Analysis of Quantum Error-Correcting Codes: Symplectic Lattice Codes and Toric Codes
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Painstakingly-Edited Typeset Lecture Notes
Physics 239: Topology from Physics Winter 2021 Lecturer: McGreevy These lecture notes live here. Please email corrections and questions to mcgreevy at physics dot ucsd dot edu. Last updated: May 26, 2021, 14:36:17 1 Contents 0.1 Introductory remarks............................3 0.2 Conventions.................................8 0.3 Sources....................................9 1 The toric code and homology 10 1.1 Cell complexes and homology....................... 21 1.2 p-form ZN toric code............................ 23 1.3 Some examples............................... 26 1.4 Higgsing, change of coefficients, exact sequences............. 32 1.5 Independence of cellulation......................... 36 1.6 Gapped boundaries and relative homology................ 39 1.7 Duality.................................... 42 2 Supersymmetric quantum mechanics and cohomology, index theory, Morse theory 49 2.1 Supersymmetric quantum mechanics................... 49 2.2 Differential forms consolidation...................... 61 2.3 Supersymmetric QM and Morse theory.................. 66 2.4 Global information from local information................ 74 2.5 Homology and cohomology......................... 77 2.6 Cech cohomology.............................. 80 2.7 Local reconstructability of quantum states................ 86 3 Quantum Double Model and Homotopy 89 3.1 Notions of `same'.............................. 89 3.2 Homotopy equivalence and cohomology.................. 90 3.3 Homotopy equivalence and homology................... 91 3.4 Morse theory and homotopy -
(CST Part II) Lecture 14: Fault Tolerant Quantum Computing
Quantum Computing (CST Part II) Lecture 14: Fault Tolerant Quantum Computing The history of the universe is, in effect, a huge and ongoing quantum computation. The universe is a quantum computer. Seth Lloyd 1 / 21 Resources for this lecture Nielsen and Chuang p474-495 covers the material of this lecture. 2 / 21 Why we need fault tolerance Classical computers perform complicated operations where bits are repeatedly \combined" in computations, therefore if an error occurs, it could in principle propagate to a huge number of other bits. Fortunately, in modern digital computers errors are so phenomenally unlikely that we can forget about this possibility for all practical purposes. Errors do, however, occur in telecommunications systems, but as the purpose of these is the simple transmittal of some information, it suffices to perform error correction on the final received data. In a sense, quantum computing is the worst of both of these worlds: errors do occur with significant frequency, and if uncorrected they will propagate, rendering the computation useless. Thus the solution is that we must correct errors as we go along. 3 / 21 Fault tolerant quantum computing set-up For fault tolerant quantum computing: We use encoded qubits, rather than physical qubits. For example we may use the 7-qubit Steane code to represent each logical qubit in the computation. We use fault tolerant quantum gates, which are defined such thata single error in the fault tolerant gate propagates to at most one error in each encoded block of qubits. By a \block of qubits", we mean (for example) each block of 7 physical qubits that represents a logical qubit using the Steane code. -
Pilot Quantum Error Correction for Global
Pilot Quantum Error Correction for Global- Scale Quantum Communications Laszlo Gyongyosi*1,2, Member, IEEE, Sandor Imre1, Member, IEEE 1Quantum Technologies Laboratory, Department of Telecommunications Budapest University of Technology and Economics 2 Magyar tudosok krt, H-1111, Budapest, Hungary 2Information Systems Research Group, Mathematics and Natural Sciences Hungarian Academy of Sciences H-1518, Budapest, Hungary *[email protected] Real global-scale quantum communications and quantum key distribution systems cannot be implemented by the current fiber and free-space links. These links have high attenuation, low polarization-preserving capability or extreme sensitivity to the environment. A potential solution to the problem is the space-earth quantum channels. These channels have no absorption since the signal states are propagated in empty space, however a small fraction of these channels is in the atmosphere, which causes slight depolarizing effect. Furthermore, the relative motion of the ground station and the satellite causes a rotation in the polarization of the quantum states. In the current approaches to compensate for these types of polarization errors, high computational costs and extra physical apparatuses are required. Here we introduce a novel approach which breaks with the traditional views of currently developed quantum-error correction schemes. The proposed solution can be applied to fix the polarization errors which are critical in space-earth quantum communication systems. The channel coding scheme provides capacity-achieving communication over slightly depolarizing space-earth channels. I. Introduction Quantum error-correction schemes use different techniques to correct the various possible errors which occur in a quantum channel. In the first decade of the 21st century, many revolutionary properties of quantum channels were discovered [12-16], [19-22] however the efficient error- correction in quantum systems is still a challenge. -
