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1

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Li, Shu-shen; Long, Gui-lu; Bai, Feng-shan; Feng, Song-lin; Zheng, Hou-zhi

2001-01-01

2

Digital Repository Infrastructure Vision for European Research (DRIVER)

The subject of quantum computing brings together ideas from classical information theory, computer science, and quantum physics. This review aims to summarise not just quantum computing, but the whole subject of quantum information theory. It turns out that information theory and quantum mechanics fit together very well. In order to explain their relationship, the review begins with an introduction to classical information theory and computer science, including Shannon's the...

Steane, Andrew

1997-01-01

3

Quantum Chaos & Quantum Computers

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 quant...

Shepelyansky, D. L.

2000-01-01

4

International Nuclear Information System (INIS)

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

1998-02-01

5

I give a general overview of recent advances in the theory of quantum computation. The basic idea is to consider computation as being performed not by a sequence of elementary boolean logic operations applied to a set of bits (of which there are many realizations employing classical mechanics), but by a sequence of elementary unitary transformations applied to a set of quantum two-level systems (``qubits''). These unitary transformations are to be effected by some specified Hamiltonians acting over a definite time duration; there are a number of experimental arenas in quantum physics, including those of magnetic resonance, atom traps and ion traps, quantum optics, superconductivity, and quantum-dots, in which such controlled Hamiltonian action is possible and in which definite experimental realizations of quantum computation are under investigation. Recent advances in quantum-computation algorithms have been focussed on finding speedups for classical mathematical problems, the most celebrated example of which is the prime-factoring quantum algorithm of Shor. But some workers have been pursuing the clear capability of quantum computers to efficiently emulate the real-time evolution of any other locally-interacting many-particle quantum system, Fermi or Bose. I would suggest that if we were to achieve this emulation, it would be as distinct from previous computational simulation as we often say that these traditional methods of simulation in computational physics are from both ordinary theory and experiment. (I thank the many colleagues with whom I have worked in this area: C. Bennett, R. Cleve, A. Peres, J. Smolin, W. Wootters, and many others. Most of the literature in this subject is to be found at

Divincenzo, David

1997-08-01

6

An overview and assessment of the rapidly developing field of quantum computing is presented as a result of the 1996 JASON Summer Study. Interest in this field is fueled by the recent discovery by P. Shor of an efficient quantum algorithm for finding the ...

H. Kimble C. Callan K. Case A. Despain N. Fortson

1996-01-01

7

Moore's Law is a famous rule of thumb that says transistor density, and hence microprocessor performance, doubles approximately every eighteen months. While this trend has stood the test of time, many experts believe it will eventually grind to a halt when physical limitations prevent further miniaturization. Although this will likely not happen for twenty years or more, researchers are already looking at a potential solution.The concept of quantum computing has been around since the 1970's, but the science is still in its infancy. To learn about its profound implications, Liquid Logic (1) is a solid article with some remarkable insights into the technology. One of the most comprehensive sources on the Web is at the Centre for Quantum Computation (2) (last mentioned in the June 24, 1998 Scout Report). This has lots of introductory materials and tutorials that explain many of the basic concepts of quantum computing. The Centre's research efforts are also detailed on the site. Another good site for people new to the subject is the home page of Magiq Technologies (3). A very informative section about quantum information processing looks at some of the history of its development and its applications for the future. The company addresses some key issues in the frequently asked questions section, such as why research in this area could be so important. The Quantum Logic and Coherent Control Project Web site (4) presents extensive advanced theory about several experiments conducted with an rf (Paul) ion trap. The discussions are replete with equations and graphs, probably most suited for post graduate research. The Institute for Quantum Information (5) offers over 30 of its publications online, most of which are very recent. Because it is located at the California Institute of Technology, there are links to course home pages with lecture notes and solutions to problems. Users of the popular Mathematica software can add a powerful library of quantum computation functions with the free QuCalc package (6). The download site has documentation for the software and a few examples that include Mathematica code. Quantum Leap: Seize the Light (7) is an insightful article that discusses two recently published papers that address two promising methods of harnessing qubits (the fundamental unit of storage for quantum computation). This is necessary for the advancement of the technology, because the current methods are quite limited. EE Times hosts another article (8) about one of the newest breakthroughs in quantum information processing. Researchers at Harvard University have successfully transferred quantum information from a laser beam into and out of the spin state of rubidium atoms. The article considers the accomplishment and looks at what the group is planning next.

Leske, Cavin.

2002-01-01

8

Quantum computers? … Coherent computers!

Attention is drawn to the fact that the computer that employs a superposition of states as the basis for its operation can be implemented by not only quantum but also classical elements, whose dynamics obey classical laws of motion. It is shown that the term "coherent computer" better reflects the physical principle of the computational devices based on the superposition of states.

Oraevsky, A. N.

2001-09-01

9

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 dire...

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

2010-01-01

10

Physics of quantum computation

International Nuclear Information System (INIS)

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

2002-05-16

11

Quantum Computer Games: Quantum Minesweeper

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…

Gordon, Michal; Gordon, Goren

2010-01-01

12

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Lloyd, Seth

2000-01-01

13

Directory of Open Access Journals (Sweden)

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.

Prashant Anil Patil

2012-04-01

14

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 ...

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

2010-01-01

15

Quantum robots and quantum computers

Energy Technology Data Exchange (ETDEWEB)

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.

Benioff, P.

1998-07-01

16

Quantum Computation as Geometry

Quantum computers hold great promise, but it remains a challenge to find efficient quantum circuits that solve interesting computational problems. We show that finding optimal quantum circuits is essentially equivalent to finding the shortest path between two points in a certain curved geometry. By recasting the problem of finding quantum circuits as a geometric problem, we open up the possibility of using the mathematical techniques of Riemannian geometry to suggest new quantum algorithms, or to prove limitations on the power of quantum computers.

Nielsen, M A; Gu, M; Doherty, A C; Nielsen, Michael A.; Dowling, Mark R.; Gu, Mile; Doherty, Andrew C.

2006-01-01

17

Quantum computing and spintronics

International Nuclear Information System (INIS)

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)

2007-09-19

18

Searching with Quantum Computers

Digital Repository Infrastructure Vision for European Research (DRIVER)

This article introduces quantum computation by analogy with probabilistic computation. A basic description of the quantum search algorithm is given by representing the algorithm as a C program in a novel way.

Grover, Lov K.

2000-01-01

19

Quantum information. Teleporation - cryptography - quantum computer

International Nuclear Information System (INIS)

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)

2010-01-01

20

Quantum computing and probability

International Nuclear Information System (INIS)

Over the past two decades, quantum computing has become a popular and promising approach to trying to solve computationally difficult problems. Missing in many descriptions of quantum computing is just how probability enters into the process. Here, we discuss some simple examples of how uncertainty and probability enter, and how this and the ideas of quantum computing challenge our interpretations of quantum mechanics. It is found that this uncertainty can lead to intrinsic decoherence, and this raises challenges for error correction. (viewpoint)

2009-11-25

21

Computing quantum phase transitions

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

Vojta, Thomas

2007-01-01

22

'Photosynthetic' Quantum Computers?

Do quantum computers already exist in Nature? It is proposed that they do. Photosynthesis is one example in which a 'quantum computer' component may play a role in the 'classical' world of complex biological systems. A 'translation' of the standard metabolic description of the 'front-end' light harvesting complex in photosynthesis into the language of quantum computers is presented. Biological systems represent an untapped resource for thinking about the design and operation of hybrid quantum-classical computers and expanding our current conceptions of what defines a 'quantum computer' in Nature.

Hitchcock, S M

2001-01-01

23

Quantum Computing for Quantum Chemistry.

This three-year project consisted on the development and application of quantum computer algorithms for chemical applications. In particular, we developed algorithms for chemical reaction dynamics, electronic structure and protein folding. The first quant...

A. Aspuru-Guzik

2010-01-01

24

Quantum information. Teleportation - cryptography - quantum computer

International Nuclear Information System (INIS)

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

2012-01-01

25

Quantum computer games: quantum minesweeper

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

Gordon, Michal; Gordon, Goren

2010-07-01

26

Physics 219: Quantum Computation

This is the course web page for an undergraduate Quantum Computation course at Caltech. A course outline, extensive lecture notes, and homework sets, some with solutions, are provided. Links to recent versions of the course are included. There are also links to important references and other web resources in quantum information theory and quantum computation.

Preskill, John

2005-04-16

27

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 wit...

Crutchfield, James P.; Wiesner, Karoline

2006-01-01

28

International Nuclear Information System (INIS)

Practical realization of quantum computers will require overcoming decoherence and operational errors, which lead to problems that are more severe than in classical computation. It is shown that arbitrarily accurate quantum computation is possible provided that the error per operation is below a threshold value. 36 refs., 1 fig

1998-01-16

29

Digital Repository Infrastructure Vision for European Research (DRIVER)

Recent theoretical results confirm that quantum theory provides the possibility of new ways of performing efficient calculations. The most striking example is the factoring problem. It has recently been shown that computers that exploit quantum features could factor large composite integers. This task is believed to be out of reach of classical computers as soon as the number of digits in the number to factor exceeds a certain limit. The additional power of quantum computers...

Barenco, Adriano

1996-01-01

30

Secure assisted quantum computation

Suppose Alice wants to perform some computation that could be done quickly on a quantum computer, but she cannot do universal quantum computation. Bob can do universal quantum computation and claims he is willing to help, but Alice wants to be sure that Bob cannot learn her input, the result of her calculation, or even the function she is trying to compute. We describe an efficient protocol by which Bob can help Alice perform the computation, but there is no way for him to learn anything about it. Furthermore, we show how Alice can efficiently detect whether Bob is honestly helping her or if he is introducing errors.

Childs, A M

2001-01-01

31

Universal blind quantum computation

We present the first protocol which allows Alice to have Bob carry out a quantum computation for her such that Alice's inputs, outputs and computation remain perfectly private, and where Alice does not require any quantum computational power or memory. She only needs to be able to prepare single qubits from a finite set and send them to Bob, who has the balance of the required quantum computational resources. Our protocol is interactive: after the initial preparation of quantum states, Alice and Bob use two-way classical communication which enables Alice to drive the computation, giving single-qubit measurement instructions to Bob, depending on previous measurement outcomes. The interaction is polynomial in the size of Alice's underlying quantum circuit. Our protocol works for inputs and outputs that are either classical or quantum. We also discuss the use of authentication in order for Alice to detect an interfering Bob. Furthermore, our construction involves a new, regular universal resource for measurement...

Broadbent, Anne; Kashefi, Elham

2008-01-01

32

Algorithms for Quantum Computers

This paper surveys the field of quantum computer algorithms. It gives a taste of both the breadth and the depth of the known algorithms for quantum computers, focusing on some of the more recent results. It begins with a brief review of quantum Fourier transform based algorithms, followed by quantum searching and some of its early generalizations. It continues with a more in-depth description of two more recent developments: algorithms developed in the quantum walk paradigm, followed by tensor network evaluation algorithms (which include approximating the Tutte polynomial).

Smith, Jamie

2010-01-01

33

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 entropy and provide closed-form expressions for a broad class of finitary quantum processes, noting when closed-form expressions cannot be given.

Crutchfield, J P; Crutchfield, James P.; Wiesner, Karoline

2006-01-01

34

Quantum Computing Without Entanglement

It is generally believed that entanglement is essential for quantum computing. We present here a few simple examples in which quantum computing without entanglement is better than anything classically achievable, in terms of the reliability of the outcome after a xed number of oracle calls. Using a separable (that is, unentangled) n-qubit state, we show that the Deutsch-Jozsa problem and the Simon problem can be solved more reliably by a quantum computer than by the best possible classical algorithm, even probabilistic. We conclude that: (a) entanglement is not essential for quantum computing; and (b) some advantage of quantum algorithms over classical algorithms persists even when the quantum state contains an arbitrarily small amount of information|that is, even when the state is arbitrarily close to being totally mixed.

Biham, E; Kenigsberg, D; Mor, T; Biham, Eli; Brassard, Gilles; Kenigsberg, Dan; Mor, Tal

2003-01-01

35

Center for Quantum Computation

Researchers at the Center for Quantum Computation (CQC) at Oxford University study "all aspects of quantum information processing" and "the implications of the quantum theory of computation for physics itself." The Center's homepage provides information on each of their four areas of research (Fundamentals, Architecture, Ion Trap, and Nuclear Magnetic Resonance), although content depth varies with subject. Also included at the site are: contact information, email addresses, and homepage links to most CQC members and associates; links to other research centers around the world; and a calendar of events related to quantum computation.

36

Computational quantum field theory

International Nuclear Information System (INIS)

The computational quantum field theory (CQFT) is considered as a part of the computational physics. The main mathematical structures of the CQFT are described in the case of quantum chromodynamics. As examples of the application of the CQFT methods the calculation of the topological susceptibility and the gluon condensates are considered

1986-01-01

37

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.

Zak, M.

1998-01-01

38

Principles of quantum computing

International Nuclear Information System (INIS)

This contribution is intended to introduce the principles of quantum computing to those who always wanted to know about quantum computing but never dared to ask. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2007-11-01

39

Quantum Computation and Quantum Error Prevention Wiki

The Quantum Computation and Quantum Error Prevention Wiki is a collaborative and live document to compliment courses on quantum computing. All edits must be made by registered users in order to maintain accuracy and integrity for the document. It is produced by Qunet, a network for quantum physicists, particularly those working in the fields of quantum information and quantum computation. It was developed as a part of a NSF funded project led by Prof. M. S. Byrd at Southern Illinois University Carbondale.

Byrd, Mark S.

2014-04-04

40

Quantum computing with trapped ions

International Nuclear Information System (INIS)

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

2008-12-01

41

International Nuclear Information System (INIS)

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

1992-08-19

42

Energy Technology Data Exchange (ETDEWEB)

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.

Lloyd, S.

1992-01-01

43

Energy Technology Data Exchange (ETDEWEB)

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.

Lloyd, S.

1992-12-01

44

Quantum computing with trapped ions

Energy Technology Data Exchange (ETDEWEB)

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.

Hughes, R.J.

1998-01-01

45

High Performance Quantum Computing

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 by many users to run algorithms and share quantum data. The scaling structure of photonics based topological cluster computing leads to an attractive future for server based QIP, where dedicated mainframes can be constructed and/or expanded to serve an increasingly hungry user base with the ideal resource for individual quantum information processing.

Devitt, Simon J; Nemoto, Kae

2008-01-01

46

Quantum computation: Honesty test

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.

Morimae, Tomoyuki

2013-11-01

47

Lectures on Quantum Computation

This series of video lectures is designed to be used either as an introduction to the quantum theory of computation or as an introduction to quantum physics itself. The level of mathematics used is relatively low, requiring only that the viewer understand the concepts of eigenvalues and vector spaces. The lectures are accompanied by problem and solutions sets.

Deutsch, David

2008-03-15

48

When quantum computing was first being invented, it was hoped that it would be able to solve NP-complete problems just through the parallelism of quantum mechanics. Such a scheme would do a brute force search and would not need to use any of the structure...

L. K. Grover

2004-01-01

49

Cluster State Quantum Computation.

This is the final report for the AFRL/RI in-house project Cluster State Quantum Computation. Under this project investigations were conducted which included: (i) the development and characterization of a new multipli- entangled photon source that increase...

G. Lott M. Fanto P. Alsing

2014-01-01

50

Quantum Computing Graduate Fellowship.

A variety of projects are carried out by 2 graduate students under the Quantum Computing and Graduate Research Fellowship' program. The students are United States citizens, with undergraduate degrees from the California Institute of Technology. The graawa...

I. H. Deutsch C. M. Caves

2005-01-01

51

Introduction to Quantum Computing

This is a short online course in quantum computation. The stated purpose of the course is to communicate the importance of quantum computing, how it works, and the ability to assess the value of new research results. The class features video lectures with slides. The user may either view the slides as an image, or view the video taped lecture in parallel with the slides using RealAudio.

Van Meter, Rod

2005-11-30

52

In the circuit model, quantum computers rely on the availability of a universal quantum gate set. A particularly intriguing example of such a set is the "matchgates" along with swap, the simple exchange of two qubits. In this paper, we show a simple decomposition of arbitrary matchgates into better known elementary gates, and implement one matchgate in a linear optics experiment using single photons. We characterize the gate performance via quantum process tomography and represent the resulting quantum process in a novel way, as a fidelity map in the space of all possible nonlocal two-qubit unitaries. In addition, we propose a new non-local, diagnostic process measure.

Ramelow, S; Steinberg, A M; White, A G

2009-01-01

53

Using Quantum Computers for Quantum Simulation

Directory of Open Access Journals (Sweden)

Full Text Available Numerical simulation of quantum systems is crucial to further our understanding of natural phenomena. Many systems of key interest and importance, in areas such as superconducting materials and quantum chemistry, are thought to be described by models which we cannot solve with sufficient accuracy, neither analytically nor numerically with classical computers. Using a quantum computer to simulate such quantum systems has been viewed as a key application of quantum computation from the very beginning of the field in the 1980s. Moreover, useful results beyond the reach of classical computation are expected to be accessible with fewer than a hundred qubits, making quantum simulation potentially one of the earliest practical applications of quantum computers. In this paper we survey the theoretical and experimental development of quantum simulation using quantum computers, from the first ideas to the intense research efforts currently underway.

Vivien M. Kendon

2010-11-01

54

Using Quantum Computers for Quantum Simulation

Numerical simulation of quantum systems is crucial to further our understanding of natural phenomena. Many systems of key interest and importance, such as superconducting materials and quantum chemistry, are thought to be described by models which we cannot solve with sufficient accuracy, neither analytically nor with classical computers. Using a quantum computer to simulate such quantum systems has been viewed as a key application of quantum computation from the very beginning of the field in the 1980s. Moreover, useful results beyond the reach of classical computation are expected to be accessible with less than a hundred qubits, making quantum simulation potentially one of the earliest practical applications of quantum computers. In this paper we provide a review of the theoretical and experimental development of quantum simulation using quantum computers, from the first ideas to the intense research efforts currently underway.

Brown, Katherine L; Kendon, Vivien M

2010-01-01

55

Polarization in quantum computations

We propose a realization of quantum computing using polarized photons. The information is coded in two polarization directions of the photons and two-qubit operations are done using conditional Faraday effect. We investigate the performance of the system as a computing device.

Torma, P

1996-01-01

56

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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.

Blaha, Stephen

2002-01-01

57

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

Pinski, Sebastian D

2011-01-01

58

We propose a (theoretical ;-) model for quantum computation where the result can be read out from the time average of the Hamiltonian dynamics of a 2-dimensional crystal on a cylinder. The Hamiltonian is a spatially local interaction among Wigner-Seitz cells containing 6 qubits. The quantum circuit that is simulated is specified by the initialization of program qubits. As in Margolus' Hamiltonian cellular automaton (implementing classical circuits), a propagating wave in a clock register controls asynchronously the application of the gates. However, in our approach all required initializations are basis states. After a while the synchronizing wave is essentially spread around the whole crystal. The circuit is designed such that the result is available with probability about 1/4 despite of the completely undefined computation step. This model reduces quantum computing to preparing basis states for some qubits, waiting, and measuring in the computational basis. Even though it may be unlikely to find our specifi...

Janzing, D; Janzing, Dominik; Wocjan, Pawel

2004-01-01

59

Computational quantum chemistry website

International Nuclear Information System (INIS)

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

1997-01-01

60

Computational quantum chemistry website

Energy Technology Data Exchange (ETDEWEB)

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.

none,

1997-08-22

61

Towards Quantum Chemistry on a Quantum Computer

Digital Repository Infrastructure Vision for European Research (DRIVER)

Exact first-principles calculations of molecular properties are currently intractable because their computational cost grows exponentially with both the number of atoms and basis set size. A solution is to move to a radically different model of computing by building a quantum computer, which is a device that uses quantum systems themselves to store and process data. Here we report the application of the latest photonic quantum computer technology to calculate properties of the smallest molecu...

Lanyon, B. P.; Whitfield, James Daniel; Gillett, G. G.; Goggin, M. E.; Almeida, M. P.; Kassal, Ivan; Biamonte, J. D.; Mohseni, Masoud; Powell, B. J.; Barbieri, M.; Aspuru-guzik, Alan; White, Andrew G.

2010-01-01

62

Demonstration of blind quantum computing.

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

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

2012-01-20

63

Parallel quantum computing in a single ensemble quantum computer

International Nuclear Information System (INIS)

We propose a parallel quantum computing mode for ensemble quantum computer. In this mode, some qubits are in pure states while other qubits are in mixed states. It enables a single ensemble quantum computer to perform 'single-instruction-multidata' type of parallel computation. Parallel quantum computing can provide additional speedup in Grover's algorithm and Shor's algorithm. In addition, it also makes a fuller use of qubit resources in an ensemble quantum computer. As a result, some qubits discarded in the preparation of an effective pure state in the Schulman-Varizani and the Cleve-DiVincenzo algorithms can be reutilized

2004-05-01

64

Computational Distinguishability of Quantum Channels

Digital Repository Infrastructure Vision for European Research (DRIVER)

The computational problem of distinguishing two quantum channels is central to quantum computing. It is a generalization of the well-known satisfiability problem from classical to quantum computation. This problem is shown to be surprisingly hard: it is complete for the class QIP of problems that have quantum interactive proof systems, which implies that it is hard for the class PSPACE of problems solvable by a classical computation in polynomial space. Several restriction...

Rosgen, Bill

2009-01-01

65

International Nuclear Information System (INIS)

We present a hybrid model of the unitary-evolution-based quantum computation model and the measurement-based quantum computation model. In the hybrid model, part of a quantum circuit is simulated by unitary evolution and the rest by measurements on star graph states, thereby combining the advantages of the two standard quantum computation models. In the hybrid model, a complicated unitary gate under simulation is decomposed in terms of a sequence of single-qubit operations, the controlled-z gates, and multiqubit rotations around the z axis. Every single-qubit and the controlled-z gate are realized by a respective unitary evolution, and every multiqubit rotation is executed by a single measurement on a required star graph state. The classical information processing in our model requires only an information flow vector and propagation matrices. We provide the implementation of multicontrol gates in the hybrid model. They are very useful for implementing Grover's search algorithm, which is studied as an illustrative example.

2011-02-01

66

Holographic quantum computing.

We propose to use a single mesoscopic ensemble of trapped polar molecules for quantum computing. A "holographic quantum register" with hundreds of qubits is encoded in collective excitations with definite spatial phase variations. Each phase pattern is uniquely addressed by optical Raman processes with classical optical fields, while one- and two-qubit gates and qubit readout are accomplished by transferring the qubit states to a stripline microwave cavity field and a Cooper pair box where controllable two-level unitary dynamics and detection is governed by classical microwave fields. PMID:18764313

Tordrup, Karl; Negretti, Antonio; Mølmer, Klaus

2008-07-25

67

From Geometry to Quantum Computation

The aim of this paper is to introduce our idea of Holonomic Quantum Computation (Computer). Our model is based on both harmonic oscillators and non-linear quantum optics, not on spins of usual quantum computation and our method is moreover completely geometrical. We hope that therefore our model may be strong for decoherence.

Fujii, K

2001-01-01

68

Relativistic quantum chemistry on quantum computers

DEFF Research Database (Denmark)

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

Veis, L.; Visnak, J.

2012-01-01

69

Quantum computing using nuclear spins

International Nuclear Information System (INIS)

In December 2001, a group of physicists at Stanford University and at the IBM research center in California announced the first experimental implementation of the Shor quantum factorization algorithm with 7 quantum bits. The nuclear magnetic resonance method applied appears to be a promising approach to the realization of quantum computers. Quantum computing, which is a very interesting field of application of the laws of the quantum world, is demonstrated on examples

2002-01-01

70

Programmable architecture for quantum computing :

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2013-01-01

71

Quantum Computation and Spin Electronics

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 ...

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

1999-01-01

72

A causal set C can describe a discrete spacetime, but this discrete spacetime is not quantum, because C is endowed with Boolean logic, as it does not allow cycles. In a quasi-ordered set Q, cycles are allowed. In this paper, we consider a subset QC of a quasi-ordered set Q, whose elements are all the cycles. In QC, which is endowed with quantum logic, each cycle of maximal outdegree N in a node, is associated with N entangled qubits. Then QC describes a quantum computing spacetime. This structure, which is non-local and non-casual, can be understood as a proto-spacetime. Micro-causality and locality can be restored in the subset U of Q whose elements are unentangled qubits which we interpret as the states of quantum spacetime. The mapping of quantum spacetime into proto-spacetime is given by the action of the XOR gate. Moreover, a mapping is possible from the Boolean causal set into U by the action of the Hadamard gate. In particular, the causal order defined on the elements of U induces the causal evolution ...

Zizzi, P A

2002-01-01

73

Quantum Computation vs. Firewalls

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

Harlow, Daniel

2013-01-01

74

Quantum Gravity on a Quantum Computer?

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

Kempf, Achim

2014-05-01

75

Quantum Gravity on a Quantum Computer?

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

Kempf, Achim

2013-01-01

76

Quantum computing for physics research

International Nuclear Information System (INIS)

Quantum computers hold great promises for the future of computation. In this paper, this new kind of computing device is presented, together with a short survey of the status of research in this field. The principal algorithms are introduced, with an emphasis on the applications of quantum computing to physics. Experimental implementations are also briefly discussed

2006-04-01

77

Quantum Computing's Classical Problem, Classical Computing's Quantum Problem

Tasked with the challenge to build better and better computers, quantum computing and classical computing face the same conundrum: the success of classical computing systems. Small quantum computing systems have been demonstrated, and intermediate-scale systems are on the horizon, capable of calculating numeric results or simulating physical systems far beyond what humans can do by hand. However, to be commercially viable, they must surpass what our wildly successful, highly advanced classical computers can already do. At the same time, those classical computers continue to advance, but those advances are now constrained by thermodynamics, and will soon be limited by the discrete nature of atomic matter and ultimately quantum effects. Technological advances benefit both quantum and classical machinery, altering the competitive landscape. Can we build quantum computing systems that out-compute classical systems capable of some 10^{30} logic gates per month? This article will discuss the interplay in these competing and cooperating technological trends.

