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Sample records for scb quantum computers

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

    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.

  2. Quantum Computation and Quantum Information

    Wang, Yazhen

    2012-01-01

    Quantum computation and quantum information are of great current interest in computer science, mathematics, physical sciences and engineering. They will likely lead to a new wave of technological innovations in communication, computation and cryptography. As the theory of quantum physics is fundamentally stochastic, randomness and uncertainty are deeply rooted in quantum computation, quantum simulation and quantum information. Consequently quantum algorithms are random in nature, and quantum ...

  3. Quantum Chaos and Quantum Computers

    Shepelyansky, D L

    2001-01-01

    The standard generic quantum computer model is studied analytically and numerically and the border for emergence of quantum chaos, induced by imperfections and residual inter-qubit couplings, is determined. This phenomenon appears in an isolated quantum computer without any external decoherence. The onset of quantum chaos leads to quantum computer hardware melting, strong quantum entropy growth and destruction of computer operability. The time scales for development of quantum chaos and ergodicity are determined. In spite the fact that this phenomenon is rather dangerous for quantum computing it is shown that the quantum chaos border for inter-qubit coupling is exponentially larger than the energy level spacing between quantum computer eigenstates and drops only linearly with the number of qubits n. As a result the ideal multi-qubit structure of the computer remains rather robust against imperfections. This opens a broad parameter region for a possible realization of quantum computer. The obtained results are...

  4. Unconventional Quantum Computing Devices

    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.

  5. Quantum information and computation

    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.

  6. Quantum Computational Complexity

    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.

  7. Quantum walk computation

    Kendon, Viv [School of Physics and Astronomy, University of Leeds, LS2 9JT (United Kingdom)

    2014-12-04

    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.

  8. Duality Computing in Quantum Computers

    LONG Gui-Lu; LIU Yang

    2008-01-01

    In this letter, we propose a duality computing mode, which resembles particle-wave duality property when a quantum system such as a quantum computer passes through a double-slit. In this mode, computing operations are not necessarily unitary. The duality mode provides a natural link between classical computing and quantum computing. In addition, the duality mode provides a new tool for quantum algorithm design.

  9. Quantum Analogue Computing

    Kendon, Vivien M; Nemoto, Kae; Munro, William J.

    2010-01-01

    We briefly review what a quantum computer is, what it promises to do for us, and why it is so hard to build one. Among the first applications anticipated to bear fruit is quantum simulation of quantum systems. While most quantum computation is an extension of classical digital computation, quantum simulation differs fundamentally in how the data is encoded in the quantum computer. To perform a quantum simulation, the Hilbert space of the system to be simulated is mapped directly onto the Hilb...

  10. Quantum Computer Games: Quantum Minesweeper

    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…

  11. Automata and Quantum Computing

    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.

  12. Physics of quantum computation

    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

  13. Quantum Computing for Computer Architects

    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

  14. Quantum Computing

    Ladd, Thaddeus D; Laflamme, Raymond; Nakamura, Yasunobu; Monroe, Christopher; O'Brien, Jeremy L; 10.1038/nature08812

    2010-01-01

    Quantum mechanics---the theory describing the fundamental workings of nature---is famously counterintuitive: it predicts that a particle can be in two places at the same time, and that two remote particles can be inextricably and instantaneously linked. These predictions have been the topic of intense metaphysical debate ever since the theory's inception early last century. However, supreme predictive power combined with direct experimental observation of some of these unusual phenomena leave little doubt as to its fundamental correctness. In fact, without quantum mechanics we could not explain the workings of a laser, nor indeed how a fridge magnet operates. Over the last several decades quantum information science has emerged to seek answers to the question: can we gain some advantage by storing, transmitting and processing information encoded in systems that exhibit these unique quantum properties? Today it is understood that the answer is yes. Many research groups around the world are working towards one ...

  15. Quantum Logic and Quantum Computation

    Pavicic, Mladen; Megill, Norman D.

    2008-01-01

    We use classes of Hilbert lattice equations for an alternative representation of Hilbert lattices and Hilbert spaces of arbitrary quantum systems that might enable a direct introduction of the states of the systems into quantum computers. More specifically, we look for a way to feed a quantum computer with algebraic equations of n-th order underlying an infinite dimensional Hilbert space description of quantum systems. A number of new results on states defined on Hilbert lattices are presente...

  16. Quantum robots and quantum computers

    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.

  17. Study of Quantum Computing

    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.

  18. Quantum Genetics, Quantum Automata and Quantum Computation

    Baianu, Professor 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 a previous publication (Baianu,1971a) the formal concept of quantum automaton was introduced and its possible implications for genetic 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 trans...

  19. Integrable Quantum Computation

    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.

  20. Duality quantum computing

    2008-01-01

    In this article,we make a review on the development of a newly proposed quantum computer,duality computer,or the duality quantum computer and the duality mode of quantum computers.The duality computer is based on the particle-wave duality principle of quantum mechanics.Compared to an ordinary quantum computer,the duality quantum computer is a quantum computer on the move and passing through a multi-slit.It offers more computing operations than is possible with an ordinary quantum computer.The most two distinct operations are:the quantum division operation and the quantum combiner operation.The division operation divides the wave function of a quantum computer into many attenuated,and identical parts.The combiner operation combines the wave functions in different parts into a single part.The duality mode is a way in which a quantum computer with some extra qubit resource simulates a duality computer.The main structure of duality quantum computer and duality mode,the duality mode,their mathematical description and algorithm designs are reviewed.

  1. Quantum Computation in Computational Geometry

    Sadakane, Kunihiko; Sugawara, Noriko; Tokuyama, Takeshi

    2002-01-01

    We discuss applications of quantum computation to geometric data processing. These applications include problems on convex hulls, minimum enclosing balls, linear programming, and intersection problems. Technically, we apply well-known Grover’s algorithm (and its variants) combined with geometric algorithms, and no further knowledge of quantum computing is required. However, revealing these applications and emphasizing potential usefulness of quantum computation in geometric data processing wi...

  2. Basics of Quantum Computation

    Vedral, Vlatko; Martin B. Plenio

    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 fac...

  3. Quantum computing and spintronics

    Tentative to build a computer, which can operate according to the quantum laws, has leaded to concept of quantum computing algorithms and hardware. In this review we highlight recent developments which point the way to quantum computing on the basis solid state nanostructures after some general considerations concerning quantum information science and introducing a set of basic requirements for any quantum computer proposal. One of the major direction of research on the way to quantum computing is to exploit the spin (in addition to the orbital) degree of freedom of the electron, giving birth to the field of spintronics. We address some semiconductor approach based on spin orbit coupling in semiconductor nanostructures. (authors)

  4. Quantum information. Teleporation - cryptography - quantum computer

    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)

  5. Uncertainty In Quantum Computation

    Kak, Subhash

    2002-01-01

    We examine the effect of previous history on starting a computation on a quantum computer. Specifically, we assume that the quantum register has some unknown state on it, and it is required that this state be cleared and replaced by a specific superposition state without any phase uncertainty, as needed by quantum algorithms. We show that, in general, this task is computationally impossible.

  6. Computing quantum phase transitions

    Vojta, Thomas

    2007-01-01

    This article first gives a concise introduction to quantum phase transitions, emphasizing similarities with and differences to classical thermal transitions. After pointing out the computational challenges posed by quantum phase transitions, a number of successful computational approaches is discussed. The focus is on classical and quantum Monte Carlo methods, with the former being based on the quantum-to classical mapping while the latter directly attack the quantum problem. These methods ar...

  7. Quantum information. Teleportation - cryptography - quantum computer

    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)

  8. Simulation of quantum computers

    De Raedt, H; Michielsen, K; Hams, AH; Miyashita, S; Saito, K; Landau, DP; Lewis, SP; Schuttler, HB

    2001-01-01

    We describe a simulation approach to study the functioning of Quantum Computer hardware. The latter is modeled by a collection of interacting spin-1/2 objects. The time evolution of this spin system maps one-to-one to a quantum program carried out by the Quantum Computer. Our simulation software con

  9. Simulation of quantum computers

    Raedt, H. De; Michielsen, K.; Hams, A.H.; Miyashita, S.; Saito, K.

    2000-01-01

    We describe a simulation approach to study the functioning of Quantum Computer hardware. The latter is modeled by a collection of interacting spin-1/2 objects. The time evolution of this spin system maps one-to-one to a quantum program carried out by the Quantum Computer. Our simulation software con

  10. Quantum Computing since Democritus

    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.

  11. Intrinsic Quantum Computation

    Crutchfield, James P; Wiesner, Karoline

    2006-01-01

    We introduce ways to measure information storage in quantum systems, using a recently introduced computation-theoretic model that accounts for measurement effects. The first, the quantum excess entropy, quantifies the shared information between a quantum process's past and its future. The second, the quantum transient information, determines the difficulty with which an observer comes to know the internal state of a quantum process through measurements. We contrast these with von Neumann entr...

  12. Quantum computation by measurement and quantum memory

    What resources are universal for quantum computation? In the standard model of a quantum computer, a computation consists of a sequence of unitary gates acting coherently on the qubits making up the computer. This requirement for coherent unitary dynamical operations is widely believed to be the critical element of quantum computation. Here we show that a very different model involving only projective measurements and quantum memory is also universal for quantum computation. In particular, no coherent unitary dynamics are involved in the computation

  13. Photonic Quantum Computing

    Barz, Stefanie

    2013-05-01

    Quantum physics has revolutionized our understanding of information processing and enables computational speed-ups that are unattainable using classical computers. In this talk I will present a series of experiments in the field of photonic quantum computing. The first experiment is in the field of photonic state engineering and realizes the generation of heralded polarization-entangled photon pairs. It overcomes the limited applicability of photon-based schemes for quantum information processing tasks, which arises from the probabilistic nature of photon generation. The second experiment uses polarization-entangled photonic qubits to implement ``blind quantum computing,'' a new concept in quantum computing. Blind quantum computing enables a nearly-classical client to access the resources of a more computationally-powerful quantum server without divulging the content of the requested computation. Finally, the concept of blind quantum computing is applied to the field of verification. A new method is developed and experimentally demonstrated, which verifies the entangling capabilities of a quantum computer based on a blind Bell test.

  14. Quantum Computation and Quantum Spin Dynamics

    Raedt, Hans De; Michielsen, Kristel; Hams, Anthony; Miyashita, Seiji; Saito, Keiji

    2001-01-01

    We analyze the stability of quantum computations on physically realizable quantum computers by simulating quantum spin models representing quantum computer hardware. Examples of logically identical implementations of the controlled-NOT operation are used to demonstrate that the results of a quantum

  15. Dissipative quantum computing with open quantum walks

    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.

  16. Probabilistic Cloning and Quantum Computation

    GAO Ting; YAN Feng-Li; WANG Zhi-Xi

    2004-01-01

    @@ We discuss the usefulness of quantum cloning and present examples of quantum computation tasks for which the cloning offers an advantage which cannot be matched by any approach that does not resort to quantum cloning.In these quantum computations, we need to distribute quantum information contained in the states about which we have some partial information. To perform quantum computations, we use a state-dependent probabilistic quantum cloning procedure to distribute quantum information in the middle of a quantum computation.

  17. Explorations in quantum computing

    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

  18. Quantum-dot computing

    A quantum computer would put the latest PC to shame. Not only would such a device be faster than a conventional computer, but by exploiting the quantum-mechanical principle of superposition it could change the way we think about information processing. However, two key goals need to be met before a quantum computer becomes reality. The first is to be able to control the state of a single quantum bit (or 'qubit') and the second is to build a two-qubit gate that can produce 'entanglement' between the qubit states. (U.K.)

  19. Quantum-dot computing

    Milburn, Gerard

    2003-10-01

    A quantum computer would put the latest PC to shame. Not only would such a device be faster than a conventional computer, but by exploiting the quantum-mechanical principle of superposition it could change the way we think about information processing. However, two key goals need to be met before a quantum computer becomes reality. The first is to be able to control the state of a single quantum bit (or 'qubit') and the second is to build a two-qubit gate that can produce 'entanglement' between the qubit states. (U.K.)

  20. Quantum Analog Computing

    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.

  1. High Performance Quantum Computing

    Simon J. Devitt; 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 farm is utilized ...

