WorldWideScience
 
 
1

Quantum computing  

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

2

Quantum Computers  

CERN Multimedia

This research paper gives an overview of quantum computers - description of their operation, differences between quantum and silicon computers, major construction problems of a quantum computer and many other basic aspects. No special scientific knowledge is necessary for the reader.

Avaliani, A

2004-01-01

3

Quantum Computation  

UK PubMed Central (United Kingdom)

Historically, Turing machines have been the paradigm by which we defined computability and efficiency. This is based on Church's thesis that everything effectively computable can also be computed on a Turing machine. But since our world behaves quantum mechanically, it seems reasonable to also consider computing models that make use of quantum mechanical properties. First stated by Benioff [Ben82] and Feynman [Fey82], this idea was formalized by Deutsch [Deu85] when he introduced his quantum computer and, later on, quantum gate arrays. This paper gives an introduction to quantum computing and briefly looks at a few results in quantum computation, not the least of which is Shor's polynomial time factoring algorithm ([Sho94] and [Sho95]). 1 The Need for Quantum Mechanics Why introduce quantum mechanics in computation? The opening quote, if a little blunt, captures the essence of the answer. At the center of computer science are two questions: what problems are computable and how efficie...

Richard P. Feynman

4

Quantum computers and quantum computations  

Energy Technology Data Exchange (ETDEWEB)

This review outlines the principles of operation of quantum computers and their elements. The theory of ideal computers that do not interact with the environment and are immune to quantum decohering processes is presented. Decohering processes in quantum computers are investigated. The review considers methods for correcting quantum computing errors arising from the decoherence of the state of the quantum computer, as well as possible methods for the suppression of the decohering processes. A brief enumeration of proposed quantum computer realizations concludes the review. (reviews of topical problems)

Valiev, Kamil' A [Institute of Physics and Technology, Russian Academy of Sciences, Moscow (Russian Federation)

2005-01-31

5

Quantum Computation  

UK PubMed Central (United Kingdom)

Historically, Turing machines have been the paradigm bywhich we defined computability and efficiency. This is based on Church'sthesis that everything effectively computable can also be computed on aTuring machine. But since our world behaves quantum mechanically, itseems reasonable to also consider computing models that make use of quantummechanical properties. First stated by Benioff [Ben82] and Feynman[Fey82], this idea was formalized by Deutsch [Deu85] when he introducedhis quantum computer and, later on, quantum gate arrays. This paper givesan introduction to quantum computing and briefly looks at a few resultsin quantum computation, not the least of which is Shor's polynomial timefactoring algorithm ([Sho94] and [Sho95]).1 The Need for Quantum MechanicsWhy introduce quantum mechanics in computation? The opening quote, ifa little blunt, captures the essence of the answer. At the center of computerscience are two questions: what problems are computable and how efficie...

Richard P. Feynman

6

Quantum Computation  

UK PubMed Central (United Kingdom)

Historically, Turing machines have been the paradigm bywhich we defined computability and efficiency. This is based on Church'sthesis that everything effectively computable can also be computed on aTuring machine. But since our world behaves quantum mechanically, itseems reasonable to also consider computing models that make use of quantummechanical properties. First stated by Benioff [Ben82] and Feynman[Fey82], this idea was formalized by Deutsch [Deu85] when he introducedhis quantum computer and, later on, quantum gate arrays. This paper givesan introduction to quantum computing and briefly looks at a few resultsin quantum computation, not the least of which is Shor's polynomial timefactoring algorithm ([Sho94] and [Sho95]).1 The Need for Quantum MechanicsWhy introduce quantum mechanics in computation? The opening quote, ifa little blunt, captures the essence of the answer. At the center of computerscience are two questions: what problems are computable and ...

Richard P. Feynman

7

Quantum Computing  

Science.gov (United States)

Quantum mechanics plays a crucial role in many day-to-day products, and has been successfully used to explain a wide variety of observations in Physics. While some quantum effects such as tunneling limit the degree to which modern CMOS devices can be scaled to ever reducing dimensions, others may potentially be exploited to build an entirely new computing architecture: The quantum computer. In this talk I will review several basic concepts of a quantum computer. Why quantum computing and how do we do it? What is the status of several (but not all) approaches towards building a quantum computer, including IBM's approach using superconducting qubits? And what will it take to build a functional machine? The promise is that a quantum computer could solve certain interesting computational problems such as factoring using exponentially fewer computational steps than classical systems. Although the most sophisticated modern quantum computing experiments to date do not outperform simple classical computations, it is increasingly becoming clear that small scale demonstrations with as many as 100 qubits are beginning to be within reach over the next several years. Such a demonstration would undoubtedly be a thrilling feat, and usher in a new era of controllably testing quantum mechanics or quantum computing aspects. At the minimum, future demonstrations will shed much light on what lies ahead.

Steffen, Matthias

2013-03-01

8

Quantum computation  

Energy Technology Data Exchange (ETDEWEB)

As computers become ever more complex, they inevitably become smaller. This leads to a need for components which are fabricated and operate on increasingly smaller size scales. Quantum theory is already taken into account in microelectronics design. This article explores how quantum theory will need to be incorporated into computers in future in order to give them their components functionality. Computation tasks which depend on quantum effects will become possible. Physicists may have to reconsider their perspective on computation in the light of understanding developed in connection with universal quantum computers. (UK).

Deutsch, D.

1992-06-01

9

Quantum computing  

Energy Technology Data Exchange (ETDEWEB)

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

Steane, Andrew [Department of Atomic and Laser Physics, University of Oxford, Clarendon Laboratory, Oxford (United Kingdom)

1998-02-01

10

Quantum computing  

International Nuclear Information System (INIS)

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

1998-01-01

11

Quantum computers.  

Science.gov (United States)

Over the past 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 unique quantum properties? Today it is understood that the answer is yes, and many research groups around the world are working towards the highly ambitious technological goal of building a quantum computer, which would dramatically improve computational power for particular tasks. A number of physical systems, spanning much of modern physics, are being developed for quantum computation. However, it remains unclear which technology, if any, will ultimately prove successful. Here we describe the latest developments for each of the leading approaches and explain the major challenges for the future. PMID:20203602

Ladd, T D; Jelezko, F; Laflamme, R; Nakamura, Y; Monroe, C; O'Brien, J L

2010-03-01

12

Quantum computers.  

UK PubMed Central (United Kingdom)

Over the past 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 unique quantum properties? Today it is understood that the answer is yes, and many research groups around the world are working towards the highly ambitious technological goal of building a quantum computer, which would dramatically improve computational power for particular tasks. A number of physical systems, spanning much of modern physics, are being developed for quantum computation. However, it remains unclear which technology, if any, will ultimately prove successful. Here we describe the latest developments for each of the leading approaches and explain the major challenges for the future.

Ladd TD; Jelezko F; Laflamme R; Nakamura Y; Monroe C; O'Brien JL

2010-03-01

13

Quantum Computing for Computer Architects  

CERN Document Server

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

Metodi, Tzvetan

2011-01-01

14

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

15

Quantum Computing  

CERN Document Server

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

16

Integrable Quantum Computation  

CERN Multimedia

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

Zhang, Yong

2011-01-01

17

Quantum Robots and Quantum Computers  

CERN Multimedia

In this paper Quantum Turing Machines, each modelled as a multistate head moving on and interacting with a 1 dimensional lattice of qubits, are reinterpreted and expanded to be models of a quantum robot interacting with an environment. The 1-D qubit lattice of qubits is the environment. The quantum robot is the head after it is expanded to contain an on board quantum Turing machine constructed from another head and a finite closed (e.g. circular) qubit lattice, and memory, output, and control systems. The quantum robot plus environment evolves by alternate on board computations followed by actions that are based on the computations.

Benioff, P

1997-01-01

18

Quantum information. Teleporation - cryptography - quantum computer  

International Nuclear Information System (INIS)

[en] 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

19

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)

2007-01-01

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

Quantum analogue computing.  

