WorldWideScience

Sample records for scb quantum computers

  1. SCB Quantum Computers Using iSWAP and 1-Qubit Rotations

    Science.gov (United States)

    Williams, Colin; Echtemach, Pierre

    2005-01-01

    Units of superconducting circuitry that exploit the concept of the single- Cooper-pair box (SCB) have been built and are undergoing testing as prototypes of logic gates that could, in principle, constitute building blocks of clocked quantum computers. These units utilize quantized charge states as the quantum information-bearing degrees of freedom. An SCB is an artificial two-level quantum system that comprises a nanoscale superconducting electrode connected to a reservoir of Cooper-pair charges via a Josephson junction. The logical quantum states of the device, .0. and .1., are implemented physically as a pair of charge-number states that differ by 2e (where e is the charge of an electron). Typically, some 109 Cooper pairs are involved. Transitions between the logical states are accomplished by tunneling of Cooper pairs through the Josephson junction. Although the two-level system contains a macroscopic number of charges, in the superconducting regime, they behave collectively, as a Bose-Einstein condensate, making possible a coherent superposition of the two logical states. This possibility makes the SCB a candidate for the physical implementation of a qubit. A set of quantum logic operations and the gates that implement them is characterized as universal if, in principle, one can form combinations of the operations in the set to implement any desired quantum computation. To be able to design a practical quantum computer, one must first specify how to decompose any valid quantum computation into a sequence of elementary 1- and 2-qubit quantum gates that are universal and that can be realized in hardware that is feasible to fabricate. Traditionally, the set of universal gates has been taken to be the set of all 1-qubit quantum gates in conjunction with the controlled-NOT (CNOT) gate, which is a 2-qubit gate. Also, it has been known for some time that the SWAP gate, which implements square root of the simple 2-qubit exchange interaction, is as computationally universal as is the CNOT operation.

  2. Universal quantum gates for Single Cooper Pair Box based quantum computing

    Science.gov (United States)

    Echternach, P.; Williams, C. P.; Dultz, S. C.; Braunstein, S.; Dowling, J. P.

    2000-01-01

    We describe a method for achieving arbitrary 1-qubit gates and controlled-NOT gates within the context of the Single Cooper Pair Box (SCB) approach to quantum computing. Such gates are sufficient to support universal quantum computation.

  3. Semiconductor bridge (SCB) detonator

    Science.gov (United States)

    Bickes, Jr., Robert W. (Albuquerque, NM); Grubelich, Mark C. (Albuquerque, NM)

    1999-01-01

    The present invention is a low-energy detonator for high-density secondary-explosive materials initiated by a semiconductor bridge igniter that comprises a pair of electrically conductive lands connected by a semiconductor bridge. The semiconductor bridge is in operational or direct contact with the explosive material, whereby current flowing through the semiconductor bridge causes initiation of the explosive material. Header wires connected to the electrically-conductive lands and electrical feed-throughs of the header posts of explosive devices, are substantially coaxial to the direction of current flow through the SCB, i.e., substantially coaxial to the SCB length.

  4. Quantum computing

    OpenAIRE

    Li, Shu-shen; Long, Gui-Lu; Bai, Feng-Shan; Feng, Song-Lin; Zheng, Hou-Zhi

    2001-01-01

    Quantum computing is a quickly growing research field. This article introduces the basic concepts of quantum computing, recent developments in quantum searching, and decoherence in a possible quantum dot realization.

  5. Quantum Computing

    OpenAIRE

    Kiili, Markus

    1997-01-01

    The aim of this thesis was to explain what quantum computing is. The information for the thesis was gathered from books, scientific publications, and news articles. The analysis of the information revealed that quantum computing can be broken down to three areas: theories behind quantum computing explaining the structure of a quantum computer, known quantum algorithms, and the actual physical realizations of a quantum computer. The thesis reveals that moving from classical memor...

  6. Quantum Computing

    CERN Document Server

    Steane, A M

    1998-01-01

    The subject of quantum computing brings together ideas from classical information theory, computer science, and quantum physics. This review aims to summarise not just quantum computing, but the whole subject of quantum information theory. It turns out that information theory and quantum mechanics fit together very well. In order to explain their relationship, the review begins with an introduction to classical information theory and computer science, including Shannon's theorem, error correcting codes, Turing machines and computational complexity. The principles of quantum mechanics are then outlined, and the EPR experiment described. The EPR-Bell correlations, and quantum entanglement in general, form the essential new ingredient which distinguishes quantum from classical information theory, and, arguably, quantum from classical physics. Basic quantum information ideas are described, including key distribution, teleportation, data compression, quantum error correction, the universal quantum computer and qua...

  7. Quantum Computation

    CERN Document Server

    Aharonov, D

    1998-01-01

    In the last few years, theoretical study of quantum systems serving as computational devices has achieved tremendous progress. We now have strong theoretical evidence that quantum computers, if built, might be used as a dramatically powerful computational tool. This review is about to tell the story of theoretical quantum computation. I left out the developing topic of experimental realizations of the model, and neglected other closely related topics which are quantum information and quantum communication. As a result of narrowing the scope of this paper, I hope it has gained the benefit of being an almost self contained introduction to the exciting field of quantum computation. The review begins with background on theoretical computer science, Turing machines and Boolean circuits. In light of these models, I define quantum computers, and discuss the issue of universal quantum gates. Quantum algorithms, including Shor's factorization algorithm and Grover's algorithm for searching databases, are explained. I w...

  8. Quantum computing

    International Nuclear Information System (INIS)

    The subject of quantum computing brings together ideas from classical information theory, computer science, and quantum physics. This review aims to summarize not just quantum computing, but the whole subject of quantum information theory. Information can be identified as the most general thing which must propagate from a cause to an effect. It therefore has a fundamentally important role in the science of physics. However, the mathematical treatment of information, especially information processing, is quite recent, dating from the mid-20th century. This has meant that the full significance of information as a basic concept in physics is only now being discovered. This is especially true in quantum mechanics. The theory of quantum information and computing puts this significance on a firm footing, and has led to some profound and exciting new insights into the natural world. Among these are the use of quantum states to permit the secure transmission of classical information (quantum cryptography), the use of quantum entanglement to permit reliable transmission of quantum states (teleportation), the possibility of preserving quantum coherence in the presence of irreversible noise processes (quantum error correction), and the use of controlled quantum evolution for efficient computation (quantum computation). The common theme of all these insights is the use of quantum entanglement as a computational resource. It turns out that information theory and quantum mechanics fit together very well. In order to explain their relationship, this review begins with an introduction to classical information theory and computer science, including Shannon's theorem, error correcting codes, Turing machines and computational complexity. The principles of quantum mechanics are then outlined, and the Einstein, Podolsky and Rosen (EPR) experiment described. The EPR-Bell correlations, and quantum entanglement in general, form the essential new ingredient which distinguishes quantum from classical information theory and, arguably, quantum from classical physics. Basic quantum information ideas are next outlined, including qubits and data compression, quantum gates, the 'no cloning' property and teleportation. Quantum cryptography is briefly sketched. The universal quantum computer (QC) is described, based on the Church-Turing principle and a network model of computation. Algorithms for such a computer are discussed, especially those for finding the period of a function, and searching a random list. Such algorithms prove that a QC of sufficiently precise construction is not only fundamentally different from any computer which can only manipulate classical information, but can compute a small class of functions with greater efficiency. This implies that some important computational tasks are impossible for any device apart from a QC. To build a universal QC is well beyond the abilities of current technology. However, the principles of quantum information physics can be tested on smaller devices. The current experimental situation is reviewed, with emphasis on the linear ion trap, high-Q optical cavities, and nuclear magnetic resonance methods. These allow coherent control in a Hilbert space of eight dimensions (three qubits) and should be extendable up to a thousand or more dimensions (10 qubits). Among other things, these systems will allow the feasibility of quantum computing to be assessed. In fact such experiments are so difficult that it seemed likely until recently that a practically useful QC (requiring, say, 1000 qubits) was actually ruled out by considerations of experimental imprecision and the unavoidable coupling between any system and its environment. However, a further fundamental part of quantum information physics provides a solution to this impasse. This is quantum error correction (QEC). An introduction to QEC is provided. The evolution of the QC is restricted to a carefully chosen subspace of its Hilbert space. Errors are almost certain to cause a departure from this subspace. QEC provides a means to detect and undo such depar

  9. Quantum computing

    OpenAIRE

    Eisert, J; M. M. Wolf

    2004-01-01

    This article gives an elementary introduction to quantum computing. It is a draft for a book chapter of the "Handbook of Nature-Inspired and Innovative Computing", Eds. A. Zomaya, G.J. Milburn, J. Dongarra, D. Bader, R. Brent, M. Eshaghian-Wilner, F. Seredynski (Springer, Berlin Heidelberg New York, 2006).

  10. Unconventional Quantum Computing Devices

    OpenAIRE

    Lloyd, Seth

    2000-01-01

    This paper investigates a variety of unconventional quantum computation devices, including fermionic quantum computers and computers that exploit nonlinear quantum mechanics. It is shown that unconventional quantum computing devices can in principle compute some quantities more rapidly than `conventional' quantum computers.

  11. Quantum walk computation

    International Nuclear Information System (INIS)

    Quantum versions of random walks have diverse applications that are motivating experimental implementations as well as theoretical studies. Recent results showing quantum walks are “universal for quantum computation” relate to algorithms, to be run on quantum computers. We consider whether an experimental implementation of a quantum walk could provide useful computation before we have a universal quantum computer

  12. Quantum information and computation

    OpenAIRE

    Bub, Jeffrey

    2005-01-01

    This article deals with theoretical developments in the subject of quantum information and quantum computation, and includes an overview of classical information and some relevant quantum mechanics. The discussion covers topics in quantum communication, quantum cryptography, and quantum computation, and concludes by considering whether a perspective in terms of quantum information sheds new light on the conceptual problems of quantum mechanics.

  13. Quantum computation for quantum chemistry

    Science.gov (United States)

    Aspuru-Guzik, Alan

    2010-03-01

    Numerically exact simulation of quantum systems on classical computers is in general, an intractable computational problem. Computational chemists have made progress in the development of approximate methods to tackle complex chemical problems. The downside of these approximate methods is that their failure for certain important cases such as long-range charge transfer states in the case of traditional density functional theory. In 1982, Richard Feynman suggested that a quantum device should be able to simulate quantum systems (in our case, molecules) exactly using quantum computers in a tractable fashion. Our group has been working in the development of quantum chemistry algorithms for quantum devices. In this talk, I will describe how quantum computers can be employed to carry out numerically exact quantum chemistry and chemical reaction dynamics calculations, as well as molecular properties. Finally, I will describe our recent experimental quantum computation of the energy of the hydrogen molecule using an optical quantum computer.

  14. Quantum Computational Complexity

    OpenAIRE

    Watrous, John

    2008-01-01

    This article surveys quantum computational complexity, with a focus on three fundamental notions: polynomial-time quantum computations, the efficient verification of quantum proofs, and quantum interactive proof systems. Properties of quantum complexity classes based on these notions, such as BQP, QMA, and QIP, are presented. Other topics in quantum complexity, including quantum advice, space-bounded quantum computation, and bounded-depth quantum circuits, are also discussed.

  15. Merging boron solid state and molecular chemistry: Energy landscapes in the exo/endo closo-borane complex Sc[B24H24]+

    Science.gov (United States)

    Oliva, Josep M.; Vegas, Ángel

    2012-04-01

    The crystal structure of ScB12 suggests the possible existence of the closo B24H242- borane and derived exo and endohedral complexes. The extraction of the B24 'perfect' truncated octahedron from the ScB12 crystal structure and the minimization of the energy by means of quantum-chemical computations leads to a snub cube structure. The two found stable exohedral structures are energetically more favorable than the endohedral complex by only ?1 and ?9 kcal/mol. The optimized geometry of the B24H242- molecular structure can be derived from the crystal fragment through a shrinkage plus pseudo-rotation of the B24 cage. Analogous solid structures embedding truncated octahedra are also compared with the title structure.

  16. Automata and Quantum Computing

    OpenAIRE

    Ambainis, Andris; Yakaryilmaz, Abuzer

    2015-01-01

    Quantum computing is a new model of computation, based on quantum physics. Quantum computers can be exponentially faster than conventional computers for problems such as factoring. Besides full-scale quantum computers, more restricted models such as quantum versions of finite automata have been studied. In this paper, we survey various models of quantum finite automata and their properties. We also provide some open questions and new directions for researchers.

  17. Quantum Computing for Computer Architects

    CERN Document Server

    Metodi, Tzvetan

    2011-01-01

    Quantum computers can (in theory) solve certain problems far faster than a classical computer running any known classical algorithm. While existing technologies for building quantum computers are in their infancy, it is not too early to consider their scalability and reliability in the context of the design of large-scale quantum computers. To architect such systems, one must understand what it takes to design and model a balanced, fault-tolerant quantum computer architecture. The goal of this lecture is to provide architectural abstractions for the design of a quantum computer and to explore

  18. Physics of quantum computation

    International Nuclear Information System (INIS)

    In the paper, the modern status of the theory of quantum computation is considered. The fundamental principles of quantum computers and their basic notions such as quantum processors and computational basis states of the quantum Turing machine as well as the quantum Fourier transform are discussed. Some possible experimental realizations on the basis of NMR methods are given

  19. Study of Quantum Computing

    Directory of Open Access Journals (Sweden)

    Prashant Anil Patil

    2012-04-01

    Full Text Available This paper gives the detailed information about Quantum computer, and difference between quantum computer and traditional computers, the basis of Quantum computers which are slightly similar but still different from traditional computer. Many research groups are working towards the highly technological goal of building a quantum computer, which would dramatically improve computational power for particular tasks. Quantum computer is very much use full for computation purpose in field of Science and Research. Large amount of data and information will be computed, processing, storing, retrieving, transmitting and displaying information in less time with that much of accuracy which is not provided by traditional computers.

  20. Hybrid quantum computing

    OpenAIRE

    Lloyd, Seth

    2000-01-01

    Necessary and sufficient conditions are given for the construction of a hybrid quantum computer that operates on both continuous and discrete quantum variables. Such hybrid computers are shown to be more efficient than conventional quantum computers for performing a variety of quantum algorithms, such as computing eigenvectors and eigenvalues.

  1. Quantum Computer Games: Quantum Minesweeper

    Science.gov (United States)

    Gordon, Michal; Gordon, Goren

    2010-01-01

    The computer game of quantum minesweeper is introduced as a quantum extension of the well-known classical minesweeper. Its main objective is to teach the unique concepts of quantum mechanics in a fun way. Quantum minesweeper demonstrates the effects of superposition, entanglement and their non-local characteristics. While in the classical…

  2. Quantum Computation via Paraconsistent Computation

    OpenAIRE

    Agudelo, Juan C.; Carnielli, Walter

    2006-01-01

    We present an original model of paraconsistent Turing machines (PTMs), a generalization of the classical Turing machines model of computation using a paraconsistent logic. Next, we briefl y describe the standard models of quantum computation: quantum Turing machines and quantum circuits, and revise quantum algorithms to solve the so-called Deutsch's problem and Deutsch-Jozsa problem. Then, we show the potentialities of the PTMs model of computation simulating the presented q...

  3. Quantum robots and quantum computers

    Energy Technology Data Exchange (ETDEWEB)

    Benioff, P.

    1998-07-01

    Validation of a presumably universal theory, such as quantum mechanics, requires a quantum mechanical description of systems that carry out theoretical calculations and systems that carry out experiments. The description of quantum computers is under active development. No description of systems to carry out experiments has been given. A small step in this direction is taken here by giving a description of quantum robots as mobile systems with on board quantum computers that interact with different environments. Some properties of these systems are discussed. A specific model based on the literature descriptions of quantum Turing machines is presented.

  4. Integrable Quantum Computation

    OpenAIRE

    Zhang, Yong

    2011-01-01

    Integrable quantum computation is defined as quantum computing via the integrable condition, in which two-qubit gates are either nontrivial unitary solutions of the Yang--Baxter equation or the Swap gate (permutation). To make the definition clear, in this article, we explore the physics underlying the quantum circuit model, and then present a unified description on both quantum computing via the Bethe ansatz and quantum computing via the Yang--Baxter equation.

  5. What is quantum computation?

    CERN Document Server

    Patel, A D

    1999-01-01

    Quantum computation is a rapidly progressing field today. What are its principles? In what sense is it distinct from conventional computation? What are its advantages and disadvantages? What type of problems can it address? How practical is it to make a quantum computer? I summarise some of the important concepts of quantum computation, in an attempt to answer these questions. A deeper

  6. Introduction to Quantum Computation

    Science.gov (United States)

    Ekert, A.

    A computation is a physical process. It may be performed by a piece of electronics or on an abacus, or in your brain, but it is a process that takes place in nature and as such it is subject to the laws of physics. Quantum computers are machines that rely on characteristically quantum phenomena, such as quantum interference and quantum entanglement in order to perform computation. In this series of lectures I want to elaborate on the computational power of such machines.

  7. Quantum mechanics and computation

    International Nuclear Information System (INIS)

    We review how some of the basic principles of Quantum Mechanics can be used in the field of computation. In particular, we explain why a quantum computer can perform certain tasks in a much more efficient way than the computers we have available nowadays. We give the requirements for a quantum system to be able to implement a quantum computer and illustrate these requirements in some particular physical situations. (Author) 16 refs

  8. Quantum Computers and Quantum Coherence

    CERN Document Server

    Di Vincenzo, D P

    1999-01-01

    If the states of spins in solids can be created, manipulated, and measured at the single-quantum level, an entirely new form of information processing, quantum computing, will be possible. We first give an overview of quantum information processing, showing that the famous Shor speedup of integer factoring is just one of a host of important applications for qubits, including cryptography, counterfeit protection, channel capacity enhancement, distributed computing, and others. We review our proposed spin-quantum dot architecture for a quantum computer, and we indicate a variety of first generation materials, optical, and electrical measurements which should be considered. We analyze the efficiency of a two-dot device as a transmitter of quantum information via the ballistic propagation of carriers in a Fermi sea.

  9. Introduction to quantum computers

    CERN Document Server

    Berman, Gennady P; Mainieri, Ronnie; Tsifrinovich, Vladimir I

    1998-01-01

    Quantum computing promises to solve problems which are intractable on digital computers. Highly parallel quantum algorithms can decrease the computational time for some problems by many orders of magnitude. This important book explains how quantum computers can do these amazing things. Several algorithms are illustrated: the discrete Fourier transform, Shor’s algorithm for prime factorization; algorithms for quantum logic gates; physical implementations of quantum logic gates in ion traps and in spin chains; the simplest schemes for quantum error correction; correction of errors caused by im

  10. Scalable optical quantum computer

    Energy Technology Data Exchange (ETDEWEB)

    Manykin, E A; Mel' nichenko, E V [Institute for Superconductivity and Solid-State Physics, Russian Research Centre ' Kurchatov Institute' , Moscow (Russian Federation)

    2014-12-31

    A way of designing a scalable optical quantum computer based on the photon echo effect is proposed. Individual rare earth ions Pr{sup 3+}, regularly located in the lattice of the orthosilicate (Y{sub 2}SiO{sub 5}) crystal, are suggested to be used as optical qubits. Operations with qubits are performed using coherent and incoherent laser pulses. The operation protocol includes both the method of measurement-based quantum computations and the technique of optical computations. Modern hybrid photon echo protocols, which provide a sufficient quantum efficiency when reading recorded states, are considered as most promising for quantum computations and communications. (quantum computer)

  11. Scalable optical quantum computer

    International Nuclear Information System (INIS)

    A way of designing a scalable optical quantum computer based on the photon echo effect is proposed. Individual rare earth ions Pr3+, regularly located in the lattice of the orthosilicate (Y2SiO5) crystal, are suggested to be used as optical qubits. Operations with qubits are performed using coherent and incoherent laser pulses. The operation protocol includes both the method of measurement-based quantum computations and the technique of optical computations. Modern hybrid photon echo protocols, which provide a sufficient quantum efficiency when reading recorded states, are considered as most promising for quantum computations and communications. (quantum computer)

  12. Basics of Quantum Computation

    CERN Document Server

    Vedral, V; Vedral, Vlatko; Plenio, Martin B.

    1998-01-01

    Quantum computers require quantum logic, something fundamentally different to classical Boolean logic. This difference leads to a greater efficiency of quantum computation over its classical counter-part. In this review we explain the basic principles of quantum computation, including the construction of basic gates, and networks. We illustrate the power of quantum algorithms using the simple problem of Deutsch, and explain, again in very simple terms, the well known algorithm of Shor for factorisation of large numbers into primes. We then describe physical implementations of quantum computers, focusing on one in particular, the linear ion-trap realization. We explain that the main obstacle to building an actual quantum computer is the problem of decoherence, which we show may be circumvented using the methods of quantum error correction.

  13. Quantum information. Teleportation - cryptography - quantum computer

    International Nuclear Information System (INIS)

    The following topics are dealt with: Reality in the test facility, quantum teleportation, the reality of quanta, interaction-free quantum measurement, rules for quantum computers, quantum computers with ions, spintronics with diamond, the limits of the quantum computers, a view in the future of quantum optics. (HSI)

  14. Quantum computer games: quantum minesweeper

    Science.gov (United States)

    Gordon, Michal; Gordon, Goren

    2010-07-01

    The computer game of quantum minesweeper is introduced as a quantum extension of the well-known classical minesweeper. Its main objective is to teach the unique concepts of quantum mechanics in a fun way. Quantum minesweeper demonstrates the effects of superposition, entanglement and their non-local characteristics. While in the classical minesweeper the goal of the game is to discover all the mines laid out on a board without triggering them, in the quantum version there are several classical boards in superposition. The goal is to know the exact quantum state, i.e. the precise layout of all the mines in all the superposed classical boards. The player can perform three types of measurement: a classical measurement that probabilistically collapses the superposition; a quantum interaction-free measurement that can detect a mine without triggering it; and an entanglement measurement that provides non-local information. The application of the concepts taught by quantum minesweeper to one-way quantum computing are also presented.

  15. Reliable Quantum Computers

    CERN Document Server

    Preskill, J

    1997-01-01

    The new field of quantum error correction has developed spectacularly since its origin less than two years ago. Encoded quantum information can be protected from errors that arise due to uncontrolled interactions with the environment. Recovery from errors can work effectively even if occasional mistakes occur during the recovery procedure. Furthermore, encoded quantum information can be processed without serious propagation of errors. Hence, an arbitrarily long quantum computation can be performed reliably, provided that the average probability of error per quantum gate is less than a certain critical value, the accuracy threshold. A quantum computer storing about 10^6 qubits, with a probability of error per quantum gate of order 10^{-6}, would be a formidable factoring engine. Even a smaller, less accurate quantum computer would be able to perform many useful tasks. (This paper is based on a talk presented at the ITP Conference on Quantum Coherence and Decoherence, 15-18 December 1996.)

  16. Quantum Computing since Democritus

    Science.gov (United States)

    Aaronson, Scott

    2013-03-01

    1. Atoms and the void; 2. Sets; 3. Gödel, Turing, and friends; 4. Minds and machines; 5. Paleocomplexity; 6. P, NP, and friends; 7. Randomness; 8. Crypto; 9. Quantum; 10. Quantum computing; 11. Penrose; 12. Decoherence and hidden variables; 13. Proofs; 14. How big are quantum states?; 15. Skepticism of quantum computing; 16. Learning; 17. Interactive proofs and more; 18. Fun with the Anthropic Principle; 19. Free will; 20. Time travel; 21. Cosmology and complexity; 22. Ask me anything.

  17. Quantum Computers and Dissipation

    CERN Document Server

    Palma, G M; Ekert, A K; Suominen, Kalle-Antti; Ekert, Artur K.

    1996-01-01

    We analyse dissipation in quantum computation and its destructive impact on efficiency of quantum algorithms. Using a general model of decoherence, we study the time evolution of a quantum register of arbitrary length coupled with an environment of arbitrary coherence length. We discuss relations between decoherence and computational complexity and show that the quantum factorization algorithm must be modified in order to be regarded as efficient and realistic.

  18. Quantum computing classical physics

    OpenAIRE

    Meyer, David A.

    2001-01-01

    In the past decade quantum algorithms have been found which outperform the best classical solutions known for certain classical problems as well as the best classical methods known for simulation of certain quantum systems. This suggests that they may also speed up the simulation of some classical systems. I describe one class of discrete quantum algorithms which do so--quantum lattice gas automata--and show how to implement them efficiently on standard quantum computers.

  19. Quantum Computing Without Entanglement

    OpenAIRE

    Biham, Eli; Brassard, Gilles; Kenigsberg, Dan; Mor, Tal

    2003-01-01

    It is generally believed that entanglement is essential for quantum computing. We present here a few simple examples in which quantum computing without entanglement is better than anything classically achievable, in terms of the reliability of the outcome after a xed number of oracle calls. Using a separable (that is, unentangled) n-qubit state, we show that the Deutsch-Jozsa problem and the Simon problem can be solved more reliably by a quantum computer than by the best pos...

  20. Explorations in quantum computing

    CERN Document Server

    Williams, Colin P

    2011-01-01

    By the year 2020, the basic memory components of a computer will be the size of individual atoms. At such scales, the current theory of computation will become invalid. ""Quantum computing"" is reinventing the foundations of computer science and information theory in a way that is consistent with quantum physics - the most accurate model of reality currently known. Remarkably, this theory predicts that quantum computers can perform certain tasks breathtakingly faster than classical computers -- and, better yet, can accomplish mind-boggling feats such as teleporting information, breaking suppos

  1. Quantum computer science

    CERN Document Server

    Lanzagorta, Marco

    2009-01-01

    In this text we present a technical overview of the emerging field of quantum computation along with new research results by the authors. What distinguishes our presentation from that of others is our focus on the relationship between quantum computation and computer science. Specifically, our emphasis is on the computational model of quantum computing rather than on the engineering issues associated with its physical implementation. We adopt this approach for the same reason that a book on computer programming doesn't cover the theory and physical realization of semiconductors. Another distin

  2. Dissipative quantum computing with open quantum walks

    Energy Technology Data Exchange (ETDEWEB)

    Sinayskiy, Ilya; Petruccione, Francesco [National Institute for Theoretical Physics and Quantum Research Group, School of Chemistry and Physics, University of KwaZulu-Natal, Durban (South Africa)

    2014-12-04

    An open quantum walk approach to the implementation of a dissipative quantum computing scheme is presented. The formalism is demonstrated for the example of an open quantum walk implementation of a 3 qubit quantum circuit consisting of 10 gates.

  3. Dissipative quantum computing with open quantum walks

    International Nuclear Information System (INIS)

    An open quantum walk approach to the implementation of a dissipative quantum computing scheme is presented. The formalism is demonstrated for the example of an open quantum walk implementation of a 3 qubit quantum circuit consisting of 10 gates

  4. Quantum Computation with Quantum Dots

    CERN Document Server

    Loss, D; Loss, Daniel; Vincenzo, David P. Di

    1998-01-01

    We propose the implementation of a universal set of one- and two-qubit gates for quantum computation using the spin states of coupled single-electron quantum dots. Desired operations are effected by the gating of the tunneling barrier between neighboring dots. Several measures of the gate quality are computed within a newly derived spin master equation incorporating decoherence caused by a prototypical magnetic environment. Dot-array experiments which would provide an initial demonstration of the desired non-equilibrium spin dynamics are proposed.

  5. Geometric Quantum Computation

    CERN Document Server

    Ekert, A K; Hayden, P; Inamori, H; Jones, J A; Oi, D K L; Vedral, V

    2000-01-01

    We describe in detail a general strategy for implementing a conditional geometric phase between two spins. Combined with single-spin operations, this simple operation is a universal gate for quantum computation, in that any unitary transformation can be implemented with arbitrary precision using only single-spin operations and conditional phase shifts. Thus quantum geometrical phases can form the basis of any quantum computation. Moreover, as the induced conditional phase depends only on the geometry of the paths executed by the spins it is resilient to certain types of errors and offers the potential of a naturally fault-tolerant way of performing quantum computation.

  6. Quantum Analog Computing

    Science.gov (United States)

    Zak, M.

    1998-01-01

    Quantum analog computing is based upon similarity between mathematical formalism of quantum mechanics and phenomena to be computed. It exploits a dynamical convergence of several competing phenomena to an attractor which can represent an externum of a function, an image, a solution to a system of ODE, or a stochastic process.

  7. Quantum computing hamiltonian cycles

    CERN Document Server

    Rudolph, T

    1996-01-01

    An algorithm for quantum computing Hamiltonian cycles of simple, cubic, bipartite graphs is discussed. It is shown that it is possible to evolve a quantum computer into an entanglement of states which map onto the set of all possible paths originating from a chosen vertex, and furthermore to subsequently project out all states not corresponding to Hamiltonian cycles.

  8. A Simple Quantum Computer

    OpenAIRE

    Chuang, I.L.; Yamamoto, Y.

    1995-01-01

    We propose an implementation of a quantum computer to solve Deutsch's problem, which requires exponential time on a classical computer but only linear time with quantum parallelism. By using a dual-rail qubit representation as a simple form of error correction, our machine can tolerate some amount of decoherence and still give the correct result with high probability. The design which we employ also demonstrates a signature for quantum parallelism which unambiguously delinea...

  9. Quantum Computational Fuzzy Logics

    OpenAIRE

    BERTINI, CESARINO; LEPORINI, ROBERTO

    2007-01-01

    The theory of logical gates in quantum computation has suggested new forms of quantum logic, called quantum computational logics. The basic semantic idea is the following: the meaning of a sentence is identified with a quregister (a system of qubits in a pure state) or, more generally, with a mixture of quregisters (called qumix). Following an approach proposed by Domenech and Freytes, we apply residuated structures associated with fuzzy logic to develop certain aspects of info...

  10. High Performance Quantum Computing

    OpenAIRE

    Devitt, Simon J.; Munro, William J.; Nemoto, Kae

    2008-01-01

    The architecture scalability afforded by recent proposals of a large scale photonic based quantum computer, utilizing the theoretical developments of topological cluster states and the photonic chip, allows us to move on to a discussion of massively scaled Quantum Information Processing (QIP). In this letter we introduce the model for a secure and unsecured topological cluster mainframe. We consider the quantum analogue of High Performance Computing, where a dedicated server...

  11. Stairway Quantum Computer

    OpenAIRE

    Vlasov, Alexander Yu.

    2004-01-01

    In the paper is considered stairway-like design of quantum computer, i.e., array of double quantum dots or wells. The model is quite general to include wide variety of physical systems from coupled quantum dots in experiments with solid state qubits, to very complex one, like DNA molecule. At the same time it is concrete enough, to describe main physical principles for implementation of universal set of quantum gates, initialization, measurement, decoherence, etc.

  12. Electrical modeling of semiconductor bridge (SCB) BNCP detonators with electrochemical capacitor firing sets

    Energy Technology Data Exchange (ETDEWEB)

    Marx, K.D. [Sandia National Labs., Livermore, CA (United States); Ingersoll, D.; Bickes, R.W. Jr. [Sandia National Labs., Albuquerque, NM (United States)

    1998-11-01

    In this paper the authors describe computer models that simulate the electrical characteristics and hence, the firing characteristics and performance of a semiconductor bridge (SCB) detonator for the initiation of BNCP [tetraammine-cis-bis (5-nitro-2H-tetrazolato-N{sup 2}) cobalt(III) perchlorate]. The electrical data and resultant models provide new insights into the fundamental behavior of SCB detonators, particularly with respect to the initiation mechanism and the interaction of the explosive powder with the SCB. One model developed, the Thermal Feedback Model, considers the total energy budget for the system, including the time evolution of the energy delivered to the powder by the electrical circuit, as well as that released by the ignition and subsequent chemical reaction of the powder. The authors also present data obtained using a new low-voltage firing set which employed an advanced electrochemical capacitor having a nominal capacitance of 350,000 {micro}F at 9 V, the maximum voltage rating for this particular device. A model for this firing set and detonator was developed by making measurements of the intrinsic capacitance and equivalent series resistance (ESR < 10 m{Omega}) of a single device. This model was then used to predict the behavior of BNCP SCB detonators fired alone, as well as in a multishot, parallel-string configuration using a firing set composed of either a single 9 V electrochemical capacitor or two of the capacitors wired in series and charged to 18 V.

  13. Quantum computing with trapped ions

    OpenAIRE

    Haeffner, H.; C. F. Roos; Blatt, R.

    2008-01-01

    Quantum computers hold the promise to solve certain computational task much more efficiently than classical computers. We review the recent experimental advancements towards a quantum computer with trapped ions. In particular, various implementations of qubits, quantum gates and some key experiments are discussed. Furthermore, we review some implementations of quantum algorithms such as a deterministic teleportation of quantum information and an error correction scheme.

  14. Duality and Recycling Computing in Quantum Computers

    OpenAIRE

    Long, Gui Lu; Liu, Yang

    2007-01-01

    Quantum computer possesses quantum parallelism and offers great computing power over classical computer \\cite{er1,er2}. As is well-know, a moving quantum object passing through a double-slit exhibits particle wave duality. A quantum computer is static and lacks this duality property. The recently proposed duality computer has exploited this particle wave duality property, and it may offer additional computing power \\cite{r1}. Simply put it, a duality computer is a moving qua...

  15. Quantum computing with trapped ions

    Energy Technology Data Exchange (ETDEWEB)

    Hughes, R.J.

    1998-01-01

    The significance of quantum computation for cryptography is discussed. Following a brief survey of the requirements for quantum computational hardware, an overview of the ion trap quantum computation project at Los Alamos is presented. The physical limitations to quantum computation with trapped ions are analyzed and an assessment of the computational potential of the technology is made.

  16. Review of quantum computation

    International Nuclear Information System (INIS)

    Digital computers are machines that can be programmed to perform logical and arithmetical operations. Contemporary digital computers are ''universal,'' in the sense that a program that runs on one computer can, if properly compiled, run on any other computer that has access to enough memory space and time. Any one universal computer can simulate the operation of any other; and the set of tasks that any such machine can perform is common to all universal machines. Since Bennett's discovery that computation can be carried out in a non-dissipative fashion, a number of Hamiltonian quantum-mechanical systems have been proposed whose time-evolutions over discrete intervals are equivalent to those of specific universal computers. The first quantum-mechanical treatment of computers was given by Benioff, who exhibited a Hamiltonian system with a basis whose members corresponded to the logical states of a Turing machine. In order to make the Hamiltonian local, in the sense that its structure depended only on the part of the computation being performed at that time, Benioff found it necessary to make the Hamiltonian time-dependent. Feynman discovered a way to make the computational Hamiltonian both local and time-independent by incorporating the direction of computation in the initial condition. In Feynman's quantum computer, the program is a carefully prepared wave packet that propagates through different computational states. Deutsch presented a quantum computer that exploits the possibility of existing in a superposition of computational states to perform tasks that a classical computer cannot, such as generating purely random numbers, and carrying out superpositions of computations as a method of parallel processing. In this paper, we show that such computers, by virtue of their common function, possess a common form for their quantum dynamics

  17. Parallel Quantum Computing in a Single Ensemble Quantum Computer

    OpenAIRE

    Long, Gui Lu; Xiao, Li

    2003-01-01

    We propose a parallel quantum computing mode for ensemble quantum computer. In this mode, some qubits can be in pure states while other qubits in mixed states. It enables a single ensemble quantum computer to perform $"$single-instruction-multi-data" type of parallel computation. In Grover's algorithm and Shor's algorithm, parallel quantum computing can provide additional speedup. In addition, it also makes a fuller use of qubit resources in an ensemble quantum computer. As ...

  18. Instantaneous Quantum Computation

    CERN Document Server

    Shepherd, Dan

    2008-01-01

    We examine theoretic architectures and an abstract model for a restricted class of quantum computation, called here instantaneous quantum computation because it allows for essentially no temporal structure within the quantum dynamics. Using the theory of binary matroids, we argue that the paradigm is rich enough to enable sampling from probability distributions that cannot, classically, be sampled from efficiently and accurately. This paradigm also admits simple interactive proof games that may convince a skeptic of the existence of truly quantum effects. Furthermore, these effects can be created using significantly fewer qubits than are required for running Shor's Algorithm.

  19. Efficient Distributed Quantum Computing

    OpenAIRE

    Beals, Robert; Brierley, Stephen; Gray, Oliver; Harrow, Aram; Kutin, Samuel; Linden, Noah; Shepherd, Dan; Stather, Mark

    2012-01-01

    We provide algorithms for efficiently addressing quantum memory in parallel. These imply that the standard circuit model can be simulated with low overhead by the more realistic model of a distributed quantum computer. As a result, the circuit model can be used by algorithm designers without worrying whether the underlying architecture supports the connectivity of the circuit. In addition, we apply our results to existing memory intensive quantum algorithms. We present a par...

  20. Quantum steady computation

    International Nuclear Information System (INIS)

    This paper reports that current conceptions of quantum mechanical computers inherit from conventional digital machines two apparently interacting features, machine imperfection and temporal development of the computational process. On account of machine imperfection, the process would become ideally reversible only in the limiting case of zero speed. Therefore the process is irreversible in practice and cannot be considered to be a fundamental quantum one. By giving up classical features and using a linear, reversible and non-sequential representation of the computational process - not realizable in classical machines - the process can be identified with the mathematical form of a quantum steady state. This form of steady quantum computation would seem to have an important bearing on the notion of cognition

  1. Entanglement and Quantum Computation

    CERN Document Server

    Jozsa, R

    1997-01-01

    We argue that entanglement is the essential non-classical ingredient which provides the computational speed-up in quantum algorithms as compared to algorithms based on the processes of classical physics.

  2. Quantum Computation The Ultimate Frontier

    CERN Document Server

    Adami, C; Adami, Chris; Dowling, Jonathan P.

    2002-01-01

    The discovery of an algorithm for factoring which runs in polynomial time on a quantum computer has given rise to a concerted effort to understand the principles, advantages, and limitations of quantum computing. At the same time, many different quantum systems are being explored for their suitability to serve as a physical substrate for the quantum computer of the future. I discuss some of the theoretical foundations of quantum computer science, including algorithms and error correction, and present a few physical systems that have shown promise as a quantum computing platform. Finally, we discuss a spin-off of the quantum computing revolution: quantum technologies.

  3. Towards Quantum Computational Logics

    Science.gov (United States)

    Ledda, Antonio; Sergioli, Giuseppe

    2010-12-01

    Quantum computational logics have recently stirred increasing attention (Cattaneo et al. in Math. Slovaca 54:87-108, 2004; Ledda et al. in Stud. Log. 82(2):245-270, 2006; Giuntini et al. in Stud. Log. 87(1):99-128, 2007). In this paper we outline their motivations and report on the state of the art of the approach to the logic of quantum computation that has been recently taken up and developed by our research group.

  4. Quantum Computation vs. Firewalls

    OpenAIRE

    Harlow, Daniel; Hayden, Patrick

    2013-01-01

    In this paper we discuss quantum computational restrictions on the types of thought experiments recently used by Almheiri, Marolf, Polchinski, and Sully to argue against the smoothness of black hole horizons. We argue that the quantum computations required to do these experiments take a time which is exponential in the entropy of the black hole under study, and we show that for a wide variety of black holes this prevents the experiments from being done. We interpret our resu...

  5. Adiabatic Quantum Computing

    OpenAIRE

    Pinski, Sebastian D.

    2011-01-01

    Adiabatic Quantum Computing (AQC) is a relatively new subject in the world of quantum computing, let alone Physics. Inspiration for this project has come from recent controversy around D-Wave Systems in British Columbia, Canada, who claim to have built a working AQC which is now commercially available and hope to be distributing a 1024 qubit chip by the end of 2008. Their 16 qubit chip was demonstrated online for the Supercomputing 2007 conference within which a few small pr...

  6. Quantum Computing: a Quantum Group Approach

    OpenAIRE

    Wang, Zhenghan

    2013-01-01

    There is compelling theoretical evidence that quantum physics will change the face of information science. Exciting progress has been made during the last two decades towards the building of a large scale quantum computer. A quantum group approach stands out as a promising route to this holy grail, and provides hope that we may have quantum computers in our future.

  7. An Introduction to Quantum Computing

    OpenAIRE

    Yanofsky, Noson S.

    2007-01-01

    Quantum Computing is a new and exciting field at the intersection of mathematics, computer science and physics. It concerns a utilization of quantum mechanics to improve the efficiency of computation. Here we present a gentle introduction to some of the ideas in quantum computing. The paper begins by motivating the central ideas of quantum mechanics and quantum computation with simple toy models. From there we move on to a formal presentation of the small fraction of (finite...

  8. Quantum Computation: A Computer Science Perspective

    OpenAIRE

    Bengtsson, Anders K. H.

    2005-01-01

    The theory of quantum computation is presented in a self contained way from a computer science perspective. The basics of classical computation and quantum mechanics is reviewed. The circuit model of quantum computation is presented in detail. Throughout there is an emphasis on the physical as well as the abstract aspects of computation and the interplay between them. This report is presented as a Master's thesis at the department of Computer Science and Engineering at G{\\...

  9. Quantum computational webs

    International Nuclear Information System (INIS)

    We discuss the notion of quantum computational webs: These are quantum states universal for measurement-based computation, which can be built up from a collection of simple primitives. The primitive elements--reminiscent of building blocks in a construction kit--are (i) one-dimensional states (computational quantum wires) with the power to process one logical qubit and (ii) suitable couplings, which connect the wires to a computationally universal web. All elements are preparable by nearest-neighbor interactions in a single pass, of the kind accessible in a number of physical architectures. We provide a complete classification of qubit wires, a physically well-motivated class of universal resources that can be fully understood. Finally, we sketch possible realizations in superlattices and explore the power of coupling mechanisms based on Ising or exchange interactions.

  10. Adiabatic Quantum Computing

    CERN Document Server

    Pinski, Sebastian D

    2011-01-01

    Adiabatic Quantum Computing (AQC) is a relatively new subject in the world of quantum computing, let alone Physics. Inspiration for this project has come from recent controversy around D-Wave Systems in British Columbia, Canada, who claim to have built a working AQC which is now commercially available and hope to be distributing a 1024 qubit chip by the end of 2008. Their 16 qubit chip was demonstrated online for the Supercomputing 2007 conference within which a few small problems were solved; although the explanations that journalists and critics received were minimal and very little was divulged in the question and answer session. This 'unconvincing' demonstration has caused physicists and computer scientists to hit back at D-Wave. The aim of this project is to give an introduction to the historic advances in classical and quantum computing and to explore the methods of AQC. Through numerical simulations an algorithm for the Max Independent Set problem is empirically obtained.

  11. Quantum Computation and Spin Electronics

    OpenAIRE

    DiVincenzo, David P.; Burkard, Guido; Loss, Daniel; Sukhorukov, Eugene V.

    1999-01-01

    In this chapter we explore the connection between mesoscopic physics and quantum computing. After giving a bibliography providing a general introduction to the subject of quantum information processing, we review the various approaches that are being considered for the experimental implementation of quantum computing and quantum communication in atomic physics, quantum optics, nuclear magnetic resonance, superconductivity, and, especially, normal-electron solid state physics...

  12. Quantum Computers and Quantum Computer Languages: Quantum Assembly Language and Quantum C Language

    OpenAIRE

    Blaha, Stephen

    2002-01-01

    We show a representation of Quantum Computers defines Quantum Turing Machines with associated Quantum Grammars. We then create examples of Quantum Grammars. Lastly we develop an algebraic approach to high level Quantum Languages using Quantum Assembly language and Quantum C language as examples.