Van Meter, Rodney

2014-06-01

78

Quantum computing on encrypted data

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.

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

2014-01-01

79

Quantum computing on encrypted data.

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. PMID:24445949

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

2014-01-01

80

Quantum Computing, Metrology, and Imaging

Information science is entering into a new era in which certain subtleties of quantum mechanics enables large enhancements in computational efficiency and communication security. Naturally, precise control of quantum systems required for the implementation of quantum information processing protocols implies potential breakthoughs in other sciences and technologies. We discuss recent developments in quantum control in optical systems and their applications in metrology and imaging.

Lee, H; Dowling, J P; Lee, Hwang; Lougovski, Pavel; Dowling, Jonathan P.

2005-01-01

81

Quantum computing with defects

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

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

2010-01-01

82

Quantum computing with defects.

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

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

83

Experimental cluster state quantum computing

International Nuclear Information System (INIS)

Full text: Standard quantum computation is based on a universal set of unitary quantum logic gates which process qubits. In contrast to the standard quantum model, Raussendorf and Briegel proposed the one-way quantum computer, based on a highly-entangled cluster state, which is entirely different. We have experimentally realized four-qubit cluster states encoded into the polarization state of four photons. We fully characterize the quantum state by implementing the first experimental four-qubit quantum state tomography. Using this cluster state we demonstrate the feasibility of one-way quantum computing through a universal set of one- and two-qubit operations. Finally, our implementation of Grover's search algorithm demonstrates that one-way quantum computation is ideally suited for such tasks. (author)

2005-05-20

84

Quantum Computing Using Superconducting Qubits.

We have performed research on several areas of control, with particular emphasis on quantum information processing, quantum computing, superconducting qubits, and related topics (e.g., controlling the motion of flux lines, since their motion produces diss...

B. Y. Zhu F. Marchesoni F. Nori P. Hanggi S. Savel'ev

2006-01-01

85

Cartoon Computation: Quantum-like computing without quantum mechanics

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

Aerts, D; Aerts, Diederik; Czachor, Marek

2006-01-01

86

THE APROACH OF CLASSICAL COMPUTER TO QUANTUM COMPUTER

Directory of Open Access Journals (Sweden)

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

SEYEDEH MOHADESEH ELTEJA

2013-09-01

87

The universe as quantum computer

This article reviews the history of digital computation, and investigates just how far the concept of computation can be taken. In particular, I address the question of whether the universe itself is in fact a giant computer, and if so, just what kind of computer it is. I will show that the universe can be regarded as a giant quantum computer. The quantum computational model of the universe explains a variety of observed phenomena not encompassed by the ordinary laws of physics. In particular, the model shows that the the quantum computational universe automatically gives rise to a mix of randomness and order, and to both simple and complex systems.

Lloyd, Seth

2013-01-01

88

Quantum Entanglement and Quantum Computational Algorithms

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 show that if no entanglement is envolved then whatever one can do with qubits can also be done with classical optical systems. 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 ...

Arvind

2000-01-01

89

Universal quantum computation by discontinuous quantum walk

International Nuclear Information System (INIS)

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

2010-10-01

90

Quantum computers, factoring, and decoherence

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

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

1995-01-01

91

Spintronics and Quantum Dots for Quantum Computing and Quantum Communication

Digital Repository Infrastructure Vision for European Research (DRIVER)

Control over electron-spin states, such as coherent manipulation, filtering and measurement promises access to new technologies in conventional as well as in quantum computation and quantum communication. We review our proposal of using electron spins in quantum confined structures as qubits and discuss the requirements for implementing a quantum computer. We describe several realizations of one- and two-qubit gates and of the read-in and read-out tasks. We discuss recently proposed schemes f...

Burkard, Guido; Engel, Hans-andreas; Loss, Daniel

2000-01-01

92

Quantum physics, simulation, and computation

International Nuclear Information System (INIS)

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)

2012-09-18

93

Quantum computing with quantum dots on quantum linear supports

International Nuclear Information System (INIS)

Motivated by the recently demonstrated ability to attach quantum dots to polymers at well-defined locations, we propose a condensed-phase analog of the ion-trap quantum computer: a scheme for quantum computation using chemically assembled semiconductor nanocrystals attached to a linear support. The linear support is either a molecular string (e.g., DNA) or a nanoscale rod. The phonon modes of the linear support are used as a quantum-information bus between the dots. Our scheme offers greater flexibility in optimizing material parameters than the ion-trap method, but has additional complications. We discuss the relevant physical parameters, provide a detailed feasibility study, and suggest materials for which quantum computation may be possible with this approach. We find that Si is a potentially promising quantum-dot material, already allowing a 5-10-qubit quantum computer to operate with an error threshold of 10-3

2002-01-01

94

Quantum Computing over Finite Fields

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

James, Roshan P; Sabry, Amr

2011-01-01

95

Quantum Computing: Solving Complex Problems

Energy Technology Data Exchange (ETDEWEB)

One of the motivating ideas of quantum computation was that there could be a new kind of machine that would solve hard problems in quantum mechanics. There has been significant progress towards the experimental realization of these machines (which I will review), but there are still many questions about how such a machine could solve computational problems of interest in quantum physics. New categorizations of the complexity of computational problems have now been invented to describe quantum simulation. The bad news is that some of these problems are believed to be intractable even on a quantum computer, falling into a quantum analog of the NP class. The good news is that there are many other new classifications of tractability that may apply to several situations of physical interest.

DiVincenzo, David (IBM Watson Research Center)

2007-04-11

96

Braid Topologies for Quantum Computation

Digital Repository Infrastructure Vision for European Research (DRIVER)

In topological quantum computation, quantum information is stored in states which are intrinsically protected from decoherence, and quantum gates are carried out by dragging particle-like excitations (quasiparticles) around one another in two space dimensions. The resulting quasiparticle trajectories define world-lines in three dimensional space-time, and the corresponding quantum gates depend only on the topology of the braids formed by these world-lines. We show how to fin...

Bonesteel, N. E.; Hormozi, Layla; Zikos, Georgios; Simon, Steven H.

2005-01-01

97

Genetic Algorithms and Quantum Computation

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

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

2004-01-01

98

Algorithms on Ensemble Quantum Computers

In ensemble (or bulk) quantum computation, measurements of qubits in an individual computer cannot be performed. Instead, only expectation values can be measured. As a result of this limitation on the model of computation, various important algorithms cannot be processed directly on such computers, and must be modified. We provide modifications of various existing protocols, including algorithms for universal fault--tolerant computation, Shor's factorization algorithm (which can be extended to any algorithm computing an NP function), and some search algorithms to enable processing them on ensemble quantum computers.

Boykin, P O; Roychowdhury, V P; Vatan, F; Mor, Tal; Roychowdhury, Vwani; Vatan, Farrokh

1999-01-01

99

Quantum Computer Using Coupled Quantum Dot Molecules

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...

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

1999-01-01

100

Quantum Computing and High Performance Computing.

GE Global Research has enhanced a previously developed general- purpose quantum computer simulator, improving its efficiency and increasing its functionality. Matrix multiplication operations in the simulator were optimized by taking advantage of the part...

K. S. Aggour R. M. Mattheyses J. Shultz B. H. Allen M. Lapinski

2006-01-01

101

Cartoon computation: quantum-like computing without quantum mechanics

International Nuclear Information System (INIS)

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

2007-03-30

102

Computing on Anonymous Quantum Network

Digital Repository Infrastructure Vision for European Research (DRIVER)

This paper considers distributed computing on an anonymous quantum network, a network in which no party has a unique identifier and quantum communication and computation are available. It is proved that the leader election problem can exactly (i.e., without error in bounded time) be solved with at most the same complexity up to a constant factor as that of exactly computing symmetric functions (without intermediate measurements for a distributed and superposed input), if the...

Kobayashi, Hirotada; Matsumoto, Keiji; Tani, Seiichiro

2010-01-01

103

Quantum computation with graphene nanoribbon

We propose a scalable scheme to implement quantum computation in graphene nanoribbon. It is shown that electron or hole can be naturally localized in each zigzag region for a graphene nanoribbon with a sequence of Z-shaped structure without exploiting any confined gate. An one-dimensional graphene quantum dots chain is formed in such graphene nanoribbon, where electron or hole spin can be encoded as qubits. The coupling interaction between neighboring graphene quantum dots is found to be always-on Heisenberg type. Applying the bang-bang control strategy and decoherence free subspaces encoding method, universal quantum computation is argued to be realizable with the present techniques.

Guo, Guo-Ping; Li, Xiao-Peng; Tu, Tao; Guo, Guang-Can

2008-01-01

104

Focus on topological quantum computation

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

Pachos, Jiannis K.; Simon, Steven H.

2014-06-01

105

Quantum computing in neural networks

According to the statistical interpretation of quantum theory, quantum computers form a distinguished class of probabilistic machines (PMs) by encoding n qubits in 2n pbits. This raises the possibility of a large-scale quantum computing using PMs, especially with neural networks which have the innate capability for probabilistic information processing. Restricting ourselves to a particular model, we construct and numerically examine the performance of neural circuits implementing universal quantum gates. A discussion on the physiological plausibility of proposed coding scheme is also provided.

Gralewicz, P

2004-01-01

106

Braid topologies for quantum computation.

In topological quantum computation, quantum information is stored in states which are intrinsically protected from decoherence, and quantum gates are carried out by dragging particlelike excitations (quasiparticles) around one another in two space dimensions. The resulting quasiparticle trajectories define world lines in three-dimensional space-time, and the corresponding quantum gates depend only on the topology of the braids formed by these world lines. We show how to find braids that yield a universal set of quantum gates for qubits encoded using a specific kind of quasiparticle which is particularly promising for experimental realization. PMID:16241636

Bonesteel, N E; Hormozi, L; Zikos, G; Simon, S H

2005-09-30

107

Towards Linear Optical Quantum Computers

Scalable quantum computation with linear optics was considered to be impossible due to the lack of efficient two-qubit logic gates, despite its ease of implementation of one-qubit gates. Two-qubit gates necessarily need a nonlinear interaction between the two photons, and the efficiency of this nonlinear interaction is typically very tiny in bulk materials. However, we recently have shown that this barrier can be circumvented with effective nonlinearities produced by projective measurements, and with this work linear-optical quantum computing becomes a new possibility of scalable quantum computation. We review several issues concerning its principles and requirements.

Dowling, J P; Lee, H; Milburn, G J; Dowling, Jonathan P.; Franson, James D.; Lee, Hwang; Milburn, Gerald J.; Dowling, Jonathan P.; Franson, James D.; Lee, Hwang; Milburn, Gerald J.

2004-01-01

108

Cryptography, quantum computation and trapped ions

Energy Technology Data Exchange (ETDEWEB)

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.

Hughes, Richard J.

1998-03-01

109

Cryptography, Quantum Computation and Trapped Ions

Digital Repository Infrastructure Vision for European Research (DRIVER)

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.

Hughes, Richard J.

1997-01-01

110

Computational Power of Quantum Machines, Quantum Grammars and Feasible Computation

This paper studies the computational power of quantum computers to explore as to whether they can recognize properties which are in nondeterministic polynomial-time class (NP) and beyond. To study the computational power, we use the Feynman's path integral (FPI) formulation of quantum mechanics. From a computational point of view the Feynman's path integral computes a quantum dynamical analogue of the k-ary relation computed by an Alternating Turing machine (ATM) using AND-OR Parallelism. Hence, if we can find a suitable mapping function between an instance of a mathematical problem and the corresponding interference problem, using suitable potential functions for which FPI can be integrated exactly, the computational power of a quantum computer can be bounded to that of an alternating Turing machine that can solve problems in NP (e.g, factorization problem) and in polynomial space. Unfortunately, FPI is exactly integrable only for a few problems (e.g., the harmonic oscillator) involving quadratic potentials; otherwise, they may be only approximately computable or noncomputable. This means we cannot in general solve all quantum dynamical problems exactly except for those special cases of quadratic potentials, e.g., harmonic oscillator. Since there is a one to one correspondence between the quantum mechanical problems that can be analytically solved and the path integrals that can be exactly evaluated, we can say that the noncomputability of FPI implies quantum unsolvability. This is the analogue of classical unsolvability. The Feynman's path graph can be considered as a semantic parse graph for the quantum mechanical sentence. It provides a semantic valuation function of the terminal sentence based on probability amplitudes to disambiguate a given quantum description and obtain an interpretation in a linear time. In Feynman's path integral, the kernels are partially ordered over time (different alternate paths acting concurrently at the same time) and multiplied. The semantic valuation is computable only if the FPI is computable. Thus both the expressive power and complexity aspects quantum computing are mirrored by the exact and efficient integrability of FPI.

Krishnamurthy, E. V.

111

Computing methods in quantum electrodynamics

International Nuclear Information System (INIS)

Algebraic and numerical computing methods used for calculations in quantum electrodynamics are reviewed. Computer algebra systems suitable for high energy physics computations are presented. The impact of these methods on the evaluation of the Lamb shift in hydrogen and of the anomalous magnetic moment of leptons is shown. (Auth.)

1981-01-01

112

Using computer algebra in quantum computation and quantum games

Research in contemporary physics is emphasizing the development and evolution of computer systems to facilitate the calculations. Quantum computing is a branch of modern physics is believed promising results for the future, Thanks to the ability of qubits to store more information than a bit. The work of this paper focuses on the simulation of certain quantum algorithms such as the prisoner's dilemma in its quantum version using the MATHEMATICAÂ® software and implementing stochastic version of the software MAPLE Â® and the Grover search algorithm that simulates finding a needle in a haystack.

Bolívar, David A.

2011-05-01

113

Quantum information and computing

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

Ohya, M; Watanabe, N

2006-01-01

114

Distinguishing Short Quantum Computations

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

Rosgen, Bill

2007-01-01

115

Computing quantum eigenvalues made easy

International Nuclear Information System (INIS)

An extremely simple and convenient method is presented for computing eigenvalues in quantum mechanics by representing position and momentum operators in matrix form. The simplicity and success of the method is illustrated by numerical results concerning eigenvalues of bound systems and resonances for Hermitian and non-Hermitian Hamiltonians as well as driven quantum systems. Various MATLAB program codes are listed. (author)

2002-07-01

116

Towards Quantum Chemistry on a Quantum Computer

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Lanyon, Benjamin P.; Whitfield, James D.; Gillet, Geoff G.; Goggin, Michael E.; Almeida, Marcelo P.; Kassal, Ivan; Biamonte, Jacob D.; Mohseni, Masoud; Powell, Ben J.; Barbieri, Marco; Aspuru-guzik, Ala?n; White, Andrew G.

2009-01-01

117

Insecurity of Quantum Secure Computations

It had been widely claimed that quantum mechanics can protect private information during public decision in for example the so-called two-party secure computation. If this were the case, quantum smart-cards could prevent fake teller machines from learning the PIN (Personal Identification Number) from the customers' input. Although such optimism has been challenged by the recent surprising discovery of the insecurity of the so-called quantum bit commitment, the security of quantum two-party computation itself remains unaddressed. Here we answer this question directly by showing that all ``one-sided'' two-party computations (which allow only one of the two parties to learn the result) are necessarily insecure. As corollaries to our results, quantum oblivious password identification and the so-called quantum one-out-of-two oblivious transfer are impossible. We also construct a class of functions that cannot be computed securely in any ``two-sided'' two-party computation. Nevertheless, quantum cryptography remain...

Lo, H K

1997-01-01

118

Unitary transformations for quantum computing

Digital Repository Infrastructure Vision for European Research (DRIVER)

The last two decades have seen an enormous increase in the computational power of digital computers. This was due to the rapid technical development in manufacturing processes and controlling semiconducting structures on submicron scale. Concurrently, the electric circuits have encountered the first signs of the realm of quantum mechanics. Those effects may induce noise and thus they are typically considered harmful. However, the manipulation of the coherent quantum states might turn out be t...

Vartiainen, Juha J.

2005-01-01

119

The unity between quantum field computation, real computation, and quantum computation

It is indicated that principal models of computation are indeed significantly related. The quantum field computation model contains the quantum computation model of Feynman. (The term "quantum field computer" was used by Freedman.) Quantum field computation (as enhanced by Wightman's model of quantum field theory) involves computation over the continuum which is remarkably related to the real computation model of Smale. The latter model was established as a generalization of Turing computation. All this is not surprising since it is well known that the physics of quantum field theory (which includes Einstein's special relativity) contains quantum mechanics which in turn contains classical mechanics. The unity of these computing models, which seem to have grown largely independently, could shed new light into questions of computational complexity, into the central P (Polynomial time) versus NP (Non-deterministic Polynomial time) problem of computer science, and also into the description of Nature by fundamenta...

Manoharan, A C

2001-01-01

120

Quantum computers in phase space

International Nuclear Information System (INIS)

We represent both the states and the evolution of a quantum computer in phase space using the discrete Wigner function. We study properties of the phase space representation of quantum algorithms: apart from analyzing important examples, such as the Fourier transform and Grover's search, we examine the conditions for the existence of a direct correspondence between quantum and classical evolutions in phase space. Finally, we describe how to measure directly the Wigner function in a given phase-space point by means of a tomographic method that, itself, can be interpreted as a simple quantum algorithm

2002-06-01

121

Physical Realizations of Quantum Computing

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

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

2006-01-01

122

Decoherence and Programmable Quantum Computation

An examination of the concept of using classical degrees of freedom to drive the evolution of quantum computers is given. Specifically, when externally generated, coherent states of the electromagnetic field are used to drive transitions within the qubit system, a decoherence results due to the back reaction from the qubits onto the quantum field. We derive an expression for the decoherence rate for two cases, that of the single-qubit Walsh-Hadamard transform, and for an implementation of the controlled-NOT gate. We examine the impact of this decoherence mechanism on Grover's search algorithm, and on the proposals for use of error-correcting codes in quantum computation.

Barnes, J P; Barnes, Jeff P.; Warren, Warren S.

1999-01-01

123

Quantum Computation and Algorithms

International Nuclear Information System (INIS)

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

1999-03-18

124

Wong's diffusion network is a stochastic, zero-input Hopfield network with a Gibbs stationary distribution over a bounded, connected continuum. Previously, logarithmic thermal annealing was demonstrated for the diffusion network and digital versions of it were studied and applied to imaging. Recently, "quantum" annealed Markov chains have garnered significant attention because of their improved performance over "pure" thermal annealing. In this note, a joint quantum and thermal version of Wong's diffusion network is described and its convergence properties are studied. Different choices for "auxiliary" functions are discussed, including those of the kinetic type previously associated with quantum annealing.

Kesidis, George

2009-01-01

125

The quantum field as a quantum computer

International Nuclear Information System (INIS)

It is supposed that at very small scales a quantum field is an infinite homogeneous quantum computer. On a quantum computer the information cannot propagate faster than c=a/?, a and ? being the minimum space and time distances between gates, respectively. For one space dimension it is shown that the information flow satisfies a Dirac equation, with speed v=?c and ?=?(m) mass-dependent. For c the speed of light ??1 is a vacuum refraction index that increases monotonically from ??1(0)=1 to ??1(M)=?, M being the Planck mass for 2a the Planck length. The Fermi anticommuting field can be entirely qubitized, i.e. it can be written in terms of local Pauli matrices and with the field interaction remaining local on qubits. Extensions to larger space dimensions are discussed. -- Highlights: ? q-Computational approach to quantum field theory, the Wheeler's “It from Bit”. ? Dirac derived as free flow of information, without requiring Lorentz covariance. ? Info-interpretation of inertial mass and h¯ and field Hamiltonian derived from gates. ? Violation of dispersion relation as mass-dependent vacuum refraction index. ? Fermi anticommuting fields substituted by qubits.

2012-01-16

126

Information, computing technology, and quantum computing

International Nuclear Information System (INIS)

Information has long been described by physical structures. The spectacularly successful modern computers use silicon transistors to hold and process information. A number of attempts to repeat the success with other kinds of solid-state devices have failed. The reasons for the unique success of silicon transistors are found in the requirements of computing, the properties of transistors, and the variability in devices manufactured in the large quantities needed to build large computing systems. New challenges will be met in building quantum computers to meet the same requirements. (topical review)

2006-05-31

127

Pfaffian States: Quantum Computation

The Pfaffian determinant is sometimes used to multiply the Laughlin's wave function at the half filled Landau level. The square of the Pfaffian gives the ordinary determinant. We find that the Pfaffian wave function leads to four times larger energies and two times faster time. By the same logic, the Pfaffian breaks the supersymmetry of the Dirac equation. By using the spin properties and the Landau levels, we correctly interpret the state with 5/2 filling. The quantum numbers which represent the state vectors are now products of n (Landau level quantum number), l(orbital angular momentum quantum number and the spin, s |n, l, s>. In a circuit, the noise measures the resistivity and hence the charge. The Pfaffian velocity is different from that of the single-particle states and hence it has important consequences in the measurement of the charge of the quasiparticles.

Shrivastava, Keshav N.

2009-09-01

128

Pfaffian States: Quantum Computation

International Nuclear Information System (INIS)

The Pfaffian determinant is sometimes used to multiply the Laughlin's wave function at the half filled Landau level. The square of the Pfaffian gives the ordinary determinant. We find that the Pfaffian wave function leads to four times larger energies and two times faster time. By the same logic, the Pfaffian breaks the supersymmetry of the Dirac equation. By using the spin properties and the Landau levels, we correctly interpret the state with 5/2 filling. The quantum numbers which represent the state vectors are now products of n (Landau level quantum number), l(orbital angular momentum quantum number and the spin, s |n, l, s>. In a circuit, the noise measures the resistivity and hence the charge. The Pfaffian velocity is different from that of the single-particle states and hence it has important consequences in the measurement of the charge of the quasiparticles.

2009-09-14

129

Computer simulation in quantum chromodynamics

International Nuclear Information System (INIS)

Traditional diagram expansion turns out not to be appropriate to obtain quantitative results in quantum chromodynamics. Computer simulation however can produce nonperturbative information about quantum fields. The QCD path-integral method on a lattic give rise to very high dimensional problems. For these problems, the Monte Carlo method is very useful. It is applied to get information on the quark-quark potential, the hadron spectrum and the free quark phase. (Auth.)

1984-01-01

130

A Quantum Computational Learning Algorithm

Digital Repository Infrastructure Vision for European Research (DRIVER)

An interesting classical result due to Jackson allows polynomial-time learning of the function class DNF using membership queries. Since in most practical learning situations access to a membership oracle is unrealistic, this paper explores the possibility that quantum computation might allow a learning algorithm for DNF that relies only on example queries. A natural extension of Fourier-based learning into the quantum domain is presented. The algorithm requires only an exam...

Ventura, Dan; Martinez, Tony

1998-01-01

131

Raman-Controlled Quantum Dots for Quantum Computing.

Optical control is fundamental to our project objective of demonstration of key quantum operations for quantum computation with spin qubits of electrons in semiconductor quantum dots. Sophia Economou, the graduate student supported by this fellowship, wor...

L. J. Sham

2005-01-01

132

Adiabatic quantum computation along quasienergies

The parametric deformations of quasienergies and eigenvectors of unitary operators are applied to the design of quantum adiabatic algorithms. The conventional, standard adiabatic quantum computation proceeds along eigenenergies of parameter-dependent Hamiltonians. By contrast, discrete adiabatic computation utilizes adiabatic passage along the quasienergies of parameter-dependent unitary operators. For example, such computation can be realized by a concatenation of parameterized quantum circuits, with an adiabatic though inevitably discrete change of the parameter. A design principle of adiabatic passage along quasienergy is recently proposed: Cheon's quasienergy and eigenspace anholonomies on unitary operators is available to realize anholonomic adiabatic algorithms [Tanaka and Miyamoto, Phys. Rev. Lett. 98, 160407 (2007)], which compose a nontrivial family of discrete adiabatic algorithms. It is straightforward to port a standard adiabatic algorithm to an anholonomic adiabatic one, except an introduction of...

Tanaka, Atushi

2009-01-01

133

Geometrical perspective on quantum states and quantum computation

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Chen, Zeqian

2013-01-01

134

Can quantum chemistry be performed on a small quantum computer?

As quantum computing technology improves and quantum computers with a small but non-trivial number of N > 100 qubits appear feasible in the near future the question of possible applications of small quantum computers gains importance. One frequently mentioned application is Feynman's original proposal of simulating quantum systems, and in particular the electronic structure of molecules and materials. In this paper, we analyze the computational requirements for one of the standard algorithms to perform quantum chemistry on a quantum computer. We focus on the quantum resources required to find the ground state of a molecule twice as large as what current classical computers can solve exactly. We find that while such a problem requires about a ten-fold increase in the number of qubits over current technology, the required increase in the number of gates that can be coherently executed is many orders of magnitude larger. This suggests that for quantum computation to become useful for quantum chemistry problems, ...

Wecker, Dave; Clark, Bryan K; Hastings, Matthew B; Troyer, Matthias

2013-01-01

135

Quantum Walks for Computer Scientists

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

Venegas-Andraca, Salvador

2008-01-01

136

Lecture Notes on Quantum Computation

This is a web site, authored by David Mermin of Cornell University, for a course on quantum computation. It includes lecture notes, soon to be published as a book, assignments, and discussions. Six chapters and seven assignments are available for download. The files are available in both PDF and PS formats.