Science.gov (United States)

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 the quantum simulation of quantum systems. While most quantum computation is an extension of classical digital computation, quantum simulation differs fundamentally in how the data are encoded in the quantum computer. To perform a quantum simulation, the Hilbert space of the system to be simulated is mapped directly onto the Hilbert space of the (logical) qubits in the quantum computer. This type of direct correspondence is how data are encoded in a classical analogue computer. There is no binary encoding, and increasing precision becomes exponentially costly: an extra bit of precision doubles the size of the computer. This has important consequences for both the precision and error-correction requirements of quantum simulation, and significant open questions remain about its practicality. It also means that the quantum version of analogue computers, continuous-variable quantum computers, becomes an equally efficient architecture for quantum simulation. Lessons from past use of classical analogue computers can help us to build better quantum simulators in future. PMID:20603371

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

2010-08-13

22

Quantum analogue computing.  

UK PubMed Central (United Kingdom)

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 the quantum simulation of quantum systems. While most quantum computation is an extension of classical digital computation, quantum simulation differs fundamentally in how the data are encoded in the quantum computer. To perform a quantum simulation, the Hilbert space of the system to be simulated is mapped directly onto the Hilbert space of the (logical) qubits in the quantum computer. This type of direct correspondence is how data are encoded in a classical analogue computer. There is no binary encoding, and increasing precision becomes exponentially costly: an extra bit of precision doubles the size of the computer. This has important consequences for both the precision and error-correction requirements of quantum simulation, and significant open questions remain about its practicality. It also means that the quantum version of analogue computers, continuous-variable quantum computers, becomes an equally efficient architecture for quantum simulation. Lessons from past use of classical analogue computers can help us to build better quantum simulators in future.

Kendon VM; Nemoto K; Munro WJ

2010-08-01

23

Quantum Computation via Paraconsistent Computation  

CERN Multimedia

We present an original model of paraconsistent Turing machines (PTMs), a generalization of the classical Turing machines model of computation using a paraconsistent logic. Next, we briefl y describe the standard models of quantum computation: quantum Turing machines and quantum circuits, and revise quantum algorithms to solve the so-called Deutsch's problem and Deutsch-Jozsa problem. Then, we show the potentialities of the PTMs model of computation simulating the presented quantum algorithms via paraconsistent algorithms. This way, we show that PTMs can resolve some problems in exponentially less time than any classical deterministic Turing machine. Finally, We show that it is not possible to simulate all characteristics (in particular entangled states) of quantum computation by the particular model of PTMs here presented, therefore we open the possibility of constructing a new model of PTMs by which it is feasible to simulate such states.

Agudelo, J C; Agudelo, Juan C.; Carnielli, Walter

2006-01-01

24

Authorized quantum computation  

CERN Multimedia

We present authorized quantum computation, where only a user with a non-cloneable quantum authorization key can perform a unitary operation created by an authenticated programmer. The security of our authorized quantum computation is based on the quantum computational complexity problem of forging the keys from an obfuscated quantum gate sequence. Under the assumption of the existence of a \\textit{sufficiently-random gate shuffling algorithm}, the problem is shown to be in the NQP (Non-deterministic Quantum Polynomial)-hard class by reducing it to a NQP-Complete problem, the exact non-identity check problem. Therefore, our authorized quantum computation can be computationally secure against attacks using quantum computers.

Tanaka, Yu

2009-01-01

25

Quantum information. Teleportation - cryptography - quantum computer  

International Nuclear Information System (INIS)

[en] 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

26

Rabi Quantum Computer.  

Science.gov (United States)

This paper sets about to examine how a quantum computer might eventually be exploited. (A quantum computer uses strange but real effects in Quantum Mechanics to explore many possibilities at the same time with the same hardware.) There are currently just ...

R. A. Krutar

2001-01-01

27

Logics from Quantum Computation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The theory of logical gates in quantum computation has suggested new forms of quantum logic, called quantum computational logics. The basic semantic idea is the following: the meaning of a sentence is identified with a quregister (a system of qubits) or, more generally, with a mixture of quregisters...

DALLA CHIARA, MARIA LUISA; GIUNTINI, ROBERTO; LEPORINI, ROBERTO

28

Quantum Knitting Computer  

CERN Multimedia

We propose a fluxon-controlled quantum computer incorporated with three-qubit quantum error correction using special gate operations, i.e., joint-phase and SWAP gate operations, inherent in capacitively coupled superconducting flux qubits. The proposed quantum computer acts exactly like a knitting machine at home.

Fujii, Toshiyuki; Hatakenaka, Noriyuki

2009-01-01

29

Cellular quantum computer architecture  

International Nuclear Information System (INIS)

[en] A cellular quantum computer architecture with two qbits per cell is presented. The computation is performed at two repeated computation stages. At the first stage the states of all the control qbits are affected by the states of the neighboring data qbits. At the second stage a quantum gate acts on the tensor product of the data and control qbits in each cell. Quantum computations using this architecture are simulated and discussed

2003-12-22

30

Cellular quantum computer architecture  

Energy Technology Data Exchange (ETDEWEB)

A cellular quantum computer architecture with two qbits per cell is presented. The computation is performed at two repeated computation stages. At the first stage the states of all the control qbits are affected by the states of the neighboring data qbits. At the second stage a quantum gate acts on the tensor product of the data and control qbits in each cell. Quantum computations using this architecture are simulated and discussed.

Karafyllidis, Ioannis G

2003-12-22

31

Atomic quantum computer  

International Nuclear Information System (INIS)

[en] The current proposals for the realization of quantum computer such as NMR, quantum dots and trapped ions are based on the using of an atom or an ion as one qubit. In these proposals a quantum computer consists of several atoms and the coupling between them provides the coupling between qubits necessary for a quantum gate. It is discussed whether a single atom can be used as a quantum computer. One can implement a single qubit in atom as a one-particle electron state and multi-qubit states as multi-particle states. Spin-orbit and spin-spin interactions provide the coupling between qubits. In particular one can use the electron spin resonance to process the information encoded in the hyperfine splitting of atomic energy levels. By using quantum state engineering one can manipulate the internal states of the natural or artificial (quantum dot) atom to make quantum computations

1999-10-06

32

Towards Robust Quantum Computation  

CERN Multimedia

Quantum computation is a subject of much theoretical promise, but has not been realized in large scale, despite the discovery of fault-tolerant procedures to overcome decoherence. Part of the reason is that the theoretically modest requirements still present daunting experimental challenges. The goal of this Dissertation is to reduce various resources required for robust quantum computation, focusing on quantum error correcting codes and solution NMR quantum computation. A variety of techniques have been developed, including high rate quantum codes for amplitude damping, relaxed criteria for quantum error correction, systematic construction of fault-tolerant gates, recipes for quantum process tomography, techniques in bulk thermal state computation, and efficient decoupling techniques to implement selective coupled logic gates. A detailed experimental study of a quantum error correcting code in NMR is also presented. The Dissertation clarifies and extends results previously reported in quant-ph/9610043, quant...

Leung, D W

2000-01-01

33

Quantum computation by measurement and quantum memory  

Energy Technology Data Exchange (ETDEWEB)

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

Nielsen, Michael A

2003-02-24

34

Quantum Computing since Democritus  

Science.gov (United States)

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

Aaronson, Scott

2013-03-01

35

Intrinsic quantum computation  

International Nuclear Information System (INIS)

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 quantum entropy rate and provide a closed-form expression for the latter for the class of deterministic quantum processes

2008-01-21

36

Quantum computer science  

CERN Multimedia

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

Lanzagorta, Marco

2009-01-01

37

Algorithms for Quantum Computers  

CERN Document Server

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

38

Quantum-dot computing  

Energy Technology Data Exchange (ETDEWEB)

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

Milburn, Gerard

2003-10-01

39

Computational quantum field theory  

International Nuclear Information System (INIS)

[en] 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

40

Principles of quantum computing  

Energy Technology Data Exchange (ETDEWEB)

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.)

Mehring, Michael [Physikalisches Institut, Universitaet Stuttgart, 70550 Stuttgart (Germany)

2007-11-15

 
 
 
 
41

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.)

2007-01-01

42

PBS: Quantum Computing  

Science.gov (United States)

This episode of the PBS program Closer to the Truth provides some insight into quantum computing technology. The program summary discusses some of the potential uses for quantum computing and features excerpts from the program in which researchers from IBM's Watson Research Center, MIT and UC Berkeley were interviewed. Visitors can also download video footage of the show and the transcript. Short definitions for key terms such as Tunneling, Superposition, Entanglement, and Quantum Mechanics are also provided.