  2. SCB thermite igniter studies

    Bickes, R.W. Jr.; Wackerbarth, D.E. [Sandia National Labs., Albuquerque, NM (United States); Mohler, J.H. [Energetic Materials Associates, Inc., Vero Beach, FL (United States)

    1996-12-31

    The authors report on recent studies comparing the ignition threshold of temperature cycled, SCB thermite devices with units that were not submitted to temperature cycling. Aluminum/copper-oxide thermite was pressed into units at two densities, 45% of theoretical maximum density (TMD) or 47% of TMD. Half of each of the density sets underwent three thermal cycles; each cycle consisted of 2 hours at 74 C and 2 hours at {minus}54 C, with a 5 minute maximum transfer time between temperatures. The temperature cycled units were brought to ambient temperature before the threshold testing. Both the density and the thermal cycling affected the all-fire voltage. Using a 5.34 {micro}F CDU (capacitor discharge unit) firing set, the all-fire voltage for the units that were not temperature cycled increased with density from 32.99 V (45% TMD) to 39.32 V (47% TMD). The all-fire voltages for the thermally cycled units were 34.42 V (45% TMD) and 58.1 V (47% TMD). They also report on no-fire levels at ambient temperature for two component designs; the 5 minute no-fire levels were greater than 1.2 A. Units were also subjected to tests in which 1 W of RF power was injected into the bridges at 10 MHz for 5 minutes. The units survived and fired normally afterwards. Finally, units were subjected to pin-to-pin electrostatic discharge (ESD) tests. None of the units fired upon application of the ESD pulse, and all of the tested units fired normally afterwards.

  3. Review of quantum computation

    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

  4. Universal quantum computation

    Möttönen, M P; Bergholm, V; Salomaa, M M; Mottonen, Mikko; Vartiainen, Juha J.; Bergholm, Ville; Salomaa, Martti M.

    2004-01-01

    Quantum-circuit optimization is essential for any practical realization of quantum computation. We present a method for decomposing an arbitrary n-bit quantum gate, using the Cosine-Sine decomposition, into a sequence of 4^n - 2^(n+1) CNOT gates and 4^n one-qubit rotations. The decomposition is optimal in the number of one-qubit rotations and scales considerably better than the previously reported decompositions in the number of CNOT gates.

  5. Quantum computing with defects

    Weber, J R; Koehl, W. F.; 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 qua...

  6. Quantum computation: Honesty test

    Morimae, Tomoyuki

    2013-11-01

    Alice does not have a quantum computer so she delegates a computation to Bob, who does own one. But how can Alice check whether the computation that Bob performs for her is correct? An experiment with photonic qubits demonstrates such a verification protocol.

  7. Quantum steady computation

    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

  8. Quantum steady computation

    Castagnoli, G. (Dipt. di Informatica, Sistemistica, Telematica, Univ. di Genova, Viale Causa 13, 16145 Genova (IT))

    1991-08-10

    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.

  9. Quantum computing by interrogation

    Supic, Ivan

    2014-01-01

    Treball final de màster oficial fet en col·laboració amb Universitat Autònoma de Barcelona (UAB), Universitat de Barcelona (UB) i Institut de Ciències Fotòniques (ICFO) [ANGLÈS] Quantum information theory forms a bridge between the foundations of quantum mechanics and its promising practical potentials. The extensive theoretical research has been conducted during the last decades and the applications such as quantum key distribution and quantum computing promise to provide real technologic...

  10. Computational Methods for Simulating Quantum Computers

    Raedt, H. De; Michielsen, K.

    2006-01-01

    This review gives a survey of numerical algorithms and software to simulate quantum computers. It covers the basic concepts of quantum computation and quantum algorithms and includes a few examples that illustrate the use of simulation software for ideal and physical models of quantum computers.

  11. Quantum computers get real

    A quantum computer has successfully factorized a number for the first time. Quantum mechanics is an extremely successful theory, but also a troubling one. For many years progress was made by concentrating on the obvious applications, and not worrying too much about the counterintuitive world view that quantum mechanics implies. More recently, however, the development of quantum-information theory has reversed this approach. If we take seriously what quantum mechanics seems to be telling us about the world, we can use this 'quantum weirdness' to do apparently impossible things. Probably the most famous application of quantum mechanics is the quantum computer, which is capable of performing calculations that are impossible with any classical device. At first the questions that quantum computers could tackle were rather esoteric, but in 1994 Peter Shor of AT and T Laboratories showed how a quantum computer could factor large numbers, thus rendering most modern cryptographic systems potentially obsolete. In 1996 David Cory and co-workers at the Massachusetts Institute of Technology (MIT) showed how nuclear magnetic resonance (NMR) - a technique best known for its applications in medical imaging and in chemistry - could be used to build small quantum computers. NMR systems are easily controlled by the magnetic component of electromagnetic fields and are only weakly affected by decoherence, and so progress was extremely rapid. Within two years, several two-qubit computers had been developed, and simple algorithms had been implemented. The race was on to build bigger and better NMR quantum computers, and to use them for more interesting tasks. The lead in this race has been held by several different research groups, but has now been decisively claimed by Isaac Chuang's group at Stanford University and IBM's Almaden Research Center in California. Chuang and co-workers have implemented the simplest example of Shor's quantum-factoring algorithm (L Vandersypen 2001 Nature 414

  12. Efficient Quantum Computation with Probabilistic Quantum Gates

    Duan, L. -M.; Raussendorf, R.

    2005-01-01

    With a combination of the quantum repeater and the cluster state approaches, we show that efficient quantum computation can be constructed even if all the entangling quantum gates only succeed with an arbitrarily small probability $p$. The required computational overhead scales efficiently both with $1/p$ and $n$, where $n$ is the number of qubits in the computation. This approach provides an efficient way to combat noise in a class of quantum computation implementation schemes, where the dom...

  13. Verifiable Quantum Computing

    Kashefi, Elham

    Over the next five to ten years we will see a state of flux as quantum devices become part of the mainstream computing landscape. However adopting and applying such a highly variable and novel technology is both costly and risky as this quantum approach has an acute verification and validation problem: On the one hand, since classical computations cannot scale up to the computational power of quantum mechanics, verifying the correctness of a quantum-mediated computation is challenging; on the other hand, the underlying quantum structure resists classical certification analysis. Our grand aim is to settle these key milestones to make the translation from theory to practice possible. Currently the most efficient ways to verify a quantum computation is to employ cryptographic methods. I will present the current state of the art of various existing protocols where generally there exists a trade-off between the practicality of the scheme versus their generality, trust assumptions and security level. EK gratefully acknowledges funding through EPSRC Grants EP/N003829/1 and EP/M013243/1.

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

    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.

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

    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.

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

    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.

  17. Spintronics and Quantum Computing with Quantum Dots

    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 superexchange. We ...

  18. Simulating Chemistry Using Quantum Computers

    Kassal, Ivan; Whitfield, James D.; Perdomo-Ortiz, Alejandro; Yung, Man-Hong; Aspuru-Guzik, Alan

    2011-01-01

    The difficulty of simulating quantum systems, well-known to quantum chemists, prompted the idea of quantum computation. One can avoid the steep scaling associated with the exact simulation of increasingly large quantum systems on conventional computers, by mapping the quantum system to another, more controllable one. In this review, we discuss to what extent the ideas in quantum computation, now a well-established field, have been applied to chemical problems. We describe algorithms that achi...

  19. Hamiltonians for Quantum Computing

    Privman, Vladimir; Mozyrsky, Dima; Hotaling, Steven P.

    1997-01-01

    We argue that the analog nature of quantum computing makes the usual design approach of constructing complicated logical operations from many simple gates inappropriate. Instead, we propose to design multi-spin quantum gates in which the input and output two-state systems (spins) are not necessarily identical. We outline the design criteria for such devices and then review recent results for single-unit Hamiltonians that accomplish the NOT and XOR functions.

  20. Quantum Computing using Photons

    Elhalawany, Ahmed; Leuenberger, Michael

    2013-03-01

    In this work, we propose a theoretical model of two-quantum bit gates for quantum computation using the polarization states of two photons in a microcavity. By letting the two photons interact non-resonantly with four quantum dots inside the cavity, we obtain an effective photon-photon interaction which we exploit for the implementation of an universal XOR gate. The two-photon Hamiltonian is written in terms of the photons' total angular momentum operators and their states are written using the Schwinger representation of the total angular momentum.

  1. Quantum information and computation

    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)

  2. Computational quantum chemistry website

    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

  3. Quantum probabilistically cloning and computation

    2008-01-01

    In this article we make a review on the usefulness of probabilistically cloning and present examples of quantum computation tasks for which quantum cloning offers an advantage which cannot be matched by any approach that does not resort to it.In these quantum computations,one needs to distribute quantum information contained in states about which we have some partial information.To perform quantum computations,one uses state-dependent probabilistic quantum cloning procedure to distribute quantum information in the middle of a quantum computation.And we discuss the achievable efficiencies and the efficient quantum logic network for probabilistic cloning the quantum states used in implementing quantum computation tasks for which cloning provides enhancement in performance.

  4. Undergraduate computational physics projects on quantum computing

    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.

  5. Quantum Computation and Spin Physics

    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.

  6. Quantum Computations: Fundamentals And Algorithms

    Duplij, Steven; Shapoval, Illia

    2007-01-01

    Basic concepts of quantum theory of information, principles of quantum calculations and the possibility of creation on this basis unique on calculation power and functioning principle device, named quantum computer, are briefly reviewed. The main blocks of quantum logic, schemes of implementation of quantum calculations, as well as some known today effective quantum algorithms, called to realize advantages of quantum calculations upon classical, are concerned. Among them special place is take...

  7. Quantum Mobile Crypto-Computation

    XIONGYan; CHENHuanhuan; GUNaijie; MIAOFuyou

    2005-01-01

    In this paper, a quantum approach for solving the mobile crypto-computation problem is proposed. In our approach, quantum signature and quantum entanglement have been employed to strengthen the security of mobile computation. Theory analysis shows that our solution is secure against classic and quantum attacks.

  8. Blind Quantum Computation

    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. Scalable Quantum Computing with "Enhancement" Quantum Dots

    Lyanda-Geller, Y B; Yang, M J

    2005-01-01

    We propose a novel scheme of solid state realization of a quantum computer based on single spin "enhancement mode" quantum dots as building blocks. In the enhancement quantum dots, just one electron can be brought into initially empty dot, in contrast to depletion mode dots based on expelling of electrons from multi-electron dots by gates. The quantum computer architectures based on depletion dots are confronted by several challenges making scalability difficult. These challenges can be successfully met by the approach based on ehnancement mode, capable of producing square array of dots with versatile functionalities. These functionalities allow transportation of qubits, including teleportation, and error correction based on straightforward one- and two-qubit operations. We describe physical properties and demonstrate experimental characteristics of enhancement quantum dots and single-electron transistors based on InAs/GaSb composite quantum wells. We discuss the materials aspects of quantum dot quantum compu...

  10. Classically-Controlled Quantum Computation

    Perdrix, Simon; Jorrand, Philippe

    2004-01-01

    Quantum computations usually take place under the control of the classical world. We introduce a Classically-controlled Quantum Turing Machine (CQTM) which is a Turing Machine (TM) with a quantum tape for acting on quantum data, and a classical transition function for a formalized classical control. In CQTM, unitary transformations and measurements are allowed. We show that any classical TM is simulated by a CQTM without loss of efficiency. The gap between classical and quantum computations, ...

  11. Quantum Computation and Spin Electronics

    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. We discuss five ...

  12. Genetic Algorithms and Quantum Computation

    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 ...

  13. Quantum Computing and Dynamical Quantum Models

    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 computers; and can...

  14. Relativistic quantum chemistry on quantum computers

    Veis, L.; Visnak, J.; Fleig, T.;

    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...

  15. Quantum computing on encrypted data

    Fisher, K. A. G.; Broadbent, A.; Shalm, L. K.; Yan, Z.; Lavoie, J.; Prevedel, R.; Jennewein, T.; Resch, K. J.

    2014-01-01

    The ability to perform computations on encrypted data is a powerful tool for protecting privacy. Recently, protocols to achieve this on classical computing systems have been found. Here, we present an efficient solution to the quantum analogue of this problem that enables arbitrary quantum computations to be carried out on encrypted quantum data. We prove that an untrusted server can implement a universal set of quantum gates on encrypted quantum bits (qubits) without learning any information about the inputs, while the client, knowing the decryption key, can easily decrypt the results of the computation. We experimentally demonstrate, using single photons and linear optics, the encryption and decryption scheme on a set of gates sufficient for arbitrary quantum computations. As our protocol requires few extra resources compared with other schemes it can be easily incorporated into the design of future quantum servers. These results will play a key role in enabling the development of secure distributed quantum systems.

  16. Quantum computing with defects.

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

    2010-05-11

    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 coordinated semiconductors. PMID:20404195

  17. Quantum computation and complexity theory

    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.

