DOCSLIB.ORG

Quantum Computing

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Quantum Computing Chapter 1 Brief overview 1.1 Linear Alzebra 1. Tensor Product: A Tensor product is a method of multiplying two tensors (matrices), given by the general (pneumonic) form: (It is represented as ) ⊗ a11 a12 a13 a14 ... a11M a12M a13M a14M ... a a a a ... a M a M a M a M ... 21 22 23 24 21 22 23 24 a31 a32 a33 a34 ... a31M a32M a33M a34M ... a a a a ... M = a M a M a M a M ... 41 42 43 44 ⊗ 41 42 43 44 ....... ....... ....... ....... ....... ....... where, M is any matrix. If the matrices on the LHS have the dimensions (D D ) and (D D )respectively, 1r × 1c 2r × 2c then the result matrix, on the RHS will have the dimensions: [(D + D ) (D + D )] DRAFT COPY1r 2r × 1c 2c It is really important to note that the above is NOT a formal definition for a tensor product, but it is just a pneumonic form. The result in this case seems to have the same dimensions as the original matrix in the LHS (first matrix). Only when we expand the RHS by putting various values of M,we will get the matrix of the dimensions (as given above). 1.2 Basic Quantum mechanics We shall look at fundamentals of quantum mechanics in greater detail in the next chapter. Some important definitions are: 1. State of a system:1 The state of a quantum system is a vector in the infinite dimensional complex vector space known as the Hilbert Space. The state of a classical system is represented by its position and momentum in a phase space. But this is not possible in Quantum Mechanics because of the built in concept of the Heisenberg’s Uncertainty principle. So, if we close in into one definite value of position for a position, the possible values that its momentum can take is infinite. So, we can only close on a given area, and say , with some probability that the particle lies within that area. So, the (classical) state of the particle lies anywhere 1Adeeperpictureofthisisgiveninthequantummechanicssection.Fornow,thisdescriptionwoulddo. 9 1.3. QUBIT - BASIC UNIT OF QUANTUM INFORMATION CHAPTER 1. BRIEF OVERVIEW in that continuous area that we define. So, the state of the particle has infinite position and momentum coordinates. Hence, it is represented as a vector in an infinite dimensional complex vector space (Hilbert Space). The state of a N-independent particle system where the individual particle wave functions are ψ , ψ , ψ ... ψ , the combined state of the N particle system is given by: | 1 | 2 | 3 | N ψ = ψ ψ ψ ...... ψ | | 1⊗| 2⊗| 3 ⊗| N In general, if ψ1 , ψ2 , ψ3 , ..... are vectors in N1, N2, N2, ..... dimensional complex vector spaces respectively, then| ψ| is a| vector in a (N + N + N + .....) dimensional complex vector space. | 1 2 2 2. Dirac Bra-c-Ket Notation: The dirac ket notation is a well known and frequently used here. In this notation, every column vector −→ψ is represented as: ψ which is also called a Ket vector. Similarly, a row vector is represented as ψ which is called a Bra| vector. Hence the name: BracKet notation. | 3. Local and non Local processes: By “local ”process between two particles , it is meant that influ- ences between the particles must travel in such a way that they pass through space continuously; i.e. the simultaneous disappearance of some quantity in one place cannot be balanced by its appearance somewhere else if that quantity didn’t travel, in some sense, across the space in between. In particular, this influence cannot travel faster than light, in order to preserve relativity theory. 4. Canonical Commutation Relations: The some observables in Quantum mechanics do not commute. That is, they have a non zero commutator. The commutator for a pair of operators is defined as: [A, B]=AB BA ——— Commutator − The basic commutator relations in quantum mechanics are: [xi,pj]=i [xi,xj]=0 [pi,pj]=0 1.3 Qubit - basic unit of quantum information A ’bit’, a classical two state system, represents the smallest unit of information. A classical bit is represented by 1 or 0. It can be thought of as ’true’ and ’false’ or any two complementary quantities whose union is the universe, and intersection is the null set. There is a profound reason to why the smallest unit of information DRAFTis a 1 or 0, or ’true’ or ’false’. This is because any logical querry COPY can be split into a series of ’yes’ or ’no’ questions. That is, with a series of ’yes’ or ’no’ answers to questions, we can perform any logical