43

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.

2008-01-01

44

Instantaneous Quantum Computation  

CERN Multimedia

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

Shepherd, Dan

2008-01-01

45

IOP: Quantum Computing  

Science.gov (United States)

The publishers of Journal of Physics A: Mathematical and General are offering free access to articles on Classical and Quantum Field Theory from January 2005 until April 2005. The Classical and Quantum Field Theory section of the journal includes articles on "high quality, innovative and significant new results on mathematical physics in areas including: topological objects (such as vortices, solitons, instantons and monopoles), gauge and conformal field theory, quantum electrodynamics and quantum chromodynamics, integrable models, mathematical and computational methods in quantum field theory, and classical field theory." After April 2005, the articles will only be available to paid subscribers.

46

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

47

Review of quantum computation  

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

48

Review of quantum computation  

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

49

Quantum Computation by Communication  

CERN Multimedia

We present a new approach to scalable quantum computing--a ``qubus computer''--which realises qubit measurement and quantum gates through interacting qubits with a quantum communication bus mode. The qubits could be ``static'' matter qubits or ``flying'' optical qubits, but the scheme we focus on here is particularly suited to matter qubits. There is no requirement for direct interaction between the qubits. Universal two-qubit quantum gates may be effected by schemes which involve measurement of the bus mode, or by schemes where the bus disentangles automatically and no measurement is needed. In effect, the approach integrates together qubit degrees of freedom for computation with quantum continuous variables for communication and interaction.

Spiller, T P; Braunstein, S L; Munro, W J; Van Loock, P; Milburn, G J; Nemoto, Kae; Braunstein, Samuel L.

2005-01-01

50

Nature as quantum computer  

CERN Multimedia

Set theory reduces all processes to assembly and disassembly. A similar architecture is proposed for nature as quantum computer. It resolves the classical space-time underlying Feynman diagrams into a quantum network of creation and annihilation processes, reducing kinematics to quantum statistics, and regularizing the Lie algebra of the Einstein diffeomorphism group. The usually separate and singular Lie algebras of kinematics, statistics, and conserved currents merge into one regular statistics Lie algebra.

Finkelstein, David Ritz

2012-01-01

51

Quantum computing with defects  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

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

52

Quantum Discord and Quantum Computing - An Appraisal  

CERN Document Server

We discuss models of computing that are beyond classical. The primary motivation is to unearth the cause of nonclassical advantages in computation. Completeness results from computational complexity theory lead to the identification of very disparate problems, and offer a kaleidoscopic view into the realm of quantum enhancements in computation. Emphasis is placed on the `power of one qubit' model, and the boundary between quantum and classical correlations as delineated by quantum discord. A recent result by Eastin on the role of this boundary in the efficient classical simulation of quantum computation is discussed. Perceived drawbacks in the interpretation of quantum discord as a relevant certificate of quantum enhancements are addressed.

Datta, Animesh

2011-01-01

53

Optical Quantum Computation  

CERN Multimedia

We review the field of Optical Quantum Computation, considering the various implementations that have been proposed and the experimental progress that has been made toward realizing them. We examine both linear and nonlinear approaches and both particle and field encodings. In particular we discuss the prospects for large scale optical quantum computing in terms of the most promising physical architectures and the technical requirements for realizing them.

Ralph, T C

2011-01-01

54

Towards Quantum Computational Logics  

Science.gov (United States)

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

Ledda, Antonio; Sergioli, Giuseppe

2010-12-01

55

Introduction to Quantum Computing  

Science.gov (United States)

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

56

Using Quantum Computers for Quantum Simulation  

CERN Multimedia

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

57

Quantum computers get real  

Energy Technology Data Exchange (ETDEWEB)

A quantum computer has successfully factorized a number for the first time. Quantum mechanics is an extremely successful theory, but also a troubling one. For many years progress was made by concentrating on the obvious applications, and not worrying too much about the counterintuitive world view that quantum mechanics implies. More recently, however, the development of quantum-information theory has reversed this approach. If we take seriously what quantum mechanics seems to be telling us about the world, we can use this 'quantum weirdness' to do apparently impossible things. Probably the most famous application of quantum mechanics is the quantum computer, which is capable of performing calculations that are impossible with any classical device. At first the questions that quantum computers could tackle were rather esoteric, but in 1994 Peter Shor of AT and T Laboratories showed how a quantum computer could factor large numbers, thus rendering most modern cryptographic systems potentially obsolete. In 1996 David Cory and co-workers at the Massachusetts Institute of Technology (MIT) showed how nuclear magnetic resonance (NMR) - a technique best known for its applications in medical imaging and in chemistry - could be used to build small quantum computers. NMR systems are easily controlled by the magnetic component of electromagnetic fields and are only weakly affected by decoherence, and so progress was extremely rapid. Within two years, several two-qubit computers had been developed, and simple algorithms had been implemented. The race was on to build bigger and better NMR quantum computers, and to use them for more interesting tasks. The lead in this race has been held by several different research groups, but has now been decisively claimed by Isaac Chuang's group at Stanford University and IBM's Almaden Research Center in California. Chuang and co-workers have implemented the simplest example of Shor's quantum-factoring algorithm (L Vandersypen 2001 Nature 414 883). In the April issue of Physics World, Jonathan Jones of Oxford University, UK, describes how Chuang's group factored the number 15 using only seven qubits. (U.K.)

Jones, Jonathan [Oxford University (United Kingdom)

2002-04-01

58

Quantum computers get real  

International Nuclear Information System (INIS)

A quantum computer has successfully factorized a number for the first time. Quantum mechanics is an extremely successful theory, but also a troubling one. For many years progress was made by concentrating on the obvious applications, and not worrying too much about the counterintuitive world view that quantum mechanics implies. More recently, however, the development of quantum-information theory has reversed this approach. If we take seriously what quantum mechanics seems to be telling us about the world, we can use this 'quantum weirdness' to do apparently impossible things. Probably the most famous application of quantum mechanics is the quantum computer, which is capable of performing calculations that are impossible with any classical device. At first the questions that quantum computers could tackle were rather esoteric, but in 1994 Peter Shor of AT and T Laboratories showed how a quantum computer could factor large numbers, thus rendering most modern cryptographic systems potentially obsolete. In 1996 David Cory and co-workers at the Massachusetts Institute of Technology (MIT) showed how nuclear magnetic resonance (NMR) - a technique best known for its applications in medical imaging and in chemistry - could be used to build small quantum computers. NMR systems are easily controlled by the magnetic component of electromagnetic fields and are only weakly affected by decoherence, and so progress was extremely rapid. Within two years, several two-qubit computers had been developed, and simple algorithms had been implemented. The race was on to build bigger and better NMR quantum computers, and to use them for more interesting tasks. The lead in this race has been held by several different research groups, but has now been decisively claimed by Isaac Chuang's group at Stanford University and IBM's Almaden Research Center in California. Chuang and co-workers have implemented the simplest example of Shor's quantum-factoring algorithm (L Vandersypen 2001 Nature 414 883). In the April issue of Physics World, Jonathan Jones of Oxford University, UK, describes how Chuang's group factored the number 15 using only seven qubits. (U.K.)

2002-01-01

59

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

CERN Multimedia

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, S

2002-01-01

60

Beyond Quantum Computation and Towards Quantum Field Computation  

CERN Multimedia

Because the subject of relativistic quantum field theory (QFT) contains all of non-relativistic quantum mechanics, we expect quantum field computation to contain (non-relativistic) quantum computation. Although we do not yet have a quantum theory of the gravitational field, and are far from a practical implementation of a quantum field computer, some pieces of the puzzle (without gravity) are now available. We consider a general model for computation with quantum field theory, and obtain some results for relativistic quantum computation. Moreover, it is possible to see new connections between principal models of computation, namely, computation over the continuum and computation over the integers (Turing computation). Thus we identify a basic problem in QFT, namely Wightman's computation problem for domains of holomorphy, which we call WHOLO. Inspired by the same analytic functions which are central to the famous CPT theorem of QFT, it is possible to obtain a computational complexity structure for QFT and she...

Manoharan, A C

2003-01-01

 
 
 
 
61

Adiabatic Quantum Computing  

CERN Multimedia

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

62

Universal computation by quantum walk.  

