DOCSLIB.ORG

Symmetry and Control in Spin-Based Quantum Computing Dimitrije Stepanenko

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Symmetry and Control in Spin-Based Quantum Computing Dimitrije Stepanenko Florida State University Libraries Electronic Theses, Treatises and Dissertations The Graduate School 2005 Symmetry and Control in Spin-Based Quantum Computing Dimitrije Stepanenko Follow this and additional works at the FSU Digital Library. For more information, please contact [email protected] THE FLORIDA STATE UNIVERSITY COLLEGE OF ARTS AND SCIENCES SYMMETRY AND CONTROL IN SPIN-BASED QUANTUM COMPUTING By DIMITRIJE STEPANENKO A Dissertation submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy Degree Awarded: Summer Semester, 2005 The members of the Committee approve the dissertation of Dimitrije Stepanenko defended on June 10, 2005. Nicholas E. Bonesteel Professor Directing Thesis Washington Mio Outside Committee Member Vladimir Dobrosavljevi´c Committee Member Stephan von Molnar Committee Member Mark Riley Committee Member The Office of Graduate Studies has verified and approved the above named committee members. ii To Andrija iii ACKNOWLEDGEMENTS It was unique privilege to spend my graduate school years working with my adviser and mentor, Professor Nick Bonesteel. The most important lessons he had taught me are that intuitive models and insights based on them are at least as important as the technical skills and that clarity and simplicity are necessary ingredients of every successful research. People who contributed to research presented in this thesis, both directly and through the inspiring discussions are Nicholas Bonesteel and Layla Hormozi from the Florida State University, Kerwin Foster from the Dillard University, David DiVincenzo from the IBM T. J. Watson Research Center and Guido Burkard and Daniel Loss from the University of Basel. I enjoyed the conversations about condensed matter physics with Professors Vladimir Dobrosavljevi´c, Pedro Schlottmann and Stephan von Molnar that kept me aware that there are many interesting faces of every problem. Darko, George, Kenny, Curt, Layla and John helped create an environment that made the long hours at the desk enjoyable. Sherry Tointigh and late Kate Caudill have shown a great deal of patience while dealing with my chaotic manner of handling paperwork, from the first day at FSU till the last signature on the last form. I would like to thank Professor LJubiˇsa Adamovi´c, Vlatko, Snjeˇzana, Marko, Vlada, Dragana, Olan, Joe, Donnato, Cheryl, Eddy, Lucas, Ann, Myongshik, Kan, Balˇsa, Ana, Ivana, Cira,´ Aleksa, Ilka, Vincent and Patricia, Marjan, Bo´ca and Dejan for their friendship and beautiful time spent together. I am especially grateful to my mother Slavica and mother in law Vanja for being with my family and me when we needed help. Without their devotion and assistance, my time in graduate school would have been much longer. My wife Jelena and son Andrija filled the years in graduate school with love and joy. I will always be thankful for their patience and understanding. iv TABLE OF CONTENTS List of Tables ................................................... .... vii List of Figures ................................................... viii Abstract ................................................... ......... x 1. INTRODUCTION ............................................... 1 1.1 Overview ........................................ ............. 2 1.2 Background on Quantum Computing .................... ........... 3 1.2.1 ClassicalComputers ............................ ............ 3 1.2.2 QuantumComputers.............................. .......... 7 1.2.3 Church-Turing Thesis ........................... ............ 11 1.3 Physical Realizations ............................ ................ 14 1.3.1 The Quantum Dot Quantum Computer .................. ....... 17 1.4 Spin-OrbitCoupling .............................. .............. 21 1.5 SymmetryandControl .............................. ............ 22 1.5.1 Reduction of the Effects of Spin-Orbit Coupling in Exchange Gates.... 24 1.5.2 Using Spin-Orbit Coupling Effects for Spin Control . ............. 26 1.6 SummaryofResults................................ ............. 28 2. SPIN-ORBIT COUPLING AS A PROBLEM: REDUCING THE GATE ANISOTROPY .................................................. 29 2.1 Reduction of Control Complexity .................... .............. 29 2.2 IsotropicExchange............................... ............... 