Mermin, David

2009-05-19

137

Quantum computing and hidden variables

International Nuclear Information System (INIS)

This paper initiates the study of hidden variables from a quantum computing perspective. For us, a hidden-variable theory is simply a way to convert a unitary matrix that maps one quantum state to another into a stochastic matrix that maps the initial probability distribution to the final one in some fixed basis. We list five axioms that we might want such a theory to satisfy and then investigate which of the axioms can be satisfied simultaneously. Toward this end, we propose a new hidden-variable theory based on network flows. In a second part of the paper, we show that if we could examine the entire history of a hidden variable, then we could efficiently solve problems that are believed to be intractable even for quantum computers. In particular, under any hidden-variable theory satisfying a reasonable axiom, we could solve the graph isomorphism problem in polynomial time, and could search an N-item database using O(N1/3) queries, as opposed to O(N1/2) queries with Grover's search algorithm. On the other hand, the N1/3 bound is optimal, meaning that we could probably not solve NP-complete problems in polynomial time. We thus obtain the first good example of a model of computation that appears slightly more powerful than the quantum computing model

2005-03-01

138

Quantum Computation by Geometrical Means

Digital Repository Infrastructure Vision for European Research (DRIVER)

A geometrical approach to quantum computation is presented, where a non-abelian connection is introduced in order to rewrite the evolution operator of an energy degenerate system as a holonomic unitary. For a simple geometrical model we present an explicit construction of a universal set of gates, represented by holonomies acting on degenerate states.

Pachos, Jiannis

2000-01-01

139

Universal quantum computing with nanowire double quantum dots

International Nuclear Information System (INIS)

We present a method for implementing universal quantum computing using a singlet and triplets of nanowire double quantum dots coupled to a one-dimensional transmission line resonator. This method is suitable and of interest for both quantum computing and quantum control with inhibition of spontaneous emission, enhanced spin qubit lifetime, strong coupling and quantum nondemolition measurements of spin qubits. We analyze the performance and stability of all the required operations and emphasize that all techniques are feasible with current experimental technology.

2011-10-01

140

Universal quantum computing with nanowire double quantum dots

Energy Technology Data Exchange (ETDEWEB)

We present a method for implementing universal quantum computing using a singlet and triplets of nanowire double quantum dots coupled to a one-dimensional transmission line resonator. This method is suitable and of interest for both quantum computing and quantum control with inhibition of spontaneous emission, enhanced spin qubit lifetime, strong coupling and quantum nondemolition measurements of spin qubits. We analyze the performance and stability of all the required operations and emphasize that all techniques are feasible with current experimental technology.

Xue Peng, E-mail: peng_xue@seu.edu.cn [Department of Physics, Southeast University, Nanjing 211189 (China)

2011-10-15

141

AN INTRODUCTION TO QUANTUM NEURAL COMPUTING

Digital Repository Infrastructure Vision for European Research (DRIVER)

The goal of the artificial neural network is to create powerful artificial problem solving systems. The field of quantum computation applies ideas from quantum mechanics to the study of computation and has made interesting progress. Quantum Neural Network (QNN) is one of the new paradigms built upon the combination of classical neural computation and quantum computation. It is argued that the study of QNN may explain the brain functionality in a better way and create new systems for informati...

Shaktikanta Nayak

2011-01-01

142

Computational quantum field theory

I will give an overview on recent attempts to solve the time-dependent Dirac equation for the electron-positron field operator. These numerical solutions permit a first temporally and spatially resolved insight into the mechanisms of how an electron-positron pair can be created from vacuum in a very strong force field. This approach has helped to illuminate a wide range of controversial questions. Some of these questions arise for complicated physical situations such as how an electron scatters off a supercritical potential barrier (Klein paradox). This requires the application of quantum field theory to study the combined effect of the pair-production due to the supercriticality of the potential together with the scattering at the barrier involving the Pauli-principle. Other phenomena include Schr"odinger's Zitterbewegung and the localization problem for a relativistic particle. This work has been supported by the NSF and Research Corporation. P. Krekora, K. Cooley, Q. Su and R. Grobe, Phys. Rev. Lett. 95, 070403 (2005). P. Krekora, Q. Su and R. Grobe, Phys. Rev. Lett. 93, 043004 (2004). P. Krekora, Q. Su and R. Grobe, Phys. Rev. Lett. 92, 040406 (2004).

Grobe, Rainer

2006-05-01

143

Are quantum walks the saviour of optical quantum computing?

Digital Repository Infrastructure Vision for European Research (DRIVER)

Quantum walks have emerged as an interesting candidate for the implementation of quantum information processing protocols. Optical implementations of quantum walks have been demonstrated by various groups and some have received high-profile coverage. It is often claimed that quantum walks provide an avenue towards universal quantum computation. In this comment I wish to dispel some misconceptions surrounding the prospects of quantum walks as a route towards universal optical...

Rohde, Peter P.

2010-01-01

144

Models of quantum computation and quantum programming languages

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

Miszczak, J. A.

2010-01-01

145

Introduction to models of quantum computation and quantum programming languages

The goal of this report is to provide an introduction to the basic computational models used in quantum information theory. We various review 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 limitations.

Miszczak, J A

2010-01-01

146

Introduction to Grassmann Manifolds and Quantum Computation

The aim of this paper is to give a hint for thinking to graduate or undergraduate students in Mathematical Physics who are interested in both Geometry and Quantum Computation. First I make a brief review of some properties on Grassmann manifolds and next I show a path between Grassmann manifolds and Quantum Computation which is related to the efficiency of quantum computing.

Fujii, K

2001-01-01

147

Brain Neurons as Quantum Computers:

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

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

148

Geometry of discrete quantum computing

International Nuclear Information System (INIS)

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

2013-05-10

149

Dynamical imperfections in quantum computers

International Nuclear Information System (INIS)

We study the effects of dynamical imperfections in quantum computers. By considering an explicit example, we identify different regimes ranging from the low-frequency case, where the imperfections can be considered as static but with renormalized parameters, to the high-frequency fluctuations, where the effects of imperfections are completely wiped out. We generalize our results by proving a theorem on the dynamical evolution of a system in the presence of dynamical perturbations

2005-06-01

150

Multibit gates for quantum computing.

We present a general technique to implement products of many qubit operators communicating via a joint harmonic oscillator degree of freedom in a quantum computer. By conditional displacements and rotations we can implement Hamiltonians which are trigonometric functions of qubit operators. With such operators we can effectively implement higher order gates such as Toffoli gates and C(n)-NOT gates, and we show that the entire Grover search algorithm can be implemented in a direct way. PMID:11329354

Wang, X; Sørensen, A; Mølmer, K

2001-04-23

151

Experimental one-way quantum computing.

Standard quantum computation is based on sequences of unitary quantum logic gates that process qubits. The one-way quantum computer proposed by Raussendorf and Briegel is entirely different. It has changed our understanding of the requirements for quantum computation and more generally how we think about quantum physics. This new model requires qubits to be initialized in a highly entangled cluster state. From this point, the quantum computation proceeds by a sequence of single-qubit measurements with classical feedforward of their outcomes. Because of the essential role of measurement, a one-way quantum computer is irreversible. In the one-way quantum computer, the order and choices of measurements determine the algorithm computed. We have experimentally realized four-qubit cluster states encoded into the polarization state of four photons. We characterize the quantum state fully by implementing experimental four-qubit quantum state tomography. Using this cluster state, we demonstrate the feasibility of one-way quantum computing through a universal set of one- and two-qubit operations. Finally, our implementation of Grover's search algorithm demonstrates that one-way quantum computation is ideally suited for such tasks. PMID:15758991

Walther, P; Resch, K J; Rudolph, T; Schenck, E; Weinfurter, H; Vedral, V; Aspelmeyer, M; Zeilinger, A

2005-03-10

152

The Next Generation Computing Brainwave-Quantum Computing

Directory of Open Access Journals (Sweden)

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

T. Venkat Narayana Rao

2010-12-01

153

The Quantum Human Computer (QHC) Hypothesis

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

Salmani-Nodoushan, Mohammad Ali

2008-01-01

154

Quantum Computing with Electron Spins in Quantum Dots

Digital Repository Infrastructure Vision for European Research (DRIVER)

Several topics on the implementation of spin qubits in quantum dots are reviewed. We first provide an introduction to the standard model of quantum computing and the basic criteria for its realization. Other alternative formulations such as measurement-based and adiabatic quantum computing are briefly discussed. We then focus on spin qubits in single and double GaAs electron quantum dots and review recent experimental achievements with respect to initialization, coherent man...

Z?ak, Robert Andrzej; Ro?thlisberger, Beat; Chesi, Stefano; Loss, Daniel

2009-01-01

155

Toward a superconducting quantum computer: Harnessing macroscopic quantum coherence

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Tsai, Jaw-shen

2010-01-01

156

Computation in Finitary Stochastic and Quantum Processes

Digital Repository Infrastructure Vision for European Research (DRIVER)

We introduce stochastic and quantum finite-state transducers as computation-theoretic models of classical stochastic and quantum finitary processes. Formal process languages, representing the distribution over a process's behaviors, are recognized and generated by suitable specializations. We characterize and compare deterministic and nondeterministic versions, summarizing their relative computational power in a hierarchy of finitary process languages. Quantum finite-state t...

Wiesner, Karoline; Crutchfield, James P.

2006-01-01

157

Parallel computing and quantum chromodynamics

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

Bowler, K C

1999-01-01

158

Complexity limitations on quantum computation

We use the powerful tools of counting complexity and generic oracles to help understand the limitations of the complexity of quantum computation. We show several results for the probabilistic quantum class BQP. 1. BQP is low for PP, i.e., PP^BQP=PP. 2. There exists a relativized world where P=BQP and the polynomial-time hierarchy is infinite. 3. There exists a relativized world where BQP does not have complete sets. 4. There exists a relativized world where P=BQP but P is not equal to UP intersect coUP and one-way functions exist. This gives a relativized answer to an open question of Simon.

Fortnow, L; Fortnow, Lance; Rogers, John D.

1998-01-01

159

Non-unitary probabilistic quantum computing

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.

Gingrich, Robert M.; Williams, Colin P.

2004-01-01

160

Mathematical Foundations of Holonomic Quantum Computer II

This is a sequel to the papers (quant-ph/9910063) and (quant-ph/0004102). The aim of this paper is to give mathematical foundations to Holonomic Quantum Computation (Computer) proposed by Zanardi and Rasetti (quant-ph/9904011) and Pachos and Chountasis (quant-ph/9912093). In 2-qubit case we give an explicit form to non-abelian Berry connection of quantum computational bundle which is associated with Holonomic Quantum Computation, on some parameter space. We also suggest a possibility that not only usual holonomy but also higher-dimensional holonomies must be used to prove a universality of our Holonomic Quantum Computation.

Fujii, K

2001-01-01

161

Fermionic measurement-based quantum computation

Digital Repository Infrastructure Vision for European Research (DRIVER)

Fermions, as a major class of quantum particles, provide platforms for quantum information processing beyond the possibilities of spins or bosons, which have been studied more extensively. One particularly interesting model to study, in view of recent progress in manipulating ultracold fermion gases, is the fermionic version of measurement-based quantum computation (MBQC), which implements full quantum computation with only single-site measurements on a proper fermionic many-body resource sta...

Chiu, Yu-ju; Chen, Xie; Chuang, Isaac L.

2012-01-01

162

Decoherence, Control, and Symmetry in Quantum Computers

In this thesis we describe methods for avoiding the detrimental effects of decoherence while at the same time still allowing for computation of the quantum information. The philosophy of the method discussed in the first part of this thesis is to use a symmetry of the decoherence mechanism to find robust encodings of the quantum information. Stability, control, and methods for using decoherence-free information in a quantum computer are presented with a specific emphasis on decoherence due to a collective coupling between the system and its environment. Universal quantum computation on such collective decoherence decoherence-free encodings is demonstrated. Rigorous definitions of control and the use of encoded universality in quantum computers are addressed. Explicit gate constructions for encoded universality on ion trap and exchange based quantum computers are given. In the second part of the thesis we examine physical systems with error correcting properties. We examine systems that can store quantum infor...

Bacon, D J

2003-01-01

163

Pseudospin and Quantum Computation in Semiconductor Nanostructures

We review the theoretical aspects of pseudospin quantum computation using vertically coupled quantum dots in the quantum Hall regime. We discuss the robustness and addressability of these collective, charge-based qubits. The low energy Hilbert space of a coupled set of qubits yields an effective quantum Ising model tunable through external gates. An experimental prediction of an even-odd effect in the Coulomb blockade spectra of the coupled quantum dot system probes the parameter regime necessary for realization of these qubits.

Scarola, V W; Sarma, S D

2005-01-01

164

Blind topological measurement-based quantum computation.

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 quantum computation in realistic noisy conditions. Here we show that fault-tolerant blind quantum computation is possible in a topologically protected manner using the Raussendorf-Harrington-Goyal scheme. The error threshold of our scheme is 4.3 × 10(-3), which is comparable to that (7.5 × 10(-3)) of non-blind topological quantum computation. As the error per gate of the order 10(-3) was already achieved in some experimental systems, our result implies that secure cloud quantum computation is within reach. PMID:22948818

Morimae, Tomoyuki; Fujii, Keisuke

2012-01-01

165

On the computation of quantum characteristic exponents

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.

Vilela-Mendes, R; Coutinho, Ricardo

1998-01-01

166

Contextuality supplies the 'magic' for quantum computation.

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

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

2014-06-19

167

Contextuality supplies the `magic' for quantum computation

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.

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

2014-06-01

168

From Monte Carlo to Quantum Computation

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

Heinrich, S

2001-01-01

169

Blind quantum computation with AKLT chains

We propose a method for the measurement-based blind quantum computation with Affleck-Kennedy-Lieb-Tasaki (AKLT) chains. Alice, a client, prepares certain quantum states which conceal some secret information, and sends them to Bob. Bob, the server, creates a two-dimensional network of AKLT chains from Alice's states, and performs the measurement-based quantum computation on the network according to the feedback from Alice. He finally returns the result of the quantum computation to Alice. Throughout the whole process, Bob learns nothing about Alice's input, the algorithm she wants to run, and the final result of the computation. Furthermore, Alice can detect an interference by dishonest Bob if any. We also consider the blind quantum computation with other ground states than the AKLT state in the gapped Haldane phase. An advantage of using these states is that the quantum computation can be sheltered in the gapped ground states space.

Morimae, Tomoyuki

2010-01-01

170

Elementary gates for quantum computation

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.

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

171

Elementary gates for quantum computation

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?y)] is universal in the sense that all unitary operations on arbitrarily many bits n [U(2n)] 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.

Barenco, Adriano; Bennett, Charles H.; Cleve, Richard; Divincenzo, David P.; Margolus, Norman; Shor, Peter; Sleator, Tycho; Smolin, John A.; Weinfurter, Harald

1995-11-01

172

Thermally Assisted Adiabatic Quantum Computation

We study the effect of a thermal environment on adiabatic quantum computation using the Bloch-Redfield formalism. We show that in certain cases the environment can enhance the performance in two different ways: (i) by introducing a time scale for thermal mixing near the anticrossing that is smaller than the adiabatic time scale, and (ii) by relaxation after the anticrossing. The former can enhance the scaling of computation when the environment is super-Ohmic, while the latter can only provide a prefactor enhancement. We apply our method to the case of adiabatic Grover search and show that performance better than classical is possible with a super-Ohmic environment, with no a priori knowledge of the energy spectrum.

Amin, M. H. S.; Love, Peter J.; Truncik, C. J. S.

2008-02-01

173

A Quantum to Classical Phase Transition in Noisy Quantum Computers

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

Aharonov, D

1999-01-01

174

Helping Students Learn Quantum Mechanics for Quantum Computing

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.

Singh, Chandralekha

2007-11-25

175

Photon echo quantum RAM integration in quantum computer

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.

Moiseev, Sergey A

2012-01-01

176

Centre for Quantum Computation & Communication Technology

This is the homepage of "an Australian multi-university collaboration undertaking research on the fundamental physics and technology of building, at the atomic level, a solid state quantum computer in silicon together with other high potential implementations." Although attempts to develop a quantum computer have met with limited success, the centre has substantial resources invested in advancing toward practical uses of quantum computing technology. The site provides a very good introduction to the principles and implications of quantum computing, as well as details about various research projects underway at the Australian universities. Links to conference and journal papers produced by members of the centre, many from 2003, are also provided.

177

Quantum computation with two-dimensional graphene quantum dots

International Nuclear Information System (INIS)

We study an array of graphene nano sheets that form a two-dimensional S = 1/2 Kagome spin lattice used for quantum computation. The edge states of the graphene nano sheets are used to form quantum dots to confine electrons and perform the computation. We propose two schemes of bang-bang control to combat decoherence and realize gate operations on this array of quantum dots. It is shown that both schemes contain a great amount of information for quantum computation. The corresponding gate operations are also proposed. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

2012-01-01

178

From EPR to quantum computing: experiments on entangled quantum systems

International Nuclear Information System (INIS)

Einstein, together with Podolski and Rosen (EPR), tried to point out inconsistencies of standard quantum mechanics using an effect which is now called entanglement. The experiments testing EPR's hypothesis laid the basis for the new field of quantum information processing, which in turn gave rise to impressive progress in methods to observe and to analyse the phenomenon of entanglement. Here we give an overview of the various systems useful for the novel applications of quantum communication and quantum computation

2005-05-14

179

Quantum computing with incoherent resources and quantum jumps.

Spontaneous emission and the inelastic scattering of photons are two natural processes usually associated with decoherence and the reduction in the capacity to process quantum information. Here we show that, when suitably detected, these photons are sufficient to build all the fundamental blocks needed to perform quantum computation in the emitting qubits while protecting them from deleterious dissipative effects. We exemplify this by showing how to efficiently prepare graph states for the implementation of measurement-based quantum computation. PMID:22680844

Santos, M F; Cunha, M Terra; Chaves, R; Carvalho, A R R

2012-04-27

180

Experimental realization of nonadiabatic holonomic quantum computation.

Because of its geometric nature, holonomic quantum computation is fault tolerant against certain types of control errors. Although proposed more than a decade ago, the experimental realization of holonomic quantum computation is still an open challenge. In this Letter, we report the first experimental demonstration of nonadiabatic holonomic quantum computation in a liquid NMR quantum information processor. Two noncommuting one-qubit holonomic gates, rotations about x and z axes, and the two-qubit holonomic CNOT gate are realized by evolving the work qubits and an ancillary qubit nonadiabatically. The successful realizations of these universal elementary gates in nonadiabatic holonomic quantum computation demonstrates the experimental feasibility of this quantum computing paradigm. PMID:23705695

Feng, Guanru; Xu, Guofu; Long, Guilu

2013-05-10

181

NMR quantum computation with indirectly coupled gates

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

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

1999-01-01

182

Quantum Computer Games: Schrodinger Cat and Hounds

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…

Gordon, Michal; Gordon, Goren

2012-01-01

183

Pseudospin Quantum Computation in Semiconductor Nanostructures

We theoretically show that spontaneously interlayer-coherent vertically coupled bilayer quantum Hall droplets should allow robust and fault-tolerant pseudospin quantum computation in semiconductor nanostructures with voltage-tuned external gates providing qubit control and a quantum Ising Hamiltonian providing qubit entanglement. Using a spin-boson model we estimate decoherence to be small (~10^{-5}).

Scarola, V W; Sarma, S D

2003-01-01

184

Pseudospin quantum computation in semiconductor nanostructures.

We theoretically show that spontaneously interlayer-coherent bilayer quantum Hall droplets should allow robust and fault-tolerant pseudospin quantum computation in semiconductor nanostructures with voltage-tuned external gates providing qubit control and a quantum Ising Hamiltonian providing qubit entanglement. Using a spin-boson model, we estimate decoherence to be small (approximately 10(-5)). PMID:14611443

Scarola, V W; Park, K; Sarma, S Das

2003-10-17

185

Communication Links for Distributed Quantum Computation

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

Van Meter, Rodney; Munro, W J

2007-01-01

186

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

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

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

2001-01-01

187

Distributed measurement-based quantum computation

We develop a formal model for distributed measurement-based quantum computations, adopting an agent-based view, such that computations are described locally where possible. Because the network quantum state is in general entangled, we need to model it as a global structure, reminiscent of global memory in classical agent systems. Local quantum computations are described as measurement patterns. Since measurement-based quantum computation is inherently distributed, this allows us to extend naturally several concepts of the measurement calculus, a formal model for such computations. Our goal is to define an assembly language, i.e. we assume that computations are well-defined and we do not concern ourselves with verification techniques. The operational semantics for systems of agents is given by a probabilistic transition system, and we define operational equivalence in a way that it corresponds to the notion of bisimilarity. With this in place, we prove that teleportation is bisimilar to a direct quantum channe...

Danos, V; Kashefi, E; Panangaden, P; Danos, Vincent; Hondt, Ellie D'; Kashefi, Elham; Panangaden, Prakash

2005-01-01

188

Models of continuous-variable quantum computing

Energy Technology Data Exchange (ETDEWEB)

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

Ohliger, Matthias; Eisert, Jens [Institut fuer Physik und Astronomie, Universitaet Potsdam (Germany)

2009-07-01

189

Models of continuous-variable quantum computing

International Nuclear Information System (INIS)

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

2009-03-02

190

Nonlinear Optics Quantum Computing with Circuit QED

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

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

2013-02-01

191

Nonlinear optics quantum computing with circuit QED.

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

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

2013-02-01

192

Mathematical Foundations of Holonomic Quantum Computer

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

Fujii, K

2000-01-01

193

Two paradigms for topological quantum computation

We present two paradigms relating algebraic, topological and quantum computational statistics for the topological model for quantum computation. In particular we suggest correspondences between the computational power of topological quantum computers, computational complexity of link invariants and images of braid group representations. While at least parts of these paradigms are well-known to experts, we provide supporting evidence for them in terms of recent results. We give a fairly comprehensive list of known examples and formulate two conjectures that would further support the paradigms.

Rowell, Eric C

2008-01-01

194

Quantum state diffusion, localization and computation

Numerical simulation of individual open quantum systems has proven advantages over density operator computations. Quantum state diffusion with a moving basis (MQSD) provides a practical numerical simulation method which takes full advantage of the localization of quantum states into wave packets occupying small regions of classical phase space. Following and extending the original proposal of Percival, Alber and Steimle, we show that MQSD can provide a further gain over ordinary QSD and other quantum trajectory methods of many orders of magnitude in computational space and time. Because of these gains, it is even possible to calculate an open quantum system trajectory when the corresponding isolated system is intractable. MQSD is particularly advantageous where classical or semiclassical dynamics provides an adequate qualitative picture but is numerically inaccurate because of significant quantum effects. The principles are illustrated by computations for the quantum Duffing oscillator and for second harmonic...

Schack, R; Percival, I C

1995-01-01

195

Quantum computing in a piece of glass

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...

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

2011-01-01

196

The potential of the quantum computer

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...

2006-01-01

197

AN INTRODUCTION TO QUANTUM NEURAL COMPUTING

Directory of Open Access Journals (Sweden)

Full Text Available The goal of the artificial neural network is to create powerful artificial problem solving systems. The field of quantum computation applies ideas from quantum mechanics to the study of computation and has made interesting progress. Quantum Neural Network (QNN is one of the new paradigms built upon the combination of classical neural computation and quantum computation. It is argued that the study of QNN may explain the brain functionality in a better way and create new systems for information processing including solving some classically intractable problems. In this paper we have given an introductory representation of quantum artificial neural network to show how it can be modelled on the basis of double-slit experiment. Also an attempt is made to show the quantum mechanical representation of a classical neuron to implement Hadamard transformation.

Shaktikanta Nayak

2011-09-01

198

Quantum computer of wire circuit architecture

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

Moiseev, S A; Andrianov, S N

2010-01-01

199

Novel Scheme for Universal Quantum Computation

A scenario for realization of a quantum computer is proposed consisting of spatially distributed q-bits fabricated in a host structure where nuclear spin-spin coupling is mediated by laser pulse controlled electron-nuclear transferred hyperfine (superhyperfine) Fermi contact interaction. Operations illustrating entanglement, nonlocality, and quantum control logic operations are presented and discussed. The notion of universality of quantum computation is introduced and the irreducible conditions are presented. It is demonstrated that the proposed generic scenario for realization of a quantum computer fulfills these conditions.

Bowden, C M

1999-01-01

200

Geometry of quantum computation with qudits.

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(d(n)). And the quantum circuit complexity is explicitly dependent of controllable approximation error bound. PMID:24509710

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

2014-01-01

201

Gate errors in solid state quantum computation

Digital Repository Infrastructure Vision for European Research (DRIVER)

We review our work on the interplay between non-resonant gates and solid state environment in various solid state quantum computer architectures and the resulting gate errors. Particular, we show that adiabatic condition can be satisfied in small quantum dots, while higher energy excited states can play important role in the evolution of a Cooper-pair-box based quantum computer model. We also show that complicated bandstructure such as that of Si can pose a severe gate contr...

Hu, Xuedong; Sarma, S. Das

2002-01-01

202

Quantum computing with electron spins in quantum dots

International Nuclear Information System (INIS)

Several topics on the implementation of spin qu bits in quantum dots are reviewed. We first provide an introduction to the standard model of quantum computing and the basic criteria for its realization. Other alternative formulations such as measurement-based and adiabatic quantum computing are briefly discussed. We then focus on spin qu bits in single and double GaAs electron quantum dots and review recent experimental achievements with respect to initialization, coherent manipulation and readout of the spin states. We extensively discuss the problem of decoherence in this system, with particular emphasis on its theoretical treatment and possible ways to overcome it.