query. This is why a ’bit’ (which can be thought of as a most general strcture of storing information) is a 1 or a 0. A quantum bit, is just an example for a two state quantum system. A qubit can can also be an electron (with spin up and down), an ammonia molecule, etc. In quantum mechanics, a two state quantum system does not mean that it has only two states. This is what distinguishes a qubit from a classical bit. The difference comes due to a very important quantum mechanical phenomena known as interferrence.Justlikehowa classical bit can take a value 0 or 1, a quantum bit can take values 0 or 1 , and any value produced by the interferrence between the states 0 and 1 (like α 0 + β 1 ). Since,| there| are infinite such superpositions (where each of the states have 0 |and 1 given| by some| probability| amplitude α and β respectively), a qubit can exist in infinite states. If each state can store a unit of information, then the qubit can hold infinite units of information. A Qubit, like any other two level quantum system, is (conventionally) represented by its state: ψ = α + β | |↑ |↓ ψ = α + + β | | |− ψ = α 0 + β 1 | | | where α 2 + β 2 =1. | | | | GO TO FIRST PAGE 10 ↑ CHAPTER 1. BRIEF OVERVIEW 1.4. MULTIPLE QUBITS This can be misleading, since it gives us the feeling that a classical bit can at most carry 2 units of information whereas a quantum bit can carry infinitely many units. But, if a measurement is done on the state of the Qubit, it collapses into one of the eigen states of the measurement. So, if measurement of ψ gives ’a’, then after this measurement, the state of the Qubit will remain a (the eigen state of the measurement| corresponding to the eigen value a). This new state a now, will got give| the same measurement results as a . In fact it will not respond to any other measurement.| Why this happens Postulates| of Quantum Mechanics. Hence, only a single→ unit of information can be retrived from a Qubit. 1.4 Multiple Qubits Any two state system (like the electron which has a spin) can be represented by a Qubit. But what about representing the state of two electrons (which are independent of each other), using a qubit? Such a repre- sentation, we saw in the beginning of the chapter, was possible. If the state of one electron is ψ and state | 1 of the other electron is ψ2 , then the system of two independent electrons can be collectively represented by the state ψ ,where: | | ψ = ψ ψ | | 1⊗| 2 Since, we take a direct product of the two states, we may represent the now state, which is the two qubit state, as: (using the convention: i j ij ) | ⊗| ≡| ψ = α 00 + α 01 + α 10 + α 11 | 00| 01| 10| 11| where : α 2 + α 2 + α 2 + α 2 =1 | 00| | 01| | 10| | 11| 2 and αij is the probability of the first qubit being in state i , and the second Qubit being in state j .If we want| | only one of them, we must sum over the other. If we| want the probability of system being in| state 2 i only, we must sum αij over all j’s. | | | 2 2 So, the probability of measuring the first qubit to be 0 is = α00 + α01 , and obviously, the measurement 2 | 2| | | α00 + α01 will collapse the state of the qubit into ψ = | | | | . | α 2 + α 2 | 00| | 01| Therefore, we can say that in ths 2 qubit system, we can retrieve 2 units of information. It certainly DRAFTcan deliver more information than a single qubit system, but COPY there are some difficulties too. In general, we need to carry the measurement process twice to determine the information stored in both the qubits. So, earlier we were carrying out the measurement only once, and now we need to do it twice. Can it be better? Can we get away in one measurement itself? In other words, can we store some amount of information about one qubit in another, such that we can guess both the qubits, by measuring only one of them? The answer is yes. We can do such a trick that can, with certainty, retrieve the information stored in one qubit, by measuring the other. Such a two qubit state is called a Bell State or the EPR pair. 00 + 11 The Bell State is given by : ψ = | | | √2 1 Here, the first Qubit being is measured to be 0 with the Probability (changing the state to : ψ = 00 ) 2 | | 1 and 1 with Probability (Changing the state to : ψ = 11 ) 2 | | Hence, P(measuring the first qubit to be 0) = P(measuring the second qubit to be 0) , also state after the measurement of the first qubit to be 0 = state after the measurement of the second qubit to be 0.
