter-wave diffraction from a quasicrystalline optical lattice Konrad Viebahn, Matteo Sbroscia, Edward Carter, Jr-Chiun Yu, and Ulrich Schneider∗ Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom (Dated: January 23, 2019) Quasicrystals are long-range ordered and yet non-periodic. This interplay results in a wealth of intriguing physical phenomena, such as the inheritance of topological properties from higher dimensions, and the presence of non-trivial structure on all scales. Here we report on the first experimental demonstration of an eightfold rotationally symmetric optical lattice, realising a two- dimensional quasicrystalline potential for ultracold atoms. Using matter-wave diffraction we observe the self-similarity of this quasicrystalline structure, in close analogy to the very first discovery of quasicrystals using electron diffraction. The diffraction dynamics on short timescales constitutes a continuous-time quantum walk on a homogeneous four-dimensional tight-binding lattice. These measurements pave the way for quantum simulations in fractal structures and higher dimensions. Quasicrystals exhibit long-range order without being and material science [1,3,4,6, 17], in photonic struc- periodic [1{6]. Their long-range order manifests itself tures [9, 13, 18{20], using laser-cooled atoms in the dissi- in sharp diffraction peaks, exactly as in their periodic pative regime [21, 22], and very recently in twisted bilayer counterparts. However, diffraction patterns from qua- graphene [23]. Quasicrystalline order can even appear sicrystals often reveal rotational symmetries, most no- spontaneously in dipolar cold-atom systems [24]. tably fivefold, eightfold, and tenfold, that are incompat- In this work we realise a quasicrystalline potential for ible with translational symmetry.
    [Show full text]
  • Fermi-Hubbard Physics with Atoms in an Optical Lattice1
    FERMI-HUBBARD PHYSICS WITH ATOMS IN AN OPTICAL LATTICE1 Tilman Esslinger, Department of Physics, ETH Zurich, Switzerland ABSTRACT The Fermi-Hubbard model is a key concept in condensed matter physics and provides crucial insights into electronic and magnetic properties of materials. Yet, the intricate nature of Fermi systems poses a barrier to answer important questions concerning d-wave superconductivity and quantum magnetism. Recently, it has become possible to experimentally realize the Fermi- Hubbard model using a fermionic quantum gas loaded into an optical lattice. In this atomic approach to the Fermi-Hubbard model the Hamiltonian is a direct result of the optical lattice potential created by interfering laser fields and short-ranged ultracold collisions. It provides a route to simulate the physics of the Hamiltonian and to address open questions and novel challenges of the underlying many-body system. This review gives an overview of the current efforts in understanding and realizing experiments with fermionic atoms in optical lattices and discusses key experiments in the metallic, band-insulating, superfluid and Mott-insulating regimes. INTRODUCTION The previous years have seen remarkable progress in the control and manipulation of quantum gases. This development may soon profoundly influence our understanding of quantum many- body physics. The quantum gas approach to many-body physics is fundamentally different from the path taken by other condensed matter systems, where experimentally observed phenomena trigger the search for a theoretical explanation. For instance, the observation of superconductivity resulted in the Bardeen-Cooper-Schrieffer (BCS) theory. In quantum gas research, the starting point is a many-body model that can be realized experimentally, such as a weakly interacting Bose gas.
    [Show full text]
  • Press Release Shaking the Topological Cocktail of Success
    Press Release EMBARGOED: 12.11.2014, until 7.00 pm CET Quantum simulations Shaking the topological cocktail of success Zürich, 12. November 2014 Take ultracold potassium atoms, place a honeycomb lattice of laser beams on top of them and shake everything in a circular motion: this recipe enabled ETH researchers to implement an idea for a new class of materials first proposed in 1988 in their laboratory. Graphene is the miracle material of the future. Consisting of a single layer of carbon atoms arranged in a honeycomb lattice, the material is extremely stable, flexible, highly conductive and of particular interest for electronic applications. ETH Professor Tilman Esslinger and his group at the Institute for Quantum Electronics investigate artificial graphene; its honeycomb structure consists not of atoms, but rather of light. The researchers align multiple laser beams in such a way that they create standing waves with a hexagonal pattern. This optical lattice is then superimposed on potassium atoms in a vacuum chamber, which are cooled to near absolute zero temperature. Trapped in the hexagonal structure, the potassium atoms behave like the electrons in graphene. “We work with atoms in laser beams because it provides us with a system that can be controlled bet- ter and observed more easily than the material itself,” explains Gregor Jotzu, a doctoral student in Physics. Since the researchers focus primarily on understanding quantum mechanical interactions, they describe their system as a quantum simulator. Thanks to this testing set-up, it has now become possible to implement an idea first published by the British physicist Duncan Haldane in 1988.