2010-01-01

203

Embedding quantum simulators for quantum computation of entanglement.

We introduce the concept of embedding quantum simulators, a paradigm allowing the efficient quantum computation of a class of bipartite and multipartite entanglement monotones. It consists in the suitable encoding of a simulated quantum dynamics in the enlarged Hilbert space of an embedding quantum simulator. In this manner, entanglement monotones are conveniently mapped onto physical observables, overcoming the necessity of full tomography and reducing drastically the experimental requirements. Furthermore, this method is directly applicable to pure states and, assisted by classical algorithms, to the mixed-state case. Finally, we expect that the proposed embedding framework paves the way for a general theory of enhanced one-to-one quantum simulators. PMID:24483635

Di Candia, R; Mejia, B; Castillo, H; Pedernales, J S; Casanova, J; Solano, E

2013-12-13

204

The scalable quantum computation based on quantum dot systems

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

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

2011-01-01

205

Transitions in the quantum computational power

We construct two spin models on lattices (both two and three dimensional) to study the capability of quantum computational power as a function of temperature and the system parameter. There exists a finite region in the phase diagram such that the thermal equilibrium states are capable of providing a universal fault-tolerant resource for measurement-based quantum computation. Moreover, in such a region the thermal resource states on the three-dimensional lattices can enable topological protection for quantum computation. The two models behave similarly in terms of quantum computational power. However, they have different properties in terms of the usual phase transitions. The first model has a first-order phase transition only at zero temperature whereas there is no transition at all in the second model. Interestingly, the transition in the quantum computational power does not coincide with the phase transition in the first model.

Wei, Tzu-Chieh; Li, Ying; Kwek, Leong Chuan

2014-05-01

206

Quantum computer: an appliance for playing market games

Digital Repository Infrastructure Vision for European Research (DRIVER)

Recent development in quantum computation and quantum information theory allows to extend the scope of game theory for the quantum world. The authors have recently proposed a quantum description of financial market in terms of quantum game theory. The paper contain an analysis of such markets that shows that there would be advantage in using quantum computers and quantum strategies.

Piotrowski, Edward W.; Sladkowski, Jan

2003-01-01

207

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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.

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

2008-01-01

208

Computational depth complexity of measurement-based quantum computation

We prove that one-way quantum computations have the same computational power as quantum circuits with unbounded fan-out. It demonstrates that the one-way model is not only one of the most promising models of physical realisation, but also a very powerful model of quantum computation. It confirms and completes previous results which have pointed out, for some specific problems, a depth separation between the one-way model and the quantum circuit model. Since one-way model has the same computational power as unbounded quantum fan-out circuits, the quantum Fourier transform can be approximated in constant depth in the one-way model, and thus the factorisation can be done by a polytime probabilistic classical algorithm which has access to a constant-depth one-way quantum computer. The extra power of the one-way model, comparing with the quantum circuit model, comes from its classical-quantum hybrid nature. We show that this extra power is reduced to the capability to perform unbounded classical parity gates in co...

Browne, Dan E; Perdrix, Simon

2009-01-01

209

Resilient Quantum Computation Error Models and Thresholds

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.

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

1997-01-01

210

Quantum computing based on semiconductor nanowires:

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

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

2013-01-01

211

Quantum Computing over Finite Fields

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 characteristi...

James, Roshan P.; Ortiz, Gerardo; Sabry, Amr

2011-01-01

212

Quantum computing with defects in diamond

International Nuclear Information System (INIS)

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)

2005-05-20

213

Quantum Computation with Generalized Binomial States in Cavity Quantum Electrodynamics

We study universal quantum computation in the cavity quantum electrodynamics (CQED) framework exploiting two orthonormal two-photon generalized binomial states as qubit and dispersive interactions of Rydberg atoms with high-$Q$ cavities. We show that an arbitrary qubit state may be generated and that controlled-NOT and 1-qubit rotation gates can be realized via standard atom-cavity interactions.

Franco, Rosario Lo; Messina, Antonino; Napoli, Anna

2008-01-01

214

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) and Cory et al. (spatial averaging) for the case of quantum computation with nuclear magnetic resonance. We give a different technique called temporal averaging. This method is based on classical randomization, requires no ancilla qubits and can be implemented in nuclear magnetic resonance without using gradient fields. We introduce several temporal averaging algorithms suitable for both high temperature and low temperature bulk quantum computing and analyze the signal to noise behavior of each.

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

1998-01-01

215

Principles of quantum computation and information

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

Benenti, Giuliano; Strini, Giuliano

2004-01-01

216

Measurement Based Quantum Computation on Fractal Lattices

Directory of Open Access Journals (Sweden)

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

Michal Hajdušek

2010-06-01

217

Fault tolerant quantum computation with nondeterministic gates.

In certain approaches to quantum computing the operations between qubits are nondeterministic and likely to fail. For example, a distributed quantum processor would achieve scalability by networking together many small components; operations between components should be assumed to be failure prone. In the ultimate limit of this architecture each component contains only one qubit. Here we derive thresholds for fault-tolerant quantum computation under this extreme paradigm. We find that computation is supported for remarkably high failure rates (exceeding 90%) providing that failures are heralded; meanwhile the rate of unknown errors should not exceed 2 in 10(4) operations. PMID:21231569

Li, Ying; Barrett, Sean D; Stace, Thomas M; Benjamin, Simon C

2010-12-17

218

Fractal Aspects of Quantum Computing

Quantum computing (QC) of MWIQM (Everett) brand uses patterns of integers (primes and factorizations) by establishing nonoverlapping segments of consecutive integers ("integer empires", IE). In spirit of Godel numbering let F be tower exponent (TE) of N+1 primes. When topmost prime runs all consecutive primes, each set of (fixed) N primes generates unique infinite set of integers. Each member of every such set can, in turn, generate infinite daughter set by adding (N+2)th running prime on top of TE. Each member (F) of this infinite fractal tree of integers (with infinite branching at each step) is a power of some single prime. To produce IE take interval T(F) to T(F+1), where function T is TE stack of 10 repeated F times. Catalan conjecture assures that so produced IEs are well "insulated" from each other. Possibility of infinite branching of F-tree at each of (infinite number) of steps makes processes of self-organization dependent and governed by patterns of primes and factorizations. Hypothetically, some "special" primes and/or patterns of K-almost primes serve as (resonant) catalysts of complexity emergence.

Berezin, Alexander A.

2000-03-01

219

Relating computational complexity and quantum spectral complexity

We present a conjecture and hypothesis regarding complex spectral measures of computations of varying degrees of difficulty. Earlier work based on the study of quantal chaotic and weakly disordered systems has established that irregular spectral fluctuations have a distribution predicted by random matrix theory, while regular spectral fluctuations are given by the Poisson distribution. We elucidate the correlation between random matrix theory and computational complexity and formalize the idea to a conjecture and experimental prediction regarding spectral regularity and computational complexity (NP-complete class) viz. the quantum adiabatic computation algorithm. We show how the result takes the form of a correspondence principle for computational systems between the quantum and classical domains.

Mitchell, David R

2008-01-01

220

One-way quantum computation with circuit quantum electrodynamics

International Nuclear Information System (INIS)

In this Brief Report, we propose a potential scheme to implement one-way quantum computation with circuit quantum electrodynamics (QED). Large cluster states of charge qubits can be generated in just one step with a superconducting transmission line resonator (TLR) playing the role of a dispersive coupler. A single-qubit measurement in the arbitrary basis can be implemented using a single electron transistor with the help of one-qubit gates. By examining the main decoherence sources, we show that circuit QED is a promising architecture for one-way quantum computation.

2010-03-01

221

Ramsey Numbers and Adiabatic Quantum Computing

The graph-theoretic Ramsey numbers are notoriously difficult to calculate. In fact, for the two-color Ramsey numbers R(m,n) with m, n?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 correctly determines the Ramsey numbers R(3,3) and R(2,s) for 5?s?7. We then discuss the algorithm’s experimental implementation, and close by showing that Ramsey number computation belongs to the quantum complexity class quantum Merlin Arthur.

Gaitan, Frank; Clark, Lane

2012-01-01

222

Hyper-parallel photonic quantum computation with coupled quantum dots

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.

Ren, Bao-Cang; Deng, Fu-Guo

2014-04-01

223

Hyper-parallel photonic quantum computation with coupled quantum dots

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.

Ren, Bao-Cang; Deng, Fu-Guo

2014-01-01

224

Hamiltonian models of quantum computers which evolve quantum ballistically

Energy Technology Data Exchange (ETDEWEB)

Quantum computation is a subject of much recent interest. In much of the work in the literature quantum computers are described as built up from a sequence of unitary operators where each unitary operator carries out a stage of the overall quantum computation. The sequence and connection of the different unitary operators is provided presumably by some external agent which governs the overall process. However there is no description of a an overall Hamiltonian needed to give the actual quantum dynamics of the computation process. In this talk, earlier work by the author is followed in that simple, time independent Hamiltonians are used to describe quantum computation, and the Schroedinger evolution of the computation system is considered to be quantum ballistic. However, the definition of quantum ballistic evolution used here is more general than that used in the earlier work. In particular, the requirement that the step operator {ital T} associated with a process be a partial isometry, used in, is relaxed to require that {ital T} be a contraction operator. (An operator {ital T} is a partial isometry if the self-adjoint operators T{sup {dagger}}T and TT{sup {dagger}} are also projection operators.{ital T} is a contraction operator if {vert_bar}{vert_bar} {ital T} {vert_bar}{vert_bar} {<=} 1.) The main purpose of this talk is to investigate some consequences for quantum computation under this weaker requirement. It will be seen that system motion along discrete paths in a basis still occurs. However the motion occurs in ,the presence of potentials whose height and distribution along the path depends on {ital T} and the path states.

Benioff, P.

1996-12-31

225

Logical and algebraic structures from Quantum Computation

Digital Repository Infrastructure Vision for European Research (DRIVER)

The main motivation for this thesis is given by the open problems regarding the axiomatisation of quantum computational logics. This thesis will be structured as follows: in Chapter 2 we will review some basics of universal algebra and functional analysis. In Chapters 3 through 6 the fundamentals of quantum gate theory will be produced. In Chapter 7 we will introduce quasi-MV algebras, a formal study of a suitable selection of algebraic operations associated with quantum gates. In Chapter 8 q...

Ledda, Antonio

2008-01-01

226

CLASSICAL AND QUANTUM COMMUNICATIONS IN GRID COMPUTING

Directory of Open Access Journals (Sweden)

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

RODICA STERIAN

2010-10-01

227

Scalable quantum information processing and the optical topological quantum computer

Optical quantum computation has represented one of the most successful testbed systems for quantum information processing. Along with ion-traps and nuclear magnetic resonance (NMR), experimentalists have demonstrated control of qubits, multi-gubit gates and small quantum algorithms. However, photonic based qubits suffer from a problematic lack of a large scale architecture for fault-tolerant computation which could conceivably be built in the near future. While optical systems are, in some regards, ideal for quantum computing due to their high mobility and low susceptibility to environmental decoherence, these same properties make the construction of compact, chip based architectures difficult. Here we discuss many of the important issues related to scalable fault-tolerant quantum computation and introduce a feasible architecture design for an optics based computer. We combine the recent development of topological cluster state computation with the photonic module, simple chip based devices which can be utilized to deterministically entangle photons. The integration of this operational unit with one of the most exciting computational models solves many of the existing problems with other optics based architectures and leads to a feasible large scale design which can continuously generate a 3D cluster state with a photonic module resource cost linear in the cross sectional size of the cluster.

Devitt, S.

2010-02-01

228

Isoholonomic Problem and Holonomic Quantum Computation

Digital Repository Infrastructure Vision for European Research (DRIVER)

Geometric phases accompanying adiabatic processes in quantum systems can be utilized as unitary gates for quantum computation. Optimization of control of the adiabatic process naturally leads to the isoholonomic problem. The isoholonomic problem in a homogeneous fiber bundle is formulated and solved completely.

Tanimura, Shogo

2005-01-01

229

Thoughts on Noise and Quantum Computation

We will try to explore, primarily from the complexity-theoretic point of view, limitations of error-correction and fault-tolerant quantum computation. We consider stochastic models of quantum computation on $n$ qubits subject to noise operators that are obtained as products of tiny noise operators acting on a small number of qubits. We conjecture that for realistic random noise operators of this kind there will be substantial dependencies between the noise on individual qubits and, in addition, we propose that the dependence structure of the noise acting on individual qubits will necessarily depend (systematically) on the dependence structure of the qubits themselves. We point out that the majority function can repair, in the classical case, some forms of stochastic noise of this kind and conjecture that this healing power of majority has no quantum analog. The main hypothesis of this paper is that these properties of noise are sufficient to reduce quantum computation to probabilistic classical computation. S...

Kalai, G

2005-01-01

230

Distributed quantum computing with single photon sources

International Nuclear Information System (INIS)

Full text: Distributed quantum computing requires the ability to perform nonlocal gate operations between the distant nodes (stationary qubits) of a large network. To achieve this, it has been proposed to interconvert stationary qubits with flying qubits. In contrast to this, we show that distributed quantum computing only requires the ability to encode stationary qubits into flying qubits but not the conversion of flying qubits into stationary qubits. We describe a scheme for the realization of an eventually deterministic controlled phase gate by performing measurements on pairs of flying qubits. Our scheme could be implemented with a linear optics quantum computing setup including sources for the generation of single photons on demand, linear optics elements and photon detectors. In the presence of photon loss and finite detector efficiencies, the scheme could be used to build large cluster states for one way quantum computing with a high fidelity. (author)

2005-05-20

231

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Tempel, David Gabriel; Aspuru-guzik, Alan

2012-01-01

232

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Tempel, David G.; Aspuru-guzik, Ala?n

2012-01-01

233

Weighing matrices and optical quantum computing

International Nuclear Information System (INIS)

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

2009-02-13

234

2D cavity grid quantum computing

International Nuclear Information System (INIS)

We propose a novel scheme for scalable solid state quantum computing, where superconducting microwave transmission line resonators (cavities) are arranged in a two-dimensional grid on the surface of a chip, coupling to superconducting qubits (charge or flux) at the intersections. We analyze how tasks of quantum information processing can be implemented in such a topology, including efficient two-qubit gates between any two qubits on the grid and elements of fault-tolerant computation

2008-02-25

235

Halting in quantum Turing computation

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

Fouché, W L; Jones, G; Potgieter, P H

2007-01-01

236

Methodological testing: Are fast quantum computers illusions?

International Nuclear Information System (INIS)

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

2013-03-01

237

Strictly contractive quantum channels and physically realizable quantum computers

International Nuclear Information System (INIS)

We study the robustness of quantum computers under the influence of errors modeled by strictly contractive channels. A channel T is defined to be strictly contractive if, for any pair of density operators ?, ? in its domain, parallel T?-T? parallel 1?k parallel ?-? parallel 1 for some 0?k1 denotes the trace norm). In other words, strictly contractive channels render the states of the computer less distinguishable in the sense of quantum detection theory. Starting from the premise that all experimental procedures can be carried out with finite precision, we argue that there exists a physically meaningful connection between strictly contractive channels and errors in physically realizable quantum computers. We show that, in the absence of error correction, sensitivity of quantum memories and computers to strictly contractive errors grows exponentially with storage time and computation time, respectively, and depends only on the constant k and the measurement precision. We prove that strict contractivity rules out the possibility of perfect error correction, and give an argument that approximate error correction, which covers previous work on fault-tolerant quantum computation as a special case, is possible

2002-03-01

238

Fundamental gravitational limitations to quantum computing

Lloyd has considered the ultimate limitations physics places on quantum computers. He concludes in particular that for an ``ultimate laptop'' (a computer of one liter of volume and one kilogram of mass) the maximum number of operations per second is bounded by $10^{51}$. The limit is derived considering ordinary quantum mechanics. Here we consider additional limits that are placed by quantum gravity ideas, namely the use of a relational notion of time and fundamental gravitational limits that exist on time measurements. We then particularize for the case of an ultimate laptop and show that the maximum number of operations is further constrained to $10^{47}$ per second.

Gambini, R; Pullin, J; Gambini, Rodolfo; Porto, Rafael A.; Pullin, Jorge

2005-01-01

239

Brain-Computer Interfaces and Quantum Robots

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...

Pessa, Eliano

2009-01-01

240

Rapid sampling through quantum computing

Digital Repository Infrastructure Vision for European Research (DRIVER)

This paper extends the quantum search class of algorithms to the multiple solution case. It is shown that, like the basic search algorithm, these too can be represented as a rotation in an appropriately defined two dimensional vector space. This yields new applications - an algorithm is presented that can create an arbitrarily specified quantum superposition on a space of size N in O(sqrt(N)) steps. By making a measurement on this superposition, it is possible to obtain a sa...

Grover, Lov K.

1999-01-01

241

Quantum computation and quantum optics with circuit QED

International Nuclear Information System (INIS)

The idea of harnessing superconducting circuits to act as artificial atoms, and coupling them to microwave transmission line resonators has come a long way since its first realization in 2004. This architecture, termed circuit quantum electrodynamics (QED), has been successfully employed in a number of experiments probing fundamental aspects of quantum mechanics and quantum optics, and has enabled impressive progress towards quantum computing. At the same time, circuit QED constitutes an appealing testbed for the theoretical understanding and modeling of driven open quantum systems. This talk gives an introduction to the basics of circuit QED, and a discussion of recent results obtained with the new transmon qubit, an improved Cooper pair box immune to 1/f charge noise

2008-02-25

242

Quantum computation and quantum optics with circuit QED

Energy Technology Data Exchange (ETDEWEB)

The idea of harnessing superconducting circuits to act as artificial atoms, and coupling them to microwave transmission line resonators has come a long way since its first realization in 2004. This architecture, termed circuit quantum electrodynamics (QED), has been successfully employed in a number of experiments probing fundamental aspects of quantum mechanics and quantum optics, and has enabled impressive progress towards quantum computing. At the same time, circuit QED constitutes an appealing testbed for the theoretical understanding and modeling of driven open quantum systems. This talk gives an introduction to the basics of circuit QED, and a discussion of recent results obtained with the new transmon qubit, an improved Cooper pair box immune to 1/f charge noise.

Koch, Jens [Departments of Physics and Applied Physics, Yale University, New Haven, Connecticut (United States)

2008-07-01

243

Quantum Computing and Quantum Simulation with Group-II Atoms

Digital Repository Infrastructure Vision for European Research (DRIVER)

Recent experimental progress in controlling neutral group-II atoms for optical clocks, and in the production of degenerate gases with group-II atoms has given rise to novel opportunities to address challenges in quantum computing and quantum simulation. In these systems, it is possible to encode qubits in nuclear spin states, which are decoupled from the electronic state in the $^1$S$_0$ ground state and the long-lived $^3$P$_0$ metastable state on the clock transition. This...

Daley, Andrew J.

2011-01-01

244

Robust dynamical decoupling for quantum computing and quantum memory.

Dynamical decoupling (DD) is a popular technique for protecting qubits from the environment. However, unless special care is taken, experimental errors in the control pulses used in this technique can destroy the quantum information instead of preserving it. Here, we investigate techniques for making DD sequences robust against different types of experimental errors while retaining good decoupling efficiency in a fluctuating environment. We present experimental data from solid-state nuclear spin qubits and introduce a new DD sequence that is suitable for quantum computing and quantum memory. PMID:21770554

Souza, Alexandre M; Alvarez, Gonzalo A; Suter, Dieter

2011-06-17

245

Quantum-cellular-automata quantum computing with endohedral fullerenes

International Nuclear Information System (INIS)

We present a scheme to perform universal quantum computation using global addressing techniques as applied to a physical system of endohedrally doped fullerenes. The system consists of an ABAB linear array of group-V endohedrally doped fullerenes. Each molecule spin site consists of a nuclear spin coupled via a hyperfine interaction to an electron spin. The electron spin of each molecule is in a quartet ground state S=3/2. Neighboring molecular electron spins are coupled via a magnetic dipole interaction. We find that an all-electron construction of a quantum cellular automaton is frustrated due to the degeneracy of the electronic transitions. However, we can construct a quantum-cellular-automata quantum computing architecture using these molecules by encoding the quantum information on the nuclear spins while using the electron spins as a local bus. We deduce the NMR and ESR pulses required to execute the basic cellular automaton operation and obtain a rough figure of merit for the number of gate operations per decoherence time. We find that this figure of merit compares well with other physical quantum computer proposals. We argue that the proposed architecture meets well the first four DiVincenzo criteria and we outline various routes toward meeting the fifth criterion: qubit readout

2003-05-01

246

Linear optical quantum computation with parity encoding

International Nuclear Information System (INIS)

Full text: We present a linear optics quantum computation scheme that employs an incremental parity encoding approach. The scheme is circuit-based but uses techniques from cluster state computation, and achieves comparable resource usage to the cluster state approach. Our scheme also offers increased tolerance to photon loss. (author)

2005-05-20

247

Review article: Linear optical quantum computing

Linear optics with photo-detection is a prominent candidate for practical quantum computing. The protocol by Knill, Laflamme and Milburn [Nature 409, 46 (2001)] explicitly demonstrates that efficient scalable quantum computing with single photons, linear optical elements, and projective measurements is possible. Subsequently, several improvements on this protocol have started to bridge the gap between theoretical scalability and practical implementation. We review the original proposal and its improvements, and we give a few examples of experimental two-qubit gates. We discuss the use of realistic components, the errors they induce in the computation, and how they can be corrected.

Kok, P; Milburn, G J; Munro, W J; Nemoto, K; Ralph, T C; Dowling, Jonathan P.; Kok, Pieter; Nemoto, Kae

2005-01-01

248

The pre-history of quantum computation

The main ideas behind developments in the theory and technology of quantum computation were formulated in the late 1970s and early 1980s by two physicists in the West and a mathematician in the former Soviet Union. It is not generally known in the West that the subject has roots in the Russian technical literature. The author hopes to present as impartial a synthesis as possible of the early history of thought on this subject. The role of reversible and irreversible computational processes is examined briefly as it relates to the origins of quantum computing and the so-called Information Paradox in physics.

Potgieter, P H

2004-01-01

249

Efficient quantum circuits for one-way quantum computing.

While Ising-type interactions are ideal for implementing controlled phase flip gates in one-way quantum computing, natural interactions between solid-state qubits are most often described by either the XY or the Heisenberg models. We show an efficient way of generating cluster states directly using either the imaginary SWAP (iSWAP) gate for the XY model, or the sqrt[SWAP] gate for the Heisenberg model. Our approach thus makes one-way quantum computing more feasible for solid-state devices. PMID:19392095

Tanamoto, Tetsufumi; Liu, Yu-Xi; Hu, Xuedong; Nori, Franco

2009-03-13

250

Modeling an adiabatic quantum computer

We map adiabatic quantum evolution on the classical Hamiltonian dynamics of a 1D gas (Pechukas gas) and simulate the latter numerically. This approach turns out to be both insightful and numerically efficient, as seen from our example of a CNOT gate simulation. For a general class of Hamiltonians we show that the escape probability from the initial state scales no faster than |\\dot{\\lambda}|^{\\gamma}, where |\\dot{\\lambda}| is the adiabaticity parameter. The scaling exponent for the escape probability is \\gamma = 1/2 for all levels, except the edge (bottom and top) ones, where \\gamma <~1/3. In principle, our method can solve arbitrarily large adiabatic quantum Hamiltonians.

Zagoskin, A M; Savel'ev, S; Nori, Franco

2007-01-01

251

Universal quantum computation with unlabelled qubits

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

Severini, Simone

2006-06-01

252

Universal quantum computation with unlabelled qubits

International Nuclear Information System (INIS)

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

2006-06-30

253

Universal quantum computation with unlabelled qubits

Energy Technology Data Exchange (ETDEWEB)

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

Severini, Simone [Department of Mathematics and Department of Computer Science, University of York, Heslington, YO10 5DD York (United Kingdom)

2006-06-30

254

Computational Studies of Quantum Spin Systems

These lecture notes introduce quantum spin systems and several computational methods for studying their ground-state and finite-temperature properties. Symmetry-breaking and critical phenomena are first discussed in the simpler setting of Monte Carlo studies of classical spin systems, to illustrate finite-size scaling at continuous and first-order phase transitions. Exact diagonalization and quantum Monte Carlo (stochastic series expansion) algorithms and their computer implementations are then discussed in detail. Applications of the methods are illustrated by results for some of the most essential models in quantum magnetism, such as the S=1/2 Heisenberg antiferromagnet in one and two dimensions, as well as extended models useful for studying quantum phase transitions between antiferromagnetic and magnetically disordered states.

Sandvik, Anders W

2011-01-01

255

Recipes for spin-based quantum computing

Technological growth in the electronics industry has historically been measured by the number of transistors that can be crammed onto a single microchip. Unfortunately, all good things must come to an end; spectacular growth in the number of transistors on a chip requires spectacular reduction of the transistor size. For electrons in semiconductors, the laws of quantum mechanics take over at the nanometre scale, and the conventional wisdom for progress (transistor cramming) must be abandoned. This realization has stimulated extensive research on ways to exploit the spin (in addition to the orbital) degree of freedom of the electron, giving birth to the field of spintronics. Perhaps the most ambitious goal of spintronics is to realize complete control over the quantum mechanical nature of the relevant spins. This prospect has motivated a race to design and build a spintronic device capable of complete control over its quantum mechanical state, and ultimately, performing computations: a quantum computer. In thi...