31 2.2.1 SimpleControl................................. ............ 34 2.2.2 Universal Gate Set Using Isotropic Exchange . ............. 35 2.3 Anisotropy...................................... .............. 37 2.4 Time Dependence, Interaction and the Gate . .............. 38 2.4.1 Control through Pulse Shaping .................... ............ 39 2.4.2 Voltage Control Program......................... ............ 40 2.5 Simplifications from Symmetry ...................... .............. 42 2.6 Removal of First Order Anisotropy ................... .............. 44 2.6.1 CalculationoftheGate .......................... ............ 44 2.6.1.1 Parity and Time Reversal ....................... ......... 45 2.6.1.2 Time Reversal Symmetric Interactions and Time Symmetric Pulses 46 2.6.2 Perturbative Evaluation of the Gate . .. .. .. ............. 48 2.6.3 LocalSymmetry ................................. .......... 52 2.7 SummaryoftheResults............................. ............. 60 v 3. MICROSCOPIC DERIVATION OF SPIN INTERACTION .......... 62 3.1 The Model of Quantum Dots Quantum Computer . ......... 64 3.1.1 Confinement to Two Dimensions . .......... 65 3.1.2 Confinement in Plane, from Two to Zero Dimensions . .......... 69 3.1.3 ControlMechanisms ............................. ........... 71 3.2 Hund-Mulliken Approximation . .............. 74 3.2.1 Spin Orbit Coupling Hamiltonian . ............ 79 3.3 Axial Symmetry of the Effective Spin Interaction . ............... 84 3.4 Pulses of Hund-Mulliken Hamiltonian . ............... 86 3.4.1 Slightly asymmetric pulses . .............. 89 3.5 RobustCNOT...................................... ........... 90 4. SPIN-ORBIT COUPLING AS A RESOURCE: USING THE GATE ANISOTROPY .................................................. 95 4.1 Universal Gate Set Construction .................... ............... 96 4.1.1 SingleQubitGates .............................. ........... 100 4.1.2 TwoQubitGates................................. .......... 103 4.2 ControlRange .................................... ............. 107 4.2.1 Control at Fabrication Level ..................... ............. 108 4.2.2 Control through Time Dependence .................. ........... 116 4.3 Summary......................................... ............ 122 APPENDIX A: Axially Symmetric Gate for CNOT Construction ......... 124 APPENDIX B: Matrix Elements of Hund-Mulliken Hamiltonian ......... 127 REFERENCES ................................................... 129 BIOGRAPHICAL SKETCH .......................................... 134 vi LIST OF TABLES 2.1 Behavior of gate parameters under parity (P ) and time reversal (T ). Quantities that are even(odd) under parity are of even(odd) order in spin interaction anisotropy. Gate parameters odd under time reversal vanish from the gates implemented by time-symmetric pulses. .............. 45 3.1 Symmetry properties of the pulse parameters r and s, and gate parameters λ, α, β and γ under parity P and time reversal T . ........................ 90 vii LIST OF FIGURES 1.1 TuringMachine ................................... .............. 5 1.2 Universal Classical Logic Gates .................... ................. 6 1.3 Classical Circuit Model ........................... ................ 7 1.4 Elements of Quantum Circuit Model . .............. 9 1.5 Universal Set of Quantum Gates ...................... .............. 10 1.6 Quantum Circuit Complexity . ............... 11 1.7 Comparing Classical and Quantum Complexity . ............... 13 1.8 Quantum Dot Quantum Computer ....................... ........... 18 1.9 Universal Quantum Gates Using Isotropic Exchange . ................ 20 2.1 Controlled Not Using Isotropic Exchange . ................. 36 2.2 LocalReferenceFrames ............................ ............... 55 2.3 Constant Anisotropy Pulses ........................ ................ 57 2.4 Loop and Local Reference Frames ..................... .............. 58 2.5 TreeTopology .................................... .............. 59 3.1 The Quantum Dot Quantum Computer.................... ........... 64 3.2 BandBending ..................................... ............. 66 3.3 Voltagecontrolled gate........................... ................. 72 3.4 Isotropic Spin Interaction Strength . .. .. .. .................. 73 3.5 The Model Potential of Coupled Quantum Dots . ............. 75 3.6 Orbital Excitations and Failure Modes of a Spin Qubit . ................ 