Load more

Recommended publications
  • An Introduction Quantum Computing
    An Introduction to Quantum Computing Michal Charemza University of Warwick March 2005 Acknowledgments Special thanks are given to Steve Flammia and Bryan Eastin, authors of the LATEX package, Qcircuit, used to draw all the quantum circuits in this document. This package is available online at http://info.phys.unm.edu/Qcircuit/. Also thanks are given to Mika Hirvensalo, author of [11], who took the time to respond to some questions. 1 Contents 1 Introduction 4 2 Quantum States 6 2.1 CompoundStates........................... 8 2.2 Observation.............................. 9 2.3 Entanglement............................. 11 2.4 RepresentingGroups . 11 3 Operations on Quantum States 13 3.1 TimeEvolution............................ 13 3.2 UnaryQuantumGates. 14 3.3 BinaryQuantumGates . 15 3.4 QuantumCircuits .......................... 17 4 Boolean Circuits 19 4.1 BooleanCircuits ........................... 19 5 Superdense Coding 24 6 Quantum Teleportation 26 7 Quantum Fourier Transform 29 7.1 DiscreteFourierTransform . 29 7.1.1 CharactersofFiniteAbelianGroups . 29 7.1.2 DiscreteFourierTransform . 30 7.2 QuantumFourierTransform. 32 m 7.2.1 Quantum Fourier Transform in F2 ............. 33 7.2.2 Quantum Fourier Transform in Zn ............. 35 8 Random Numbers 38 9 Factoring 39 9.1 OneWayFunctions.......................... 39 9.2 FactorsfromOrder.......................... 40 9.3 Shor’sAlgorithm ........................... 42 2 CONTENTS 3 10 Searching 46 10.1 BlackboxFunctions. 46 10.2 HowNotToSearch.......................... 47 10.3 Single Query Without (Grover’s) Amplification . ... 48 10.4 AmplitudeAmplification. 50 10.4.1 SingleQuery,SingleSolution . 52 10.4.2 KnownNumberofSolutions. 53 10.4.3 UnknownNumberofSolutions . 55 11 Conclusion 57 Bibliography 59 Chapter 1 Introduction The classical computer was originally a largely theoretical concept usually at- tributed to Alan Turing, called the Turing Machine.
    [Show full text]
  • Introductory Topics in Quantum Paradigm
    Introductory Topics in Quantum Paradigm Subhamoy Maitra Indian Statistical Institute [[email protected]] 21 May, 2016 Subhamoy Maitra Quantum Information Outline of the talk Preliminaries of Quantum Paradigm What is a Qubit? Entanglement Quantum Gates No Cloning Indistinguishability of quantum states Details of BB84 Quantum Key Distribution Algorithm Description Eavesdropping State of the art: News and Industries Walsh Transform in Deutsch-Jozsa (DJ) Algorithm Deutsch-Jozsa Algorithm Walsh Transform Relating the above two Some implications Subhamoy Maitra Quantum Information Qubit and Measurement A qubit: αj0i + βj1i; 2 2 α; β 2 C, jαj + jβj = 1. Measurement in fj0i; j1ig basis: we will get j0i with probability jαj2, j1i with probability jβj2. The original state gets destroyed. Example: 1 + i 1 j0i + p j1i: 2 2 After measurement: we will get 1 j0i with probability 2 , 1 j1i with probability 2 . Subhamoy Maitra Quantum Information Basic Algebra Basic algebra: (α1j0i + β1j1i) ⊗ (α2j0i + β2j1i) = α1α2j00i + α1β2j01i + β1α2j10i + β1β2j11i, can be seen as tensor product. Any 2-qubit state may not be decomposed as above. Consider the state γ1j00i + γ2j11i with γ1 6= 0; γ2 6= 0. This cannot be written as (α1j0i + β1j1i) ⊗ (α2j0i + β2j1i). This is called entanglement. Known as Bell states or EPR pairs. An example of maximally entangled state is j00i + j11i p : 2 Subhamoy Maitra Quantum Information Quantum Gates n inputs, n outputs. Can be seen as 2n × 2n unitary matrices where the elements are complex numbers. Single input single output quantum gates. Quantum input Quantum gate Quantum Output αj0i + βj1i X βj0i + αj1i αj0i + βj1i Z αj0i − βj1i j0i+j1i j0i−|1i αj0i + βj1i H α p + β p 2 2 Subhamoy Maitra Quantum Information Quantum Gates (contd.) 1 input, 1 output.