Cerletti, V; Gywat, O; Loss, D; Cerletti, Veronica; Gywat, Oliver; Loss, Daniel

2005-01-01

256

Free spin quantum computation with semiconductor nanostructures

Taking the excess electron spin in a unit cell of semiconductor multiple quantum-dot structure as a qubit, we can implement scalable quantum computation without resorting to spin-spin interactions. The technique of single electron tunnelings and the structure of quantum-dot cellular automata (QCA) are used to create a charge entangled state of two electrons which is then converted into spin entanglement states by using single spin rotations. Deterministic two-qubit quantum gates can also be manipulated using only single spin rotations with help of QCA. A single-short read-out of spin states can be realized by coupling the unit cell to a quantum point contact.

Zhang, W M; Soo, C; Zhang, Wei-Min; Wu, Yin-Zhong; Soo, Chopin

2005-01-01

257

2D cavity grid quantum computing

International Nuclear Information System (INIS)

We propose a novel scheme for scalable solid state quantum computing, where superconducting on-chip microwave resonators (cavities) are arranged in a two-dimensional grid, coupling to superconducting qubits (charge or flux) at the intersections. We analyze how tasks of quantum information processing can be implemented in such a topology, including efficient two-qubit gates between any two qubits, initialization and read-out. The effects of decoherence, fabrication imperfections and inhomogeneities will be addressed. (orig.)

2007-03-26

258

Universal Dephasing Control During Quantum Computation

Dephasing is a ubiquitous phenomenon that leads to the loss of coherence in quantum systems and the corruption of quantum information. We present a universal dynamical control approach to combat dephasing during all stages of quantum computation, namely, storage, single- and two-qubit operators. We show that (a) tailoring multi-frequency gate pulses to the dephasing dynamics can increase fidelity; (b) cross-dephasing, introduced by entanglement, can be eliminated by appropriate control fields; (c) counter-intuitively and contrary to previous schemes, one can increase the gate duration, while simultaneously increasing the total gate fidelity.

Gordon, Goren

2007-01-01

259

Universal dephasing control during quantum computation

International Nuclear Information System (INIS)

Dephasing is a ubiquitous phenomenon that leads to the loss of coherence in quantum systems and the corruption of quantum information. We present a universal dynamical control approach to combat dephasing during all stages of quantum computation, namely, storage and single- and two-qubit operators. We show that (a) tailoring multifrequency gate pulses to the dephasing dynamics can increase fidelity; (b) cross-dephasing, introduced by entanglement, can be eliminated by appropriate control fields; (c) counterintuitively and contrary to previous schemes, one can increase the gate duration, while simultaneously increasing the total gate fidelity

2007-10-01

260

Neuromorphic quantum computation with energy dissipation

International Nuclear Information System (INIS)

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

2005-11-01

261

Neuromorphic quantum computation with energy dissipation

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

Kinjo, Mitsunaga; Sato, Shigeo; Nakamiya, Yuuki; Nakajima, Koji

2005-11-01

262

Quantum Computing, NP-complete Problems and Chaotic Dynamics

Digital Repository Infrastructure Vision for European Research (DRIVER)

An approach to the solution of NP-complete problems based on quantum computing and chaotic dynamics is proposed. We consider the satisfiability problem and argue that the problem, in principle, can be solved in polynomial time if we combine the quantum computer with the chaotic dynamics amplifier based on the logistic map. We discuss a possible implementation of such a chaotic quantum computation by using the atomic quantum computer with quantum gates described by the Hartre...

Ohya, Masanori; Volovich, Igor V.

1999-01-01

263

Ancilla-driven universal quantum computation

International Nuclear Information System (INIS)

We introduce a model of quantum computation intermediate between the gate-based and measurement-based models. A quantum register is manipulated remotely with the help of a single ancilla that ''drives'' the evolution of the register. The fully controlled ancilla qubit is coupled to the computational register only via a fixed unitary two-qubit interaction and then measured in suitable bases, driving both single- and two-qubit operations on the register. Arbitrary single-qubit operations directly on register qubits are not needed. We characterize all interactions E that induce a unitary, stepwise deterministic measurement back-action on the register sufficient to implement any quantum channel. Our scheme offers experimental advantages for computation, state preparation, and generalized measurements, since no tunable control of the register is required.

2010-08-01

264

Universal quantum computation with little entanglement

We show that universal quantum computation can be achieved in the standard pure-state circuit model while, at any time, the entanglement entropy of all bipartitions is small---even tending to zero with growing system size. The result is obtained by showing that a quantum computer operating within a small region around the set of unentangled states still has universal computational power, and by using continuity of entanglement entropy. In fact an analogous conclusion applies to every entanglement measure which is continuous in a certain natural sense, which amounts to a large class. Other examples include the geometric measure, localizable entanglement, smooth epsilon-measures, multipartite concurrence, squashed entanglement, and several others. We discuss implications of these results for the believed role of entanglement as a key necessary resource for quantum speed-ups.

Nest, Maarten Van den

2012-01-01

265

Silicon enhancement mode nanostructures for quantum computing.

Energy Technology Data Exchange (ETDEWEB)

Development of silicon, enhancement mode nanostructures for solid-state quantum computing will be described. A primary motivation of this research is the recent unprecedented manipulation of single electron spins in GaAs quantum dots, which has been used to demonstrate a quantum bit. Long spin decoherence times are predicted possible in silicon qubits. This talk will focus on silicon enhancement mode quantum dot structures that emulate the GaAs lateral quantum dot qubit but use an enhancement mode field effect transistor (FET) structure. One critical concern for silicon quantum dots that use oxides as insulators in the FET structure is that defects in the metal oxide semiconductor (MOS) stack can produce both detrimental electrostatic and paramagnetic effects on the qubit. Understanding the implications of defects in the Si MOS system is also relevant for other qubit architectures that have nearby dielectric passivated surfaces. Stable, lithographically defined, single-period Coulomb-blockade and single-electron charge sensing in a quantum dot nanostructure using a MOS stack will be presented. A combination of characterization of defects, modeling and consideration of modified approaches that incorporate SiGe or donors provides guidance about the enhancement mode MOS approach for future qubits and quantum circuit micro-architecture.

Carroll, Malcolm S.

2010-03-01

266

An obstacle affecting any proposal for a topological quantum computer based on Ising anyons is that quasiparticle braiding can only implement a finite (non-universal) set of quantum operations. The computational power of this restricted set of operations (often called stabilizer operations) has been studied in quantum information theory, and it is known that no quantum-computational advantage can be obtained without the help of an additional non-stabilizer operation. Similarly, a bipartite two-qubit system based on Ising anyons cannot exhibit non-locality (in the sense of violating a Bell inequality) when only topologically protected stabilizer operations are performed. To produce correlations that cannot be described by a local hidden variable model again requires the use of a non-stabilizer operation. Using geometric techniques, we relate the sets of operations that enable universal quantum computing (UQC) with those that enable violation of a Bell inequality. Motivated by the fact that non-stabilizer opera...

Howard, Mark

2011-01-01

267

More on Optical Holonomic Quantum Computer

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

Fujii, K

2000-01-01

268

Discrete Cosine Transforms on Quantum Computers

Digital Repository Infrastructure Vision for European Research (DRIVER)

A classical computer does not allow to calculate a discrete cosine transform on N points in less than linear time. This trivial lower bound is no longer valid for a computer that takes advantage of quantum mechanical superposition, entanglement, and interference principles. In fact, we show that it is possible to realize the discrete cosine transforms and the discrete sine transforms of size NxN and types I,II,III, and IV with as little as O(log^2 N) operations on a quantum ...

Klappenecker, Andreas; Roetteler, Martin

2001-01-01

269

Ancilla-Driven Universal Quantum Computation

We propose a method of manipulating a quantum register remotely with the help of a single ancilla that steers the evolution of the register. The fully controlled ancilla qubit is coupled to the computational register solely via a fixed unitary two-qubit interaction, E, and then measured in suitable bases. We characterize all interactions E that induce a unitary, step-wise deterministic measurement back-action on the register sufficient to implement any arbitrary quantum channel. Our scheme offers significant experimental advantages for implementing computations, preparing states and performing generalized measurements as no direct control of the register is required.

Anders, Janet; Kashefi, Elham; Browne, Dan E; Andersson, Erika

2009-01-01

270

Towards universal quantum computation through relativistic motion

We show how to use relativistic motion to generate continuous variable Gaussian cluster states within cavity modes. Our results can be demonstrated experimentally using superconducting circuits where tunable boundary conditions correspond to mirrors moving with velocities close to the speed of light. In particular, we propose the generation of a quadripartite square cluster state as a first example that can be readily implemented in the laboratory. Since cluster states are universal resources for universal one-way quantum computation, our results pave the way for relativistic quantum computation schemes.

Bruschi, David Edward; Kok, Pieter; Johansson, Göran; Delsing, Per; Fuentes, Ivette

2013-01-01

271

Processor core model for quantum computing.

We describe an architecture based on a processing "core," where multiple qubits interact perpetually, and a separate "store," where qubits exist in isolation. Computation consists of single qubit operations, swaps between the store and the core, and free evolution of the core. This enables computation using physical systems where the entangling interactions are "always on." Alternatively, for switchable systems, our model constitutes a prescription for optimizing many-qubit gates. We discuss implementations of the quantum Fourier transform, Hamiltonian simulation, and quantum error correction. PMID:16803291

Yung, Man-Hong; Benjamin, Simon C; Bose, Sougato

2006-06-01

272

Quantum cellular automata quantum computing with endohedral fullerenes

We present a scheme to perform universal quantum computation using global addressing techniques as applied to a physical system of endohedrally doped fullerenes. The system consists of an ABAB linear array of Group V endohedrally doped fullerenes. Each molecule spin site consists of a nuclear spin coupled via a Hyperfine interaction to an electron spin. The electron spin of each molecule is in a quartet ground state $S=3/2$. Neighboring molecular electron spins are coupled via a magnetic dipole interaction. We find that an all-electron construction of a quantum cellular automata is frustrated due to the degeneracy of the electronic transitions. However, we can construct a quantum celluar automata quantum computing architecture using these molecules by encoding the quantum information on the nuclear spins while using the electron spins as a local bus. We deduce the NMR and ESR pulses required to execute the basic cellular automata operation and obtain a rough figure of merit for the the number of gate operatio...

Twamley, J

2003-01-01

273

From Cbits to Qbits: Teaching computer scientists quantum mechanics

In this article, a strategy is suggested for teaching mathematically literate students, with no background in physics, just enough quantum mechanics for them to understand and develop algorithms in quantum computation and quantum information theory.

Mermin, N. D.

2004-04-29

274

The study of mutual entropy (information) and capacity in classica l system was extensively done after Shannon by several authors like Kolmogor ov and Gelfand. In quantum systems, there have been several definitions of t he mutual entropy for classical input and quantum output. In 1983, the autho r defined the fully quantum mechanical mutual entropy by means of the relati ve entropy of Umegaki, and it has been used to compute the capacity of quant um channel for quantum communication process; quantum input-quantum output. Recently, a correlated state in quantum syatems, so-called quantum entangled state or quantum entanglement, are used to study quntum information, in part icular, quantum computation, quantum teleportation, quantum cryptography. In this paper, we mainly discuss three things below: (1) We point out the di fference between the capacity of quantum channel and that of classical-quant um-classical channel. (2) So far the entangled state is merely defined as a non-separable state, we give a wider d...

Ohya, M

1998-01-01

275

Realizable Hamiltonians for universal adiabatic quantum computers

It has been established that local lattice spin Hamiltonians can be used for universal adiabatic quantum computation. However, the two-local model Hamiltonians used in these proofs are general and hence do not limit the types of interactions required between spins. To address this concern, the present paper provides two simple model Hamiltonians that are of practical interest to experimentalists working toward the realization of a universal adiabatic quantum computer. The model Hamiltonians presented are the simplest known quantum-Merlin-Arthur-complete (QMA-complete) two-local Hamiltonians. The two-local Ising model with one-local transverse field which has been realized using an array of technologies, is perhaps the simplest quantum spin model but is unlikely to be universal for adiabatic quantum computation. We demonstrate that this model can be rendered universal and QMA-complete by adding a tunable two-local transverse ?x?x coupling. We also show the universality and QMA-completeness of spin models with only one-local ?z and ?x fields and two-local ?z?x interactions.

Biamonte, Jacob D.; Love, Peter J.

2008-07-01

276

Quantum computer games: Schrödinger cat and hounds

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

Gordon, Michal; Gordon, Goren

2012-05-01

277

Another Look at Quantum Neural Computing

The term quantum neural computing was coined to indicate a unity in the functioning of the brain. We revisit the concept and also summarize new arguments related to the learning modes of the brain in response to sensory input that may be aggregated in three types: associative, reorganizational, and quantum. The associative and reorganizational types are quite apparent based on experimental findings; it is much harder to establish that the brain as an entity exhibits quantum properties. We argue that the reorganizational behavior of the brain may be viewed as inner adjustment corresponding to its quantum behavior at the system level. Not only neural structures but their higher abstractions also may be seen as whole entities. We consider the dualities associated with the behavior of the brain and how these dualities are bridged.

Kak, Subhash

2009-01-01

278

Universal quantum computation with unlabeled qubits

We show that an n-th root of the Walsh-Hadamard transform (obtained from the Hadamard gate and a cyclic permutation of the qubits) and two diagonal matrices, namely a local qubit-flip (for a fixed but arbitrary qubit) and a non-local phase-flip (for a fixed but arbitrary coefficient), form a universal set for quantum computation on n qubits. A quantum circuit, with n-qubits and based on this set, is then a product of unitaries whose factors are chosen from a pool of three. A quantum algorithm based on this set can be interpreted as a discrete diffusion of a quantum particle on a de Bruijn graph, with auxiliary modifications of the phases associated to the arcs.

Severini, S

2006-01-01

279

Quantum computing implementations with neutral particles

DEFF Research Database (Denmark)

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

Negretti, Antonio; Treutlein, Philipp

2011-01-01

280

Scalable quantum computing with atomic ensembles

International Nuclear Information System (INIS)

Atomic ensembles, comprising clouds of atoms addressed by laser fields, provide an attractive system for both the storage of quantum information and the coherent conversion of quantum information between atomic and optical degrees of freedom. We describe a scheme for full-scale quantum computing with atomic ensembles, in which qubits are encoded in symmetric collective excitations of many atoms. We consider the most important sources of error-imperfect exciton-photon coupling and photon losses-and demonstrate that the scheme is extremely robust against these processes: the required photon emission and collection efficiency threshold is ?>86%. Our scheme uses similar methods to those already demonstrated experimentally in the context of quantum repeater schemes and yet has information processing capabilities far beyond those proposals.

2010-09-01

281

Scalable quantum computing with atomic ensembles

Energy Technology Data Exchange (ETDEWEB)

Atomic ensembles, comprising clouds of atoms addressed by laser fields, provide an attractive system for both the storage of quantum information and the coherent conversion of quantum information between atomic and optical degrees of freedom. We describe a scheme for full-scale quantum computing with atomic ensembles, in which qubits are encoded in symmetric collective excitations of many atoms. We consider the most important sources of error-imperfect exciton-photon coupling and photon losses-and demonstrate that the scheme is extremely robust against these processes: the required photon emission and collection efficiency threshold is {approx}>86%. Our scheme uses similar methods to those already demonstrated experimentally in the context of quantum repeater schemes and yet has information processing capabilities far beyond those proposals.

Barrett, Sean D [Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2BZ (United Kingdom); Rohde, Peter P [Department of Materials, University of Oxford, Parks Road Oxford OX1 3PH (United Kingdom); Stace, Thomas M, E-mail: stace@physics.uq.edu.a [Department of Physics, University of Queensland, Brisbane, QLD 4072 (Australia)

2010-09-15

282

Imperfect Detectors in Linear Optical Quantum Computers

Digital Repository Infrastructure Vision for European Research (DRIVER)

We discuss the effects of imperfect photon detectors suffering from loss and noise on the reliability of linear optical quantum computers. We show that for a given detector efficiency, there is a maximum achievable success probability, and that increasing the number of ancillary photons and detectors used for one controlled sign flip gate beyond a critical point will decrease the probability that the computer will function correctly. We have also performed simulations of som...

Glancy, Scott; Losecco, J. M.; Vasconcelos, H. M.; Tanner, C. E.

2002-01-01

283

Quantum computation over the butterfly network

In order to investigate distributed quantum computation under restricted network resources, we introduce a quantum computation task over the butterfly network where both quantum and classical communications are limited. We consider performing a two qubit global unitary operation on two unknown inputs given at different nodes, with outputs at two distinct nodes. By using a particular resource scenario introduced by Hayashi, which is capable of performing a swap operation by adding two maximally entangled qubits (ebits) between the two input nodes, we show that any controlled unitary operation can be performed without adding any entanglement resource. We also construct protocols for performing controlled traceless unitary operations with a 1-ebit resource and for performing global Clifford operations with a 2-ebit resource.

Kinjo, Yoshiyuki; Soeda, Akihito; Turner, Peter S

2010-01-01

284

Adiabatic quantum computing for random satisfiability problems

International Nuclear Information System (INIS)

The discrete formulation of adiabatic quantum computing is compared with other search methods, classical and quantum, for random satisfiability (SAT) problems. With the number of steps growing only as the cube of the number of variables, the adiabatic method gives solution probabilities close to 1 for problem sizes feasible to evaluate via simulation on current computers. However, for these sizes the minimum energy gaps of most instances are fairly large, so the good performance scaling seen for small problems may not reflect asymptotic behavior where costs are dominated by tiny gaps. Moreover, the resulting search costs are much higher than for other methods. Variants of the quantum algorithm that do not match the adiabatic limit give lower costs, on average, and slower growth than the conventional GSAT heuristic method

2003-02-01

285

Efficient quantum computing with weak measurements

International Nuclear Information System (INIS)

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

2011-05-01

286

On Computational Power of Quantum Branching Programs

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this paper we study a model of a Quantum Branching Program (QBP) and investigate its computational power. We prove a general lower bound on the width of read-once QBPs, which we show to be almost tight on certain symmetric function.

Ablayev, Farid; Gainutdinova, Aida; Karpinski, Marek

2003-01-01

287

Simulations of Probabilities for Quantum Computing

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

Zak, M.

1996-01-01

288

Exact Solution of Holonomic Quantum Computation

Holonomic quantum computation is analyzed from geometrical viewpoint. We develop an optimization scheme in which an arbitrary unitary gate is implemented with a small circle in a complex projective space. Exact solutions for the Hadamard, CNOT and 2-qubit discrete Fourier transform gates are explicitly constructed.

Tanimura, S; Nakahara, M; Tanimura, Shogo; Hayashi, Daisuke; Nakahara, Mikio

2003-01-01

289

The geometry of quantum computation

Determining the quantum circuit complexity of a unitary operation is closely related to the problem of finding minimal length paths in a particular curved geometry [Nielsen et al, Science 311, 1133-1135 (2006)]. This paper investigates many of the basic geometric objects associated to this space, including the Levi-Civita connection, the geodesic equation, the curvature, and the Jacobi equation. We show that the optimal Hamiltonian evolution for synthesis of a desired unitary necessarily obeys a simple universal geodesic equation. As a consequence, once the initial value of the Hamiltonian is set, subsequent changes to the Hamiltonian are completely determined by the geodesic equation. We develop many analytic solutions to the geodesic equation, and a set of invariants that completely determine the geodesics. We investigate the problem of finding minimal geodesics through a desired unitary, U, and develop a procedure which allows us to deform the (known) geodesics of a simple and well understood metric to the...

Dowling, M R; Dowling, Mark R.; Nielsen, Michael A.

2006-01-01

290

Distributed Quantum Computation Based-on Small Quantum Registers

We describe and analyze an efficient register-based hybrid quantum computation scheme. Our scheme is based on probabilistic, heralded optical connection among local five-qubit quantum registers. We assume high fidelity local unitary operations within each register, but the error probability for initialization, measurement, and entanglement generation can be very high (~5%). We demonstrate that with a reasonable time overhead our scheme can achieve deterministic non-local coupling gates between arbitrary two registers with very high fidelity, limited only by the imperfections from the local unitary operation. We estimate the clock cycle and the effective error probability for implementation of quantum registers with ion-traps or nitrogen-vacancy (NV) centers. Our new scheme capitalizes on a new efficient two-level pumping scheme that in principle can create Bell pairs with arbitrarily high fidelity. We introduce a Markov chain model to study the stochastic process of entanglement pumping and map it to a determ...

Jiang, L; Sørensen, A S; Lukin, M D

2007-01-01

291

Interactive Quantum Mechanics Quantum Experiments on the Computer

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

Brandt, S; Dahmen, H.D

2011-01-01

292

Control and Dynamic Approach to Robust Quantum Computing.

During the entire performance period, from 12 May 2003 through 31 December 2006, we have conducted theoretical and computational research on quantum control problems central to quantum computation. In particular we completed a thorough and rigorous analys...

H. Mabuchi

2006-01-01

293

Quantum Computation and Information From Theory to Experiment

Recently, the field of quantum computation and information has been developing through a fusion of results from various research fields in theoretical and practical areas. This book consists of the reviews of selected topics charterized by great progress and cover the field from theoretical areas to experimental ones. It contains fundamental areas, quantum query complexity, quantum statistical inference, quantum cloning, quantum entanglement, additivity. It treats three types of quantum security system, quantum public key cryptography, quantum key distribution, and quantum steganography. A photonic system is highlighted for the realization of quantum information processing.

Imai, Hiroshi

2006-01-01

294

NMR spectra simulation for quantum computing

Energy Technology Data Exchange (ETDEWEB)

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

Diaz Bulnes, J.; Sarthour, R.S.; Guimaraes, A.P.; Oliveira, I.S. [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil); Freitas, J.C.C. [Universidade Federal do Espirito Santo (UFES), Vitoria, ES (Brazil). Dept. de Fisica

2002-07-01

295

NMR spectra simulation for quantum computing

International Nuclear Information System (INIS)

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

2002-05-07

296

Design constraints for nanometer scale quantum computers

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

Mainieri, R

1994-01-01

297

A Note on Adiabatic Quantum Computing

Most investigations devoted to the conditions for adiabatic quantum computing are based on the first-order correction ${\\bra{\\Psi_{\\rm ground}(t)}\\dot H(t)\\ket{\\Psi_{\\rm excited}(t)} /\\Delta E^2(t)\\ll1}$. However, it is demonstrated that this first-order correction does not yield a good estimate for the computational error. Therefore, a more general criterion is proposed, which includes higher-order corrections as well and shows that the computational error can be made exponentially small. Based on this criterion and rather general arguments, it can be demonstrated that a run-time $T$ of order of the inverse minimum energy gap $\\Delta E_{\\rm min}$ is sufficient and necessary, i.e., $T=\\ord(\\Delta E_{\\rm min}^{-1})$. For the example of Grovers quantum search algorithm, these analytical investigations are confirmed by numerical simulations. PACS: 03.67.Lx, 03.67.-a.

Schaller, G; Schützhold, R; Mostame, Sarah; Sch\\"utzhold, Ralf; Schaller, Gernot

2005-01-01

298

Discrete Wigner functions and quantum computation

International Nuclear Information System (INIS)

Full text: Gibbons et al. have recently defined a class of discrete Wigner functions W to represent quantum states in a finite Hilbert space dimension d. I characterize the set Cd of states having non-negative W simultaneously in all definitions of W in this class. I then argue that states in this set behave classically in a well-defined computational sense. I show that one-qubit states in C2 do not provide for universal computation in a recent model proposed by Bravyi and Kitaev [quant-ph/0403025]. More generally, I show that the only pure states in Cd are stabilizer states, which have an efficient description using the stabilizer formalism. This result shows that two different notions of 'classical' states coincide: states with non-negative Wigner functions are those which have an efficient description. This suggests that negativity of W may be necessary for exponential speed-up in pure-state quantum computation. (author)

2005-05-20

299

A repeat-until-success quantum computing scheme

International Nuclear Information System (INIS)

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

2007-06-01

300

Quantum Annealing and Computation: A Brief Documentary Note

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Ghosh, Asim; Mukherjee, Sudip

2013-01-01

301

A repeat-until-success quantum computing scheme

Energy Technology Data Exchange (ETDEWEB)

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

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

2007-06-15

302

Dynamical description of quantum computing: Generic nonlocality of quantum noise

International Nuclear Information System (INIS)

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

2002-06-01

303

Quantum Computers: A New Paradigm in Information Technology

Directory of Open Access Journals (Sweden)

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

Mahesh S. Raisinghani

2001-01-01

304

Quantum computation with nuclear spins in quantum dots

Energy Technology Data Exchange (ETDEWEB)

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

Christ, H.

2008-01-24

305

Quantum computation with nuclear spins in quantum dots

International Nuclear Information System (INIS)

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

2008-01-01

306

Compact quantum circuits from one-way quantum computation

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this paper we address the problem of translating one-way quantum computation (1WQC) into the circuit model. We start by giving a straightforward circuit representation of any 1WQC, at the cost of introducing many ancilla wires. We then propose a set of four simple circuit identities that explore the relationship between the entanglement resource and correction structure of a 1WQC, allowing one to obtain equivalent circuits acting on fewer qubits. We conclude with some exa...

Da Silva, Raphael Dias; Galva?o, Ernesto F.

2012-01-01

307

Mathematical optics classical, quantum, and computational methods

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

Lakshminarayanan, Vasudevan

2012-01-01

308

Scheme for Quantum Computing Immune to Decoherence

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

Williams, Colin; Vatan, Farrokh

2008-01-01

309

Measurement-Based and Universal Blind Quantum Computation

Measurement-based quantum computation (MBQC) is a novel approach to quantum computation where the notion of measurement is the main driving force of computation. This is in contrast with the more traditional circuit model which is based on unitary operation. We review here the mathematical model underlying MBQC and the first quantum cryptographic protocol designed using the unique features of MBQC.