    [Show full text]
  • Solid State Cavity Quantum Electrodynamics with Quantum Dots Coupled to Photonic Crystal Cavities
    SOLID STATE CAVITY QUANTUM ELECTRODYNAMICS WITH QUANTUM DOTS COUPLED TO PHOTONIC CRYSTAL CAVITIES A DISSERTATION SUBMITTED TO THE DEPARTMENT OF ELECTRICAL ENGINEERING AND THE COMMITTEE ON GRADUATE STUDIES OF STANFORD UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Arka Majumdar August 2012 c Copyright by Arka Majumdar 2012 All Rights Reserved ii I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. (Dr. Jelena Vuckovic) Principal Adviser I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. (Dr. David Miller) I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. (Dr. Hideo Mabuchi) Approved for the University Committee on Graduate Studies iii Acknowledgements Many people have made my five years as a graduate student fun and productive. First, I would like to thank my advisor, Professor Jelena Vuckovic, for her guidance and support. I also want to thank her for giving me so many opportunities to grow as an academic, sending me to conferences early and often, and giving me responsibili- ties with equipment purchases, teaching assistantships, mentoring new students etc. When I joined Stanford, I did not have much knowledge on quantum mechanics, and my background was mostly on RF electronics.
    [Show full text]
  • 2.1 Bose-Einstein Condensation
    Diss. ETH No.16336 One-dimensional Atomic Gases A dissertation submitted to the SWISS FEDERAL INSTITUTE OF TECHNOLOGY ZURICH for the degree of Doctor of Natural Sciences presented by HENNING MORITZ Dipl.-Phys., University of Heidelberg, Germany born 25.10.1974 citizen of Germany accepted on the recommendation of Prof. Dr. Tilman Esslinger, examiner Prof. Dr. Thierry Giamarchi, co-examiner 2006 Kurzfassung In dieser Arbeit werden Experimente vorgestellt, in denen es gelungen ist, die Quantenphysik eindimensionaler Systeme mit ultrakalten atomaren Gasen zu untersuchen. Mithilfe von opti- schen Gittern wird die Bewegungsfreiheit der Atome auf eine Dimension beschränkt, während in den transversalen Richtungen nur quantenmechanische Grundzustandsbewegungen erlaubt sind. Zusätzlich zur Dimensionalität kann auch die Stärke und das Vorzeichen der Wechselwir- kung zwischen den Atomen verändert werden. Diese einzigartige Flexibilität erlaubt die präzise Untersuchung grundlegender Fragen der Festkörper- und Quantenphysik. Der Zustand eines kinematisch eindimensionalen Bose Gases wurde durch die Messung der kollektiven Moden charakterisiert. Diese geben Auskunft über den Quantenzustand des Viel- teilchensystems und belegen, daß ein eindimensionales Bose-Einstein Kondensat erzeugt wur- de. Indem wir ein zusätzliches periodisches Potential entlang der Bewegungsrichtung anlegten, konnten wir in das Regime stark korrelierter Systeme vordringen: wir beobachteten den Über- gang von einer eindimensionalen Supraflüssigkeit in den Mott-Isolator Zustand und
    [Show full text]
  • Cavity Quantum Electrodynamics of Systems from Few Atoms to Controlled Ensembles