    [Show full text]
  • A Gentle Introduction to Quantum Computing Algorithms With
    A Gentle Introduction to Quantum Computing Algorithms with Applications to Universal Prediction Elliot Catt1 Marcus Hutter1,2 1Australian National University, 2Deepmind {elliot.carpentercatt,marcus.hutter}@anu.edu.au May 8, 2020 Abstract In this technical report we give an elementary introduction to Quantum Computing for non- physicists. In this introduction we describe in detail some of the foundational Quantum Algorithms including: the Deutsch-Jozsa Algorithm, Shor’s Algorithm, Grocer Search, and Quantum Count- ing Algorithm and briefly the Harrow-Lloyd Algorithm. Additionally we give an introduction to Solomonoff Induction, a theoretically optimal method for prediction. We then attempt to use Quan- tum computing to find better algorithms for the approximation of Solomonoff Induction. This is done by using techniques from other Quantum computing algorithms to achieve a speedup in com- puting the speed prior, which is an approximation of Solomonoff’s prior, a key part of Solomonoff Induction. The major limiting factors are that the probabilities being computed are often so small that without a sufficient (often large) amount of trials, the error may be larger than the result. If a substantial speedup in the computation of an approximation of Solomonoff Induction can be achieved through quantum computing, then this can be applied to the field of intelligent agents as a key part of an approximation of the agent AIXI. arXiv:2005.03137v1 [quant-ph] 29 Apr 2020 1 Contents 1 Introduction 3 2 Preliminaries 4 2.1 Probability ......................................... 4 2.2 Computability ....................................... 5 2.3 ComplexityTheory................................... .. 7 3 Quantum Computing 8 3.1 Introduction...................................... ... 8 3.2 QuantumTuringMachines .............................. .. 9 3.2.1 Church-TuringThesis ..............................
    [Show full text]
  • Encryption of Binary and Non-Binary Data Using Chained Hadamard Transforms
    Encryption of Binary and Non-Binary Data Using Chained Hadamard Transforms Rohith Singi Reddy Computer Science Department Oklahoma State University, Stillwater, OK 74078 ABSTRACT This paper presents a new chaining technique for the use of Hadamard transforms for encryption of both binary and non-binary data. The lengths of the input and output sequence need not be identical. The method may be used also for hashing. INTRODUCTION The Hadamard transform is an example of generalized class of Fourier transforms [4], and it may be defined either recursively, or by using binary representation. Its symmetric form lends itself to applications ranging across many technical fields such as data encryption [1], signal processing [2], data compression algorithms [3], randomness measures [6], and so on. Here we consider an application of the Hadamard matrix to non-binary numbers. To do so, Hadamard transform is generalized such that all the values in the matrix are non negative. Each negative number is replaced with corresponding modulo number; for example while performing modulo 7 operations -1 is replaced with 6 to make the matrix non-binary. Only prime modulo operations are performed because non prime numbers can be divisible with numbers other than 1 and itself. The use of modulo operation along with generalized Hadamard matrix limits the output range and decreases computation complexity. In the method proposed in this paper, the input sequence is split into certain group of bits such that each group bit count is a prime number. As we are dealing with non-binary numbers, for each group of binary bits their corresponding decimal value is calculated.