  13. Simulating quantum mechanics on a quantum computer

    CERN Document Server

    Boghosian, B M; Boghosian, Bruce M.; Taylor, Washington

    1998-01-01

    Algorithms are described for efficiently simulating quantum mechanical systems on quantum computers. A class of algorithms for simulating the Schrodinger equation for interacting many-body systems are presented in some detail. These algorithms would make it possible to simulate nonrelativistic quantum systems on a quantum computer with an exponential speedup compared to simulations on classical computers. Issues involved in simulating relativistic systems of Dirac and gauge particles are discussed.

  14. Spintronics and Quantum Computing with Quantum Dots

    OpenAIRE

    Recher, P.; Loss, D.; Levy, J.

    2000-01-01

    The creation, coherent manipulation, and measurement of spins in nanostructures open up completely new possibilities for electronics and information processing, among them quantum computing and quantum communication. We review our theoretical proposal for using electron spins in quantum dots as quantum bits. We present single- and two qubit gate mechanisms in laterally as well as vertically coupled quantum dots and discuss the possibility to couple spins in quantum dots via ...

  15. I, Quantum Robot: Quantum Mind control on a Quantum Computer

    OpenAIRE

    zizzi, Paola

    2008-01-01

    The logic which describes quantum robots is not orthodox quantum logic, but a deductive calculus which reproduces the quantum tasks (computational processes, and actions) taking into account quantum superposition and quantum entanglement. A way toward the realization of intelligent quantum robots is to adopt a quantum metalanguage to control quantum robots. A physical implementation of a quantum metalanguage might be the use of coherent states in brain signals.

  16. Quantum information and computation

    International Nuclear Information System (INIS)

    During the past two decades, there has emerged the new subject of quantum information and computation which both offers the possibility of powerful new modes of computing and communication and also suggests deep links between the well established disciplines of quantum theory and information theory and computer science. In recent years, the growth of the subject has been explosive, with significant progress in theory and experiment. The area has a highly interdisciplinary character with contributions from physicists, mathematicians and computer scientists in particular. Developments have occurred in diverse areas including quantum algorithms, quantum communication, quantum cryptography, entanglement and nonlocality. This progress has been reflected in contributions to Journal of Physics A: Mathematical and General which traditionally provides a natural home for this area of research. Furthermore, the journal's commitment to this field has recently been strengthened by the appointments of Sandu Popescu and Nicolas Gisin to the Editorial Board, and in this special issue we take the opportunity to present a snapshot of the present state of the art. (author)

  17. Undergraduate computational physics projects on quantum computing

    Science.gov (United States)

    Candela, D.

    2015-08-01

    Computational projects on quantum computing suitable for students in a junior-level quantum mechanics course are described. In these projects students write their own programs to simulate quantum computers. Knowledge is assumed of introductory quantum mechanics through the properties of spin 1/2. Initial, more easily programmed projects treat the basics of quantum computation, quantum gates, and Grover's quantum search algorithm. These are followed by more advanced projects to increase the number of qubits and implement Shor's quantum factoring algorithm. The projects can be run on a typical laptop or desktop computer, using most programming languages. Supplementing resources available elsewhere, the projects are presented here in a self-contained format especially suitable for a short computational module for physics students.

  18. Demonstration of blind quantum computing.

    Science.gov (United States)

    Barz, Stefanie; Kashefi, Elham; Broadbent, Anne; Fitzsimons, Joseph F; Zeilinger, Anton; Walther, Philip

    2012-01-20

    Quantum computers, besides offering substantial computational speedups, are also expected to preserve the privacy of a computation. We present an experimental demonstration of blind quantum computing in which the input, computation, and output all remain unknown to the computer. We exploit the conceptual framework of measurement-based quantum computation that enables a client to delegate a computation to a quantum server. Various blind delegated computations, including one- and two-qubit gates and the Deutsch and Grover quantum algorithms, are demonstrated. The client only needs to be able to prepare and transmit individual photonic qubits. Our demonstration is crucial for unconditionally secure quantum cloud computing and might become a key ingredient for real-life applications, especially when considering the challenges of making powerful quantum computers widely available. PMID:22267806

  19. Computational quantum chemistry website

    International Nuclear Information System (INIS)

    This report contains the contents of a web page related to research on the development of quantum chemistry methods for computational thermochemistry and the application of quantum chemistry methods to problems in material chemistry and chemical sciences. Research programs highlighted include: Gaussian-2 theory; Density functional theory; Molecular sieve materials; Diamond thin-film growth from buckyball precursors; Electronic structure calculations on lithium polymer electrolytes; Long-distance electronic coupling in donor/acceptor molecules; and Computational studies of NOx reactions in radioactive waste storage

  20. Quantum++ - A C++11 quantum computing library

    OpenAIRE

    Gheorghiu, Vlad

    2014-01-01

    Quantum++ is a general-purpose multi-threaded quantum computing library written in C++11 and composed solely of header files. The library is not restricted to qubit systems or specific quantum information processing tasks, being capable of simulating arbitrary quantum processes. The main design factors taken in consideration were ease of use, portability, and performance.

  1. Quantum Computing Pro and Con

    CERN Document Server

    Preskill, J

    1997-01-01

    I assess the potential of quantum computation. Broad and important applications must be found to justify construction of a quantum computer; I review some of the known quantum algorithms and consider the prospects for finding new ones. Quantum computers are notoriously susceptible to making errors; I discuss recently developed fault-tolerant procedures that enable a quantum computer with noisy gates to perform reliably. Quantum computing hardware is still in its infancy; I comment on the specifications that should be met by future hardware. Over the past few years, work on quantum computation has erected a new classification of computational complexity, has generated profound insights into the nature of decoherence, and has stimulated the formulation of new techniques in high-precision experimental physics. A broad interdisciplinary effort will be needed if quantum computers are to fulfill their destiny as the world's fastest computing devices. (This paper is an expanded version of remarks that were prepared ...

  2. Adiabatic Quantum Computing

    Science.gov (United States)

    Landahl, Andrew

    2012-10-01

    Quantum computers promise to exploit counterintuitive quantum physics principles like superposition, entanglement, and uncertainty to solve problems using fundamentally fewer steps than any conventional computer ever could. The mere possibility of such a device has sharpened our understanding of quantum coherent information, just as lasers did for our understanding of coherent light. The chief obstacle to developing quantum computer technology is decoherence--one of the fastest phenomena in all of physics. In principle, decoherence can be overcome by using clever entangled redundancies in a process called fault-tolerant quantum error correction. However, the quality and scale of technology required to realize this solution appears distant. An exciting alternative is a proposal called ``adiabatic'' quantum computing (AQC), in which adiabatic quantum physics keeps the computer in its lowest-energy configuration throughout its operation, rendering it immune to many decoherence sources. The Adiabatic Quantum Architectures In Ultracold Systems (AQUARIUS) Grand Challenge Project at Sandia seeks to demonstrate this robustness in the laboratory and point a path forward for future hardware development. We are building devices in AQUARIUS that realize the AQC architecture on up to three quantum bits (``qubits'') in two platforms: Cs atoms laser-cooled to below 5 microkelvin and Si quantum dots cryo-cooled to below 100 millikelvin. We are also expanding theoretical frontiers by developing methods for scalable universal AQC in these platforms. We have successfully demonstrated operational qubits in both platforms and have even run modest one-qubit calculations using our Cs device. In the course of reaching our primary proof-of-principle demonstrations, we have developed multiple spinoff technologies including nanofabricated diffractive optical elements that define optical-tweezer trap arrays and atomic-scale Si lithography commensurate with placing individual donor atoms with scanning-tunneling microscopy. I will review our experimental and theoretical progress in this plenary talk.[4pt] This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  3. An Introduction to Quantum Computing

    CERN Document Server

    Yanofsky, Noson S

    2007-01-01

    Quantum Computing is a new and exciting field at the intersection of mathematics, computer science and physics. It concerns a utilization of quantum mechanics to improve the efficiency of computation. Here we present a gentle introduction to some of the ideas in quantum computing. The paper begins by motivating the central ideas of quantum mechanics and quantum computation with simple toy models. From there we move on to a formal presentation of the small fraction of (finite dimensional) quantum mechanics that we will need for basic quantum computation. Central notions of quantum architecture (qubits and quantum gates) are described. The paper ends with a presentation of one of the simplest quantum algorithms: Deutsch's algorithm. Our presentation demands neither advanced mathematics nor advanced physics.

  4. Quantum Computations: Fundamentals and Algorithms

    International Nuclear Information System (INIS)

    Basic concepts of quantum information theory, principles of quantum calculations and the possibility of creation on this basis unique on calculation power and functioning principle device, named quantum computer, are concerned. The main blocks of quantum logic, schemes of quantum calculations implementation, as well as some known today effective quantum algorithms, called to realize advantages of quantum calculations upon classical, are presented here. Among them special place is taken by Shor's algorithm of number factorization and Grover's algorithm of unsorted database search. Phenomena of decoherence, its influence on quantum computer stability and methods of quantum errors correction are described

  5. An optically driven quantum dot quantum computer

    CERN Document Server

    Sanders, G D; Holton, W C

    1999-01-01

    We propose a quantum computer structure based on coupled asymmetric single-electron quantum dots. Adjacent dots are strongly coupled by means of electric dipole-dipole interactions enabling rapid computation rates. Further, the asymmetric structures can be tailored for a long coherence time. The result maximizes the number of computation cycles prior to loss of coherence.

  6. Optically driven quantum-dot quantum computer

    Science.gov (United States)

    Sanders, G. D.; Kim, K. W.; Holton, W. C.

    1999-11-01

    We propose a quantum computer structure based on coupled asymmetric single-electron quantum dots. Adjacent dots are strongly coupled by means of electric dipole-dipole interactions enabling rapid computation rates. Further, the asymmetric structures can be tailored for a long coherence time. The result maximizes the number of computation cycles prior to loss of coherence.

  7. Quantum Computation and Spin Physics

    OpenAIRE

    DiVincenzo, David P.

    1996-01-01

    A brief review is given of the physical implementation of quantum computation within spin systems or other two-state quantum systems. The importance of the controlled-NOT or quantum XOR gate as the fundamental primitive operation of quantum logic is emphasized. Recent developments in the use of quantum entanglement to built error-robust quantum states, and the simplest protocol for quantum error correction, are discussed.

  8. Blind Quantum Computation

    CERN Document Server

    Arrighi, P; Arrighi, Pablo; Salvail, Louis

    2003-01-01

    We investigate the possibility of having someone carry out the work of executing a function for you, but without letting him learn anything about your input. Say Alice wants Bob to compute some well-known function f upon her input x, but wants to prevent Bob from learning anything about x. The situation arises for instance if client Alice has limited computational resources in comparison with mistrusted server Bob, or if x is an inherently mobile piece of data. Could there be a protocol whereby Bob is forced to compute f(x) "blindly", i.e. without observing x? We provide such a blind computation protocol for the class of functions which admit an efficient procedure to generate random input-output pairs, e.g. factorization. The setting is quantum, the security is unconditional, the eavesdropper is as malicious as can be. Keywords: Secure Circuit Evaluation, Secure Two-party Computation, Information Hiding, Information gain vs disturbance.

  9. Relativistic quantum chemistry on quantum computers

    DEFF Research Database (Denmark)

    Veis, L.; Visnak, J.

    2012-01-01

    The past few years have witnessed a remarkable interest in the application of quantum computing for solving problems in quantum chemistry more efficiently than classical computers allow. Very recently, proof-of-principle experimental realizations have been reported. However, so far only the nonrelativistic regime (i.e., the Schrodinger equation) has been explored, while it is well known that relativistic effects can be very important in chemistry. We present a quantum algorithm for relativistic computations of molecular energies. We show how to efficiently solve the eigenproblem of the Dirac-Coulomb Hamiltonian on a quantum computer and demonstrate the functionality of the proposed procedure by numerical simulations of computations of the spin-orbit splitting in the SbH molecule. Finally, we propose quantum circuits with three qubits and nine or ten controlled-NOT (CNOT) gates, which implement a proof-of-principle relativistic quantum chemical calculation for this molecule and might be suitable for an experimental realization.

  10. Programmable architecture for quantum computing :

    OpenAIRE

    Chen, J.; WANG, L; Charbon, E.; Wang, B

    2013-01-01

    A programmable architecture called “quantum FPGA (field-programmable gate array)” (QFPGA) is presented for quantum computing, which is a hybrid model combining the advantages of the qubus system and the measurement-based quantum computation. There are two kinds of buses in QFPGA, the local bus and the global bus, which generate the cluster states and general multiqubit rotations around the z axis, respectively. QFPGA consists of quantum logic blocks (QLBs) and quantum routing channels (QRCs)....

  11. Quantum computing of semiclassical formulas

    OpenAIRE

    Georgeot, Bertrand; Giraud, Olivier

    2008-01-01

    We show that semiclassical formulas such as the Gutzwiller trace formula can be implemented on a quantum computer more efficiently than on a classical device. We give explicit quantum algorithms which yield quantum observables from classical trajectories, and which alternatively test the semiclassical approximation by computing classical actions from quantum evolution. The gain over classical computation is in general quadratic, and can be larger in some specific cases.

  12. Embedding classical into quantum computation

    CERN Document Server

    Jozsa, Richard

    2008-01-01

    We describe a simple formalism for generating classes of quantum circuits that are classically efficiently simulatable and show that the efficient simulation of Clifford circuits (Gottesman-Knill theorem) and of matchgate circuits (Valiant's theorem) appear as two special cases. Viewing these simulatable classes as subsets of the space of all quantum computations, we may consider minimal extensions that suffice to regain full quantum computational power, which provides an approach to exploring the efficacy of quantum over classical computation.

  13. Quantum computing of semiclassical formulas.

    Science.gov (United States)

    Georgeot, B; Giraud, O

    2008-04-01

    We show that semiclassical formulas such as the Gutzwiller trace formula can be implemented on a quantum computer more efficiently than on a classical device. We give explicit quantum algorithms which yield quantum observables from classical trajectories, and which alternatively test the semiclassical approximation by computing classical actions from quantum evolution. The gain over classical computation is in general quadratic, and can be larger in some specific cases. PMID:18517721

  14. Quantum computation vs. firewalls

    Science.gov (United States)

    Harlow, Daniel; Hayden, Patrick

    2013-06-01

    In this paper we discuss quantum computational restrictions on the types of thought experiments recently used by Almheiri, Marolf, Polchinski, and Sully to argue against the smoothness of black hole horizons. We argue that the quantum computations required to do these experiments would take a time which is exponential in the entropy of the black hole under study, and we show that for a wide variety of black holes this prevents the experiments from being done. We interpret our results as motivating a broader type of nonlocality than is usually considered in the context of black hole thought experiments, and claim that once this type of nonlocality is allowed there may be no need for firewalls. Our results do not threaten the unitarity of black hole evaporation or the ability of advanced civilizations to test it.

  15. Quantum Computation vs. Firewalls

    CERN Document Server

    Harlow, Daniel

    2013-01-01

    In this paper we discuss quantum computational restrictions on the types of thought experiments recently used by Almheiri, Marolf, Polchinski, and Sully to argue against the smoothness of black hole horizons. We argue that the quantum computations required to do these experiments take a time which is exponential in the entropy of the black hole under study, and we show that for a wide variety of black holes this prevents the experiments from being done. We interpret our results as motivating a broader type of non-locality than is usually considered in the context of black hole thought experiments, and claim that once this type of non-locality is allowed there is no need for firewalls. Our results do not threaten the unitarity of of black hole evaporation or the ability of advanced civilizations to test it.

  16. New Trends in Quantum Computing

    OpenAIRE

    Brassard, Gilles

    1996-01-01

    Classical and quantum information are very different. Together they can perform feats that neither could achieve alone, such as quantum computing, quantum cryptography and quantum teleportation. Some of the applications range from helping to preventing spies from reading private communications. Among the tools that will facilitate their implementation, we note quantum purification and quantum error correction. Although some of these ideas are still beyond the grasp of curren...

  17. Genetic Algorithms and Quantum Computation

    OpenAIRE

    Giraldi, Gilson A.; Portugal, Renato; Thess, Ricardo N.

    2004-01-01

    Recently, researchers have applied genetic algorithms (GAs) to address some problems in quantum computation. Also, there has been some works in the designing of genetic algorithms based on quantum theoretical concepts and techniques. The so called Quantum Evolutionary Programming has two major sub-areas: Quantum Inspired Genetic Algorithms (QIGAs) and Quantum Genetic Algorithms (QGAs). The former adopts qubit chromosomes as representations and employs quantum gates for the s...

  18. Quantum computer for dummies (in Russian)

    OpenAIRE

    Grozin, Andrey

    2011-01-01

    An introduction (in Russian) to quantum computers, quantum cryptography, and quantum teleportation for students who have no previous knowledge of these subjects, but know quantum mechanics. Several simple examples are considered in detail using the quantum computer emulator QCL.

  19. Relativistic quantum chemistry on quantum computers

    DEFF Research Database (Denmark)

    Veis, L.; Visnak, J.; Fleig, T.; Knecht, S.; Saue, T.; Visscher, L.; Pittner, J.

    2012-01-01

    The past few years have witnessed a remarkable interest in the application of quantum computing for solving problems in quantum chemistry more efficiently than classical computers allow. Very recently, proof-of-principle experimental realizations have been reported. However, so far only the nonrelativistic regime (i.e., the Schrodinger equation) has been explored, while it is well known that relativistic effects can be very important in chemistry. We present a quantum algorithm for relativistic ...

  20. Spin-Based Quantum Dot Quantum Computing

    OpenAIRE

    Hu, Xuedong

    2004-01-01

    We present a brief overview of the current theoretical and experimental progresses in the study of quantum dot-based quantum computing schemes, then focus on the spin-based varieties, which are generally regarded as the most scalable because of the relatively long coherence times of electron and nuclear spins. Reviewed topics include spin coherence, spin interaction, spin detection, and the current status of the experimental studies of spin-based quantum computing.

  1. Quantum Gravity on a Quantum Computer?

    CERN Document Server

    Kempf, Achim

    2013-01-01

    EPR-type measurements on spatially separated entangled spin qubits allow one, in principle, to detect curvature. Also the entanglement of the vacuum state is affected by curvature. Here, we ask if the curvature of spacetime can be expressed entirely in terms of the spatial entanglement structure of the vacuum. This would open up the prospect that quantum gravity could be simulated on a quantum computer and that quantum information techniques could be fully employed in the study of quantum gravity.

  2. Decoherence in adiabatic quantum computation

    Science.gov (United States)

    Albash, Tameem; Lidar, Daniel A.

    2015-06-01

    Recent experiments with increasingly larger numbers of qubits have sparked renewed interest in adiabatic quantum computation, and in particular quantum annealing. A central question that is repeatedly asked is whether quantum features of the evolution can survive over the long time scales used for quantum annealing relative to standard measures of the decoherence time. We reconsider the role of decoherence in adiabatic quantum computation and quantum annealing using the adiabatic quantum master-equation formalism. We restrict ourselves to the weak-coupling and singular-coupling limits, which correspond to decoherence in the energy eigenbasis and in the computational basis, respectively. We demonstrate that decoherence in the instantaneous energy eigenbasis does not necessarily detrimentally affect adiabatic quantum computation, and in particular that a short single-qubit T2 time need not imply adverse consequences for the success of the quantum adiabatic algorithm. We further demonstrate that boundary cancellation methods, designed to improve the fidelity of adiabatic quantum computing in the closed-system setting, remain beneficial in the open-system setting. To address the high computational cost of master-equation simulations, we also demonstrate that a quantum Monte Carlo algorithm that explicitly accounts for a thermal bosonic bath can be used to interpolate between classical and quantum annealing. Our study highlights and clarifies the significantly different role played by decoherence in the adiabatic and circuit models of quantum computing.

  3. Quantum computing with mixed states

    OpenAIRE

    Siomau, Michael; Fritzsche, Stephan

    2011-01-01

    We discuss a model for quantum computing with initially mixed states. Although such a computer is known to be less powerful than a quantum computer operating with pure (entangled) states, it may efficiently solve some problems for which no efficient classical algorithms are known. We suggest a new implementation of quantum computation with initially mixed states in which an algorithm realization is achieved by means of optimal basis independent transformations of qubits.

  4. THE APROACH OF CLASSICAL COMPUTER TO QUANTUM COMPUTER

    Directory of Open Access Journals (Sweden)

    SEYEDEH MOHADESEH ELTEJA

    2013-09-01

    Full Text Available The aim of this paper is to guide computer scientists through the barriers that separate quantum computing from conventional computing. We introduce basic principles of quantum mechanics to explain where the power of quantum computers comes from and why it is difficult to harness. We describe the diffrences between classical and quantum computers, bit and quantum bit and quantum key distribution.

  5. THE APROACH OF CLASSICAL COMPUTER TO QUANTUM COMPUTER

    OpenAIRE

    SEYEDEH MOHADESEH ELTEJA

    2013-01-01

    The aim of this paper is to guide computer scientists through the barriers that separate quantum computing from conventional computing. We introduce basic principles of quantum mechanics to explain where the power of quantum computers comes from and why it is difficult to harness. We describe the diffrences between classical and quantum computers, bit and quantum bit and quantum key distribution.

  6. Pulse controlled noise suppressed quantum computation

    OpenAIRE

    Duan, Lu-ming; Guo, Guang-Can

    1998-01-01

    To make arbitrarily accurate quantum computation possible, practical realization of quantum computers will require suppressing noise in quantum memory and gate operations to make it below a threshold value. A scheme based on realistic quantum computer models is described for suppressing noise in quantum computation without the cost of stringent quantum computing resources.

  7. Communication Capacity of Quantum Computation

    CERN Document Server

    Bose, S; Vedral, V

    2000-01-01

    By considering quantum computation as a communication process, we relate its efficiency to a communication capacity. This formalism allows us to rederive lower bounds on the complexity of search algorithms. It also enables us to link the mixedness of a quantum computer to its efficiency. We discuss the implications of our results for quantum measurement.

  8. Quantum computation and complexity theory

    OpenAIRE

    Svozil, K

    1994-01-01

    The Hilbert space formalism of quantum mechanics is reviewed with emphasis on applications to quantum computing. Standard interferomeric techniques are used to construct a physical device capable of universal quantum computation. Some consequences for recursion theory and complexity theory are discussed.

  9. Quantum buses and quantum computer architecture based on quantum dots

    CERN Document Server

    D'Amico, I

    2005-01-01

    We propose a quantum computer architecture based on quantum dots both for short distance and for long distance communication/computation. Our scheme exploits the natural characteristics of self-assembled quantum dots and it is scalable. It is centered on the idea of a quantum bus based on semiconductor self-assembled quantum dots. This allows for transmission of qubits between the different quantum registers, and could be integrated in most of the present proposal for semiconductor quantum dot-based quantum computation. Our proposal exploits the peculiar properties of {\\it relatively short} spin-chains, and advantages and disadvantages of two possible implementations, both based on spin-chain global dynamics, are discussed in details. A clear advantage of the scheme is to avoid the use of microcavities for long distance communication between different elements of the quantum computer. In this respect our scheme is comparatively faster than hybrid quantum dot-microcavity schemes.

  10. Quantum information. Teleporation - cryptography - quantum computer; Quanteninformation. Teleportation - Kryptografie - Quantencomputer

    Energy Technology Data Exchange (ETDEWEB)

    Breuer, Reinhard (comp.)

    2010-07-01

    The following topics are dealt with: Reality in the test house, quantum teleportation, 100 years of quantum theory, the reality of quanta, interactionless quantum measurement, rules for quantum computers, quantum computers with ions, spintronics with diamond, the limits of the quantum computers, a view into the future of quantum optics. (HSI)

  11. Cartoon Computation: Quantum-like computing without quantum mechanics

    OpenAIRE

    Aerts, Diederik; Czachor, Marek

    2006-01-01

    We present a computational framework based on geometric structures. No quantum mechanics is involved, and yet the algorithms perform tasks analogous to quantum computation. Tensor products and entangled states are not needed -- they are replaced by sets of basic shapes. To test the formalism we solve in geometric terms the Deutsch-Jozsa problem, historically the first example that demonstrated the potential power of quantum computation. Each step of the algorithm has a clear...

  12. Quantum computing with defects

    CERN Document Server

    Weber, J R; Varley, J B; Janotti, A; Buckley, B B; Van de Walle, C G; Awschalom, D D

    2010-01-01

    Identifying and designing physical systems for use as qubits, the basic units of quantum information, are critical steps in the development of a quantum computer. Among the possibilities in the solid state, a defect in diamond known as the nitrogen-vacancy (NV-1) center stands out for its robustness - its quantum state can be initialized, manipulated, and measured with high fidelity at room temperature. Here we describe how to systematically identify other deep center defects with similar quantum-mechanical properties. We present a list of physical criteria that these centers and their hosts should meet and explain how these requirements can be used in conjunction with electronic structure theory to intelligently sort through candidate defect systems. To illustrate these points in detail, we compare electronic structure calculations of the NV-1 center in diamond with those of several deep centers in 4H silicon carbide (SiC). We then discuss the proposed criteria for similar defects in other tetrahedrally-coor...

  13. Addition on a Quantum Computer

    CERN Document Server

    Draper, Thomas G

    2000-01-01

    A new method for computing sums on a quantum computer is introduced. This technique uses the quantum Fourier transform and reduces the number of qubits necessary for addition by removing the need for temporary carry bits. This approach also allows the addition of a classical number to a quantum superposition without encoding the classical number in the quantum register. This method also allows for massive parallelization in its execution.

  14. Quantum computing for pattern classification

    OpenAIRE

    Schuld, Maria; Sinayskiy, Ilya; Petruccione, Francesco

    2014-01-01

    It is well known that for certain tasks, quantum computing outperforms classical computing. A growing number of contributions try to use this advantage in order to improve or extend classical machine learning algorithms by methods of quantum information theory. This paper gives a brief introduction into quantum machine learning using the example of pattern classification. We introduce a quantum pattern classification algorithm that draws on Trugenberger's proposal for measur...

  15. Cluster-state quantum computation

    CERN Document Server

    Nielsen, M A

    2005-01-01

    This article is a short introduction to and review of the cluster-state model of quantum computation, in which coherent quantum information processing is accomplished via a sequence of single-qubit measurements applied to a fixed quantum state known as a cluster state. We also discuss a few novel properties of the model, including a proof that the cluster state cannot occur as the exact ground state of any naturally occurring physical system, and a proof that measurements on any quantum state which is linearly prepared in one dimension can be efficiently simulated on a classical computer, and thus are not candidates for use as a substrate for quantum computation.

  16. Experimental Aspects of Quantum Computing

    CERN Document Server

    Everitt, Henry O

    2005-01-01

    Practical quantum computing still seems more than a decade away, and researchers have not even identified what the best physical implementation of a quantum bit will be. There is a real need in the scientific literature for a dialog on the topic of lessons learned and looming roadblocks. These papers, which appeared in the journal of "Quantum Information Processing" are dedicated to the experimental aspects of quantum computing These papers highlight the lessons learned over the last ten years, outline the challenges over the next ten years, and discuss the most promising physical implementations of quantum computing.

  17. The Semi-Quantum Computer

    OpenAIRE

    Vianna, Reinaldo O.; Rabelo, Wilson R. M.; Monken, C. H.

    2003-01-01

    We discuss the performance of the Search and Fourier Transform algorithms on a hybrid computer constituted of classical and quantum processors working together. We show that this semi-quantum computer would be an improvement over a pure classical architecture, no matter how few qubits are available and, therefore, it suggests an easier implementable technology than a pure quantum computer with arbitrary number of qubits.

  18. Superconducting Quantum Computing Without Entanglement?

    OpenAIRE

    Kadin, Alan M.; Kaplan, Steven B.

    2014-01-01

    In recent years, quantum computing has promised a revolution in computing performance, based on massive parallelism enabled by many entangled qubits. Josephson junction integrated circuits have emerged as the key technology to implement such a universal digital quantum computer. Indeed, prior experiments have demonstrated simple Josephson qubit configurations with quantized energy levels and long coherence times, which are a necessary prerequisite for a practical quantum com...

  19. Database Manipulation on Quantum Computers

    OpenAIRE

    Younes, Ahmed

    2007-01-01

    Manipulating a database system on a quantum computer is an essential aim to benefit from the promising speed-up of quantum computers over classical computers in areas that take a vast amount of storage and processing time such as in databases. In this paper, the basic operations for manipulating the data in a quantum database will be defined, e.g. INSERT, UPDATE, DELETE, SELECT, backing up and restoring a database file. This gives the ability to perform the data processing t...

  20. Are Quantum Computing Models Realistic?

    OpenAIRE

    Kak, Subhash

    2001-01-01

    The commonly used circuit model of quantum computing leaves out the problems of imprecision in the initial state preparation, particle statistics (indistinguishability of particles belonging to the same quantum state), and error correction (current techniques cannot correct all small errors). The initial state in the circuit model computation is obtained by applying potentially imprecise Hadamard gate operations whereas useful quantum computation requires a state with no unc...

  1. Pure NQR quantum computing

    Energy Technology Data Exchange (ETDEWEB)

    Furman, G.B. [Coll. ' ' Ogalo' ' , Katzrin (Israel); Physics Dept., Ben Gurion Univ., Beer Sheva (Israel); Goren, S.D. [Physics Dept., Ben Gurion Univ., Beer Sheva (Israel)

    2002-07-01

    It is shown that pure NQR can be utilized as a platform for quantum computing without applying a high external magnetic field. By exciting each resonance transition between quadrupole energy levels with two radio-frequency fields differing in phase and direction, the double degeneracy of the spin energy spectrum in an electric field gradient is removed. As an example, in the case of I=7/2 (nuclei {sup 133}Cs or {sup 123}Sb) the energy spectrum has eight levels which can be used as three qubits. (orig.)

  2. Pure NQR quantum computing

    International Nuclear Information System (INIS)

    It is shown that pure NQR can be utilized as a platform for quantum computing without applying a high external magnetic field. By exciting each resonance transition between quadrupole energy levels with two radio-frequency fields differing in phase and direction, the double degeneracy of the spin energy spectrum in an electric field gradient is removed. As an example, in the case of I=7/2 (nuclei 133Cs or 123Sb) the energy spectrum has eight levels which can be used as three qubits. (orig.)

  3. Quantum computers, factoring, and decoherence

    CERN Document Server

    Chuang, I; Shor, P W; Zurek, W H; Chuang, I; Laflamme, Raymond; Shor, P; Zurek, W

    1995-01-01

    In a quantum computer any superposition of inputs evolves unitarily into the corresponding superposition of outputs. It has been recently demonstrated that such computers can dramatically speed up the task of finding factors of large numbers -- a problem of great practical significance because of its cryptographic applications. Instead of the nearly exponential (\\sim \\exp L^{1/3}, for a number with L digits) time required by the fastest classical algorithm, the quantum algorithm gives factors in a time polynomial in L (\\sim L^2). This enormous speed-up is possible in principle because quantum computation can simultaneously follow all of the paths corresponding to the distinct classical inputs, obtaining the solution as a result of coherent quantum interference between the alternatives. Hence, a quantum computer is sophisticated interference device, and it is essential for its quantum state to remain coherent in the course of the operation. In this report we investigate the effect of decoherence on the quantum...

  4. Quantum Computing and Dynamical Quantum Models

    OpenAIRE

    Aaronson, Scott

    2002-01-01

    A dynamical quantum model assigns an eigenstate to a specified observable even when no measurement is made, and gives a stochastic evolution rule for that eigenstate. Such a model yields a distribution over classical histories of a quantum state. We study what can be computed by sampling from that distribution, i.e., by examining an observer's entire history. We show that, relative to an oracle, one can solve problems in polynomial time that are intractable even for quantum ...

  5. Quantum information. Teleportation - cryptography - quantum computer; Quanteninformation. Teleportation - Kryptografie - Quantencomputer

    Energy Technology Data Exchange (ETDEWEB)

    Koenneker, Carsten (comp.)

    2012-11-01

    The following topics are dealt with: Reality in the test facility, quantum teleportation, the reality of quanta, interaction-free quantum measurement, rules for quantum computers, quantum computers with ions, spintronics with diamond, the limits of the quantum computers, a view in the future of quantum optics. (HSI)

  6. Universal quantum computation by discontinuous quantum walk

    International Nuclear Information System (INIS)

    Quantum walks are the quantum-mechanical analog of random walks, in which a quantum ''walker'' evolves between initial and final states by traversing the edges of a graph, either in discrete steps from node to node or via continuous evolution under the Hamiltonian furnished by the adjacency matrix of the graph. We present a hybrid scheme for universal quantum computation in which a quantum walker takes discrete steps of continuous evolution. This ''discontinuous'' quantum walk employs perfect quantum-state transfer between two nodes of specific subgraphs chosen to implement a universal gate set, thereby ensuring unitary evolution without requiring the introduction of an ancillary coin space. The run time is linear in the number of simulated qubits and gates. The scheme allows multiple runs of the algorithm to be executed almost simultaneously by starting walkers one time step apart.

  7. Universal quantum computation by discontinuous quantum walk

    CERN Document Server

    Underwood, Michael S

    2010-01-01

    Quantum walks are the quantum-mechanical analog of random walks, in which a quantum `walker' evolves between initial and final states by traversing the edges of a graph, either in discrete steps from node to node or via continuous evolution under the Hamiltonian furnished by the adjacency matrix of the graph. We present a hybrid scheme for universal quantum computation in which a quantum walker takes discrete steps of continuous evolution. This `discontinuous' quantum walk employs perfect quantum state transfer between two nodes of specific subgraphs chosen to implement a universal gate set, thereby ensuring unitary evolution without requiring the introduction of an ancillary coin space. The run time is linear in the number of simulated qubits and gates. The scheme allows multiple runs of the algorithm to be executed almost simultaneously by starting walkers one timestep apart.

  8. Quantum Computing over Finite Fields

    CERN Document Server

    James, Roshan P; Sabry, Amr

    2011-01-01

    In recent work, Benjamin Schumacher and Michael~D. Westmoreland investigate a version of quantum mechanics which they call "modal quantum theory" but which we prefer to call "discrete quantum theory". This theory is obtained by instantiating the mathematical framework of Hilbert spaces with a finite field instead of the field of complex numbers. This instantiation collapses much the structure of actual quantum mechanics but retains several of its distinguishing characteristics including the notions of superposition, interference, and entanglement. Furthermore, discrete quantum theory excludes local hidden variable models, has a no-cloning theorem, and can express natural counterparts of quantum information protocols such as superdense coding and teleportation. Our first result is to distill a model of discrete quantum computing from this quantum theory. The model is expressed using a monadic metalanguage built on top of a universal reversible language for finite computations, and hence is directly implementab...

  9. The Physics of Quantum Computation

    Science.gov (United States)

    Falci, Giuseppe; Paladino, Elisabette

    2015-10-01

    Quantum Computation has emerged in the past decades as a consequence of down-scaling of electronic devices to the mesoscopic regime and of advances in the ability of controlling and measuring microscopic quantum systems. QC has many interdisciplinary aspects, ranging from physics and chemistry to mathematics and computer science. In these lecture notes we focus on physical hardware, present day challenges and future directions for design of quantum architectures.

  10. Silicon-based Quantum Computation

    OpenAIRE

    S. Simmons

    2013-01-01

    There is a worldwide race to build a computer which exploits the counterintuitive principles of quantum mechanics1. Silicon is one of the most promising platforms for emerging quantum information technologies for two reasons: one, it possesses many of the key desirable criteria for low-error quantum information processing, and two, the microelectronics industry has decades of experience with producing ultrapure silicon and nanoscale silicon devices, which makes silicon-based quantum devices a...

  11. Genetic Algorithms and Quantum Computation

    CERN Document Server

    Giraldi, G A; Thess, R N; Giraldi, Gilson A.; Portugal, Renato; Thess, Ricardo N.

    2004-01-01

    Recently, researchers have applied genetic algorithms (GAs) to address some problems in quantum computation. Also, there has been some works in the designing of genetic algorithms based on quantum theoretical concepts and techniques. The so called Quantum Evolutionary Programming has two major sub-areas: Quantum Inspired Genetic Algorithms (QIGAs) and Quantum Genetic Algorithms (QGAs). The former adopts qubit chromosomes as representations and employs quantum gates for the search of the best solution. The later tries to solve a key question in this field: what GAs will look like as an implementation on quantum hardware? As we shall see, there is not a complete answer for this question. An important point for QGAs is to build a quantum algorithm that takes advantage of both the GA and quantum computing parallelism as well as true randomness provided by quantum computers. In the first part of this paper we present a survey of the main works in GAs plus quantum computing including also our works in this area. He...

  12. Quantum Computer Using Coupled Quantum Dot Molecules

    CERN Document Server

    Wu, N J; Natori, A; Yasunaga, H; Wu*, Nan-Jian

    1999-01-01

    We propose a method for implementation of a quantum computer using artificial molecules. The artificial molecule consists of two coupled quantum dots stacked along z direction and one single electron. One-qubit and two-qubit gates are constructed by one molecule and two coupled molecules, respectively.The ground state and the first excited state of the molecule are used to encode the |0> and |1> states of a qubit. The qubit is manipulated by a resonant electromagnetic wave that is applied directly to the qubit through a microstrip line. The coupling between two qubits in a quantum controlled NOT gate is switched on (off) by floating (grounding) the metal film electrodes. We study the operations of the gates by using a box-shaped quantum dot model and numerically solving a time-dependent Schridinger equation, and demonstrate that the quantum gates can perform the quantum computation. The operating speed of the gates is about one operation per 4ps. The reading operation of the output of the quantum computer can...

  13. Cartoon computation: quantum-like computing without quantum mechanics

    International Nuclear Information System (INIS)

    We present a computational framework based on geometric structures. No quantum mechanics is involved, and yet the algorithms perform tasks analogous to quantum computation. Tensor products and entangled states are not needed-they are replaced by sets of basic shapes. To test the formalism we solve in geometric terms the Deutsch-Jozsa problem, historically the first example that demonstrated the potential power of quantum computation. Each step of the algorithm has a clear geometric interpretation and allows for a cartoon representation. (fast track communication)

  14. Controlling the quantum computational speed

    OpenAIRE

    Metwally, N.; Abdel-Aty, M.; Abdalla, M. Sebawe

    2008-01-01

    The speed of quantum computation is investigated through the time evolution of the speed of the orthogonality. The external field components for classical treatment beside the detuning and the coupling parameters for quantum treatment play important roles on the computational speed. It has been shown that the number of photons has no significant effect on the speed of computation. However, it is very sensitive to the variation in both detuning and the interaction coupling pa...

  15. Cryptography, quantum computation and trapped ions

    Energy Technology Data Exchange (ETDEWEB)

    Hughes, Richard J.

    1998-03-01

    The significance of quantum computation for cryptography is discussed. Following a brief survey of the requirements for quantum computational hardware, an overview of the ion trap quantum computation project at Los Alamos is presented. The physical limitations to quantum computation with trapped ions are analyzed and an assessment of the computational potential of the technology is made.

  16. Focus on topological quantum computation

    International Nuclear Information System (INIS)

    Topological quantum computation started as a niche area of research aimed at employing particles with exotic statistics, called anyons, for performing quantum computation. Soon it evolved to include a wide variety of disciplines. Advances in the understanding of anyon properties inspired new quantum algorithms and helped in the characterization of topological phases of matter and their experimental realization. The conceptual appeal of topological systems as well as their promise for building fault-tolerant quantum technologies fuelled the fascination in this field. This ‘focus on’ collection brings together several of the latest developments in the field and facilitates the synergy between different approaches. (editorial)

  17. Avoiding Quantum Chaos in Quantum Computation

    CERN Document Server

    Berman, G P; Izrailev, F M; Tsifrinovich, V I

    2001-01-01

    We study a one-dimensional chain of nuclear $1/2-$spins in an external time-dependent magnetic field. This model is considered as a possible candidate for experimental realization of quantum computation. According to the general theory of interacting particles, one of the most dangerous effects is quantum chaos which can destroy the stability of quantum operations. According to the standard viewpoint, the threshold for the onset of quantum chaos due to an interaction between spins (qubits) strongly decreases with an increase of the number of qubits. Contrary to this opinion, we show that the presence of a magnetic field gradient helps to avoid quantum chaos which turns out to disappear with an increase of the number of qubits. We give analytical estimates which explain this effect, together with numerical data supporting

  18. Quantum entanglement and quantum computational algorithms

    Indian Academy of Sciences (India)

    Arvind

    2001-02-01

    The existence of entangled quantum states gives extra power to quantum computers over their classical counterparts. Quantum entanglement shows up qualitatively at the level of two qubits. We demonstrate that the one- and the two-bit Deutsch-Jozsa algorithm does not require entanglement and can be mapped onto a classical optical scheme. It is only for three and more input bits that the DJ algorithm requires the implementation of entangling transformations and in these cases it is impossible to implement this algorithm classically

  19. Testing a Quantum Computer

    OpenAIRE

    Biamonte, Jacob D.; Perkowski, Marek A.

    2004-01-01

    The problem of quantum test is formally addressed. The presented method attempts the quantum role of classical test generation and test set reduction methods known from standard binary and analog circuits. QuFault, the authors software package generates test plans for arbitrary quantum circuits using the very efficient simulator QuIDDPro[1]. The quantum fault table is introduced and mathematically formalized, and the test generation method explained.

  20. Duality quantum computer and the efficient quantum simulations

    OpenAIRE

    Wei, Shi-Jie; Long, Gui-Lu

    2015-01-01

    In this paper, we firstly briefly review the duality quantum computer. Distinctly, the generalized quantum gates, the basic evolution operators in a duality quantum computer are no longer unitary, and they can be expressed in terms of linear combinations of unitary operators. All linear bounded operators can be realized in a duality quantum computer, and unitary operators are just the extreme points of the set of generalized quantum gates. A d-slits duality quantum computer ...

  1. Quantum measurements with a quantum computer

    CERN Document Server

    D'Helon, C

    1997-01-01

    We present a scheme in which an ion trap quantum computer can be used to make arbitrarily accurate measurements of the quadrature phase variables for the collective vibrational motion of the ion. The electronic states of the ion become the `apparatus', and the method is based on regarding the `apparatus' as a quantum computer register which can be prepared in appropriate states by running a Fourier transform algorithm on the data stored within it. The resolution of the measurement rises exponentially with the number of ions used.

  2. Quantum Computing with Very Noisy Devices

    OpenAIRE

    Knill, E.

    2004-01-01

    In theory, quantum computers can efficiently simulate quantum physics, factor large numbers and estimate integrals, thus solving otherwise intractable computational problems. In practice, quantum computers must operate with noisy devices called ``gates'' that tend to destroy the fragile quantum states needed for computation. The goal of fault-tolerant quantum computing is to compute accurately even when gates have a high probability of error each time they are used. Here we ...

  3. Minimal ancilla mediated quantum computation

    Energy Technology Data Exchange (ETDEWEB)

    Proctor, Timothy J. [University of Leeds, School of Physics and Astronomy, Leeds (United Kingdom); Kendon, Viv [University of Leeds, School of Physics and Astronomy, Leeds (United Kingdom); Durham University, Department of Physics, Durham (United Kingdom)

    2014-12-01

    Schemes of universal quantum computation in which the interactions between the computational elements, in a computational register, are mediated by some ancillary system are of interest due to their relevance to the physical implementation of a quantum computer. Furthermore, reducing the level of control required over both the ancillary and register systems has the potential to simplify any experimental implementation. In this paper we consider how to minimise the control needed to implement universal quantum computation in an ancilla-mediated fashion. Considering computational schemes which require no measurements and hence evolve by unitary dynamics for the global system, we show that when employing an ancilla qubit there are certain fixed-time ancilla-register interactions which, along with ancilla initialisation in the computational basis, are universal for quantum computation with no additional control of either the ancilla or the register. We develop two distinct models based on locally inequivalent interactions and we then discuss the relationship between these unitary models and the measurement-based ancilla-mediated models known as ancilla-driven quantum computation. (orig.)