  18. Communication Capacity of Quantum Computation

    Bose, S; Rallan, L.; 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.

  19. Quantum computer for dummies (in Russian)

    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.

  20. Quantum computation with scattering matrices

    Giorgadze, G.; Tevzadze, R.

    2006-01-01

    We discuss possible applications of the 1-D direct and inverse scattering problem to design of universal quantum gates for quantum computation. The potentials generating some universal gates are described.

  1. Interfacing External Quantum Devices to a Universal Quantum Computer

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

    2011-01-01

    We present a scheme to use external quantum devices using the universal quantum computer previously constructed. We thereby show how the universal quantum computer can utilize networked quantum information resources to carry out local computations. Such information may come from specialized quantum devices or even from remote universal quantum computers. We show how to accomplish this by devising universal quantum computer programs that implement well known oracle based quantum algorithms, na...

  2. Hypercomputation based on quantum computing

    Sicard, A; Ospina, J; Sicard, Andr\\'es; V\\'elez, Mario; Ospina, Juan

    2004-01-01

    We present a quantum algorithm for a (classically) incomputable decision problem: the Hilbert's tenth problem; namely, we present a hypercomputation model based on quantum computation. The model is inspired by the one proposed by Tien D. Kieu. Our model exploits the quantum adiabatic process and the characteristics of the representation of the dynamical algebra su(1,1) associated to the infinite square well. Furthermore, it is demonstrated that the model proposed is a universal quantum computation model.

  3. Addition on a Quantum Computer

    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.

  4. Quantum computing for pattern classification

    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 measuring the Hamming di...

  5. Multi-party Quantum Computation

    Smith, A

    2001-01-01

    We investigate definitions of and protocols for multi-party quantum computing in the scenario where the secret data are quantum systems. We work in the quantum information-theoretic model, where no assumptions are made on the computational power of the adversary. For the slightly 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 establish that any multi-party quantum computation can be securely performed as long as the number of dishonest players is less than n/6.

  6. Smart semiconductor bridge (SCB) igniter for explosives

    Bickes, R. W., Jr.

    We have developed a silicon semiconductor bridge (SCB) igniter which, when driven with a low-energy current pulse, produces a plasma discharge that ignites explosive materials pressed against the bridge. Our experiments have demonstrated that SCB explosive devices function in a few tens of microseconds at one-tenth the input energy of hot-wire devices. Despite the low input energies for ignition, tests have revealed SCB devices to be explosively safe, passing electrostatic discharge (ESD) requirements and no-fire current levels. In fact, SCB devices have better no-fire characteristics than hot-wire devices, because of the intimate bridge contact with the underlying thermally conductive substrate. We have tested several different prototype explosive devices including pyrotechnic actuators, secondary explosive deflagration-to-detonation detonators and a primary explosive detonator. In addition, we have tested SCB actuators with breadboarded smart firing sets that will fire the SCB actuators only after transmission of a digital code, after a preset delay, or in a preprogrammed sequence. We have also tested an optical system that requires only a single fiber optic cable connecting the SCB device to a low power laser that both energizes the firing set and transmits a coded firing signal.

  7. Blind Quantum Computation

    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 situa......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 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 cheat-sensitive security achieved relies only upon quantum theory being true. The security analysis carried out assumes the eavesdropper performs individual attacks....

  8. Massively parallel quantum computer simulator

    De Raedt, K.; Michielsen, K.; De Raedt, H.; Trieu, B.; Arnold, G.; Richter, M.; Lippert, Th.; Watanabe, H.; Ito, N.

    2007-01-01

    We describe portable software to simulate universal quantum computers on massive parallel Computers. We illustrate the use of the simulation software by running various quantum algorithms on different computer architectures, such as a IBM BlueGene/L, a IBM Regatta p690+, a Hitachi SR11000/J1, a Cray

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

    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)

  10. Superposition, Entanglement and Quantum Computation

    Forcer, T.M.; Hey, A. J. G.; Ross, D. A.; P.G.R.Smith

    2002-01-01

    The paper examines the roles played by superposition and entanglement in quantum computing. The analysis is illustrated by discussion of a 'classical' electronic implementation of Grover's quantum search algorithm. It is shown explicitly that the absence of multi-particle entanglement leads to exponentially rising resources for implementing such quantum algorithms.

  11. Quantum physics, simulation, and computation

    Full text: The ultimate scope and power of computers will be determined by the laws of physics. Quantum computers exploit the rules of quantum mechanics, using quantum coherence and entanglement for new ways of information processing. Up to date, the realization of these systems requires extremely precise control of matter on the atomic scale and a nearly perfect isolation from the environment. The question, to what extent quantum information processing can also be exploited in 'natural' and less controlled systems, including biological ones, is exciting but still open. In this talk, I will present some of our recent work on (quantum) physically and biologically motivated models of information processing. (author)

  12. Quantum Nash Equilibria and Quantum Computing

    Fellman, Philip Vos; Post, Jonathan Vos

    In 2004, At the Fifth International Conference on Complex Systems, we drew attention to some remarkable findings by researchers at the Santa Fe Institute (Sato, Farmer and Akiyama, 2001) about hitherto unsuspected complexity in the Nash Equilibrium. As we progressed from these findings about heteroclinic Hamiltonians and chaotic transients hidden within the learning patterns of the simple rock-paper-scissors game to some related findings on the theory of quantum computing, one of the arguments we put forward was just as in the late 1990's a number of new Nash equilibria were discovered in simple bi-matrix games (Shubik and Quint, 1996; Von Stengel, 1997, 2000; and McLennan and Park, 1999) we would begin to see new Nash equilibria discovered as the result of quantum computation. While actual quantum computers remain rather primitive (Toibman, 2004), and the theory of quantum computation seems to be advancing perhaps a bit more slowly than originally expected, there have, nonetheless, been a number of advances in computation and some more radical advances in an allied field, quantum game theory (Huberman and Hogg, 2004) which are quite significant. In the course of this paper we will review a few of these discoveries and illustrate some of the characteristics of these new "Quantum Nash Equilibria". The full text of this research can be found at http://necsi.org/events/iccs6/viewpaper.php?id-234

  13. Quantum computation and hidden variables

    Aristov, V V

    2010-01-01

    Many physicists limit oneself to an instrumentalist description of quantum phenomena and ignore the problems of foundation and interpretation of quantum mechanics. This instrumentalist approach results to "specialization barbarism" and mass delusion concerning the problem, how a quantum computer can be made. The idea of quantum computation can be described within the limits of quantum formalism. But in order to understand how this idea can be put into practice one should realize the question: "What could the quantum formalism describe?", in spite of the absence of an universally recognized answer. Only a realization of this question and the undecided problem of quantum foundations allows to see in which quantum systems the superposition and EPR correlation could be expected. Because of the "specialization barbarism" many authors are sure that Bell proved full impossibility of any hidden-variables interpretation. Therefore it is important to emphasize that in reality Bell has restricted to validity limits of t...

  14. Quantum Computer Using Coupled Quantum Dot Molecules

    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...

  15. Quantum Computation with Magnetic Clusters

    Dorroh, Daniel D.; Olmez, Serkay; Wang, Jian-Ping

    2013-01-01

    We propose a complete, quantitative quantum computing system which satisfies the five DiVincenzo criteria. The model is based on magnetic clusters with uniaxial anisotropy, where standard, two-state qubits are formed utilizing the two lowest-lying states of an anisotropic potential energy. We outline the quantum dynamics required by quantum computing for single qubit structures, and then define a novel measurement scheme in which qubit sates can be measured by sharp changes in current as volt...

  16. The Physics of Quantum Computation

    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.

  17. Quantum information processing in nanostructures Quantum optics; Quantum computing

    Reina-Estupinan, J H

    2002-01-01

    Since information has been regarded os a physical entity, the field of quantum information theory has blossomed. This brings novel applications, such as quantum computation. This field has attracted the attention of numerous researchers with backgrounds ranging from computer science, mathematics and engineering, to the physical sciences. Thus, we now have an interdisciplinary field where great efforts are being made in order to build devices that should allow for the processing of information at a quantum level, and also in the understanding of the complex structure of some physical processes at a more basic level. This thesis is devoted to the theoretical study of structures at the nanometer-scale, 'nanostructures', through physical processes that mainly involve the solid-state and quantum optics, in order to propose reliable schemes for the processing of quantum information. Initially, the main results of quantum information theory and quantum computation are briefly reviewed. Next, the state-of-the-art of ...

  18. Quantum entanglement and quantum computational algorithms

    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. Programming Pulse Driven Quantum Computers

    Lloyd, Seth

    1999-01-01

    Arrays of weakly-coupled quantum systems can be made to compute by subjecting them to a sequence of electromagnetic pulses of well-defined frequency and length. Such pulsed arrays are true quantum computers: bits can be placed in superpositions of 0 and 1, logical operations take place coherently, and dissipation is required only for error correction. Programming such computers is accomplished by selecting the proper sequence of pulses.

  20. Quantum computation and hidden variables

    Aristov, V. V.; Nikulov, A. V.

    2008-03-01

    Many physicists limit oneself to an instrumentalist description of quantum phenomena and ignore the problems of foundation and interpretation of quantum mechanics. This instrumentalist approach results to "specialization barbarism" and mass delusion concerning the problem, how a quantum computer can be made. The idea of quantum computation can be described within the limits of quantum formalism. But in order to understand how this idea can be put into practice one should realize the question: "What could the quantum formalism describe?", in spite of the absence of an universally recognized answer. Only a realization of this question and the undecided problem of quantum foundations allows to see in which quantum systems the superposition and EPR correlation could be expected. Because of the "specialization barbarism" many authors are sure that Bell proved full impossibility of any hidden-variables interpretation. Therefore it is important to emphasize that in reality Bell has restricted to validity limits of the no-hidden-variables proof and has shown that two-state quantum system can be described by hidden variables. The later means that no experimental result obtained on two-state quantum system can prove the existence of superposition and violation of the realism. One should not assume before unambiguous experimental evidence that any two-state quantum system is quantum bit. No experimental evidence of superposition of macroscopically distinct quantum states and of a quantum bit on base of superconductor structure was obtained for the present. Moreover same experimental results can not be described in the limits of the quantum formalism.

  1. Quantum computation using geometric algebra

    Matzke, Douglas James

    This dissertation reports that arbitrary Boolean logic equations and operators can be represented in geometric algebra as linear equations composed entirely of orthonormal vectors using only addition and multiplication Geometric algebra is a topologically based algebraic system that naturally incorporates the inner and anticommutative outer products into a real valued geometric product, yet does not rely on complex numbers or matrices. A series of custom tools was designed and built to simplify geometric algebra expressions into a standard sum of products form, and automate the anticommutative geometric product and operations. Using this infrastructure, quantum bits (qubits), quantum registers and EPR-bits (ebits) are expressed symmetrically as geometric algebra expressions. Many known quantum computing gates, measurement operators, and especially the Bell/magic operators are also expressed as geometric products. These results demonstrate that geometric algebra can naturally and faithfully represent the central concepts, objects, and operators necessary for quantum computing, and can facilitate the design and construction of quantum computing tools.

  2. Cryptography, Quantum Computation and Trapped Ions

    Hughes, Richard J.

    1997-01-01

    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.

  3. Duality quantum computer and the efficient quantum simulations

    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 can be realized in...

  4. Blind topological measurement-based quantum computation

    Morimae, Tomoyuki; Fujii, Keisuke

    2011-01-01

    Blind quantum computation is a novel secure quantum-computing protocol that enables Alice, who does not have sufficient quantum technology at her disposal, to delegate her quantum computation to Bob, who has a fully fledged quantum computer, in such a way that Bob cannot learn anything about Alice's input, output and algorithm. A recent proof-of-principle experiment demonstrating blind quantum computation in an optical system has raised new challenges regarding the scalability of blind quantu...

  5. An Algebra of Reversible Quantum Computing

    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 reversible computing are ...

  6. Quantum Computing Using Dissipation

    Beige, A; Tregenna, B; Knight, P L

    2000-01-01

    We propose a new approach to the implementation of quantum gates in which decoherence during the gate operations is strongly reduced. This is achieved by making use of an environment induced quantum Zeno effect that confines the dynamics effectively to a decoherence-free subspace.

  7. Stability of holonomic quantum computations

    Kuvshinov, V. I.; Kuzmin, A. V.

    2003-01-01

    We study the stability of holonomic quantum computations with respect to errors in assignment of control parameters. The general expression for fidelity is obtaned. In the small errors limit the simple formulae for the fidelity decrease rate is derived.