    Hungarian Scientific Research Fund NF proposal Cavity quantum electrodynamics of systems from few atoms to controlled ensembles Peter Domokos Research Institute for Solid State Physics and Optics of the Hungarian Academy of Sciences 1 INTRODUCTION 1 1 Introduction The interaction of the electromagnetic field and atoms is significantly changed if, instead of being in free space, the field is limited by boundaries. The substantial modification of the radiative properties of single atoms or ensembles in a cavity is of fundamental interest, and has an impact on spectroscopy as well as on the current evolution of nanoscale technologies. Cavity quantum electrodynamics (cavity QED, CQED) has been studied for several decades now, however, it is in the last few years that this subject has undergone a breathtaking progress in the laboratories. Recent spectacular advances include, for example, the tracking of atomic trajectories [Hood et al., 2000; Pinkse et al., 2000], the realization of single-atom lasing [McKeever et al., 2003a] and that of deterministic single- photon source [Keller et al., 2004], the cooling of atomic motion by cavity fields [Maunz et al., 2004], the generation of Fock states of the cavity field [Varcoe et al., 2000], and a test of the complementarity principle [Bertet et al., 2001]. The prototype system of cavity QED is a single atomic dipole coupled to the elec- tromagnetic radiation field in a tiny, high-finesse resonator (cavity) composed of mirrors with extremely high reflection coefficients. The interaction is strongly enhanced due to “recycling” the photons by reflections. Whereas lasers act on atoms merely as external fields, the resonator mode becomes a genuine dynamical variable of the coupled system.
    [Show full text]
  • Microscopic Probing and Manupulation of Ultracold Fermions
    Diss. ETH No. 19606 Microscopic Probing and Manipulation of Ultracold Fermions A dissertation submitted to the ETH ZURICH for the degree of Doctor of Sciences presented by TORBEN MÜLLER Dipl.-Phys., Johannes Gutenberg-Universität Mainz, Germany born 18.06.1980 in Weilburg, Germany citizen of Germany accepted on the recommendation of Prof. Dr. Tilman Esslinger, examiner Prof. Dr. Jonathan Home, co-examiner 2011 Kurzfassung Diese Arbeit beschreibt Experimente, die erstmals einen lokalen Zugang zur mikrosko- pischen Quanten-Vielteilchen-Physik ultrakalter atomarer Fermionen erlauben. Ein Quantengas aus 6Li Atomen wird in-situ mit zuvor nie erreichter Auflösung un- tersucht, wodurch ein direkter Einblick in die charakteristischen Fluktuations- und Korrelationseigenschaften des Systems gegeben ist. Auf derselben Längenskala von einem Mikrometer wird mit flexibel formbaren optischen Dipolfallen zudem eine lo- kale Manipulation erreicht. Wichtigstes Instrument für die gezeigten Experimente bilden zwei identische hochauflösende Mikroskopobjektive, die das Kernstück der im Rahmen dieser Arbeit aufgebauten Apparatur darstellen. Eines der beiden Mikroskopobjektive dient zur hochauflösenden Abbildung. Mit des- sen Hilfe werden räumlich aufgelöste Dichte- und Dichtefluktuationsprofile eines ge- fangenen, schwach wechselwirkenden Fermi-Gases gemessen und analysiert. Für Quan- tenentartung zeigt das Fermi-Gas unterdrückte Dichtefluktuationen unterhalb des Niveaus für thermisches Schrotrauschen. Dahingegen wird im nicht entarteten Fall thermisches, atomares Schrotrauschen beobachtet. Die gemessenen sub-Poisson’schen Fluktuationen sind eine direkte Folge des Pauli-Prinzips und manifestieren damit fer- mionisches Antibunching im Ortsraum. Zudem liefern die ortsaufgelösten Messungen lokale Informationen über thermodynamische Eigenschaften des Systems, wie zum Beispiel den Grad der Quantenentartung und die Kompressibilität. Gestützt auf die Aussagen des Fluktuations-Dissipations-Theorems wird eine neue fluktuationsbasier- te Methode zur Temperaturmessung in atomaren Fermi-Gasen realisiert.
    [Show full text]