Broadbent, Anne; Fitzsimons, Joseph; Kashefi, Elham

310

Some Notes on Quantum Information Theory and Emerging Computing Technologies

It is considered interdependence of theory of quantum computing and some perspective information technologies. Couple illustrative and useful examples are discussed. The reversible computing from very beginning had serious impact on design of quantum computers and it is revisited first. Some applications of ternary circuits are also quite instructive and it may be useful in quantum information theory.

Vlasov, Alexander Yu

2011-01-01

311

Quantum mechanics on the personal computer

International Nuclear Information System (INIS)

'Quantum Mechanics on the PC' presents the most up-to-date access to elementary quantum mechanics. Based on the interactive program Interquanta (included on a 5 1/4'' Floppy Disk, MS-DOS) and its extensive 3D colour graphic features, the book guides its readers through computer experiments on - free particles and wave packets - bound states in various potentials - coherent and squeezed states in time-dependent motion - scattering and resonances - analogies in optics - quantized angular momentum - distinguishable and indistinguishable particles - special functions of mathematical physics. The course with a wide variety of more than 250 detailed, class-tested problems provides students with a unique practical experience of complex probability amplitudes, eigenvalues, scattering cross sections and the like. Lecturers and teachers will find excellent, hands-on classroom demonstrations for their quantum mechanics course. (orig.)

1989-01-01

312

Quantum mechanics on the personal computer

Energy Technology Data Exchange (ETDEWEB)

'Quantum Mechanics on the PC' presents the most up-to-date access to elementary quantum mechanics. Based on the interactive program Interquanta (included on a 5 1/4'' Floppy Disk, MS-DOS) and its extensive 3D colour graphic features, the book guides its readers through computer experiments on - free particles and wave packets - bound states in various potentials - coherent and squeezed states in time-dependent motion - scattering and resonances - analogies in optics - quantized angular momentum - distinguishable and indistinguishable particles - special functions of mathematical physics. The course with a wide variety of more than 250 detailed, class-tested problems provides students with a unique practical experience of complex probability amplitudes, eigenvalues, scattering cross sections and the like. Lecturers and teachers will find excellent, hands-on classroom demonstrations for their quantum mechanics course. (orig.).

Brandt, S.; Dahmen, H.D. (Siegen Univ. (Gesamthochschule) (Germany, F.R.). Fachbereich 7 - Physik)

1989-01-01

313

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Belaga, Edward G.; Grucker, Daniel

2003-01-01

314

Nonlinear Optics Quantum Computing with Circuit-QED

Digital Repository Infrastructure Vision for European Research (DRIVER)

One approach to quantum information processing is to use photons as quantum bits and rely on linear optical elements for most operations. However, some optical nonlinearity is necessary to enable universal quantum computing. Here, we suggest a circuit-QED approach to nonlinear optics quantum computing in the microwave regime, including a deterministic two-photon phase gate. Our specific example uses a hybrid quantum system comprising a LC resonator coupled to a superconducti...

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

2012-01-01

315

Fermionic measurement-based quantum computation

Fermions, as a major class of quantum particles, provide platforms for quantum information processing beyond the possibilities of spins or bosons, which have been studied more extensively. One particularly interesting model to study, in view of recent progress in manipulating ultracold fermion gases, is the fermionic version of measurement-based quantum computation (MBQC), which implements full quantum computation with only single-site measurements on a proper fermionic many-body resource state. However, it is not known which fermionic states can be used as the resource states for MBQC and how to find them. In this paper, we generalize the framework of spin MBQC to fermions. In particular, we provide a general formalism to construct many-body entangled fermion resource states for MBQC based on the fermionic projected entangled pair state representation. We give a specific fermionic state which enables universal MBQC and demonstrate that the nonlocality inherent in fermion systems can be properly taken care of with suitable measurement schemes. Such a framework opens up possibilities of finding MBQC resource states which can be more readily realized in the laboratory.

Chiu, Yu-Ju; Chen, Xie; Chuang, Isaac L.

2013-01-01

316

Non-unitary probabilistic quantum computing circuit and method

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

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

2009-01-01

317

Algorithmic Cooling and Scalable NMR Quantum Computers

We present here algorithmic cooling (via polarization-heat-bath)- a powerful method for obtaining a large number of highly polarized spins in liquid nuclear-spin systems at finite temperature. Given that spin-half states represent (quantum) bits, algorithmic cooling cleans dirty bits beyond the Shannon's bound on data compression, by employing a set of rapidly thermal-relaxing bits. Such auxiliary bits could be implemented using spins that rapidly get into thermal equilibrium with the environment, e.g., electron spins. Cooling spins to a very low temperature without cooling the environment could lead to a breakthrough in nuclear magnetic resonance experiments, and our ``spin-refrigerating'' method suggests that this is possible. The scaling of NMR ensemble computers is probably the main obstacle to building useful quantum computing devices, and our spin-refrigerating method suggests that this problem can be resolved.

Boykin, P O; Roychowdhury, V P; Vatan, F; Vrijen, R; Mor, Tal; Roychowdhury, Vwani; Vatan, Farrokh; Vrijen, Rutger

2001-01-01

318

A quantum computation architecture using optical tweezers

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

Weitenberg, Christof; Mølmer, Klaus; Sherson, Jacob F

2011-01-01

319

Quantum computation architecture using optical tweezers

International Nuclear Information System (INIS)

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

2011-09-01

320

Quantum computation architecture using optical tweezers

DEFF Research Database (Denmark)

We present a complete architecture for scalable quantum computation with ultracold atoms in optical lattices using optical tweezers focused to the size of a lattice spacing. We discuss three different two-qubit gates based on local collisional interactions. The gates between arbitrary qubits require the transport of atoms to neighboring sites. We numerically optimize the nonadiabatic transport of the atoms through the lattice and the intensity ramps of the optical tweezer in order to maximize the gate fidelities. We find overall gate times of a few 100 Î¼s, while keeping the error probability due to vibrational excitations and spontaneous scattering below 10â??3. The requirements on the positioning error and intensity noise of the optical tweezer and the magnetic field stability are analyzed and we show that atoms in optical lattices could meet the requirements for fault-tolerant scalable quantum computing.

Weitenberg, Christof; Kuhr, Stefan

2011-01-01

321

Quantum computation architecture using optical tweezers

Energy Technology Data Exchange (ETDEWEB)

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

Weitenberg, Christof [Max-Planck-Institut fuer Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching (Germany); Kuhr, Stefan [Max-Planck-Institut fuer Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching (Germany); University of Strathclyde, Department of Physics, SUPA, Glasgow G4 0NG (United Kingdom); Moelmer, Klaus; Sherson, Jacob F. [Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark)

2011-09-15

322

Quantum computation with coupled-quantum-dots embedded in optical microcavities

Digital Repository Infrastructure Vision for European Research (DRIVER)

Based on an idea that spatial separation of charge states can enhance quantum coherence, we propose a scheme for quantum computation with quantum bit (qubit) constructed from two coupled quantum dots. Quantum information is stored in electron-hole pair state with the electron and hole locating in different dots, which enables the qubit state being very long-lived. Universal quantum gates involving any pair of qubits are realized by coupling the quantum dots through cavity ph...

Li, Xin-qi; Yan, Yijing

2002-01-01

323

Photonic entanglement as a resource in quantum computation and quantum communication

Entanglement is an essential resource in current experimental implementations for quantum information processing. We review a class of experiments exploiting photonic entanglement, ranging from one-way quantum computing over quantum communication complexity to long-distance quantum communication. We then propose a set of feasible experiments that will underline the advantages of photonic entanglement for quantum information processing.

Prevedel, Robert; Brukner, Caslav; Jennewein, Thomas; Zeilinger, Anton

2008-01-01

324

Experimental demonstration of one-way quantum computation on an ensemble quantum computer

We report the first experimental investigation of the one-way quantum computation in the liquid-state NMR system, by demonstrating a two-qubit Deutsch-Josza algorithm on a star-like 4-qubit graph state. Due to the ensemble quantum computing technology we used, no active feed-forward is needed in our experiment, yet the computation is still deterministic. This advantage avoids the technical challenges in realizing the active feed-forward. Our experimental results are in good agreement with the theoretical expectation.

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

2008-01-01

325

Robust gates for holonomic quantum computation

International Nuclear Information System (INIS)

Non-Abelian geometric phases are attracting increasing interest because of possible experimental application in quantum computation. We study the effects of the environment (modeled as an ensemble of harmonic oscillators) on a holonomic transformation and write the corresponding master equation. The solution is analytically and numerically investigated and the behavior of the fidelity analyzed: fidelity revivals are observed and an optimal finite operation time is determined at which the gate is most robust against noise

2006-02-01

326

Nuclear spin quantum computing with trapped ions

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

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

2011-01-01

327

Quantum computing with spatially delocalized qubits

Digital Repository Infrastructure Vision for European Research (DRIVER)

We analyze the operation of quantum gates for neutral atoms with qubits that are delocalized in space, i.e., the computational basis states are defined by the presence of a neutral atom in the ground state of one out of two trapping potentials. The implementation of single-qubit gates as well as a controlled phase gate between two qubits is discussed and explicit calculations are presented for rubidium atoms in optical microtraps. Furthermore, we show how multiqubit highly entangled states ca...

Mompart Penina, Jordi

2003-01-01

328

Spin quantum computation in silicon nanostructures

Digital Repository Infrastructure Vision for European Research (DRIVER)

Proposed silicon-based quantum-computer architectures have attracted attention because of their promise for scalability and their potential for synergetically utilizing the available resources associated with the existing Si technology infrastructure. Electronic and nuclear spins of shallow donors (e.g. phosphorus) in Si are ideal candidates for qubits in such proposals because of their long spin coherence times due to their limited interactions with their environments. For ...

Sarma, S. Das; Sousa, Rogerio; Hu, Xuedong; Koiller, Belita

2004-01-01

329

Universal quantum gates for Single Cooper Pair Box based quantum computing

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.

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

2000-01-01

330

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

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

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

2004-01-01

331

PREFACE: Quantum Information, Communication, Computation and Cryptography

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

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

2007-07-01

332

Extending scientific computing system with structural quantum programming capabilities

We present a basic high-level structures used for developing quantum programming languages. The presented structures are commonly used in many existing quantum programming languages and we use quantum pseudo-code based on QCL quantum programming language to describe them. We also present the implementation of introduced structures in GNU Octave language for scientific computing. Procedures used in the implementation are available as a package quantum-octave, providing a library of functions, which facilitates the simulation of quantum computing. This package allows also to incorporate high-level programming concepts into the simulation in GNU Octave and Matlab. As such it connects features unique for high-level quantum programming languages, with the full palette of efficient computational routines commonly available in modern scientific computing systems. To present the major features of the described package we provide the implementation of selected quantum algorithms. We also show how quantum errors can be...

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

2010-01-01

333

A Geometric Algebra Perspective On Quantum Computational Gates And Universality In Quantum Computing

We investigate the utility of geometric (Clifford) algebras (GA) methods in two specific applications to quantum information science. First, using the multiparticle spacetime algebra (MSTA, the geometric algebra of a relativistic configuration space), we present an explicit algebraic description of one and two-qubit quantum states together with a MSTA characterization of one and two-qubit quantum computational gates. Second, using the above mentioned characterization and the GA description of the Lie algebras SO(3) and SU(2) based on the rotor group Spin+(3, 0) formalism, we reexamine Boykin's proof of universality of quantum gates. We conclude that the MSTA approach does lead to a useful conceptual unification where the complex qubit space and the complex space of unitary operators acting on them become united, with both being made just by multivectors in real space. Finally, the GA approach to rotations based on the rotor group does bring conceptual and computational advantages compared to standard vectoria...

Cafaro, Carlo

2010-01-01

334

An Introduction to Quantum Computing using Cavity QED concepts

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Burell, Zachary

2012-01-01

335

Hybrid architecture for encoded measurement-based quantum computation

We present a hybrid scheme for quantum computation that combines the modular structure of elementary building blocks used in the circuit model with the advantages of a measurement-based approach to quantum computation. We show how to construct optimal resource states of minimal size to implement elementary building blocks for encoded quantum computation in a measurement-based way, including states for error correction and encoded gates. The performance of the scheme is determined by the quality of the resource states, where within the considered error model a threshold of the order of 10% local noise per particle for fault-tolerant quantum computation and quantum communication.

Zwerger, M.; Briegel, H. J.; Dur, W.

2014-01-01

336

Hybrid architecture for encoded measurement-based quantum computation.

We present a hybrid scheme for quantum computation that combines the modular structure of elementary building blocks used in the circuit model with the advantages of a measurement-based approach to quantum computation. We show how to construct optimal resource states of minimal size to implement elementary building blocks for encoded quantum computation in a measurement-based way, including states for error correction and encoded gates. The performance of the scheme is determined by the quality of the resource states, where within the considered error model a threshold of the order of 10% local noise per particle for fault-tolerant quantum computation and quantum communication. PMID:24946906

Zwerger, M; Briegel, H J; Dür, W

2014-01-01

337

Universal Quantum Computing with Spin and Valley

We investigate a two-electron double quantum dot with both spin and valley degrees of freedom as they occur in graphene, carbon nanotubes, or silicon, and regard the 16-dimensional space with one electron per dot as a four-qubit logic space. In the spin-only case, it is well known that the exchange coupling between the dots combined with arbitrary single-qubit operations is sufficient for universal quantum computation. The presence of the valley degeneracy in the electronic band structure alters the form of the exchange coupling and in general leads to spin-valley entanglement. Here, we show that universal quantum computation can still be performed by exchange interaction and single-qubit gates in the presence of the additional (valley) degree of freedom. We present an explicit pulse sequence for a spin-only controlled-NOT consisting of the generalized exchange coupling and single-electron spin and valley rotations. We also propose state preparations and projective measurements with the use of adiabatic trans...

Rohling, Niklas

2012-01-01

338

We introduce the notion of a class of abstract digital computers based on quantum reversibility and indeterminism (not 011 the classical sequential architecture), which are compatible with quantum laws and may perform nondeterministic and non-recursive computation.

Castagnoli, Giuseppe; Rasetti, Mario; Vincenzi, Antonio

339

Computing the Exit Complexity of Knowledge in Distributed Quantum Computers

Directory of Open Access Journals (Sweden)

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

M.A.Abbas

2013-01-01

340

Distributed quantum computation based on small quantum registers

International Nuclear Information System (INIS)

We describe and analyze an efficient register-based hybrid quantum computation scheme. Our scheme is based on a probabilistic, heralded optical connection among local five-qubit quantum registers. We assume high-fidelity local unitary operations within each register, but the error probability for initialization, measurement, and entanglement generation can be very high (?5%). We demonstrate that with a reasonable time overhead our scheme can achieve deterministic nonlocal coupling gates between arbitrary two registers with very high fidelity, limited only by the imperfections from the local unitary operation. We estimate the clock cycle and the effective error probability for implementation of quantum registers with ion traps or nitrogen-vacancy centers. Our scheme capitalizes on an efficient two-level pumping scheme that in principle can create Bell pairs with arbitrarily high fidelity. We introduce a Markov chain model to study the stochastic process of entanglement pumping and map it onto a deterministic process. Finally we discuss requirements for achieving fault-tolerant operation with our register-based hybrid scheme and also present an alternative approach to fault-tolerant preparation of Greenberger-Horne-Zeilinger states

2007-12-01

341

High-fidelity quantum memory using nitrogen-vacancy center ensemble for hybrid quantum computation

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study a hybrid quantum computing system using nitrogen-vacancy center ensemble (NVE) as quantum memory, current-biased Josephson junction (CBJJ) superconducting qubit fabricated in a transmission line resonator (TLR) as quantum computing processor and the microwave photons in TLR as quantum data bus. The storage process is seriously treated by considering all kinds of decoherence mechanisms. Such a hybrid quantum device can also be used to create multi-qubit W states of N...

Yang, W. L.; Yin, Zhang-qi; Hu, Y.; Feng, M.; Du, J. F.

2011-01-01

342

Poly-locality in quantum computing

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

Freedman, M H

2000-01-01

343

Quiet SDS Josephson Junctions for Quantum Computing

Unconventional superconductors exhibit an order parameter symmetry lower than the symmetry of the underlying crystal lattice. Recent phase sensitive experiments have established the d-wave (D) nature of the copper-oxide materials, thus identifying unambiguously the first unconventional superconductor. The sign change in the order parameter can be exploited to construct a new type of SDS Josephson junction exhibiting a degenerate ground state and a double-periodic current - phase characteristic. Here, we demonstrate how to make use of these special junction characteristics in the construction of a quantum computer. Combining such junctions together with a usual s-wave (S) link into a SQUID loop we obtain what we call a `quiet' qubit - a solid state implementation of a quantum bit which remains optimally isolated from its environment.

Ioffe, L B; Feigelman, M V; Fauchère, A L; Blatter, G

1999-01-01

344

Trapped Ion Quantum Computer Research at Los Alamos

We briefly review the development and theory of an experiment to investigate quantum computation with trapped calcium ions. The ion trap, laser and ion requirements are determined, and the parameters required for simple quantum logic operations are described

James, D F V; Holzscheiter, M H; Hughes, R J; Kwiat, P G; Lamoreaux, S K; Peterson, C G; Sandberg, V D; Schauer, M M; Simmons, C M; Tupa, D; Wang, P Z; White, A G

1998-01-01

345

Quantum Computation In The Neuronal Microtubules Quantum Gates, Ordered Water And Superradiance

Stuart Hameroff and Roger Penrose have widely discussed possible quantum effects in the brain microtubules assuming that computation occurs. However, for now there is no special publication dealing exactly with the problems of quantum gate appliance in the microtubule network, nor the problems of quantum computation are taken into consideration while studying the quantum computation in the neuronal microtubules. It is the essence of the present paper.

Georgiev, D D

2002-01-01

346

Quantum computers can search rapidly by using almost any transformation

Digital Repository Infrastructure Vision for European Research (DRIVER)

A quantum computer has a clear advantage over a classical computer for exhaustive search. The quantum mechanical algorithm for exhaustive search was originally derived by using subtle properties of a particular quantum mechanical operation called the Walsh-Hadamard (W-H) transform. This paper shows that this algorithm can be implemented by replacing the W-H transform by almost any quantum mechanical operation. This leads to several new applications where it improves the numb...

Grover, Lov K.

1997-01-01

347

On Computational Power of Quantum Read-Once Branching Programs

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Ablayev, Farid; Vasiliev, Alexander

2011-01-01

348

A deterministic optical quantum computer using photonic modules

The optical quantum computer is one of the few experimental systems to have demonstrated small scale quantum information processing. Making use of cavity quantum electrodynamics approaches to operator measurements, we detail an optical network for the deterministic preparation of arbitrarily large two-dimensional cluster states. We show that this network can form the basis of a large scale deterministic optical quantum computer that can be fabricated entirely on chip.

Stephens, A M; Devitt, S J; Greentree, A D; Fowler, A G; Munro, W J; O'Brien, J L; Nemoto, Kae; Hollenberg, L C L

2008-01-01

349

Experimental realization of order-finding with a quantum computer

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

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

2000-01-01

350

Measurement-based quantum computation with trapped ions.

Measurement-based quantum computation represents a powerful and flexible framework for quantum information processing, based on the notion of entangled quantum states as computational resources. The most prominent application is the one-way quantum computer, with the cluster state as its universal resource. Here we demonstrate the principles of measurement-based quantum computation using deterministically generated cluster states, in a system of trapped calcium ions. First we implement a universal set of operations for quantum computing. Second we demonstrate a family of measurement-based quantum error correction codes and show their improved performance as the code length is increased. The methods presented can be directly scaled up to generate graph states of several tens of qubits. PMID:24313469

Lanyon, B P; Jurcevic, P; Zwerger, M; Hempel, C; Martinez, E A; Dür, W; Briegel, H J; Blatt, R; Roos, C F

2013-11-22

351

From Cbits to Qbits Teaching computer scientists quantum mechanics

A strategy is suggested for teaching mathematically literate students, with no background in physics, just enough quantum mechanics for them to understand and develop algorithms in quantum computation and quantum information theory. Although the article as a whole addresses teachers of physics, well versed in quantum mechanics, the central pedagogical development is addressed directly to computer scientists and mathematicians, with only occasional asides to their teacher. Physicists uninterested in quantum pedagogy may be amused (or irritated) by some of the views of standard quantum mechanics that arise naturally from this unorthodox perspective.

Mermin, N David

2002-01-01

352

Methods for Scalable Optical Quantum Computation

We propose a scalable method for implementing linear optics quantum computation using the “linked-state” approach. Our method avoids the two-dimensional spread of errors occurring in the preparation of the linked state. Consequently, a proof is given for the scalability of this modified linked-state model, and an exact expression for the efficiency of the method is obtained. Moreover, a considerable improvement in the efficiency, relative to the original linked-state method, is achieved. The proposed method is applicable to Nielsen’s optical “cluster-state” approach as well.

Mor, Tal; Yoran, Nadav

2006-09-01

353

Methods for scalable optical quantum computation

We propose a scalable method for implementing linear optics quantum computation using the ``linked-state'' approach. Our method avoids the two-dimensional spread of errors occurring in the preparation of the linked-state. Consequently, a proof is given for the scalability of this modified linked-state model, and an exact expression for the efficiency of the method is obtained. Moreover, a considerable improvement in the efficiency, relative to the original linked-state method, is achieved. The proposed method is applicable to Nielsen's optical ``cluster-state'' approach as well.

Mor, T; Mor, Tal; Yoran, Nadav

2006-01-01

354

Quantum computing in a macroscopic dark period

International Nuclear Information System (INIS)

Decoherence-free subspaces allow for the preparation of coherent and entangled qubits for quantum computing. Decoherence can be dramatically reduced, yet dissipation is an integral part of the scheme in generating stable qubits and manipulating them via one- and two-bit gate operations. How this works can be understood by comparing the system with a three-level atom exhibiting a macroscopic dark period. In addition, a dynamical explanation is given for a scheme based on atoms inside an optical cavity in the strong-coupling regime and we show how spontaneous emission by the atoms can be highly suppressed

2002-03-01

355

Quantum computing with spatially delocalized qubits

International Nuclear Information System (INIS)

We analyze the operation of quantum gates for neutral atoms with qubits that are delocalized in space, i.e., the computational basis states are defined by the presence of a neutral atom in the ground state of one out of two trapping potentials. The implementation of single-qubit gates as well as a controlled phase gate between two qubits is discussed and explicit calculations are presented for rubidium atoms in optical microtraps. Furthermore, we show how multiqubit highly entangled states can be created in this scheme

2003-04-11

356

Graph isomorphism and adiabatic quantum computing

Digital Repository Infrastructure Vision for European Research (DRIVER)

In the Graph Isomorphism problem two N-vertex graphs G and G' are given and the task is to determine whether there exists a permutation of the vertices of G that preserves adjacency and transforms G into G'. If yes, then G and G' are said to be isomorphic; otherwise they are non-isomorphic. The GI problem is an important problem in computer science and is thought to be of comparable difficulty to integer factorization. In this paper we present a quantum algorithm that solves...

Gaitan, Frank; Clark, Lane

2013-01-01

357

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

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

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

1999-01-01

358

Verification for measurement-only blind quantum computing

Blind quantum computing is a new secure quantum computing protocol where a client who does not have any sophisticated quantum technology can delegate her quantum computing to a server without leaking any privacy. It is known that a client who has only a measurement device can perform blind quantum computing [T. Morimae and K. Fujii, Phys. Rev. A 87, 050301(R) (2013), 10.1103/PhysRevA.87.050301]. It has been an open problem whether the protocol can enjoy the verification, i.e., the ability of the client to check the correctness of the computing. In this paper, we propose a protocol of verification for the measurement-only blind quantum computing.

Morimae, Tomoyuki

2014-06-01

359

Tomography and spectroscopy as quantum computations

Determining the state of a system and measuring properties of its evolution are two of the most important tasks a physicist faces. For the first purpose one can use tomography, a method that after subjecting the system to a number of experiments determines all independent elements of the density matrix. For the second task, one can resort to spectroscopy, a set of techniques used to determine the spectrum of eigenvalues of the evolution operator. In this letter, we show that tomography and spectroscopy can be naturally interpreted as dual forms of quantum computation. We show how to adapt the simplest case of the well-known phase estimation quantum algorithm to perform both tasks, giving it a natural interpretation as a simulated scattering experiment. We show how this algorithm can be used to implement an interesting form of tomography by performing a direct measurement of the Wigner function of a quantum system. We present results of such measurements performed on a system of three qubits using liquid state...

Miquel, C; Saraceno, M; Knill, E H; Laflamme, R; Negrevergne, C; Miquel, Cesar; Paz, Juan Pablo; Saraceno, Marcos; Knill, Emmanuel; Laflamme, Raymond; Negrevergne, Camille

2001-01-01

360

Topological quantum computing with only one mobile quasiparticle.

In a topological quantum computer, universal quantum computation is performed by dragging quasiparticle excitations of certain two dimensional systems around each other to form braids of their world lines in 2 + 1 dimensional space-time. In this Letter we show that any such quantum computation that can be done by braiding n identical quasiparticles can also be done by moving a single quasiparticle around n - 1 other identical quasiparticles whose positions remain fixed. PMID:16606068

Simon, S H; Bonesteel, N E; Freedman, M H; Petrovic, N; Hormozi, L

2006-02-24

361

State of the art and prospects for quantum computing

Digital Repository Infrastructure Vision for European Research (DRIVER)

This is a brief review of the experimental and theoretical quantum computing. The hopes for eventually building a useful quantum computer rely entirely on the so-called "threshold theorem". In turn, this theorem is based on a number of assumptions, treated as axioms, i.e. as being satisfied exactly. Since in reality this is not possible, the prospects of scalable quantum computing will remain uncertain until the required precision, with which these assumptions should be appr...