  4. Cluster-state quantum computation

    OpenAIRE

    Nielsen, Michael A.

    2005-01-01

    This article is a short introduction to and review of the cluster-state model of quantum computation, in which coherent quantum information processing is accomplished via a sequence of single-qubit measurements applied to a fixed quantum state known as a cluster state. We also discuss a few novel properties of the model, including a proof that the cluster state cannot occur as the exact ground state of any naturally occurring physical system, and a proof that measurements on...

  5. Quantum chromodynamics with advanced computing

    Energy Technology Data Exchange (ETDEWEB)

    Kronfeld, Andreas S.; /Fermilab

    2008-07-01

    We survey results in lattice quantum chromodynamics from groups in the USQCD Collaboration. The main focus is on physics, but many aspects of the discussion are aimed at an audience of computational physicists.

  6. Towards Quantum Chemistry on a Quantum Computer

    OpenAIRE

    Lanyon, BP; Whitfield, JD; Gillett, GG; Goggin, ME; Almeida, MP; Kassal, I.; Biamonte, JD; Mohseni, M; Powell, BJ; Barbieri, M; Aspuru-Guzik, A.; White, AG

    2010-01-01

    The fundamental problem faced in quantum chemistry is the calculation of molecular properties, which are of practical importance in fields ranging from materials science to biochemistry. Within chemical precision, the total energy of a molecule as well as most other properties, can be calculated by solving the Schrodinger equation. However, the computational resources required to obtain exact solutions on a conventional computer generally increase exponentially with the numb...

  7. An Algebra of Reversible Quantum Computing

    OpenAIRE

    WANG, YONG

    2015-01-01

    Based on the axiomatization of reversible computing RACP, we generalize it to quantum reversible computing which is called qRACP. By use of the framework of quantum configuration, we show that structural reversibility and quantum state reversibility must be satisfied simultaneously in quantum reversible computation. RACP and qRACP has the same axiomatization modulo the so-called quantum forward-reverse bisimularity, that is, classical reversible computing and quantum reversi...

  8. Quantum Computing via The Bethe Ansatz

    OpenAIRE

    Zhang, Yong

    2011-01-01

    We recognize quantum circuit model of computation as factorisable scattering model and propose that a quantum computer is associated with a quantum many-body system solved by the Bethe ansatz. As an typical example to support our perspectives on quantum computation, we study quantum computing in one-dimensional nonrelativistic system with delta-function interaction, where the two-body scattering matrix satisfies the factorisation equation (the quantum Yang--Baxter equation) ...

  9. Prospective Algorithms for Quantum Evolutionary Computation

    OpenAIRE

    Sofge, Donald A.

    2008-01-01

    This effort examines the intersection of the emerging field of quantum computing and the more established field of evolutionary computation. The goal is to understand what benefits quantum computing might offer to computational intelligence and how computational intelligence paradigms might be implemented as quantum programs to be run on a future quantum computer. We critically examine proposed algorithms and methods for implementing computational intelligence paradigms, pri...

  10. Distinguishing Short Quantum Computations

    CERN Document Server

    Rosgen, Bill

    2007-01-01

    Distinguishing logarithmic depth quantum circuits on mixed states is shown to be complete for QIP, the class of problems having quantum interactive proof systems. Circuits in this model can represent arbitrary quantum processes, and thus this result has implications for the verification of implementations of quantum algorithms. The distinguishability problem is also complete for QIP on constant depth circuits containing the unbounded fan-out gate. These results are shown by reducing a QIP-complete problem to a logarithmic depth version of itself using a parallelization technique.

  11. Quantum information and computing

    CERN Document Server

    Ohya, M; Watanabe, N

    2006-01-01

    The main purpose of this volume is to emphasize the multidisciplinary aspects of this very active new line of research in which concrete technological and industrial realizations require the combined efforts of experimental and theoretical physicists, mathematicians and engineers. Contents: Coherent Quantum Control of ?-Atoms through the Stochastic Limit (L Accardi et al.); Recent Advances in Quantum White Noise Calculus (L Accardi & A Boukas); Joint Extension of States of Fermion Subsystems (H Araki); Fidelity of Quantum Teleportation Model Using Beam Splittings (K-H Fichtner et al.); Quantum

  12. Physical Realizations of Quantum Computing

    CERN Document Server

    Kanemitsu, Shigeru; Salomaa, Martti; Takagi, Shin; Are the DiVincenzo Criteria Fulfilled in 2004 ?

    2006-01-01

    The contributors of this volume are working at the forefront of various realizations of quantum computers. They survey the recent developments in each realization, in the context of the DiVincenzo criteria, including nuclear magnetic resonance, Josephson junctions, quantum dots, and trapped ions. There are also some theoretical contributions which have relevance in the physical realizations of a quantum computer. This book fills the gap between elementary introductions to the subject and highly specialized research papers to allow beginning graduate students to understand the cutting-edge of r

  13. Development and production of two explosive components using SCB technology

    Science.gov (United States)

    Tarbell, William W.; Sanchez, Daniel H.; Oestreich, Michael L.; Prentice, Jerry W.

    For many years, explosive components have used hotwires to convert an electrical stimulus into the thermal energy required to initiate the device. A Semi-Conductor Bridge (SCB) performs the same function, but with the advantage of requiring approximately 1/10 the input energy of a comparable hotwire, while retaining excellent no-fire characteristics. The SCB also demonstrates faster function times due to its inherently-lower thermal mass. This paper discusses the development and production of two SCB-based devices, the MC4491 Initiator and the MC4492 Actuator. The initiator is designed to shock initiate a linear shaped charge by accelerating a thin metal plate across a small gap. The actuator functions several different components, serving as either an actuator by producing a rapidly expanding gas to activate piston mechanisms or as an ignitor by providing hot particles for initiating pyrotechnic mixtures. Details are provided on the construction of both devices, methods of assembly, and performance characteristics (function time, flyer velocity, pressure in a closed bomb, heat content, and no-fire and all-fire levels).

  14. Warp-Drive Quantum Computation

    CERN Document Server

    Nakahara, M; Kondo, Y; Tanimura, S; Hata, K; Nakahara, Mikio; Vartiainen, Juha J.; Kondo, Yasushi; Tanimura, Shogo; Hata, Kazuya

    2004-01-01

    Recently it has been shown that time-optimal quantum computation is attained by using the Cartan decomposition of a unitary matrix. We extend this approach by noting that the unitary group is compact. This allows us to reduce the execution time of a quantum algorithm $U_{\\rm alg}$ further by adding an extra gate $W$ to it. This gate $W$ sends $U_{\\rm alg}$ to another algorithm $WU_{\\rm alg}$ which is executable in a shorter time than $U_{\\rm alg}$. We call this technique warp-drive. Here we show both theoretically and experimentally that the execution time of Grover's algorithm is reduced in two-qubit NMR quantum computer. Warp-drive is potentially a powerful tool in accelerating algorithms and reducing the errors in any realization. of a quantum computer

  15. Quantum Computation and Algorithms

    International Nuclear Information System (INIS)

    It is now firmly established that quantum algorithms provide a substantial speedup over classical algorithms for a variety of problems, including the factorization of large numbers and the search for a marked element in an unsorted database. In this talk I will review the principles of quantum algorithms, the basic quantum gates and their operation. The combination of superposition and interference, that makes these algorithms efficient, will be discussed. In particular, Grover's search algorithm will be presented as an example. I will show that the time evolution of the amplitudes in Grover's algorithm can be found exactly using recursion equations, for any initial amplitude distribution

  16. Reversible computing fundamentals, quantum computing, and applications

    CERN Document Server

    De Vos, Alexis

    2010-01-01

    Written by one of the few top internationally recognized experts in the field, this book concentrates on those topics that will remain fundamental, such as low power computing, reversible programming languages, and applications in thermodynamics. It describes reversible computing from various points of view: Boolean algebra, group theory, logic circuits, low-power electronics, communication, software, quantum computing. It is this multidisciplinary approach that makes it unique.Backed by numerous examples, this is useful for all levels of the scientific and academic community, from undergr

  17. Quantum Computation--The Ultimate Frontier

    OpenAIRE

    Adami, Chris; Dowling, Jonathan P

    2002-01-01

    The discovery of an algorithm for factoring which runs in polynomial time on a quantum computer has given rise to a concerted effort to understand the principles, advantages, and limitations of quantum computing. At the same time, many different quantum systems are being explored for their suitability to serve as a physical substrate for the quantum computer of the future. I discuss some of the theoretical foundations of quantum computer science, including algorithms and err...

  18. Handbook of computational quantum chemistry

    CERN Document Server

    Cook, David B

    2005-01-01

    Quantum chemistry forms the basis of molecular modeling, a tool widely used to obtain important chemical information and visual images of molecular systems. Recent advances in computing have resulted in considerable developments in molecular modeling, and these developments have led to significant achievements in the design and synthesis of drugs and catalysts. This comprehensive text provides upper-level undergraduates and graduate students with an introduction to the implementation of quantum ideas in molecular modeling, exploring practical applications alongside theoretical explanations.Wri

  19. Computable functions, quantum measurements, and quantum dynamics

    CERN Document Server

    Nielsen, M A

    1997-01-01

    We construct quantum mechanical observables and unitary operators which, if implemented in physical systems as measurements and dynamical evolutions, would contradict the Church-Turing thesis which lies at the foundation of computer science. We conclude that either the Church-Turing thesis needs revision, or that only restricted classes of observables may be realized, in principle, as measurements, and that only restricted classes of unitary operators may be realized, in principle, as dynamics.

  20. Efficient quantum computing insensitive to phase errors

    OpenAIRE

    Georgeot, B.; Shepelyansky, D. L.

    2001-01-01

    We show that certain computational algorithms can be simulated on a quantum computer with exponential efficiency and be insensitive to phase errors. Our explicit algorithm simulates accurately the classical chaotic dynamics for exponentially many orbits even when the quantum fidelity drops to zero. Such phase-insensitive algorithms open new possibilities for computation on realistic quantum computers.

  1. Quantum Computation of Jones' Polynomials

    CERN Document Server

    Subramanian, V

    2002-01-01

    It is one of the challenging problems to construct an efficient quantum algorithm which can compute the Jones' polynomial for any knot or link obtained from closure or capping of a $n$-strand braid. We recapitulate the construction of braid-group ${\\cal B}_n$ representations from vertex models. We perform orthogonal transformation involving quantum Clebsch-Gordan coefficient matrix on the qubit basis to obtain eigen basis for the braiding generators. Using the transformed bases, we propose a quantum algorithm to determine the Jones' Polynomial for any knot or link.

  2. Phase Information in Quantum Oracle Computing

    OpenAIRE

    Machta, J.

    1998-01-01

    Computational devices may be supplied with external sources of information (oracles). Quantum oracles may transmit phase information which is available to a quantum computer but not a classical computer. One consequence of this observation is that there is an oracle which is of no assistance to a classical computer but which allows a quantum computer to solve undecidable problems. Thus useful relativized separations between quantum and classical complexity classes must exclu...

  3. Geometrical perspective on quantum states and quantum computation

    OpenAIRE

    Chen, Zeqian

    2013-01-01

    We interpret quantum computing as a geometric evolution process by reformulating finite quantum systems via Connes' noncommutative geometry. In this formulation, quantum states are represented as noncommutative connections, while gauge transformations on the connections play a role of unitary quantum operations. Thereby, a geometrical model for quantum computation is presented, which is equivalent to the quantum circuit model. This result shows a geometric way of realizing q...

  4. Theoretical issues in spin-based quantum dot quantum computation

    OpenAIRE

    Hu, Xuedong; Sarma, S. Das

    2001-01-01

    We review our recent work addressing various theoretical issues in spin-based quantum dot quantum computation and quantum information processing. In particular, we summarize our calculation of electron exchange interaction in two-electron double quantum dots and multi-electron double dots, and discuss the physical implication of our results. We also discuss possible errors and how they can be corrected in spin-based quantum dot quantum computation. We critically assess the c...

  5. Quantum Walks for Computer Scientists

    CERN Document Server

    Venegas-Andraca, Salvador

    2008-01-01

    Quantum computation, one of the latest joint ventures between physics and the theory of computation, is a scientific field whose main goals include the development of hardware and algorithms based on the quantum mechanical properties of those physical systems used to implement such algorithms. Solving difficult tasks (for example, the Satisfiability Problem and other NP-complete problems) requires the development of sophisticated algorithms, many of which employ stochastic processes as their mathematical basis. Discrete random walks are a popular choice among those stochastic processes. Inspir

  6. Quantumness, Randomness and Computability

    Science.gov (United States)

    Solis, Aldo; Hirsch, Jorge G.

    2015-06-01

    Randomness plays a central role in the quantum mechanical description of our interactions. We review the relationship between the violation of Bell inequalities, non signaling and randomness. We discuss the challenge in defining a random string, and show that algorithmic information theory provides a necessary condition for randomness using Borel normality. We close with a view on incomputablity and its implications in physics.

  7. The universal quantum driving force to speed up a quantum computation -- The unitary quantum dynamics

    OpenAIRE

    Miao, Xijia

    2011-01-01

    It is shown in the paper that the unitary quantum dynamics in quantum mechanics is the universal quantum driving force to speed up a quantum computation. This assertion supports strongly in theory that the unitary quantum dynamics is the fundamental and universal principle in nature. On the other hand, the symmetric structure of Hilbert space of a composite quantum system is the quantum-computing resource that is not owned by classical computation. A new quantum-computing sp...

  8. Quantum computing of quantum chaos and imperfection effects

    OpenAIRE

    Song, Pil Hun; Shepelyansky, Dima L.

    2000-01-01

    We study numerically the imperfection effects in the quantum computing of the kicked rotator model in the regime of quantum chaos. It is shown that there are two types of physical characteristics: for one of them the quantum computation errors grow exponentially with the number of qubits in the computer while for the other the growth is polynomial. Certain similarity between classical and quantum computing errors is also discussed.

  9. Using a quantum computer to investigate quantum chaos

    OpenAIRE

    Schack, Ruediger

    1997-01-01

    We show that the quantum baker's map, a prototypical map invented for theoretical studies of quantum chaos, has a very simple realization in terms of quantum gates. Chaos in the quantum baker's map could be investigated experimentally on a quantum computer based on only 3 qubits.

  10. ASCR Workshop on Quantum Computing for Science

    Energy Technology Data Exchange (ETDEWEB)

    Aspuru-Guzik, Alan [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Van Dam, Wim [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Farhi, Edward [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Gaitan, Frank [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Humble, Travis [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Jordan, Stephen [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Landahl, Andrew J [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Love, Peter [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Lucas, Robert [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Preskill, John [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Muller, Richard P. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Svore, Krysta [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Wiebe, Nathan [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Williams, Carl [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2015-06-01

    This report details the findings of the DOE ASCR Workshop on Quantum Computing for Science that was organized to assess the viability of quantum computing technologies to meet the computational requirements of the DOE’s science and energy mission, and to identify the potential impact of quantum technologies. The workshop was held on February 17-18, 2015, in Bethesda, MD, to solicit input from members of the quantum computing community. The workshop considered models of quantum computation and programming environments, physical science applications relevant to DOE's science mission as well as quantum simulation, and applied mathematics topics including potential quantum algorithms for linear algebra, graph theory, and machine learning. This report summarizes these perspectives into an outlook on the opportunities for quantum computing to impact problems relevant to the DOE’s mission as well as the additional research required to bring quantum computing to the point where it can have such impact.

  11. Distributed quantum computing: A distributed Shor algorithm

    OpenAIRE

    Yimsiriwattana, Anocha; Lomonaco Jr, Samuel J.

    2004-01-01

    We present a distributed implementation of Shor's quantum factoring algorithm on a distributed quantum network model. This model provides a means for small capacity quantum computers to work together in such a way as to simulate a large capacity quantum computer. In this paper, entanglement is used as a resource for implementing non-local operations between two or more quantum computers. These non-local operations are used to implement a distributed factoring circuit with po...

  12. Computations in Quantum Tensor Networks

    OpenAIRE

    Huckle T.; Waldherr K.; Schulte-Herbruggen T.

    2012-01-01

    The computation of the ground state (i.e. the eigenvector related to the smallest eigenvalue) is an important task in the simulation of quantum many-body systems. As the dimension of the underlying vector space grows exponentially in the number of particles, one has to consider appropriate subsets promising both convenient approximation properties and efficient computations. The variational ansatz for this numerical approach leads to the minimization of the Rayleigh quotient...

  13. Geometric phases and quantum computation

    International Nuclear Information System (INIS)

    Full text: In my lectures I will talk about the notion of the geometric phase and explain its relevance for both fundamental quantum mechanics as well as quantum computation. The phase will be at first introduced via the idea of Pancharatnam which involves interference of three or more light beams. This notion will then be generalized to the evolving quantum systems. I will discuss both pure and mixed states as well as unitary and non-unitary evolutions. I will also show how the concept of the vacuum induced geometric phase arises in quantum optics. A simple measurement scheme involving a Mach Zehnder interferometer will be presented and will be used to illustrate all the concepts in the lecture. Finally, I will expose a simple generalization of the geometric phase to evolving degenerate states. This will be seen to lead to the possibility of universal quantum computation using geometric effects only. Moreover, this contains a promise of intrinsically fault tolerant quantum information processing, whose prospects will be outlined at the end of the lecture. (author)

  14. Computational model underlying the one-way quantum computer

    CERN Document Server

    Raussendorf, R; Raussendorf, Robert; Briegel, Hans

    2001-01-01

    In this paper we present the computational model underlying the one-way quantum computer which we introduced recently [Phys. Rev. Lett 86, 5188 (2001)]. The one-way quantum computer has the property that any quantum logic network can be simulated on it. Conversely, not all ways of quantum information processing that are possible with the one-way quantum computer can be explained within a network model. As a consequence, the temporal complexity is, for certain algorithms, lower than in networks. For example, every circuit in the Clifford group can be performed on the one-way quantum computer in a single time step.

  15. Classical computing, quantum computing, and Shor's factoring algorithm

    CERN Document Server

    Manin, Yu I

    1999-01-01

    This is an expository talk written for the Bourbaki Seminar. After a brief introduction, Section 1 discusses in the categorical language the structure of the classical deterministic computations. Basic notions of complexity icluding the P/NP problem are reviewed. Section 2 introduces the notion of quantum parallelism and explains the main issues of quantum computing. Section 3 is devoted to four quantum subroutines: initialization, quantum computing of classical Boolean functions, quantum Fourier transform, and Grover's search algorithm. The central Section 4 explains Shor's factoring algorithm. Section 5 relates Kolmogorov's complexity to the spectral properties of computable function. Appendix contributes to the prehistory of quantum computing.

  16. The Quantum Way of Doing Computations

    International Nuclear Information System (INIS)

    Full text: Since the mid nineties of the 20th century it became apparent that one of the centuries’ most important technological inventions, computers in general and many of their applications could possibly be further enormously enhanced by using operations based on quantum. This is timely since the classical road maps for the development of computational devices, commonly known as Moore’s law, will cease to be applicable within the next decade due to the ever smaller sizes of the electronic components that soon will enter the quantum physics realm. Computations, whether they happen in our heads or with any computational device, always rely on real physical processes, which are data input, data representation in a memory, data manipulation using algorithms and finally, the data output. Building a quantum computer then requires the implementation of quantum bits (qubits) as storage sites for quantum information, quantum registers and quantum gates for data handling and processing and the development of quantum algorithms. In this talk, the basic functional principle of a quantum computer will be reviewed and a few technologies for their implementation will be highlighted. In particular, the quantum way of doing computations will be illustrated by showing how quantum correlations, commonly known as entanglement can enhance computational processes. Aside from their use for quantum computers, these quantum technologies open wide perspectives for applications in many technical areas. Examples such as quantum enhanced metrology and quantum simulations will be presented. (author)

  17. Interaction-free quantum computation

    CERN Document Server

    Azuma, H

    2004-01-01

    In this paper, we study the quantum computation realized by an interaction-free measurement (IFM). Using Kwiat et al.'s interferometer, we construct a two-qubit quantum gate that changes one particle's trajectory according to whether or not the other particle exists in the interferometer. We propose a method for distinguishing Bell-basis vectors, each of which consists of a pair of an electron and a positron, by this gate. (This is called the Bell-basis measurement.) This method succeeds with probability 1 in the limit of $N \\to \\infty$, where N is the number of beam splitters in the interferometer. Moreover, we can carry out a controlled-NOT gate operation by the above Bell-basis measurement and the method proposed by Gottesman and Chuang. Therefore, we can prepare a universal set of quantum gates by the IFM. This means that we can execute any quantum algorithm by the IFM.

  18. The Next Generation Computing Brainwave-Quantum Computing

    OpenAIRE

    T.Venkat Narayana Rao; Shirish Pathania

    2010-01-01

    This paper is written to explicate the working of Quantum Computing and its mechanics. Quantum Computing is basically a minute field from Nanotechnology. The main purpose of this paper is to explain an inexperienced user about the technology and principles used while designing the architect of a quantum computer. Operational quantum computers would be a reality in forth coming years by the virtue of new mechanisms to explore and implementations. This paper is sectioned into 7 parts. Part 1 is...

  19. Using Quantum Computers to Learn Physics

    OpenAIRE

    Wiebe, Nathan

    2014-01-01

    Since its inception at the beginning of the twentieth century, quantum mechanics has challenged our conceptions of how the universe ought to work; however, the equations of quantum mechanics can be too computationally difficult to solve using existing computers for even modestly large systems. Here I will show that quantum computers can sometimes be used to address such problems and that quantum computer science can assign formal complexities to learning facts about nature. ...

  20. Fault tolerance for holonomic quantum computation

    OpenAIRE

    Oreshkov, Ognyan; Brun, Todd A.; Lidar, Daniel A.

    2013-01-01

    Comment: 16 pages, this is a chapter in the book "Quantum Error Correction", edited by Daniel A. Lidar and Todd A. Brun, (Cambridge University Press, 2013), at http://www.cambridge.org/us/academic/subjects/physics/quantum-physics-quantum-information-and-quantum-computation/quantum-error-correction

  1. KLM quantum computation as a measurement based computation

    OpenAIRE

    Popescu, Sandu

    2006-01-01

    We show that the Knill Laflamme Milburn method of quantum computation with linear optics gates can be interpreted as a one-way, measurement based quantum computation of the type introduced by Briegel and Rausendorf. We also show that the permanent state of n n-dimensional systems is a universal state for quantum computation.

  2. Quantum computing with complex instruction sets

    Science.gov (United States)

    Sanders, G. D.; Kim, K. W.; Holton, W. C.

    1999-02-01

    In most current quantum computers simple electromagnetic pulses implement computations using a minimal set of universal gates. We propose an approach in which quantum control techniques combined with flexible electromagnetic pulse shaping are used to replace several universal gates with a single instruction. We show that this complex instruction set approach can significantly reduce the time required to perform quantum computations.

  3. Blind Quantum Computation

    DEFF Research Database (Denmark)

    Salvail, Louis; Arrighi, Pablo

    2006-01-01

    We investigate the possibility of "having someone carry out the work of executing a function for you, but without letting him learn anything about your input". Say Alice wants Bob to compute some known function f upon her input x, but wants to prevent Bob from learning anything about x. The situation arises for instance if client Alice has limited computational resources in comparison with mistrusted server Bob, or if x is an inherently mobile piece of data. Could there be a protocol whereby Bob...

  4. Quantum ballistic evolution in quantum mechanics: Application to quantum computers

    International Nuclear Information System (INIS)

    Quantum computers are important examples of processes whose evolution can be described in terms of iterations of single-step operators or their adjoints. Based on this, Hamiltonian evolution of processes with associated step operators T is investigated here. The main limitation of this paper is to processes which evolve quantum ballistically, i.e., motion restricted to a collection of nonintersecting or distinct paths on an arbitrary basis. The main goal of this paper is proof of a theorem which gives necessary and sufficient conditions that T must satisfy so that there exists a Hamiltonian description of quantum ballistic evolution for the process, namely, that T is a partial isometry and is orthogonality preserving and stable on some basis. Simple examples of quantum ballistic evolution for quantum Turing machines with one and with more than one type of elementary step are discussed. It is seen that for nondeterministic machines the basis set can be quite complex with much entanglement present. It is also proven that, given a step operator T for an arbitrary deterministic quantum Turing machine, it is decidable if T is stable and orthogonality preserving, and if quantum ballistic evolution is possible. The proof fails if T is a step operator for a nondeterministic machine. It is an open question if such a decision procedure exists for nondeterministic machines. This problem does not occur in classical mechanics. Also the definition of quantum Turing machines used here is compared with that used by other authors. copyright 1996 The American Physical Society

  5. Universal quantum computing with nanowire double quantum dots

    OpenAIRE

    Xue, P.

    2011-01-01

    We show a method for implementing universal quantum computing using of a singlet and triplets of nanowire double quantum dots coupled to a one-dimensional transmission line resonator. This method is attractive for both quantum computing and quantum control with inhibition of spontaneous emission, enhanced spin qubit lifetime, strong coupling and quantum nondemolition measurements of spin qubits. We analyze the performance and stability of all required operations and emphasiz...

  6. Simulating quantum dynamics on a quantum computer

    International Nuclear Information System (INIS)

    We explicitly show how to simulate time-dependent sparse Hamiltonian evolution on a quantum computer, with complexity that is close to linear in the evolution time. The complexity also depends on the magnitude of the derivatives of the Hamiltonian. We propose a range of techniques to simulate Hamiltonians with badly behaved derivatives. These include using adaptive time steps, adapting the order of the integrators, and omitting regions about discontinuities. The complexity of the algorithm is quantified by calls to an oracle, which yields information about the Hamiltonian, and accounts for all computational resources. We explicitly determine the number of bits of output that this oracle needs to provide, and show how to efficiently perform the required 1-sparse unitary operations using these bits. We also account for discretization error in the time, as well as accounting for Hamiltonians that are a sum of terms that are sparse in different bases. (paper)

  7. Cove: A Practical Quantum Computer Programming Framework

    CERN Document Server

    Purkeypile, Matt

    2009-01-01

    While not yet in commercial existence, quantum computers have the ability to solve certain classes of problems that are not efficiently solvable on existing Turing Machine based (classical) computers. For quantum computers to be of use, methods of programming them must exist. Proposals exist for programming quantum computers, but all of the existing ones suffer from flaws that make them impractical in commercial software development environments. Cove is a framework for programming quantum computers that extends existing classical languages to allow for quantum computation, thus providing a quantum computing toolkit for commercial software developers. Since the target users of Cove are commercial developers, it is an object oriented framework that can be used by multiple languages and also places emphasis on complete documentation. The focus of Cove is not so much on the software product, but on the fundamental concepts that make quantum computing practical for common developers.

  8. Warp-Drive Quantum Computation

    OpenAIRE

    Nakahara, Mikio; Vartiainen, Juha J.; Kondo, Yasushi; Tanimura, Shogo; Hata, Kazuya

    2004-01-01

    Recently it has been shown that time-optimal quantum computation is attained by using the Cartan decomposition of a unitary matrix. We extend this approach by noting that the unitary group is compact. This allows us to reduce the execution time of a quantum algorithm $U_{\\rm alg}$ further by adding an extra gate $W$ to it. This gate $W$ sends $U_{\\rm alg}$ to another algorithm $WU_{\\rm alg}$ which is executable in a shorter time than $U_{\\rm alg}$. We call this technique war...

  9. EXPLORATIONS IN QUANTUM COMPUTING FOR FINANCIAL APPLICATIONS

    OpenAIRE

    Gare, Jesse

    2010-01-01

    Quantum computers have the potential to increase the solution speed for many computational problems. This paper is a first step into possible applications for quantum computing in the context of computational finance. The fundamental ideas of quantum computing are introduced, followed by an exposition of the algorithms of Deutsch and Grover. Improved mean and median estimation are shown as results of Grover?s generalized framework. The algorithm for mean estimation is refined to an improved M...

  10. Models of quantum computation and quantum programming languages

    OpenAIRE

    Miszczak, J. A.

    2010-01-01

    The goal of the presented paper is to provide an introduction to the basic computational models used in quantum information theory. We review various models of quantum Turing machine, quantum circuits and quantum random access machine (QRAM) along with their classical counterparts. We also provide an introduction to quantum programming languages, which are developed using the QRAM model. We review the syntax of several existing quantum programming languages and discuss their...

  11. The scalable quantum computation based on quantum dot systems

    OpenAIRE

    Zhang, Jian-Qi; Yu, Ya-Fei; Feng, Xun-Li; ZHANG, ZHI-MING

    2011-01-01

    We propose a scheme for realizing the scalable quantum computation based on nonidentical quantum dots trapped in a single-mode waveguide. In this system, the quantum dots simultaneously interact with a large detuned waveguide and classical light fields. During the process, neither the waveguide mode nor the quantum dots are excited, while the sub-system composed of any two quantum dots can acquire phases conditional upon the states of these two quantum dots and the certain d...

  12. Experimental realization of the quantum games on a quantum computer

    CERN Document Server

    Du, J; Xu, X; Shi, M; Wu, J; Zhou, X; Han, R; Du, Jiangfeng; Li, Hui; Xu, Xiaodong; Shi, Mingjun; Wu, Jihui; Zhou, Xianyi; Han, Rongdian

    2002-01-01

    Many previous works on quantum games are based on maximally entangled state. In this letter, we investigate the role of entanglement in quantum games. For the particular case of the quantum Prisoners' Dilemma, the property of the game changes fascinatingly with the variation of the measure of the game's entanglement. Furthermore this quantum game is experimental realized on our nuclear magnetic resonance quantum computer. Up to now, there is no quantum game in any form become pratical.

  13. Quantum computing and the entanglement frontier

    CERN Document Server

    Preskill, John

    2012-01-01

    Quantum information science explores the frontier of highly complex quantum states, the "entanglement frontier." This study is motivated by the observation (widely believed but unproven) that classical systems cannot simulate highly entangled quantum systems efficiently, and we hope to hasten the day when well controlled quantum systems can perform tasks surpassing what can be done in the classical world. One way to achieve such "quantum supremacy" would be to run an algorithm on a quantum computer which solves a problem with a super-polynomial speedup relative to classical computers, but there may be other ways that can be achieved sooner, such as simulating exotic quantum states of strongly correlated matter. To operate a large scale quantum computer reliably we will need to overcome the debilitating effects of decoherence, which might be done using "standard" quantum hardware protected by quantum error-correcting codes, or by exploiting the nonabelian quantum statistics of anyons realized in solid state sy...

  14. The Next Generation Computing Brainwave-Quantum Computing

    Directory of Open Access Journals (Sweden)

    T. Venkat Narayana Rao

    2010-12-01

    Full Text Available This paper is written to explicate the working of Quantum Computing and its mechanics. Quantum Computing is basically a minute field from Nanotechnology. The main purpose of this paper is to explain an inexperienced user about the technology and principles used while designing the architect of a quantum computer. Operational quantum computers would be a reality in forth coming years by the virtue of new mechanisms to explore and implementations. This paper is sectioned into 7 parts. Part 1 is a brief introduction to Quantum Computing i.e. basic working principle of a Qubit. Part 2 covers Qubit and the architect of the whole system. It also enlightens us about the Qubit in more detail like how data is represented, principles like superposition and state of composite system. Part 3 narrates how quantum Computing can be built using Qubits and applies the above mentioned principles. Part 4 deals with the basic introduction to Quantum Mechanics and some principles like dual nature of light and Uncertainty Principle. Part 5 depicts about the advantages of Quantum Computer over present computing systems. Part 6 discusses the overheads of Quantum Computing. Part 7 describes about implementation of Quantum Computing in today’s world. Finally this paper offers an insight about how and by when we would be able to design a full time Quantum Computer and what are the probable considerations to be taken in to account.

  15. Classical computing, quantum computing, and Shor's factoring algorithm

    OpenAIRE

    Manin, Yuri I.

    1999-01-01

    This is an expository talk written for the Bourbaki Seminar. After a brief introduction, Section 1 discusses in the categorical language the structure of the classical deterministic computations. Basic notions of complexity icluding the P/NP problem are reviewed. Section 2 introduces the notion of quantum parallelism and explains the main issues of quantum computing. Section 3 is devoted to four quantum subroutines: initialization, quantum computing of classical Boolean func...

  16. Quantum Computation and Decision Trees

    CERN Document Server

    Farhi, E; Farhi, Edward; Gutmann, Sam

    1998-01-01

    Many interesting computational problems can be reformulated in terms of decision trees. A natural classical algorithm is to then run a random walk on the tree, starting at the root, to see if the tree contains a node n levels from the root. We devise a quantum mechanical algorithm that evolves a state, initially localized at the root, through the tree. We prove that if the classical strategy succeeds in reaching level n in time polynomial in n, then so does the quantum algorithm. Moreover, we find examples of trees for which the classical algorithm requires time exponential in n, but for which the quantum algorithm succeeds in polynomial time. The examples we have so far, however, could also be solved in polynomial time by different classical algorithms.

  17. Quantum computing with itinerant microwave photons

    OpenAIRE

    Kokkala, Janne

    2013-01-01

    Microwave photons in superconducting circuits is a promising approach for quantum computing due to long coherence times and the easy controllability of superconducting devices. However, as the search of the ultimate design of a quantum computer is still ongoing, various suggestions for the realization of a quantum bit, qubit, exist even in the area of superconducting circuits. In this thesis, we study theoretically quantum computing using itinerant microwave photons as qubits. Basic tools ...

  18. Transparallel mind: Classical computing with quantum power

    OpenAIRE

    van der Helm, Peter A.

    2014-01-01

    Inspired by the extraordinary computing power promised by quantum computers, the quantum mind hypothesis postulated that quantum mechanical phenomena are the source of neuronal synchronization, which, in turn, might underlie consciousness. Here, I present an alternative inspired by a classical computing method with quantum power. This method relies on special distributed representations called hyperstrings. Hyperstrings are superpositions of up to an exponential number of st...

  19. From Monte Carlo to Quantum Computation

    OpenAIRE

    Heinrich, Stefan

    2001-01-01

    Quantum computing was so far mainly concerned with discrete problems. Recently, E. Novak and the author studied quantum algorithms for high dimensional integration and dealt with the question, which advantages quantum computing can bring over classical deterministic or randomized methods for this type of problem. In this paper we give a short introduction to the basic ideas of quantum computing and survey recent results on high dimensional integration. We discuss conne...

  20. RISQ - reduced instruction set quantum computers

    OpenAIRE

    Molmer, Klaus; Sorensen, Anders

    2000-01-01

    Candidates for quantum computing which offer only restricted control, e.g., due to lack of access to individual qubits, are not useful for general purpose quantum computing. We present concrete proposals for the use of systems with such limitations as RISQ - reduced instruction set quantum computers and devices - for simulation of quantum dynamics, for multi-particle entanglement and squeezing of collective spin variables. These tasks are useful in their own right, and they ...

  1. Exponential Gain in Quantum Computing of Quantum Chaos and Localization

    OpenAIRE

    Georgeot, B.; Shepelyansky, D. L.

    2000-01-01

    We present a quantum algorithm which simulates the quantum kicked rotator model exponentially faster than classical algorithms. This shows that important physical problems of quantum chaos, localization and Anderson transition can be modelled efficiently on a quantum computer. We also show that a similar algorithm simulates efficiently classical chaos in certain area-preserving maps.

  2. The Quantum Human Computer (QHC) Hypothesis

    Science.gov (United States)

    Salmani-Nodoushan, Mohammad Ali

    2008-01-01

    This article attempts to suggest the existence of a human computer called Quantum Human Computer (QHC) on the basis of an analogy between human beings and computers. To date, there are two types of computers: Binary and Quantum. The former operates on the basis of binary logic where an object is said to exist in either of the two states of 1 and…

  3. Problems and solutions in quantum computing and quantum information

    CERN Document Server

    Steeb, Willi-Hans

    2012-01-01

    Quantum computing and quantum information are two of the fastest growing and most exciting research fields in physics. Entanglement, teleportation and the possibility of using the non-local behavior of quantum mechanics to factor integers in random polynomial time have also added to this new interest. This book supplies a huge collection of problems in quantum computing and quantum information together with their detailed solutions, which will prove to be invaluable to students as well as researchers in these fields. All the important concepts and topics such as quantum gates and quantum circuits, product Hilbert spaces, entanglement and entanglement measures, deportation, Bell states, Bell inequality, Schmidt decomposition, quantum Fourier transform, magic gate, von Neumann entropy, quantum cryptography, quantum error corrections, number states and Bose operators, coherent states, squeezed states, Gaussian states, POVM measurement, quantum optics networks, beam splitter, phase shifter and Kerr Hamilton opera...

  4. Geometry of discrete quantum computing

    International Nuclear Information System (INIS)

    Conventional quantum computing entails a geometry based on the description of an n-qubit state using 2n infinite precision complex numbers denoting a vector in a Hilbert space. Such numbers are in general uncomputable using any real-world resources, and, if we have the idea of physical law as some kind of computational algorithm of the universe, we would be compelled to alter our descriptions of physics to be consistent with computable numbers. Our purpose here is to examine the geometric implications of using finite fields Fp and finite complexified fields Fp2 (based on primes p congruent to 3 (mod4)) as the basis for computations in a theory of discrete quantum computing, which would therefore become a computable theory. Because the states of a discrete n-qubit system are in principle enumerable, we are able to determine the proportions of entangled and unentangled states. In particular, we extend the Hopf fibration that defines the irreducible state space of conventional continuous n-qubit theories (which is the complex projective space CP2n-1) to an analogous discrete geometry in which the Hopf circle for any n is found to be a discrete set of p + 1 points. The tally of unit-length n-qubit states is given, and reduced via the generalized Hopf fibration to DCP2n-1, the discrete analogue of the complex projective space, which has p2n-1(p-1) ?k=1n-1( p2k+1) irreducible states. Using a measure of entanglement, the purity, we explore the entanglement features of discrete quantum states and find that the n-qubit states based on the complexified field Fp2 have pn(p ? 1)n unentangled states (the product of the tally for a single qubit) with purity 1, and they have pn+1(p ? 1)(p + 1)n?1 maximally entangled states with purity zero. (paper)

  5. A quantum computing primer for operator theorists

    OpenAIRE

    Kribs, David W

    2004-01-01

    This is an exposition of some of the aspects of quantum computation and quantum information that have connections with operator theory. After a brief introduction, we discuss quantum algorithms. We outline basic properties of quantum channels, or equivalently, completely positive trace preserving maps. The main theorems for quantum error detection and correction are presented and we conclude with a description of a particular passive method of quantum error correction.

  6. Brain Neurons as Quantum Computers:

    Science.gov (United States)

    Bershadskii, A.; Dremencov, E.; Bershadskii, J.; Yadid, G.

    The question: whether quantum coherent states can sustain decoherence, heating and dissipation over time scales comparable to the dynamical timescales of brain neurons, has been actively discussed in the last years. A positive answer on this question is crucial, in particular, for consideration of brain neurons as quantum computers. This discussion was mainly based on theoretical arguments. In the present paper nonlinear statistical properties of the Ventral Tegmental Area (VTA) of genetically depressive limbic brain are studied in vivo on the Flinders Sensitive Line of rats (FSL). VTA plays a key role in the generation of pleasure and in the development of psychological drug addiction. We found that the FSL VTA (dopaminergic) neuron signals exhibit multifractal properties for interspike frequencies on the scales where healthy VTA dopaminergic neurons exhibit bursting activity. For high moments the observed multifractal (generalized dimensions) spectrum coincides with the generalized dimensions spectrum calculated for a spectral measure of a quantum system (so-called kicked Harper model, actively used as a model of quantum chaos). This observation can be considered as a first experimental (in vivo) indication in the favor of the quantum (at least partially) nature of brain neurons activity.

  7. Exploiting locality in quantum computation for quantum chemistry

    CERN Document Server

    McClean, Jarrod R; Love, Peter J; Aspuru-Guzik, Alán

    2014-01-01

    Accurate prediction of chemical and material properties from first principles quantum chemistry is a challenging task on traditional computers. Recent developments in quantum computation offer a route towards highly accurate solutions with polynomial cost, however this solution still carries a large overhead. In this perspective, we aim to bring together known results about the locality of physical interactions from quantum chemistry with ideas from quantum computation. We show that the utilization of spatial locality combined with the Bravyi-Kitaev transformation offers an improvement in the scaling of known quantum algorithms for quantum chemistry and provide numerical examples to help illustrate this point. We combine these developments to improve the outlook for the future of quantum chemistry on quantum computers.

  8. Topological Quantum Computation by Manipulating Toric Code

    CERN Document Server

    Kou, Su-Peng

    2008-01-01

    Quantum computers are predicted to utilize quantum states to perform memory and to process tasks far faster than those of conventional classical computers. In this paper we show a new road towards building {fault tolerance} quantum computer by tuning the tunneling of the degenerate quantum states in Z2 topological order, instead of by braiding anyons. Using a designer Hamiltonian - the Wen-Plaquette model as an example, we show how to control the toric code to realize topological quantum computation (TQC). In particular, we give a proposal to the measurement of TQC. In the end the realization of the Wen-Plaquette model in cold atoms is discussed.

  9. Composite pulses in NMR quantum computation

    OpenAIRE

    Jones, Jonathan A.

    2009-01-01

    I describe the use of techniques based on composite rotations to combat systematic errors in quantum logic gates. Although developed and described within the context of Nuclear Magnetic Resonance (NMR) quantum computing these sequences should be applicable to other implementations of quantum computation.

  10. Geometry of Quantum Computation with Qudits

    OpenAIRE

    Luo, Ming-Xing; Chen, Xiu-Bo; Yang, Yi-Xian; Wang, Xiaojun

    2014-01-01

    The circuit complexity of quantum qubit system evolution as a primitive problem in quantum computation has been discussed widely. We investigate this problem in terms of qudit system. Using the Riemannian geometry the optimal quantum circuits are equivalent to the geodetic evolutions in specially curved parametrization of SU(dn). And the quantum circuit complexity is explicitly dependent of controllable approximation error bound.

  11. Suppression of quantum chaos in a quantum computer hardware

    International Nuclear Information System (INIS)

    We present numerical and analytical studies of a quantum computer proposed by the Yamamoto group in Phys. Rev. Lett. 89, 017901 (2002). The stable and quantum chaos regimes in the quantum computer hardware are identified as a function of magnetic field gradient and dipole-dipole couplings between qubits on a square lattice. It is shown that a strong magnetic field gradient leads to suppression of quantum chaos

  12. Suppression of quantum chaos in a quantum computer hardware.

    Science.gov (United States)

    Lages, J; Shepelyansky, D L

    2006-08-01

    We present numerical and analytical studies of a quantum computer proposed by the Yamamoto group in Phys. Rev. Lett. 89, 017901 (2002). The stable and quantum chaos regimes in the quantum computer hardware are identified as a function of magnetic field gradient and dipole-dipole couplings between qubits on a square lattice. It is shown that a strong magnetic field gradient leads to suppression of quantum chaos. PMID:17025526

  13. Toward a superconducting quantum computer: Harnessing macroscopic quantum coherence

    OpenAIRE

    Tsai, Jaw-Shen

    2010-01-01

    Intensive research on the construction of superconducting quantum computers has produced numerous important achievements. The quantum bit (qubit), based on the Josephson junction, is at the heart of this research. This macroscopic system has the ability to control quantum coherence. This article reviews the current state of quantum computing as well as its history, and discusses its future. Although progress has been rapid, the field remains beset with unsolved issues, and there are still man...