UK PubMed Central (United Kingdom)

In some of the earliest work on quantum computing, Feynman showed how to implement universal quantum computation with a time-independent Hamiltonian. I show that this remains possible even if the Hamiltonian is restricted to be the adjacency matrix of a low-degree graph. Thus quantum walk can be regarded as a universal computational primitive, with any quantum computation encoded in some graph. The main idea is to implement quantum gates by scattering processes.

Childs AM

2009-05-01

63

Quantum information and computation  

International Nuclear Information System (INIS)

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

2001-09-07

64

Quantum information and computation  

Energy Technology Data Exchange (ETDEWEB)

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

Popescu, Sandu; Linden, Noah; Jozsa, Richard

2001-09-07

65

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

66

Adiabatic Quantum Computing  

Science.gov (United States)

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

Landahl, Andrew

2012-10-01

67

Fault-tolerant quantum computation  

Energy Technology Data Exchange (ETDEWEB)

It has recently been realized that use of the properties of quantum mechanics might speed up certain computations dramatically. Interest in quantum computation has since been growing. One of the main difficulties in realizing quantum computation is that decoherence tends to destroy the information in a superposition of states in a quantum computer, making long computations impossible. A further difficulty is that inaccuracies in quantum state transformations throughout the computation accumulate, rendering long computations unreliable. However, these obstacles may not be as formidable as originally believed. For any quantum computation with t gates, we show how to build a polynomial size quantum circuit that tolerates O(1/log{sup c}t) amounts of inaccuracy and decoherence per gate, for some constant c; the previous bound was O(1/t). We do this by showing that operations can be performed on quantum data encoded by quantum error-correcting codes without decoding this data.

Shor, P.W. [AT& T Research, Murray Hill, NJ (United States)

1996-12-31

68

Optically Controlled Quantum Dots for Quantum Computing.  

Science.gov (United States)

This program conducted experimental AND theoretical research aimed at developing an optically driven quantum dot quantum computer. In addition to the 2 %Pl's, the work was done in collaboration with Dan Gammon at the Naval Research laboratory. D. Gammon h...

D. G. Steel L. J. Sham

2005-01-01

69

An Introduction to Quantum Computing  

CERN Multimedia

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

Yanofsky, Noson S

2007-01-01

70

Demonstration of blind quantum computing.  

Science.gov (United States)

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

71

Quantum Computations: Fundamentals and Algorithms  

International Nuclear Information System (INIS)

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

2007-01-01

72

Parallel quantum computing in a single ensemble quantum computer  

International Nuclear Information System (INIS)

[en] 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

2004-01-01

73

Relativistic quantum chemistry on quantum computers  

CERN Multimedia

Last years witnessed a remarkable interest in application of quantum computing for solving problems in quantum chemistry more efficiently than classical computers allow. Very recently, even first proof-of-principle experimental realizations have been reported. However, so far only the non-relativistic regime (i.e. Schroedinger equation) has been explored, while it is well known that relativistic effects can be very important in chemistry. In this letter we present the first 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 3 qubits and 9 or 10 CNOTs, which implement a proof-of-principle relativistic quantum chemical calculation for this molecule and might be suitable for an experimental realizatio...

Veis, Libor; Fleig, Timo; Knecht, Stefan; Saue, Trond; Visscher, Lucas; Pittner, Ji?í

2011-01-01

74

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

75

Quantum computers: Definition and implementations  

International Nuclear Information System (INIS)

The DiVincenzo criteria for implementing a quantum computer have been seminal in focusing both experimental and theoretical research in quantum-information processing. These criteria were formulated specifically for the circuit model of quantum computing. However, several new models for quantum computing (paradigms) have been proposed that do not seem to fit the criteria well. Therefore, the question is what are the general criteria for implementing quantum computers. To this end, a formal operational definition of a quantum computer is introduced. It is then shown that, according to this definition, a device is a quantum computer if it obeys the following criteria: Any quantum computer must consist of a quantum memory, with an additional structure that (1) facilitates a controlled quantum evolution of the quantum memory; (2) includes a method for information theoretic cooling of the memory; and (3) provides a readout mechanism for subsets of the quantum memory. The criteria are met when the device is scalable and operates fault tolerantly. We discuss various existing quantum computing paradigms and how they fit within this framework. Finally, we present a decision tree for selecting an avenue toward building a quantum computer. This is intended to help experimentalists determine the most natural paradigm given a particular physical implementation.

2011-01-01

76

Duality and Recycling Computing in Quantum Computers  

CERN Document Server

Quantum computer possesses quantum parallelism and offers great computing power over classical computer \\cite{er1,er2}. As is well-know, a moving quantum object passing through a double-slit exhibits particle wave duality. A quantum computer is static and lacks this duality property. The recently proposed duality computer has exploited this particle wave duality property, and it may offer additional computing power \\cite{r1}. Simply put it, a duality computer is a moving quantum computer passing through a double-slit. A duality computer offers the capability to perform separate operations on the sub-waves coming out of the different slits, in the so-called duality parallelism. Here we show that an $n$-dubit duality computer can be modeled by an $(n+1)$-qubit quantum computer. In a duality mode, computing operations are not necessarily unitary. A $n$-qubit quantum computer can be used as an $n$-bit reversible classical computer and is energy efficient. Our result further enables a $(n+1)$-qubit quantum compute...

Long, Gui Lu

2007-01-01

77

New trends in quantum computing  

CERN Multimedia

Classical and quantum information are very different. Together they can perform feats that neither could achieve alone, such as quantum computing, quantum cryptography and quantum teleportation. Some of the applications range from helping to preventing spies from reading private communications. Among the tools that will facilitate their implementation, we note quantum purification and quantum error correction. Although some of these ideas are still beyond the grasp of current technology, quantum cryptography has been implemented and the prospects are encouraging for small-scale prototypes of quantum computation devices before the end of the millennium.

Brassard, G

1996-01-01

78

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

79

Quantum Gravity on a Quantum Computer?  

Science.gov (United States)

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

2013-08-01

80

Quantum Gravity on a Quantum Computer?  

CERN Document Server

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

 
 
 
 
81

Vibrational coherent quantum computation  

CERN Multimedia

A long-lived coherent state and non-linear interaction have been experimentally demonstrated for the vibrational mode of a trapped ion. We propose an implementation of quantum computation using coherent states of the vibrational modes of trapped ions. Differently from earlier experiments, we consider a far-off resonance for the interaction between external fields and the ion in a bidimensional trap. By appropriate choices of the detunings between the external fields, the adiabatic elimination of the ionic excited level from the Hamiltonian of the system allows for beam splitting between orthogonal vibrational modes, production of coherent states and non-linear interactions of various kinds. In particular, this model enables the generation of the four coherent Bell states. Furthermore, all the necessary operations for quantum computation such as preparation of qubits, one-qubit and controlled two-qubit operations, are possible. The detection of the state of a vibrational mode in a Bell state is made possible b...

Paternostro, M; Knight, P L; Paternostro, Mauro

2005-01-01

82

Quantum discord in quantum computation  

International Nuclear Information System (INIS)

Quantum discord is a measure of the quantumness of correlations. After reviewing its different versions and properties, we apply it to the questions of quantum information processing. First we show that changes in discord in the processed unentangled states indicate the need for entanglement in the distributed implementation of quantum gates. On the other hand, it was shown that zero system-environment discord is a necessary and sufficient condition for applicability of the standard completely positive description of the system's evolution. We demonstrate that this result does not translate into useful quantum process tomography. Depending on the details of the preparation procedure only absence of any initial correlations may guarantees consistency of the process tomography.

2011-07-08

83

Quantum discord in quantum computation  

CERN Multimedia

Quantum discord is a measure of the quantumness of correlations. After reviewing its different versions and properties, we apply it to the questions of quantum information processing. First we show that changes in discord in the processed unentangled states indicate the need for entanglement in the distributed implementation of quantum gates. On the other hand, it was shown that zero system-environment discord is a necessary and sufficient condition for applicability of the standard completely positive description of the system's evolution. We demonstrate that this result does not translate into useful quantum process tomography. Depending on the details of the preparation procedure only absence of any initial correlations may guarantees consistency of the process tomography.