    [Show full text]
  • Dominant Strategies of Quantum Games on Quantum Periodic Automata
    Computation 2015, 3, 586-599; doi:10.3390/computation3040586 OPEN ACCESS computation ISSN 2079-3197 www.mdpi.com/journal/computation Article Dominant Strategies of Quantum Games on Quantum Periodic Automata Konstantinos Giannakis y;*, Christos Papalitsas y, Kalliopi Kastampolidou y, Alexandros Singh y and Theodore Andronikos y Department of Informatics, Ionian University, 7 Tsirigoti Square, Corfu 49100, Greece; E-Mails: [email protected] (C.P.); [email protected] (K.K.); [email protected] (A.S.); [email protected] (T.A.) y These authors contributed equally to this work. * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +30-266-108-7712. Academic Editor: Demos T. Tsahalis Received: 29 August 2015 / Accepted: 16 November 2015 / Published: 20 November 2015 Abstract: Game theory and its quantum extension apply in numerous fields that affect people’s social, political, and economical life. Physical limits imposed by the current technology used in computing architectures (e.g., circuit size) give rise to the need for novel mechanisms, such as quantum inspired computation. Elements from quantum computation and mechanics combined with game-theoretic aspects of computing could open new pathways towards the future technological era. This paper associates dominant strategies of repeated quantum games with quantum automata that recognize infinite periodic inputs. As a reference, we used the PQ-PENNY quantum game where the quantum strategy outplays the choice of pure or mixed strategy with probability 1 and therefore the associated quantum automaton accepts with probability 1. We also propose a novel game played on the evolution of an automaton, where players’ actions and strategies are also associated with periodic quantum automata.
    [Show full text]
  • Hadamard Phylogenetic Methods and the N-Taxon Process
    Bulletin of Mathematical Biology (2009) 71: 339–351 DOI 10.1007/s11538-008-9364-8 ORIGINAL ARTICLE Hadamard Phylogenetic Methods and the n-taxon Process David Bryant Department of Mathematics, University of Auckland, Auckland, New Zealand Received: 11 December 2007 / Accepted: 18 September 2008 / Published online: 10 October 2008 © Society for Mathematical Biology 2008 Abstract The Hadamard transform (Hendy and Penny, Syst. Zool. 38(4):297–309, 1989; Hendy, Syst. Zool. 38(4):310–321, 1989) provides a way to work with stochastic mod- els for sequence evolution without having to deal with the complications of tree space and the graphical structure of trees. Here we demonstrate that the transform can be ex- pressed in terms of the familiar P[τ]=eQ[τ] formula for Markov chains. The key idea is to study the evolution of vectors of states, one vector entry for each taxa; we call this the n-taxon process. We derive transition probabilities for the process. Significantly, the find- ings show that tree-based models are indeed in the family of (multi-variate) exponential distributions. Keywords Phylogenetics · Stochastic models · Hadamard conjugation · Spectral decomposition 1. Introduction 1.1. Stochastic models and the Hadamard transform Stochastic models for sequence evolution now play a part in most phylogenetic analyses. Given a tree, and a set of branch lengths, the models determine a probability distribution for the patterns of nucleotides/amino acids observed at a site in the alignment (the site patterns). The real difficulty of these tree-based models is that they are, indeed, based on a tree. The graphical structure of the tree is intrinsic to the probability formulas.
    [Show full text]
  • Quantum Computing: Lecture Notes
    Quantum Computing: Lecture Notes Ronald de Wolf Preface These lecture notes were formed in small chunks during my “Quantum computing” course at the University of Amsterdam, Feb-May 2011, and compiled into one text thereafter. Each chapter was covered in a lecture of 2 45 minutes, with an additional 45-minute lecture for exercises and × homework. The first half of the course (Chapters 1–7) covers quantum algorithms, the second half covers quantum complexity (Chapters 8–9), stuff involving Alice and Bob (Chapters 10–13), and error-correction (Chapter 14). A 15th lecture about physical implementations and general outlook was more sketchy, and I didn’t write lecture notes for it. These chapters may also be read as a general introduction to the area of quantum computation and information from the perspective of a theoretical computer scientist. While I made an effort to make the text self-contained and consistent, it may still be somewhat rough around the edges; I hope to continue polishing and adding to it. Comments & constructive criticism are very welcome, and can be sent to [email protected] Attribution and acknowledgements Most of the material in Chapters 1–6 comes from the first chapter of my PhD thesis [71], with a number of additions: the lower bound for Simon, the Fourier transform, the geometric explanation of Grover. Chapter 7 is newly written for these notes, inspired by Santha’s survey [62]. Chapters 8 and 9 are largely new as well. Section 3 of Chapter 8, and most of Chapter 10 are taken (with many changes) from my “quantum proofs” survey paper with Andy Drucker [28].