  14. Nanophotonic quantum computer based on atomic quantum transistor

    Science.gov (United States)

    Andrianov, S. N.; Moiseev, S. A.

    2015-10-01

    We propose a scheme of a quantum computer based on nanophotonic elements: two buses in the form of nanowaveguide resonators, two nanosized units of multiatom multiqubit quantum memory and a set of nanoprocessors in the form of photonic quantum transistors, each containing a pair of nanowaveguide ring resonators coupled via a quantum dot. The operation modes of nanoprocessor photonic quantum transistors are theoretically studied and the execution of main logical operations by means of them is demonstrated. We also discuss the prospects of the proposed nanophotonic quantum computer for operating in high-speed optical fibre networks.

  15. Quantum machine learning what quantum computing means to data mining

    CERN Document Server

    Wittek, Peter

    2014-01-01

    Quantum Machine Learning bridges the gap between abstract developments in quantum computing and the applied research on machine learning. Paring down the complexity of the disciplines involved, it focuses on providing a synthesis that explains the most important machine learning algorithms in a quantum framework. Theoretical advances in quantum computing are hard to follow for computer scientists, and sometimes even for researchers involved in the field. The lack of a step-by-step guide hampers the broader understanding of this emergent interdisciplinary body of research. Quantum Machine L

  16. Adiabatic quantum computation and quantum annealing theory and practice

    CERN Document Server

    McGeoch, Catherine C

    2014-01-01

    Adiabatic quantum computation (AQC) is an alternative to the better-known gate model of quantum computation. The two models are polynomially equivalent, but otherwise quite dissimilar: one property that distinguishes AQC from the gate model is its analog nature. Quantum annealing (QA) describes a type of heuristic search algorithm that can be implemented to run in the ``native instruction set'''' of an AQC platform. D-Wave Systems Inc. manufactures {quantum annealing processor chips} that exploit quantum properties to realize QA computations in hardware. The chips form the centerpiece of a nov

  17. Quantum computation speedup limits from quantum metrological precision bounds

    OpenAIRE

    Demkowicz-Dobrzanski, Rafal; Markiewicz, Marcin

    2014-01-01

    We propose a scheme for translating metrological precision bounds into lower bounds on query complexity of quantum search algorithms. Within the scheme the link between quadratic performance enhancement in idealized quantum metrological and quantum computing schemes becomes clear. More importantly, we utilize results from the field of quantum metrology on a generic loss of quadratic quantum precision enhancement in presence of decoherence to infer an analogous generic loss o...

  18. Parallel computing and quantum chromodynamics

    CERN Document Server

    Bowler, K C

    1999-01-01

    The study of Quantum Chromodynamics (QCD) remains one of the most challenging topics in elementary particle physics. The lattice formulation of QCD, in which space-time is treated as a four- dimensional hypercubic grid of points, provides the means for a numerical solution from first principles but makes extreme demands upon computational performance. High Performance Computing (HPC) offers us the tantalising prospect of a verification of QCD through the precise reproduction of the known masses of the strongly interacting particles. It is also leading to the development of a phenomenological tool capable of disentangling strong interaction effects from weak interaction effects in the decays of one kind of quark into another, crucial for determining parameters of the standard model of particle physics. The 1980s saw the first attempts to apply parallel architecture computers to lattice QCD. The SIMD and MIMD machines used in these pioneering efforts were the ICL DAP and the Cosmic Cube, respectively. These wer...

  19. Physics and computer science: quantum computation and other approaches

    OpenAIRE

    Venegas-Andraca, Salvador E.

    2011-01-01

    This is a position paper written as an introduction to the special volume on quantum algorithms I edited for the journal Mathematical Structures in Computer Science (Volume 20 - Special Issue 06 (Quantum Algorithms), 2010).

  20. Non-unitary probabilistic quantum computing

    Science.gov (United States)

    Gingrich, Robert M.; Williams, Colin P.

    2004-01-01

    We present a method for designing quantum circuits that perform non-unitary quantum computations on n-qubit states probabilistically, and give analytic expressions for the success probability and fidelity.

  1. Quantum computing with superconductors I: Architectures

    OpenAIRE

    Geller, Michael R.; Pritchett, Emily J.; Sornborger, Andrew T.; Wilhelm, F.K.

    2006-01-01

    Josephson junctions have demonstrated enormous potential as qubits for scalable quantum computing architectures. Here we discuss the current approaches for making multi-qubit circuits and performing quantum information processing with them.

  2. Quantum Computations and Images Recognition

    CERN Document Server

    Vlasov, A Yu

    1997-01-01

    The using of quantum parallelism is often connected with consideration of quantum system with huge dimension of space of states. The n-qubit register can be described by complex vector with 2^n components (it belongs to n'th tensor power of qubit spaces). For example, for algorithm of factorization of numbers by quantum computer n can be about a few hundreds for some realistic applications for cryptography. The applications described further are used some other properties of quantum systems and they do not demand such huge number of states. The term "images recognition" is used here for some broad class of problems. For example, we have a set of some objects V_i and function of "likelihood": F(V,W) < F(V,V) = 1 If we have some "noisy" or "distorted" image W, we can say that recognition of W is V_i, if F(W,V_i) is near 1 for some V_i.

  3. Quantum ballistic evolution in quantum mechanics application to quantum computers

    CERN Document Server

    Benioff, P

    1996-01-01

    Quantum computers are important examples of processes whose evolution can be described in terms of iterations of single step operators or their adjoints. Based on this, Hamiltonian evolution of processes with associated step operators T is investigated here. The main limitation of this paper is to processes which evolve quantum ballistically, i.e. motion restricted to a collection of nonintersecting or distinct paths on an arbitrary basis. The main goal of this paper is proof of a theorem which gives necessary and sufficient conditions that T must satisfy so that there exists a Hamiltonian description of quantum ballistic evolution for the process, namely, that T is a partial isometry and is orthogonality preserving and stable on some basis. Simple examples of quantum ballistic evolution for quantum Turing machines with one and with more than one type of elementary step are discussed. It is seen that for nondeterministic machines the basis set can be quite complex with much entanglement present. It is also pr...

  4. Information and Computation: Classical and Quantum Aspects

    OpenAIRE

    Galindo, A; Martin-Delgado, M. A.

    2001-01-01

    Quantum theory has found a new field of applications in the realm of information and computation during the recent years. This paper reviews how quantum physics allows information coding in classically unexpected and subtle nonlocal ways, as well as information processing with an efficiency largely surpassing that of the present and foreseeable classical computers. Some outstanding aspects of classical and quantum information theory will be addressed here. Quantum teleportat...

  5. Quantum Computing and Zeroes of Zeta Functions

    OpenAIRE

    van Dam, Wim

    2004-01-01

    A possible connection between quantum computing and Zeta functions of finite field equations is described. Inspired by the 'spectral approach' to the Riemann conjecture, the assumption is that the zeroes of such Zeta functions correspond to the eigenvalues of finite dimensional unitary operators of natural quantum mechanical systems. The notion of universal, efficient quantum computation is used to model the desired quantum systems. Using eigenvalue estimation, such quantu...

  6. The Halting Problem for Quantum Computers

    OpenAIRE

    Linden, Noah; Popescu, Sandu

    1998-01-01

    We argue that the halting problem for quantum computers which was first raised by Myers, is by no means solved, as has been claimed recently. We explicitly demonstrate the difficulties that arise in a quantum computer when different branches of the computation halt at different, unknown, times.

  7. Disciplines, models, and computers: the path to computational quantum chemistry.

    Science.gov (United States)

    Lenhard, Johannes

    2014-12-01

    Many disciplines and scientific fields have undergone a computational turn in the past several decades. This paper analyzes this sort of turn by investigating the case of computational quantum chemistry. The main claim is that the transformation from quantum to computational quantum chemistry involved changes in three dimensions. First, on the side of instrumentation, small computers and a networked infrastructure took over the lead from centralized mainframe architecture. Second, a new conception of computational modeling became feasible and assumed a crucial role. And third, the field of computa- tional quantum chemistry became organized in a market-like fashion and this market is much bigger than the number of quantum theory experts. These claims will be substantiated by an investigation of the so-called density functional theory (DFT), the arguably pivotal theory in the turn to computational quantum chemistry around 1990. PMID:25571750

  8. Contextuality supplies the 'magic' for quantum computation.

    Science.gov (United States)

    Howard, Mark; Wallman, Joel; Veitch, Victor; Emerson, Joseph

    2014-06-19

    Quantum computers promise dramatic advantages over their classical counterparts, but the source of the power in quantum computing has remained elusive. Here we prove a remarkable equivalence between the onset of contextuality and the possibility of universal quantum computation via 'magic state' distillation, which is the leading model for experimentally realizing a fault-tolerant quantum computer. This is a conceptually satisfying link, because contextuality, which precludes a simple 'hidden variable' model of quantum mechanics, provides one of the fundamental characterizations of uniquely quantum phenomena. Furthermore, this connection suggests a unifying paradigm for the resources of quantum information: the non-locality of quantum theory is a particular kind of contextuality, and non-locality is already known to be a critical resource for achieving advantages with quantum communication. In addition to clarifying these fundamental issues, this work advances the resource framework for quantum computation, which has a number of practical applications, such as characterizing the efficiency and trade-offs between distinct theoretical and experimental schemes for achieving robust quantum computation, and putting bounds on the overhead cost for the classical simulation of quantum algorithms. PMID:24919152

  9. From Monte Carlo to Quantum Computation

    CERN Document Server

    Heinrich, S

    2001-01-01

    Quantum computing was so far mainly concerned with discrete problems. Recently, E. Novak and the author studied quantum algorithms for high dimensional integration and dealt with the question, which advantages quantum computing can bring over classical deterministic or randomized methods for this type of problem. In this paper we give a short introduction to the basic ideas of quantum computing and survey recent results on high dimensional integration. We discuss connections to the Monte Carlo methology and compare the optimal error rates of quantum algorithms to those of classical deterministic and randomized algorithms.

  10. The Physical Implementation of Quantum Computation

    OpenAIRE

    DiVincenzo, David P.; IBM

    2000-01-01

    After a brief introduction to the principles and promise of quantum information processing, the requirements for the physical implementation of quantum computation are discussed. These five requirements, plus two relating to the communication of quantum information, are extensively explored and related to the many schemes in atomic physics, quantum optics, nuclear and electron magnetic resonance spectroscopy, superconducting electronics, and quantum-dot physics, for achievin...

  11. An introduction to reliable quantum computation

    CERN Document Server

    Aliferis, Panos

    2011-01-01

    This is an introduction to software methods of quantum fault tolerance. Broadly speaking, these methods describe strategies for using the noisy hardware components of a quantum computer to perform computations while continually monitoring and actively correcting the hardware faults. We discuss parallels and differences with similar methods for ordinary digital computation, we discuss some of the noise models used in designing and analyzing noisy quantum circuits, and we sketch the logic of some of the central results in this area of research.

  12. Mini-maximizing two qubit quantum computations

    Science.gov (United States)

    Khan, Faisal Shah; Phoenix, Simon J. D.

    2013-12-01

    Two qubit quantum computations are viewed as two player, strictly competitive games and a game-theoretic measure of optimality of these computations is developed. To this end, the geometry of Hilbert space of quantum computations is used to establish the equivalence of game-theoretic solution concepts of Nash equilibrium and mini-max outcomes in games of this type, and quantum mechanisms are designed for realizing these mini-max outcomes.

  13. Quantum fields on the computer

    CERN Document Server

    1992-01-01

    This book provides an overview of recent progress in computer simulations of nonperturbative phenomena in quantum field theory, particularly in the context of the lattice approach. It is a collection of extensive self-contained reviews of various subtopics, including algorithms, spectroscopy, finite temperature physics, Yukawa and chiral theories, bounds on the Higgs meson mass, the renormalization group, and weak decays of hadrons.Physicists with some knowledge of lattice gauge ideas will find this book a useful and interesting source of information on the recent developments in the field.

  14. Quantum Computing in Solid State Systems

    CERN Document Server

    Ruggiero, B; Granata, C

    2006-01-01

    The aim of Quantum Computation in Solid State Systems is to report on recent theoretical and experimental results on the macroscopic quantum coherence of mesoscopic systems, as well as on solid state realization of qubits and quantum gates. Particular attention has been given to coherence effects in Josephson devices. Other solid state systems, including quantum dots, optical, ion, and spin devices which exhibit macroscopic quantum coherence are also discussed. Quantum Computation in Solid State Systems discusses experimental implementation of quantum computing and information processing devices, and in particular observations of quantum behavior in several solid state systems. On the theoretical side, the complementary expertise of the contributors provides models of the various structures in connection with the problem of minimizing decoherence.

  15. Quantum Computational Logics and Possible Applications

    Science.gov (United States)

    Chiara, Maria Luisa Dalla; Giuntini, Roberto; Leporini, Roberto; di Francia, Giuliano Toraldo

    2008-01-01

    In quantum computational logics meanings of formulas are identified with quantum information quantities: systems of qubits or, more generally, mixtures of systems of qubits. We consider two kinds of quantum computational semantics: (1) a compositional semantics, where the meaning of a compound formula is determined by the meanings of its parts; (2) a holistic semantics, which makes essential use of the characteristic “holistic” features of the quantum-theoretic formalism. The compositional and the holistic semantics turn out to characterize the same logic. In this framework, one can introduce the notion of quantum-classical truth table, which corresponds to the most natural way for a quantum computer to calculate classical tautologies. Quantum computational logics can be applied to investigate different kinds of semantic phenomena where holistic, contextual and gestaltic patterns play an essential role (from natural languages to musical compositions).

  16. Active stabilisation, quantum computation and quantum state synthesis

    CERN Document Server

    Steane, A M

    1997-01-01

    Active stabilisation of a quantum system is the active suppression of noise (such as decoherence) in the system, without disrupting its unitary evolution. Quantum error correction suggests the possibility of achieving this, but only if the recovery network can suppress more noise than it introduces. A general method of constructing such networks is proposed, which gives a substantial improvement over previous fault tolerant designs. The construction permits quantum error correction to be understood as essentially quantum state synthesis. An approximate analysis implies that algorithms involving very many computational steps on a quantum computer can thus be made possible.

  17. Computing quantum discord is NP-complete

    International Nuclear Information System (INIS)

    We study the computational complexity of quantum discord (a measure of quantum correlation beyond entanglement), and prove that computing quantum discord is NP-complete. Therefore, quantum discord is computationally intractable: the running time of any algorithm for computing quantum discord is believed to grow exponentially with the dimension of the Hilbert space so that computing quantum discord in a quantum system of moderate size is not possible in practice. As by-products, some entanglement measures (namely entanglement cost, entanglement of formation, relative entropy of entanglement, squashed entanglement, classical squashed entanglement, conditional entanglement of mutual information, and broadcast regularization of mutual information) and constrained Holevo capacity are NP-hard/NP-complete to compute. These complexity-theoretic results are directly applicable in common randomness distillation, quantum state merging, entanglement distillation, superdense coding, and quantum teleportation; they may offer significant insights into quantum information processing. Moreover, we prove the NP-completeness of two typical problems: linear optimization over classical states and detecting classical states in a convex set, providing evidence that working with classical states is generically computationally intractable. (paper)

  18. The Heisenberg representation of quantum computers

    Energy Technology Data Exchange (ETDEWEB)

    Gottesman, D.

    1998-06-24

    Since Shor`s discovery of an algorithm to factor numbers on a quantum computer in polynomial time, quantum computation has become a subject of immense interest. Unfortunately, one of the key features of quantum computers--the difficulty of describing them on classical computers--also makes it difficult to describe and understand precisely what can be done with them. A formalism describing the evolution of operators rather than states has proven extremely fruitful in understanding an important class of quantum operations. States used in error correction and certain communication protocols can be described by their stabilizer, a group of tensor products of Pauli matrices. Even this simple group structure is sufficient to allow a rich range of quantum effects, although it falls short of the full power of quantum computation.

  19. The Heisenberg Representation of Quantum Computers

    CERN Document Server

    Gottesman, D

    1998-01-01

    Since Shor's discovery of an algorithm to factor numbers on a quantum computer in polynomial time, quantum computation has become a subject of immense interest. Unfortunately, one of the key features of quantum computers - the difficulty of describing them on classical computers - also makes it difficult to describe and understand precisely what can be done with them. A formalism describing the evolution of operators rather than states has proven extremely fruitful in understanding an important class of quantum operations. States used in error correction and certain communication protocols can be described by their stabilizer, a group of tensor products of Pauli matrices. Even this simple group structure is sufficient to allow a rich range of quantum effects, although it falls short of the full power of quantum computation.

  20. A Quantum to Classical Phase Transition in Noisy Quantum Computers

    CERN Document Server

    Aharonov, D

    1999-01-01

    The fundamental problem of the transition from quantum to classical physics is usually explained by decoherence, and viewed as a gradual process. The study of entanglement, or quantum correlations, in noisy quantum computers implies that in some cases the transition from quantum to classical is actually a phase transition. We define the notion of entanglement length in $d$-dimensional noisy quantum computers, and show that a phase transition in entanglement occurs at a critical noise rate, where the entanglement length transforms from infinite to finite. Above the critical noise rate, macroscopic classical behavior is expected, whereas below the critical noise rate, subsystems which are macroscopically distant one from another can be entangled. The macroscopic classical behavior in the super-critical phase is shown to hold not only for quantum computers, but for any quantum system composed of macroscopically many finite state particles, with local interactions and local decoherence, subjected to some addition...

  1. Quantum computation speedup limits from quantum metrological precision bounds

    Science.gov (United States)

    Demkowicz-Dobrza?ski, Rafa?; Markiewicz, Marcin

    2015-06-01

    We propose a scheme for translating metrological precision bounds into lower bounds on query complexity of quantum search algorithms. Within the scheme the link between quadratic performance enhancement in idealized quantum metrological and quantum computing schemes becomes clear. More importantly, we utilize results from the field of quantum metrology on a generic loss of quadratic quantum precision enhancement in the presence of decoherence to infer an analogous generic loss of quadratic speedup in oracle based quantum computing. While most of our reasoning is rigorous, at one of the final steps, we need to make use of an unproven technical conjecture. We hope that we will be able to amend this deficiency in the near future, but we are convinced that even without the conjecture proven our results provide a deep insight into the relationship between quantum algorithms and quantum metrology protocols.

  2. The one-way quantum computer - a non-network model of quantum computation

    CERN Document Server

    Raussendorf, R; Briegel, H J; Raussendorf, Robert; Browne, Daniel E.; Briegel, Hans J.

    2001-01-01

    A one-way quantum computer works by only performing a sequence of one-qubit measurements on a particular entangled multi-qubit state, the cluster state. No non-local operations are required in the process of computation. Any quantum logic network can be simulated on the one-way quantum computer. On the other hand, the network model of quantum computation cannot explain all ways of processing quantum information possible with the one-way quantum computer. In this paper, two examples of the non-network character of the one-way quantum computer are given. First, circuits in the Clifford group can be performed in a single time step. Second, the realisation of a particular circuit --the bit-reversal gate-- on the one-way quantum computer has no network interpretation. (Submitted to J. Mod. Opt, Gdansk ESF QIT conference issue.)

  3. Mathematical Foundations of Holonomic Quantum Computer

    OpenAIRE

    Fujii, Kazuyuki

    2000-01-01

    We make a brief review of (optical) Holonomic Quantum Computer (or Computation) proposed by Zanardi and Rasetti (quant-ph/9904011) and Pachos and Chountasis (quant-ph/9912093), and give a mathematical reinforcement to their works.

  4. An introduction to measurement based quantum computation

    CERN Document Server

    Jozsa, R

    2005-01-01

    In the formalism of measurement based quantum computation we start with a given fixed entangled state of many qubits and perform computation by applying a sequence of measurements to designated qubits in designated bases. The choice of basis for later measurements may depend on earlier measurement outcomes and the final result of the computation is determined from the classical data of all the measurement outcomes. This is in contrast to the more familiar gate array model in which computational steps are unitary operations, developing a large entangled state prior to some final measurements for the output. Two principal schemes of measurement based computation are teleportation quantum computation (TQC) and the so-called cluster model or one-way quantum computer (1WQC). We will describe these schemes and show how they are able to perform universal quantum computation. We will outline various possible relationships between the models which serve to clarify their workings. We will also discuss possible novel co...

  5. Models of continuous-variable quantum computing

    International Nuclear Information System (INIS)

    We discuss strictly efficient models for measurement-based quantum computing using physical continuous variables, such as field modes of light. Such measurement-based quantum computing (MBQC) provides a promising paradigm for quantum computation as it does not require performing unitary gates during the computation, but rather appropriate readout. Here, we introduce novel schemes for which the resource state can be reasonably and efficiently prepared, and which notably do not require having infinite squeezing or mean energy available. What is more, error correction techniques are implementable, as the logical information is stored in finite-dimensional objects grasping correlations of the quantum states. Using the ideas of computational tensor networks we discuss how to sequentially prepare suitable physical resource states with cavity QED or with non-linear optics and how to efficiently implement a computational universal set of quantum operations with feasible optical measurements like homodyne detection and photon counting

  6. Schrodinger cat animated on a quantum computer

    CERN Document Server

    Chepelianskii, A D

    2002-01-01

    We present a quantum algorithm which allows to simulate chaos-assisted tunneling in deep semiclassical regime on existing quantum computers. This opens new possibilities for investigation of macroscopic quantum tunneling and realization of semiclassical Schr\\"odinger cat oscillations. Our numerical studies determine the decoherence rate induced by noisy gates for these oscillations and propose a suitable parameter regime for their experimental implementation.

  7. Communication Links for Distributed Quantum Computation

    CERN Document Server

    Van Meter, Rodney; Munro, W J

    2007-01-01

    Distributed quantum computation requires quantum operations that act over a distance on error-correction encoded states of logical qubits, such as the transfer of qubits via teleportation. We evaluate the performance of several quantum error correction codes, and find that teleportation failure rates of one percent or more are tolerable when two levels of the [[23,1,7

  8. Quantum Computer Games: Schrodinger Cat and Hounds

    Science.gov (United States)

    Gordon, Michal; Gordon, Goren

    2012-01-01

    The quantum computer game "Schrodinger cat and hounds" is the quantum extension of the well-known classical game fox and hounds. Its main objective is to teach the unique concepts of quantum mechanics in a fun way. "Schrodinger cat and hounds" demonstrates the effects of superposition, destructive and constructive interference, measurements and…

  9. Quantum Teleportation is a Universal Computational Primitive

    CERN Document Server

    Gottesman, D; Gottesman, Daniel; Chuang, Isaac L.

    1999-01-01

    We present a method to create a variety of interesting gates by teleporting quantum bits through special entangled states. This allows, for instance, the construction of a quantum computer based on just single qubit operations, Bell measurements, and GHZ states. We also present straightforward constructions of a wide variety of fault-tolerant quantum gates.

  10. NMR quantum computation with indirectly coupled gates

    CERN Document Server

    Collins, D; Holton, W C; Sierzputowska-Gracz, H; Stejskal, E O; Collins, David

    1999-01-01

    An NMR realization of a two-qubit quantum gate which processes quantum information indirectly via couplings to a spectator qubit is presented in the context of the Deutsch-Jozsa algorithm. This enables a successful comprehensive NMR implementation of the Deutsch-Jozsa algorithm for functions with three argument bits and demonstrates a technique essential for multi-qubit quantum computation.

  11. Nonlinear optics quantum computing with circuit QED.

    Science.gov (United States)

    Adhikari, Prabin; Hafezi, Mohammad; Taylor, J M

    2013-02-01

    One approach to quantum information processing is to use photons as quantum bits and rely on linear optical elements for most operations. However, some optical nonlinearity is necessary to enable universal quantum computing. Here, we suggest a circuit-QED approach to nonlinear optics quantum computing in the microwave regime, including a deterministic two-photon phase gate. Our specific example uses a hybrid quantum system comprising a LC resonator coupled to a superconducting flux qubit to implement a nonlinear coupling. Compared to the self-Kerr nonlinearity, we find that our approach has improved tolerance to noise in the qubit while maintaining fast operation. PMID:23432228

  12. Quantum computer of wire circuit architecture

    CERN Document Server

    Moiseev, S A; Andrianov, S N

    2010-01-01

    First solid state quantum computer was built using transmons (cooper pair boxes). The operation of the computer is limited because of using a number of the rigit cooper boxes working with fixed frequency at temperatures of superconducting material. Here, we propose a novel architecture of quantum computer based on a flexible wire circuit of many coupled quantum nodes containing controlled atomic (molecular) ensembles. We demonstrate wide opportunities of the proposed computer. Firstly, we reveal a perfect storage of external photon qubits to multi-mode quantum memory node and demonstrate a reversible exchange of the qubits between any arbitrary nodes. We found optimal parameters of atoms in the circuit and self quantum modes for quantum processing. The predicted perfect storage has been observed experimentally for microwave radiation on the lithium phthalocyaninate molecule ensemble. Then also, for the first time we show a realization of the efficient basic two-qubit gate with direct coupling of two arbitrary...

  13. Mathematical Aspects of Quantum Computing 2007

    Science.gov (United States)

    Nakahara, Mikio; Rahimi, Robabeh; SaiToh, Akira

    2008-04-01

    Quantum computing: an overview / M. Nakahara -- Braid group and topological quantum computing / T. Ootsuka, K. Sakuma -- An introduction to entanglement theory / D. J. H. Markham -- Holonomic quantum computing and its optimization / S. Tanimura -- Playing games in quantum mechanical settings: features of quantum games / S. K. Özdemir, J. Shimamura, N. Imoto -- Quantum error-correcting codes / M. Hagiwara -- Poster summaries. Controled teleportation of an arbitrary unknown two-qubit entangled state / V. Ebrahimi, R. Rahimi, M. Nakahara. Notes on the Dür-Cirac classification / Y. Ota, M. Yoshida, I. Ohba. Bang-bang control of entanglement in Spin-Bus-Boson model / R. Rahimi, A. SaiToh, M. Nakahara. Numerical computation of time-dependent multipartite nonclassical correlation / A. SaiToh ... [et al.]. On classical no-cloning theorem under Liouville dynamics and distances / T. Yamano, O. Iguchi.

  14. The potential of the quantum computer

    CERN Multimedia

    2006-01-01

    The Physics Section of the University of Geneva is continuing its series of lectures, open to the general public, on the most recent developments in the field of physics. The next lecture, given by Professor Michel Devoret of Yale University in the United States, will be on the potential of the quantum computer. The quantum computer is, as yet, a hypothetical machine which would operate on the basic principles of quantum mechanics. Compared to standard computers, it represents a significant gain in computing power for certain complex calculations. Quantum operations can simultaneously explore a very large number of possibilities. The correction of quantum errors, which until recently had been deemed impossible, has now become a well-established technique. Several prototypes for, as yet, very simple quantum processors have been developed. The lecture will begin with a demonstration in the auditorium of the detection of cosmic rays and, in collaboration with Professor E. Ellberger of the Conservatoire de M...

  15. Quantum computing in a piece of glass

    CERN Document Server

    Miller, Warner A; Tison, Christopher; Alsing, Paul M; McDonald, Jonathan R

    2011-01-01

    Quantum gates and simple quantum algorithms can be designed utilizing the diffraction phenomena of a photon within a multiplexed holographic element. The quantum eigenstates we use are the photon's linear momentum (LM) as measured by the number of waves of tilt across the aperture. Two properties of quantum computing within the circuit model make this approach attractive. First, any conditional measurement can be commuted in time with any unitary quantum gate - the timeless nature of quantum computing. Second, photon entanglement can be encoded as a superposition state of a single photon in a higher-dimensional state space afforded by LM. Our theoretical and numerical results indicate that OptiGrate's photo-thermal refractive (PTR) glass is an enabling technology. We will review our previous design of a quantum projection operator and give credence to this approach on a representative quantum gate grounded on coupled-mode theory and numerical simulations, all with parameters consistent with PTR glass. We disc...

  16. An Axiomatic System Suggested by Quantum Computation

    OpenAIRE

    LEPORINI, ROBERTO; BERTINI, CESARINO

    2009-01-01

    The theory of logical gates in quantum computation has suggested new forms of quantum logic, called quantum computational logics. The basic semantic idea is the following: the meaning of a sentence is identified with a quregister (a system of qubits in a pure state) or, more generally, with a mixture of quregisters (called qumix). Following an approach proposed by Domenech and Freytes, we apply residuated structures associated with fuzzy logic to develop certain aspects of information process...

  17. Prospects for Spin-Based Quantum Computing

    OpenAIRE

    Kloeffel, Christoph; Loss, Daniel

    2012-01-01

    Experimental and theoretical progress toward quantum computation with spins in quantum dots (QDs) is reviewed, with particular focus on QDs formed in GaAs heterostructures, on nanowire-based QDs, and on self-assembled QDs. We report on a remarkable evolution of the field where decoherence, one of the main challenges for realizing quantum computers, no longer seems to be the stumbling block it had originally been considered. General concepts, relevant quantities, and basic re...

  18. Decoherence, Control, and Symmetry in Quantum Computers

    OpenAIRE

    Bacon, D

    2003-01-01

    In this thesis we describe methods for avoiding the detrimental effects of decoherence while at the same time still allowing for computation of the quantum information. The philosophy of the method discussed in the first part of this thesis is to use a symmetry of the decoherence mechanism to find robust encodings of the quantum information. Stability, control, and methods for using decoherence-free information in a quantum computer are presented with a specific emphasis on ...

  19. Quantum Computation explained to my Mother

    OpenAIRE

    Arrighi, Pablo

    2003-01-01

    There are many falsely intuitive introductions to quantum theory and quantum computation in a handwave. There are also numerous documents which teach those subjects in a mathematically sound manner. To my knowledge this paper is the shortest of the latter category. The aim is to deliver a short yet rigorous and self-contained introduction to Quantum Computation, whilst assuming the reader has no prior knowledge of anything but the fundamental operations on real numbers. Succ...

  20. Quantum Computing and the Jones Polynomial

    OpenAIRE

    Kauffman, Louis H

    2001-01-01

    This paper is an exploration of relationships between the Jones polynomial and quantum computing. We discuss the structure of the Jones polynomial in relation to representations of the Temperley Lieb algebra, and give an example of a unitary representation of the braid group. We discuss the evaluation of the polynomial as a generalized quantum amplitude and show how the braiding part of the evaluation can be construed as a quantum computation when the braiding representation...

  1. Quantum Computing and the Limits of the Efficiently Computable

    CERN Document Server

    CERN. Geneva

    2015-01-01

    I'll discuss how computational complexity---the study of what can and can't be feasibly computed---has been interacting with physics in interesting and unexpected ways. I'll first give a crash course about computer science's P vs. NP problem, as well as about the capabilities and limits of quantum computers. I'll then touch on speculative models of computation that would go even beyond quantum computers, using (for example) hypothetical nonlinearities in the Schrodinger equation. Finally, I'll discuss BosonSampling ---a proposal for a simple form of quantum computing, which nevertheless seems intractable to simulate using a classical computer---as well as the role of computational complexity in the black hole information puzzle.

  2. Monte Carlo Simulation of Quantum Computation

    CERN Document Server

    Cerf, N J

    1998-01-01

    The many-body dynamics of a quantum computer can be reduced to the time evolution of non-interacting quantum bits in auxiliary fields by use of the Hubbard-Stratonovich representation of two-bit quantum gates in terms of one-bit gates. This makes it possible to perform the stochastic simulation of a quantum algorithm, based on the Monte Carlo evaluation of an integral of dimension polynomial in the number of quantum bits. As an example, the simulation of the quantum circuit for the Fast Fourier Transform is discussed.

  3. Quantum Computer Condition: Stability, Classical Computation and Norms

    CERN Document Server

    Gilbert, G; Thayer, F J; Weinstein, Yu S; Gilbert, Gerald; Hamrick, Michael; Weinstein, Yaakov S.

    2005-01-01

    The Quantum Computer Condition (QCC) provides a rigorous and completely general framework for carrying out analyses of questions pertaining to fault-tolerance in quantum computers. In this paper we apply the QCC to the problem of fluctuations and systematic errors in the values of characteristic parameters in realistic systems. We show that fault-tolerant quantum computation is possible despite variations in these parameters. We also use the QCC to explicitly show that reliable classical computation can be carried out using as input the results of fault-tolerant, but imperfect, quantum computation. Finally, we consider the advantages and disadvantages of the superoperator and diamond norms in connection with application of the QCC to various quantum information-theoretic problems.

  4. Geometry of Quantum Computation with Qudits

    Science.gov (United States)

    Luo, Ming-Xing; Chen, Xiu-Bo; Yang, Yi-Xian; Wang, Xiaojun

    2014-01-01

    The circuit complexity of quantum qubit system evolution as a primitive problem in quantum computation has been discussed widely. We investigate this problem in terms of qudit system. Using the Riemannian geometry the optimal quantum circuits are equivalent to the geodetic evolutions in specially curved parametrization of SU(dn). And the quantum circuit complexity is explicitly dependent of controllable approximation error bound. PMID:24509710

  5. Quantum Neural Computation for Option Price Modelling

    OpenAIRE

    Ivancevic, Vladimir G.

    2009-01-01

    We propose a new cognitive framework for option price modelling, using quantum neural computation formalism. Briefly, when we apply a classical nonlinear neural-network learning to a linear quantum Schr\\"odinger equation, as a result we get a nonlinear Schr\\"odinger equation (NLS), performing as a quantum stochastic filter. In this paper, we present a bidirectional quantum associative memory model for the Black--Scholes--like option price evolution, consisting of a pair of c...

  6. Dynamical description of quantum computing generic nonlocality of quantum noise

    CERN Document Server

    Alicki, R; Horodecki, P; Horodecki, R; Alicki, Robert; Horodecki, Michal; Horodecki, Pawel; Horodecki, Ryszard

    2001-01-01

    We develop dynamical non-Markovian description of quantum computing in weak coupling limit, in lowest order approximation. We show that long range memory of quantum reservoir produces strong interrelation between structure of noise and quantum algorithm, implying nonlocal attacks of noise. We then argue that the quantum error correction method fails to protect quantum computation against electromagnetic or phonon vacuum which exhibit $1/t^4$ memory. This shows that the implicit assumption of quantum error correction theory -- independence of noise and self-dynamics -- fails in long time regimes. We also use our approach to present {\\it pure} decoherence and decoherence accompanied by dissipation in terms of spectral density of reservoir. The so-called {\\it dynamical decoupling} method is discussed in this context. Finally, we propose {\\it minimal decoherence model}, in which the only source of decoherence is vacuum. We optimize fidelity of quantum information processing under the trade-off between speed of ga...

  7. No quantum advantage for nonlocal computation

    CERN Document Server

    Linden, N; Short, A J; Winter, A; Linden, Noah; Popescu, Sandu; Short, Anthony J.; Winter, Andreas

    2006-01-01

    We investigate the problem of "nonlocal" computation, in which separated parties must compute a function with nonlocally encoded inputs and output, such that each party individually learns nothing, yet together they compute the correct function output. We show that the best that can be done classically is a trivial linear approximation. Surprisingly, we also show that quantum entanglement provides no advantage over the classical case. On the other hand, generalized (i.e. super-quantum) nonlocal correlations allow perfect nonlocal computation. This gives new insights into the nature of quantum nonlocality and its relationship to generalised nonlocal correlations.

  8. Secure Multi-party Quantum Computing

    CERN Document Server

    Crepeau, C; Smith, A; Crepeau, Claude; Gottesman, Daniel; Smith, Adam

    2002-01-01

    Secure multi-party computing, also called "secure function evaluation", has been extensively studied in classical cryptography. We consider the extension of this task to computation with quantum inputs and circuits. Our protocols are information-theoretically secure, i.e. no assumptions are made on the computational power of the adversary. For the weaker task of verifiable quantum secret sharing, we give a protocol which tolerates any t < n/4 cheating parties (out of n). This is shown to be optimal. We use this new tool to show how to perform any multi-party quantum computation as long as the number of dishonest players is less than n/6.

  9. Quantum computing with incoherent resources and quantum jumps

    CERN Document Server

    Santos, Marcelo F; Chaves, Rafael; Carvalho, Andre R R

    2011-01-01

    Spontaneous emission and the inelastic scattering of photons are two natural processes usually associated with decoherence and the reduction in the capacity to process quantum information. Here we show that when suitably detected, these photons are sufficient to build all the fundamental blocks needed to perform quantum computation in the emitting qubits while protecting them from deleterious dissipative effects. We exemplify by showing how to teleport an unknown quantum state and how to efficiently prepare graph states for the implementation of measurement-based quantum computation.

  10. The scalable quantum computation based on quantum dot systems

    CERN Document Server

    Zhang, Jian-Qi; Feng, Xun-Li; Zhang, Zhi-Ming

    2011-01-01

    We propose a scheme for realizing the scalable quantum computation based on the system of quantum dots trapped in a single-mode waveguide. In this system, the quantum dots simultaneously interact with a large detuned waveguide and classical light fields. During the process, neither the waveguide mode nor the quantum dots are excited, so the decoherence can be suppressed, while the system can acquire phases conditional upon the states of any two quantum dots. Therefore, it can be used to realize graph states, one qubit controlling multi-qubit phase $\\pi $ gate, and cluster states.

  11. KLM quantum computation with bosonic atoms

    CERN Document Server

    Popescu, S

    2006-01-01

    A Knill-Laflamme-Milburn (KLM) type quantum computation with bosonic neutral atoms or bosonic ions is suggested. Crucially, as opposite to other quantum computation schemes involving atoms (ions), no controlled interactions between atoms (ions) involving their internal levels are required. Versus photonic KLM computation this scheme has the advantage that single atom (ion) sources are more natural than single photon sources, and single atom (ion) detectors are far more efficient than single photon ones.

  12. Non-Mechanism in Quantum Oracle Computing

    OpenAIRE

    Castagnoli, Giuseppe

    1999-01-01

    A typical oracle problem is finding which software program is installed on a computer, by running the computer and testing its input-output behaviour. The program is randomly chosen from a set of programs known to the problem solver. As well known, some oracle problems are solved more efficiently by using quantum algorithms; this naturally implies changing the computer to quantum, while the choice of the software program remains sharp. In order to highlight the non-mechanist...

  13. Reversible Mapping for Tree Structured Quantum Computation

    CERN Document Server

    Burkot, W

    1997-01-01

    A hierarchical, reversible mapping between levels of tree structured computation, applicable for structuring the Quantum Computation algorithm for NP-complete problem is presented. It is proven that confining the state of a quantum computer to a subspace of the available Hilbert space, where states are consistent with the problem constraints, can be done in polynomial time. The proposed mapping, together with the method of state reduction can be potentially used for solving NP-complete problems in polynomial time.

  14. The case for biological quantum computer elements

    Science.gov (United States)

    Baer, Wolfgang; Pizzi, Rita

    2009-05-01

    An extension to vonNeumann's analysis of quantum theory suggests self-measurement is a fundamental process of Nature. By mapping the quantum computer to the brain architecture we will argue that the cognitive experience results from a measurement of a quantum memory maintained by biological entities. The insight provided by this mapping suggests quantum effects are not restricted to small atomic and nuclear phenomena but are an integral part of our own cognitive experience and further that the architecture of a quantum computer system parallels that of a conscious brain. We will then review the suggestions for biological quantum elements in basic neural structures and address the de-coherence objection by arguing for a self- measurement event model of Nature. We will argue that to first order approximation the universe is composed of isolated self-measurement events which guaranties coherence. Controlled de-coherence is treated as the input/output interactions between quantum elements of a quantum computer and the quantum memory maintained by biological entities cognizant of the quantum calculation results. Lastly we will present stem-cell based neuron experiments conducted by one of us with the aim of demonstrating the occurrence of quantum effects in living neural networks and discuss future research projects intended to reach this objective.

  15. Universal quantum computation with weakly integral anyons

    Science.gov (United States)

    Cui, Shawn X.; Hong, Seung-Moon; Wang, Zhenghan

    2015-08-01

    Harnessing non-abelian statistics of anyons to perform quantum computational tasks is getting closer to reality. While the existence of universal anyons by braiding alone such as the Fibonacci anyon is theoretically a possibility, accessible anyons with current technology all belong to a class that is called weakly integral—anyons whose squared quantum dimensions are integers. We analyze the computational power of the first non-abelian anyon system with only integral quantum dimensions—, the quantum double of . Since all anyons in have finite images of braid group representations, they cannot be universal for quantum computation by braiding alone. Based on our knowledge of the images of the braid group representations, we set up three qutrit computational models. Supplementing braidings with some measurements and ancillary states, we find a universal gate set for each model.

  16. Resilient Quantum Computation Error Models and Thresholds

    CERN Document Server

    Knill, E H; Zurek, W H; Knill, Emanuel; Laflamme, Raymond; Zurek, Wojciech H.

    1997-01-01

    Recent research has demonstrated that quantum computers can solve certain types of problems substantially faster than the known classical algorithms. These problems include factoring integers and certain physics simulations. Practical quantum computation requires overcoming the problems of environmental noise and operational errors, problems which appear to be much more severe than in classical computation due to the inherent fragility of quantum superpositions involving many degrees of freedom. Here we show that arbitrarily accurate quantum computations are possible provided that the error per operation is below a threshold value. The result is obtained by combining quantum error-correction, fault tolerant state recovery, fault tolerant encoding of operations and concatenation. It holds under physically realistic assumptions on the errors.

  17. The experimental research on the principle of semi-conductor bridge (SCB) detonator

    International Nuclear Information System (INIS)

    When the electrical exploding semi-conductor bridge (SCB) is used to initiate the HE, the safety properties are better and required energies are smaller than the HE initiated by electrical exploding conductor bridge because the special electrical performances of semi-conductor materials. The HE initiated by SCB is researched by changing the parameters of the capacitor discharge unit (CDU) and the density of the original charge. The explosive initiated is re-crystallized PETN filled in a copper shell with diameter 6.2 mm and it's wall thickness 0.3 mm. The filled explosive's size is ?5.6 mm x 14 mm and it's density is ? = (1.0 - 1.3)g/cm3. The detonator's total size is ?6.2 mm x 20 mm. The experimental results show that it is possibly a faster DDT (deflagration to detonation transition) process that explosives initiated by SCB and the energy required for the re-crystallized PETN with density 1.0 g/cm3 reliably initiated by this SCB detonator is about 290 mJ. The function time (the time from the start of the capacitor discharge to steady detonation formation in the PETN) of this detonator is t ? 3.27?s and the distance run to detonation of the initiated explosive is ??6.31 mm. This new SCB detonator can reliably initiate the inert PETN booster (PETN/wax = 95/5) with density 1.64 g/cm3

  18. Effective pure states for bulk quantum computation

    Energy Technology Data Exchange (ETDEWEB)

    Knill, E.; Chuang, I.; Laflamme, R.

    1997-11-01

    In bulk quantum computation one can manipulate a large number of indistinguishable quantum computers by parallel unitary operations and measure expectation values of certain observables with limited sensitivity. The initial state of each computer in the ensemble is known but not pure. Methods for obtaining effective pure input states by a series of manipulations have been described by Gershenfeld and Chuang (logical labeling) and Corey et al. (spatial averaging) for the case of quantum computation with nuclear magnetic resonance. We give a different technique called temporal averaging. This method is based on classical randomization, requires no ancilla qubits and can be implemented in nuclear magnetic resonance without using gradient fields. We introduce several temporal averaging algorithms suitable for both high temperature and low temperature bulk quantum computing and analyze the signal to noise behavior of each.