77 3.7 Zinc-Blende Crystal Structure ..................... ................. 81 3.8 Precession andHopping ............................ ............... 83 3.9 Anisotropy in Spin Interaction ..................... ................. 86 3.10 Time Dependent Hund-Mulliken Hamiltonian . ................ 89 3.11 GateHamiltonian................................ ................ 91 3.12 RobustCNOT ..................................... ............. 93 4.1 Range of Anisotropic Control....................... ................ 100 viii 4.2 Sequence for pseudospin x rotation .................................. 101 4.3 Two-SpinQubits .................................. .............. 104 4.4 CNOTcircuit..................................... .............. 106 4.5 Angle
Load more

Recommended publications
  • CURRICULUM VITAE Daniel Loss
    CURRICULUM VITAE Daniel Loss Department of Physics Nationality: Swiss University of Basel Born: February 25, 1958, Winterthur (CH) Klingelbergstrasse 82 Marital status: Married, 2 children 4056 Basel, Switzerland [email protected]; quantumtheory.physik.unibas.ch Positions August 2020-2032: Co-Director and founding member of National Center on Spin Qubits (NCCR SPIN), University of Basel & IBM Zurich. Since May 2006: Co-Director of the Swiss Nanoscale Center SNI, University of Basel. Since April 2005: Director of the Center for Quantum Computing and Quantum Coherence (QC2), University of Basel. 1998-1999, 2004-2005, 2008-2010 Chairman, Department of Physics, University of Basel. Since Oct. 1996: Professor of Theoretical Physics (Ordinarius), University of Basel, Switzerland. Sept. 1995 { Sept. 1996: Associate Professor of Physics, Simon Fraser University, Vancouver, Canada. Jan. 1993 { Aug. 1995: Assistant Professor of Physics, Simon Fraser University, Vancouver, Canada. Sept. 1991 { Jan. 1993: Research Scientist, condensed matter theory division, IBM T. J. Watson Research Center, Yorktown Heights, USA. Oct. 1989 { Sept. 1991: Postdoctoral Research Fellow with Prof. A. J. Leggett (Nobel Laureate 2003) at the University of Illinois, Urbana, USA. Dec. 1985 { Sept. 1989: Postdoctoral Research Associate, University of Z¨urich. Education Aug. 1983 { Dec. 1985: Ph. D. student and teaching assistant at the Univ. of Z¨urich. Dissertation in statistical mechanics; advisor: Prof. A. Thellung. Oct. 1979 { July 1983: Study of theoretical physics at the University of Z¨urich; received diploma with distinction. Diploma thesis in general relativity; advisor: Prof. N. Straumann. Oct. 1977 { Oct. 1979: Medical School (1. & 2. Propaedeuticum), University of Z¨urich, then transfer to physics.
    [Show full text]
  • Report to Industry Canada
    Report to Industry Canada 2013/14 Annual Report and Final Report for 2008-2014 Granting Period Institute for Quantum Computing University of Waterloo June 2014 1 CONTENTS From the Executive Director 3 Executive Summary 5 The Institute for Quantum Computing 8 Strategic Objectives 9 2008-2014 Overview 10 2013/14 Annual Report Highlights 23 Conducting Research in Quantum Information 23 Recruiting New Researchers 32 Collaborating with Other Researchers 35 Building, Facilities & Laboratory Support 43 Become a Magnet for Highly Qualified Personnel in the Field of Quantum Information 48 Establishing IQC as the Authoritative Source of Insight, Analysis and Commentary on Quantum Information 58 Communications and Outreach 62 Administrative and Technical Support 69 Risk Assessment & Mitigation Strategies 70 Appendix 73 2 From the Executive Director The next great technological revolution – the quantum age “There is a second quantum revolution coming – which will be responsible for most of the key physical technological advances for the 21st Century.” Gerard J. Milburn, Director, Centre for Engineered Quantum Systems, University of Queensland - 2002 There is no doubt now that the next great era in humanity’s history will be the quantum age. IQC was created in 2002 to seize the potential of quantum information science for Canada. IQC’s vision was bold, positioning Canada as a leader in research and providing the necessary infrastructure for Canada to emerge as a quantum industry powerhouse. Today, IQC stands among the top quantum information research institutes in the world. Leaders in all fields of quantum information science come to IQC to participate in our research, share their knowledge and encourage the next generation of scientists to continue on this incredible journey.