    [Show full text]
  • Experimental Demonstration of a Hadamard Gate for Coherent State Qubits
    Downloaded from orbit.dtu.dk on: Sep 24, 2021 Experimental demonstration of a Hadamard gate for coherent state qubits Tipsmark, Anders; Dong, Ruifang; Laghaout, Amine; Marek, Petr; Jezek, Miroslav; Andersen, Ulrik Lund Published in: Physical Review A Link to article, DOI: 10.1103/PhysRevA.84.050301 Publication date: 2011 Document Version Publisher's PDF, also known as Version of record Link back to DTU Orbit Citation (APA): Tipsmark, A., Dong, R., Laghaout, A., Marek, P., Jezek, M., & Andersen, U. L. (2011). Experimental demonstration of a Hadamard gate for coherent state qubits. Physical Review A, 84(5), -. https://doi.org/10.1103/PhysRevA.84.050301 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. RAPID COMMUNICATIONS PHYSICAL REVIEW A 84, 050301(R) (2011) Experimental demonstration of a Hadamard gate for coherent state qubits Anders Tipsmark,1,* Ruifang Dong,2,1 Amine Laghaout,1 Petr Marek,3 Miroslav Jezek,ˇ 3,1 and Ulrik L.
    [Show full text]
  • On Quantum Algorithms
    Contribution to Complexity On quantum algorithms Richard Cleve, Artur Ekert, Leah Henderson, Chiara Macchiavello and Michele Mosca Centre for Quantum Computation Clarendon Laboratory, University of Oxford, Oxford OX1 3PU, U.K. Department of Computer Science University of Calgary, Calgary, Alberta, Canada T2N 1N4 Theoretical Quantum Optics Group Dipartimento di Fisica “A. Volta” and I.N.F.M. - Unit`adi Pavia Via Bassi 6, I-27100 Pavia, Italy Abstract Quantum computers use the quantum interference of different computational paths to en- hance correct outcomes and suppress erroneous outcomes of computations. In effect, they follow the same logical paradigm as (multi-particle) interferometers. We show how most known quan- tum algorithms, including quantum algorithms for factorising and counting, may be cast in this manner. Quantum searching is described as inducing a desired relative phase between two eigen- vectors to yield constructive interference on the sought elements and destructive interference on the remaining terms. 1 From Interferometers to Computers Richard Feynman [1] in his talk during the First Conference on the Physics of Computation held at MIT in 1981 observed that it appears to be impossible to simulate a general quantum evolution on a classical probabilistic computer in an efficient way. He pointed out that any classical simulation of quantum evolution appears to involve an exponential slowdown in time as compared to the natural evolution since the amount of information required to describe the evolving quantum state in classical terms generally grows exponentially in time. However, instead of viewing this as an obstacle, Feynman regarded it as an opportunity. If it requires so much computation to work out what will happen in a arXiv:quant-ph/9903061v1 17 Mar 1999 complicated multiparticle interference experiment then, he argued, the very act of setting up such an experiment and measuring the outcome is tantamount to performing a complex computation.