  8. Quantum computation in photonic crystals

    Angelakis, D G; Yannopapas, V; Ekert, A; Angelakis, Dimitris G.; Santos, Marcelo Franca; Yannopapas, Vassilis; Ekert, Artur

    2004-01-01

    Quantum computers require technologies that offer both sufficient control over coherent quantum phenomena and minimal spurious interactions with the environment. We show, that photons confined to photonic crystals, and in particular to highly efficient waveguides formed from linear chains of defects doped with atoms can generate strong non-linear interactions which allow to implement both single and two qubit quantum gates. The simplicity of the gate switching mechanism, the experimental feasibility of fabricating two dimensional photonic crystal structures and integrability of this device with optoelectronics offers new interesting possibilities for optical quantum information processing networks.

  9. Quantum Computation and Algorithms

    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

  10. Quantum Computing with Very Noisy Devices

    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 give evidence that...

  11. Quantum Computation with Ballistic Electrons

    Ionicioiu, Radu; Amaratunga, Gehan; Udrea, Florin

    2000-01-01

    We describe a solid state implementation of a quantum computer using ballistic single electrons as flying qubits in 1D nanowires. We show how to implement all the steps required for universal quantum computation: preparation of the initial state, measurement of the final state and a universal set of quantum gates. An important advantage of this model is the fact that we do not need ultrafast optoelectronics for gate operations. We use cold programming (or pre-programming), i.e., the gates are...

  12. Physical Realizations of Quantum Computing

    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. Self-Correcting Quantum Computers

    Bombin, H; Horodecki, M; Martín-Delgado, M A

    2009-01-01

    Is the notion of a quantum computer resilient to thermal noise unphysical? We address this question from a constructive perspective and show that local quantum Hamiltonian models provide self-correcting quantum computers. To this end, we first give a sufficient condition on the connectedness of excitations for a stabilizer code model to be a self-correcting quantum memory. We then study the two main examples of topological stabilizer codes in arbitrary dimensions and establish their self-correcting capabilities. Also, we address the transversality properties of topological color codes, showing that 6D color codes provide a self-correcting model that allows the transversal and local implementation of a universal set of operations in seven spatial dimensions. Finally, we give a procedure to initialize such quantum memories at finite temperature.

  14. Towards A Theory Of Quantum Computability

    Guerrini, Stefano; Martini, Simone; Masini, Andrea

    2015-01-01

    We propose a definition of quantum computable functions as mappings between superpositions of natural numbers to probability distributions of natural numbers. Each function is obtained as a limit of an infinite computation of a quantum Turing machine. The class of quantum computable functions is recursively enumerable, thus opening the door to a quantum computability theory which may follow some of the classical developments.

  15. Faster Quantum Chemistry Simulation on Fault-Tolerant Quantum Computers

    Jones, N. Cody; Whitfield, James D.; McMahon, Peter L.; Yung, Man-Hong; Van Meter, Rodney; Aspuru-Guzik, Alan; Yamamoto, Yoshihisa

    2012-01-01

    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...

  16. Warp-Drive Quantum Computation

    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

  17. Semiconductor bridge, SCB, ignition of energetic materials

    Bickes, R.W.; Grubelich, M.D.; Harris, S.M.; Merson, J.A.; Tarbell, W.W.

    1997-04-01

    Sandia National Laboratories` semiconductor bridge, SCB, is now being used for the ignition or initiation of a wide variety of exeoergic materials. Applications of this new technology arose because of a need at the system level to provide light weight, small volume and low energy explosive assemblies. Conventional bridgewire devices could not meet the stringent size, weight and energy requirements of our customers. We present an overview of SCB technology and the ignition characteristics for a number of energetic materials including primary and secondary explosives, pyrotechnics, thermites and intermetallics. We provide examples of systems designed to meet the modern requirements that sophisticated systems must satisfy in today`s market environments.

  18. Quantum Computing using Linear Optics

    Pittman, T B; Franson, J D

    2004-01-01

    Quantum computers are expected to be able to solve mathematical problems that cannot be solved using conventional computers. Many of these problems are of practical importance, especially in the areas of cryptography and secure communications. APL is developing an optical approach to quantum computing in which the bits, or "qubits", are represented by single photons. Our approach allows the use of ordinary (linear) optical elements that are available for the most part as off-the-shelf components. Recent experimental demonstrations of a variety of logic gates for single photons, a prototype memory device, and other devices will be described.

  19. Handbook of computational quantum chemistry

    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

  20. Entanglement Echoes in Quantum Computation

    Rossini, Davide; Benenti, Giuliano; Casati, Giulio

    2003-01-01

    We study the stability of entanglement in a quantum computer implementing an efficient quantum algorithm, which simulates a quantum chaotic dynamics. For this purpose, we perform a forward-backward evolution of an initial state in which two qubits are in a maximally entangled Bell state. If the dynamics is reversed after an evolution time $t_r$, there is an echo of the entanglement between these two qubits at time $t_e=2t_r$. Perturbations attenuate the pairwise entanglement echo and generate...

  1. QCE : A Simulator for Quantum Computer Hardware

    Michielsen, Kristel; Raedt, Hans De

    2003-01-01

    The Quantum Computer Emulator (QCE) described in this paper consists of a simulator of a generic, general purpose quantum computer and a graphical user interface. The latter is used to control the simulator, to define the hardware of the quantum computer and to debug and execute quantum algorithms.

  2. On the Problem of Programming Quantum Computers

    De Raedt, Hans; Hams, Anthony; Michielsen, Kristel; MIYASHITA, Seiji; Saito, Keiji

    2000-01-01

    We study effects of the physical realization of quantum computers on their logical operation. Through simulation of physical models of quantum computer hardware, we analyse the difficulties that are encountered in programming physical implementations of quantum computers. We discuss the origin of the instabilities of quantum algorithms and explore physical mechanisms to enlarge the region(s) of stable operation.

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

    Bao-Cang Ren; Fu-Guo Deng

    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 ...

  4. Using a quantum computer to investigate quantum chaos

    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.

  5. An all silicon quantum computer

    Ladd, T D; Yamaguchi, F; Yamamoto, Y; Abe, E; Itoh, K M

    2002-01-01

    A solid-state implementation of a quantum computer composed entirely of silicon is proposed. Qubits are Si-29 nuclear spins arranged as chains in a Si-28 (spin-0) matrix with Larmor frequencies separated by a large magnetic field gradient. No impurity dopants or electrical contacts are needed. Initialization is accomplished by optical pumping, algorithmic cooling, and pseudo-pure state techniques. Magnetic resonance force microscopy is used for readout. This proposal takes advantage of many of the successful aspects of solution NMR quantum computation, including ensemble measurement, RF control, and long decoherence times, but it allows for more qubits and improved initialization.

  6. Quantum Walks for Computer Scientists

    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

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

    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 speedup theory is se...

  8. Atomic physics: A milestone in quantum computing

    Bartlett, Stephen D.

    2016-08-01

    Quantum computers require many quantum bits to perform complex calculations, but devices with more than a few bits are difficult to program. A device based on five atomic quantum bits shows a way forward. See Letter p.63

  9. Self-correcting quantum computers

    Is the notion of a quantum computer (QC) resilient to thermal noise unphysical? We address this question from a constructive perspective and show that local quantum Hamiltonian models provide self-correcting QCs. To this end, we first give a sufficient condition on the connectedness of excitations for a stabilizer code model to be a self-correcting quantum memory. We then study the two main examples of topological stabilizer codes in arbitrary dimensions and establish their self-correcting capabilities. Also, we address the transversality properties of topological color codes, showing that six-dimensional color codes provide a self-correcting model that allows the transversal and local implementation of a universal set of operations in seven spatial dimensions. Finally, we give a procedure for initializing such quantum memories at finite temperature. (paper)

  10. Topological cluster state quantum computing

    Fowler, Austin G.; Goyal, Kovid

    2009-01-01

    The quantum computing scheme described in Phys. Rev. Lett. 98, 190504 (2007), when viewed as a cluster state computation, features a 3-D cluster state, novel adjustable strength error correction capable of correcting general errors through the correction of Z errors only, a threshold error rate approaching 1% and low overhead arbitrarily long-range logical gates. In this work, we review the scheme in detail framing discussion solely in terms of the required 3-D cluster state and its stabilizers.

  11. Brokered Graph State Quantum Computing

    Benjamin, Simon C.; Browne, Dan E.; Fitzsimons, Joe; Morton, John J. L.

    2005-01-01

    We describe a procedure for graph state quantum computing that is tailored to fully exploit the physics of optically active multi-level systems. Leveraging ideas from the literature on distributed computation together with the recent work on probabilistic cluster state synthesis, our model assigns to each physical system two logical qubits: the broker and the client. Groups of brokers negotiate new graph state fragments via a probabilistic optical protocol. Completed fragments are mapped from...

  12. An Early Quantum Computing Proposal

    Lee, Stephen Russell [Los Alamos National Laboratory; Alexander, Francis Joseph [Los Alamos National Laboratory; Barros, Kipton Marcos [Los Alamos National Laboratory; Daniels, Marcus G. [Los Alamos National Laboratory; Gattiker, James R. [Los Alamos National Laboratory; Hamada, Michael Scott [Los Alamos National Laboratory; Howse, James Walter [Los Alamos National Laboratory; Loncaric, Josip [Los Alamos National Laboratory; Pakin, Scott D. [Los Alamos National Laboratory; Somma, Rolando Diego [Los Alamos National Laboratory; Vernon, Louis James [Los Alamos National Laboratory

    2016-04-04

    The D-Wave 2X is the third generation of quantum processing created by D-Wave. NASA (with Google and USRA) and Lockheed Martin (with USC), both own D-Wave systems. Los Alamos National Laboratory (LANL) purchased a D-Wave 2X in November 2015. The D-Wave 2X processor contains (nominally) 1152 quantum bits (or qubits) and is designed to specifically perform quantum annealing, which is a well-known method for finding a global minimum of an optimization problem. This methodology is based on direct execution of a quantum evolution in experimental quantum hardware. While this can be a powerful method for solving particular kinds of problems, it also means that the D-Wave 2X processor is not a general computing processor and cannot be programmed to perform a wide variety of tasks. It is a highly specialized processor, well beyond what NNSA currently thinks of as an “advanced architecture.”A D-Wave is best described as a quantum optimizer. That is, it uses quantum superposition to find the lowest energy state of a system by repeated doses of power and settling stages. The D-Wave produces multiple solutions to any suitably formulated problem, one of which is the lowest energy state solution (global minimum). Mapping problems onto the D-Wave requires defining an objective function to be minimized and then encoding that function in the Hamiltonian of the D-Wave system. The quantum annealing method is then used to find the lowest energy configuration of the Hamiltonian using the current D-Wave Two, two-level, quantum processor. This is not always an easy thing to do, and the D-Wave Two has significant limitations that restrict problem sizes that can be run and algorithmic choices that can be made. Furthermore, as more people are exploring this technology, it has become clear that it is very difficult to come up with general approaches to optimization that can both utilize the D-Wave and that can do better than highly developed algorithms on conventional computers for

  13. Quantum Chromodynamics: Computational Aspects

    Schaefer, Thomas

    2016-01-01

    We present a brief introduction to QCD, the QCD phase diagram, and non-equilibrium phenomena in QCD. We emphasize aspects of the theory that can be addressed using computational methods, in particular euclidean path integral Monte Carlo, fluid dynamics, kinetic theory, classical field theory and holographic duality.

  14. Universality of Black Hole Quantum Computing

    Dvali, Gia; Gomez, Cesar; Lust, Dieter; Omar, Yasser; Richter, Benedikt

    2016-01-01

    By analyzing the key properties of black holes from the point of view of quantum information, we derive a model-independent picture of black hole quantum computing. It has been noticed that this picture exhibits striking similarities with quantum critical condensates, allowing the use of a common language to describe quantum computing in both systems. We analyze such quantum computing by allowing coupling to external modes, under the condition that the external influence must be soft-enough i...

  15. QCE: A Simulator for Quantum Computer Hardware

    Michielsen, Kristel; De Raedt, Hans

    2003-01-01

    The Quantum Computer Emulator (QCE) described in this paper consists of a simulator of a generic, general purpose quantum computer and a graphical user interface. The latter is used to control the simulator, to define the hardware of the quantum computer and to debug and execute quantum algorithms. QCE runs in a Windows 98/NT/2000/ME/XP environment. It can be used to validate designs of physically realizable quantum processors and as an interactive educational tool to learn about qu...

  16. ASCR Workshop on Quantum Computing for Science

    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.