    [Show full text]
  • Hybrid Qubits Solve Key Hurdle to Quantum Computing 28 December 2018
    Hybrid qubits solve key hurdle to quantum computing 28 December 2018 In 1998, Daniel Loss, one of the authors of the current study, came up with a proposal, along with David DiVincenzo of IBM, to build a quantum computer by using the spins of electrons embedded in a quantum dot—a small particle that behaves like an atom, but that can be manipulated, so that they are sometimes called "artificial atoms." In the time since then, Loss and his team have endeavored to build practical devices. There are a number of barriers to developing practical devices in terms of speed. First, the device must be able to be initialized quickly. Initialization is the process of putting a qubit into a certain state, and if that cannot be done rapidly it slows down the device. Second, it must maintain coherence for a time long enough to make a measurement. Coherence refers to the Schematic of the device. Credit: RIKEN entanglement between two quantum states, and ultimately this is used to make the measurement, so if qubits become decoherent due to environmental noise, for example, the device Spin-based quantum computers have the potential becomes worthless. And finally, the ultimate state to tackle difficult mathematical problems that of the qubit must be able to be quickly read out. cannot be solved using ordinary computers, but many problems remain in making these machines While a number of methods have been proposed scalable. Now, an international group of for building a quantum computer, the one proposed researchers led by the RIKEN Center for Emergent by Loss and DiVincenzo remains one of the most Matter Science have crafted a new architecture for practically feasible, as it is based on quantum computing.
    [Show full text]
  • The Quantum Times) in Producing the First in Their List of Guidelines Nor Was It Reported As Operating Laser, Are All Interesting and Enlightening
    TThhee QQuuaannttuumm TTiimmeess APS Topical Group on Quantum Information, Concepts, and Computation Summer 2007 Volume 2, Number 2 Advances & Challenges in Quantum Key Distribution Quantum Key Distribution (QKD) is the flagship success of quantum communication. Since Bennett and Brassard’s 1984 publication [2] it has given a new direction to the field. (For a review see e.g. [3].) Up to then in quantum communication, the properties of quantum mechanics were used, for example, to improve on the through-put of optical channels. With the arrival of QKD an application has been created that achieves what Inside… cannot be achieved with classical communication alone: … you will find a little bit of provably secure protocols with no assumption about the everything. We begin with an computational power of an adversary. (This scenario is referred article from Norbert Lütkenhaus on to as unconditional security, a technical term in cryptography. quantum key distribution (QKD) Still, the devices of sender and receiver are assumed to be that grew out of a news article from perfect and out of bound of the adversary, an assumption without our last issue. Norbert speaks from which no cryptography is possible at all.) It is sufficient to the standpoint of someone at the prepare non-orthogonal states as signals and to measure them at forefront of quantum cryptography the receiver’s end. Then, using an authenticated public channel, and his article should be read by both parties can distill a secret key from the data. The procedure anyone interested in the current needs to be kick-started with some secret key in order to state and future direction of QKD.