Dyakonov, M. I.

2012-01-01

362

Surface code quantum computing by lattice surgery

In recent years, surface codes have become the preferred method for quantum error correction in large scale computational and communications architectures. Their comparatively high fault-tolerant thresholds and their natural 2-dimensional nearest neighbour (2DNN) structure make them an obvious choice for large scale designs in experimentally realistic systems. While fundamentally based on the toric code of Kitaev, there are many variants, two of which are the planar- and defect- based codes. Planar codes require fewer qubits to implement (for the same strength of error correction), but are restricted to encoding a single qubit of information. Interactions between encoded qubits are achieved via transversal operations, thus destroying the inherent 2DNN nature of the code. In this paper we introduce a new technique enabling the coupling of two planar codes without transversal operations, maintaining the 2DNN of the encoded computer. Our lattice surgery technique comprises splitting and merging planar code surfa...

Horsman, Clare; Devitt, Simon; Van Meter, Rodney

2011-01-01

363

An introduction to many worlds in quantum computation

The interpretation of quantum mechanics is an area of increasing interest to many working physicists. In particular, interest has come from those involved in quantum computing and information theory, as there has always been a strong foundational element in this field. This paper introduces one interpretation of quantum mechanics, a modern `many-worlds' theory, from the perspective of quantum computation. Reasons for seeking to interpret quantum mechanics are discussed, then the specific `neo-Everettian' theory is introduced and its claim as the best available interpretation defended. The main objections to the interpretation, including the so-called ``problem of probability'' are shown to fail. The local nature of the interpretation is demonstrated, and the implications of this both for the interpretation and for quantum mechanics more generally are discussed. Finally, the consequences of the theory for quantum computation are investigated, and common objections to using many worlds to describe quantum compu...

Hewitt-Horsman, Clare

2008-01-01

364

Identifying phases of matter that are universal for quantum computation

A recent breakthrough in quantum computing has been the realization that quantum computation can proceed solely through single-qubit measurements on an appropriate quantum state - for example, the ground state of an interacting many-body system. It would be unfortunate, however, if the usefulness of a ground state for quantum computation was critically dependent on the details of the system's Hamiltonian; a much more powerful result would be the existence of a robust ordered phase which is characterized by the ability to perform measurement-based quantum computation (MBQC). To identify such phases, we propose to use nonlocal correlation functions that quantify the fidelity of quantum gates performed between distant qubits. We investigate a simple spin-lattice system based on the cluster-state model for MBQC, and demonstrate that it possesses a zero temperature phase transition between a disordered phase and an ordered "cluster phase" in which it is possible to perform a universal set of quantum gates.

Doherty, Andrew C

2008-01-01

365

Quantum computing with trapped ions, atoms and light

International Nuclear Information System (INIS)

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

2001-01-30

366

Spin-free quantum computational simulations and symmetry adapted states

The ideas of digital simulation of quantum systems using a quantum computer parallel the original ideas of numerical simulation using a classical computer. In order for quantum computational simulations to advance to a competitive point, many techniques from classical simulations must be imported into the quantum domain. In this article, we consider the applications of symmetry in the context of quantum simulation. Building upon well established machinery, we propose a form of first quantized simulation that only requires the spatial part of the wave function, thereby allowing spin-free quantum computational simulations. We go further and discuss the preparation of N-body states with specified symmetries based on projection techniques. We consider two simple examples, molecular hydrogen and cyclopropenyl cation, to illustrate the ideas. While the methods here represent adaptations of known quantum algorithms, they are the first to explicitly deal with preparing N-body symmetry-adapted states.

Whitfield, James Daniel

2013-01-01

367

Quantum Annealing and Computation: A Brief Documentary Note

Major breakthrough in quantum computation has recently been achieved using quantum annealing to develop analog quantum computers instead of gate based computers. After a short introduction to quantum computation, we retrace very briefly the history of these developments and discuss the Indian researches in this connection and provide some interesting documents (in the Figs.) obtained from a chosen set of high impact papers (and also some recent news etc. blogs appearing in the Internet). This note is also designed to supplement an earlier note by Bose (Science and Culture, 79, pp. 337-378, 2013).

Ghosh, Asim

2013-01-01

368

Computer science approach to quantum control

International Nuclear Information System (INIS)

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

2006-01-01

369

Quantum computing with Josephson junction circuits

This work concerns the study of Josephson junction circuits in the context of their usability for quantum computing. The zero-voltage state of a current-biased Josephson junction has a set of metastable quantum energy levels. If a junction is well isolated from its environment, it will be possible to use the two lowest states as a qubit in a quantum computer. I first examine the meaning of isolation theoretically. Using a master equation, I analyzed the effect of dissipation on escape rates and suggested a simple method, population depletion technique, to measure the relaxation time (T1). Using a stochastic Bloch equation to analyze the dependence of microwave resonance peak width on current noise, I found decoherence due to current noise depends on the noise spectrum. For high frequency noise with a cutoff frequency fc much larger than 1/T1, I found decoherence due to noise can be described by a dephasing rate that is proportional to the noise spectral density. However, for low frequency noise such that its cutoff frequency fc is much smaller than 1/T 1, decoherence due to noise depends on the total rms current noise. I then analyze and test a few qubit isolation schemes, including resistive isolation, inductor-capacitor (LC) isolation, half-wavelength resonant isolation and inductor-junction (LJ) isolation. I found the resistive isolation scheme has a severe heating problem. Macroscopic quantum tunneling and energy level quantization were observed in the LC isolated Nb/AlOx/Nb and AL/ALOx/Al junction qubits at 25 mK. Relaxation times of 4--12 ns and spectroscopic coherence times of 1--3 ns were obtained for these LC isolated qubits. I found the half-wavelength isolated junction qubit has a relaxation time of about 20 ns measured by the population-depletion techniques, but no energy levels were observed in this qubit. Experimental results suggest the LJ isolated qubit has a longer relaxation and coherence times than all my previously examined samples. Using a microwave pulse technique, a relaxation time of 50 ns was measured on this sample, the spectroscopic coherence time obtained using continuous microwave pumping is about 5--8 ns. Coherent quantum oscillations (Rabi oscillations) were also observed on this sample with a decay time of around 10 ns for a |0 >? |1 > level spacing of 7.6 GHz. The relaxation times are much smaller than what I would expect from my designs for all isolation schemes. Possible reasons for this inconsistency were discussed. Using microwave spectroscopy techniques, I probed quantum phenomena in a coupled macroscopic three-qubit system that is comprised of two Nb/AlOx/Nb Josephson junctions and an LC resonator. The measured spectrum at 25 mK in the frequency range 4--15 GHz agrees well with quantum mechanical calculations, consistent with the existence of entangled states between the three degrees of freedom. These entangled states and a first-order strong coupling between two junction qubits open the possibility of using a resonator as a data bus for information storage and manipulation in a multi-qubit system. The measurements also demonstrate spectroscopy is a powerful tool and can be used to study a composite system with many qubits.

Xu, Huizhong

370

Quantum Computing in Condensed Matter Systems.

Specific theoretical calculations of Hamiltonians corresponding to several quantum logic gates, including the NOT gate, quantum signal splitting, and quantum copying, were obtained and prepared for publication. Directions for future work have been identif...

V. Privman

1997-01-01

371

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

Directory of Open Access Journals (Sweden)

Full Text Available Quantum computer is the current topic of research in the field of computational science, which uses principles of quantum mechanics. Quantum computers will be much more powerful than the classical computer due to its enormous computational speed. Recent developments in quantum computers which are based on the laws of quantum mechanics, shows different ways of performing efficient calculations along with the various results which are not possible on the classical computers in an efficient period of time. One of the most striking results that have obtained on the quantum computers is the prime factorization of the large integer in a polynomial time. The idea of involvement of the quantum mechanics for the computational purpose is outlined briefly in the present work that reflects the importance and advantages of the next generation of the 21st century classical computers, named as quantum computers, in terms of the cost as well as time period required for the computation purpose. Present paper presents a quantum computer simulator for executing the limitations of classical computer with respect to time and the number of digits of a composite integer used for calculating its prime factors.

Sanjaykumar DALVI

2011-12-01

372

Surface code quantum computing by lattice surgery

International Nuclear Information System (INIS)

In recent years, surface codes have become a leading method for quantum error correction in theoretical large-scale computational and communications architecture designs. Their comparatively high fault-tolerant thresholds and their natural two-dimensional nearest-neighbour (2DNN) structure make them an obvious choice for large scale designs in experimentally realistic systems. While fundamentally based on the toric code of Kitaev, there are many variants, two of which are the planar- and defect-based codes. Planar codes require fewer qubits to implement (for the same strength of error correction), but are restricted to encoding a single qubit of information. Interactions between encoded qubits are achieved via transversal operations, thus destroying the inherent 2DNN nature of the code. In this paper we introduce a new technique enabling the coupling of two planar codes without transversal operations, maintaining the 2DNN of the encoded computer. Our lattice surgery technique comprises splitting and merging planar code surfaces, and enables us to perform universal quantum computation (including magic state injection) while removing the need for braided logic in a strictly 2DNN design, and hence reduces the overall qubit resources for logic operations. Those resources are further reduced by the use of a rotated lattice for the planar encoding. We show how lattice surgery allows us to distribute encoded GHZ states in a more direct (and overhead friendly) manner, and how a demonstration of an encoded CNOT between two distance-3 logical states is possible with 53 physical qubits, half of that required in any other known construction in 2D. (paper)

2012-12-01

373

Preparing projected entangled pair states on a quantum computer

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present a quantum algorithm to prepare injective PEPS on a quantum computer, a class of open tensor networks representing quantum states. The run-time of our algorithm scales polynomially with the inverse of the minimum condition number of the PEPS projectors and, essentially, with the inverse of the spectral gap of the PEPS' parent Hamiltonian.

Schwarz, Martin; Temme, Kristan; Verstraete, Frank

2011-01-01

374

Simulation of Quantum Computation: A deterministic event-based approach

We demonstrate that locally connected networks of machines that have primitive learning capabilities can be used to perform a deterministic, event-based simulation of quantum computation. We present simulation results for basic quantum operations such as the Hadamard and the controlled-NOT gate, and for seven-qubit quantum networks that implement Shor's numbering factoring algorithm.

Michielsen, K; De Raedt, H

2005-01-01

375

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

Baianu,I C

2004-01-01

376

Quantum computing based on space states without charge transfer

International Nuclear Information System (INIS)

An implementation of a quantum computer based on space states in double quantum dots is discussed. There is no charge transfer in qubits during a calculation, therefore, uncontrolled entanglement between qubits due to long-range Coulomb interaction is suppressed. Encoding and processing of quantum information is merely performed on symmetric and antisymmetric states of the electron in double quantum dots. Other plausible sources of decoherence caused by interaction with phonons and gates could be substantially suppressed in the structure as well. We also demonstrate how all necessary quantum logic operations, initialization, writing, and read-out could be carried out in the computer.

2010-07-19

377

Quantum computers can search rapidly by using almost any transformation

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

Grover, L K

1998-01-01

378

QCMPI: A parallel environment for quantum computing

QCMPI is a quantum computer (QC) simulation package written in Fortran 90 with parallel processing capabilities. It is an accessible research tool that permits rapid evaluation of quantum algorithms for a large number of qubits and for various "noise" scenarios. The prime motivation for developing QCMPI is to facilitate numerical examination of not only how QC algorithms work, but also to include noise, decoherence, and attenuation effects and to evaluate the efficacy of error correction schemes. The present work builds on an earlier Mathematica code QDENSITY, which is mainly a pedagogic tool. In that earlier work, although the density matrix formulation was featured, the description using state vectors was also provided. In QCMPI, the stress is on state vectors, in order to employ a large number of qubits. The parallel processing feature is implemented by using the Message-Passing Interface (MPI) protocol. A description of how to spread the wave function components over many processors is provided, along with how to efficiently describe the action of general one- and two-qubit operators on these state vectors. These operators include the standard Pauli, Hadamard, CNOT and CPHASE gates and also Quantum Fourier transformation. These operators make up the actions needed in QC. Codes for Grover's search and Shor's factoring algorithms are provided as examples. A major feature of this work is that concurrent versions of the algorithms can be evaluated with each version subject to alternate noise effects, which corresponds to the idea of solving a stochastic Schrödinger equation. The density matrix for the ensemble of such noise cases is constructed using parallel distribution methods to evaluate its eigenvalues and associated entropy. Potential applications of this powerful tool include studies of the stability and correction of QC processes using Hamiltonian based dynamics. Program summaryProgram title: QCMPI Catalogue identifier: AECS_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AECS_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 4866 No. of bytes in distributed program, including test data, etc.: 42 114 Distribution format: tar.gz Programming language: Fortran 90 and MPI Computer: Any system that supports Fortran 90 and MPI Operating system: developed and tested at the Pittsburgh Supercomputer Center, at the Barcelona Supercomputer (BSC/CNS) and on multi-processor Macs and PCs. For cases where distributed density matrix evaluation is invoked, the BLACS and SCALAPACK packages are needed. Has the code been vectorized or parallelized?: Yes Classification: 4.15 External routines: LAPACK, SCALAPACK, BLACS Nature of problem: Analysis of quantum computation algorithms and the effects of noise. Solution method: A Fortran 90/MPI package is provided that contains modular commands to create and analyze quantum circuits. Shor's factorization and Grover's search algorithms are explained in detail. Procedures for distributing state vector amplitudes over processors and for solving concurrent (multiverse) cases with noise effects are implemented. Density matrix and entropy evaluations are provided in both single and parallel versions. Running time: Test run takes less than 1 minute using 2 processors.

Tabakin, Frank; Juliá-Díaz, Bruno

2009-06-01

379

Computational quantum magnetism: Role of noncollinear magnetism

Energy Technology Data Exchange (ETDEWEB)

We are witnessing today a golden age of innovation with novel magnetic materials and with discoveries important for both basic science and device applications. Computation and simulation have played a key role in the dramatic advances of the past and those we are witnessing today. A goal-driving computational science-simulations of every-increasing complexity of more and more realistic models has been brought into greater focus with greater computing power to run sophisticated and powerful software codes like our highly precise full-potential linearized augmented plane wave (FLAPW) method. Indeed, significant progress has been achieved from advanced first-principles FLAPW calculations for the predictions of surface/interface magnetism. One recently resolved challenging issue is the role of noncollinear magnetism (NCM) that arises not only through the SOC, but also from the breaking of symmetry at surfaces and interfaces. For this, we will further review some specific advances we are witnessing today, including complex magnetic phenomena from noncollinear magnetism with no shape approximation for the magnetization (perpendicular MCA in transition-metal overlayers and superlattices; unidirectional anisotropy and exchange bias in FM and AFM bilayers; constricted domain walls important in quantum spin interfaces; and curling magnetic nano-scale dots as new candidates for non-volatile memory applications) and most recently providing new predictions and understanding of magnetism in novel materials such as magnetic semiconductors and multi-ferroic systems.

Freeman, Arthur J. [Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208 (United States)], E-mail: ajf328@northwestern.edu; Nakamura, Kohji [Department of Physics Engineering, Mie University, Tsu, Mie 514-8507 (Japan)

2009-04-15

380

A quantum computer based on recombination processes in microelectronic devices

Energy Technology Data Exchange (ETDEWEB)

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

Theodoropoulos, K [Computer Engineering and Informatics Department, University of Patras, Patras (Greece); Ntalaperas, D [Computer Engineering and Informatics Department, University of Patras, Patras (Greece); Research Academic Computer Technology Institute, Riga Feraiou 61, 26110, Patras (Greece); Petras, I [Computer Engineering and Informatics Department, University of Patras, Patras (Greece); Konofaos, N [Computer Engineering and Informatics Department, University of Patras, Patras (Greece)

2005-01-01

381

Twisted graph states for ancilla-driven quantum computation

We introduce a new paradigm for quantum computing called Ancilla-Driven Quantum Computation (ADQC) which combines aspects of the quantum circuit and the one-way model to overcome challenging issues in building large-scale quantum computers. Instead of directly manipulating each qubit to perform universal quantum logic gates or measurements, ADQC uses a fixed two-qubit interaction to couple the memory register of a quantum computer to an ancilla qubit. By measuring the ancilla, the measurement-induced back-action on the system performs the desired logical operations. The underlying mathematical model is based on a new entanglement resource called twisted graph states generated from non-commuting operators. The ADQC model is formalised in an algebraic framework similar to the Measurement Calculus. Furthermore, we present the notion of causal flow for twisted graph states, based on the stabiliser formalism, to characterise the determinism. Finally we demonstrate compositional embedding between ADQC and both the ...

Kashefi, Elham; Browne, Daniel E; Anders, Janet; Andersson, Erika

2009-01-01

382

Practical experimental certification of computational quantum gates via twirling

Due to the technical difficulty of building large quantum computers, it is important to be able to estimate how faithful a given implementation is to an ideal quantum computer. The common approach of completely characterizing the computation process via quantum process tomography requires an exponential amount of resources, and thus is not practical even for relatively small devices. We solve this problem by demonstrating that twirling experiments previously used to characterize the average fidelity of quantum memories efficiently can be easily adapted to estimate the average fidelity of the experimental implementation of important quantum computation processes, such as unitaries in the Clifford group, in a practical and efficient manner with applicability in current quantum devices. Using this procedure, we demonstrate state-of-the-art coherent control of an ensemble of magnetic moments of nuclear spins in a single crystal solid by implementing the encoding operation for a 3 qubit code with only a 1% degrada...

Moussa, Osama; Ryan, Colm A; Laflamme, Raymond

2011-01-01

383

Simulating quantum systems on classical computers with matrix product states

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this thesis, the numerical simulation of strongly-interacting many-body quantum-mechanical systems using matrix product states (MPS) is considered. Compared to classical systems, quantum many-body systems possess an exponentially enlarged number of degrees of freedom, significantly complicating a simulation on a classical computer. Matrix-Product-States are a novel representation of arbitrary quantum many-body states. Using quantum information theory, it is possible to show that Matrix-Pro...

Kleine, Adrian

2010-01-01

384

Magnetic qubits as hardware for quantum computers

We propose two potential realisations for quantum bits based on nanometre scale magnetic particles of large spin S and high anisotropy molecular clusters. In case (1) the bit-value basis states |0> and |1> are the ground and first excited spin states Sz = S and S-1, separated by an energy gap given by the ferromagnetic resonance (FMR) frequency. In case (2), when there is significant tunnelling through the anisotropy barrier, the qubit states correspond to the symmetric, |0>, and antisymmetric, |1>, combinations of the two-fold degenerate ground state Sz = +- S. In each case the temperature of operation must be low compared to the energy gap, \\Delta, between the states |0> and |1>. The gap \\Delta in case (2) can be controlled with an external magnetic field perpendicular to the easy axis of the molecular cluster. The states of different molecular clusters and magnetic particles may be entangled by connecting them by superconducting lines with Josephson switches, leading to the potential for quantum computing ...

Tejada, J; Barco, E; Hernández, J M; Spiller, T P

2000-01-01

385

The Universe as a Quantum Computer

This article presents a sequential growth model for the universe that acts like a quantum computer. The basic constituents of the model are a special type of causal set (causet) called a $c$-causet. A $c$-causet is defined to be a causet that is independent of its labeling. We characterize $c$-causets as those causets that form a multipartite graph or equivalently those causets whose elements are comparable whenever their heights are different. We show that a $c$-causet has precisely two $c$-causet offspring. It follows that there are $2^n$ $c$-causets of cardinality $n+1$. This enables us to classify $c$-causets of cardinality $n+1$ in terms of $n$-bits. We then quantize the model by introducing a quantum sequential growth process. This is accomplished by replacing the $n$-bits by $n$-qubits and defining transition amplitudes for the growth transitions. We mainly consider two types of processes called stationary and completely stationary. We show that for stationary processes, the probability operators are t...

Gudder, Stan

2014-01-01

386

Spin quantum computation in silicon nanostructures

Proposed silicon-based quantum-computer architectures have attracted attention because of their promise for scalability and their potential for synergetically utilizing the available resources associated with the existing Si technology infrastructure. Electronic and nuclear spins of shallow donors (e.g. phosphorus) in Si are ideal candidates for qubits in such proposals because of their long spin coherence times due to their limited interactions with their environments. For these spin qubits, shallow donor exchange gates are frequently invoked to perform two-qubit operations. We discuss in this review a particularly important spin decoherence channel, and bandstructure effects on the exchange gate control. Specifically, we review our work on donor electron spin spectral diffusion due to background nuclear spin flip-flops, and how isotopic purification of silicon can significantly enhance the electron spin dephasing time. We then review our calculation of donor electron exchange coupling in the presence of deg...

Sarma, S D; Hu, X; Koiller, B; Sousa, Rogerio de; Hu, Xuedong; Koiller, Belita

2004-01-01

387

Quantum computing with magnetically interacting atoms

We propose a scalable quantum-computing architecture based on cold atoms confined to sites of a tight optical lattice. The lattice is placed in a non-uniform magnetic field and the resulting Zeeman sublevels define qubit states. Microwave pulses tuned to space-dependent resonant frequencies are used for individual addressing. The atoms interact via magnetic-dipole interactions allowing implementation of a universal controlled-NOT gate. The resulting gate operation times for alkalis are on the order of milliseconds, much faster then the anticipated decoherence times. Single qubit operations take about 10 microseconds. Analysis of motional decoherence due to NOT operations is given. We also comment on the improved feasibility of the proposed architecture with complex open-shell atoms, such as Cr, Eu and metas

Derevianko, A; Derevianko, Andrei; Cannon, Caleb C.

2004-01-01

388

Number Partitioning via Quantum Adiabatic Computation

We study both analytically and numerically the complexity of the adiabatic quantum evolution algorithm applied to random instances of combinatorial optimization problems. We use as an example the NP-complete set partition problem and obtain an asymptotic expression for the minimal gap separating the ground and exited states of a system during the execution of the algorithm. We show that for computationally hard problem instances the size of the minimal gap scales exponentially with the problem size. This result is in qualitative agreement with the direct numerical simulation of the algorithm for small instances of the set partition problem. We describe the statistical properties of the optimization problem that are responsible for the exponential behavior of the algorithm.

Smelyanskiy, Vadim N.; Toussaint, Udo; Clancy, Daniel (Technical Monitor)

2002-01-01

389

The General Quantum Interference Principle and the Duality Computer

In this article, we propose a general principle of quantum interference for quantum system, and based on this general principle of quantum interference we propose a new type of computing machine, the duality computer, that outperforms in principle both classical computer and the quantum computer. This duality computer is superior to the quantum computer, which can be viewed as the special case of the duality computer with only one wave path. Salient features of this duality computer are : 1) it can find a marked item from an unsorted database using only a single query. This contrasts not only to the classical computer which solves the same problem with O(N) number of queries, but also to the quantum computer which requires $O(\\sqrt{N})$ number of queries; 2) Using duality computer, the famous question in computer science whether nondeterministic polynomial complete (NPC) problem is equivalent to polynomial problem, i.e. NPC=P, is solved completely: all NP-complete problems have polynomial algorithms in the du...

Long, G L

2005-01-01

390

Universal quantum computation on the power of quantum non-demolition measurements

International Nuclear Information System (INIS)

In this Letter we investigate the linear and nonlinear models of optical quantum computation and discuss their scalability and efficiency. We show how there are significantly different scaling properties in single photon computation when weak cross-Kerr nonlinearities are allowed to supplement the usual linear optical set. In particular, we show how quantum non-demolition measurements are an efficient resource for universal quantum computation

2005-09-05

391

Universal quantum computation on the power of quantum non-demolition measurements

In this paper we investigate the linear and nonlinear models of optical quantum computation and discuss their scalability and efficiency. We show how there are significantly different scaling properties in single photon computation when weak cross-Kerr nonlinearities are allowed to supplement the usual linear optical set. In particular we show how quantum non-demolition measurements are an efficient resource for universal quantum computation.

Nemoto, K; Nemoto, Kae

2005-01-01

392

Quantum computing based on space states without charge transfer

An implementation of a quantum computer based on space states in double quantum dots is discussed. There is no charge transfer in qubits during calculation, therefore, uncontrollable entan-glement between them due to long-range Coulomb interaction is suppressed. Other plausible sources of decoherence caused by interaction with phonons and gates could be substantially suppressed in the structure too. We also demonstrate how all necessary quantum logic operations, initialization, writing, and read-out could be carried out in the computer.

Filippov, S; Gorelik, L

2009-01-01

393

Quantum computing a view from the enemy camp

Quantum computing relies on processing information within a quantum system with many continuous degrees of freedom. The practical implementation of this idea requires complete control over all of the 2^n independent amplitudes of a many-particle wavefunction, where n>1000. The principles of quantum computing are discussed from the practical point of view with the conclusion that no working device will be built in the forseeable future.

Dyakonov, M I

2001-01-01

394

A Review of Freely Available Quantum Computer Simulation Software

Digital Repository Infrastructure Vision for European Research (DRIVER)

A study has been made of a few different freely available Quantum Computer simulators.All the simulators tested are available online on their respective websites. A number oftests have been performed to compare the different simulators against each other. Someuntested simulators of various programming languages are included to show the diversityof the quantum computer simulator applications. The conclusion of the review is that LibQuantum is the best of the simulatorstested because of ease of...