Superconducting Quantum Simulator for Topological Order and the Toric Code
Superconducting Quantum Simulator for Topological Order and the Toric Code Mahdi Sameti,1 Anton Potoˇcnik,2 Dan E. Browne,3 Andreas Wallraff,2 and Michael J. Hartmann1 1Institute of Photonics and Quantum Sciences, Heriot-Watt University Edinburgh EH14 4AS, United Kingdom 2Department of Physics, ETH Z¨urich,CH-8093 Z¨urich,Switzerland 3Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom (Dated: March 20, 2017) Topological order is now being established as a central criterion for characterizing and classifying ground states of condensed matter systems and complements categorizations based on symmetries. Fractional quantum Hall systems and quantum spin liquids are receiving substantial interest because of their intriguing quantum correlations, their exotic excitations and prospects for protecting stored quantum information against errors. Here we show that the Hamiltonian of the central model of this class of systems, the Toric Code, can be directly implemented as an analog quantum simulator in lattices of superconducting circuits. The four-body interactions, which lie at its heart, are in our concept realized via Superconducting Quantum Interference Devices (SQUIDs) that are driven by a suitably oscillating flux bias. All physical qubits and coupling SQUIDs can be individually controlled with high precision. Topologically ordered states can be prepared via an adiabatic ramp of the stabilizer interactions. Strings of qubit operators, including the stabilizers and correlations along non-contractible loops, can be read out via a capacitive coupling to read-out resonators. Moreover, the available single qubit operations allow to create and propagate elementary excitations of the Toric Code and to verify their fractional statistics. -
Some Open Problems in Quantum Information Theory
Some Open Problems in Quantum Information Theory Mary Beth Ruskai∗ Department of Mathematics, Tufts University, Medford, MA 02155 [email protected] June 14, 2007 Abstract Some open questions in quantum information theory (QIT) are described. Most of them were presented in Banff during the BIRS workshop on Operator Structures in QIT 11-16 February 2007. 1 Extreme points of CPT maps In QIT, a channel is represented by a completely-positive trace-preserving (CPT) map Φ: Md1 7→ Md2 , which is often written in the Choi-Kraus form X † X † Φ(ρ) = AkρAk with AkAk = Id1 . (1) k k The state representative or Choi matrix of Φ is 1 X Φ(|βihβ|) = d |ejihek|Φ(|ejihek|) (2) jk where |βi is a maximally entangled Bell state. Choi [3] showed that the Ak can be obtained from the eigenvectors of Φ(|βihβ|) with non-zero eigenvalues. The operators Ak in (1) are known to be defined only up to a partial isometry and are often called Kraus operators. When a minimal set is obtained from Choi’s prescription using eigenvectors of (2), they are defined up to mixing of those from degenerate eigenvalues ∗Partially supported by the National Science Foundation under Grant DMS-0604900 1 and we will refer to them as Choi-Kraus operators. Choi showed that Φ is an extreme † point of the set of CPT maps Φ : Md1 7→ Md2 if and only if the set {AjAk} is linearly independent in Md1 . This implies that the Choi matrix of an extreme CPT map has rank at most d1. -
Lecture 6: Quantum Error Correction and Quantum Capacity
Lecture 6: Quantum error correction and quantum capacity Mark M. Wilde∗ The quantum capacity theorem is one of the most important theorems in quantum Shannon theory. It is a fundamentally \quantum" theorem in that it demonstrates that a fundamentally quantum information quantity, the coherent information, is an achievable rate for quantum com- munication over a quantum channel. The fact that the coherent information does not have a strong analog in classical Shannon theory truly separates the quantum and classical theories of information. The no-cloning theorem provides the intuition behind quantum error correction. The goal of any quantum communication protocol is for Alice to establish quantum correlations with the receiver Bob. We know well now that every quantum channel has an isometric extension, so that we can think of another receiver, the environment Eve, who is at a second output port of a larger unitary evolution. Were Eve able to learn anything about the quantum information that Alice is attempting to transmit to Bob, then Bob could not be retrieving this information|otherwise, they would violate the no-cloning theorem. Thus, Alice should figure out some subspace of the channel input where she can place her quantum information such that only Bob has access to it, while Eve does not. That the dimensionality of this subspace is exponential in the coherent information is perhaps then unsurprising in light of the above no-cloning reasoning. The coherent information is an entropy difference H(B) − H(E)|a measure of the amount of quantum correlations that Alice can establish with Bob less the amount that Eve can gain. -
An Ecological Perspective on the Future of Computer Trading