Brodutch, Aharon; Terno, Daniel R; Wood, Christopher J

2010-01-01

84

Quantum discord in quantum computation  

Energy Technology Data Exchange (ETDEWEB)

Quantum discord is a measure of the quantumness of correlations. After reviewing its different versions and properties, we apply it to the questions of quantum information processing. First we show that changes in discord in the processed unentangled states indicate the need for entanglement in the distributed implementation of quantum gates. On the other hand, it was shown that zero system-environment discord is a necessary and sufficient condition for applicability of the standard completely positive description of the system's evolution. We demonstrate that this result does not translate into useful quantum process tomography. Depending on the details of the preparation procedure only absence of any initial correlations may guarantees consistency of the process tomography.

Brodutch, Aharon; Gilchrist, Alexei; Terno, Daniel R [Centre for Quantum Computer Technology, Department of Physics and Astronomy, Macquarie University, Sydney NSW 2113 (Australia); Wood, Christopher J, E-mail: aharon.brodutch@mq.edu.au [Institute for Quantum Computing, University of Waterloo, 200 University Av. West Waterloo Ontario N2L 3G1 (Canada)

2011-07-08

85

Quantum computer for dummies (in Russian)  

CERN Multimedia

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

Grozin, Andrey

2011-01-01

86

Quantum computing for physics research  

Energy Technology Data Exchange (ETDEWEB)

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.

Georgeot, B. [Laboratoire de Physique Theorique, UMR 5152 du CNRS, Universite Paul Sabatier, 118 Route de Narbonne, 31062 Toulouse cedex 04 (France)]. E-mail: georgeot@irsamc.ups-tlse.fr

2006-04-01

87

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

Energy Technology Data Exchange (ETDEWEB)

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)

Breuer, Reinhard (comp.)

2010-07-01

88

Quantum computing with defects.  

UK PubMed Central (United Kingdom)

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.

Weber JR; Koehl WF; Varley JB; Janotti A; Buckley BB; Van de Walle CG; Awschalom DD

2010-05-01

89

Quantum computing with defects.  

Science.gov (United States)

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

2010-04-19

90

Quantum computing with defects  

Science.gov (United States)

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.

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

2010-01-01

91

Pulse controlled noise suppressed quantum computation  

CERN Multimedia

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

Duan, L M; Duan, Lu-Ming; Guo, Guang-Can

1998-01-01

92

Quantum computing via measurements only  

CERN Multimedia

A quantum computer promises efficient processing of certain computational tasks that are intractable with classical computer technology. While basic principles of a quantum computer have been demonstrated in the laboratory, scalability of these systems to a large number of qubits, essential for practical applications such as the Shor algorithm, represents a formidable challenge. Most of the current experiments are designed to implement sequences of highly controlled interactions between selected particles (qubits), thereby following models of a quantum computer as a (sequential) network of quantum logic gates. Here we propose a different model of a scalable quantum computer. In our model, the entire resource for the quantum computation is provided initially in form of a specific entangled state (a so-called cluster state) of a large number of qubits. Information is then written onto the cluster, processed, and read out form the cluster by one-particle measurements only. The entangled state of the cluster thus...

Raussendorf, R; Raussendorf, Robert; Briegel, Hans J.

2000-01-01

93

Quantum Computation and Many Worlds  

CERN Multimedia

An Everett (`Many Worlds') interpretation of quantum mechanics due to Saunders and Zurek is presented in detail. This is used to give a physical description of the process of a quantum computation. Objections to such an understanding are discussed.

Hewitt-Horsman, C

2002-01-01

94

Geometric phases and quantum computations  

Energy Technology Data Exchange (ETDEWEB)

Calculation aspects of holonomic quantum computer (HQC) are considered. Wilczek-Zee potential defining the set of quantum calculations for HQC is explicitly evaluated. Principal possibility of realization of the logical gates for this case is discussed.

Margolin, A.E.; Strazhev, V.I.; Tregubovich, A.Ya

2002-10-14

95

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)

2005-01-01

96

Can Quantum Computers Replace the Classical Computer?  

Directory of Open Access Journals (Sweden)

Full Text Available The first computer originated as an ordinary calculator in 19th century. Subsequently, the rapid evolution of computers began. The massive amount of processing power generated by computer manufacturers has always failed to quench the thirst for speed and computing capacity. If, as Moore's Law states, the number of transistors on a microprocessor continues to double every 18 months, then soon we will find the circuits on a microprocessor being measured on an atomic scale. Today's advanced lithographic techniques can squeeze fraction of micron wide logic gates and wires onto the surface of silicon chips. Thus it can be seen that very soon we will be facing the need to create quantum computers which can harness the power of atoms and molecules to perform memory and processing tasks. Quantum computers have the potential to perform calculations a billion times faster than any silicon-based computer. Also, theories suggest that every physical object, even the universe, is in some sense a quantum computer. If this is the case, then according to Turing's work which says that all computers are functionally equivalent; computers should be able to model every physical process. Scientists have already built basic quantum computers that can perform certain calculations; but a practical quantum computer is still years away. In this paper, we will be discussing about the history, development and the future scope of quantum computing. The pros and cons of this future technology have also been compared and our analysis has been put forth.

Nikhil Talele; Sumant Bhat; Ajinkya Shukla

2012-01-01

97

Measures of quantum computing speedup  

Science.gov (United States)

We introduce the concept of strong quantum speedup. We prove that approximating the ground-state energy of an instance of the time-independent Schrödinger equation, with d degrees of freedom and large d, enjoys strong exponential quantum speedup. It can be easily solved on a quantum computer. Some researchers in discrete complexity theory believe that quantum computation is not effective for eigenvalue problems. One of our goals in this paper is to explain this dissonance.

Papageorgiou, Anargyros; Traub, Joseph F.

2013-08-01

98

Toward a superconducting quantum computer  

Science.gov (United States)

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 many new research opportunities open to physicists and engineers.

Tsai, Jaw-Shen

2010-01-01

99

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

2013-01-01

100

Interfacing external quantum devices to a universal quantum computer.  

Science.gov (United States)

We present a scheme to use external quantum devices using the universal quantum computer previously constructed. We thereby show how the universal quantum computer can utilize networked quantum information resources to carry out local computations. Such information may come from specialized quantum devices or even from remote universal quantum computers. We show how to accomplish this by devising universal quantum computer programs that implement well known oracle based quantum algorithms, namely the Deutsch, Deutsch-Jozsa, and the Grover algorithms using external black-box quantum oracle devices. In the process, we demonstrate a method to map existing quantum algorithms onto the universal quantum computer. PMID:22216276

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

2011-12-28

 
 
 
 
101

Interfacing external quantum devices to a universal quantum computer.  

UK PubMed Central (United Kingdom)

We present a scheme to use external quantum devices using the universal quantum computer previously constructed. We thereby show how the universal quantum computer can utilize networked quantum information resources to carry out local computations. Such information may come from specialized quantum devices or even from remote universal quantum computers. We show how to accomplish this by devising universal quantum computer programs that implement well known oracle based quantum algorithms, namely the Deutsch, Deutsch-Jozsa, and the Grover algorithms using external black-box quantum oracle devices. In the process, we demonstrate a method to map existing quantum algorithms onto the universal quantum computer.

Lagana AA; Lohe MA; von Smekal L

2011-01-01

102

Multi-party Quantum Computation  

UK PubMed Central (United Kingdom)

We investigate definitions of and protocols for multi-party quantum computing in the scenario where the secret data are quantum systems. We work in the quantum information-theoretic model, where no assumptions are made on the computational power of the adversary. For the slightly weaker task of verifiable quantum secret sharing, we give a protocol which tolerates any t < n=4 cheating parties (out of n). This is shown to be optimal. We use this new tool to establish that any multi-party quantum computation can be securely performed as long as the number of dishonest players is less than n=6.

103

Multi-party Quantum Computation  

CERN Multimedia

We investigate definitions of and protocols for multi-party quantum computing in the scenario where the secret data are quantum systems. We work in the quantum information-theoretic model, where no assumptions are made on the computational power of the adversary. For the slightly weaker task of verifiable quantum secret sharing, we give a protocol which tolerates any t < n/4 cheating parties (out of n). This is shown to be optimal. We use this new tool to establish that any multi-party quantum computation can be securely performed as long as the number of dishonest players is less than n/6.