Brandhorst-satzkorn, Johan

2012-01-01

395

A Review of Freely Available Quantum Computer Simulation Software

Digital Repository Infrastructure Vision for European Research (DRIVER)

A study has been made of a few different freely available Quantum Computer simulators. All the simulators tested are available online on their respective websites. A number of tests have been performed to compare the different simulators against each other. Some untested simulators of various programming languages are included to show the diversity of the quantum computer simulator applications. The conclusion of the review is that LibQuantum is the best of the simulators tested because of ea...

Brandhorst-satzkorn, Johan

2012-01-01

396

I argue that the program on operational foundations of Quantum Mechanics should have top-priority, and that the Lucien Hardy's program on Quantum Gravity should be paralleled by an analogous program on Quantum Field Theory (QFT), which needs to be reformulated, notwithstanding its experimental success. In this paper, after reviewing recently proposed operational "principles of the quantumness", I address the problem on whether Quantum Mechanics and Special Relativity are unrelated theories, or instead, if the one implies the other. I show how Special Relativity can be indeed derived from Quantum Mechanics, within the computational paradigm "the universe is a huge quantum computer", reformulating QFT as a Quantum-Circuit Field Theory (QCFT). In QCFT Special Relativity emerges from the fabric of the computational network, which also naturally embeds gauge invariance, and even the quantization rule and the Plank constant, which resort to being properties of the underlying causal tapestry of space-time. In this w...

D'Ariano, Giacomo Mauro

2010-01-01

397

Computation in Sofic Quantum Dynamical Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

We analyze how measured quantum dynamical systems store and process information, introducing sofic quantum dynamical systems. Using recently introduced information-theoretic measures for quantum processes, we quantify their information storage and processing in terms of entropy rate and excess entropy, giving closed-form expressions where possible. To illustrate the impact of measurement on information storage in quantum processes, we analyze two spin-1 sofic quantum systems...

Wiesner, Karoline; Crutchfield, James P.

2007-01-01

398

Computation in Sofic Quantum Dynamical Systems

We analyze how measured quantum dynamical systems store and process information, introducing sofic quantum dynamical systems. Using recently introduced information-theoretic measures for quantum processes, we quantify their information storage and processing in terms of entropy rate and excess entropy, giving closed-form expressions where possible. To illustrate the impact of measurement on information storage in quantum processes, we analyze two spin-1 sofic quantum systems that differ only in how they are measured.

Wiesner, Karoline

2007-01-01

399

Parallel photonic quantum computation assisted by quantum dots in one-side optical microcavities.

Universal quantum logic gates are important elements for a quantum computer. In contrast to previous constructions on one degree of freedom (DOF) of quantum systems, we investigate the possibility of parallel quantum computations dependent on two DOFs of photon systems. We construct deterministic hyper-controlled-not (hyper-CNOT) gates operating on the spatial-mode and the polarization DOFs of two-photon or one-photon systems by exploring the giant optical circular birefringence induced by quantum-dot spins in one-sided optical microcavities. These hyper-CNOT gates show that the quantum states of two DOFs can be viewed as independent qubits without requiring auxiliary DOFs in theory. This result can reduce the quantum resources by half for quantum applications with large qubit systems, such as the quantum Shor algorithm. PMID:25030424

Luo, Ming-Xing; Wang, Xiaojun

2014-01-01

400

Quantum computation in continuous time using dynamic invariants

International Nuclear Information System (INIS)

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

2011-09-05

401

Elementary Particles as Gates for Universal Quantum Computation

It is shown that there exists a mapping between the fermions of the Standard Model (SM) represented as braids in the Bilson-Thompson model, and a set of gates which can perform Universal Quantum Computation (UQC). This leads us to conjecture that the "Computational Universe Hypothesis" (CUH) can be given a concrete implementation in a new physical framework where elementary particles and the gauge bosons (which intermediate interactions between fermions) are interpreted as the components of a quantum computational network, with the particles serving as quantum computational gates and the gauge fields as the information carrying entities.

Vaid, Deepak

2013-01-01

402

Experimental magic state distillation for fault-tolerant quantum computing

Any physical quantum device for quantum information processing is subject to errors in implementation. In order to be reliable and efficient, quantum computers will need error correcting or error avoiding methods. Fault-tolerance achieved through quantum error correction will be an integral part of quantum computers. Of the many methods that have been discovered to implement it, a highly successful approach has been to use transversal gates and specific initial states. A critical element for its implementation is the availability of high-fidelity initial states such as |0> and the Magic State. Here we report an experiment, performed in a nuclear magnetic resonance (NMR) quantum processor, showing sufficient quantum control to improve the fidelity of imperfect initial magic states by distilling five of them into one with higher fidelity.

Souza, Alexandre M; Ryan, Colm A; Laflamme, Raymond; 10.1038/ncomms1166

2011-01-01

403

The 2004 Latsis Symposium: Quantum optics for Communication and Computing

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

2004-01-01

404

The 2004 Latsis Symposium: Quantum optics for Communication and Computing

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

2004-01-01

405

The 2004 Latsis Symposium: Quantum optics for Communication and Computing

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

2004-01-01

406

Quantum Monte Carlo Endstation for Petascale Computing

Energy Technology Data Exchange (ETDEWEB)

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

Lubos Mitas

2011-01-26

407

Quantum Computing Using an Open System and Projected Subspace

Using the subdynamical kinetic equation for an open quantum system, a formulation is presented for performing decoherence-free (DF) quantum computing in Rigged Liouville Space (RLS). Three types of interactions were considered, and in each case, stationary and evolutionary states were evaluated for DF behavior in both the total space and the projected subspace. Projected subspaces were found using the subdynamics kinetic equation. It was shown that although the total space may be decoherent, the subspace can be DF. In the projected subspace, the evolution of the density operator may be time asymmetric. Hence, a formulation for performing quantum computing in RLS or rigged Hilbert space (RHS) was proposed, and a quantum Controlled-Not Logical gate with corresponding operations in RLS (RHS) was constructed. A generalized quantum Turing machine in RHS was also discussed. Key Words: Quantum Computing, Subdynamics, Rigged Liouvile Space, Decoherence, Open System PACS: 05.30.-d+85.30+82.20.Db+84.35.+i

Qiao, B; Zhen, X H; Qiao, Bi; Ruda, Harry. E.

2001-01-01

408

Selected topics in computational quantum field theory

International Nuclear Information System (INIS)

The main mathematical structures of the quantum field theory on the lattice; fractal lattices; the problem of the continual limit and the method of finite element for a solution of the operator equations of the quantum theory are considered

1985-01-01

409

High-fidelity quantum memory using nitrogen-vacancy center ensemble for hybrid quantum computation

International Nuclear Information System (INIS)

We study a hybrid quantum computing system using a nitrogen-vacancy center ensemble (NVE) as quantum memory, a current-biased Josephson junction (CBJJ) superconducting qubit fabricated in a transmission line resonator (TLR) as the quantum computing processor, and the microwave photons in TLR as the quantum data bus. The storage process is seriously treated by considering all kinds of decoherence mechanisms. Such a hybrid quantum device can also be used to create multiqubit W states of NVEs through a common CBJJ. The experimental feasibility is achieved using currently available technology.

2011-07-01

410

The Signals and Systems Approach to Quantum Computation

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this note we point out the fact that the proper conceptual setting of quantum computation is the theory of Linear Time Invariant systems. To convince readers of the utility of the approach, we introduce a new model of computation based on the orthogonal group. This makes the link to traditional electronics engineering clear. We conjecture that the speed up achieved in quantum computation is at the cost of increased circuit complexity.

Gadiyar, H. Gopalkrishna; Maini, K. M. Sangeeta; Padma, R.; Sharatchandra, H. S.

2003-01-01

411

From transistor to trapped-ion computers for quantum chemistry

Digital Repository Infrastructure Vision for European Research (DRIVER)

Over the last few decades, quantum chemistry has progressed through the development of computational methods based on modern digital computers. However, these methods can hardly fulfill the exponentially-growing resource requirements when applied to large quantum systems. As pointed out by Feynman, this restriction is intrinsic to all computational models based on classical physics. Recently, the rapid advancement of trapped-ion technologies has opened new possibilities for ...

Yung, M. -h; Casanova, J.; Mezzacapo, A.; Mcclean, J.; Lamata, L.; Aspuru-guzik, A.; Solano, E.

2013-01-01

412

A Magnetic Resonance Realization of Decoherence-Free Quantum Computation

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report the realization, using nuclear magnetic resonance techniques, of the first quantum computer that reliably executes an algorithm in the presence of strong decoherence. The computer is based on a quantum error avoidance code that protects against a class of multiple-qubit errors. The code stores two decoherence-free logical qubits in four noisy physical qubits. The computer successfully executes Grover's search algorithm in the presence of arbitrarily strong engineer...

Ollerenshaw, Jason E.; Lidar, Daniel A.; Kay, Lewis E.

2003-01-01

413

Holographic description of quantum black hole on a computer

The discovery of the fact that black holes radiate particles and eventually evaporate led Hawking to pose the well-known information loss paradox. This paradox caused a long and serious debate since it claims that the fundamental laws of quantum mechanics may be violated. A possible cure appeared recently from superstring theory, a consistent theory of quantum gravity: if the holographic description of a quantum black hole based on the gauge/gravity duality is correct, the information is not lost and quantum mechanics remains valid. Here we test this gauge/gravity duality on a computer at the level of quantum gravity for the first time. The black hole mass obtained by Monte Carlo simulation of the dual gauge theory reproduces precisely the quantum gravity effects in an evaporating black hole. This result opens up totally new perspectives towards quantum gravity since one can simulate quantum black holes through dual gauge theories.

Hanada, Masanori; Ishiki, Goro; Nishimura, Jun

2013-01-01

414

Universal Quantum Computation through Control of Spin-Orbit Coupling

We propose a method for quantum computation which uses control of spin-orbit coupling in a linear array of single electron quantum dots. Quantum gates are carried out by pulsing the exchange interaction between neighboring electron spins, including the anisotropic corrections due to spin-orbit coupling. Control over these corrections, even if limited, is sufficient for universal quantum computation over qubits encoded into pairs of electron spins. The number of voltage pulses required to carry out either single qubit rotations or controlled-Not gates scales as the inverse of a dimensionless measure of the degree of control of spin-orbit coupling.

Stepanenko, D

2004-01-01

415

On Computational Power of Quantum Read-Once Branching Programs

Directory of Open Access Journals (Sweden)

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

Farid Ablayev

2011-03-01

416

On Computational Power of Quantum Read-Once Branching Programs

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

Ablayev, Farid; 10.4204/EPTCS.52.1

2011-01-01

417

Pseudo-spin quantum computation in semiconductor nanostructures

Energy Technology Data Exchange (ETDEWEB)

We review the theoretical aspects of pseudo-spin quantum computation using vertically coupled quantum dots in the quantum Hall regime. We discuss the robustness and addressability of these collective, charge-based qubits. The low-energy Hilbert space of a coupled set of qubits yields an effective quantum Ising model tunable through external gates. An experimental prediction of an even-odd effect in the Coulomb-blockade spectra of the coupled quantum dot system allows for a probe of the parameter regime necessary for realization of these qubits.

Scarola, V W; Park, K; Sarma, S Das [Condensed Matter Theory Center, Department of Physics, University of Maryland, College Park, MD 20742 (United States)

2005-08-01

418

Pseudo-spin quantum computation in semiconductor nanostructures

International Nuclear Information System (INIS)

We review the theoretical aspects of pseudo-spin quantum computation using vertically coupled quantum dots in the quantum Hall regime. We discuss the robustness and addressability of these collective, charge-based qubits. The low-energy Hilbert space of a coupled set of qubits yields an effective quantum Ising model tunable through external gates. An experimental prediction of an even-odd effect in the Coulomb-blockade spectra of the coupled quantum dot system allows for a probe of the parameter regime necessary for realization of these qubits

2005-08-01

419

Quantum computation in a quantum-dot-Majorana-fermion hybrid system

We propose a scheme to implement universal quantum computation in a quantum-dot-Majorana-fermion hybrid system. Quantum information is encoded on pairs of Majorana fermions, which live on the the interface between topologically trivial and nontrivial sections of a quantum nanowire deposited on an s-wave superconductor. Universal single-qubit gates on topological qubit can be achieved. A measurement-based two-qubit Controlled-Not gate is produced with the help of parity measurements assisted by the quantum-dot and followed by prescribed single-qubit gates. The parity measurement, on the quantum-dot and a topological qubit, is achieved by the Aharonov- Casher effect.

Xue, Zheng-Yuan

2012-01-01

420

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

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

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

2008-01-01

421

Architectural design for a topological cluster state quantum computer

International Nuclear Information System (INIS)

The development of a large scale quantum computer is a highly sought after goal of fundamental research and consequently a highly non-trivial problem. Scalability in quantum information processing is not just a problem of qubit manufacturing and control but it crucially depends on the ability to adapt advanced techniques in quantum information theory, such as error correction, to the experimental restrictions of assembling qubit arrays into the millions. In this paper, we introduce a feasible architectural design for large scale quantum computation in optical systems. We combine the recent developments in topological cluster state computation with the photonic module, a simple chip-based device that can be used as a fundamental building block for a large-scale computer. The integration of the topological cluster model with this comparatively simple operational element addresses many significant issues in scalable computing and leads to a promising modular architecture with complete integration of active error correction, exhibiting high fault-tolerant thresholds.

2009-08-01

422

Architectural design for a topological cluster state quantum computer

Energy Technology Data Exchange (ETDEWEB)

The development of a large scale quantum computer is a highly sought after goal of fundamental research and consequently a highly non-trivial problem. Scalability in quantum information processing is not just a problem of qubit manufacturing and control but it crucially depends on the ability to adapt advanced techniques in quantum information theory, such as error correction, to the experimental restrictions of assembling qubit arrays into the millions. In this paper, we introduce a feasible architectural design for large scale quantum computation in optical systems. We combine the recent developments in topological cluster state computation with the photonic module, a simple chip-based device that can be used as a fundamental building block for a large-scale computer. The integration of the topological cluster model with this comparatively simple operational element addresses many significant issues in scalable computing and leads to a promising modular architecture with complete integration of active error correction, exhibiting high fault-tolerant thresholds.

Devitt, Simon J; Munro, William J; Nemoto, Kae [National Institute for Informatics, 2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo 101-8430 (Japan); Fowler, Austin G [Institute for Quantum Computing, University of Waterloo, Waterloo (Canada); Stephens, Ashley M; Greentree, Andrew D; Hollenberg, Lloyd C L [Centre for Quantum Computer Technology, School of Physics, University of Melbourne, Victoria 3010 (Australia)], E-mail: devitt@nii.ac.jp

2009-08-15

423

Performing measurement based quantum computation on ground states

One of the most exciting developments in quantum computing in recent years has been the realisation that there exist states of quantum many-body systems that can serve as a universal resource for quantum computing, where computation proceeds solely through single-qubit measurements. Although currently only a few isolated examples of such universal resource states are known, we discuss the possibility that there exist models of interacting spin systems in which an ordered phase is characterized by the ability to perform measurement-based quantum computation (MBQC). To identify such phases, we propose to use nonlocal correlation functions that quantify the fidelity of quantum gates performed between well separated qubits. The quantum computing phase is then characterized by set of order parameters corresponding to a universal set of quantum gates. We investigate a simple spin-lattice system based on the cluster-state model for MBQC by using a series of dualities with better studied models. We demonstrate that the model possesses a zero temperature phase transition between a disordered phase and an ordered ``cluster phase'' in which it is possible to perform a large class of one and two qubit quantum gates.

Doherty, Andrew; Bartlett, Stephen

2009-03-01

424

Blind quantum computation for Alice who does only measurements

Blind quantum computation is a secure quantum computing protocol which enables Alice who does not have sufficient quantum technology to ask Bob to perform quantum computation on Bob's fully-fledged quantum computer in such a way that Bob cannot learn anything about Alice's input, output, and algorithm. In previous proposals, Alice needs to have a device which generates quantum states, such as single-photon states. Here we show that Alice who does only measurements, such as the polarization measurements with a threshold detector, can perform the blind quantum computation. In several experimental setups, such as optical systems, the measurement of a state is much easier than the generation of a single-qubit state. Therefore our protocols can ease Alice's burden. Furthermore, the security of our protocols is device independent in the sense that Alice does not need to trust her measurement device. Finally, the security of our protocols is based on the no-signaling principle, which is more fundamental than quantum...

Morimae, Tomoyuki

2012-01-01

425

Integrated photonic qubit quantum computing on a superconducting chip

International Nuclear Information System (INIS)

We study a quantum computing system using microwave photons in transmission line resonators on a superconducting chip as qubits. We show that linear optics and other controls necessary for quantum computing can be implemented by coupling to Josephson devices on the same chip. By taking advantage of the strong nonlinearities in Josephson junctions, photonic qubit interactions can be realized. We analyze the gate error rate to demonstrate that our scheme is realistic even for Josephson devices with limited decoherence times. As a conceptually innovative solution based on existing technologies, our scheme provides an integrated and scalable approach to the next key milestone for photonic qubit quantum computing.

2010-06-01

426

Cavity-assisted quantum computing in a silicon nanostructure

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

Tang, Bao; Qin, Hao; Zhang, Rong; Liu, Jin-Ming; Xue, Peng

2014-05-01

427

Integrated photonic qubit quantum computing on a superconducting chip

Energy Technology Data Exchange (ETDEWEB)

We study a quantum computing system using microwave photons in transmission line resonators on a superconducting chip as qubits. We show that linear optics and other controls necessary for quantum computing can be implemented by coupling to Josephson devices on the same chip. By taking advantage of the strong nonlinearities in Josephson junctions, photonic qubit interactions can be realized. We analyze the gate error rate to demonstrate that our scheme is realistic even for Josephson devices with limited decoherence times. As a conceptually innovative solution based on existing technologies, our scheme provides an integrated and scalable approach to the next key milestone for photonic qubit quantum computing.

Du Lianghui; Hu Yong; Zhou Zhengwei; Guo Guangcan; Zhou Xingxiang, E-mail: xizhou@ustc.edu.c [Key Laboratory of Quantum Information, University of Science and Technology of China, Chinese Academy of Sciences, Hefei 230026 (China)

2010-06-15

428

Secrecy, Computational Loads and Rates in Practical Quantum Cryptography

Digital Repository Infrastructure Vision for European Research (DRIVER)

A number of questions associated with practical implementations of quantum cryptography systems having to do with unconditional secrecy, computational loads and effective secrecy rates in the presence of perfect and imperfect sources are discussed. The different types of unconditional secrecy, and their relationship to general communications security, are discussed in the context of quantum cryptography. In order to actually carry out a quantum cryptography protocol it is ne...

Gilbert, G.; Hamrick, M.

2001-01-01

429

Modified Grover's algorithm for an expectation value quantum computer

Digital Repository Infrastructure Vision for European Research (DRIVER)

The translation of Grover's search algorithm from its standard version, designed for implementation on a single quantum system amenable to projective measurements, into one suitable for an ensemble of quantum computers, whose outputs are expectation values of observables, is described in detail. A filtering scheme, which effectively determines expectation values on a limited portion of the quantum state, is presented and used to locate a single item for searches involving mo...

Collins, David

2001-01-01

430

Topological Quantum Computing with Read-Rezayi States

Digital Repository Infrastructure Vision for European Research (DRIVER)

Read-Rezayi fractional quantum Hall states are among the prime candidates for realizing non-Abelian anyons which in principle can be used for topological quantum computation. We present a prescription for efficiently finding braids which can be used to carry out a universal set of quantum gates on encoded qubits based on anyons of the Read-Rezayi states with $k>2$, $k\

Hormozi, L.; Bonesteel, N. E.; Simon, S. H.

2009-01-01

431

Phonon-mediated entanglement for trapped ion quantum computing

International Nuclear Information System (INIS)

Trapped ions are a near ideal system to study quantum information processing due to the high degree of control over the ion's external confinement and internal degrees of freedom. We demonstrate the key steps necessary for trapped ion quantum computing and focus on phonon-mediated entangling gates. We highlight several key algorithms implemented over the last decade with these gates and give a detailed description of Grover's quantum database search implemented with two trapped ion qubits.

2010-03-01

432

Phonon-mediated entanglement for trapped ion quantum computing

Energy Technology Data Exchange (ETDEWEB)

Trapped ions are a near ideal system to study quantum information processing due to the high degree of control over the ion's external confinement and internal degrees of freedom. We demonstrate the key steps necessary for trapped ion quantum computing and focus on phonon-mediated entangling gates. We highlight several key algorithms implemented over the last decade with these gates and give a detailed description of Grover's quantum database search implemented with two trapped ion qubits.

Soderberg, K-A Brickman [Department of Physics, James Franck Institute, University of Chicago, Chicago, IL 60637 (United States); Monroe, C [Joint Quantum Institute, University of Maryland Department of Physics, and National Institute of Standards and Technology, College Park, MD 20742 (United States)], E-mail: brickman@uchicago.edu

2010-03-15

433

Exploiting Geometric Degrees of Freedom in Topological Quantum Computing

Digital Repository Infrastructure Vision for European Research (DRIVER)

In a topological quantum computer, braids of non-Abelian anyons in a (2+1)-dimensional space-time form quantum gates, whose fault tolerance relies on the topological, rather than geometric, properties of the braids. Here we propose to create and exploit redundant geometric degrees of freedom to improve the theoretical accuracy of topological single- and two-qubit quantum gates. We demonstrate the power of the idea using explicit constructions in the Fibonacci model. We compa...

Xu, Haitan; Wan, Xin

2008-01-01

434

How Quantum Computers Fail: Quantum Codes, Correlations in Physical Systems, and Noise Accumulation

The feasibility of computationally superior quantum computers is one of the most exciting and clear-cut scientific questions of our time. The question touches on fundamental issues regarding probability, physics, and computability, as well as on exciting problems in experimental physics, engineering, computer science, and mathematics. We propose three related directions towards a negative answer. The first is a conjecture about physical realizations of quantum codes, the second has to do with correlations in stochastic physical systems, and the third proposes a model for quantum evolutions when noise accumulates. The paper is dedicated to the memory of Itamar Pitowsky.

Kalai, Gil

2011-01-01

435

Brain as quantum-like computer

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present a contextualist statistical realistic model for quantum-like representations in physics, cognitive science and psychology. We apply this model to describe cognitive experiments to check quantum-like structures of mental processes. The crucial role is played by interference of probabilities for mental observables. Recently one of such experiments based on recognition of images was performed. This experiment confirmed our prediction on quantum-like behaviour of mind...

Khrennikov, Andrei

2002-01-01

436

Directory of Open Access Journals (Sweden)

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

Alexis De Vos

2011-06-01

437

Quantum computing, phase estimation and applications

In this thesis, attention is paid to small experimental testbed applications with respect to the quantum phase estimation algorithm, the core approach for finding energy eigenvalues. An iterative scheme for quantum phase estimation (IPEA) is derived from the Kitaev phase estimation, a study of robustness of the IPEA utilized as a few-qubit testbed application is performed, and an improved protocol for phase reference alignment is presented. Additionally, a short overview of quantum cryptography is given, with a particular focus on quantum steganography and authentication.

Dob?í?ek, Miroslav

2008-01-01

438

A Quantum Logic Array Microarchitecture: Scalable Quantum Data Movement and Computation

Recent experimental advances have demonstrated technologies capable of supporting scalable quantum computation. A critical next step is how to put those technologies together into a scalable, fault-tolerant system that is also feasible. We propose a Quantum Logic Array (QLA) microarchitecture that forms the foundation of such a system. The QLA focuses on the communication resources necessary to efficiently support fault-tolerant computations. We leverage the extensive groundwork in quantum error correction theory and provide analysis that shows that our system is both asymptotically and empirically fault tolerant. Specifically, we use the QLA to implement a hierarchical, array-based design and a logarithmic expense quantum-teleportation communication protocol. Our goal is to overcome the primary scalability challenges of reliability, communication, and quantum resource distribution that plague current proposals for large-scale quantum computing.

Metodi, T S; Cross, A W; Chong, F T; Chuang, I L; Metodi, Tzvetan S.; Thaker, Darshan D.; Cross, Andrew W.; Chong, Frederic T.; Chuang, Isaac L.

2005-01-01

439

Quantum Computing of Quantum Chaos in the Kicked Rotator Model

We investigate a quantum algorithm which simulates efficiently the quantum kicked rotator model, a system which displays rich physical properties, and enables to study problems of quantum chaos, atomic physics and localization of electrons in solids. The effects of errors in gate operations are tested on this algorithm in numerical simulations with up to 20 qubits. In this way various physical quantities are investigated. Some of them, such as second moment of probability distribution and tunneling transitions through invariant curves are shown to be particularly sensitive to errors. However, investigations of the fidelity and Wigner and Husimi distributions show that many physical quantities are robust in presence of imperfections. This implies that the algorithm can simulate the dynamics of quantum chaos in presence of a moderate amount of noise.

Levi, B; Shepelyansky, D L

2003-01-01

440

Quantum computing of quantum chaos in the kicked rotator model.

We investigate a quantum algorithm that simulates efficiently the quantum kicked rotator model, a system that displays rich physical properties and enables to study problems of quantum chaos, atomic physics, and localization of electrons in solids. The effects of errors in gate operations are tested on this algorithm in numerical simulations with up to 20 qubits. In this way various physical quantities are investigated. Some of them, such as second moment of probability distribution and tunneling transitions through invariant curves, are shown to be particularly sensitive to errors. However, investigations of the fidelity and the Wigner and Husimi distributions show that these physical quantities are robust in presence of imperfections. This implies that the algorithm can simulate the dynamics of quantum chaos in presence of a moderate amount of noise. PMID:12786473

Lévi, B; Georgeot, B; Shepelyansky, D L

2003-04-01