    [Show full text]
  • Issues in Physics & Astronomy
    Issues in Physics & Astronomy Board on Physics and Astronomy • The National Academies • Washington, D.C. • 202-334-3520 • national-academies.org/bpa • Summer 2008 Understanding the Impact of Selling the Helium Reserve Michael H. Moloney, BPA Staff nder the sponsorship of the monatomic element, it passes easily containing 0.3 percent helium is consid- Bureau of Land Management at through tiny orifices and is therefore used ered economically viable. A few gas Uthe Department of the Interior, for leak detection in many scientific and deposits contain as much as 8 percent the BPA, in cooperation with the Na- technical applications. Its density is only helium. By comparison, the atmosphere tional Materials Advisory Board, has 15 percent that of air, making it useful as a contains only about 0.0005 percent. He- initiated a study to understand the lifting gas for aerostats and other devices. lium from wells that produce impact on the scientific community of Its high heat capacity, along with its uneconomically low concentrations, or the continuing sale of the U.S. helium inertness, makes it the preferred quench- from wells that produce higher concentra- reserve and recent developments in the ing medium for many applications in tions but do not flow through an extrac- helium market. materials processing, such as the produc- tion plant, is often vented to the atmo- The element helium has unique tion of high-quality superalloy powders. It sphere when the natural gas is burned. A properties. Liquefying near absolute is the preferred carrier gas for gas chroma- relatively minor amount of helium also is zero, it is the only option for many tography, a widely applied technique for vented at extraction plants that have no cryogenic applications, such as cooling chemical separations.
    [Show full text]
  • Topological Phases and Applications to Quantum Information Processing" ______List of Organizers
    Proposed title: "Topological Phases and Applications to Quantum Information Processing" __________________________________________________________ List of organizers: Nicholas E. Bonesteel (Florida State University and NHMFL) Phone: (850) 644-7805, E-mail: [email protected] James P. Eisenstein (Caltech) Phone: (626) 395-4649, E-mail: [email protected] Michael H. Freedman (Microsoft Research) Phone: (805) 893-6313, E-mail: [email protected] Kirill Shtengel (UC Riverside) Phone: (951) 827-1058, E-mail: [email protected] Steven H. Simon (Lucent Technologies, Bell Labs) Phone: (908) 582-6006, E-mail: [email protected] __________________________________________________________ Proposed length: 4 weeks, preferably July 2 through July 29 or June 25 through July 22. However, anytime between June 18 and Sept 2, 2007 is acceptable. Pushing it toward earlier or later dates will result in conflicts with teaching for many of the potential attendees. __________________________________________________________ Abstract: Quantum computers, if realized in practice, promise exponential speed-up of some of the computational tasks that conventional classical algorithms are intrinsically incapable of handling efficiently. Perhaps even more intriguing possibility arises from being able to use quantum computers to simulate the behavior of other physical systems -- an exciting idea dating back to Feynman. Unfortunately, realizing a quantum computer in practice proves to be very difficult, chiefly due to the debilitating effects of decoherence plaguing all possible schemes which use microscopic degrees of freedom (such as nuclear or electronic spins) as basic building blocks. >From this perspective, topological quantum computing offers an attractive alternative by encoding quantum information in nonlocal topological degrees of freedom that are intrinsically protected from decoherence due to local noise.
    [Show full text]
  • Quantum Computation with Spins in Quantum Dots
    Quantum Computation With Spins In Quantum Dots Fikeraddis Damtie June 10, 2013 1 Introduction Physical implementation of quantum computating has been an active area of research since the last couple of decades. In classical computing, the transmission and manipulation of classical information is carried out by physical machines (computer hardwares, etc.). In theses machines the manipulation and transmission of information can be described using the laws of classical physics. Since Newtonian mechanics is a special limit of quantum mechanics, computers making use of the laws of quantum mechanics have greater computational power than classical computers. This need to create a powerful computing machine is the driving motor for research in the field of quantum computing. Until today, there are a few different schemes for implementing a quantum computer based on the David Divincenzo chriterias. Among these are: Spectral hole burning, Trapped ion, e-Helium, Gated qubits, Nuclear Magnetic Resonance, Optics, Quantum dots, Neutral atom, superconductors and doped silicon. In this project only the quantum dot scheme will be discussed. In the year 1997 Daniel Loss and David P.DiVincenzo proposed a spin-qubit quantum computer also called The Loss-DiVincenzo quantum computer. This proposal is now considered to be one of the most promising candidates for quantum computation in the solid state. The main idea of the proposal was to use the intrinsic spin-1=2 degrees of freedom of individual elecrons confined in semiconductor quantum dots. The proposal was made in a way to satisfy the five requirements for quantum computing by David diVincenzo which will be described in sec.