  17. Quantum computation with ions in thermal motion

    Sorensen, Anders; Molmer, Klaus

    1998-01-01

    We propose an implementation of quantum logic gates via virtual vibrational excitations in an ion trap quantum computer. Transition paths involving unpopulated, vibrational states interfere destructively to eliminate the dependence of rates and revolution frequencies on vibrational quantum numbers. As a consequence quantum computation becomes feasible with ions whos vibrations are strongly coupled to a thermal reservoir.

  18. Universal Quantum Computation with Shutter Logic

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

    2005-01-01

    We show that universal quantum logic can be achieved using only linear optics and a quantum shutter device. With these elements, we design a quantum memory for any number of qubits and a CNOT gate which are the basis of a universal quantum computer. An interaction-free model for a quantum shutter is given.

  19. Models of quantum computation and quantum programming languages

    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 features and limi...

  20. Geometry of Discrete Quantum Computing

    Hanson, Andrew J.; Ortiz, Gerardo; Sabry, Amr; Tai, Yu-Tsung

    2012-01-01

    Conventional quantum computing entails a geometry based on the description of an n-qubit state using 2^{n} 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 ...

  1. Warp-Drive Quantum Computation

    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 s...

  2. General Quantum Interference Principle and Duality Computer

    LONG Gui-Lu

    2006-01-01

    In this article, we propose a general principle of quantum interference for quantum system, and based on this we propose a new type of computing machine, the duality computer, that may outperform in principle both classical computer and the quantum computer. According to the general principle of quantum interference, the very essence of quantum interference is the interference of thesub-waves of the quantum system itself. A quantum system considered here can be any quantum system: a single microscopic particle, a composite quantum system such as an atom or a molecule, or a loose collection of a few quantum objects such as two independent photons. In the duality computer,the wave of the duality computer is split into several sub-waves and they pass through different routes, where different computing gate operations are performed. These sub-waves are then re-combined to interfere to give the computational results. The quantum computer, however, has only used the particle nature of quantum object. In a duality computer,it may be possible to find a marked item from an unsorted database using only a single query, and all NP-complete problems may have polynomial algorithms. Two proof-of-the-principle designs of the duality computer are presented:the giant molecule scheme and the nonlinear quantum optics scheme. We also propose thought experiment to check the related fundamental issues, the measurement efficiency of a partial wave function.

  3. Cove: A Practical Quantum Computer Programming Framework

    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 co...

  4. Programming physical realizations of quantum computers

    De Raedt, Hans; Michielsen, Kristel; Hams, Anthony; MIYASHITA, Seiji; Saito, Keiji

    2001-01-01

    We study effects of the physical realization of quantum computers on their logical operation. Through simulation of physical models of quantum computer hardware, we analyze the difficulties that are encountered in programming physical realizations of quantum computers. Examples of logically identical implementations of the controlled-NOT operation and Grover's database search algorithm are used to demonstrate that the results of a quantum computation are unstable with respect to the physical ...

  5. Quantum computing from the ground up

    Perry, Riley Tipton

    2012-01-01

    Quantum computing - the application of quantum mechanics to information - represents a fundamental break from classical information and promises to dramatically increase a computer's power. Many difficult problems, such as the factorization of large numbers, have so far resisted attack by classical computers yet are easily solved with quantum computers. If they become feasible, quantum computers will end standard practices such as RSA encryption. Most of the books or papers on quantum computing require (or assume) prior knowledge of certain areas such as linear algebra or quantum mechanics. The majority of the currently-available literature is hard to understand for the average computer enthusiast or interested layman. This text attempts to teach quantum computing from the ground up in an easily readable way, providing a comprehensive tutorial that includes all the necessary mathematics, computer science and physics.

  6. Strange attractor simulated on a quantum computer

    M. Terraneo; Georgeot, B.; D.L. Shepelyansky

    2002-01-01

    We show that dissipative classical dynamics converging to a strange attractor can be simulated on a quantum computer. Such quantum computations allow to investigate efficiently the small scale structure of strange attractors, yielding new information inaccessible to classical computers. This opens new possibilities for quantum simulations of various dissipative processes in nature.

  7. Quantum computing with parafermions

    Hutter, Adrian; Loss, Daniel

    2016-03-01

    Zd parafermions are exotic non-Abelian quasiparticles generalizing Majorana fermions, which correspond to the case d =2 . In contrast to Majorana fermions, braiding of parafermions with d >2 allows one to perform an entangling gate. This has spurred interest in parafermions, and a variety of condensed matter systems have been proposed as potential hosts for them. In this work, we study the computational power of braiding parafermions more systematically. We make no assumptions on the underlying physical model but derive all our results from the algebraical relations that define parafermions. We find a family of 2 d representations of the braid group that are compatible with these relations. The braiding operators derived this way reproduce those derived previously from physical grounds as special cases. We show that if a d -level qudit is encoded in the fusion space of four parafermions, braiding of these four parafermions allows one to generate the entire single-qudit Clifford group (up to phases), for any d . If d is odd, then we show that in fact the entire many-qudit Clifford group can be generated.

  8. Quantum dissonance and deterministic quantum computation with a single qubit

    Ali, Mazhar

    2014-11-01

    Mixed state quantum computation can perform certain tasks which are believed to be efficiently intractable on a classical computer. For a specific model of mixed state quantum computation, namely, deterministic quantum computation with a single qubit (DQC1), recent investigations suggest that quantum correlations other than entanglement might be responsible for the power of DQC1 model. However, strictly speaking, the role of entanglement in this model of computation was not entirely clear. We provide conclusive evidence that there are instances where quantum entanglement is not present in any part of this model, nevertheless we have advantage over classical computation. This establishes the fact that quantum dissonance (a kind of quantum correlations) present in fully separable (FS) states provide power to DQC1 model.

  9. Quantum computing in a piece of glass

    Miller, Warner A.; Kreymerman, Grigoriy; 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 ...

  10. Geometry of discrete quantum computing

    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) Πk=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)

  11. A Quantum Computer Architecture using Nonlocal Interactions

    Brennen, Gavin K; Song, Daegene; Williams, Carl J.

    2003-01-01

    Several authors have described the basic requirements essential to build a scalable quantum computer. Because many physical implementation schemes for quantum computing rely on nearest neighbor interactions, there is a hidden quantum communication overhead to connect distant nodes of the computer. In this paper we propose a physical solution to this problem which, together with the key building blocks, provides a pathway to a scalable quantum architecture using nonlocal interactions. Our solu...

  12. Diamond NV centers for quantum computing and quantum networks

    Childress, L.; Hanson, R.

    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 co

  13. A theory of quantum gravity based on quantum computation

    Lloyd, Seth

    2005-01-01

    This paper proposes a method of unifying quantum mechanics and gravity based on quantum computation. In this theory, fundamental processes are described in terms of pairwise interactions between quantum degrees of freedom. The geometry of space-time is a construct, derived from the underlying quantum information processing. The computation gives rise to a superposition of four-dimensional spacetimes, each of which obeys the Einstein-Regge equations. The theory makes explicit predictions for t...

  14. Quantum computation speedup limits from quantum metrological precision bounds

    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 of quadratic speed-...

  15. Computational multiqubit tunnelling in programmable quantum annealers

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

    2016-01-01

    Quantum tunnelling is a phenomenon in which a quantum state traverses energy barriers higher than the energy of the state itself. Quantum tunnelling has been hypothesized as an advantageous physical resource for optimization in quantum annealing. However, computational multiqubit tunnelling has not yet been observed, and a theory of co-tunnelling under high- and low-frequency noises is lacking. Here we show that 8-qubit tunnelling plays a computational role in a currently available programmable quantum annealer. We devise a probe for tunnelling, a computational primitive where classical paths are trapped in a false minimum. In support of the design of quantum annealers we develop a nonperturbative theory of open quantum dynamics under realistic noise characteristics. This theory accurately predicts the rate of many-body dissipative quantum tunnelling subject to the polaron effect. Furthermore, we experimentally demonstrate that quantum tunnelling outperforms thermal hopping along classical paths for problems with up to 200 qubits containing the computational primitive.

  16. Layered Architectures for Quantum Computers and Quantum Repeaters

    Jones, Nathan C.

    This chapter examines how to organize quantum computers and repeaters using a systematic framework known as layered architecture, where machine control is organized in layers associated with specialized tasks. The framework is flexible and could be used for analysis and comparison of quantum information systems. To demonstrate the design principles in practice, we develop architectures for quantum computers and quantum repeaters based on optically controlled quantum dots, showing how a myriad of technologies must operate synchronously to achieve fault-tolerance. Optical control makes information processing in this system very fast, scalable to large problem sizes, and extendable to quantum communication.

  17. Nanophotonic quantum computer based on atomic quantum transistor

    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.

  18. Quantum Computing with Very Noisy Devices

    Knill, E

    2004-01-01

    There are quantum algorithms that can efficiently simulate quantum physics, factor large numbers and estimate integrals. As a result, quantum computers can solve otherwise intractable computational problems. One of the main problems of experimental quantum computing is to preserve fragile quantum states in the presence of errors. It is known that if the needed elementary operations (gates) can be implemented with error probabilities below a threshold, then it is possible to efficiently quantum compute with arbitrary accuracy. Here we give evidence that for independent errors the theoretical threshold is well above 3%, which is a significant improvement over that of earlier calculations. However, the resources required at such high error probabilities are excessive. Fortunately, they decrease rapidly with decreasing error probabilities. If we had quantum resources comparable to the considerable resources available in today's digital computers, we could implement non-trivial quantum algorithms at error probabil...

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

    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.

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

    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

  1. Adiabatic quantum computation and quantum annealing theory and practice

    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

  2. Non-unitary probabilistic quantum computing

    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.

  3. Zeno effect for quantum computation and control

    Paz-Silva, G A; Lidar, D A

    2011-01-01

    It is well known that the quantum Zeno effect can protect specific quantum states from decoherence by using projective measurements. Here we combine the theory of weak measurements with stabilizer quantum error correction and detection codes. We derive rigorous performance bounds which demonstrate that the Zeno effect can be used to protect appropriately encoded arbitrary states to arbitrary accuracy, while at the same time allowing for universal quantum computation or quantum control.

  4. Quantum fields on the computer

    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.

  5. DNA as Topological Quantum Computer

    Pitkänen, Matti

    2010-01-01

    This article represents a vision about how DNA might act as a topological quantum computer (tqc). Tqc means that the braidings of braid strands define tqc programs and M-matrix (generalization of S-matrix in zero energy ontology) defining the entanglement between states assignable to the end points of strands define the tqc usually coded as unitary time evolution for Schödinger equation. One can ends up to the model in the following manner. a) Darwinian selection for which the standa...

  6. On the computation of quantum characteristic exponents

    Vilela-Mendes, R; Coutinho, Ricardo

    1998-01-01

    A quantum characteristic exponent may be defined, with the same operational meaning as the classical Lyapunov exponent when the latter is expressed as a functional of densities. Existence conditions and supporting measure properties are discussed as well as the problems encountered in the numerical computation of the quantum exponents. Although an example of true quantum chaos may be exhibited, the taming effect of quantum mechanics on chaos is quite apparent in the computation of the quantum exponents. However, even when the exponents vanish, the functionals used for their definition may still provide a characterization of distinct complexity classes for quantum behavior.

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

    Salvador E. Venegas-Andraca

    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).

  8. Contextuality supplies the `magic' for quantum computation

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

    2014-06-01

    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.

  9. Elementary gates for quantum computation

    Barenco, A; Cleve, R; Di Vincenzo, D P; Margolus, N H; Shor, P W; Sleator, T; Smolin, J A; Weinfurter, H; Barenco, A; Bennett, C H; Cleve, R; DiVincenzo, D P; Margolus, N; Shor, P; Sleator, T; Smolin, J; Weinfurter, H

    1995-01-01

    We show that a set of gates that consists of all one-bit quantum gates (U(2)) and the two-bit exclusive-or gate (that maps Boolean values (x,y) to (x,x \\oplus y)) is universal in the sense that all unitary operations on arbitrarily many bits n (U(2^n)) can be expressed as compositions of these gates. We investigate the number of the above gates required to implement other gates, such as generalized Deutsch-Toffoli gates, that apply a specific U(2) transformation to one input bit if and only if the logical AND of all remaining input bits is satisfied. These gates play a central role in many proposed constructions of quantum computational networks. We derive upper and lower bounds on the exact number of elementary gates required to build up a variety of two-and three-bit quantum gates, the asymptotic number required for n-bit Deutsch-Toffoli gates, and make some observations about the number required for arbitrary n-bit unitary operations.