  19. Effective Pure States for Bulk Quantum Computation

    CERN Document Server

    Knill, E H; Laflamme, R; Knill, Emanuel; Chuang, Isaac; Laflamme, Raymond

    1998-01-01

    In bulk quantum computation one can manipulate a large number of indistinguishable quantum computers by parallel unitary operations and measure expectation values of certain observables with limited sensitivity. The initial state of each computer in the ensemble is known but not pure. Methods for obtaining effective pure input states by a series of manipulations have been described by Gershenfeld and Chuang (logical labeling) and Cory et al. (spatial averaging) for the case of quantum computation with nuclear magnetic resonance. We give a different technique called temporal averaging. This method is based on classical randomization, requires no ancilla qubits and can be implemented in nuclear magnetic resonance without using gradient fields. We introduce several temporal averaging algorithms suitable for both high temperature and low temperature bulk quantum computing and analyze the signal to noise behavior of each.

  20. Video Encryption and Decryption on Quantum Computers

    Science.gov (United States)

    Yan, Fei; Iliyasu, Abdullah M.; Venegas-Andraca, Salvador E.; Yang, Huamin

    2015-08-01

    A method for video encryption and decryption on quantum computers is proposed based on color information transformations on each frame encoding the content of the encoding the content of the video. The proposed method provides a flexible operation to encrypt quantum video by means of the quantum measurement in order to enhance the security of the video. To validate the proposed approach, a tetris tile-matching puzzle game video is utilized in the experimental simulations. The results obtained suggest that the proposed method enhances the security and speed of quantum video encryption and decryption, both properties required for secure transmission and sharing of video content in quantum communication.

  1. Measurement Based Quantum Computation on Fractal Lattices

    Directory of Open Access Journals (Sweden)

    Michal Hajdušek

    2010-06-01

    Full Text Available In this article we extend on work which establishes an analology between one-way quantum computation and thermodynamics to see how the former can be performed on fractal lattices. We find fractals lattices of arbitrary dimension greater than one which do all act as good resources for one-way quantum computation, and sets of fractal lattices with dimension greater than one all of which do not. The difference is put down to other topological factors such as ramification and connectivity. This work adds confidence to the analogy and highlights new features to what we require for universal resources for one-way quantum computation.

  2. Principles of quantum computation and information

    CERN Document Server

    Benenti, Giuliano; Strini, Giuliano

    2004-01-01

    Quantum computation and information is a new, rapidly developing interdisciplinary field. Therefore, it is not easy to understand its fundamental concepts and central results without facing numerous technical details. This book provides the reader a useful and not-too-heavy guide. It offers a simple and self-contained introduction; no previous knowledge of quantum mechanics or classical computation is required. Volume I may be used as a textbook for a one-semester introductory course in quantum information and computation, both for upper-level undergraduate students and for graduate students.

  3. Quantum Computation Using Optically Coupled Quantum Dot Arrays

    Science.gov (United States)

    Pradhan, Prabhakar; Anantram, M. P.; Wang, K. L.; Roychowhury, V. P.; Saini, Subhash (Technical Monitor)

    1998-01-01

    A solid state model for quantum computation has potential advantages in terms of the ease of fabrication, characterization, and integration. The fundamental requirements for a quantum computer involve the realization of basic processing units (qubits), and a scheme for controlled switching and coupling among the qubits, which enables one to perform controlled operations on qubits. We propose a model for quantum computation based on optically coupled quantum dot arrays, which is computationally similar to the atomic model proposed by Cirac and Zoller. In this model, individual qubits are comprised of two coupled quantum dots, and an array of these basic units is placed in an optical cavity. Switching among the states of the individual units is done by controlled laser pulses via near field interaction using the NSOM technology. Controlled rotations involving two or more qubits are performed via common cavity mode photon. We have calculated critical times, including the spontaneous emission and switching times, and show that they are comparable to the best times projected for other proposed models of quantum computation. We have also shown the feasibility of accessing individual quantum dots using the NSOM technology by calculating the photon density at the tip, and estimating the power necessary to perform the basic controlled operations. We are currently in the process of estimating the decoherence times for this system; however, we have formulated initial arguments which seem to indicate that the decoherence times will be comparable, if not longer, than many other proposed models.

  4. Foundations of Quantum Mechanics and Quantum Computation

    Science.gov (United States)

    Aspect, Alain; Leggett, Anthony; Preskill, John; Durt, Thomas; Pironio, Stefano

    2013-03-01

    I ask the question: What can we infer about the nature and structure of the physical world (a) from experiments already done to test the predictions of quantum mechanics (b) from the assumption that all future experiments will agree with those predictions? I discuss existing and projected experiments related to the two classic paradoxes of quantum mechanics, named respectively for EPR and Schrödinger's Cat, and show in particular that one natural conclusion from both types of experiment implies the abandonment of the concept of macroscopic counterfactual definiteness.

  5. Quantum Multiplexing for Quantum Computer Networks

    CERN Document Server

    Garcia-Escartin, J C; Chamorro-Posada, Pedro; Garcia-Escartin, Juan Carlos

    2007-01-01

    In communication networks many different channels must share a limited amount of resources. In order to allow for multiple simultaneous communications, multiple access techniques are routinely employed. With quantum communication, it is possible to share a new kind of resource. All of the system channels can be accommodated into a single channel in a larger Hilbert space. In the scheme, a single line combines the information of all the users, and, at the receiver, the original quantum channels are recovered. The given multiplexer/demultiplexer circuit can perform this n qubits to qudit transformation. Connections with superdense coding and classical multiple access schemes are discussed.

  6. Information free quantum bus for universal quantum computation

    CERN Document Server

    Devitt, S J; Hollenberg, L C L; Devitt, Simon J.; Greentree, Andrew D.; Hollenberg, Lloyd C.L.

    2005-01-01

    Long range transport of quantum information is of huge importance to the physical realisation of large scale quantum computers. This letter introduces a transport bus that deterministically mediates entanglment pairwise between isolated data qubits, while the bus itself never carries information. We demonstrate how this scheme generates standard two qubit operator measurements and its application to the preparation of linear cluster states and teleportation based universal computation.

  7. Why now is the right time to study quantum computing

    OpenAIRE

    Harrow, Aram W.

    2014-01-01

    Quantum computing is a good way to justify difficult physics experiments. But until quantum computers are built, do computer scientists need to know anything about quantum information? In fact, quantum computing is not merely a recipe for new computing devices, but a new way of looking at the world that has been astonishingly intellectually productive. In this article, I'll talk about where quantum computing came from, what it is, and what we can learn from it.

  8. Quantum Computation explained to my Mother

    CERN Document Server

    Arrighi, P

    2003-01-01

    There are many falsely intuitive introductions to quantum theory and quantum computation in a handwave. There are also numerous documents which teach those subjects in a mathematically sound manner. To my knowledge this paper is the shortest of the latter category. The aim is to deliver a short yet rigorous and self-contained introduction to Quantum Computation, whilst assuming the reader has no prior knowledge of anything but the fundamental operations on real numbers. Successively I introduce complex matrices; the postulates of quantum theory and the simplest quantum algorithm. The document originates from a fifty minutes talk addressed to a non-specialist audience, in which I sought to take the shortest mathematical path that proves a quantum algorithm right.

  9. Materials Frontiers to Empower Quantum Computing

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, Antoinette Jane [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Sarrao, John Louis [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Richardson, Christopher [Laboratory for Physical Sciences, College Park, MD (United States)

    2015-06-11

    This is an exciting time at the nexus of quantum computing and materials research. The materials frontiers described in this report represent a significant advance in electronic materials and our understanding of the interactions between the local material and a manufactured quantum state. Simultaneously, directed efforts to solve materials issues related to quantum computing provide an opportunity to control and probe the fundamental arrangement of matter that will impact all electronic materials. An opportunity exists to extend our understanding of materials functionality from electronic-grade to quantum-grade by achieving a predictive understanding of noise and decoherence in qubits and their origins in materials defects and environmental coupling. Realizing this vision systematically and predictively will be transformative for quantum computing and will represent a qualitative step forward in materials prediction and control.

  10. Elements of quantum computing history, theories and engineering applications

    CERN Document Server

    Akama, Seiki

    2015-01-01

    A quantum computer is a computer based on a computational model which uses quantum mechanics, which is a subfield of physics to study phenomena at the micro level. There has been a growing interest on quantum computing in the 1990's, and some quantum computers at the experimental level were recently implemented. Quantum computers enable super-speed computation, and can solve some important problems whose solutions were regarded impossible or intractable with traditional computers. This book provides a quick introduction to quantum computing for readers who have no backgrounds of both theory of computation and quantum mechanics. “Elements of Quantum Computing” presents the history, theories, and engineering applications of quantum computing. The book is suitable to computer scientists, physicist, and software engineers.

  11. An introduction to quantum computing algorithms

    CERN Document Server

    Pittenger, Arthur O

    2000-01-01

    In 1994 Peter Shor [65] published a factoring algorithm for a quantum computer that finds the prime factors of a composite integer N more efficiently than is possible with the known algorithms for a classical com­ puter. Since the difficulty of the factoring problem is crucial for the se­ curity of a public key encryption system, interest (and funding) in quan­ tum computing and quantum computation suddenly blossomed. Quan­ tum computing had arrived. The study of the role of quantum mechanics in the theory of computa­ tion seems to have begun in the early 1980s with the publications of Paul Benioff [6]' [7] who considered a quantum mechanical model of computers and the computation process. A related question was discussed shortly thereafter by Richard Feynman [35] who began from a different perspec­ tive by asking what kind of computer should be used to simulate physics. His analysis led him to the belief that with a suitable class of "quantum machines" one could imitate any quantum system.

  12. Iterated Gate Teleportation and Blind Quantum Computation

    Science.gov (United States)

    Pérez-Delgado, Carlos A.; Fitzsimons, Joseph F.

    2015-06-01

    Blind quantum computation allows a user to delegate a computation to an untrusted server while keeping the computation hidden. A number of recent works have sought to establish bounds on the communication requirements necessary to implement blind computation, and a bound based on the no-programming theorem of Nielsen and Chuang has emerged as a natural limiting factor. Here we show that this constraint only holds in limited scenarios, and show how to overcome it using a novel method of iterated gate teleportations. This technique enables drastic reductions in the communication required for distributed quantum protocols, extending beyond the blind computation setting. Applied to blind quantum computation, this technique offers significant efficiency improvements, and in some scenarios offers an exponential reduction in communication requirements.

  13. Can Quantum Communication Speed Up Distributed Computation?

    OpenAIRE

    Elkin, Michael; Klauck, Hartmut; Nanongkai, Danupon; Pandurangan, Gopal

    2012-01-01

    The focus of this paper is on {\\em quantum distributed} computation, where we investigate whether quantum communication can help in {\\em speeding up} distributed network algorithms. Our main result is that for certain fundamental network problems such as minimum spanning tree, minimum cut, and shortest paths, quantum communication {\\em does not} help in substantially speeding up distributed algorithms for these problems compared to the classical setting. In order to obtain...

  14. Space-Efficient Simulation of Quantum Computers

    OpenAIRE

    Frank, Michael P.; Meyer-Baese, Uwe H.; Chiorescu, Irinel; Oniciuc, Liviu; van Engelen, Robert A.

    2008-01-01

    Traditional algorithms for simulating quantum computers on classical ones require an exponentially large amount of memory, and so typically cannot simulate general quantum circuits with more than about 30 or so qubits on a typical PC-scale platform with only a few gigabytes of main memory. However, more memory-efficient simulations are possible, requiring only polynomial or even linear space in the size of the quantum circuit being simulated. In this paper, we describe one s...

  15. Universal Dephasing Control During Quantum Computation

    OpenAIRE

    Gordon, Goren; Kurizki, Gershon

    2007-01-01

    Dephasing is a ubiquitous phenomenon that leads to the loss of coherence in quantum systems and the corruption of quantum information. We present a universal dynamical control approach to combat dephasing during all stages of quantum computation, namely, storage, single- and two-qubit operators. We show that (a) tailoring multi-frequency gate pulses to the dephasing dynamics can increase fidelity; (b) cross-dephasing, introduced by entanglement, can be eliminated by appropri...

  16. Quantum Computing Without Wavefunctions: Time-Dependent Density Functional Theory for Universal Quantum Computation

    OpenAIRE

    Tempel, David Gabriel; Aspuru-Guzik, Alan

    2011-01-01

    We prove that the theorems of TDDFT can be extended to a class of qubit Hamiltonians that are universal for quantum computation. The theorems of TDDFT applied to universal Hamiltonians imply that single-qubit expectation values can be used as the basic variables in quantum computation and information theory, rather than wavefunctions. From a practical standpoint this opens the possibility of approximating observables of interest in quantum computations directly in terms of single-qubit quan...

  17. Quantum Computational Representation of the Bosonic Oscillator

    CERN Document Server

    Jaroszkiewicz, G

    2005-01-01

    By the early eighties, Fredkin, Feynman, Minsky and others were exploring the notion that the laws of physics could be simulated with computers. Feynman's particular contribution was to bring quantum mechanics into the discussion and his ideas played a key role in the development of quantum computation. It was shown in 1995 by Barenco et al that all quantum computation processes could be written in terms of local operations and CNOT gates. We show how one of the most important of all physical systems, the quantized bosonic oscillator, can be rewritten in precisely those terms and therefore described as a quantum computational process, exactly in line with Feynman's ideas. We discuss single particle excitations and coherent states.

  18. Is the Brain a Quantum Computer?

    Science.gov (United States)

    Litt, Abninder; Eliasmith, Chris; Kroon, Frederick W.; Weinstein, Steven; Thagard, Paul

    2006-01-01

    We argue that computation via quantum mechanical processes is irrelevant to explaining how brains produce thought, contrary to the ongoing speculations of many theorists. First, quantum effects do not have the temporal properties required for neural information processing. Second, there are substantial physical obstacles to any organic…

  19. Directional Coupling for Quantum Computing and Communication

    OpenAIRE

    Nikolopoulos, Georgios M.

    2008-01-01

    We introduce the concept of directional coupling, i.e., the selective transfer of a state between adjacent quantum wires, in the context of quantum computing and short-distance communication. Our analysis rests upon a mathematical analogy between a dual-channel directional coupler and a composite spin system.

  20. Quantum Computing and Shor`s Factoring Algorithm

    OpenAIRE

    Volovich, Igor V.

    2001-01-01

    Lectures on quantum computing. Contents: Algorithms. Quantum circuits. Quantum Fourier transform. Elements of number theory. Modular exponentiation. Shor`s algorithm for finding the order. Computational complexity of Schor`s algorithm. Factoring integers. NP-complete problems.

  1. Hyper-parallel photonic quantum computation with coupled quantum dots.

    Science.gov (United States)

    Ren, Bao-Cang; Deng, Fu-Guo

    2014-01-01

    It is well known that a parallel quantum computer is more powerful than a classical one. So far, there are some important works about the construction of universal quantum logic gates, the key elements in quantum computation. However, they are focused on operating on one degree of freedom (DOF) of quantum systems. Here, we investigate the possibility of achieving scalable hyper-parallel quantum computation based on two DOFs of photon systems. We construct a deterministic hyper-controlled-not (hyper-CNOT) gate operating on both the spatial-mode and the polarization DOFs of a two-photon system simultaneously, by exploiting the giant optical circular birefringence induced by quantum-dot spins in double-sided optical microcavities as a result of cavity quantum electrodynamics (QED). This hyper-CNOT gate is implemented by manipulating the four qubits in the two DOFs of a two-photon system without auxiliary spatial modes or polarization modes. It reduces the operation time and the resources consumed in quantum information processing, and it is more robust against the photonic dissipation noise, compared with the integration of several cascaded CNOT gates in one DOF. PMID:24721781

  2. Faster quantum chemistry simulation on fault-tolerant quantum computers

    International Nuclear Information System (INIS)

    Quantum computers can in principle simulate quantum physics exponentially faster than their classical counterparts, but some technical hurdles remain. We propose methods which substantially improve the performance of a particular form of simulation, ab initio quantum chemistry, on fault-tolerant quantum computers; these methods generalize readily to other quantum simulation problems. Quantum teleportation plays a key role in these improvements and is used extensively as a computing resource. To improve execution time, we examine techniques for constructing arbitrary gates which perform substantially faster than circuits based on the conventional Solovay–Kitaev algorithm (Dawson and Nielsen 2006 Quantum Inform. Comput. 6 81). For a given approximation error ?, arbitrary single-qubit gates can be produced fault-tolerantly and using a restricted set of gates in time which is O(log??) or O(log?log??); with sufficient parallel preparation of ancillas, constant average depth is possible using a method we call programmable ancilla rotations. Moreover, we construct and analyze efficient implementations of first- and second-quantized simulation algorithms using the fault-tolerant arbitrary gates and other techniques, such as implementing various subroutines in constant time. A specific example we analyze is the ground-state energy calculation for lithium hydride. (paper)

  3. Quantum Communication and Quantum Computation with Entangled Photons

    Science.gov (United States)

    Zeilinger, Anton

    2006-06-01

    Entangled photons provided the first evidence of a violation of Bell's inequality which implies a breakdown of the philosophical world-view of local realism. These experiments, having been extended over the years over ever longer distances, also provided the experimental foundation of the emerging field of quantum communication. There, quantum cryptography and quantum teleportation are key topics, which are already fairly advanced, being able to cover significant distances. Originally, it was thought that in a future quantum internet scheme, communication would be provided by photons while the local computers were to be realized with ions, atoms, atomic nuclei, solid state devices and the like. Interestingly, most recently the field of linear optics quantum computation has emerged with interesting possibilities and advantages.

  4. Image segmentation on a quantum computer

    Science.gov (United States)

    Caraiman, Simona; Manta, Vasile I.

    2015-05-01

    In this paper, we address the field of quantum information processing and analyze the prospects of applying quantum computation concepts to image processing tasks. Specifically, we discuss the development of a quantum version for the image segmentation operation. This is an important technique that comes up in many image processing applications. We consider the threshold-based segmentation and show that a quantum circuit to achieve this operation can be built using a quantum oracle that implements the thresholding function. We discuss the circuit implementation of the oracle operator and provide examples of segmenting synthetic and real images. The main advantage of the quantum version for image segmentation over the classical approach is its speedup and is provided by the special properties of quantum information processing: superposition of states and inherent parallelism.

  5. Superadiabatic Controlled Evolutions and Universal Quantum Computation.

    Science.gov (United States)

    Santos, Alan C; Sarandy, Marcelo S

    2015-01-01

    Adiabatic state engineering is a powerful technique in quantum information and quantum control. However, its performance is limited by the adiabatic theorem of quantum mechanics. In this scenario, shortcuts to adiabaticity, such as provided by the superadiabatic theory, constitute a valuable tool to speed up the adiabatic quantum behavior. Here, we propose a superadiabatic route to implement universal quantum computation. Our method is based on the realization of piecewise controlled superadiabatic evolutions. Remarkably, they can be obtained by simple time-independent counter-diabatic Hamiltonians. In particular, we discuss the implementation of fast rotation gates and arbitrary n-qubit controlled gates, which can be used to design different sets of universal quantum gates. Concerning the energy cost of the superadiabatic implementation, we show that it is dictated by the quantum speed limit, providing an upper bound for the corresponding adiabatic counterparts. PMID:26511064

  6. Superadiabatic Controlled Evolutions and Universal Quantum Computation

    Science.gov (United States)

    Santos, Alan C.; Sarandy, Marcelo S.

    2015-01-01

    Adiabatic state engineering is a powerful technique in quantum information and quantum control. However, its performance is limited by the adiabatic theorem of quantum mechanics. In this scenario, shortcuts to adiabaticity, such as provided by the superadiabatic theory, constitute a valuable tool to speed up the adiabatic quantum behavior. Here, we propose a superadiabatic route to implement universal quantum computation. Our method is based on the realization of piecewise controlled superadiabatic evolutions. Remarkably, they can be obtained by simple time-independent counter-diabatic Hamiltonians. In particular, we discuss the implementation of fast rotation gates and arbitrary n-qubit controlled gates, which can be used to design different sets of universal quantum gates. Concerning the energy cost of the superadiabatic implementation, we show that it is dictated by the quantum speed limit, providing an upper bound for the corresponding adiabatic counterparts. PMID:26511064

  7. Quantum vs. Classical Communication and Computation

    CERN Document Server

    Buhrman, H; Wigderson, A; Buhrman, Harry; Cleve, Richard; Wigderson, Avi

    1998-01-01

    We present a simple and general simulation technique that transforms any black-box quantum algorithm (a la Grover's database search algorithm) to a quantum communication protocol for a related problem, in a way that fully exploits the quantum parallelism. This allows us to obtain new positive and negative results. The positive results are novel quantum communication protocols that are built from nontrivial quantum algorithms via this simulation. These protocols, combined with (old and new) classical lower bounds, are shown to provide the first asymptotic separation results between the quantum and classical (probabilistic) two-party communication complexity models. In particular, we obtain a quadratic separation for the bounded-error model, and an exponential separation for the zero-error model. The negative results transform known quantum communication lower bounds to computational lower bounds in the black-box model. In particular, we show that the quadratic speed-up achieved by Grover for the OR function is...

  8. CLASSICAL AND QUANTUM COMMUNICATIONS IN GRID COMPUTING

    Directory of Open Access Journals (Sweden)

    RODICA STERIAN

    2010-10-01

    Full Text Available The Quantum Crypted GRID Port developed under the D11-044 QUANTGRID project financed by the Romanian Center for Programme Management CNMP is presented: specifically the technology developed and the proprietary software used in the project. Quantum crypted communications eliminate the possibility of quantum-computer deciphering of messages (Shor's Lemma, while functioning with a public key exchange scheme – being secure by the very essence of quantum nature: any quantum state measured in any way collapses into one of its projections, thus it cannot be cloned and impossible to keep a copy thereof. The distribution of quantum public key is hence similar to the Vernam cipher (symmetrical – with secret key. The ongoing activities in this technology pertain to GRID communications through optical fiber and allow optimising the quantum security technology and experimenting proprietary algorithms for optimum data-volume/security for this new type of communications.

  9. Quantum computation and Biological stress: A Hypothesis

    OpenAIRE

    Grover Monendra

    2014-01-01

    We propose that biological systems may behave as quantum computers.We have earlier hypothesized that patterns of quantum computation may be altered in stress and this leads to the change in the consciousness vector of biological systems. We further propose in this paper that the biological systems with a sufficient consciousness vector behave as objects which are entangled with the universal consciousness and as a consequence wormholes exist between the universal consciousness and the bio...

  10. More on Optical Holonomic Quantum Computer

    OpenAIRE

    Fujii, Kazuyuki

    2000-01-01

    We in this paper consider a further generalization of the (optical) holonomic quantum computation proposed by Zanardi and Rasetti (quant-ph/9904011), and reinforced by Fujii (quant-ph/9910069) and Pachos and Chountasis (quant-ph/9912093). We construct a quantum computational bundle on some parameter space, and calculate non-abelian Berry connections and curvatures explicitly in the special cases. Our main tool is unitary coherent operators based on Lie algebras su(n+1) and s...

  11. Delayed commutation in quantum computer networks

    OpenAIRE

    Garcia-Escartin, Juan Carlos; Chamorro-Posada, Pedro

    2005-01-01

    In the same way that classical computer networks connect and enhance the capabilities of classical computers, quantum networks can combine the advantages of quantum information and communications. We propose a non-classical network element, a delayed commutation switch, that can solve the problem of switching time in packet switching networks. With the help of some local ancillary qubits and superdense codes we can route the information after part of it has left the network ...

  12. Accounting Principles are Simulated on Quantum Computers

    OpenAIRE

    Diep, Do Ngoc; Giang, Do Hoang

    2005-01-01

    The paper is devoted to a new idea of simulation of accounting by quantum computing. We expose the actual accounting principles in a pure mathematics language. After that we simulated the accounting principles on quantum computers. We show that all arbitrary accounting actions are exhausted by the described basic actions. The main problem of accounting are reduced to some system of linear equations in the economic model of Leontief. In this simulation we use our constructed ...

  13. Computational Studies of Quantum Spin Systems

    OpenAIRE

    Sandvik, Anders. W.

    2011-01-01

    These lecture notes introduce quantum spin systems and several computational methods for studying their ground-state and finite-temperature properties. Symmetry-breaking and critical phenomena are first discussed in the simpler setting of Monte Carlo studies of classical spin systems, to illustrate finite-size scaling at continuous and first-order phase transitions. Exact diagonalization and quantum Monte Carlo (stochastic series expansion) algorithms and their computer impl...

  14. Methodological testing: Are fast quantum computers illusions?

    International Nuclear Information System (INIS)

    Popularity of the idea for computers constructed from the principles of QM started with Feynman's 'Lectures On Computation', but he called the idea crazy and dependent on statistical mechanics. In 1987, Feynman published a paper in 'Quantum Implications - Essays in Honor of David Bohm' on negative probabilities which he said gave him cultural shock. The problem with imagined fast quantum computers (QC) is that speed requires both statistical behavior and truth of the mathematical formalism. The Swedish Royal Academy 2012 Nobel Prize in physics press release touted the discovery of methods to control ''individual quantum systems'', to ''measure and control very fragile quantum states'' which enables ''first steps towards building a new type of super fast computer based on quantum physics.'' A number of examples where widely accepted mathematical descriptions have turned out to be problematic are examined: Problems with the use of Oracles in P=NP computational complexity, Paul Finsler's proof of the continuum hypothesis, and Turing's Enigma code breaking versus William tutte's Colossus. I view QC research as faith in computational oracles with wished for properties. Arther Fine's interpretation in 'The Shaky Game' of Einstein's skepticism toward QM is discussed. If Einstein's reality as space-time curvature is correct, then space-time computers will be the next type of super fast computer.

  15. Mathematical Models of Contemporary Elementary Quantum Computing Devices

    OpenAIRE

    Chen, G.; Church, D. A.; Englert, B. -G.; Zubairy, M. S.

    2003-01-01

    Computations with a future quantum computer will be implemented through the operations by elementary quantum gates. It is now well known that the collection of 1-bit and 2-bit quantum gates are universal for quantum computation, i.e., any n-bit unitary operation can be carried out by concatenations of 1-bit and 2-bit elementary quantum gates. Three contemporary quantum devices--cavity QED, ion traps and quantum dots--have been widely regarded as perhaps the most promising ...

  16. Prospects for Spin-Based Quantum Computing in Quantum Dots

    Science.gov (United States)

    Kloeffel, Christoph; Loss, Daniel

    2013-04-01

    Experimental and theoretical progress toward quantum computation with spins in quantum dots (QDs) is reviewed, with particular focus on QDs formed in GaAs heterostructures, on nanowire-based QDs, and on self-assembled QDs. We report on a remarkable evolution of the field, where decoherence—one of the main challenges for realizing quantum computers—no longer seems to be the stumbling block it had originally been considered. General concepts, relevant quantities, and basic requirements for spin-based quantum computing are explained; opportunities and challenges of spin-orbit interaction and nuclear spins are reviewed. We discuss recent achievements, present current theoretical proposals, and make several suggestions for further experiments.

  17. From quantum computation to quantum simulation: becoming more realistic

    International Nuclear Information System (INIS)

    The purpose of this talk is to introduce the basic tasks and goals of the EU FP7-project ''COQUIT (Collective quantum operations for information technology)''. Quantum systems are investigated which allow only a partial control by a constrained set of quantum operations. Typical examples are many particle quantum systems like cold atoms in optical lattices or other multi-atom ensembles, which can be manipulated collectively but not individually. Such restrictions are currently one of the biggest obstacles against working quantum computers. Instead of improving the corresponding experimental methods, we aim at a systematic study of the tasks which can be performed with currently available techniques. To this end we want to develop theoretical models which can on the one hand reflect the limitations of current experimental setups, but are on the other hand powerful enough to allow non-trivial practical applications. This point of view is new and complementary to most other research in quantum information science, where complete control over a small number of particles is assumed. One basic pillar of the COQUIT project is based on the concept of quantum simulation. Here a limited set of implementable operations is used to simulate physical properties of another quantum system. In this sense a quantum simulation device is a computational device for special purposes. We present the actual status of the project including new results and future perspectives.

  18. Characteristics of semiconductor bridge (SCB) plasma generated in a micro-electro-mechanical system (MEMS)

    International Nuclear Information System (INIS)

    Plasma ignition method has been applied in various fields particularly to the rocket propulsion, pyrotechnics, explosives, and to the automotive air-bag system. Ignition method for those applications should be safe and also operate reliably in hostile environments such as; electromagnetic noise, drift voltage, electrostatic background and so on. In the present Letter, a semiconductor bridge (SCB) plasma ignition device was fabricated and its plasma characteristics including the propagation speed of the plasma, plasma size, and plasma temperature were investigated with the aid of the visualization of micro scale plasma (i.e., ?350 ?m), which generated from a micro-electro-mechanical poly-silicon semiconductor bridge (SCB)

  19. Quantum algorithms for computational nuclear physics

    Directory of Open Access Journals (Sweden)

    Viš?ák Jakub

    2015-01-01

    Full Text Available While quantum algorithms have been studied as an efficient tool for the stationary state energy determination in the case of molecular quantum systems, no similar study for analogical problems in computational nuclear physics (computation of energy levels of nuclei from empirical nucleon-nucleon or quark-quark potentials have been realized yet. Although the difference between the above mentioned studies might seem negligible, it will be examined. First steps towards a particular simulation (on classical computer of the Iterative Phase Estimation Algorithm for deuterium and tritium nuclei energy level computation will be carried out with the aim to prove algorithm feasibility (and extensibility to heavier nuclei for its possible practical realization on a real quantum computer.

  20. Quantum algorithms for computational nuclear physics

    Science.gov (United States)

    Viš?ák, Jakub

    2015-07-01

    While quantum algorithms have been studied as an efficient tool for the stationary state energy determination in the case of molecular quantum systems, no similar study for analogical problems in computational nuclear physics (computation of energy levels of nuclei from empirical nucleon-nucleon or quark-quark potentials) have been realized yet. Although the difference between the above mentioned studies might seem negligible, it will be examined. First steps towards a particular simulation (on classical computer) of the Iterative Phase Estimation Algorithm for deuterium and tritium nuclei energy level computation will be carried out with the aim to prove algorithm feasibility (and extensibility to heavier nuclei) for its possible practical realization on a real quantum computer.

  1. Theory of fault-tolerant quantum computation

    Energy Technology Data Exchange (ETDEWEB)

    Gottesman, D. [California Institute of Technology, Pasadena, California 91125 (United States)]|[Los Alamos National Laboratories, Los Alamos, New Mexico 87545 (United States)

    1998-01-01

    In order to use quantum error-correcting codes to improve the performance of a quantum computer, it is necessary to be able to perform operations fault-tolerantly on encoded states. I present a theory of fault-tolerant operations on stabilizer codes based on symmetries of the code stabilizer. This allows a straightforward determination of which operations can be performed fault-tolerantly on a given code. I demonstrate that fault-tolerant universal computation is possible for any stabilizer code. I discuss a number of examples in more detail, including the five-quantum-bit code. {copyright} {ital 1998} {ital The American Physical Society}

  2. Stabilisation of quantum computations by symmetrisation

    CERN Document Server

    Barenco, A; Ekert, A K; Jozsa, R; Macchiavello, C; Barenco, Adriano; Deutsch, David; Ekert, Artur; Jozsa, Richard; Macchiavello, Chiara

    1996-01-01

    We propose a method for the stabilisation of quantum computations (including quantum state storage). The method is based on the operation of projection into \\cal SYM, the symmetric subspace of the full state space of R redundant copies of the computer. We describe an efficient algorithm and quantum network effecting \\cal SYM--projection and discuss the stabilising effect of the proposed method in the context of unitary errors generated by hardware imprecision, and nonunitary errors arising from external environmental interaction. Finally, limitations of the method are discussed.

  3. Consequences and Limitations of Conventional Computers and their Solutions through Quantum Computers

    OpenAIRE

    Sanjaykumar DALVI; Pranav BARDAPURKAR; Nilesh BARDE; Deepak THAKUR

    2011-01-01

    Quantum computer is the current topic of research in the field of computational science, which uses principles of quantum mechanics. Quantum computers will be much more powerful than the classical computer due to its enormous computational speed. Recent developments in quantum computers which are based on the laws of quantum mechanics, shows different ways of performing efficient calculations along with the various results which are not possible on the classical computers in an efficient peri...

  4. Brain-Computer Interfaces and Quantum Robots

    CERN Document Server

    Pessa, Eliano

    2009-01-01

    The actual (classical) Brain-Computer Interface attempts to use brain signals to drive suitable actuators performing the actions corresponding to subject's intention. However this goal is not fully reached, and when BCI works, it does only in particular situations. The reason of this unsatisfactory result is that intention cannot be conceived simply as a set of classical input-output relationships. It is therefore necessary to resort to quantum theory, allowing the occurrence of stable coherence phenomena, in turn underlying high-level mental processes such as intentions and strategies. More precisely, within the context of a dissipative Quantum Field Theory of brain operation it is possible to introduce generalized coherent states associated, within the framework of logic, to the assertions of a quantum metalanguage. The latter controls the quantum-mechanical computing corresponding to standard mental operation. It thus become possible to conceive a Quantum Cyborg in which a human mind controls, through a qu...

  5. Halting in quantum Turing computation

    OpenAIRE

    Fouché, W. L.; J. Heidema; Jones, G.(Department of Physics, University of Warwick, Coventry, UK); Potgieter, P. H.

    2007-01-01

    The paper considers the halting scheme for quantum Turing machines. The scheme originally proposed by Deutsch appears to be correct, but not exactly as originally intended. We discuss the result of Ozawa as well as the objections raised by Myers, Kieu and Danos and others. Finally, the relationship of the halting scheme to the quest for a universal quantum Turing machine is considered.

  6. Relativistic quantum chemistry on quantum computers.

    Czech Academy of Sciences Publication Activity Database

    Veis, Libor; Viš?ák, Jakub; Fleig, T.; Knecht, S.; Saue, T.; Visscher, L.; Pittner, Ji?í

    2012-01-01

    Ro?. 85, ?. 3 (2012), 030304. ISSN 1050-2947 R&D Projects: GA ?R GA203/08/0626 Institutional support: RVO:61388955 Keywords : simulation * algorithm * computation Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.042, year: 2012

  7. Computer science approach to quantum control

    OpenAIRE

    Janzing, Dominik

    2006-01-01

    This work considers several hypothetical control processes on the nanoscopic level and show their analogy to computation processes. It shows that measuring certain types of quantum observables is such a complex task that every instrument that is able to perform it would necessarily be an extremely powerful computer.

  8. Qubus ancilla-driven quantum computation

    International Nuclear Information System (INIS)

    Hybrid matter-optical systems offer a robust, scalable path to quantum computation. Such systems have an ancilla which acts as a bus connecting the qubits. We demonstrate how using a continuous variable qubus as the ancilla provides savings in the total number of operations required when computing with many qubits

  9. Construction of a universal quantum computer

    International Nuclear Information System (INIS)

    We construct a universal quantum computer following Deutsch's original proposal of a universal quantum Turing machine (UQTM). Like Deutsch's UQTM, our machine can emulate any classical Turing machine and can execute any algorithm that can be implemented in the quantum gate array framework but under the control of a quantum program, and hence is universal. We present the architecture of the machine, which consists of a memory tape and a processor and describe the observables that comprise the registers of the processor and the instruction set, which includes a set of operations that can approximate any unitary operation to any desired accuracy and hence is quantum computationally universal. We present the unitary evolution operators that act on the machine to achieve universal computation and discuss each of them in detail and specify and discuss explicit program halting and concatenation schemes. We define and describe a set of primitive programs in order to demonstrate the universal nature of the machine. These primitive programs facilitate the implementation of more complex algorithms and we demonstrate their use by presenting a program that computes the NAND function, thereby also showing that the machine can compute any classically computable function.

  10. Construction of a universal quantum computer

    Science.gov (United States)

    Lagana, Antonio A.; Lohe, M. A.; von Smekal, Lorenz

    2009-05-01

    We construct a universal quantum computer following Deutsch’s original proposal of a universal quantum Turing machine (UQTM). Like Deutsch’s UQTM, our machine can emulate any classical Turing machine and can execute any algorithm that can be implemented in the quantum gate array framework but under the control of a quantum program, and hence is universal. We present the architecture of the machine, which consists of a memory tape and a processor and describe the observables that comprise the registers of the processor and the instruction set, which includes a set of operations that can approximate any unitary operation to any desired accuracy and hence is quantum computationally universal. We present the unitary evolution operators that act on the machine to achieve universal computation and discuss each of them in detail and specify and discuss explicit program halting and concatenation schemes. We define and describe a set of primitive programs in order to demonstrate the universal nature of the machine. These primitive programs facilitate the implementation of more complex algorithms and we demonstrate their use by presenting a program that computes the NAND function, thereby also showing that the machine can compute any classically computable function.

  11. Theory of Quantum Computing and Communication

    CERN Document Server

    Fortnow, L

    2002-01-01

    A workshop sponsored by NSF C-CR and organized by the Center for Discrete Math and Theoretical Computer Science (DIMACS) was held at Elmsford, New York, January 17-18, 2002 where we had several discussions that gave structure to this report. The workshop immediately followed the Fifth Annual Quantum Information Processing Workshop that was held January 14-17 at IBM Yorktown. This is the report from that workshop. The report recommends that the NSF Division of Computer-Communications Research (C-CR) develop a new initiative in "Theory of Quantum Computing and Communication" and describes several research directions that this initiative could support.

  12. Simulating Grover's Quantum Search in a Classical Computer

    OpenAIRE

    Ningtyas, D. K.; A.B. Mutiara

    2010-01-01

    The rapid progress of computer science has been accompanied by a corresponding evolution of computation, from classical computation to quantum computation. As quantum computing is on its way to becoming an established discipline of computing science, much effort is being put into the development of new quantum algorithms. One of quantum algorithms is Grover algorithm, which is used for searching an element in an unstructured list of N elements with quadratic speed-up over cl...

  13. Quantum-State-Engineering for Spin-Quantum-Computing

    OpenAIRE

    Heidebrecht, Andreas

    2006-01-01

    The subject of this thesis are experimental procedures for preparation, manipulation, and detection of specific quantum states of spin systems in the context of quantum computing. Nuclear magnetic resonance (NMR) and electron spin resonance (ESR) methods were used. The systems studied were small molecules in liquid state, small molecules embedded in a liquid crystal matrix, and paramagnetic centers in single crystals. The nuclear 19F spins of 2,3,4-Trifluoroaniline were u...

  14. Diamond NV centers for quantum computing and quantum networks

    OpenAIRE

    Lilian Childress; Ronald Hanson

    2013-01-01

    The exotic features of quantum mechanics have the potential to revolutionize information technologies. Using superposition and entanglement, a quantum processor could efficiently tackle problems inaccessible to current-day computers. Nonlocal correlations may be exploited for intrinsically secure communication across the globe. Finding and controlling a physical system suitable for fulfi lling these promises is one of the greatest challenges of our time. The nitrogen-vacancy (NV) center in di...

  15. Quantum state transition diagram: a bridge from classical computing to quantum computing

    Science.gov (United States)

    Hook, Loyd R., IV; Lee, Samuel C.

    2010-04-01

    Very few papers have been written on the topic of a quantum version of the finite state machine, (or finite state automata). Furthermore, these papers only serve to define what a quantum finite state machine might be in the mathematical sense using the early languages of Turing machines. This paper seeks to further develop the notion of a quantum finite state machine (FSM) using constructs developed for the classical FSM and utilized for classical FSM design. In particular the quantum state transition diagram (QSTD) is constructed to further the understanding and realization of quantum finite state machines and quantum computers.

  16. Quantum computing with black-box quantum subroutines

    International Nuclear Information System (INIS)

    In classical computation a subroutine is treated as a black box and we do not need to know its exact physical implementation to use it. A complex problem can be decomposed into smaller problems using such modularity. We show that quantum mechanically applying an unknown quantum process as a subroutine is impossible, and this restricts computation models such as DQC1 from operating on unknown inputs. We present a method to avoid this situation for certain computational problems and apply to a modular version of Shor's factoring algorithm. We examine how quantum entanglement and discord fare in this implementation. In this way we are able to study the role of discord in Shor's factoring algorithm.

  17. Effects of aminopropyltriethoxysilane (?-APS) on tensile properties and morphology of polypropylene (PP), recycle acrylonitrile butadiene rubber (NBRr) and sugarcane bagasse (SCB) composites

    Science.gov (United States)

    Santiagoo, Ragunathan; Omar, Latifah; Zainal, Mustaffa; Ting, Sam Sung; Ismail, Hanafi

    2015-07-01

    The performance of sugarcane baggase (SCB) treated with ?-APS filled polypropylene (PP)/recycled acrylonitrile butadiene rubber (NBRr) biocomposites were investigated. The composites with different filler loading ranging from 5 to 30 wt % were prepared using heated two roll mill by melt mixing at temperature of 180 °C. Tensile properties of the PP/NBRr/SCB composites which is tensile strength, Young Modulus and elongation at break were investigated. Increasing of treated SCB filler loading in PP/NBRr/SCB composites have increased the Young modulus however decreased the tensile strength and elongation at break of the PP/NBRr/SCB composites. From the results, ?-APS treated SCB composites shown higher tensile strength and Young Modulus but lower elongation at break when compared to the untreated SCB composites. This is due to the stronger bonding between ?-APS treated SCB with PP/NBRr matrices. These findings was supported by micrograph pictures from morphological study. SCB filler treated with ?-APS has improved the adhesion as well as gave strong interfacial bonding between SCB filler and PP/NBRr matrices which results in good tensile strength of PP/NBRr/SCB composites.

  18. Quantum Computers: A New Paradigm in Information Technology

    OpenAIRE

    Mahesh S. Raisinghani

    2001-01-01

    The word 'quantum' comes from the Latin word quantus meaning 'how much'. Quantum computing is a fundamentally new mode of information processing that can be performed only by harnessing physical phenomena unique to quantum mechanics (especially quantum interference). Paul Benioff of the Argonne National Laboratory first applied quantum theory to computers in 1981 and David Deutsch of Oxford proposed quantum parallel computers in 1985, years before the realization of qubits in 1995. However, i...

  19. Quantum Computing with Electron Spins in Quantum Dots

    OpenAIRE

    L. M. K. Vandersypen; Hanson, R.; van Beveren, L. H. Willems; Elzerman, J. M.; Greidanus, J.S.; Franceschi, S; Kouwenhoven, L. P.

    2002-01-01

    We present a set of concrete and realistic ideas for the implementation of a small-scale quantum computer using electron spins in lateral GaAs/AlGaAs quantum dots. Initialization is based on leads in the quantum Hall regime with tunable spin-polarization. Read-out hinges on spin-to-charge conversion via spin-selective tunneling to or from the leads, followed by measurement of the number of electron charges on the dot via a charge detector. Single-qubit manipulation relies on...

  20. Verification for measurement-only blind quantum computing

    OpenAIRE

    Morimae, Tomoyuki

    2012-01-01

    Blind quantum computing is a new secure quantum computing protocol where a client who does not have any sophisticated quantum technlogy can delegate her quantum computing to a server without leaking any privacy. It is known that a client who has only a measurement device can perform blind quantum computing [T. Morimae and K. Fujii, Phys. Rev. A {\\bf87}, 050301(R) (2013)]. It has been an open problem whether the protocol can enjoy the verification, i.e., the ability of client...