    [Show full text]
  • Local and Distributed Quantum Computation
    Local and Distributed Quantum Computation Rodney Van Meter and Simon J. Devitt May 24, 2016 Abstract Experimental groups are now fabricating quantum processors powerful enough to execute small instances of quantum algorithms and definitively demonstrate quantum error correction that extends the lifetime of quantum data, adding ur- gency to architectural investigations. Although other options continue to be ex- plored, effort is coalescing around topological coding models as the most prac- tical implementation option for error correction on realizable microarchitectures. Scalability concerns have also motivated architects to propose distributed memory multicomputer architectures, with experimental efforts demonstrating some of the basic building blocks to make such designs possible. We compile the latest re- sults from a variety of different systems aiming at the construction of a scalable quantum computer. arXiv:1605.06951v1 [quant-ph] 23 May 2016 1 1 Introduction Quantum computers and networks look like increasingly inevitable extensions to our already astonishing classical computing and communication capabilities [1, 2]. How do they work, and once built, what capabilities will they bring? Quantum computation and communication can be understood through seven key con- cepts (see sidebar). Each concept is simple, but collectively they imply that our clas- sical notion of computation is incomplete, and that quantum effects can be used to efficiently solve some previously intractable problems. In the 1980s and 90s, a handful of algorithms were developed and the foundations of quantum computational complexity were laid, but the full range of capabilities and the process of creating new algorithms were poorly understood [1, 3, 4, 5, 6]. Over the last fifteen years, a deeper understanding of this process has developed, and the num- ber of proposed algorithms has exploded 1.
    [Show full text]
  • X 5 Quantum Computing with Semiconductor Quantum Dots
    X 5 Quantum Computing with Semiconductor Quantum Dots Carola Meyer Institut fur¨ Festkorperforschung¨ (IFF-9) Forschungszentrum Julich¨ GmbH Contents 1 Introduction 2 2 The ”Loss-DiVincenzo” proposal 2 3 Read-out of a single electron spin 3 3.1 Single shot read-out . 4 3.2 Singlet-Triplet read-out . 7 4 Manipulation of electron spins 8 4.1 Singlep spin rotation . 9 4.2 The SW AP operation . 10 5 Relaxation mechanisms 14 5.1 Spin-energy relaxation . 15 5.2 Dephasing and decoherence . 18 6 Summary and outlook 20 X5.2 Carola Meyer 1 Introduction Quantum dots can be used to confine single electrons as discussed by M. Wegewijs in the lecture ”Spin and Transport in Quantum Dots”. The quantum computing concepts based on quantum dots can be subdivided in two main branches: optical concepts and electrical concepts. In most of the optical concepts, the two level system representing the quantum bit (qubit) consists of exciton states. These are manipulated using polarized light. In electrical concepts, the spin states of electrons are used as qubit and manipulation can be done all-electrically. This contribution will concentrate on spin states of electrons for quantum information focusing on the most important electrical concept known as ”Loss-DiVincenzo proposal” [1]. It has been shown experimentally for this proposal that all of the ”DiVincenzo criteria” (for a general intro- duction into Quantum Computing see lecture ”Fundamental Concepts of Quantum Information Processing” by T. Schapers)¨ can be met as we shall see in the following. 2 The ”Loss-DiVincenzo” proposal A few years after the first implementation of the CNOT quantum gate using hyperfine and vibrational states of a 9Be+ ion in an ion trap as qubits [2], a row of proposals for a solid state quantum computer appeared, based on cooper pairs [3], nuclear spins in silicon [4], and last but not least electron spins in GaAs quantum dots [1].