An ecological perspective on the future of computer trading The Future of Computer Trading in Financial Markets - Foresight Driver Review – DR 6 An ecological perspective on the future of computer trading Contents 2. The role of computers in modern markets .................................................................................. 7 2.1 Computerization and trading ............................................................................................... 7 Execution................................................................................................................................7 Investment research ................................................................................................................ 7 Clearing and settlement ........................................................................................................... 7 2.2 A coarse preliminary taxonomy of computer trading .............................................................. 7 Execution algos....................................................................................................................... 8 Algorithmic trading................................................................................................................... 9 High Frequency Trading / Latency arbitrage............................................................................... 9 Algorithmic market making ....................................................................................................... 9 3. Ecology and evolution as key -
Arxiv:1803.00026V4 [Cond-Mat.Str-El] 8 Feb 2019 3 Variational Quantum-Classical Simulation (VQCS) 5
SciPost Physics Submission Efficient variational simulation of non-trivial quantum states Wen Wei Ho1*, Timothy H. Hsieh2,3, 1 Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA 2 Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106, USA 3 Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2L 2Y5, Canada *[email protected] February 12, 2019 Abstract We provide an efficient and general route for preparing non-trivial quantum states that are not adiabatically connected to unentangled product states. Our approach is a hybrid quantum-classical variational protocol that incorporates a feedback loop between a quantum simulator and a classical computer, and is experimen- tally realizable on near-term quantum devices of synthetic quantum systems. We find explicit protocols which prepare with perfect fidelities (i) the Greenberger- Horne-Zeilinger (GHZ) state, (ii) a quantum critical state, and (iii) a topologically ordered state, with L variational parameters and physical runtimes T that scale linearly with the system size L. We furthermore conjecture and support numeri- cally that our protocol can prepare, with perfect fidelity and similar operational costs, the ground state of every point in the one dimensional transverse field Ising model phase diagram. Besides being practically useful, our results also illustrate the utility of such variational ans¨atzeas good descriptions of non-trivial states of matter. Contents 1 Introduction 2 2 Non-trivial quantum states -
Capacity Estimates Via Comparison with TRO Channels
Commun. Math. Phys. 364, 83–121 (2018) Communications in Digital Object Identifier (DOI) https://doi.org/10.1007/s00220-018-3249-y Mathematical Physics Capacity Estimates via Comparison with TRO Channels Li Gao1 , Marius Junge1, Nicholas LaRacuente2 1 Department of Mathematics, University of Illinois, Urbana, IL 61801, USA. E-mail: [email protected]; [email protected] 2 Department of Physics, University of Illinois, Urbana, IL 61801, USA. E-mail: [email protected] Received: 1 November 2017 / Accepted: 27 July 2018 Published online: 8 September 2018 – © Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract: A ternary ring of operators (TRO) in finite dimensions is an operator space as an orthogonal sum of rectangular matrices. TROs correspond to quantum channels that are diagonal sums of partial traces, we call TRO channels. TRO channels have simple, single-letter entropy expressions for quantum, private, and classical capacity. Using operator space and interpolation techniques, we perturbatively estimate capacities, capacity regions, and strong converse rates for a wider class of quantum channels by comparison to TRO channels. 1. Introduction Channel capacity, introduced by Shannon in his foundational paper [45], is the ultimate rate at which information can be reliably transmitted over a communication channel. During the last decades, Shannon’s theory on noisy channels has been adapted to the framework of quantum physics. A quantum channel has various capacities depending on different communication tasks, such as quantum capacity for transmitting qubits, and private capacity for transmitting classical bits with physically ensured security. The coding theorems, which characterize these capacities by entropic expressions, were major successes in quantum information theory (see e.g. -
QIP 2010 Tutorial and Scientific Programmes