    [Show full text]
  • Efficient Classical Simulation of Random Shallow 2D Quantum Circuits
    Efficient classical simulation of random shallow 2D quantum circuits John Napp* Rolando L. La Placa† Alexander M. Dalzell‡ Fernando G. S. L. Brandao˜ § Aram W. Harrow¶ February 13, 2020 Abstract Random quantum circuits are commonly viewed as hard to simulate classically. In some regimes this has been formally conjectured — in the context of deep 2D circuits, this is the basis for Google’s recent announcement of “quantum computational supremacy” — and there had been no evidence against the more general possibility that for circuits with uniformly ran- dom gates, approximate simulation of typical instances is almost as hard as exact simulation. We prove that this is not the case by exhibiting a shallow random circuit family that cannot be efficiently classically simulated exactly under standard hardness assumptions, but can be simulated approximately for all but a superpolynomially small fraction of circuit instances in time linear in the number of qubits and gates; this example limits the robustness of re- cent worst-case-to-average-case reductions for random circuit simulation. While our proof is based on a contrived random circuit family, we furthermore conjecture that sufficiently shal- low constant-depth random circuits are efficiently simulable more generally. To this end, we propose and analyze two simulation algorithms. Implementing one of our algorithms for the depth-3 “brickwork” architecture, for which exact simulation is hard, we found that a laptop could simulate typical instances on a 409 409 grid with variational distance error less than 0:01 in approximately one minute per sample,× a task intractable for previously known cir- cuit simulation algorithms.
    [Show full text]
  • Quantum Algorithms
    Quantum algorithms Andrew Childs Pawel Wocjan University of Waterloo University of Central Florida 10th Canadian Summer School on Quantum Information 17{19 July 2010 Outline I. Quantum circuits II. Elementary quantum algorithms III. The QFT and phase estimation IV. Factoring V. Quantum search VI. Quantum walk Part I Quantum circuits Quantum circuit model Quantum circuits are generalizations of Boolean circuits input transformation output (probabilistic) 1 U1 0 j i U3 U6 1 U5 1 j i U2 NM 0 0 j i U6 NM 1 U4 1 j i U3 U7 NM 0 1 j i NM NM Classical bit Classical bit (bit): B := 0; 1 f g I Basis state: either 0 or 1 I General state: a probability distribution p = (p0; p1) on B Classical register n Classical register: B := B B ::: B × × × | {zn } n I Basis state: a binary string x B 2 n I General state: a probability distribution p = (px : x B ) on n 2 B (written as a column vector) Remark: Note that p is a vector with positive entries that is normalized with respect to the `1-norm (the sum of the absolute values of the entries) Classical transformation Transformations on the classical register B are described by stochastic matrices Stochastic matrices preserve the `1-norm, i.e., probability distributions are mapped on probability distributions Let p be the state of the register. The state after the transformation P is given by the matrix-vector-product Pp Qubit 2 Quantum bit (qubit): two-dimensional complex Hilbert space C I Computational basis states (classical states): 1 0 0 := and 1 := j i 0 j i 1 I General states: superpositions α0
    [Show full text]
  • Quantum Algorithms Via Linear Algebra: a Primer / Richard J
    QUANTUM ALGORITHMS VIA LINEAR ALGEBRA A Primer Richard J. Lipton Kenneth W. Regan The MIT Press Cambridge, Massachusetts London, England c 2014 Massachusetts Institute of Technology All rights reserved. No part of this book may be reproduced in any form or by any electronic or mechanical means (including photocopying, recording, or information storage and retrieval) without permission in writing from the publisher. MIT Press books may be purchased at special quantity discounts for business or sales promotional use. For information, please email special [email protected]. This book was set in Times Roman and Mathtime Pro 2 by the authors, and was printed and bound in the United States of America. Library of Congress Cataloging-in-Publication Data Lipton, Richard J., 1946– Quantum algorithms via linear algebra: a primer / Richard J. Lipton and Kenneth W. Regan. p. cm. Includes bibliographical references and index. ISBN 978-0-262-02839-4 (hardcover : alk. paper) 1. Quantum computers. 2. Computer algorithms. 3. Algebra, Linear. I. Regan, Kenneth W., 1959– II. Title QA76.889.L57 2014 005.1–dc23 2014016946 10987654321 We dedicate this book to all those who helped create and nourish the beautiful area of quantum algorithms, and to our families who helped create and nourish us. RJL and KWR Contents Preface xi Acknowledgements xiii 1 Introduction 1 1.1 The Model 2 1.2 The Space and the States 3 1.3 The Operations 5 1.4 Where Is the Input? 6 1.5 What Exactly Is the Output? 7 1.6 Summary and Notes 8 2 Numbers and Strings 9 2.1 Asymptotic Notation
    [Show full text]