  10. Quantum Computation: Theory, Practice, and Future Prospects

    Chuang, Isaac

    2000-03-01

    Information is physical, and computation obeys physical laws. Ones and zeros -- elementary classical bits of information -- must be represented in physical media to be stored and processed. Traditionally, these objects are well described by classical physics, but increasingly, as we edge towards the limits of semiconductor technology, we reach a new regime where the laws of quantum physics become dominant. Strange new phenomena, like entanglement and quantum coherence, become available as new resources. How can such resources be utilized for computation? What physical systems allow construction and control of quantum phenomena? How is this relevant to future directions in information technology? The theoretical promise of quantum computation is polynomial speedup of searches, and exponentially speedups for other certain problems such as factoring. But the experimental challenge to realize such algorithms in practice is enormous: to date, quantum computers with only a handful of quantum bits have been realized in the laboratory, using electromagnetically trapped ions, and with magnetic resonance techniques. On the other hand, quantum information has been communicated over long distances using single photons. The future of quantum computation is currently subject to intense scrutiny. It may well be that these machines will not be practical. More quantum algorithms must be discovered, and new physical implementations must be realized. Quantum computation and quantum information are young fields with major issues to be overcome, but already, they have forever changed the way we think of the physical world and what can be computed with it.

  11. Photon echo quantum RAM integration in quantum computer

    Moiseev, Sergey A

    2012-01-01

    We have analyzed an efficient integration of the multi-qubit echo quantum memory into the quantum computer scheme on the atomic resonant ensembles in quantum electrodynamics cavity. Here, one atomic ensemble with controllable inhomogeneous broadening is used for the quantum memory node and other atomic ensembles characterized by the homogeneous broadening of the resonant line are used as processing nodes. We have found optimal conditions for efficient integration of multi-qubit quantum memory modified for this analyzed physical scheme and we have determined a specified shape of the self temporal modes providing a perfect reversible transfer of the photon qubits between the quantum memory node and arbitrary processing nodes. The obtained results open the way for realization of full-scale solid state quantum computing based on using the efficient multi-qubit quantum memory.

  12. Helping Students Learn Quantum Mechanics for Quantum Computing

    Singh, Chandralekha

    2016-01-01

    Quantum information science and technology is a rapidly growing interdisciplinary field drawing researchers from science and engineering fields. Traditional instruction in quantum mechanics is insufficient to prepare students for research in quantum computing because there is a lack of emphasis in the current curriculum on quantum formalism and dynamics. We are investigating the difficulties students have with quantum mechanics and are developing and evaluating quantum interactive learning tutorials (QuILTs) to reduce the difficulties. Our investigation includes interviews with individual students and the development and administration of free-response and multiple-choice tests. We discuss the implications of our research and development project on helping students learn quantum mechanics relevant for quantum computing.

  13. Brokered Graph State Quantum Computing

    Benjamin, S C; Fitzsimons, J; Morton, J J L; Benjamin, Simon C.; Browne, Dan E.; Fitzsimons, Joe; Morton, John J. L.

    2005-01-01

    We describe a procedure for graph state quantum computing that is tailored to fully exploit the physics of optically active multi-level systems. Leveraging ideas from the literature on distributed computation together with the recent work on probabilistic cluster state synthesis, our model assigns to each physical system two logical qubits: the broker and the client. Groups of brokers negotiate new graph state fragments via a probabilistic optical protocol. Completed fragments are mapped from broker to clients via a simple state transition and measurement. The clients, whose role is to store the nascent graph state long term, remain entirely insulated from failures during the brokerage. We describe an implementation in terms of NV-centres in diamond, where brokers and clients are very naturally embodied as electron and nuclear spins.

  14. Quantum Computing in Solid State Systems

    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. Effective Pure States for Bulk Quantum Computation

    Knill, Emanuel; Chuang, Isaac; Laflamme, Raymond

    1997-01-01

    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 computa...

  16. The Heisenberg representation of quantum computers

    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.

  17. Quantum Computer Games: Schrodinger Cat and Hounds

    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…

  18. Spin network setting of topological quantum computation

    Marzuoli, Annalisa; Rasetti, Mario

    2004-01-01

    The spin network simulator model represents a bridge between (generalised) circuit schemes for standard quantum computation and approaches based on notions from Topological Quantum Field Theories (TQFTs). The key tool is provided by the fiber space structure underlying the model which exhibits combinatorial properties closely related to SU(2) state sum models, widely employed in discretizing TQFTs and quantum gravity in low spacetime dimensions.

  19. Computational quantum-classical boundary of noisy commuting quantum circuits

    Fujii, Keisuke; Tamate, Shuhei

    2016-01-01

    It is often said that the transition from quantum to classical worlds is caused by decoherence originated from an interaction between a system of interest and its surrounding environment. Here we establish a computational quantum-classical boundary from the viewpoint of classical simulatability of a quantum system under decoherence. Specifically, we consider commuting quantum circuits being subject to decoherence. Or equivalently, we can regard them as measurement-based quantum computation on decohered weighted graph states. To show intractability of classical simulation in the quantum side, we utilize the postselection argument and crucially strengthen it by taking noise effect into account. Classical simulatability in the classical side is also shown constructively by using both separable criteria in a projected-entangled-pair-state picture and the Gottesman-Knill theorem for mixed state Clifford circuits. We found that when each qubit is subject to a single-qubit complete-positive-trace-preserving noise, the computational quantum-classical boundary is sharply given by the noise rate required for the distillability of a magic state. The obtained quantum-classical boundary of noisy quantum dynamics reveals a complexity landscape of controlled quantum systems. This paves a way to an experimentally feasible verification of quantum mechanics in a high complexity limit beyond classically simulatable region. PMID:27189039

  20. Computational quantum-classical boundary of noisy commuting quantum circuits.

    Fujii, Keisuke; Tamate, Shuhei

    2016-01-01

    It is often said that the transition from quantum to classical worlds is caused by decoherence originated from an interaction between a system of interest and its surrounding environment. Here we establish a computational quantum-classical boundary from the viewpoint of classical simulatability of a quantum system under decoherence. Specifically, we consider commuting quantum circuits being subject to decoherence. Or equivalently, we can regard them as measurement-based quantum computation on decohered weighted graph states. To show intractability of classical simulation in the quantum side, we utilize the postselection argument and crucially strengthen it by taking noise effect into account. Classical simulatability in the classical side is also shown constructively by using both separable criteria in a projected-entangled-pair-state picture and the Gottesman-Knill theorem for mixed state Clifford circuits. We found that when each qubit is subject to a single-qubit complete-positive-trace-preserving noise, the computational quantum-classical boundary is sharply given by the noise rate required for the distillability of a magic state. The obtained quantum-classical boundary of noisy quantum dynamics reveals a complexity landscape of controlled quantum systems. This paves a way to an experimentally feasible verification of quantum mechanics in a high complexity limit beyond classically simulatable region. PMID:27189039

  1. Quantum computing in a piece of glass

    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...

  2. Multivariable Optimization: Quantum Annealing & Computation

    Mukherjee, Sudip; Chakrabarti, Bikas K.

    2014-01-01

    Recent developments in quantum annealing techniques have been indicating potential advantage of quantum annealing for solving NP-hard optimization problems. In this article we briefly indicate and discuss the beneficial features of quantum annealing techniques and compare them with those of simulated annealing techniques. We then briefly discuss the quantum annealing studies of some model spin glass and kinetically constrained systems.

  3. Monte Carlo Simulation of Quantum Computation

    Cerf, N. J.; Koonin, S. E.

    1997-01-01

    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 Fouri...

  4. Quantum Computing: Linear Optics Implementations

    Sundsøy, Pål

    2016-01-01

    One of the main problems that optical quantum computing has to overcome is the efficient construction of two-photon gates. Theoretically these gates can be realized using Kerr-nonlinearities, but the techniques involved are experimentally very difficult. We therefore employ linear optics with projective measurements to generate these non-linearities. The downside is that the measurement-induced nonlinearities achieved with linear optics are less versatile and the success rate can be quite low. This project is mainly the result of a literature study but also a theoretical work on the physics behind quantum optical multiports which is essential for realizing two-photon gates. By applying different postcorrection techniques we increase the probability of success in a modifed non-linear sign shift gate which is foundational for the two photon controlled-NOT gate. We prove that it's not possible to correct the states by only using a single beam splitter. We show that it might be possible to increase the probabilit...

  5. An overview of quantum computation models: quantum automata

    2008-01-01

    Quantum automata,as theoretical models of quantum computers,include quantum finite automata (QFA),quantum sequential machines (QSM),quantum pushdown automata (QPDA),quantum Turing machines (QTM),quantum cellular automata (QCA),and the others,for example,automata theory based on quantum logic (orthomodular lattice-valued automata).In this paper,we try to outline a basic progress in the research on these models,focusing on QFA,QSM,QPDA,QTM,and orthomodular lattice-valued automata.Also,other models closely relative to them are mentioned.In particular,based on the existing results in the literature,we finally address a number of problems to be studied in future.

  6. Quantum and classical dynamics in adiabatic computation

    Crowley, P. J. D.; Duric, T.; Vinci, W.; Warburton, P. A.; Green, A. G.

    2014-01-01

    Adiabatic transport provides a powerful way to manipulate quantum states. By preparing a system in a readily initialized state and then slowly changing its Hamiltonian, one may achieve quantum states that would otherwise be inaccessible. Moreover, a judicious choice of final Hamiltonian whose ground state encodes the solution to a problem allows adiabatic transport to be used for universal quantum computation. However, the dephasing effects of the environment limit the quantum correlations th...

  7. Quantum Field Symbolic Analog Computation: Relativity Model

    Manoharan, A. C.

    2000-01-01

    It is natural to consider a quantum system in the continuum limit of space-time configuration. Incorporating also, Einstein's special relativity, leads to the quantum theory of fields. Non-relativistic quantum mechanics and classical mechanics are special cases. By studying vacuum expectation values (Wightman functions W(n; z) where z denotes the set of n complex variables) of products of quantum field operators in a separable Hilbert space, one is led to computation of holomorphy domains for...

  8. Geometry of Quantum Computation with Qudits

    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

  9. The potential of the quantum computer

    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...

  10. Geometry of abstraction in quantum computation

    Pavlovic, Dusko

    2010-01-01

    Quantum algorithms are sequences of abstract operations, performed on non-existent computers. They are in obvious need of categorical semantics. We present some steps in this direction, following earlier contributions of Abramsky, Coecke and Selinger. In particular, we analyze function abstraction in quantum computation, which turns out to characterize its classical interfaces. Some quantum algorithms provide feasible solutions of important hard problems, such as factoring and discrete log (which are the building blocks of modern cryptography). It is of a great practical interest to precisely characterize the computational resources needed to execute such quantum algorithms. There are many ideas how to build a quantum computer. Can we prove some necessary conditions? Categorical semantics help with such questions. We show how to implement an important family of quantum algorithms using just abelian groups and relations.

  11. Problems and solutions in quantum computing and quantum information

    Steeb, Willi-Hans

    2004-01-01

    Quantum computing and quantum information are two of thefastest-growing and most exciting research areas in physics. Thepossibilities of using non-local behaviour of quantum mechanics tofactorize integers in random polynomial time have added to this newinterest. This invaluable book provides a collection of problems inquantum computing and quantum information together with detailedsolutions. It consists of two parts: in the first partfinite-dimensional systems are considered, while the second part dealswith finite-dimensional systems. All the important concepts and topics are included, such as

  12. Determine Ramsey numbers on a quantum computer

    Wang, Hefeng

    2015-01-01

    We present a quantum algorithm for computing the Ramsey numbers whose computational complexity grows super-exponentially with the number of vertices of a graph on a classical computer. The problem is mapped to a decision problem on a quantum computer, a probe qubit is coupled to a register that represents the problem and detects the energy levels of the problem Hamiltonian. The decision problem is solved by determining whether the probe qubit exhibits resonance dynamics. The algorithm shows a...

  13. Quantum computation architecture using optical tweezers

    Weitenberg, Christof; Kuhr, Stefan; Mølmer, Klaus;

    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...... quantum computing....

  14. Wavelets and Wavelet Packets on Quantum Computers

    Klappenecker, Andreas

    1999-01-01

    We show how periodized wavelet packet transforms and periodized wavelet transforms can be implemented on a quantum computer. Surprisingly, we find that the implementation of wavelet packet transforms is less costly than the implementation of wavelet transforms on a quantum computer.