Smith, A

2001-01-01

104

Universal quantum computation by discontinuous quantum walk  

CERN Document Server

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

Underwood, Michael S

2010-01-01

105

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 de...

Lanyon, B. P.; Whitfield, James Daniel; Gillett, G. G.; Goggin, M. E.; Almeida, M. P.; Kassal, Ivan; Biamonte, J. D.

106

Quantum Computational Logics. A Survey  

CERN Document Server

Quantum computation has suggested new forms of quantum logic, called quantum computational logics. The basic semantic idea is the following: the meaning of a sentence is identified with a quregister, a system of qubits, representing a possible pure state of a compound quantum system. The generalization to mixed states, which might be useful to analyse entanglement-phenomena, is due to Gudder. Quantum computational logics represent non standard examples of unsharp quantum logic, where the non-contradiction principle is violated, while conjunctions and disjunctions are strongly non-idempotent. In this framework, any sentence of the language gives rise to a quantum tree: a kind of quantum circuit that transforms the quregister associated to the atomic subformulas of the sentence into the quregister associated to the sentence.

Chiara, M L D; Leporini, R

2003-01-01

107

Towards quantum chemistry on a quantum computer.  

Science.gov (United States)

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 molecular system: the hydrogen molecule in a minimal basis. We calculate the complete energy spectrum to 20 bits of precision and discuss how the technique can be expanded to solve large-scale chemical problems that lie beyond the reach of modern supercomputers. These results represent an early practical step toward a powerful tool with a broad range of quantum-chemical applications. PMID:21124400

Lanyon, B P; Whitfield, J D; Gillett, G G; Goggin, M E; Almeida, M P; Kassal, I; Biamonte, J D; Mohseni, M; Powell, B J; Barbieri, M; Aspuru-Guzik, A; White, A G

2010-01-10

108

Towards quantum chemistry on a quantum computer.  

UK PubMed Central (United Kingdom)

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 molecular system: the hydrogen molecule in a minimal basis. We calculate the complete energy spectrum to 20 bits of precision and discuss how the technique can be expanded to solve large-scale chemical problems that lie beyond the reach of modern supercomputers. These results represent an early practical step toward a powerful tool with a broad range of quantum-chemical applications.

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

2010-02-01

109

Visualizing a silicon quantum computer  

International Nuclear Information System (INIS)

[en] Quantum computation is a fast-growing, multi-disciplinary research field. The purpose of a quantum computer is to execute quantum algorithms that efficiently solve computational problems intractable within the existing paradigm of 'classical' computing built on bits and Boolean gates. While collaboration between computer scientists, physicists, chemists, engineers, mathematicians and others is essential to the project's success, traditional disciplinary boundaries can hinder progress and make communicating the aims of quantum computing and future technologies difficult. We have developed a four minute animation as a tool for representing, understanding and communicating a silicon-based solid-state quantum computer to a variety of audiences, either as a stand-alone animation to be used by expert presenters or embedded into a longer movie as short animated sequences. The paper includes a generally applicable recipe for successful scientific animation production.

2008-01-01

110

Visualizing a silicon quantum computer  

Energy Technology Data Exchange (ETDEWEB)

Quantum computation is a fast-growing, multi-disciplinary research field. The purpose of a quantum computer is to execute quantum algorithms that efficiently solve computational problems intractable within the existing paradigm of 'classical' computing built on bits and Boolean gates. While collaboration between computer scientists, physicists, chemists, engineers, mathematicians and others is essential to the project's success, traditional disciplinary boundaries can hinder progress and make communicating the aims of quantum computing and future technologies difficult. We have developed a four minute animation as a tool for representing, understanding and communicating a silicon-based solid-state quantum computer to a variety of audiences, either as a stand-alone animation to be used by expert presenters or embedded into a longer movie as short animated sequences. The paper includes a generally applicable recipe for successful scientific animation production.

Sanders, Barry C [Institute for Quantum Information Science, University of Calgary, Calgary, Alberta T2N 1N4 (Canada); Hollenberg, Lloyd C L [ARC Centre of Excellence for Quantum Computer Technology, School of Physics, University of Melbourne, Victoria 3010 (Australia); Edmundson, Darran; Edmundson, Andrew [EDM Studio Inc., Level 2, 850 16 Avenue SW, Calgary, Alberta T2R 0S9 (Canada)], E-mail: bsanders@qis.ucalgary.ca, E-mail: lloydch@unimelb.edu.au, E-mail: darran@edmstudio.com

2008-12-15

111

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

Energy Technology Data Exchange (ETDEWEB)

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)

Koenneker, Carsten (comp.)

2012-11-01

112

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

113

The Quantum Field as a Quantum Computer  

CERN Multimedia

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 $c=a/\\tau$, $a$ and $\\tau$ being the minimum space and time distances between gates, respectively. It is shown that the information flow satisfies a Dirac equation, with speed $v=\\zeta c$ and $\\zeta=\\zeta(m)$ mass-dependent. For $a/\\tau=c$ the speed of light $\\zeta^{-1}$ is a vacuum refraction index increasing monotonically from $\\zeta^{-1}(0)=1$ to $\\zeta^{-1}(M)=\\infty$, $M$ being the Planck mass for $2a$ the Planck length.

D'Ariano, Giacomo Mauro

2010-01-01

114

Quantum computation and hidden variables  

CERN Multimedia

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

Aristov, V V

2010-01-01

115

Quantum Computing over Finite Fields  

CERN Document Server

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

116

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

117

Quantum Computer Using Coupled Quantum Dot Molecules  

CERN Document Server

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

118

Programmable architecture for quantum computing  

Science.gov (United States)

A programmable architecture called “quantum FPGA (field-programmable gate array)” (QFPGA) is presented for quantum computing, which is a hybrid model combining the advantages of the qubus system and the measurement-based quantum computation. There are two kinds of buses in QFPGA, the local bus and the global bus, which generate the cluster states and general multiqubit rotations around the z axis, respectively. QFPGA consists of quantum logic blocks (QLBs) and quantum routing channels (QRCs). The QLB is used to generate a small quantum logic while the QRC is used to combine them properly for larger logic realization. Considering the error accumulating on the qubus, the small logic is the general two-qubit quantum gate. However, for the application such as n-qubit quantum Fourier transform, one QLB can be reconfigured for four-qubit quantum Fourier transform. Although this is an implementation-independent architecture, we still make a rough analysis of its performance based on the qubus system. In a word, QFPGA provides a general architecture to integrate different quantum computing models for efficient quantum logic construction.

Chen, Jialin; Wang, Lingli; Charbon, Edoardo; Wang, Bin

2013-08-01

119

Interfacing External Quantum Devices to a Universal Quantum Computer  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present a scheme to use external quantum devices using the universal quantum computer previously constructed. We thereby show how the universal quantum computer can utilize networked quantum information resources to carry out local computations. Such information may come from specialized quantum ...

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

120

Quantum computation with graphene nanoribbon  

CERN Document Server

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

 
 
 
 
121

Universal quantum computer from a quantum magnet  

International Nuclear Information System (INIS)

[en] We show that a local Hamiltonian of spin-(3/2) particles with only two-body nearest-neighbor Affleck-Kennedy-Lieb-Tasaki and exchange-type interactions has a unique ground state, which can be used to implement universal quantum computation merely with single-spin measurements. We prove that the Hamiltonian is gapped, independent of the system size. Our result provides a further step toward utilizing systems with condensed-matter-type interactions for measurement-based quantum computation.

2010-01-01

122

Quantum Computing via The Bethe Ansatz  

CERN Document Server

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

Zhang, Yong

2011-01-01

123

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

124

Cryptography, Quantum Computation and Trapped Ions  

CERN Multimedia

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

1997-01-01

125

Fast Quantum Computing with Buckyballs  

CERN Multimedia

We have found that encapsulated atoms in fullerene molecules, which carry a spin, can be used for fast quantum computing. We describe the scheme for performing quantum computations, going through the preparation of the qubit state and the realization of a two-qubit quantum gate. When we apply a static magnetic field to each encased spin, we find out the ideal design for the preparation of the quantum state. Therefore, adding to our system a time dependent magnetic field, we can perform a phase-gate. The operational time related to a $\\pi-$phase gate is of the order of $ns$. This finding shows that, during the decoherence time, which is proportional to $\\mu s$, we can perform many thousands of gate operations. In addition, the two-qubit state which arises after a $\\pi-$gate is characterized by a high degree of entanglement. This opens a new avenue for the implementation of fast quantum computation.