  1. Universal quantum computation with unlabelled qubits

    International Nuclear Information System (INIS)

    We show that an nth root of the Walsh-Hadamard transform (obtained from the Hadamard gate and a cyclic permutation of the qubits), together with two diagonal matrices, namely a local qubit-flip (for a fixed but arbitrary qubit) and a non-local phase-flip (for a fixed but arbitrary coefficient), can do universal quantum computation on n qubits. A quantum computation, making use of n qubits and based on these operations, is then a word of variable length, but whose letters are always taken from an alphabet of cardinality three. Therefore, in contrast with other universal sets, no choice of qubit lines is needed for the application of the operations described here. A quantum algorithm based on this set can be interpreted as a discrete diffusion of a quantum particle on a de Bruijn graph, corrected on-the-fly by auxiliary modifications of the phases associated with the arcs

  2. Space-Efficient Simulation of Quantum Computers

    CERN Document Server

    Frank, Michael P; Chiorescu, Irinel; Oniciuc, Liviu; van Engelen, Robert A

    2008-01-01

    Traditional algorithms for simulating quantum computers on classical ones require an exponentially large amount of memory, and so typically cannot simulate general quantum circuits with more than about 30 or so qubits on a typical PC-scale platform with only a few gigabytes of main memory. However, more memory-efficient simulations are possible, requiring only polynomial or even linear space in the size of the quantum circuit being simulated. In this paper, we describe one such technique, which was recently implemented at FSU in the form of a C++ program called SEQCSIM, which we releasing publicly. We also discuss the potential benefits of this simulation in quantum computing research and education, and outline some possible directions for further progress.

  3. Factoring in a dissipative quantum computer

    CERN Document Server

    Miquel, C; Perazzo, R P J; Miquel, Cesar; Paz, Juan Pablo; Perazzo, Roberto

    1996-01-01

    We describe an array of quantum gates implementing Shor's algorithm for prime factorization in a quantum computer. The array includes a circuit for modular exponentiation with several subcomponents (such as controlled multipliers, adders, etc) which are described in terms of elementary Toffoli gates. We present a simple analysis of the impact of losses and decoherence on the performance of this quantum factoring circuit. For that purpose, we simulate a quantum computer which is running the program to factor N = 15 while interacting with a dissipative environment. As a consequence of this interaction randomly selected qubits may spontaneously decay. Using the results of our numerical simulations we analyze the efficiency of some simple error correction techniques.

  4. Quantum Theory of Computation and Relativistic Physics

    CERN Document Server

    Vlasov, A Yu

    1997-01-01

    In the e-print is discussed a few steps to introducing of "vocabulary" of relativistic physics in quantum theory of information and computation (QTI&C). The behavior of a few simple quantum systems those are used as models in QTI&C is tested by usual relativistic tools (transformation properties of wave vectors, etc.). Massless and charged massive particles with spin 1/2 is considered. Field theory is also discussed briefly.

  5. Entanglement and Quantum Computation: An Overview

    Energy Technology Data Exchange (ETDEWEB)

    Perez, R.B.

    2000-06-27

    This report presents a selective compilation of basic facts from the fields of particle entanglement and quantum information processing prepared for those non-experts in these fields that may have interest in an area of physics showing counterintuitive, ''spooky'' (Einstein's words) behavior. In fact, quantum information processing could, in the near future, provide a new technology to sustain the benefits to the U.S. economy due to advanced computer technology.

  6. Qdensity - a Mathematica Quantum Computer Simulation

    OpenAIRE

    Juliá-Díaz, B.; Burdis, J. M.; Tabakin, F.

    2005-01-01

    This Mathematica 5.2 package~\\footnote{QDENSITY is available at http://www.pitt.edu/~tabakin/QDENSITY} is a simulation of a Quantum Computer. The program provides a modular, instructive approach for generating the basic elements that make up a quantum circuit. The main emphasis is on using the density matrix, although an approach using state vectors is also implemented in the package. The package commands are defined in {\\it Qdensity.m} which contains the tools needed in qua...

  7. Quantum computing by pairing trapped ultracold ions

    OpenAIRE

    Mang, Feng; Xiwen, Zhu; Kelin, Gao; Lei, Shi

    2000-01-01

    The superpositional wave function oscillations for finite-time implementation of quantum algorithms modifies the desired interference required for quantum computing. We propose a scheme with trapped ultracold ion-pairs being qubits to diminish the detrimental effect of the wave function oscillations, and apply the scheme to the two-qubit Grover's search. It can be also found that the qubits in our scheme are more robust against the decoherence caused by the environment, and ...

  8. Can the human brain do quantum computing?

    Science.gov (United States)

    Rocha, A F; Massad, E; Coutinho, F A B

    2004-01-01

    The electrical membrane properties have been the key issues in the understanding of the cerebral physiology for more than almost two centuries. But, molecular neurobiology has now discovered that biochemical transactions play an important role in neuronal computations. Quantum computing (QC) is becoming a reality both from the theoretical point of view as well as from practical applications. Quantum mechanics is the most accurate description at atomic level and it lies behind all chemistry that provides the basis for biology ... maybe the magic of entanglement is also crucial for life. The purpose of the present paper is to discuss the dendrite spine as a quantum computing device, taking into account what is known about the physiology of the glutamate receptors and the cascade of biochemical transactions triggered by the glutamate binding to these receptors. PMID:15488665

  9. Methodological testing: Are fast quantum computers illusions?

    Energy Technology Data Exchange (ETDEWEB)

    Meyer, Steven [Tachyon Design Automation, San Francisco, CA (United States)

    2013-07-01

    Popularity of the idea for computers constructed from the principles of QM started with Feynman's 'Lectures On Computation', but he called the idea crazy and dependent on statistical mechanics. In 1987, Feynman published a paper in 'Quantum Implications - Essays in Honor of David Bohm' on negative probabilities which he said gave him cultural shock. The problem with imagined fast quantum computers (QC) is that speed requires both statistical behavior and truth of the mathematical formalism. The Swedish Royal Academy 2012 Nobel Prize in physics press release touted the discovery of methods to control ''individual quantum systems'', to ''measure and control very fragile quantum states'' which enables ''first steps towards building a new type of super fast computer based on quantum physics.'' A number of examples where widely accepted mathematical descriptions have turned out to be problematic are examined: Problems with the use of Oracles in P=NP computational complexity, Paul Finsler's proof of the continuum hypothesis, and Turing's Enigma code breaking versus William tutte's Colossus. I view QC research as faith in computational oracles with wished for properties. Arther Fine's interpretation in 'The Shaky Game' of Einstein's skepticism toward QM is discussed. If Einstein's reality as space-time curvature is correct, then space-time computers will be the next type of super fast computer.

  10. Neuromorphic quantum computation with energy dissipation

    International Nuclear Information System (INIS)

    Real parallel computing with a quantum computer attracts vast interest due to its extreme high potential. We propose a neuromorphic quantum computation algorithm based on an adiabatic Hamiltonian evolution with energy dissipation. This algorithm can be applied to problems if a cost function can be expressed in a quadratic form. This requirement results from the fact that our Hamiltonian is designed by following a method similar to an artificial neural network (ANN). The state of an ANN is often trapped at local minima, and the network outputs an error. Since the state of a quantum system with the proposed algorithm is always in the ground state according to the adiabatic theorem, it is not necessary to be concerned that the quantum state is trapped at local minima. However, there is no guarantee that a quantum algorithm based on an adiabatic Hamiltonian evolution with degeneration or level crossing is successfully executed. We show successful numerical simulation results with the proposed algorithm by introducing energy dissipation to keep the quantum state staying in the ground state, and then we show an application to the n-queen problem, which is one of the combinatorial optimization problems

  11. Local Search Methods for Quantum Computers

    CERN Document Server

    Hogg, T; Hogg, Tad; Yanik, Mehmet

    1998-01-01

    Local search algorithms use the neighborhood relations among search states and often perform well for a variety of NP-hard combinatorial search problems. This paper shows how quantum computers can also use these neighborhood relations. An example of such a local quantum search is evaluated empirically for the satisfiability (SAT) problem and shown to be particularly effective for highly constrained instances. For problems with an intermediate number of constraints, it is somewhat less effective at exploiting problem structure than incremental quantum methods, in spite of the much smaller search space used by the local method.

  12. Quantum computing without wavefunctions: time-dependent density functional theory for universal quantum computation.

    Science.gov (United States)

    Tempel, David G; Aspuru-Guzik, Alán

    2012-01-01

    We prove that the theorems of TDDFT can be extended to a class of qubit Hamiltonians that are universal for quantum computation. The theorems of TDDFT applied to universal Hamiltonians imply that single-qubit expectation values can be used as the basic variables in quantum computation and information theory, rather than wavefunctions. From a practical standpoint this opens the possibility of approximating observables of interest in quantum computations directly in terms of single-qubit quantities (i.e. as density functionals). Additionally, we also demonstrate that TDDFT provides an exact prescription for simulating universal Hamiltonians with other universal Hamiltonians that have different, and possibly easier-to-realize two-qubit interactions. This establishes the foundations of TDDFT for quantum computation and opens the possibility of developing density functionals for use in quantum algorithms. PMID:22553483

  13. Statistical mechanics of classical and quantum computational complexity

    OpenAIRE

    Laumann, C. R.; Moessner, R.; A. Scardicchio; Sondhi, S. L.

    2010-01-01

    The quest for quantum computers is motivated by their potential for solving problems that defy existing, classical, computers. The theory of computational complexity, one of the crown jewels of computer science, provides a rigorous framework for classifying the hardness of problems according to the computational resources, most notably time, needed to solve them. Its extension to quantum computers allows the relative power of quantum computers to be analyzed. This framework ...

  14. Adiabatic graph-state quantum computation

    International Nuclear Information System (INIS)

    Measurement-based quantum computation (MBQC) and holonomic quantum computation (HQC) are two very different computational methods. The computation in MBQC is driven by adaptive measurements executed in a particular order on a large entangled state. In contrast in HQC the system starts in the ground subspace of a Hamiltonian which is slowly changed such that a transformation occurs within the subspace. Following the approach of Bacon and Flammia, we show that any MBQC on a graph state with generalized flow (gflow) can be converted into an adiabatically driven holonomic computation, which we call adiabatic graph-state quantum computation (AGQC). We then investigate how properties of AGQC relate to the properties of MBQC, such as computational depth. We identify a trade-off that can be made between the number of adiabatic steps in AGQC and the norm of H-dot as well as the degree of H, in analogy to the trade-off between the number of measurements and classical post-processing seen in MBQC. Finally the effects of performing AGQC with orderings that differ from standard MBQC are investigated. (paper)

  15. Generalized GHZ State and Distributed Quantum Computing

    CERN Document Server

    Yimsiriwattana, A

    2004-01-01

    A key problem in quantum computing is finding a viable technological path toward the creation of a scalable quantum computer. One possible approach toward solving part of this problem is distributed computing, which provides an effective way of utilizing a network of limited capacity quantum computers. In this paper, we present two primitive operations, cat-entangler and cat-disentangler, which in turn can be used to implement non-local operations, e.g. non-local CNOT and quantum teleportation. We also show how to establish an entangled pair, and use entangled pairs to efficiently create a generalized GHZ state. Furthermore, we present procedures which allow us to reuse channel qubits in a sequence of non-local operations. These non-local operations work on the principle that a cat-like state, created by cat-entangler, can be used to distribute a control qubit among multiple computers. Using this principle, we show how to efficiently implement non-local control operations in many situation, including a parall...

  16. The viability and performance characterization of nano scale energetic materials on a semiconductor bridge (SCB)

    Science.gov (United States)

    Strohm, Gianna Sophia

    The move from conventional energetic composites to nano scale energetic mixtures (nano energetics) has shown dramatic improvement in energy release rate and sensitivity to ignition. A possible application of nano energetics is on a semiconductor bridge (SCB). An SCB typically requires a tenth of the energy input as compared to a bridge wire design with the same no-fire and is capable of igniting in tens of microseconds. For very low energy applications, SCBs can be manufactured to extremely small sizes and it is necessary to find materials with particle sizes that are even smaller to function. Reactive particles of comparable size to the bridge can lead to problems with ignition reliability for small bridges. Nano-energetic composites and the use of SCBs have been significantly studied individually, however, the process of combining nano energetics with an SCB has not been investigated extensively and is the focus of this work. Goals of this study are to determine if nano energetics can be used with SCBs to further reduce the minimum energy required and improve reliability. The performance of nano-scale aluminum (nAl) and bismuth oxide (Bi2O3) with nitrocellulose (NC), Fluorel(TM) FC 2175 (chemically equivalent to VitonRTM) and Glycidyl Azide Polymer (GAP) as binders where quantified initially using the SenTest(TM) algorithm at three weight fractions (5, 7, and 9%) of binder. The threshold energy was calculated and compared to previous data using conventional materials such as zirconium potassium chlorate (ZPC), mercuric 5-Nitrotetrazol (DXN-1) and titanium sub-hydride potassium per-chlorate (TSPP). It was found that even though there where only slight differences in performance between the binders with nAl/Bi2O 3 at any of the three binder weight fractions, the results show that these nano energetic materials require about half of the threshold energy compared to conventional materials using an SCB with an 84x42 mum bridge. Binder limit testing was conducted to find the critical limit of binder when the output of the SCB declines. The binder was evaluated at 13, 17 and 20% and it was found that the limit amount of binder falls between 17 and 20% by weight of material. Scaling of the SCB bridge was evaluated using a 36x15 mum bridge size and tested using 5, 7 and 9% nAl/Bi2O 3 FC 2175 slurry, creating a functioning SCB compared to previous no-ignition results using TSPP. It was also postulated that the compaction of a secondary material onto the SCB would alter the SCB output during testing. It was found that increased energy values where required for both the 5 and 7% binder amounts and no change was seen at the 9% level.

  17. Robustness and device independence of verifiable blind quantum computing

    OpenAIRE

    Gheorghiu, Alexandru; Kashefi, Elham; Wallden, Petros

    2015-01-01

    Recent advances in theoretical and experimental quantum computing bring us closer to scalable quantum computing devices. This makes the need for protocols that verify the correct functionality of quantum operations timely and has led to the field of quantum verification. In this paper we address key challenges to make quantum verification protocols applicable to experimental implementations. We prove the robustness of the single server verifiable universal blind quantum comp...

  18. Universal Single-Server Blind Quantum Computation for Classical Client

    OpenAIRE

    Xu, Hai-Ru; Wang, Bang-Hai

    2014-01-01

    Blind quantum computation allows a client without enough quantum technologies to delegate her quantum computation to quantum server, while keeping her input, output and algorithm secure. In this paper, we propose a universal single-server and classical-client blind quantum computation protocol based on entanglement swapping technology. In our protocol, the client interface with only one server and the only ability of the client requires is to get particles from trusted cente...

  19. Dominant Strategies in Two Qubit Quantum Computations

    OpenAIRE

    Khan, Faisal Shah

    2014-01-01

    Nash equilibrium is a solution concept in non-strictly competitive, non-cooperative game theory that finds applications in various scientific and engineering disciplines. A non-strictly competitive, non-cooperative game model is presented here for two qubit quantum computations that allows for the characterization of Nash equilibrium in these computations via the inner product of their state space. Nash equilibrium outcomes are optimal under given constraints and therefore o...

  20. Quantum Computing in Non Euclidean Geometry

    CERN Document Server

    Resconi, Germano

    2009-01-01

    The recent debate on hyper-computation has raised new questions both on the computational abilities of quantum systems and the Church-Turing Thesis role in Physics. We propose here the idea of geometry of effective physical process as the essentially physical notion of computation. In Quantum mechanics we cannot use the traditional Euclidean geometry but we introduce more sophisticate non Euclidean geometry which include a new kind of information diffuse in the entire universe and that we can represent as Fisher information or active information. We remark that from the Fisher information we can obtain the Bohm and Hiley quantum potential and the classical Schrodinger equation. We can see the quantum phenomena do not affect a limited region of the space but is reflected in a change of the geometry of all the universe. In conclusion any local physical change or physical process is reflected in all the universe by the change of its geometry, This is the deepest meaning of the entanglement in Quantum mechanics a...

  1. The resource theory of stabilizer quantum computation

    International Nuclear Information System (INIS)

    Recent results on the non-universality of fault-tolerant gate sets underline the critical role of resource states, such as magic states, to power scalable, universal quantum computation. Here we develop a resource theory, analogous to the theory of entanglement, that is relevant for fault-tolerant stabilizer computation. We introduce two quantitative measures—monotones—for the amount of non-stabilizer resource. As an application we give absolute bounds on the efficiency of magic state distillation. One of these monotones is the sum of the negative entries of the discrete Wigner representation of a quantum state, thereby resolving a long-standing open question of whether the degree of negativity in a quasi-probability representation is an operationally meaningful indicator of quantum behavior. (paper)

  2. Semiclassical Fourier transform for quantum computation

    CERN Document Server

    Griffiths, R B; Griffiths, Robert B; Niu, Chi Sheng

    1995-01-01

    Shor's algorithms for factorization and discrete logarithms on a quantum computer employ Fourier transforms preceding a final measurement. It is shown that such a Fourier transform can be carried out in a semi-classical way in which a ``classical'' (macroscopic) signal resulting from the measurement of one bit (embodied in a two-state quantum system) is employed to determine the type of measurement carried out on the next bit, and so forth. In this way the two-bit gates in the Fourier transform can all be replaced by a smaller number of one-bit gates controlled by classical signals. Success in simplifying the Fourier transform suggests that it may be worthwhile looking for other ways of using semi-classical methods in quantum computing.

  3. Efficient quantum computing with weak measurements

    International Nuclear Information System (INIS)

    Projective measurements with high quantum efficiency are often assumed to be required for efficient circuit-based quantum computing. We argue that this is not the case and show that the fact that they are not required was actually known previously but was not deeply explored. We examine this issue by giving an example of how to perform the quantum-ordering-finding algorithm efficiently using non-local weak measurements considering that the measurements used are of bounded weakness and some fixed but arbitrary probability of success less than unity is required. We also show that it is possible to perform the same computation with only local weak measurements, but this must necessarily introduce an exponential overhead.

  4. Computer animations of quantum field theory

    International Nuclear Information System (INIS)

    A visualization mehtod for quantum field theories based on the transfer matrix formalism is presented. It generates computer animations simulating the time evolution of complex physical systems subject to local Hamiltonians. The method may be used as a means of gaining insight to theories such as QCD, and as an educational tool in explaining high-energy physics. (orig.)

  5. The quantum computer game: citizen science

    Science.gov (United States)

    Damgaard, Sidse; Mřlmer, Klaus; Sherson, Jacob

    2013-05-01

    Progress in the field of quantum computation is hampered by daunting technical challenges. Here we present an alternative approach to solving these by enlisting the aid of computer players around the world. We have previously examined a quantum computation architecture involving ultracold atoms in optical lattices and strongly focused tweezers of light. In The Quantum Computer Game (see http://www.scienceathome.org/), we have encapsulated the time-dependent Schrödinger equation for the problem in a graphical user interface allowing for easy user input. Players can then search the parameter space with real-time graphical feedback in a game context with a global high-score that rewards short gate times and robustness to experimental errors. The game which is still in a demo version has so far been tried by several hundred players. Extensions of the approach to other models such as Gross-Pitaevskii and Bose-Hubbard are currently under development. The game has also been incorporated into science education at high-school and university level as an alternative method for teaching quantum mechanics. Initial quantitative evaluation results are very positive. AU Ideas Center for Community Driven Research, CODER.

  6. Adiabatic Quantum Computation and Deutsch's Algorithm

    OpenAIRE

    Das, Saurya; Kobes, Randy; Kunstatter, Gabor

    2001-01-01

    We show that by a suitable choice of a time dependent Hamiltonian, Deutsch's algorithm can be implemented by an adiabatic quantum computer. We extend our analysis to the Deutsch-Jozsa problem and estimate the required running time for both global and local adiabatic evolutions.

  7. Simulations of Probabilities for Quantum Computing

    Science.gov (United States)

    Zak, M.

    1996-01-01

    It has been demonstrated that classical probabilities, and in particular, probabilistic Turing machine, can be simulated by combining chaos and non-LIpschitz dynamics, without utilization of any man-made devices (such as random number generators). Self-organizing properties of systems coupling simulated and calculated probabilities and their link to quantum computations are discussed.

  8. Quantum computer games: Schrödinger cat and hounds

    Science.gov (United States)

    Gordon, Michal; Gordon, Goren

    2012-05-01

    The quantum computer game 'Schrödinger cat and hounds' is the quantum extension of the well-known classical game fox and hounds. Its main objective is to teach the unique concepts of quantum mechanics in a fun way. 'Schrödinger cat and hounds' demonstrates the effects of superposition, destructive and constructive interference, measurements and entanglement. More advanced concepts, like particle-wave duality and decoherence, can also be taught using the game as a model. The game that has an optimal solution in the classical version, can have many different solutions and a new balance of powers in the quantum world. Game-aided lectures were given to high-school students which showed that it is a valid and entertaining teaching platform.

  9. Temporal resources for global quantum computing architectures

    Scientific Electronic Library Online (English)

    Juan D., Jaramillo; John H., Reina.

    2008-12-01

    Full Text Available Using the methods for optimal simulation of quantum logic gates, we perform a quantitative estimation of the time resources involved in the execution of universal gate sets for the case of three representative models of quantum computation based on global control. The importance of such models stems [...] from the solution to the problem of experimentally addressing and locally manipulating the qubits in a given quantum register. The numerical estimation of the temporal efficiency for each model is performed by assuming that the qubits in the register can be coupled to each other via the Ising and the Förster interactions. Finally, we discuss the feasibility of the physical realization of such architectures under quantum error correction conditions.

  10. Quantum computing implementations with neutral particles

    DEFF Research Database (Denmark)

    Negretti, Antonio; Treutlein, Philipp

    2011-01-01

    We review quantum information processing with cold neutral particles, that is, atoms or polar molecules. First, we analyze the best suited degrees of freedom of these particles for storing quantum information, and then we discuss both single- and two-qubit gate implementations. We focus our discussion mainly on collisional quantum gates, which are best suited for atom-chip-like devices, as well as on gate proposals conceived for optical lattices. Additionally, we analyze schemes both for cold atoms confined in optical cavities and hybrid approaches to entanglement generation, and we show how optimal control theory might be a powerful tool to enhance the speed up of the gate operations as well as to achieve high fidelities required for fault tolerant quantum computation.

  11. A surface code quantum computer in silicon

    Science.gov (United States)

    Hill, Charles D.; Peretz, Eldad; Hile, Samuel J.; House, Matthew G.; Fuechsle, Martin; Rogge, Sven; Simmons, Michelle Y.; Hollenberg, Lloyd C. L.

    2015-01-01

    The exceptionally long quantum coherence times of phosphorus donor nuclear spin qubits in silicon, coupled with the proven scalability of silicon-based nano-electronics, make them attractive candidates for large-scale quantum computing. However, the high threshold of topological quantum error correction can only be captured in a two-dimensional array of qubits operating synchronously and in parallel—posing formidable fabrication and control challenges. We present an architecture that addresses these problems through a novel shared-control paradigm that is particularly suited to the natural uniformity of the phosphorus donor nuclear spin qubit states and electronic confinement. The architecture comprises a two-dimensional lattice of donor qubits sandwiched between two vertically separated control layers forming a mutually perpendicular crisscross gate array. Shared-control lines facilitate loading/unloading of single electrons to specific donors, thereby activating multiple qubits in parallel across the array on which the required operations for surface code quantum error correction are carried out by global spin control. The complexities of independent qubit control, wave function engineering, and ad hoc quantum interconnects are explicitly avoided. With many of the basic elements of fabrication and control based on demonstrated techniques and with simulated quantum operation below the surface code error threshold, the architecture represents a new pathway for large-scale quantum information processing in silicon and potentially in other qubit systems where uniformity can be exploited. PMID:26601310

  12. A surface code quantum computer in silicon.

    Science.gov (United States)

    Hill, Charles D; Peretz, Eldad; Hile, Samuel J; House, Matthew G; Fuechsle, Martin; Rogge, Sven; Simmons, Michelle Y; Hollenberg, Lloyd C L

    2015-10-01

    The exceptionally long quantum coherence times of phosphorus donor nuclear spin qubits in silicon, coupled with the proven scalability of silicon-based nano-electronics, make them attractive candidates for large-scale quantum computing. However, the high threshold of topological quantum error correction can only be captured in a two-dimensional array of qubits operating synchronously and in parallel-posing formidable fabrication and control challenges. We present an architecture that addresses these problems through a novel shared-control paradigm that is particularly suited to the natural uniformity of the phosphorus donor nuclear spin qubit states and electronic confinement. The architecture comprises a two-dimensional lattice of donor qubits sandwiched between two vertically separated control layers forming a mutually perpendicular crisscross gate array. Shared-control lines facilitate loading/unloading of single electrons to specific donors, thereby activating multiple qubits in parallel across the array on which the required operations for surface code quantum error correction are carried out by global spin control. The complexities of independent qubit control, wave function engineering, and ad hoc quantum interconnects are explicitly avoided. With many of the basic elements of fabrication and control based on demonstrated techniques and with simulated quantum operation below the surface code error threshold, the architecture represents a new pathway for large-scale quantum information processing in silicon and potentially in other qubit systems where uniformity can be exploited. PMID:26601310

  13. Quantum Annealing and Computation: A Brief Documentary Note

    OpenAIRE

    Ghosh, Asim; Mukherjee, Sudip

    2013-01-01

    Major breakthrough in quantum computation has recently been achieved using quantum annealing to develop analog quantum computers instead of gate based computers. After a short introduction to quantum computation, we retrace very briefly the history of these developments and discuss the Indian researches in this connection and provide some interesting documents (in the Figs.) obtained from a chosen set of high impact papers (and also some recent news etc. blogs appearing in t...

  14. A repeat-until-success quantum computing scheme

    Energy Technology Data Exchange (ETDEWEB)

    Beige, A [School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom); Lim, Y L [DSO National Laboratories, 20 Science Park Drive, Singapore 118230, Singapore (Singapore); Kwek, L C [Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore (Singapore)

    2007-06-15

    Recently we proposed a hybrid architecture for quantum computing based on stationary and flying qubits: the repeat-until-success (RUS) quantum computing scheme. The scheme is largely implementation independent. Despite the incompleteness theorem for optical Bell-state measurements in any linear optics set-up, it allows for the implementation of a deterministic entangling gate between distant qubits. Here we review this distributed quantum computation scheme, which is ideally suited for integrated quantum computation and communication purposes.

  15. Quantum Computers: A New Paradigm in Information Technology

    Directory of Open Access Journals (Sweden)

    Mahesh S. Raisinghani

    2001-01-01

    Full Text Available The word 'quantum' comes from the Latin word quantus meaning 'how much'. Quantum computing is a fundamentally new mode of information processing that can be performed only by harnessing physical phenomena unique to quantum mechanics (especially quantum interference. Paul Benioff of the Argonne National Laboratory first applied quantum theory to computers in 1981 and David Deutsch of Oxford proposed quantum parallel computers in 1985, years before the realization of qubits in 1995. However, it may be well into the 21st century before we see quantum computing used at a commercial level for a variety of reasons discussed in this paper. The subject of quantum computing brings together ideas from classical information theory, computer science, and quantum physics. This paper discusses some of the current advances, applications, and chal-lenges of quantum computing as well as its impact on corporate computing and implications for management. It shows how quantum computing can be utilized to process and store information, as well as impact cryptography for perfectly secure communication, algorithmic searching, factorizing large numbers very rapidly, and simulating quantum-mechanical systems efficiently. A broad interdisciplinary effort will be needed if quantum com-puters are to fulfill their destiny as the world's fastest computing devices.

  16. Deterministic quantum computation with one photonic qubit

    Science.gov (United States)

    Hor-Meyll, M.; Tasca, D. S.; Walborn, S. P.; Ribeiro, P. H. Souto; Santos, M. M.; Duzzioni, E. I.

    2015-07-01

    We show that deterministic quantum computing with one qubit (DQC1) can be experimentally implemented with a spatial light modulator, using the polarization and the transverse spatial degrees of freedom of light. The scheme allows the computation of the trace of a high-dimension matrix, being limited by the resolution of the modulator panel and the technical imperfections. In order to illustrate the method, we compute the normalized trace of unitary matrices and implement the Deutsch-Jozsa algorithm. The largest matrix that can be manipulated with our setup is 1080 ×1920 , which is able to represent a system with approximately 21 qubits.

  17. Design constraints for nanometer scale quantum computers

    CERN Document Server

    Mainieri, R

    1994-01-01

    Nanometer scale electronics present a challenge for the computer architect. These quantum devices have small gain and are difficult to interconnect. I have analyzed current device capabilities and explored two general design requirements for the design of computers: error correction and long range connections. These two principles follow when Turing machines are implemented as integrated circuits. I consider the roles of electromigration through thin wires, circuit layout, and error rates for devices with small gain. The analysis brings into sharp focus the future of nanocomputers and suggests solutions to some of its difficulties. It gives a theoretical model for a nanocomputer, separating the roles of devices and algorithms. Within the model one can implement a stochastic computer, which operates despite quantum device limitations.

  18. An Introduction to Quantum Computing for Non-Physicists

    CERN Document Server

    Rieffel, E G; Rieffel, Eleanor G.; Polak, Wolfgang

    1998-01-01

    Richard Feynman's observation that quantum mechanical effects could not be simulated efficiently on a computer led to speculation that computation in general could be done more efficiently if it used quantum effects. This speculation appeared justified when Peter Shor described a polynomial time quantum algorithm for factoring integers. In quantum systems, the computational space increases exponentially with the size of the system which enables exponential parallelism. This parallelism could lead to exponentially faster quantum algorithms than possible classically. The catch is that accessing the results, which requires measurement, proves tricky and requires new non-traditional programming techniques. The aim of this paper is to guide computer scientists and other non-physicists through the conceptual and notational barriers that separate quantum computing from conventional computing. We introduce basic principles of quantum mechanics to explain where the power of quantum computers comes from and why it is d...

  19. Quantum Computing: Theoretical versus Practical Possibility

    CERN Document Server

    Paraoanu, G S

    2011-01-01

    An intense effort is being made today to build a quantum computer. Instead of presenting what has been achieved, I invoke here analogies from the history of science in an attempt to glimpse what the future might hold. Quantum computing is possible in principle - there are no known laws of Nature that prevent it - yet scaling up the few qubits demonstrated so far has proven to be exceedingly difficult. While this could be regarded merely as a technological or practical impediment, I argue that this difficulty might be a symptom of new laws of physics waiting to be discovered. I also introduce a distinction between "strong" and "weak" emergentist positions. The former assumes that a critical value of a parameter exists (one that is most likely related to the complexity of the states involved) at which the quantum-mechanical description breaks down, in other words, that quantum mechanics will turn out to be an incomplete description of reality. The latter assumes that quantum mechanics will remain as a universal...

  20. NMR spectra simulation for quantum computing

    International Nuclear Information System (INIS)

    Full text: Pulse NMR is one of the most serious candidates as an experimental technique for implementing quantum algorithms. To the present date, this technique is in fact the only one where full demonstrations of quantum algorithms implementations have been carried out, in spite of various technical difficulties. On NMR quantum computers, gates and subroutines are encoded as radiofrequency pulse sequences. A 'program output' is read directly on the measured spectra. On this work we simulate NMR spectra and show their evolution during algorithms implementations for two and three qubits systems. We will focus on Grover search, Quantum Fourier Transform, Shor factorization and Teleportation algorithms. Calculated spectra are compared to experimental data extracted from the literature. The main difficulties associated to the use of NMR to quantum computing, such as the exponential decrease of the signal upon increasing the number of qubits could, in principle, be partially removed by using ferromagnetic materials. However, broad NMR linewidths in these materials can mask logical operation. Some simulations are also presented to illustrate this point. (author)

  1. Interactive Quantum Mechanics Quantum Experiments on the Computer

    CERN Document Server

    Brandt, S; Dahmen, H.D

    2011-01-01

    Extra Materials available on extras.springer.com INTERACTIVE QUANTUM MECHANICS allows students to perform their own quantum-physics experiments on their computer, in vivid 3D color graphics. Topics covered include: •        harmonic waves and wave packets, •        free particles as well as bound states and scattering in various potentials in one and three dimensions (both stationary and time dependent), •        two-particle systems, coupled harmonic oscillators, •        distinguishable and indistinguishable particles, •        coherent and squeezed states in time-dependent motion, •        quantized angular momentum, •        spin and magnetic resonance, •        hybridization. For the present edition the physics scope has been widened appreciably. Moreover, INTERQUANTA can now produce user-defined movies of quantum-mechanical situations. Movies can be viewed directly and also be saved to be shown later in any browser. Sections on spec...

  2. Scheme for Quantum Computing Immune to Decoherence

    Science.gov (United States)

    Williams, Colin; Vatan, Farrokh

    2008-01-01

    A constructive scheme has been devised to enable mapping of any quantum computation into a spintronic circuit in which the computation is encoded in a basis that is, in principle, immune to quantum decoherence. The scheme is implemented by an algorithm that utilizes multiple physical spins to encode each logical bit in such a way that collective errors affecting all the physical spins do not disturb the logical bit. The scheme is expected to be of use to experimenters working on spintronic implementations of quantum logic. Spintronic computing devices use quantum-mechanical spins (typically, electron spins) to encode logical bits. Bits thus encoded (denoted qubits) are potentially susceptible to errors caused by noise and decoherence. The traditional model of quantum computation is based partly on the assumption that each qubit is implemented by use of a single two-state quantum system, such as an electron or other spin-1.2 particle. It can be surprisingly difficult to achieve certain gate operations . most notably, those of arbitrary 1-qubit gates . in spintronic hardware according to this model. However, ironically, certain 2-qubit interactions (in particular, spin-spin exchange interactions) can be achieved relatively easily in spintronic hardware. Therefore, it would be fortunate if it were possible to implement any 1-qubit gate by use of a spin-spin exchange interaction. While such a direct representation is not possible, it is possible to achieve an arbitrary 1-qubit gate indirectly by means of a sequence of four spin-spin exchange interactions, which could be implemented by use of four exchange gates. Accordingly, the present scheme provides for mapping any 1-qubit gate in the logical basis into an equivalent sequence of at most four spin-spin exchange interactions in the physical (encoded) basis. The complexity of the mathematical derivation of the scheme from basic quantum principles precludes a description within this article; it must suffice to report that the derivation provides explicit constructions for finding the exchange couplings in the physical basis needed to implement any arbitrary 1-qubit gate. These constructions lead to spintronic encodings of quantum logic that are more efficient than those of a previously published scheme that utilizes a universal but fixed set of gates.

  3. Mathematical optics classical, quantum, and computational methods

    CERN Document Server

    Lakshminarayanan, Vasudevan

    2012-01-01

    Going beyond standard introductory texts, Mathematical Optics: Classical, Quantum, and Computational Methods brings together many new mathematical techniques from optical science and engineering research. Profusely illustrated, the book makes the material accessible to students and newcomers to the field. Divided into six parts, the text presents state-of-the-art mathematical methods and applications in classical optics, quantum optics, and image processing. Part I describes the use of phase space concepts to characterize optical beams and the application of dynamic programming in optical wave

  4. Nonlinear quantum optical computing via measurement

    CERN Document Server

    Hutchinson, G D

    2004-01-01

    We show how the measurement induced model of quantum computation proposed by Raussendorf and Briegel [Phys. Rev. Letts. 86, 5188 (2001)] can be adapted to a nonlinear optical interaction. This optical implementation requires a Kerr nonlinearity, a single photon source, a single photon detector and fast feed forward. Although nondeterministic optical quantum information proposals such as that suggested by KLM [Nature 409, 46 (2001)] do not require a Kerr nonlinearity they do require complex reconfigurable optical networks. The proposal in this paper has the benefit of a single static optical layout with fixed device parameters, where the algorithm is defined by the final measurement procedure.

  5. Accuracy threshold for postselected quantum computation

    CERN Document Server

    Aliferis, Panos; Preskill, John

    2007-01-01

    We prove an accuracy threshold theorem for fault-tolerant quantum computation based on error detection and postselection. Our proof provides a rigorous foundation for the scheme suggested by Knill, in which preparation circuits for ancilla states are protected by a concatenated error-detecting code and the preparation is aborted if an error is detected. The proof applies to independent stochastic noise but (in contrast to proofs of the quantum accuracy threshold theorem based on concatenated error-correcting codes) not to strongly-correlated adversarial noise. Our rigorously established lower bound on the accuracy threshold, 1.04 \\times 10^{-3}, is well below Knill's numerical estimates.

  6. Implementation of Quantum Computing Algorithms on a Nuclear Magnetic Resonance Quantum Computer Based on Polarized Solid 129Xe.

    OpenAIRE

    Belaga, Edward G.; Grucker, Daniel

    2003-01-01

    We briefly summarize here the history, conceptual base, as well as challenges and implications of quantum computing. Then, we present the theoretical requirements for viable quantum computation, as well as thestate-of-the-art experimental approach and a project of solid 129Xe NMR-based quantum computer.

  7. Quantum computation with devices whose contents are never read

    OpenAIRE

    Yakaryilmaz, Abuzer; Freivalds, Rusins; Say, A. C. Cem; Agadzanyan, Ruben

    2010-01-01

    In classical computation, a "write-only memory" (WOM) is little more than an oxymoron, and the addition of WOM to a (deterministic or probabilistic) classical computer brings no advantage. We prove that quantum computers that are augmented with WOM can solve problems that neither a classical computer with WOM nor a quantum computer without WOM can solve, when all other resource bounds are equal. We focus on realtime quantum finite automata, and examine the increase in their ...

  8. Quantum picturalism for topological cluster-state computing

    OpenAIRE

    Horsman, Clare

    2011-01-01

    Topological quantum computing is a way of allowing precise quantum computations to run on noisy and imperfect hardware. One implementation uses surface codes created by forming defects in a highly-entangled cluster state. Such a method of computing is a leading candidate for large-scale quantum computing. However, there has been a lack of sufficiently powerful high-level languages to describe computing in this form without resorting to single-qubit operations, which quickly ...

  9. [Studies on the genome size and structure of Gluconobacter oxydans SCB329].

    Science.gov (United States)

    Lin, W; Yin, G

    2001-10-01

    In the "Two-step fermentation" of Vitamin C synthesis, Gluconobacter oxydans SCB329 is responsible for the production of 2-keto-L-gulonic acid (2-KLG), which is an important precuror of vitamin C synthesis. The intact chromosome was prepared from logarithmic phase cells by agaraseembedded method and was analysized by restriction endonucleases and contour-clamped homogeneous electric field pulsed-field gel electrophoresis (PFGE). Spe I (5-ACTAGT) produced 24 fragments, ranging in size from 10 to 320 kilobases (kb). Xba I (5-TCTAGA) yielded 40 fragments (4 to 200 kb). A total genome size of approximately 2,700 kb was determined by summing the fragment length. Analysis of the entire genome of SCB329 by PFGE revealed that the genome of SCB329 consist of a chromosome which is 2,500 Kb in length and a large plasmid which is 245 kb. After linearization of the DNA by DNase I and S1 nuclease, in contrast with the band which can not be viewed, the band of chromosome and plasmid were appeared, this suggest that structure of the chromosome and the plasmid were circular. PMID:12552798

  10. Quantum linear network coding as one-way quantum computation

    OpenAIRE

    de Beaudrap, Niel; Roetteler, Martin

    2014-01-01

    Network coding is a technique to maximize communication rates within a network, in communication protocols for simultaneous multi-party transmission of information. Linear network codes are examples of such protocols in which the local computations performed at the nodes in the network are limited to linear transformations of their input data (represented as elements of a ring, such as the integers modulo 2). The quantum linear network coding protocols of Kobayashi et al [ar...

  11. Strictly contractive quantum channels and physically realizable quantum computers

    OpenAIRE

    Raginsky, Maxim

    2001-01-01

    We study the robustness of quantum computers under the influence of errors modelled by strictly contractive channels. A channel $T$ is defined to be strictly contractive if, for any pair of density operators $\\rho,\\sigma$ in its domain, $\\| T\\rho - T\\sigma \\|_1 \\le k \\| \\rho-\\sigma \\|_1$ for some $0 \\le k < 1$ (here $\\| \\cdot \\|_1$ denotes the trace norm). In other words, strictly contractive channels render the states of the computer less distinguishable in the sense of qua...

  12. Multi-photon entanglement: from quantum curiosity to quantum computing and quantum repeaters

    Science.gov (United States)

    Walther, P.; Eisaman, M. D.; Nemiroski, A.; Gorshkov, A. V.; Zibrov, A. S.; Zeilinger, A.; Lukin, M. D.

    2007-08-01

    In the emerging field of quantum information technology the two basic subfields are quantum communication and quantum computation. Photonic qubits are considered as most promising information carriers for this new technology due to the immense advantage of suffering negligible decoherence. Additionally, the very small photon-photon interactions can be replaced by inducing effective nonlinearities via measurements which allow for the implementation of crucial two-qubit gate operations. Although the spontaneous parametric down-conversion gives access to the generation of highly entangled few-photon states, such as four-qubit cluster states which allow to demonstrate the new concept of the one-way quantum computer, its applicability is highly limited due to the poor scaling of the simultaneous emission of more than one-entangled photon pair. Therefore of particular interest is the reversible mapping of qubits from photon states to atomic states. This might allow the implementation of photonic quantum repeaters for long-distance quantum communication or the generation of arbitrary multi-photon states as required for linear-optics quantum computing. Thus for the realization of such a quantum network several approaches for achieving the required quantum control between matter and photons have been studied during the past few years. Recent experiments demonstrating the generation of narrow-bandwidth single photons using a room-temperature ensemble of 87Rb atoms and electromagnetically induced transparency should emphasize the progress towards such a quantum network.

  13. Dynamical description of quantum computing: Generic nonlocality of quantum noise

    International Nuclear Information System (INIS)

    We develop a dynamical non-Markovian description of quantum computing in the weak-coupling limit, in the lowest-order approximation. We show that the long-range memory of the quantum reservoir (such as the 1/t4 one exhibited by electromagnetic vacuum) produces a strong interrelation between the structure of noise and the quantum algorithm, implying nonlocal attacks of noise. This shows that the implicit assumption of quantum error correction theory--independence of noise and self-dynamics--fails in long time regimes. We also use our approach to present pure decoherence and decoherence accompanied by dissipation in terms of the spectral density of the reservoir. The so-called dynamical decoupling method is discussed in this context. Finally, we propose a minimal decoherence model, in which the only source of decoherence is vacuum. We optimize the fidelity of quantum-information processing under the trade-off between the speed of the gate and the strength of decoherence

  14. Non-unitary probabilistic quantum computing circuit and method

    Science.gov (United States)

    Williams, Colin P. (Inventor); Gingrich, Robert M. (Inventor)

    2009-01-01

    A quantum circuit performing quantum computation in a quantum computer. A chosen transformation of an initial n-qubit state is probabilistically obtained. The circuit comprises a unitary quantum operator obtained from a non-unitary quantum operator, operating on an n-qubit state and an ancilla state. When operation on the ancilla state provides a success condition, computation is stopped. When operation on the ancilla state provides a failure condition, computation is performed again on the ancilla state and the n-qubit state obtained in the previous computation, until a success condition is obtained.