QIP 2010 15th – 22nd January, Zürich, Switzerland Tutorial and Scientific Programmes asymptotically large number of channel uses. Such “regularized” formulas tell us Friday, 15th January very little. The purpose of this talk is to give an overview of what we know about 10:00 – 17:10 Jiannis Pachos (Univ. Leeds) this need for regularization, when and why it happens, and what it means. I will Why should anyone care about computing with anyons? focus on the quantum capacity of a quantum channel, which is the case we understand best. This is a short course in topological quantum computation. The topics to be covered include: 1. Introduction to anyons and topological models. 15:00 – 16:55 Daniel Nagaj (Slovak Academy of Sciences) 2. Quantum Double Models. These are stabilizer codes, that can be described Local Hamiltonians in quantum computation very much like quantum error correcting codes. They include the toric code This talk is about two Hamiltonian Complexity questions. First, how hard is it to and various extensions. compute the ground state properties of quantum systems with local Hamiltonians? 3. The Jones polynomials, their relation to anyons and their approximation by Second, which spin systems with time-independent (and perhaps, translationally- quantum algorithms. invariant) local interactions could be used for universal computation? 4. Overview of current state of topological quantum computation and open Aiming at a participant without previous understanding of complexity theory, we will discuss two locally-constrained quantum problems: k-local Hamiltonian and questions. quantum k-SAT. Learning the techniques of Kitaev and others along the way, our first goal is the understanding of QMA-completeness of these problems. -
Arxiv:Quant-Ph/0110141V1 24 Oct 2001 Itr.Teuies a Aepromdn Oethan More Perf No Have Performed Can Have It Can Universe That the Operations History
Computational capacity of the universe Seth Lloyd d’ArbeloffLaboratory for Information Systems and Technology MIT Department of Mechanical Engineering MIT 3-160, Cambridge, Mass. 02139 [email protected] Merely by existing, all physical systems register information. And by evolving dynamically in time, they transform and process that information. The laws of physics determine the amount of information that aphysicalsystem can register (number of bits) and the number of elementary logic operations that a system can perform (number of ops). The universe is a physical system. This paper quantifies the amount of information that the universe can register and the number of elementary operations that it can have performed over its history. The universe can have performed no more than 10120 ops on 1090 bits. ‘Information is physical’1.ThisstatementofLandauerhastwocomplementaryinter- pretations. First, information is registered and processedbyphysicalsystems.Second,all physical systems register and process information. The description of physical systems in arXiv:quant-ph/0110141v1 24 Oct 2001 terms of information and information processing is complementary to the conventional de- scription of physical system in terms of the laws of physics. Arecentpaperbytheauthor2 put bounds on the amount of information processing that can beperformedbyphysical systems. The first limit is on speed. The Margolus/Levitin theorem3 implies that the total number of elementary operations that a system can perform persecondislimitedbyits energy: #ops/sec 2E/π¯h,whereE is the system’s average energy above the ground ≤ state andh ¯ =1.0545 10−34 joule-sec is Planck’s reduced constant. As the presence × of Planck’s constant suggests, this speed limit is fundamentally quantum mechanical,2−4 and as shown in (2), is actually attained by quantum computers,5−27 including existing 1 devices.15,16,21,23−27 The second limit is on memory space. -
Fault-Tolerant Quantum Computation: Theory and Practice
FAULT-TOLERANT QUANTUM COMPUTATION: THEORY AND PRACTICE FAULT-TOLERANT QUANTUM COMPUTATION: THEORY AND PRACTICE Dissertation for the purpose of obtaining the degree of doctor at Delft University of Technology, by the authority of the Rector Magnificus prof. dr. ir. T.H.J.J. van der Hagen, Chair of the Board of Doctorates, to be defended publicly on Wednesday 15th, January 2020 at 12:30 o’clock by Christophe VUILLOT Master of Science in Computer Science, Université Paris Diderot, Paris, France, born in Clamart, France. This dissertation has been approved by the promotor. promotor: prof. dr. B. M. Terhal Composition of the doctoral committee: Rector Magnificus, chairperson Prof. dr. B. M. Terhal Technische Universiteit Delft, promotor Independent members: Prof. dr. C.W.J. Beenakker Universiteit Leiden Prof. dr. L. DiCarlo Technische Universiteit Delft Prof. dr. R.T. König Technische Universität München Dr. A. Leverrier Inria Paris Prof. dr. ir. L.M.K. Vandersypen Technische Universiteit Delft Prof. dr. R.M. de Wolf Centrum Wiskunde & Informatica Keywords: quantum computing, quantum error correction, fault-tolerance Printed by: Gildeprint - www.gildeprint.nl Front: Kandinsky Vassily (1866-1944), Auf Weiss II, 1923 Photo © Centre Pompidou, MNAM-CCI, Dist. RMN-Grand Palais / image Centre Pompidou, MNAM-CCI Copyright © 2019 by C. Vuillot ISBN 978-94-6384-097-2 An electronic version of this dissertation is available at http://repository.tudelft.nl/. This thesis is dedicated to my daughter Andréa and her mother Lisa. CONTENTS Summary xi Preface xiii 1 Introduction 1 1.1 Introduction to quantum computing . 2 1.1.1 Quantum mechanics. 2 1.1.2 Elementary quantum systems .