Garelli, M S; Garelli, Maria Silvia; Kusmartsev, Feodor V

2005-01-01

126

PERTURBATION APPROACH FOR QUANTUM COMPUTATION  

Energy Technology Data Exchange (ETDEWEB)

We discuss how to simulate errors in the implementation of simple quantum logic operations in a nuclear spin quantum computer with many qubits, using radio-frequency pulses. We verify our perturbation approach using the exact solutions for relatively small (L = 10) number of qubits.

G. P. BERMAN; D. I. KAMENEV; V. I. TSIFRINOVICH

2001-04-01

127

Distinguishing Short Quantum Computations  

CERN Multimedia

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

128

Computing on Anonymous Quantum Network  

CERN Multimedia

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 number of parties is given to every party. A corollary of this result is a more efficient quantum leader election algorithm than existing ones: the new quantum algorithm runs in O(n) rounds with bit complexity O(mn^2), on an anonymous quantum network with n parties and m communication links. Another corollary is the first quantum algorithm that exactly computes any computable Boolean function with round complexity O(n) and with smaller bit complexity than that of existing classical algorithms in the worst case over all (computable) Boolea...

Kobayashi, Hirotada; Tani, Seiichiro

2010-01-01

129

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

CERN Multimedia

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

130

Massive Parallel Quantum Computer Simulator  

CERN Multimedia

We describe portable software to simulate universal quantum computers on massive parallel computers. We illustrate the use of the simulation software by running various quantum algorithms on different computer architectures, such as a IBM BlueGene/L, a IBM Regatta p690+, a Hitachi SR11000/J1, a Cray X1E, a SGI Altix 3700 and clusters of PCs running Windows XP. We study the performance of the software by simulating quantum computers containing up to 36 qubits, using up to 4096 processors and up to 1 TB of memory. Our results demonstrate that the simulator exhibits nearly ideal scaling as a function of the number of processors and suggest that the simulation software described in this paper may also serve as benchmark for testing high-end parallel computers.

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

2006-01-01

131

A quantum computer network  

CERN Multimedia

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

132

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

133

EXPLORATIONS IN QUANTUM COMPUTING FOR FINANCIAL APPLICATIONS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Quantum computers have the potential to increase the solution speed for many computational problems. This paper is a first step into possible applications for quantum computing in the context of computational finance. The fundamental ideas of quantum computing are introduced, followed by an expositi...

Gare, Jesse

134

Quantum Computation Beyond the Circuit Model  

CERN Multimedia

The quantum circuit model is the most widely used model of quantum computation. It provides both a framework for formulating quantum algorithms and an architecture for the physical construction of quantum computers. However, several other models of quantum computation exist which provide useful alternative frameworks for both discovering new quantum algorithms and devising new physical implementations of quantum computers. In this thesis, I first present necessary background material for a general physics audience and discuss existing models of quantum computation. Then, I present three results relating to various models of quantum computation: a scheme for improving the intrinsic fault tolerance of adiabatic quantum computers using quantum error detecting codes, a proof that a certain problem of estimating Jones polynomials is complete for the one clean qubit complexity class, and a generalization of perturbative gadgets which allows k-body interactions to be directly simulated using 2-body interactions. Las...

Jordan, Stephen P

2008-01-01

135

A Short Survey on Quantum Computers  

Energy Technology Data Exchange (ETDEWEB)

Quantum computing is an emerging technology. The clock frequency of current computer processor systems may reach about 40 GHz within the next 10 years. By then, one atom may represent one bit. Electrons under such conditions are no longer described by classical physics and a new model of the computer may be necessary by then. The quantum computer is one proposal that may have merit in dealing with the problems associated with the fact that certain important computationally intense problems present that current (classical) computers cannot solve because they require too much processing time. For example, Shor's algorithm performs factoring a large integer in polynomial time while classical factoring algorithms can do it in exponential time. In this paper we briefly survey the current status of quantum computers, quantum computer systems, and quantum simulators. Keywords Classical computers, quantum computers, quantum computer systems, quantum simulators, Shor's algorithm.

Kanamori, Yoshito [University of Alabama, Huntsville; Yoo, Seong-Moo [University of Alabama, Huntsville; Pan, W. D. [University of Alabama, Huntsville; Sheldon, Frederick T [ORNL

2006-01-01

136

Efficient quantum computing insensitive to phase errors  

CERN Document Server

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

Georgeot, B

2001-01-01

137

Continuous-variable blind quantum computation.  

UK PubMed Central (United Kingdom)

Blind quantum computation is a secure delegated quantum computing protocol where Alice, who does not have sufficient quantum technology at her disposal, delegates her 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. Protocols of blind quantum computation have been proposed for several qudit measurement-based computation models, such as the graph state model, the Affleck-Kennedy-Lieb-Tasaki model, and the Raussendorf-Harrington-Goyal topological model. Here, we consider blind quantum computation for the continuous-variable measurement-based model. We show that blind quantum computation is possible for the infinite squeezing case. We also show that the finite squeezing causes no additional problem in the blind setup apart from the one inherent to the continuous-variable measurement-based quantum computation.

Morimae T

2012-12-01

138

Continuous-Variable Blind Quantum Computation  

Science.gov (United States)

Blind quantum computation is a secure delegated quantum computing protocol where Alice, who does not have sufficient quantum technology at her disposal, delegates her 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. Protocols of blind quantum computation have been proposed for several qudit measurement-based computation models, such as the graph state model, the Affleck-Kennedy-Lieb-Tasaki model, and the Raussendorf-Harrington-Goyal topological model. Here, we consider blind quantum computation for the continuous-variable measurement-based model. We show that blind quantum computation is possible for the infinite squeezing case. We also show that the finite squeezing causes no additional problem in the blind setup apart from the one inherent to the continuous-variable measurement-based quantum computation.

Morimae, Tomoyuki

2012-12-01

139

Continuous-variable blind quantum computation.  

Science.gov (United States)

Blind quantum computation is a secure delegated quantum computing protocol where Alice, who does not have sufficient quantum technology at her disposal, delegates her 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. Protocols of blind quantum computation have been proposed for several qudit measurement-based computation models, such as the graph state model, the Affleck-Kennedy-Lieb-Tasaki model, and the Raussendorf-Harrington-Goyal topological model. Here, we consider blind quantum computation for the continuous-variable measurement-based model. We show that blind quantum computation is possible for the infinite squeezing case. We also show that the finite squeezing causes no additional problem in the blind setup apart from the one inherent to the continuous-variable measurement-based quantum computation. PMID:23368174

Morimae, Tomoyuki

2012-12-05

140

Self-correcting quantum computers  

Science.gov (United States)

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

Bombin, H.; Chhajlany, R. W.; Horodecki, M.; Martin-Delgado, M. A.

2013-05-01

 
 
 
 
141

Is sequential quantum computing possible?  

CERN Multimedia

We consider a general quantum computation that can be described as a global unitary operation acting simultaneously on several qubits, performing a prescribed task without measurements. Though the design of such operations grows in difficulty with the system size, they can be implemented with universal sets of one- and two-qubit gates acting in a convenient order. Here, we study the possibility for a global unitary applied on an arbitrary number of qubits to be decomposed in a sequential unitary procedure, where an ancillary system is allowed to interact only once with each qubit. Surprisingly, we prove that sequential unitary decompositions are in general impossible for genuine entangling operations, even with an infinite-dimensional ancilla, being the paradigmatic controlled-NOT gate a striking example. Nevertheless, we find particular nontrivial operations in quantum information that can be performed in a sequential unitary manner, as is the case of quantum error correction and quantum cloning.

Lamata, L; Perez-Garcia, D; Salgado, D; Solano, E

2007-01-01

142

Analogical Modeling and Quantum Computing  

CERN Multimedia

This paper serves as a bridge between quantum computing and analogical modeling (a general theory for predicting categories of behavior in varying contexts). Since its formulation in the early 1980s, analogical modeling has been successfully applied to a variety of problems in language. Several striking similarities between quantum mechanics and analogical modeling have recently been noted: (1) traditional statistics can be derived from a non-statistical basis by assuming data occurrences are accessed through a spin-up state (given two equally probable quantum states, spin-up and spin-down); (2) the probability of predicting a particular outcome is determined by the squaring of an underlying linear measure and is the result of decoherence (which occurs when a quantum system is observed); and (3) a natural measure of certainty (called the agreement) is based on one chance of guessing the right outcome and corresponds to the integrated squaring of Schroedinger's wave equation. Analogical modeling considers all ...