  15. Quantum computation with nuclear spins in quantum dots

    International Nuclear Information System (INIS)

    The role of nuclear spins for quantum information processing in quantum dots is theoretically investigated in this thesis. Building on the established fact that the most strongly coupled environment for the potential electron spin quantum bit are the surrounding lattice nuclear spins interacting via the hyperfine interaction, we turn this vice into a virtue by designing schemes for harnessing this strong coupling. In this perspective, the ensemble of nuclear spins can be considered an asset, suitable for an active role in quantum information processing due to its intrinsic long coherence times. We present experimentally feasible protocols for the polarization, i.e. initialization, of the nuclear spins and a quantitative solution to our derived master equation. The polarization limiting destructive interference effects, caused by the collective nature of the nuclear coupling to the electron spin, are studied in detail. Efficient ways of mitigating these constraints are presented, demonstrating that highly polarized nuclear ensembles in quantum dots are feasible. At high, but not perfect, polarization of the nuclei the evolution of an electron spin in contact with the spin bath can be efficiently studied by means of a truncation of the Hilbert space. It is shown that the electron spin can function as a mediator of universal quantum gates for collective nuclear spin qubits, yielding a promising architecture for quantum information processing. Furthermore, we show that at high polarization the hyperfine interaction of electron and nuclear spins resembles the celebrated Jaynes-Cummings model of quantum optics. This result opens the door for transfer of knowledge from the mature field of quantum computation with atoms and photons. Additionally, tailored specifically for the quantum dot environment, we propose a novel scheme for the generation of highly squeezed collective nuclear states. Finally we demonstrate that even an unprepared completely mixed nuclear spin ensemble can be utilized for the important task of sequentially generating entanglement between electrons. This is true despite the fact that electrons and nuclei become only very weakly entangled through the hyperfine interaction. Straightforward experimentally feasible protocols for the generation of multipartite entangled (GHZ- and W-)states are presented. (orig.)

  16. Quantum computation with nuclear spins in quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Christ, H.

    2008-01-24

    The role of nuclear spins for quantum information processing in quantum dots is theoretically investigated in this thesis. Building on the established fact that the most strongly coupled environment for the potential electron spin quantum bit are the surrounding lattice nuclear spins interacting via the hyperfine interaction, we turn this vice into a virtue by designing schemes for harnessing this strong coupling. In this perspective, the ensemble of nuclear spins can be considered an asset, suitable for an active role in quantum information processing due to its intrinsic long coherence times. We present experimentally feasible protocols for the polarization, i.e. initialization, of the nuclear spins and a quantitative solution to our derived master equation. The polarization limiting destructive interference effects, caused by the collective nature of the nuclear coupling to the electron spin, are studied in detail. Efficient ways of mitigating these constraints are presented, demonstrating that highly polarized nuclear ensembles in quantum dots are feasible. At high, but not perfect, polarization of the nuclei the evolution of an electron spin in contact with the spin bath can be efficiently studied by means of a truncation of the Hilbert space. It is shown that the electron spin can function as a mediator of universal quantum gates for collective nuclear spin qubits, yielding a promising architecture for quantum information processing. Furthermore, we show that at high polarization the hyperfine interaction of electron and nuclear spins resembles the celebrated Jaynes-Cummings model of quantum optics. This result opens the door for transfer of knowledge from the mature field of quantum computation with atoms and photons. Additionally, tailored specifically for the quantum dot environment, we propose a novel scheme for the generation of highly squeezed collective nuclear states. Finally we demonstrate that even an unprepared completely mixed nuclear spin ensemble can be utilized for the important task of sequentially generating entanglement between electrons. This is true despite the fact that electrons and nuclei become only very weakly entangled through the hyperfine interaction. Straightforward experimentally feasible protocols for the generation of multipartite entangled (GHZ- and W-)states are presented. (orig.)

  17. Efficiency of open quantum walk implementation of dissipative quantum computing algorithms

    OpenAIRE

    Sinayskiy, I.; F. Petruccione

    2014-01-01

    An open quantum walk formalism for dissipative quantum computing is presented. The approach is illustrated with the examples of the Toffoli gate and the Quantum Fourier Transform for 3 and 4 qubits. It is shown that the algorithms based on the open quantum walk formalism are more efficient than the canonical dissipative quantum computing approach. In particular, the open quantum walks can be designed to converge faster to the desired steady state and to increase the probabil...

  18. A Rosetta Stone for Quantum Mechanics with an Introduction to Quantum Computation

    OpenAIRE

    Lomonaco, Samuel J.; jr.

    2000-01-01

    The purpose of these lecture notes is to provide readers, who have some mathematical background but little or no exposure to quantum mechanics and quantum computation, with enough material to begin reading the research literature in quantum computation and quantum information theory. This paper is a written version of the first of eight one hour lectures given in the American Mathematical Society (AMS) Short Course on Quantum Computation held in conjunction with the Annual M...

  19. Q#, a quantum computation package for the .NET platform

    OpenAIRE

    A.S. Tolba; Rashad, M Z; M. A. El-Dosuky

    2013-01-01

    Quantum computing is a promising approach of computation that is based on equations from Quantum Mechanics. A simulator for quantum algorithms must be capable of performing heavy mathematical matrix transforms. The design of the simulator itself takes one of three forms: Quantum Turing Machine, Network Model or circuit model of connected gates or, Quantum Programming Language, yet, some simulators are hybrid. We studied previous simulators and then we adopt features from thr...

  20. An Introduction to Quantum Computing for Non-Physicists

    OpenAIRE

    Rieffel, Eleanor G.; Polak, Wolfgang

    1998-01-01

    Richard Feynman's observation that quantum mechanical effects could not be simulated efficiently on a computer led to speculation that computation in general could be done more efficiently if it used quantum effects. This speculation appeared justified when Peter Shor described a polynomial time quantum algorithm for factoring integers. In quantum systems, the computational space increases exponentially with the size of the system which enables exponential parallelism. Thi...

  1. Adiabatic Quantum Computation with Neutral Atoms

    Science.gov (United States)

    Biedermann, Grant

    2013-03-01

    We are implementing a new platform for adiabatic quantum computation (AQC)[2] based on trapped neutral atoms whose coupling is mediated by the dipole-dipole interactions of Rydberg states. Ground state cesium atoms are dressed by laser fields in a manner conditional on the Rydberg blockade mechanism,[3,4] thereby providing the requisite entangling interactions. As a benchmark we study a Quadratic Unconstrained Binary Optimization (QUBO) problem whose solution is found in the ground state spin configuration of an Ising-like model. In collaboration with Lambert Parazzoli, Sandia National Laboratories; Aaron Hankin, Center for Quantum Information and Control (CQuIC), University of New Mexico; James Chin-Wen Chou, Yuan-Yu Jau, Peter Schwindt, Cort Johnson, and George Burns, Sandia National Laboratories; Tyler Keating, Krittika Goyal, and Ivan Deutsch, Center for Quantum Information and Control (CQuIC), University of New Mexico; and Andrew Landahl, Sandia National Laboratories. We are implementing a new platform for adiabatic quantum computation (AQC)[2] based on trapped neutral atoms whose coupling is mediated by the dipole-dipole interactions of Rydberg states. Ground state cesium atoms are dressed by laser fields in a manner conditional on the Rydberg blockade mechanism,[3,4] thereby providing the requisite entangling interactions. As a benchmark we study a Quadratic Unconstrained Binary Optimization (QUBO) problem whose solution is found in the ground state spin configuration of an Ising-like model. In collaboration with Lambert Parazzoli, Sandia National Laboratories; Aaron Hankin, Center for Quantum Information and Control (CQuIC), University of New Mexico; James Chin-Wen Chou, Yuan-Yu Jau, Peter Schwindt, Cort Johnson, and George Burns, Sandia National Laboratories; Tyler Keating, Krittika Goyal, and Ivan Deutsch, Center for Quantum Information and Control (CQuIC), University of New Mexico; and Andrew Landahl, Sandia National Laboratories. This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories

  2. Quantum computation and Biological stress: A Hypothesis

    Directory of Open Access Journals (Sweden)

    Grover Monendra

    2014-04-01

    Full Text Available We propose that biological systems may behave as quantum computers.We have earlier hypothesized that patterns of quantum computation may be altered in stress and this leads to the change in the consciousness vector of biological systems. We further propose in this paper that the biological systems with a sufficient consciousness vector behave as objects which are entangled with the universal consciousness and as a consequence wormholes exist between the universal consciousness and the biological systems.The decrease in the consciousness vector of the biological systemsdue to stress(abiotic and/or bioticleads to disruption of wormholes between biological systems and the universal consciousness. This leads to appearance of the stress symptoms in the biological systems. However the application of pesticides/fertilisers or introduction of novel proteins through genetic engineering leads torestoration of wormholes and increase in consciousness vector of the biological systemsand in turn results in to alleviation of stress symptoms.

  3. Quantum computation architecture using optical tweezers

    DEFF Research Database (Denmark)

    Weitenberg, Christof; Kuhr, Stefan

    2011-01-01

    We present a complete architecture for scalable quantum computation with ultracold atoms in optical lattices using optical tweezers focused to the size of a lattice spacing. We discuss three different two-qubit gates based on local collisional interactions. The gates between arbitrary qubits require the transport of atoms to neighboring sites. We numerically optimize the nonadiabatic transport of the atoms through the lattice and the intensity ramps of the optical tweezer in order to maximize the gate fidelities. We find overall gate times of a few 100 ?s, while keeping the error probability due to vibrational excitations and spontaneous scattering below 10?3. The requirements on the positioning error and intensity noise of the optical tweezer and the magnetic field stability are analyzed and we show that atoms in optical lattices could meet the requirements for fault-tolerant scalable quantum computing.

  4. Dual-code quantum computation model

    Science.gov (United States)

    Choi, Byung-Soo

    2015-08-01

    In this work, we propose the dual-code quantum computation model—a fault-tolerant quantum computation scheme which alternates between two different quantum error-correction codes. Since the chosen two codes have different sets of transversal gates, we can implement a universal set of gates transversally, thereby reducing the overall cost. We use code teleportation to convert between quantum states in different codes. The overall cost is decreased if code teleportation requires fewer resources than the fault-tolerant implementation of the non-transversal gate in a specific code. To analyze the cost reduction, we investigate two cases with different base codes, namely the Steane and Bacon-Shor codes. For the Steane code, neither the proposed dual-code model nor another variation of it achieves any cost reduction since the conventional approach is simple. For the Bacon-Shor code, the three proposed variations of the dual-code model reduce the overall cost. However, as the encoding level increases, the cost reduction decreases and becomes negative. Therefore, the proposed dual-code model is advantageous only when the encoding level is low and the cost of the non-transversal gate is relatively high.

  5. Cluster state quantum computing in optical fibers

    OpenAIRE

    Soudagar, Yasaman; Bussieres, Felix; Berlin, Guido; Lacroix, Suzanne; Fernandez, Jose M.; Godbout, Nicolas

    2006-01-01

    A scheme for the implementation of the cluster state model of quantum computing in optical fibers, which enables the feedforward feature, is proposed. This scheme uses the time-bin encoding of qubits. Following previously suggested methods of applying arbitrary one-qubit gates in optical fibers, two different ways for the realization of fusion gate types I and II for cluster production are proposed: a fully time-bin based encoding scheme and a combination of time-bin and pol...

  6. Nuclear spin quantum computing with trapped ions

    CERN Document Server

    Wang, Kunling; Feng, Mang; Mintert, Florian; Wunderlich, Christof

    2011-01-01

    Quantum computing with qubits encoded in nuclear spins of trapped ions is studied with particular attention to the Yb$^+$ ion. For this purpose we consider the Paschen-Back regime (strong magnetic field) and employ a high-field approximation in this treatment. An efficient scheme is proposed to carry out gate operations on an array of trapped ions, and the feasibility of generating the required high magnetic field is discussed.

  7. Holonomic quantum computing with cat-codes

    OpenAIRE

    Albert, Victor V.; Krastanov, Stefan; Shen, Chao; Liu, Ren-Bao; Schoelkopf, Robert J.; Mirrahimi, Mazyar; Devoret, Michel H.; Jiang, Liang

    2015-01-01

    Universal quantum computation on a space consisting of superpositions of $d$ well-separated coherent states can be achieved by two families of adiabatic holonomic gates. The first gate consists of moving a coherent state around a closed path in phase space, resulting in a relative Berry phase between that state and the other states. The second gate consists of colliding two coherent states, resulting in coherent population transfer between them. Such gates should be realizab...

  8. Optimization strategies in measurement based quantum computation

    OpenAIRE

    Ferrini, Giulia; Roslund, Jonathan; Arzani, Francesco; Cai, Yin; Fabre, Claude; Treps, Nicolas

    2014-01-01

    This work introduces optimization strategies to continuous variable measurement based quantum computation (MBQC) at different levels. We provide a recipe for mitigating the effects of finite squeezing, which affect the production of cluster states and the result of a traditional MBQC. These strategies are readily implementable by several experimental groups. Furthermore, a more general scheme for MBQC is introduced that does not necessarily rely on the use of ancillary clust...

  9. Brain-Computer Interfaces and Quantum Robots

    OpenAIRE

    Pessa, Eliano; zizzi, Paola

    2009-01-01

    The actual (classical) Brain-Computer Interface attempts to use brain signals to drive suitable actuators performing the actions corresponding to subject's intention. However this goal is not fully reached, and when BCI works, it does only in particular situations. The reason of this unsatisfactory result is that intention cannot be conceived simply as a set of classical input-output relationships. It is therefore necessary to resort to quantum theory, allowing the occurrenc...

  10. Quantum computation architecture using optical tweezers

    DEFF Research Database (Denmark)

    Weitenberg, Christof; Kuhr, Stefan; Mřlmer, Klaus; Sherson, Jacob

    2011-01-01

    We present a complete architecture for scalable quantum computation with ultracold atoms in optical lattices using optical tweezers focused to the size of a lattice spacing. We discuss three different two-qubit gates based on local collisional interactions. The gates between arbitrary qubits require the transport of atoms to neighboring sites. We numerically optimize the nonadiabatic transport of the atoms through the lattice and the intensity ramps of the optical tweezer in order to maximize th...

  11. Quantum computing of molecular magnet Mn$_{12}$

    OpenAIRE

    Zhou, B.; R. Tao; Liang, JQ; Shen, SQ

    2002-01-01

    Quantum computation in molecular magnets is studied by solving the time-dependent Schrödinger equation numerically. Following Leuenberger and Loss [Nature (London) 410, 789 (2001)], an external alternating magnetic field is applied to populate and manipulate a superposition of single-spin states in molecular magnet Mn12. The conditions to realize parallel recording and reading databases of Grover algorithms in molecular magnets are discussed in detail. It is found that an accurate time durati...

  12. Universal quantum computation with metaplectic anyons

    International Nuclear Information System (INIS)

    We show that braidings of the metaplectic anyons X? in SO(3)2 = SU(2)4 with their total charge equal to the metaplectic mode Y supplemented with projective measurements of the total charge of two metaplectic anyons are universal for quantum computation. We conjecture that similar universal anyonic computing models can be constructed for all metaplectic anyon systems SO(p)2 for any odd prime p ? 5. In order to prove universality, we find new conceptually appealing universal gate sets for qutrits and qupits

  13. A Rosetta Stone for Quantum Mechanics with an Introduction to Quantum Computation

    CERN Document Server

    Lomonaco, S J

    2000-01-01

    The purpose of these lecture notes is to provide readers, who have some mathematical background but little or no exposure to quantum mechanics and quantum computation, with enough material to begin reading the research literature in quantum computation and quantum information theory. This paper is a written version of the first of eight one hour lectures given in the American Mathematical Society (AMS) Short Course on Quantum Computation held in conjunction with the Annual Meeting of the AMS in Washington, DC, USA in January 2000, and will appear in the AMS PSAPM volume entitled "Quantum Computation." Part 1 of the paper is an introduction the to the concept of the qubit. Part 2 gives an introduction to quantum mechanics covering such topics as Dirac notation, quantum measurement, Heisenberg uncertainty, Schrodinger's equation, density operators, partial trace, multipartite quantum systems, the Heisenberg versus the Schrodinger picture, quantum entanglement, EPR paradox, quantum entropy. Part 3 gives a brief ...

  14. Photonic Quantum Computation with Waveguide-Linked Optical Cavities and Quantum Dots

    OpenAIRE

    Yamaguchi, Makoto; Asano, Takashi; Sato, Yoshiya; Noda, Susumu

    2011-01-01

    We propose a new scheme for solid-state photonic quantum computation in which trapped photons in optical cavities are taken as a quantum bit. Quantum gates can be realized by coupling the cavities with quantum dots through waveguides. The proposed scheme allows programmable and deterministic gate operations and the system can be scaled up to many quantum bits.

  15. How detrimental is decoherence in adiabatic quantum computation?

    CERN Document Server

    Albash, Tameem

    2015-01-01

    Recent experiments with increasingly larger numbers of qubits have sparked renewed interest in adiabatic quantum computation, and in particular quantum annealing. A central question that is repeatedly asked is whether quantum features of the evolution can survive over the long time-scales used for quantum annealing relative to standard measures of the decoherence time. We reconsider the role of decoherence in adiabatic quantum computation and quantum annealing using the adiabatic quantum master equation formalism. We restrict ourselves to the weak-coupling and singular-coupling limits, which correspond to decoherence in the energy eigenbasis and in the computational basis, respectively. We demonstrate that decoherence in the instantaneous energy eigenbasis does not necessarily detrimentally affect adiabatic quantum computation, and in particular that a short single-qubit $T_2$ time need not imply adverse consequences for the success of the quantum adiabatic algorithm. We further demonstrate that boundary canc...

  16. Applications of computational quantum mechanics

    Science.gov (United States)

    Temel, Burcin

    This original research dissertation is composed of a new numerical technique based on Chebyshev polynomials that is applied on scattering problems, a phenomenological kinetics study for CO oxidation on RuO2 surface, and an experimental study on methanol coupling with doped metal oxide catalysts. Minimum Error Method (MEM), a least-squares minimization method, provides an efficient and accurate alternative to solve systems of ordinary differential equations. Existing methods usually utilize matrix methods which are computationally costful. MEM, which is based on the Chebyshev polynomials as a basis set, uses the recursion relationships and fast Chebyshev transforms which scale as O(N). For large basis set calculations this provides an enormous computational efficiency in the calculations. Chebyshev polynomials are also able to represent non-periodic problems very accurately. We applied MEM on elastic and inelastic scattering problems: it is more efficient and accurate than traditionally used Kohn variational principle, and it also provides the wave function in the interaction region. Phenomenological kinetics (PK) is widely used in industry to predict the optimum conditions for a chemical reaction. PK neglects the fluctuations, assumes no lateral interactions, and considers an ideal mix of reactants. The rate equations are tested by fitting the rate constants to the results of the experiments. Unfortunately, there are numerous examples where a fitted mechanism was later shown to be erroneous. We have undertaken a thorough comparison between the phenomenological equations and the results of kinetic Monte Carlo (KMC) simulations performed on the same system. The PK equations are qualitatively consistent with the KMC results but are quantitatively erroneous as a result of interplays between the adsorption and desorption events. The experimental study on methanol coupling with doped metal oxide catalysts demonstrates the doped metal oxides as a new class of catalysts with novel properties. Doping a metal oxide may alter its intrinsic properties drastically. A catalytically non-active material can be activated by doping. In this study, we showed that pure zirconia (ZrO2) has almost no activity in methanol coupling reaction, whereas when it is doped with aluminum, the doped catalyst produces dimethyl ether (DME), which is valuable as an alternative future energy source.

  17. Scalable quantum computer architecture with coupled donor-quantum dot qubits

    Science.gov (United States)

    Schenkel, Thomas; Lo, Cheuk Chi; Weis, Christoph; Lyon, Stephen; Tyryshkin, Alexei; Bokor, Jeffrey

    2014-08-26

    A quantum bit computing architecture includes a plurality of single spin memory donor atoms embedded in a semiconductor layer, a plurality of quantum dots arranged with the semiconductor layer and aligned with the donor atoms, wherein a first voltage applied across at least one pair of the aligned quantum dot and donor atom controls a donor-quantum dot coupling. A method of performing quantum computing in a scalable architecture quantum computing apparatus includes arranging a pattern of single spin memory donor atoms in a semiconductor layer, forming a plurality of quantum dots arranged with the semiconductor layer and aligned with the donor atoms, applying a first voltage across at least one aligned pair of a quantum dot and donor atom to control a donor-quantum dot coupling, and applying a second voltage between one or more quantum dots to control a Heisenberg exchange J coupling between quantum dots and to cause transport of a single spin polarized electron between quantum dots.

  18. Hybrid hypercomputing: towards a unification of quantum and classical computation

    OpenAIRE

    Horsman, Clare; Munro, William J.

    2009-01-01

    We investigate the computational power and unified resource use of hybrid quantum-classical computations, such as teleportation and measurement-based computing. We introduce a physically causal and local graphical calculus for quantum information theory, which enables high-level intuitive reasoning about quantum information processes. The graphical calculus defines a local information flow in a computation which satisfies conditions for physical causality. We show how quantu...

  19. Towards A Novel Environment For Simulation Of Quantum Computing

    Directory of Open Access Journals (Sweden)

    Joanna Patrzyk

    2015-01-01

    Full Text Available In this paper we analyze existing quantum computer simulation techniquesand their realizations to minimize the impact of the exponentialcomplexity of simulated quantum computations. As a result of thisinvestigation, we propose a quantum computer simulator with an integrateddevelopment environment - QuIDE - supporting development of algorithms forfuture quantum computers. The simulator simplifies building and testingquantum circuits and understand quantum algorithms in an efficient way.The development environment provides  flexibility of source codeedition and ease of graphical building of circuit diagrams.  We alsodescribe and analyze the complexity of algorithms used for simulationand present performance results of the simulator as well as results ofits deployment during university classes.

  20. A 2 rebit gate universal for quantum computing

    OpenAIRE

    Rudolph, Terry; Grover, Lov

    2002-01-01

    We show, within the circuit model, how any quantum computation can be efficiently performed using states with only real amplitudes (a result known within the Quantum Turing Machine model). This allows us to identify a 2-qubit (in fact 2-rebit) gate which is universal for quantum computing, although it cannot be used to perform arbitrary unitary transformations.

  1. An Introduction to Quantum Computing using Cavity QED concepts

    OpenAIRE

    Burell, Zachary

    2012-01-01

    We present a concise but complete conceptual treatment of quantum computing implemented with Cavity Quantum Electrodynamics (CQED. The paper is intended as a brief overview for professionals who are coming over to the field from other areas and who may have not discussed the concepts behind quantum computing during their technical training.

  2. PREFACE: Quantum Information, Communication, Computation and Cryptography

    Science.gov (United States)

    Benatti, F.; Fannes, M.; Floreanini, R.; Petritis, D.

    2007-07-01

    The application of quantum mechanics to information related fields such as communication, computation and cryptography is a fast growing line of research that has been witnessing an outburst of theoretical and experimental results, with possible practical applications. On the one hand, quantum cryptography with its impact on secrecy of transmission is having its first important actual implementations; on the other hand, the recent advances in quantum optics, ion trapping, BEC manipulation, spin and quantum dot technologies allow us to put to direct test a great deal of theoretical ideas and results. These achievements have stimulated a reborn interest in various aspects of quantum mechanics, creating a unique interplay between physics, both theoretical and experimental, mathematics, information theory and computer science. In view of all these developments, it appeared timely to organize a meeting where graduate students and young researchers could be exposed to the fundamentals of the theory, while senior experts could exchange their latest results. The activity was structured as a school followed by a workshop, and took place at The Abdus Salam International Center for Theoretical Physics (ICTP) and The International School for Advanced Studies (SISSA) in Trieste, Italy, from 12-23 June 2006. The meeting was part of the activity of the Joint European Master Curriculum Development Programme in Quantum Information, Communication, Cryptography and Computation, involving the Universities of Cergy-Pontoise (France), Chania (Greece), Leuven (Belgium), Rennes1 (France) and Trieste (Italy). This special issue of Journal of Physics A: Mathematical and Theoretical collects 22 contributions from well known experts who took part in the workshop. They summarize the present day status of the research in the manifold aspects of quantum information. The issue is opened by two review articles, the first by G Adesso and F Illuminati discussing entanglement in continuous variable systems, the second by T Prosen, discussing chaos and complexity in quantum systems. Both topics have theoretical as well as experimental relevance and are likely to witness a fast growing development in the near future. The remaining contributions present more specific and very recent results. They involve the study of the structure of quantum states and their estimation (B Baumgartner et al, C King et al, S Olivares et al, D Petz et al and W van Dam et al), of entanglement generation and its quantification (G Brida et al, F Ciccarello et al, G Costantini et al, O Romero-Isart et al, D Rossini et al, A Serafini et al and D Vitali et al), of randomness related effects on entanglement behaviour (I Akhalwaya et al, O Dahlsten et al and L Viola et al), and of abstract and applied aspects of quantum computation and communication (K Audenart, G M D'Ariano et al, N Datta et al, L C Kwek et al and M Nathanson et al). We would like to express our gratitude to the European Commission, the Abdus Salam ICTP, SISSA and Eurotech SpA (Amaro, Udine, Italy) for financial and/or logistic support. Special thanks also go to the workshop secretary Marina De Comelli, and the secretaries of the Department of Theoretical Physics, University of Trieste, Sabrina Gaspardis and Rosita Glavina for their precious help and assistance.

  3. The Third Life of Quantum Logic: Quantum Logic Inspired by Quantum Computing

    OpenAIRE

    Dunn, J. Michael; Moss, Lawrence S; Wang, Zhenghan

    2013-01-01

    We begin by discussing the history of quantum logic, dividing it into three eras or lives. The first life has to do with Birkhoff and von Neumann's algebraic approach in the 1930's. The second life has to do with attempt to understand quantum logic as logic that began in the late 1950's and blossomed in the 1970's. And the third life has to do with recent developments in quantum logic coming from its connections to quantum computation. We discuss our own work connecting quan...

  4. Quantum Computation and Quantum Information: Are They Related to Quantum Paradoxology?

    CERN Document Server

    Gyftopoulos, E P; Gyftopoulos, Elias P.; Spakovsky, Michael R. von

    2004-01-01

    We review both the Einstein, Podolsky, Rosen (EPR) paper about the completeness of quantum theory, and Schrodinger's responses to the EPR paper. We find that both the EPR paper and Schrodinger's responses, including the cat paradox, are not consistent with the current understanding of quantum theory and thermodynamics. Because both the EPR paper and Schrodinger's responses play a leading role in discussions of the fascinating and promising fields of quantum computation and quantum information, we hope our review will be helpful to researchers in these fields.

  5. Computing the Exit Complexity of Knowledge in Distributed Quantum Computers

    Directory of Open Access Journals (Sweden)

    M.A.Abbas

    2013-01-01

    Full Text Available Distributed Quantum computers abide from the exit complexity of the knowledge. The exit complexity is the accrue of the nodal information needed to clarify the total egress system with deference to a distinguished exit node. The core objective of this paper is to compile an arrogant methodology for assessing the exit complexity of the knowledge in distributed quantum computers. The proposed methodology is based on contouring the knowledge using the unlabeled binary trees, hence building an benchmarked and a computer based model. The proposed methodology dramatizes knowledge autocratically calculates the exit complexity. The methodology consists of several amphitheaters, starting with detecting the baron aspect of the tree of others entitled express knowledge and then measure the volume of information and the complexity of behavior destining from the bargain of information. Then calculate egress resulting from episodes that do not lead to the withdrawal of the information. In the end is calculated total egress complexity and then appraised total exit complexity of the system. Given the complexity of the operations within the Distributed Computing Quantity, this research addresses effective transactions that could affect the three-dimensional behavior of knowledge. The results materialized that the best affair where total exit complexity as minimal as possible is a picture of a binary tree is entitled at the rate of positive and negative cardinal points medium value. It could be argued that these cardinal points should not amass the upper bound apex or minimum.

  6. Symmetry Groups for the Decomposition of Reversible Computers, Quantum Computers, and Computers in between

    OpenAIRE

    Alexis De Vos; Stijn De Baerdemacker

    2011-01-01

    Whereas quantum computing circuits follow the symmetries of the unitary Lie group, classical reversible computation circuits follow the symmetries of a finite group, i.e., the symmetric group. We confront the decomposition of an arbitrary classical reversible circuit with w bits and the decomposition of an arbitrary quantum circuit with w qubits. Both decompositions use the control gate as building block, i.e., a circuit transforming only one (qu)bit, the transformation being controlled by th...

  7. Reversible logic synthesis methodologies with application to quantum computing

    CERN Document Server

    Taha, Saleem Mohammed Ridha

    2016-01-01

    This book opens the door to a new interesting and ambitious world of reversible and quantum computing research. It presents the state of the art required to travel around that world safely. Top world universities, companies and government institutions  are in a race of developing new methodologies, algorithms and circuits on reversible logic, quantum logic, reversible and quantum computing and nano-technologies. In this book, twelve reversible logic synthesis methodologies are presented for the first time in a single literature with some new proposals. Also, the sequential reversible logic circuitries are discussed for the first time in a book. Reversible logic plays an important role in quantum computing. Any progress in the domain of reversible logic can be directly applied to quantum logic. One of the goals of this book is to show the application of reversible logic in quantum computing. A new implementation of wavelet and multiwavelet transforms using quantum computing is performed for this purpose. Rese...

  8. Experimental realization of order-finding with a quantum computer

    CERN Document Server

    Vandersypen, L M K; Breyta, G; Yannoni, C S; Cleve, R; Chuang, I L; Vandersypen, Lieven M.K.; Steffen, Matthias; Breyta, Gregory; Yannoni, Costantino S.; Cleve, Richard; Chuang, Isaac L.

    2000-01-01

    Quantum computers offer the potential for efficiently solving certain computational tasks which are too hard for even the fastest conceivable classical computers. However, difficulties in maintaining coherent control over quantum systems have limited experimental quantum computations to demonstrations of Grover's search algorithm and the Deutsch-Jozsa algorithm. Shor's remarkable quantum factoring algorithm has remained beyond the reach of these small-scale realizations. Here we report the experimental implementation of a quantum algorithm which generalizes Shor's algorithm to find the order of a permutation in fewer steps than is possible using a deterministic or probabilistic classical computer. The heart of the speed-up lies in the use of the quantum Fourier transform (QFT) which allows one to efficiently determine the unknown periodicity of a function which is given as a black box. In this experiment, the spins of five $^{19}$F nuclei in a molecule subject to a static magnetic field acted as the quantum b...

  9. Models to Reduce the Complexity of Simulating a Quantum Computer

    CERN Document Server

    Obenland, K M; Obenland, Kevin M.; Despain, Alvin M.

    1997-01-01

    Recently Quantum Computation has generated a lot of interest due to the discovery of a quantum algorithm which can factor large numbers in polynomial time. The usefulness of a quantum com puter is limited by the effect of errors. Simulation is a useful tool for determining the feasibility of quantum computers in the presence of errors. The size of a quantum computer that can be simulat ed is small because faithfully modeling a quantum computer requires an exponential amount of storage and number of operations. In this paper we define simulation models to study the feasibility of quantum computers. The most detailed of these models is based directly on a proposed imple mentation. We also define less detailed models which are exponentially less complex but still pro duce accurate results. Finally we show that the two different types of errors, decoherence and inaccuracies, are uncorrelated. This decreases the number of simulations which must be per formed.

  10. Quantum computational tensor network on string-net condensate

    OpenAIRE

    Morimae, Tomoyuki

    2010-01-01

    The string-net condensate is a new class of materials which exhibits the quantum topological order. In order to answer the important question, "how useful is the string-net condensate in quantum information processing?", we consider the most basic example of the string-net condensate, namely the $Z_2$ gauge string-net condensate on the two-dimensional hexagonal lattice, and show that the universal measurement-based quantum computation (in the sense of the quantum computation...

  11. Quantum Computation: Particle and Wave Aspects of Algorithms

    OpenAIRE

    Patel, Apoorva

    2011-01-01

    The driving force in the pursuit for quantum computation is the exciting possibility that quantum algorithms can be more efficient than their classical analogues. Research on the subject has unraveled several aspects of how that can happen. Clever quantum algorithms have been discovered in recent years, although not systematically, and the field remains under active investigation. Richard Feynman was one of the pioneers who foresaw the power of quantum computers. In this iss...

  12. An Overview of Quantum Computing for Technology Managers

    OpenAIRE

    Rieffel, Eleanor G.

    2008-01-01

    Faster algorithms, novel cryptographic mechanisms, and alternative methods of communication become possible when the model underlying information and computation changes from a classical mechanical model to a quantum mechanical one. Quantum algorithms perform a select set of tasks vastly more efficiently than any classical algorithm, but for many tasks it has been proved that quantum algorithms provide no advantage. The breadth of quantum computing applications is still bein...

  13. Automatic quantum computer programming a genetic programming approach

    CERN Document Server

    Spector, Lee

    2006-01-01

    This is an introduction both to quantum computing for non-physicists and to genetic programming for non-computer-scientists. The book explores ways in which genetic programming can support automatic quantum computer programming, offering specific techniques in detail, with examples of their human-competitive performance on real-world problems..

  14. Qcmpi: A Parallel Environment for Quantum Computing

    CERN Document Server

    Tabakin, F

    2009-01-01

    QCMPI is a quantum computer (QC) simulation package written in Fortran 90 with parallel processing capabilities. It is an accessible research tool that permits rapid evaluation of quantum algorithms for a large number of qubits and for various "noise" scenarios. The prime motivation for developing QCMPI is to facilitate numerical examination of not only how QC algorithms work, but also to include noise, decoherence, and attenuation effects and to evaluate the efficacy of error correction schemes. The present work builds on an earlier Mathematica code QDENSITY, which is mainly a pedagogic tool. In QCMPI, the stress is on state vectors, in order to employ a large number of qubits. The parallel processing feature is implemented by using the Message-Passing Interface (MPI) protocol. Codes for Grover's search and Shor's factoring algorithms are provided as examples. A major feature of this work is that concurrent versions of the algorithms can be evaluated with each version subject to alternate noise effects, whic...

  15. Poly-locality in quantum computing

    CERN Document Server

    Freedman, M H

    2000-01-01

    A polynomial depth quantum circuit effects, by definition a poly-local unitary transformation of tensor product state space. It is a physically reasonable belief [Fy][L][FKW] that these are precisely the transformations which will be available from physics to help us solve computational problems. The poly-locality of discrete Fourier transform on cyclic groups is at the heart of Shor's factoring algorithm. We describe a class of poly-local transformations, including all the discrete orthogonal wavelet transforms in the hope that these may be helpful in constructing new quantum algorithms. We also observe that even a rather mild violation of poly-locality leads to a model without one-way functions, giving further evidence that poly-locality is an essential concept.

  16. Quantum Computation: Particle and Wave Aspects of Algorithms

    CERN Document Server

    Patel, Apoorva

    2011-01-01

    The driving force in the pursuit for quantum computation is the exciting possibility that quantum algorithms can be more efficient than their classical analogues. Research on the subject has unraveled several aspects of how that can happen. Clever quantum algorithms have been discovered in recent years, although not systematically, and the field remains under active investigation. Richard Feynman was one of the pioneers who foresaw the power of quantum computers. In this issue dedicated to him, I give an introduction to how particle and wave aspects contribute to the power of quantum computers. Shor's and Grover's algorithms are analysed as examples.

  17. Quantum Computing, $NP$-complete Problems and Chaotic Dynamics

    CERN Document Server

    Ohya, M; Ohya, Masanori; Volovich, Igor V.

    1999-01-01

    An approach to the solution of NP-complete problems based on quantumcomputing and chaotic dynamics is proposed. We consider the satisfiabilityproblem and argue that the problem, in principle, can be solved in polynomialtime if we combine the quantum computer with the chaotic dynamics amplifierbased on the logistic map. We discuss a possible implementation of such achaotic quantum computation by using the atomic quantum computer with quantumgates described by the Hartree-Fock equations. In this case, in principle, onecan build not only standard linear quantum gates but also nonlinear gates andmoreover they obey to Fermi statistics. This new type of entaglement relatedwith Fermi statistics can be interesting also for quantum communication theory.

  18. Computational Role of Collective Tunneling in a Quantum Annealer

    OpenAIRE

    Boixo, Sergio; Smelyanskiy, Vadim N.; Shabani, Alireza; Sergei V. Isakov; Dykman, Mark; Denchev, Vasil S; Amin, Mohammad; Smirnov, Anatoly; Mohseni, Masoud; Neven, Hartmut

    2014-01-01

    Quantum tunneling is a phenomenon in which a quantum state traverses energy barriers above the energy of the state itself. Tunneling has been hypothesized as an advantageous physical resource for optimization. Here we present the first experimental evidence of a computational role of multiqubit quantum tunneling in the evolution of a programmable quantum annealer. We develop a theoretical model based on a NIBA Quantum Master Equation to describe the multiqubit dissipative tu...

  19. Quantum Computing and a Unified Approach to Fast Unitary Transforms

    OpenAIRE

    Agaian, Sos S.; Klappenecker, Andreas

    2002-01-01

    A quantum computer directly manipulates information stored in the state of quantum mechanical systems. The available operations have many attractive features but also underly severe restrictions, which complicate the design of quantum algorithms. We present a divide-and-conquer approach to the design of various quantum algorithms. The class of algorithm includes many transforms which are well-known in classical signal processing applications. We show how fast quantum algorit...

  20. Extending scientific computing system with structural quantum programming capabilities

    OpenAIRE

    Gawron, P.; Klamka, J.; Miszczak, J. A.; Winiarczyk, R.

    2010-01-01

    We present a basic high-level structures used for developing quantum programming languages. The presented structures are commonly used in many existing quantum programming languages and we use quantum pseudo-code based on QCL quantum programming language to describe them. We also present the implementation of introduced structures in GNU Octave language for scientific computing. Procedures used in the implementation are available as a package quantum-octave, providing a libr...

  1. Spacetime Foam, Holographic Principle, and Black Hole Quantum Computers

    OpenAIRE

    NG, Y. Jack; van Dam, H.

    2004-01-01

    Spacetime foam, also known as quantum foam, has its origin in quantum fluctuations of spacetime. Arguably it is the source of the holographic principle, which severely limits how densely information can be packed in space. Its physics is also intimately linked to that of black holes and computation. In particular, the same underlying physics is shown to govern the computational power of black hole quantum computers.

  2. Measurement-based quantum computation with cluster states

    OpenAIRE

    Raussendorf, Robert

    2003-01-01

    In this thesis we describe the one-way quantum computer (QCc), a scheme of universal quantum computation that consists entirely of one-qubit measurements on a highly entangled multi-particle state, the cluster state. We prove universality of the QCc, describe the underlying computational model and demonstrate that the QCc can be operated fault-tolerantly. In Chapter 2 we show that the QCc can be regarded as a simulator of quantum logic networks. In this way, we give...

  3. Non-adiabatic geometric quantum computation with trapped ions

    CERN Document Server

    Li Xue Qian; Huang, G X; Ma, L; Yan, Y J; Li, Xin-Qi; Cen, Li-Xiang; Huang, Guo-Xiang; Ma, Lei; Yan, YiJing

    2002-01-01

    In this paper we propose a non-adiabatic scheme for geometric quantum computation with ion-traps. The desired geometric feature is rooted in the global nature of the Aharonov-Anandam phase, meanwhile the non-adiabaticity removes the disadvantage of slow evolutions in the adiabatic schemes for geometric quantum computation. Additionally, only two atomic levels of each ion are required in the suggested scheme. This simple setup is also expected to interest the community of ion-trap quantum computation.

  4. Measurement-based quantum computation and undecidable logic

    OpenAIRE

    Nest, M. Van den; Briegel, H. J.

    2006-01-01

    We establish a connection between measurement-based quantum computation and the field of mathematical logic. We show that the computational power of an important class of quantum states called graph states, representing resources for measurement-based quantum computation, is reflected in the expressive power of (classical) formal logic languages defined on the underlying mathematical graphs. In particular, we show that for all graph state resources which can yield a computat...

  5. Quantum computing accelerator I/O : LDRD 52750 final report.

    Energy Technology Data Exchange (ETDEWEB)

    Schroeppel, Richard Crabtree; Modine, Normand Arthur; Ganti, Anand; Pierson, Lyndon George; Tigges, Christopher P.

    2003-12-01

    In a superposition of quantum states, a bit can be in both the states '0' and '1' at the same time. This feature of the quantum bit or qubit has no parallel in classical systems. Currently, quantum computers consisting of 4 to 7 qubits in a 'quantum computing register' have been built. Innovative algorithms suited to quantum computing are now beginning to emerge, applicable to sorting and cryptanalysis, and other applications. A framework for overcoming slightly inaccurate quantum gate interactions and for causing quantum states to survive interactions with surrounding environment is emerging, called quantum error correction. Thus there is the potential for rapid advances in this field. Although quantum information processing can be applied to secure communication links (quantum cryptography) and to crack conventional cryptosystems, the first few computing applications will likely involve a 'quantum computing accelerator' similar to a 'floating point arithmetic accelerator' interfaced to a conventional Von Neumann computer architecture. This research is to develop a roadmap for applying Sandia's capabilities to the solution of some of the problems associated with maintaining quantum information, and with getting data into and out of such a 'quantum computing accelerator'. We propose to focus this work on 'quantum I/O technologies' by applying quantum optics on semiconductor nanostructures to leverage Sandia's expertise in semiconductor microelectronic/photonic fabrication techniques, as well as its expertise in information theory, processing, and algorithms. The work will be guided by understanding of practical requirements of computing and communication architectures. This effort will incorporate ongoing collaboration between 9000, 6000 and 1000 and between junior and senior personnel. Follow-on work to fabricate and evaluate appropriate experimental nano/microstructures will be proposed as a result of this work.

  6. Quantum computing accelerator I/O : LDRD 52750 final report

    International Nuclear Information System (INIS)

    In a superposition of quantum states, a bit can be in both the states '0' and '1' at the same time. This feature of the quantum bit or qubit has no parallel in classical systems. Currently, quantum computers consisting of 4 to 7 qubits in a 'quantum computing register' have been built. Innovative algorithms suited to quantum computing are now beginning to emerge, applicable to sorting and cryptanalysis, and other applications. A framework for overcoming slightly inaccurate quantum gate interactions and for causing quantum states to survive interactions with surrounding environment is emerging, called quantum error correction. Thus there is the potential for rapid advances in this field. Although quantum information processing can be applied to secure communication links (quantum cryptography) and to crack conventional cryptosystems, the first few computing applications will likely involve a 'quantum computing accelerator' similar to a 'floating point arithmetic accelerator' interfaced to a conventional Von Neumann computer architecture. This research is to develop a roadmap for applying Sandia's capabilities to the solution of some of the problems associated with maintaining quantum information, and with getting data into and out of such a 'quantum computing accelerator'. We propose to focus this work on 'quantum I/O technologies' by applying quantum optics on semiconductor nanostructures to leverage Sandia's expertise in semiconductor microelectronic/photonic fabrication techniques, as well as its expertise in information theory, processing, and algorithms. The work will be guided by understanding of practical requirements of computing and communication architectures. This effort will incorporate ongoing collaboration between 9000, 6000 and 1000 and between junior and senior personnel. Follow-on work to fabricate and evaluate appropriate experimental nano/microstructures will be proposed as a result of this work

  7. Two Way Coupling RAM-SCB to the Space Weather Modeling Framework

    Science.gov (United States)

    Welling, D. T.; Jordanova, V. K.; Zaharia, S. G.; Toth, G.