    [Show full text]
  • Interface Between Topological and Superconducting Qubits
    University of Pennsylvania ScholarlyCommons Department of Physics Papers Department of Physics 3-28-2011 Interface Between Topological and Superconducting Qubits Liang Jiang California Institute of Technology Charles L. Kane University of Pennsylvania, [email protected] John Preskill California Institute of Technology Follow this and additional works at: https://repository.upenn.edu/physics_papers Part of the Physics Commons Recommended Citation Jiang, L., Kane, C. L., & Preskill, J. (2011). Interface Between Topological and Superconducting Qubits. Retrieved from https://repository.upenn.edu/physics_papers/129 Suggested Citation: Jiang, L., Kane, C.L. and Preskill, J. (2011). Interface between Topological and Superconducting Qubits. Physical Review Letters. 106, 130504. © 2011 The American Physical Society http://dx.doi.org/10.1103/PhysRevLett.106.130504 This paper is posted at ScholarlyCommons. https://repository.upenn.edu/physics_papers/129 For more information, please contact [email protected]. Interface Between Topological and Superconducting Qubits Abstract We propose and analyze an interface between a topological qubit and a superconducting flux qubit. In our scheme, the interaction between Majorana fermions in a topological insulator is coherently controlled by a superconducting phase that depends on the quantum state of the flux qubit. A controlled-phase gate, achieved by pulsing this interaction on and off, can transfer quantum information between the topological qubit and the superconducting qubit. Disciplines
    [Show full text]
  • Pulse Sequences for Exchange-Based Quantum
    Prospects for Superconducting Qubits David DiVincenzo 24.01.2013 QIP Beijing Masters/PhD/postdocs available! http://www.physik.rwth-aachen.de/ institute/institut-fuer-quanteninformation/ (G: IQI Aachen) Prospects for Superconducting Qubits David DiVincenzo 24.01.2013 QIP Beijing Prospects for Superconducting Qubits Outline • Basic physics of Josephson devices • A short history of quantum effects in electric circuits • A Moore’s law for quantum coherence • Approaching fault tolerant fidelities (95%) • Scaling up with cavities – towards a surface code architecture • Will it work?? Interesting claim: Go direct from lumped electric circuit V To Schrodinger equation I Current controlled by f µ ò V dt Some other history: IBM had a large project (1975-85) to make a Josephson junction digital computer. “0” was the Current controlled by zero-voltage state, “1” was the finite-voltage state. f µ ò V dt Very different from a quantum computer. (Al or Nb) 2 1 (Al2O3) I Ic sin1 2 Coherent control of macroscopic quantum states in a single-Cooper-pair box Y. Nakamura, Yu. A. Pashkin and J. S. Tsai Nature 398, 786-788(29 April 1999) Feeble signs of quantum coherence Saclay Josephson junction qubit Science 296, 886 (2002) Oscillations show rotation of qubit at constant rate, with noise. s m Simple electric circuit… a l l harmonic oscillator with resonant frequency L C 0 1/ LC Quantum mechanically, like a kind of atom (with harmonic potential): x is any circuit variable (capacitor charge/current/voltage, Inductor flux/current/voltage) That is to say, it is a “macroscopic” variable that is being quantized.
    [Show full text]
  • In Accordance with the 'Partnerconvenant Qutech'
    2017 Annual Report In accordance with the ‘Partnerconvenant QuTech’ 1 Foreword Annual report 2017 QuTech On behalf of the whole of QuTech, In 2017, QuTech has attracted some of the I am proud to present the yearly best researchers in quantum technology to join report for 2017. It presents an over- our mission. Prof. Barbara Terhal (0,8 FTE) and view of the research ‘roadmaps’ part-time Prof. David DiVincenzo, both leading along with several other activities, experts in quantum information theory and error such as QuTech partnerships, correction, started at QuTech in September. outreach and academy. From our own ranks, Dr. Srijit Goswami has been contracted as a senior researcher on topological In my view, 2017 marks the completion of the first qubits. phase of QuTech, in which we have transitioned to a mission-driven research program, enabled With the internal research programs now running by both scientific breakthroughs and engineering at full steam, QuTech is ready for its next phase, efforts. Most PhD students that started their in which we will form stronger connections to research in the pre-QuTech era have now the outside world. The demonstrator projects graduated. The roadmaps of QuTech have a will allow external researchers to connect to and clear direction and demonstrate a strong synergy use our hardware and software platforms. The between science and engineering. The scientific establishment of a Microsoft research lab – foundation of QuTech is stronger than ever with, formally agreed upon in a joint signing ceremony for example, four publications making it into top in June 2017 - marks the start of a Quantum scientific journals Nature and Science in 2017, Campus in Delft.
    [Show full text]