  15. On the completeness of quantum computation models

    Arrighi, Pablo; Dowek, Gilles

    2010-01-01

    The notion of computability is stable (i.e. independent of the choice of an indexing) over infinite-dimensional vector spaces provided they have a finite "tensorial dimension". Such vector spaces with a finite tensorial dimension permit to define an absolute notion of completeness for quantum computation models and give a precise meaning to the Church-Turing thesis in the framework of quantum theory. (Extra keywords: quantum programming languages, denotational semantics, universality.)

  16. Linear Optics Quantum Computation: an Overview

    Myers, C R; Laflamme, R

    2005-01-01

    We give an overview of linear optics quantum computing, focusing on the results from the original KLM paper. First we give a brief summary of the advances made with optics for quantum computation prior to KLM. We next discuss the KLM linear optics scheme, giving detailed examples. Finally we go through quantum error correction for the LOQC theory, showing how to obtain the threshold when dealing with Z-measurement errors.

  17. Accounting Principles are Simulated on Quantum Computers

    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 quantum Gau\\ss-Jor...

  18. Bifurcation-based adiabatic quantum computation with a nonlinear oscillator network: Toward quantum soft computing

    Hayato Goto

    2015-01-01

    The dynamics of nonlinear systems qualitatively change depending on their parameters, which is called bifurcation. A quantum-mechanical nonlinear oscillator can yield a quantum superposition of two oscillation states, known as a Schr\\"odinger cat state, via quantum adiabatic evolution through its bifurcation point. Here we propose a quantum computer comprising such quantum nonlinear oscillators, instead of quantum bits, to solve hard combinatorial optimization problems. The nonlinear oscillat...

  19. Experimental demonstration of deterministic one-way quantum computing on a NMR quantum computer

    Ju, Chenyong; Zhu, Jing; Peng, Xinhua; Chong, Bo; Zhou, Xianyi; Du, Jiangfeng

    2008-01-01

    One-way quantum computing is an important and novel approach to quantum computation. By exploiting the existing particle-particle interactions, we report the first experimental realization of the complete process of deterministic one-way quantum Deutsch-Josza algorithm in NMR, including graph state preparation, single-qubit measurements and feed-forward corrections. The findings in our experiment may shed light on the future scalable one-way quantum computation.

  20. Computing a Turing-Incomputable Problem from Quantum Computing

    Sicard, A; Ospina, J; Sicard, Andr\\'es; V\\'elez, Mario; Ospina, Juan

    2003-01-01

    A hypercomputation model named Infinite Square Well Hypercomputation Model (ISWHM) is built from quantum computation. This model is inspired by the model proposed by Tien D. Kieu quant-ph/0203034 and solves an Turing-incomputable problem. For the proposed model and problem, a simulation of its behavior is made. Furthermore, it is demonstrated that ISWHM is a universal quantum computation model.

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

    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.

  2. Quantum Computing over Finite Fields

    James, Roshan P.; Ortiz, Gerardo; 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 n...

  3. Resilient Quantum Computation Error Models and Thresholds

    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.

  4. Quantum Computing and the Limits of the Efficiently Computable

    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.

  5. Quantum computing with defects in diamond

    Full text: Single spins in semiconductors, in particular associated with defect centers, are promising candidates for practical and scalable implementation of quantum computing even at room temperature. Such an implementation may also use the reliable and well known gate constructions from bulk nuclear magnetic resonance (NMR) quantum computing. Progress in development of quantum processor based on defects in diamond will be discussed. By combining optical microscopy, and magnetic resonance techniques, the first quantum logical operations on single spins in a solid are now demonstrated. The system is perspective for room temperature operation because of a weak dependence of decoherence on temperature (author)

  6. Numerical computation for teaching quantum statistics

    Price, Tyson; Swendsen, Robert H.

    2013-11-01

    The study of ideal quantum gases reveals surprising quantum effects that can be observed in macroscopic systems. The properties of bosons are particularly unusual because a macroscopic number of particles can occupy a single quantum state. We describe a computational approach that supplements the usual analytic derivations applicable in the thermodynamic limit. The approach involves directly summing over the quantum states for finite systems and avoids the need for doing difficult integrals. The results display the unusual behavior of quantum gases even for relatively small systems.

  7. Quantum computing based on semiconductor nanowires

    S.M. Frolov; Plissard, S.R. (Sebastien) (Postdoc); Nadj-Perge, S.; Kouwenhoven, L.P.; Bakkers, E.P.A.M. (Erik) (Professor)

    2013-01-01

    A quantum computer will have computational power beyond that of conventional computers, which can be exploited for solving important and complex problems, such as predicting the conformations of large biological molecules. Materials play a major role in this emerging technology, as they can enable sophisticated operations, such as control over single degrees of freedom and their quantum states, as well as preservation and coherent transfer of these states between distant nodes. Here we assess...

  8. Conceptual aspects of geometric quantum computation

    Sjöqvist, Erik; Azimi Mousolou, Vahid; Canali, Carlo M.

    2016-07-01

    Geometric quantum computation is the idea that geometric phases can be used to implement quantum gates, i.e., the basic elements of the Boolean network that forms a quantum computer. Although originally thought to be limited to adiabatic evolution, controlled by slowly changing parameters, this form of quantum computation can as well be realized at high speed by using nonadiabatic schemes. Recent advances in quantum gate technology have allowed for experimental demonstrations of different types of geometric gates in adiabatic and nonadiabatic evolution. Here, we address some conceptual issues that arise in the realizations of geometric gates. We examine the appearance of dynamical phases in quantum evolution and point out that not all dynamical phases need to be compensated for in geometric quantum computation. We delineate the relation between Abelian and non-Abelian geometric gates and find an explicit physical example where the two types of gates coincide. We identify differences and similarities between adiabatic and nonadiabatic realizations of quantum computation based on non-Abelian geometric phases.

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

    Ren, Bao-Cang; Deng, Fu-Guo

    2014-04-01

    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.

  10. Non-Mechanism in Quantum Oracle Computing

    Castagnoli, G C

    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-mechanistic origin of this higher efficiency, also the uncertainty about which program is installed must be represented in a quantum way.

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

    Cody Jones, N.; Whitfield, James D.; McMahon, Peter L.; Yung, Man-Hong; Van Meter, Rodney; Aspuru-Guzik, Alán; Yamamoto, Yoshihisa

    2012-11-01

    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 ɛ, arbitrary single-qubit gates can be produced fault-tolerantly and using a restricted set of gates in time which is O(log ɛ) or O(log log ɛ) 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.

  12. Materials Frontiers to Empower Quantum Computing

    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.

  13. Efficiency of Ground State Quantum Computer

    Mao, Wenjin

    2004-01-01

    The energy gap is calculated for the ground state quantum computer circuit, which was recently proposed by Mizel et.al. When implementing a quantum algorithm by Hamiltonians containing only pairwise interaction, the inverse of energy gap $1/\\Delta$ is proportional to $N^{4k}$, where $N$ is the number of bits involved in the problem, and $N^k$ is the number of control operations performed in a standard quantum paradigm. Besides suppressing decoherence due to the energy gap, in polynomial time ...

  14. Quantum computing based on semiconductor nanowires

    Frolov, S.M.; Plissard, S.R.; Nadj-Perge, S.; Kouwenhoven, L.P.; Bakkers, E.P.A.M.

    2013-01-01

    A quantum computer will have computational power beyond that of conventional computers, which can be exploited for solving important and complex problems, such as predicting the conformations of large biological molecules. Materials play a major role in this emerging technology, as they can enable s

  15. Carmichael Numbers on a Quantum Computer

    Carlini, A.; Hosoya, A.

    1999-01-01

    We present a quantum probabilistic algorithm which tests with a polynomial computational complexity whether a given composite number is of the Carmichael type. We also suggest a quantum algorithm which could verify a conjecture by Pomerance, Selfridge and Wagstaff concerning the asymptotic distribution of Carmichael numbers smaller than a given integer.

  16. An introduction to quantum computing algorithms

    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.

  17. Relativistic quantum chemistry on quantum computers

    Veis, Libor; Višňák, Jakub; Fleig, T.; Knecht, S.; Saue, T.; Visscher, L.; Pittner, Jiří

    2012-01-01

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

  18. Universality of Black Hole Quantum Computing

    Dvali, Gia; Lust, Dieter; Omar, Yasser; Richter, Benedikt

    2016-01-01

    By analyzing the key properties of black holes from the point of view of quantum information, we derive a model-independent picture of black hole quantum computing. It has been noticed that this picture exhibits striking similarities with quantum critical condensates, allowing the use of a common language to describe quantum computing in both systems. We analyze such quantum computing by allowing coupling to external modes, under the condition that the external influence must be soft-enough in order not to offset the basic properties of the system. We derive model-independent bounds on some crucial time-scales, such as the times of gate operation, decoherence, maximal entanglement and total scrambling. We show that for black hole type quantum computers all these time-scales are of the order of the black hole half-life time. Furthermore, we construct explicitly a set of Hamiltonians that generates a universal set of quantum gates for the black hole type computer. We find that the gates work at maximal energy e...

  19. Iterated Gate Teleportation and Blind Quantum Computation.

    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. PMID:26196609

  20. Weighing matrices and optical quantum computing

    Flammia, Steven T.; Severini, Simone

    2008-01-01

    Quantum computation in the one-way model requires the preparation of certain resource states known as cluster states. We describe how the construction of continuous-variable cluster states for optical quantum computing relate to the existence of certain families of matrices. The relevant matrices are known as weighing matrices, with a few additional constraints. We prove some results regarding the structure of these matrices, and their associated graphs.

  1. Thresholds for Linear Optics Quantum Computation

    Knill, E.; Laflamme, R; Milburn, G.

    2000-01-01

    We previously established that in principle, it is possible to quantum compute using passive linear optics with photo-detectors (quant-ph/0006088). Here we describe techniques based on error detection and correction that greatly improve the resource and device reliability requirements needed for scalability. The resource requirements are analyzed for ideal linear optics quantum computation (LOQC). The coding methods can be integrated both with loss detection and phase error-correction to deal...

  2. Braid group representation on quantum computation

    There are many studies about topological representation of quantum computation recently. One of diagram representation of quantum computation is by using ZX-Calculus. In this paper we will make a diagrammatical scheme of Dense Coding. We also proved that ZX-Calculus diagram of maximally entangle state satisfies Yang-Baxter Equation and therefore, we can construct a Braid Group representation of set of maximally entangle state

  3. Performing Quantum Computing Experiments in the Cloud

    Simon J. Devitt

    2016-01-01

    Quantum computing technology has reached a second renaissance in the past five years. Increased interest from both the private and public sector combined with extraordinary theoretical and experimental progress has solidified this technology as a major advancement in the 21st century. As anticipated by many, the first realisation of quantum computing technology would occur over the cloud, with users logging onto dedicated hardware over the classical internet. Recently IBM has released the {\\e...

  4. Braid group representation on quantum computation

    Aziz, Ryan Kasyfil, E-mail: kasyfilryan@gmail.com [Department of Computational Sciences, Bandung Institute of Technology (Indonesia); Muchtadi-Alamsyah, Intan, E-mail: ntan@math.itb.ac.id [Algebra Research Group, Bandung Institute of Technology (Indonesia)

    2015-09-30

    There are many studies about topological representation of quantum computation recently. One of diagram representation of quantum computation is by using ZX-Calculus. In this paper we will make a diagrammatical scheme of Dense Coding. We also proved that ZX-Calculus diagram of maximally entangle state satisfies Yang-Baxter Equation and therefore, we can construct a Braid Group representation of set of maximally entangle state.

  5. Delayed commutation in quantum computer networks

    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 node.

  6. Quantum Mechanical Nature in Liquid NMR Quantum Computing

    LONGGui-Lu; YANHai-Yang; 等

    2002-01-01

    The quantum nature of bulk ensemble NMR quantum computing-the center of recent heated debate,is addressed.Concepts of the mixed state and entanglement are examined,and the data in a two-qubit liquid NMR quantum computation are analyzed.the main points in this paper are;i) Density matrix describes the "state" of an average particle in an ensemble.It does not describe the state of an individual particle in an ensemble;ii) Entanglement is a property of the wave function of a microscopic particle(such as a molecule in a liquid NMR sample),and separability of the density matrix canot be used to measure the entanglement of mixed ensemble;iii) The state evolution in bulkensemble NMR quantum computation is quantum-mechanical;iv) The coefficient before the effective pure state density matrix,ε,is a measure of the simultaneity of the molecules in an ensemble,It reflets the intensity of the NMR signal and has no significance in quantifying the entanglement in the bulk ensemble NMR system.The decomposition of the density matrix into product states is only an indication that the ensemble can be prepared by an ensemble with the particles unentangeld.We conclude that effective-pure-state NMR quantum computation is genuine,not just classical simulations.