    2010-12-01

    The Ring current Atmosphere interaction Model with Self-Consistently calculated 3D Magnetic field (RAM-SCB) has been used to successfully study inner magnetosphere dynamics during different solar wind and magnetosphere conditions. Recently, one way coupling of RAM-SCB with the Space Weather Modeling Framework (SWMF) has been achieved to replace all data or empirical inputs with those obtained through first-principles-based codes: magnetic field and plasma flux outer boundary conditions are provided by the Block Adaptive Tree Solar wind Roe-type Upwind Scheme (BATS-R-US) MHD code, convection electric field is provided by the Ridley Ionosphere Model (RIM), and ion composition is provided by the Polar Wind Outflow Model (PWOM) combined with a multi-species MHD approach. These advances, though creating a powerful inner magnetosphere virtual laboratory, neglect the important mechanisms through which the ring current feeds back into the whole system, primarily the stretching of the magnetic field lines and shielding of the convection electric field through strong region two Field Aligned Currents (FACs). In turn, changing the magnetosphere in this way changes the evolution of the ring current. To address this shortcoming, the coupling has been expanded to include feedback from RAM-SCB to the other coupled codes: region two FACs are returned to the RIM while total plasma pressure is used to nudge the MHD solution towards the RAM-SCB values. The impacts of the two way coupling are evaluated on three levels: the global magnetospheric level, focusing on the impact on the ionosphere and the shape of the magnetosphere, the regional level, examining the impact on the development of the ring current in terms of energy density, anisotropy, and plasma distribution, and the local level to compare the new results to in-situ measurements of magnetic and electric field and plasma. The results will also be compared to past simulations using the one way coupling and no coupling whatsoever. This work is the first to fully couple an anisotropic kinetic ring current code with a self-consistently calculated magnetic field to a set of global models.

  8. Electronic structure, phonon spectra and electron-phonon interaction in ScB2

    International Nuclear Information System (INIS)

    The electronic structure, Fermi surface, angle dependence of the cyclotron masses and extremal cross sections of the Fermi surface, phonon spectra, electron-phonon Eliashberg and transport spectral functions, temperature dependence of electrical resistivity of the ScB2 diboride were investigated from first principles using the fully relativistic and full potential linear muffin-tin orbital methods. The calculations of the dynamic matrix were carried out within the framework of the linear response theory. A good agreement with experimental data of electron-phonon spectral functions, electrical resistivity, cyclotron masses and extremal cross sections of the Fermi surface was achieved.

  9. Reviving Nuclear Magnetic Resonance as a viable approach for quantum computation and Solving simultaneous Pell equations by quantum computational means

    OpenAIRE

    Van Schenk Brill, Kees

    2010-01-01

    This thesis consists of two parts. I describe an approach for a physical realization of a quantum computer by Nuclear Magnetic Resonance (NMR). I propose a new framework for NMR that gives such a physical realization. I construct a quantum mechanical description of NMR from which I can build the fundamental elementary operators for quantum computation. I describe the experiments that build these operators. I give a polynomial time quantum algorithm to solve simultaneous Pell equations as an e...

  10. Quantum computing with trapped ions, atoms and light

    International Nuclear Information System (INIS)

    We consider experimental issues relevant to quantum computing, and discuss the best way to achieve the essential requirements of reliable quantum memory and gate operations. Nuclear spins in trapped ions or atoms are a very promising candidate for the qubits. We estimate the parameters required to couple atoms using light via cavity QED in order to achieve quantum gates. We briefly comment on recent improvements to the Cirac-Zoller method for coupling trapped ions via their vibrational degree of freedom. Error processes result in a trade-off between quantum gate speed and failure probability. A useful quantum computer does appear to be feasible using a combination of ion trap and optical methods. The best understood method to stabilize a large computer relies on quantum error correction. The essential ideas of this are discussed, and recent estimates of the noise requirements in a quantum computing device are given

  11. Quantum computation and simulation with trapped ions using dissipation

    International Nuclear Information System (INIS)

    Quantum information processing combines two of the most successful and fascinating ideas of the 20th century - quantum physics and computer science. A quantum computer promises to solve certain problems more efficient than classical computers. But building such a quantum computer is a cumbersome task as the quantum system needs to be manipulated with tremendous accuracy while being well shielded from the classical environment to preserve its quantum nature. An unwanted coupling to the surrounding environment manifests itself in computational errors. This coupling can be suppressed with the aid of quantum error correction schemes that are still a mainly theoretical construct. These error correcting protocols can only protect the information if they are applied multiple times subsequently. For this, it is necessary to remove the information about previous errors from the quantum system before performing the actual correction. However, this removal of information requires a controlled coupling to the environment which is beyond the standard set of operations available in a quantum computer. In this work, an experimental realization of repetitive quantum error correction in an ion-trap quantum information processor is presented, performing up to three consecutive rounds of correction. Moreover such an error correction algorithm can also be used to demonstrate a physical connection between information processing and quantum mechanics - computational errors are mapped onto quantum mechanical measurements. Therefore, a quantum error correction protocol is able to undo quantum measurements - a task that seemingly contradicts the foundations of quantum physics. In this work, we show that it is indeed possible to undo a partial measurement on a quantum register using an error correction protocol. After closer inspection it becomes obvious this does not violate the laws of quantum mechanics. However, the realization of a large-scale quantum computer lies in the far future as current quantum systems do not allow for the required level of control. Nevertheless it seems promising to adapt the techniques developed for quantum information processing to build a quantum simulator. Such a device is able to efficiently reproduce the dynamics of any quantum system - a task that is only possible for small systems on existing classical computers. However, the quantum system of interest may be coupled to a classical environment where many examples for such systems can be found in quantum biology and quantum chemistry. These systems are often embedded in a thermal environment and, analogous to classical physics, show non-reversible, or dissipative, dynamics. Thus, also the quantum simulator should be able to reproduce dissipative dynamics which requires an extension of the usual quantum computing toolbox. In the context of quantum computing, such a coupling is usually treated as a noise process that defeats the possible gain from using such a device. Interestingly it has been shown that an environment can be engineered that drives the system towards a state that features entanglement and can serve as a resource for quantum information processing. In this thesis, an extended toolbox that goes beyond coherent operations is introduced in our small-scale ion-trap quantum information processor. This is then used to create an entangled state through dissipative dynamics. In the next step a quantum simulation of a dissipative many-body system is performed, demonstrating the hallmark feature of a novel type of quantum phase transitions. (author)

  12. Actual computational time-cost of the Quantum Fourier Transform in a quantum computer using nuclear spins

    OpenAIRE

    Saito, A.; Kioi, K.; Akagi, Y; Hashizume, N.; Ohta, K.

    2000-01-01

    We found that the actual computational time-cost of the QFT is O(n 2^n) for large n in a quantum computer using nuclear spins. The computational cost of a quantum algorithm has usually been estimated as the sum of the universal gates required in such ideal mathematical models as the Quantum Turing Machine(QTM) and the quantum circuit. This cost is proportional to an actual time-cost in the physical implementation where all quantum operations can be achieved in the same time....

  13. Computer science approach to quantum control

    Energy Technology Data Exchange (ETDEWEB)

    Janzing, D.

    2006-07-01

    Whereas it is obvious that every computation process is a physical process it has hardly been recognized that many complex physical processes bear similarities to computation processes. This is in particular true for the control of physical systems on the nanoscopic level: usually the system can only be accessed via a rather limited set of elementary control operations and for many purposes only a concatenation of a large number of these basic operations will implement the desired process. This concatenation is in many cases quite similar to building complex programs from elementary steps and principles for designing algorithm may thus be a paradigm for designing control processes. For instance, one can decrease the temperature of one part of a molecule by transferring its heat to the remaining part where it is then dissipated to the environment. But the implementation of such a process involves a complex sequence of electromagnetic pulses. This work considers several hypothetical control processes on the nanoscopic level and show their analogy to computation processes. We show that measuring certain types of quantum observables is such a complex task that every instrument that is able to perform it would necessarily be an extremely powerful computer. Likewise, the implementation of a heat engine on the nanoscale requires to process the heat in a way that is similar to information processing and it can be shown that heat engines with maximal efficiency would be powerful computers, too. In the same way as problems in computer science can be classified by complexity classes we can also classify control problems according to their complexity. Moreover, we directly relate these complexity classes for control problems to the classes in computer science. Unifying notions of complexity in computer science and physics has therefore two aspects: on the one hand, computer science methods help to analyze the complexity of physical processes. On the other hand, reasonable definitions of complexity in computer science must be based upon a notion of elementary computation steps that correspond to not too complex real physical processes. This book tries to shed light on both aspects of this unification. (orig.)

  14. Lecture Script: Introduction to Computational Quantum Mechanics

    CERN Document Server

    Schmied, Roman

    2014-01-01

    This document is the lecture script of a one-semester course taught at the University of Basel in the Fall semesters of 2012 and 2013. It is aimed at advanced students of physics who are familiar with the concepts and notations of quantum mechanics. Quantum mechanics lectures can often be separated into two classes. In the first class you get to know Schroedinger's equation and find the form and dynamics of simple physical systems (square well, harmonic oscillator, hydrogen atom); most calculations are analytic and inspired by calculations originally done in the 1920s and 1930s. In the second class you learn about large systems such as molecular structures, crystalline solids, or lattice models; these calculations are usually so complicated that it is difficult for the student to understand them in all detail. This lecture tries to bridge the gap between simple analytic calculations and complicated large-scale computations. We will revisit most of the problems encountered in introductory quantum mechanics, fo...

  15. Control aspects of quantum computing using pure and mixed states.

    Science.gov (United States)

    Schulte-Herbrüggen, Thomas; Marx, Raimund; Fahmy, Amr; Kauffman, Louis; Lomonaco, Samuel; Khaneja, Navin; Glaser, Steffen J

    2012-10-13

    Steering quantum dynamics such that the target states solve classically hard problems is paramount to quantum simulation and computation. And beyond, quantum control is also essential to pave the way to quantum technologies. Here, important control techniques are reviewed and presented in a unified frame covering quantum computational gate synthesis and spectroscopic state transfer alike. We emphasize that it does not matter whether the quantum states of interest are pure or not. While pure states underly the design of quantum circuits, ensemble mixtures of quantum states can be exploited in a more recent class of algorithms: it is illustrated by characterizing the Jones polynomial in order to distinguish between different (classes of) knots. Further applications include Josephson elements, cavity grids, ion traps and nitrogen vacancy centres in scenarios of closed as well as open quantum systems. PMID:22946034

  16. Clifford quantum computer and the Mathieu groups

    CERN Document Server

    Planat, Michel

    2007-01-01

    One learned from Gottesman-Knill theorem that the Clifford model of quantum computing \\cite{Clark07} may be generated from a few quantum gates, the Hadamard, Phase and Controlled-Z gates, and efficiently simulated on a classical computer. We employ the group theoretical package GAP\\cite{GAP} for simulating the two qubit Clifford group $\\mathcal{C}_2$. We already found that the symmetric group S(6), aka the automorphism group of the generalized quadrangle W(2), controls the geometry of the two-qubit Pauli graph \\cite{Pauligraphs}. Now we find that the {\\it inner} group ${Inn}(\\mathcal{C}_2)=\\mathcal{C}_2/{Center}(\\mathcal{C}_2)$ exactly contains two normal subgroups, one isomorphic to $\\mathcal{Z}_2^{\\times 4}$ (of order 16), and the second isomorphic to the parent $A'(6)$ (of order 5760) of the alternating group A(6). The group $A'(6)$ stabilizes an {\\it hexad} in the Steiner system $S(3,6,22)$ attached to the Mathieu group M(22). Both groups A(6) and $A'(6)$ have an {\\it outer} automorphism group $\\mathcal{Z...

  17. A quantum computer based on recombination processes in microelectronic devices

    International Nuclear Information System (INIS)

    In this paper a quantum computer based on the recombination processes happening in semiconductor devices is presented. A 'data element' and a 'computational element' are derived based on Schokley-Read-Hall statistics and they can later be used to manifest a simple and known quantum computing process. Such a paradigm is shown by the application of the proposed computer onto a well known physical system involving traps in semiconductor devices

  18. Fault-Tolerant Quantum Computation with Higher-Dimensional Systems

    CERN Document Server

    Gottesman, D

    1998-01-01

    Instead of a quantum computer where the fundamental units are 2-dimensional qubits, we can consider a quantum computer made up of d-dimensional systems. There is a straightforward generalization of the class of stabilizer codes to d-dimensional systems, and I will discuss the theory of fault-tolerant computation using such codes. I prove that universal fault-tolerant computation is possible with any higher-dimensional stabilizer code for prime d.

  19. A Self Assembled Nanoelectronic Quantum Computer Based on the Rashba Effect in Quantum Dots

    CERN Document Server

    Bandyopadhyay, S

    2000-01-01

    Quantum computers promise vastly enhanced computational power and an uncanny ability to solve classically intractable problems. However, few proposals exist for robust, solid state implementation of such computers where the quantum gates are sufficiently miniaturized to have nanometer-scale dimensions. Here I present a new approach whereby a complete computer with nanoscale gates might be self-assembled using chemical synthesis. Specifically, I demonstrate how to self-assemble the fundamental unit of this quantum computer - a 2-qubit universal quantum controlled-NOT gate - based on two exchange coupled multilayered quantum dots. Then I show how these gates can be wired using thiolated conjugated molecules as electrical connectors. A qubit is encoded in the ground state of a quantum dot spin-split by the Rashba interaction. Arbitrary qubit rotations are effected by bringing the spin splitting energy in a target quantum dot in resonance with a global ac magnetic field by applying a potential pulse of appropriat...

  20. Quantum Computation, Spectroscopy of Trapped Ions, and Schrodinger's Cat

    CERN Document Server

    Wineland, D J; Itano, W M; Kielpinski, D; King, B E; Myatt, C J; Turchette, Q A; Wood, C S

    1998-01-01

    We summarize efforts at NIST to implement quantum computation using trapped ions, based on a scheme proposed by J.I. Cirac and P. Zoller (Innsbruck University). The use of quantum logic to create entangled states, which can maximize the quantum-limited signal-to-noise ratio in spectroscopy, is discussed.

  1. Quantum computers can search rapidly by using almost any transformation

    CERN Document Server

    Grover, L K

    1998-01-01

    A quantum computer has a clear advantage over a classical computer for exhaustive search. The quantum mechanical algorithm for exhaustive search was originally derived by using subtle properties of a particular quantum mechanical operation called the Walsh-Hadamard (W-H) transform. This paper shows that this algorithm can be implemented by replacing the W-H transform by almost any quantum mechanical operation. This leads to several new applications where it improves the number of steps by a square-root. It also broadens the scope for implementation since it demonstrates quantum mechanical algorithms that can readily adapt to available technology.

  2. Quantum Genetics in terms of Quantum Reversible Automata and Quantum Computation of Genetic Codes and Reverse Transcription

    CERN Document Server

    Baianu,I C

    2004-01-01

    The concepts of quantum automata and quantum computation are studied in the context of quantum genetics and genetic networks with nonlinear dynamics. In previous publications (Baianu,1971a, b) the formal concept of quantum automaton and quantum computation, respectively, were introduced and their possible implications for genetic processes and metabolic activities in living cells and organisms were considered. This was followed by a report on quantum and abstract, symbolic computation based on the theory of categories, functors and natural transformations (Baianu,1971b; 1977; 1987; 2004; Baianu et al, 2004). The notions of topological semigroup, quantum automaton, or quantum computer, were then suggested with a view to their potential applications to the analogous simulation of biological systems, and especially genetic activities and nonlinear dynamics in genetic networks. Further, detailed studies of nonlinear dynamics in genetic networks were carried out in categories of n-valued, Lukasiewicz Logic Algebra...

  3. Quantum computational tensor network on string-net condensate

    CERN Document Server

    Morimae, Tomoyuki

    2010-01-01

    The string-net condensate is a new class of materials which exhibits the quantum topological order. In order to answer the important question, "how useful is the string-net condensate in quantum information processing?", we consider the most basic example of the string-net condensate, namely the $Z_2$ gauge string-net condensate on the two-dimensional hexagonal lattice, and show that the universal measurement-based quantum computation (in the sense of the quantum computational webs) is possible on it by using the framework of the quantum computational tensor network. This result implies that even the most basic example of the string-net condensate is equipped with the correlation space that has the capacity for the universal quantum computation.

  4. Quantum computational tensor network on string-net condensate

    Science.gov (United States)

    Morimae, Tomoyuki

    2012-06-01

    String-net condensate is a new class of materials which exhibits quantum topological order. Here we study the measurement-based quantum computation on the simplest example of string-net condensate, namely the Z2 gauge string-net condensate on the two-dimensional hexagonal lattice, by using the framework of quantum computational tensor network. We show that universal measurement-based quantum computation is possible by coupling two correlation space wires with a physical two-body interaction. We also show that universal measurement-based quantum computation is possible solely with single-qubit measurements if the sign of the coefficient of each closed-loop configuration in the state is tuned. These results suggest that even the simplest example of string-net condensate is equipped with the correlation space that has the capacity for the application to quantum information processing.

  5. The Brain Is both Neurocomputer and Quantum Computer

    Science.gov (United States)

    Hameroff, Stuart R.

    2007-01-01

    In their article, "Is the Brain a Quantum Computer,?" Litt, Eliasmith, Kroon, Weinstein, and Thagard (2006) criticize the Penrose-Hameroff "Orch OR" quantum computational model of consciousness, arguing instead for neurocomputation as an explanation for mental phenomena. Here I clarify and defend Orch OR, show how Orch OR and neurocomputation are…

  6. A scalable solid-state quantum computer based on quantum dot pillar structures

    OpenAIRE

    Sanders, G. D.; Kim, K.W.; Holton, W. C.

    2000-01-01

    We investigate an optically driven quantum computer based on electric dipole transitions within coupled single-electron quantum dots. Our quantum register consists of a freestanding n-type pillar containing a series of pair wise coupled asymmetric quantum dots, each with a slightly different energy structure, and with grounding leads at the top and bottom of the pillar. Asymmetric quantum wells confine electrons along the pillar axis and a negatively biased gate wrapped arou...

  7. Measurement-Based Quantum Computing with Valence-Bond-Solids

    OpenAIRE

    Kwek, Leong Chuan; Wei, Zhaohui; Zeng, Bei

    2011-01-01

    Measurement-based quantum computing (MBQC) is a model of quantum computing that proceeds by sequential measurements of individual spins in an entangled resource state. However, it remains a challenge to produce efficiently such resource states. Would it be possible to generate these states by simply cooling a quantum many-body system to its ground state? Cluster states, the canonical resource states for MBQC, do not occur naturally as unique ground states of physical systems...

  8. Dynamically Error-Corrected Gates for Universal Quantum Computation

    CERN Document Server

    Khodjasteh, Kaveh

    2008-01-01

    Scalable quantum computation in realistic devices requires that precise control can be implemented efficiently in the presence of decoherence and operational errors. We propose a constructive procedure for designing robust unitary gates on an open quantum system without encoding or measurement overhead. Our results allow for a low-level error correction strategy solely based on Hamiltonian control under realistic constraints and may substantially reduce implementation requirements for fault-tolerant quantum computing architectures.

  9. Spacetime at the Planck Scale: The Quantum Computer View

    OpenAIRE

    zizzi, Paola

    2003-01-01

    We assume that space-time at the Planck scale is discrete, quantised in Planck units and "qubitsed" (each pixel of Planck area encodes one qubit), that is, quantum space-time can be viewed as a quantum computer. Within this model, one finds that quantum space-time itself is entangled, and can quantum-evaluate Boolean functions which are the laws of Physics in their discrete and fundamental form.

  10. Physical basis of quantum computation and cryptography. Poster

    OpenAIRE

    Calixto Molina, Manuel

    2007-01-01

    Quantum computing combines two of the main scientific achievements of the 20th century: Information Theory and Quantum Mechanics. Its interdisciplinary character is one of the most stimulating and appealing attributes. The new Quantum Information Theory augurs powerful machines that obey the “entangled” logic of the subatomic world. Parallelism, entanglement, teleportation, no-cloning and quantum cryptography are typical peculiarities of this novel way of understanding...

  11. Finding Matches between Two Databases on a Quantum Computer

    CERN Document Server

    Heiligman, M

    2000-01-01

    Given two unsorted lists each of length N that have a single common entry, a quantum computer can find that matching element with a work factor of $O(N^{3/4}\\log N)$ (measured in quantum memory accesses and accesses to each list). The amount of quantum memory required is $O(N^{1/2})$. The quantum algorithm that accomplishes this consists of an inner Grover search combined with a partial sort all sitting inside of an outer Grover search.

  12. Quantum computation in continuous time using dynamic invariants

    International Nuclear Information System (INIS)

    We introduce an approach for quantum computing in continuous time based on the Lewis-Riesenfeld dynamic invariants. This approach allows, under certain conditions, for the design of quantum algorithms running on a nonadiabatic regime. We show that the relaxation of adiabaticity can be achieved by processing information in the eigenlevels of a time dependent observable, namely, the dynamic invariant operator. Moreover, we derive the conditions for which the computation can be implemented by time independent as well as by adiabatically varying Hamiltonians. We illustrate our results by providing the implementation of both Deutsch-Jozsa and Grover algorithms via dynamic invariants. -- Highlights: ? An approach for quantum computing in continuous time based on the Lewis-Riesenfeld dynamic invariants is introduced. ? Nonadiabatic quantum computation is performed in the eigenlevels of the dynamic invariant operator. ? Condition of equivalence with adiabatic quantum computation is analyzed. ? Implementation of Deutsch-Jozsa and Grover algorithms is provided.

  13. Applications of superconducting circuits to quantum computing

    Science.gov (United States)

    Wilhelm, Frank

    2014-03-01

    Superconducting circuits containing Josephson junctions are strong contenders for the implementation of a quantum computer. At its 15 year mark, the field has seen tremendous progress with an increase of coherence by six orders of magnitude and it is now taking off from the few- to the multi-qubit level. I will present highlights of research on the level of single devices, in particular the strong increase of coherence that counter-intuitively comes with a growth in device size, as well as readout. I will cover challenges related to multi-qubit systems focusing on precise multi-qubit control and calibration, and present an outlook on future architectures dictated by the requirements of fault tolerance.

  14. Optical Quantum Computation with Perpetually Coupled Spins

    CERN Document Server

    Benjamin, S C; Reina, J H; Benjamin, Simon C.; Lovett, Brendon W.; Reina, John H.

    2004-01-01

    The possibility of using strongly and continuously interacting spins for quantum computation has recently been discussed. Here we present a simple optical scheme that achieves this goal while avoiding the drawbacks of earlier proposals. We employ a third state, accessed by a classical laser field, to create an effective barrier to information transfer. The mechanism proves to be highly efficient both for continuous and pulsed laser modes; moreover it is very robust, tolerating high decay rates for the excited states. The approach is applicable to a broad range of systems, in particular dense structures such as solid state self-assembled (e.g., molecular) devices. Importantly, there are existing structures upon which 'first step' experiments could be immediately performed.

  15. Symmetry-protected topologically ordered states for universal quantum computation

    Science.gov (United States)

    Nautrup, Hendrik Poulsen; Wei, Tzu-Chieh

    2015-11-01

    Measurement-based quantum computation is a model for quantum information processing utilizing local measurements on suitably entangled resource states for the implementation of quantum gates. A complete characterization for universal resource states is still missing. It has been shown that symmetry-protected topological order in one dimension can be exploited for the protection of certain quantum gates in measurement-based quantum computation. In this paper we show that the two-dimensional (2D) plaquette states on arbitrary lattices exhibit nontrivial symmetry-protected topological order in terms of symmetry fractionalization and that they are universal resource states for quantum computation. Our results of the nontrivial symmetry-protected topological order on arbitrary 2D lattices are based on an extension of the recent construction by Chen et al. [Phys. Rev. B 87, 155114 (2013), 10.1103/PhysRevB.87.155114] on the square lattice.

  16. Insights into classical irreversible computation using quantum information concepts

    OpenAIRE

    Groisman, Berry

    2008-01-01

    The method of using concepts and insight from quantum information theory in order to solve problems in reversible classical computing (introduced in Ref. [1]) have been generalized to irreversible classical computing. The method have been successfully tested on two computational tasks. Several basic logic gates have been analyzed and the nonlocal content of the associate quantum transformations have been calculated. The results provide us with new interesting insight into th...

  17. Insights into classical irreversible computation using quantum information concepts

    CERN Document Server

    Groisman, Berry

    2008-01-01

    The method of using concepts and insight from quantum information theory in order to solve problems in reversible classical computing (introduced in Ref. [1]) have been generalized to irreversible classical computing. The method have been successfully tested on two computational tasks. Several basic logic gates have been analyzed and the nonlocal content of the associate quantum transformations have been calculated. The results provide us with new interesting insight into the notion of complexity of logic operations.

  18. Impossibility of secure cloud quantum computing for classical client

    OpenAIRE

    Morimae, Tomoyuki; Koshiba, Takeshi

    2014-01-01

    The first generation quantum computer will be implemented in the cloud style, since only few groups will be able to access such an expensive and high-maintenance machine. How the privacy of the client can be protected in such a cloud quantum computing? It was theoretically shown [A. Broadbent, J. F. Fitzsimons, and E. Kashefi, Proceedings of the 50th Annual IEEE Symposium on Foundation of Computer Science, 517 (2009)], and experimentally demonstrated [S. Barz, E. Kashefi, A....

  19. The 2004 Latsis Symposium: Quantum optics for Communication and Computing

    CERN Multimedia

    2004-01-01

    1-3 March 2004 Ecole Polytechnique Fédérale de Lausanne Auditoire SG1 The field of Quantum Optics covers topics that extend from basic physical concepts, regarding the quantum description of light, matter, and light-matter interaction, to the applications of these concepts in future information and communication technologies. This field is of primary importance for science and society for two reasons. Firstly, it brings a deeper physical understanding of the fundamental aspects of modern quantum physics. Secondly, it offers perspectives for the invention and implementation of new devices and systems in the fields of communications, information management and computing. The themes that will be addressed in the Latsis Symposium on Quantum Optics are quantum communications, quantum computation, and quantum photonic devices. The objective of the symposium is to give an overview of this fascinating and rapidly evolving field. The different talks will establish links between new fundamental c...

  20. The 2004 Latsis Symposium: Quantum optics for Communication and Computing

    CERN Multimedia

    2004-01-01

    1-3 March 2004 Ecole Polytechnique Fédérale de Lausanne Auditoire SG1 The field of Quantum Optics covers topics that extend from basic physical concepts, regarding the quantum description of light, matter, and light-matter interaction, to the applications of these concepts in future information and communication technologies. This field is of primary importance for science and society for two reasons. Firstly, it brings a deeper physical understanding of the fundamental aspects of modern quantum physics. Secondly, it offers perspectives for the invention and implementation of new devices and systems in the fields of communications, information management and computing. The themes that will be addressed in the Latsis Symposium on Quantum Optics are quantum communications, quantum computation, and quantum photonic devices. The objective of the symposium is to give an overview of this fascinating and rapidly evolving field. The different talks will establish links between new fundamental...

  1. The 2004 Latsis Symposium: Quantum optics for Communication and Computing

    CERN Multimedia

    2004-01-01

    1-3 March 2004 Ecole Polytechnique Fédérale de Lausanne Auditoire SG1 The field of Quantum Optics covers topics that extend from basic physical concepts, regarding the quantum description of light, matter, and light-matter interaction, to the applications of these concepts in future information and communication technologies. This field is of primary importance for science and society for two reasons. Firstly, it brings a deeper physical understanding of the fundamental aspects of modern quantum physics. Secondly, it offers perspectives for the invention and implementation of new devices and systems in the fields of communications, information management and computing. The themes that will be addressed in the Latsis Symposium on Quantum Optics are quantum communications, quantum computation, and quantum photonic devices. The objective of the symposium is to give an overview of this fascinating and rapidly evolving field. The different talks will establish links between new fundamental ...

  2. Quantum Monte Carlo Endstation for Petascale Computing

    Energy Technology Data Exchange (ETDEWEB)

    Lubos Mitas

    2011-01-26

    NCSU research group has been focused on accomplising the key goals of this initiative: establishing new generation of quantum Monte Carlo (QMC) computational tools as a part of Endstation petaflop initiative for use at the DOE ORNL computational facilities and for use by computational electronic structure community at large; carrying out high accuracy quantum Monte Carlo demonstration projects in application of these tools to the forefront electronic structure problems in molecular and solid systems; expanding the impact of QMC methods and approaches; explaining and enhancing the impact of these advanced computational approaches. In particular, we have developed quantum Monte Carlo code (QWalk, www.qwalk.org) which was significantly expanded and optimized using funds from this support and at present became an actively used tool in the petascale regime by ORNL researchers and beyond. These developments have been built upon efforts undertaken by the PI's group and collaborators over the period of the last decade. The code was optimized and tested extensively on a number of parallel architectures including petaflop ORNL Jaguar machine. We have developed and redesigned a number of code modules such as evaluation of wave functions and orbitals, calculations of pfaffians and introduction of backflow coordinates together with overall organization of the code and random walker distribution over multicore architectures. We have addressed several bottlenecks such as load balancing and verified efficiency and accuracy of the calculations with the other groups of the Endstation team. The QWalk package contains about 50,000 lines of high quality object-oriented C++ and includes also interfaces to data files from other conventional electronic structure codes such as Gamess, Gaussian, Crystal and others. This grant supported PI for one month during summers, a full-time postdoc and partially three graduate students over the period of the grant duration, it has resulted in 13 published papers, 15 invited talks and lectures nationally and internationally. My former graduate student and postdoc Dr. Michal Bajdich, who was supported byt this grant, is currently a postdoc with ORNL in the group of Dr. F. Reboredo and Dr. P. Kent and is using the developed tools in a number of DOE projects. The QWalk package has become a truly important research tool used by the electronic structure community and has attracted several new developers in other research groups. Our tools use several types of correlated wavefunction approaches, variational, diffusion and reptation methods, large-scale optimization methods for wavefunctions and enables to calculate energy differences such as cohesion, electronic gaps, but also densities and other properties, using multiple runs one can obtain equations of state for given structures and beyond. Our codes use efficient numerical and Monte Carlo strategies (high accuracy numerical orbitals, multi-reference wave functions, highly accurate correlation factors, pairing orbitals, force biased and correlated sampling Monte Carlo), are robustly parallelized and enable to run on tens of thousands cores very efficiently. Our demonstration applications were focused on the challenging research problems in several fields of materials science such as transition metal solids. We note that our study of FeO solid was the first QMC calculation of transition metal oxides at high pressures.

  3. Is Quantum Mechanics Falsifiable? A computational perspective on the foundations of Quantum Mechanics

    OpenAIRE

    Dorit Aharonov; Umesh Vazirani

    2012-01-01

    Quantum computation teaches us that quantum mechanics exhibits exponential complexity. We argue that the standard scientific paradigm of "predict and verify" cannot be applied to testing quantum mechanics in this limit of high complexity. We describe how QM can be tested in this regime by extending the usual scientific paradigm to include {\\it interactive experiments}.

  4. Statistical constraints on state preparation for a quantum computer

    Indian Academy of Sciences (India)

    Subhash Kak

    2001-10-01

    Quantum computing algorithms require that the quantum register be initially present in a superposition state. To achieve this, we consider the practical problem of creating a coherent superposition state of several qubits. We show that the constraints of quantum statistics require that the entropy of the system be brought down when several independent qubits are assembled together. In particular, we have: (i) not all initial states are realizable as pure states; (ii) the temperature of the system must be reduced. These factors, in addition to decoherence and sensitivity to errors, must be considered in the implementation of quantum computers.

  5. On Computational Power of Quantum Read-Once Branching Programs

    Directory of Open Access Journals (Sweden)

    Farid Ablayev

    2011-03-01

    Full Text Available In this paper we review our current results concerning the computational power of quantum read-once branching programs. First of all, based on the circuit presentation of quantum branching programs and our variant of quantum fingerprinting technique, we show that any Boolean function with linear polynomial presentation can be computed by a quantum read-once branching program using a relatively small (usually logarithmic in the size of input number of qubits. Then we show that the described class of Boolean functions is closed under the polynomial projections.

  6. Actual computational time-cost of the Quantum Fourier Transform in a quantum computer using nuclear spins

    CERN Document Server

    Saito, A; Akagi, Y; Hashizume, N; Ohta, K

    2000-01-01

    We found that the actual computational time-cost of the QFT is O(n 2^n) for large n in a quantum computer using nuclear spins. The computational cost of a quantum algorithm has usually been estimated as the sum of the universal gates required in such ideal mathematical models as the Quantum Turing Machine(QTM) and the quantum circuit. This cost is proportional to an actual time-cost in the physical implementation where all quantum operations can be achieved in the same time. However, if the implementation takes a different time for each quantum gate, there is a possibility that the actual time-cost will have a different behavior from the ideal cost. So we estimated the actual time-cost of the QFT in these implementations by considering the gating time. The actual time-cost is drastically different from O(n^2) estimated by complexity analysis.

  7. Quantum Computing on Multi-atomic Ensembles in Quantum Electrodynamics Cavity

    CERN Document Server

    Ablayev, Farid; Vasiliev, Alexander; Moiseev, Sergey A

    2011-01-01

    We propose an effective realization of a complete set of elementary quantum gates in the solid-state quantum computer based on the multi-atomic coherent (MAC-) ensembles in the QED cavity. Here, we use the two-ensemble qubit encoding and swapping-based operations that together provide implementation of any encoded single-qubit operation by three elementary gates and the encoded controlled-NOT operation is performed in a single step. This approach simplifies a physical realization of universal quantum computing and adds the immunity to a number of errors. We also demonstrate that the proposed architecture of quantum computer satisfies DiVincenzo criteria.

  8. Secure Multiparty Quantum Computation with (Only) a Strict Honest Majority

    CERN Document Server

    Ben-Or, Michael; Gottesman, Daniel; Hassidim, Avinatan; Smith, Adam

    2008-01-01

    Secret sharing and multiparty computation (also called "secure function evaluation") are fundamental primitives in modern cryptography, allowing a group of mutually distrustful players to perform correct, distributed computations under the sole assumption that some number of them will follow the protocol honestly. This paper investigates how much trust is necessary -- that is, how many players must remain honest -- in order for distributed quantum computations to be possible. We present a verifiable quantum secret sharing (VQSS) protocol, and a general secure multiparty quantum computation (MPQC) protocol, which can tolerate any (n-1)/2 (rounded down) cheaters among n players. Previous protocols for these tasks tolerated (n-1)/4 (rounded down) and (n-1)/6 (rounded down) cheaters, respectively. The threshold we achieve is tight - even in the classical case, ``fair'' multiparty computation is not possible if any set of n/2 players can cheat. Our protocols rely on approximate quantum error-correcting codes, whic...

  9. Mathematical Models of Contemporary Elementary Quantum Computing Devices

    CERN Document Server

    Chen, G; Englert, Berthold-Georg; Zubairy, M S

    2003-01-01

    Computations with a future quantum computer will be implemented through the operations by elementary quantum gates. It is now well known that the collection of 1-bit and 2-bit quantum gates are universal for quantum computation, i.e., any n-bit unitary operation can be carried out by concatenations of 1-bit and 2-bit elementary quantum gates. Three contemporary quantum devices--cavity QED, ion traps and quantum dots--have been widely regarded as perhaps the most promising candidates for the construction of elementary quantum gates. In this paper, we describe the physical properties of these devices, and show the mathematical derivations based on the interaction of the laser field as control with atoms, ions or electron spins, leading to the following: (i) the 1-bit unitary rotation gates; and (ii) the 2-bit quantum phase gates and the controlled-not gate. This paper is aimed at providing a sufficiently self-contained survey account of analytical nature for mathematicians, physicists and computer scientists to...

  10. Is the quantum computer a dream or a nightmare?

    International Nuclear Information System (INIS)

    Some researchers think that the quantum computer is impracticable in the present state of our knowledge. For them, the promises are elsewhere: lighting the fundamental questions about this physics opposite to intuition. The basic components of the quantum computer is a logic gate. The candidates are ions traps or atoms cavities or photons cavities. The stability of this kind of components during interactions is the key issue due to decoherence. The best work of a quantum computer seems to be the factorization of 15. So the best interest is to progress in our understanding of the mesoscopic systems dissipation. (O.M.)

  11. Quantum entanglement and classical separability in NMR computing

    CERN Document Server

    Kessel, A R; Kessel, Alexander R.; Ermakov, Vladimir L.

    2000-01-01

    In the discussion about the quantumness of NMR computation a conclusion is done that computational states are separable and therefore can not be entangled. This conclusion is based on the assumption that the initial density matrix of an individual molecule coincides with whole sample molecules distribution over single molecule energy levels. This means that quantum stochasticity is replaced by classical stochasticity. In the present paper it is shown, that quantum NMR computation can create genuine entangled states if initial system states are thermodynamical equilibrium ones. A separability analysis problem can arise when one interprets the readout signal from whole sample.

  12. Cavity-assisted quantum computing in a silicon nanostructure

    International Nuclear Information System (INIS)

    We present a scheme of quantum computing with charge qubits corresponding to one excess electron shared between dangling-bond pairs of surface silicon atoms that couple to a microwave stripline resonator on a chip. By choosing a certain evolution time, we propose the realization of a set of universal single- and two-qubit logical gates. Due to its intrinsic stability and scalability, the silicon dangling-bond charge qubit can be regarded as one of the most promising candidates for quantum computation. Compared to the previous schemes on quantum computing with silicon bulk systems, our scheme shows such advantages as a long coherent time and direct control and readout. (general)

  13. Symbolic Quantum Computation Simulation in SymPy

    Science.gov (United States)

    Cugini, Addison; Curry, Matt; Granger, Brian

    2010-10-01

    Quantum computing is an emerging field which aims to use quantum mechanics to solve difficult computational problems with greater efficiency than on a classical computer. There is a need to create software that i) helps newcomers to learn the field, ii) enables practitioners to design and simulate quantum circuits and iii) provides an open foundation for further research in the field. Towards these ends we have created a package, in the open-source symbolic computation library SymPy, that simulates the quantum circuit model of quantum computation using Dirac notation. This framework builds on the extant powerful symbolic capabilities of SymPy to preform its simulations in a fully symbolic manner. We use object oriented design to abstract circuits as ordered collections of quantum gate and qbit objects. The gate objects can either be applied directly to the qbit objects or be represented as matrices in different bases. The package is also capable of performing the quantum Fourier transform and Shor's algorithm. A notion of measurement is made possible through the use of a non-commutative gate object. In this talk, we describe the software and show examples of quantum circuits on single and multi qbit states that involve common algorithms, gates and measurements.

  14. Cluster quantum computer on the basis of quasi-part

    CERN Document Server

    Voronov, V K

    2011-01-01

    The present paper deals with the possibility of creation of the quantum computer in which the role of q-bits is played by quasi-particles. In such a computer, the elementary computation block should represent a cluster created on the basis of the paramagnetic molecules. The latter form heterogeneous spin states in the cluster owing to the presence of interelectron correlations.

  15. Computational Nuclear Quantum Many-Body Problem: The UNEDF Project

    CERN Document Server

    Bogner, Scott; Carlson, Joseph A; Engel, Jonathan; Fann, George; Furnstahl, Richard J; Gandolfi, Stefano; Hagen, Gaute; Horoi, Mihai; Johnson, Calvin W; Kortelainen, Markus; Lusk, Ewing; Maris, Pieter; Nam, Hai Ah; Navratil, Petr; Nazarewicz, Witold; Ng, Esmond G; Nobre, Gustavo P A; Ormand, Erich; Papenbrock, Thomas; Pei, Junchen; Pieper, Steven C; Quaglioni, Sofia; Roche, Kenneth J; Sarich, Jason; Schunck, Nicolas; Sosonkina, Masha; Terasaki, Jun; Thompson, Ian J; Vary, James P; Wild, Stefan M

    2013-01-01

    The UNEDF project was a large-scale collaborative effort that applied high-performance computing to the nuclear quantum many-body problem. UNEDF demonstrated that close associations among nuclear physicists, mathematicians, and computer scientists can lead to novel physics outcomes built on algorithmic innovations and computational developments. This review showcases a wide range of UNEDF science results to illustrate this interplay.

  16. An Introduction to Quantum Error Correction and Fault-Tolerant Quantum Computation

    CERN Document Server

    Gottesman, Daniel

    2009-01-01

    Quantum states are very delicate, so it is likely some sort of quantum error correction will be necessary to build reliable quantum computers. The theory of quantum error-correcting codes has some close ties to and some striking differences from the theory of classical error-correcting codes. Many quantum codes can be described in terms of the stabilizer of the codewords. The stabilizer is a finite Abelian group, and allows a straightforward characterization of the error-correcting properties of the code. The stabilizer formalism for quantum codes also illustrates the relationships to classical coding theory, particularly classical codes over GF(4), the finite field with four elements. To build a quantum computer which behaves correctly in the presence of errors, we also need a theory of fault-tolerant quantum computation, instructing us how to perform quantum gates on qubits which are encoded in a quantum error-correcting code. The threshold theorem states that it is possible to create a quantum computer to ...

  17. Quantum and classical structures in nondeterminstic computation

    OpenAIRE

    Pavlovic, Dusko

    2008-01-01

    In categorical quantum mechanics, classical structures characterize the classical interfaces of quantum resources on one hand, while on the other hand giving rise to some quantum phenomena. In the standard Hilbert space model of quantum theories, classical structures over a space correspond to its orthonormal bases. In the present paper, we show that classical structures in the category of relations correspond to biproducts of abelian groups. Although relations are, of cours...

  18. Symmetry Groups for the Decomposition of Reversible Computers, Quantum Computers, and Computers in between

    Directory of Open Access Journals (Sweden)

    Alexis De Vos

    2011-06-01

    Full Text Available Whereas quantum computing circuits follow the symmetries of the unitary Lie group, classical reversible computation circuits follow the symmetries of a finite group, i.e., the symmetric group. We confront the decomposition of an arbitrary classical reversible circuit with w bits and the decomposition of an arbitrary quantum circuit with w qubits. Both decompositions use the control gate as building block, i.e., a circuit transforming only one (qubit, the transformation being controlled by the other w?1 (qubits. We explain why the former circuit can be decomposed into 2w ? 1 control gates, whereas the latter circuit needs 2w ? 1 control gates. We investigate whether computer circuits, not based on the full unitary group but instead on a subgroup of the unitary group, may be decomposable either into 2w ? 1 or into 2w ? 1 control gates.

  19. Towards minimal resources of measurement-based quantum computation

    International Nuclear Information System (INIS)

    We improve the upper bound on the minimal resources required for measurement-only quantum computation (M A Nielsen 2003 Phys. Rev. A 308 96-100; D W Leung 2004 Int. J. Quantum Inform. 2 33; S Perdrix 2005 Int. J. Quantum Inform. 3 219-23). Minimizing the resources required for this model is a key issue for experimental realization of a quantum computer based on projective measurements. This new upper bound also allows one to reply in the negative to the open question presented by Perdrix (2004 Proc. Quantum Communication Measurement and Computing) about the existence of a trade-off between observable and ancillary qubits in measurement-only QC

  20. Architectural design for a topological cluster state quantum computer

    OpenAIRE

    Devitt, Simon J.; Fowler, Austin G.; Stephens, Ashley M.; Greentree, Andrew D.; Hollenberg, Lloyd C. L; Munro, William J.; Nemoto, Kae

    2008-01-01

    The development of a large scale quantum computer is a highly sought after goal of fundamental research and consequently a highly non-trivial problem. Scalability in quantum information processing is not just a problem of qubit manufacturing and control but it crucially depends on the ability to adapt advanced techniques in quantum information theory, such as error correction, to the experimental restrictions of assembling qubit arrays into the millions. In this paper we int...