  7. Methodological testing: Are fast quantum computers illusions?

    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.

  8. Topological Code Architectures for Quantum Computation

    Cesare, Christopher Anthony

    This dissertation is concerned with quantum computation using many-body quantum systems encoded in topological codes. The interest in these topological systems has increased in recent years as devices in the lab begin to reach the fidelities required for performing arbitrarily long quantum algorithms. The most well-studied system, Kitaev's toric code, provides both a physical substrate for performing universal fault-tolerant quantum computations and a useful pedagogical tool for explaining the way other topological codes work. In this dissertation, I first review the necessary formalism for quantum information and quantum stabilizer codes, and then I introduce two families of topological codes: Kitaev's toric code and Bombin's color codes. I then present three chapters of original work. First, I explore the distinctness of encoding schemes in the color codes. Second, I introduce a model of quantum computation based on the toric code that uses adiabatic interpolations between static Hamiltonians with gaps constant in the system size. Lastly, I describe novel state distillation protocols that are naturally suited for topological architectures and show that they provide resource savings in terms of the number of required ancilla states when compared to more traditional approaches to quantum gate approximation.

  9. Quantum Computing and Shor`s Factoring Algorithm

    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.

  10. Waveguide-QED-Based Photonic Quantum Computation

    Zheng, Huaixiu; Gauthier, Daniel J.; Baranger, Harold U.

    2013-08-01

    We propose a new scheme for quantum computation using flying qubits—propagating photons in a one-dimensional waveguide interacting with matter qubits. Photon-photon interactions are mediated by the coupling to a four-level system, based on which photon-photon π-phase gates (controlled-not) can be implemented for universal quantum computation. We show that high gate fidelity is possible, given recent dramatic experimental progress in superconducting circuits and photonic-crystal waveguides. The proposed system can be an important building block for future on-chip quantum networks.

  11. Ramsey numbers and adiabatic quantum computing

    Gaitan, Frank; Clark, Lane

    2011-01-01

    The graph-theoretic Ramsey numbers are notoriously difficult to calculate. In fact, for the two-color Ramsey numbers $R(m,n)$ with $m,n\\geq 3$, only nine are currently known. We present a quantum algorithm for the computation of the Ramsey numbers $R(m,n)$. We show how the computation of $R(m,n)$ can be mapped to a combinatorial optimization problem whose solution can be found using adiabatic quantum evolution. We numerically simulate this adiabatic quantum algorithm and show that it correctl...

  12. Universal Quantum Computation Using Continuous Dynamical Decoupling

    Fanchini, Felipe F; Caldeira, Amir O

    2010-01-01

    We show, for the first time, that continuous dynamical decoupling can preserve the coherence of a two-qubit state as it evolves during a SWAP quantum operation. Hence, because the Heisenberg exchange interaction alone can be used for achieving universal quantum computation, its combination with continuous dynamical decoupling can also make the computation robust against general environmental perturbations. Furthermore, since the exchange-interaction Hamiltonian is invariant under rotations, the same control-field arrangement used to protect a stationary quantum-memory state can also preserve the coherence of the driven qubits. The simplicity of the required control fields greatly improves prospects for an experimental realization.

  13. Brain-Computer Interfaces and Quantum Robots

    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...

  14. Simulating physical phenomena with a quantum computer

    Ortiz, Gerardo

    2003-03-01

    In a keynote speech at MIT in 1981 Richard Feynman raised some provocative questions in connection to the exact simulation of physical systems using a special device named a ``quantum computer'' (QC). At the time it was known that deterministic simulations of quantum phenomena in classical computers required a number of resources that scaled exponentially with the number of degrees of freedom, and also that the probabilistic simulation of certain quantum problems were limited by the so-called sign or phase problem, a problem believed to be of exponential complexity. Such a QC was intended to mimick physical processes exactly the same as Nature. Certainly, remarks coming from such an influential figure generated widespread interest in these ideas, and today after 21 years there are still some open questions. What kind of physical phenomena can be simulated with a QC?, How?, and What are its limitations? Addressing and attempting to answer these questions is what this talk is about. Definitively, the goal of physics simulation using controllable quantum systems (``physics imitation'') is to exploit quantum laws to advantage, and thus accomplish efficient imitation. Fundamental is the connection between a quantum computational model and a physical system by transformations of operator algebras. This concept is a necessary one because in Quantum Mechanics each physical system is naturally associated with a language of operators and thus can be considered as a possible model of quantum computation. The remarkable result is that an arbitrary physical system is naturally simulatable by another physical system (or QC) whenever a ``dictionary'' between the two operator algebras exists. I will explain these concepts and address some of Feynman's concerns regarding the simulation of fermionic systems. Finally, I will illustrate the main ideas by imitating simple physical phenomena borrowed from condensed matter physics using quantum algorithms, and present experimental

  15. Quantum algorithms for computational nuclear physics

    Višňák 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.

  16. Quantum memory and quantum computations in the optical subradiance regime

    The possibilities of creation and manipulation of subradiant states in an extended atomic system by coherent 2π pulses are analysed. It is shown that excitation of the atomic system to collective subradiant states eliminates the superradiant broadening of the resonance line in quantum optical memory devices. The scheme of a nonlinear sign-shift two-qubit gate is proposed, which can be used in optical quantum computers. (fourth seminar to the memory of d.n. klyshko)

  17. Diamond NV centers for quantum computing and quantum networks

    Childress, Lilian; Hanson, Ronald

    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...

  18. Irreconcilable difference between quantum walks and adiabatic quantum computing

    Wong, Thomas G.; Meyer, David A.

    2016-06-01

    Continuous-time quantum walks and adiabatic quantum evolution are two general techniques for quantum computing, both of which are described by Hamiltonians that govern their evolutions by Schrödinger's equation. In the former, the Hamiltonian is fixed, while in the latter, the Hamiltonian varies with time. As a result, their formulations of Grover's algorithm evolve differently through Hilbert space. We show that this difference is fundamental; they cannot be made to evolve along each other's path without introducing structure more powerful than the standard oracle for unstructured search. For an adiabatic quantum evolution to evolve like the quantum walk search algorithm, it must interpolate between three fixed Hamiltonians, one of which is complex and introduces structure that is stronger than the oracle for unstructured search. Conversely, for a quantum walk to evolve along the path of the adiabatic search algorithm, it must be a chiral quantum walk on a weighted, directed star graph with structure that is also stronger than the oracle for unstructured search. Thus, the two techniques, although similar in being described by Hamiltonians that govern their evolution, compute by fundamentally irreconcilable means.

  19. Computer science approach to quantum control

    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.

  20. Qubus ancilla-driven quantum computation

    Brown, Katherine Louise [School of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70808, United States and School of Physics and Astronomy, University of Leeds, LS2 9JT (United Kingdom); De, Suvabrata; Kendon, Viv [School of Physics and Astronomy, University of Leeds, LS2 9JT (United Kingdom); Munro, Bill [National Institute of Informatics, 2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo 101-8430, Japan and NTT Basic Research Laboratories, 3-1, Morinosato Wakamiya Atsugi-shi, Kanagawa 243-0198 (Japan)

    2014-12-04

    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.

  1. Composable security of measuring-Alice blind quantum computation

    Morimae, Tomoyuki; Koshiba, Takeshi

    2013-01-01

    Blind quantum computing [A. Broadbent, J. Fitzsimons, and E. Kashefi, Proceedings of the 50th Annual IEEE Symposium on Foundations of Computer Science 517 (2009)] is a secure cloud quantum computing protocol which enables a client (who does not have enough quantum technology at her disposal) to delegate her quantum computation to a server (who has a universal quantum computer) without leaking any relevant information to the server. In [T. Morimae and K. Fujii, Phys. Rev. A {\\bf87}, 050301(R) ...

  2. Strictly contractive quantum channels and physically realizable quantum computers

    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 quantum detection the...

  3. Biologically inspired path to quantum computer

    Ogryzko, Vasily; Ozhigov, Yuri

    2014-12-01

    We describe an approach to quantum computer inspired by the information processing at the molecular level in living cells. It is based on the separation of a small ensemble of qubits inside the living system (e.g., a bacterial cell), such that coherent quantum states of this ensemble remain practically unchanged for a long time. We use the notion of a quantum kernel to describe such an ensemble. Quantum kernel is not strictly connected with certain particles; it permanently exchanges atoms and molecules with the environment, which makes quantum kernel a virtual notion. There are many reasons to expect that the state of quantum kernel of a living system can be treated as the stationary state of some Hamiltonian. While the quantum kernel is responsible for the stability of dynamics at the time scale of cellular life, at the longer inter-generation time scale it can change, varying smoothly in the course of biological evolution. To the first level of approximation, quantum kernel can be described in the framework of qubit modification of Jaynes-Cummings-Hubbard model, in which the relaxation corresponds to the exchange of matter between quantum kernel and the rest of the cell and is represented as Lindblad super-operators.

  4. Effective pure states for bulk quantum computation

    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) [Science 275, 350 (1997)] and Cory et al. (spatial averaging) [Proc. Natl. Acad. Sci. USA 94, 1634 (1997)] 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 quantum bits, 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. Most of these algorithms require only a constant multiple of the number of experiments needed by the other methods for creating effective pure states. copyright 1998 The American Physical Society

  5. Quantum computations: algorithms and error correction

    Kitaev, A. Yu

    1997-12-01

    Contents §0. Introduction §1. Abelian problem on the stabilizer §2. Classical models of computations2.1. Boolean schemes and sequences of operations2.2. Reversible computations §3. Quantum formalism3.1. Basic notions and notation3.2. Transformations of mixed states3.3. Accuracy §4. Quantum models of computations4.1. Definitions and basic properties4.2. Construction of various operators from the elements of a basis4.3. Generalized quantum control and universal schemes §5. Measurement operators §6. Polynomial quantum algorithm for the stabilizer problem §7. Computations with perturbations: the choice of a model §8. Quantum codes (definitions and general properties)8.1. Basic notions and ideas8.2. One-to-one codes8.3. Many-to-one codes §9. Symplectic (additive) codes9.1. Algebraic preparation9.2. The basic construction9.3. Error correction procedure9.4. Torus codes §10. Error correction in the computation process: general principles10.1. Definitions and results10.2. Proofs §11. Error correction: concrete procedures11.1. The symplecto-classical case11.2. The case of a complete basis Bibliography

  6. Power of one qumode for quantum computation

    Liu, Nana; Thompson, Jayne; Weedbrook, Christian; Lloyd, Seth; Vedral, Vlatko; Gu, Mile; Modi, Kavan

    2016-05-01

    Although quantum computers are capable of solving problems like factoring exponentially faster than the best-known classical algorithms, determining the resources responsible for their computational power remains unclear. An important class of problems where quantum computers possess an advantage is phase estimation, which includes applications like factoring. We introduce a computational model based on a single squeezed state resource that can perform phase estimation, which we call the power of one qumode. This model is inspired by an interesting computational model known as deterministic quantum computing with one quantum bit (DQC1). Using the power of one qumode, we identify that the amount of squeezing is sufficient to quantify the resource requirements of different computational problems based on phase estimation. In particular, we can use the amount of squeezing to quantitatively relate the resource requirements of DQC1 and factoring. Furthermore, we can connect the squeezing to other known resources like precision, energy, qudit dimensionality, and qubit number. We show the circumstances under which they can likewise be considered good resources.

  7. Quantum Computation by Pairing Trapped Ultracold Ions

    冯芒; 朱熙文; 高克林; 施磊

    2001-01-01

    Superpositional wavefunction oscillations for the implementation of quantum algorithms modify the desired interference required for the quantum computation. We propose a scheme with trapped ultracold ion-pairs beingqubits to diminish the detrimental effect of the wavefunction oscillations, which is applied to the two-qubitGrover's search. It can be also found that the qubits in our scheme are more robust against the decoherencecaused by the environment, and the model is scalable.

  8. Quantum computation of discrete logarithms in semigroups

    Childs, Andrew M.; Ivanyos, Gábor

    2014-01-01

    We describe an efficient quantum algorithm for computing discrete logarithms in semigroups using Shor's algorithms for period finding and discrete log as subroutines. Thus proposed cryptosystems based on the presumed hardness of discrete logarithms in semigroups are insecure against quantum attacks. In contrast, we show that some generalizations of the discrete log problem are hard in semigroups despite being easy in groups. We relate a shifted version of the discrete log problem in semigroup...

  9. Entanglement and Quantum Computation: An Overview

    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.

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

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

    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 classical algorithms...