Skousen, R

2000-01-01

143

Quantum Computing in the Dark  

CERN Multimedia

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. Previous explanations of decoherence-free operations have used an environment-induced quantum Zeno effect. In this paper a purely dynamical explanation is given for why the scheme based on atoms inside an {\\em optical cavity} works. In addition, we show how spontaneous emission by the atoms can be highly suppressed. Because the system behaves very similarly to three-level atoms exhibiting macroscopic dark periods the proposed scheme can be called ``quantum computing in the dark.''

Tregenna, B; Knight, P L; Tregenna, Ben; Beige, Almut; Knight, Peter L.

2002-01-01

144

Quantum computational logics and Fock space semantics  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The theory of logical gates in quantum computation has suggested new forms of quantum logic, called quantum computational logics. The basic semantic idea is the following: the meaning of a sentence is identified with a quantum information quantity, represented by a density operator of a Hilbert spac...

DALLA CHIARA, MARIA LUISA; GIUNTINI, ROBERTO; LEPORINI, ROBERTO

145

Organic materials for quantum computation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Quantum mechanics has a long history of helping computer science. For a long time, it provided help only at the hardware level by giving a better understanding of the properties of matter and thus allowing the design of ever smaller and ever more efficient components. For the last few decades, much ...

Rival, Olivier; Ardavan, Arzhang; Blundell, Stephen

146

Fault Tolerant Adiabatic Quantum Computation  

CERN Document Server

We develop a theory of fault tolerant adiabatic quantum computation (AQC), using a hybrid methodology involving subsystem and stabilizer codes, concatenated dynamical decoupling, and energy gaps. As an example we show how to perform fault tolerant AQC against 1-local noise using only 2-local interactions, as suitable for capacitively coupled flux qubits and polar molecules.

Lidar, Daniel A

2007-01-01

147

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.

2005-01-01

148

Quantum-computer architecture using nonlocal interactions  

International Nuclear Information System (INIS)

[en] Several authors have described the basic requirements essential to build a scalable quantum computer. Because many physical implementation schemes for quantum computing rely on nearest-neighbor interactions, there is a hidden quantum communication overhead to connect distant nodes of the computer. In this paper, we propose a physical solution to this problem, which, together with the key building blocks, provides a pathway to a scalable quantum architecture using nonlocal interactions. Our solution involves the concept of a quantum bus that acts as a refreshable entanglement resource to connect distant memory nodes, providing an architectural concept for quantum computers analogous to the von Neumann architecture for classical computers

2003-01-01

149

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

150

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.

2011-01-01

151

Simulating quantum dynamics on a quantum computer  

International Nuclear Information System (INIS)

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

2011-11-04

152

Simulating quantum dynamics on a quantum computer  

Energy Technology Data Exchange (ETDEWEB)

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

Wiebe, Nathan; Hoyer, Peter; Sanders, Barry C [Institute for Quantum Information Science, University of Calgary, Alberta T2N 1N4 (Canada); Berry, Dominic W, E-mail: nathanwiebe@gmail.com [Institute for Quantum Computing, University of Waterloo, Ontario N2 L 3G1 (Canada)

2011-11-04

153

Introduction to models of quantum computation and quantum programming languages  

CERN Multimedia

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

154

Quantum mechanics and computation; Quanta y Computacion  

Energy Technology Data Exchange (ETDEWEB)

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

Cirac Sasturain, J. I.

2000-07-01

155

Simulating Quantum Dynamics On A Quantum Computer  

CERN Multimedia

We develop an efficient quantum algorithm for simulating time-dependent Hamiltonian evolution of general input states on a quantum computer. Given conditions on the smoothness of the Hamiltonian, the complexity of the algorithm is close to linear in the evolution time, and therefore is comparable to algorithms for time-independent Hamiltonians. In addition, we show how the complexity can be reduced by optimizing the time steps. The complexity of the algorithm is quantified by calls to an oracle, which yields information about the Hamiltonian, and accounts for all computational resources. In contrast to previous work, which allowed an oracle query to yield an arbitrary number of bits or qubits, we assign a cost for each bit or qubit accessed. This per-bit or per-qubit costing of oracle calls reveals hitherto unnoticed simulation costs. We also account for discretization errors in the time and the representation of the Hamiltonian. We generalize the requirement of sparse Hamiltonians to being a sum of sparse Ha...

Wiebe, Nathan; Hoyer, Peter; Sanders, Barry C

2010-01-01

156

Quantum computing from the ground up  

CERN Document Server

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

Perry, Riley Tipton

2012-01-01

157

Experimental Demonstration of Blind Quantum Computing  

CERN Document Server

Quantum computers, besides offering substantial computational speedups, are also expected to provide the possibility of preserving the privacy of a computation. Here we show the first such experimental demonstration of blind quantum computation where 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. We demonstrate various blind delegated computations, including one- and two-qubit gates and the Deutsch and Grover algorithms. Remarkably, the client only needs to be able to prepare and transmit individual photonic qubits. Our demonstration is crucial for future 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.

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

2011-01-01

158

Quantum Computation and Lattice Problems  

CERN Multimedia

We present the first explicit connection between quantum computation and lattice problems. Namely, we show a solution to the Unique Shortest Vector Problem (SVP) under the assumption that there exists an algorithm that solves the hidden subgroup problem on the dihedral group by coset sampling. Moreover, we solve the hidden subgroup problem on the dihedral group by using an average case subset sum routine. By combining the two results, we get a quantum reduction from $\\Theta(n^{2.5})$-unique-SVP to the average case subset sum problem.

Regev, O

2003-01-01

159

Problems and solutions in quantum computing and quantum information  

CERN Multimedia

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

Steeb, Willi-Hans

2012-01-01

160

Experimental realization of quantum games on a quantum computer.  

UK PubMed Central (United Kingdom)

We generalize the quantum prisoner's dilemma to the case where the players share a nonmaximally entangled states. We show that the game exhibits an intriguing structure as a function of the amount of entanglement with two thresholds which separate a classical region, an intermediate region, and a fully quantum region. Furthermore this quantum game is experimentally realized on our nuclear magnetic resonance quantum computer.

Du J; Li H; Xu X; Shi M; Wu J; Zhou X; Han R

2002-04-01

 
 
 
 
161

Ancilla-driven universal blind quantum computation  

Science.gov (United States)

Blind quantum computation is a new quantum secure protocol, which enables Alice who does not have enough quantum technology to delegate her computation to Bob who has a fully fledged quantum power without revealing her input, output, and algorithm. So far, blind quantum computation has been considered only for the circuit model and the measurement-based model. Here we consider the possibility and the limitation of blind quantum computation in the ancilla-driven model, which is a hybrid of the circuit and the measurement-based models.

Sueki, Takahiro; Koshiba, Takeshi; Morimae, Tomoyuki

2013-06-01

162

Quantum computing and the entanglement frontier  

CERN Document Server

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

Preskill, John

2012-01-01

163

KLM quantum computation as a measurement based computation  

CERN Document Server

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

Popescu, S

2006-01-01

164

Cove: A Practical Quantum Computer Programming Framework  

CERN Multimedia

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

Purkeypile, Matt

2009-01-01

165

Quantum Computation and Decision Trees  

CERN Multimedia

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

Farhi, E; Farhi, Edward; Gutmann, Sam

1998-01-01

166

Geometry of Quantum Computation with Qutrits  

Science.gov (United States)

Determining the quantum circuit complexity of a unitary operation is an important problem in quantum computation. By using the mathematical techniques of Riemannian geometry, we investigate the efficient quantum circuits in quantum computation with n qutrits. We show that the optimal quantum circuits are essentially equivalent to the shortest path between two points in a certain curved geometry of SU(3n). As an example, three-qutrit systems are investigated in detail.

Li, Bin; Yu, Zu-Huan; Fei, Shao-Ming

2013-01-01

167

Geometry of quantum computation with qutrits.  

UK PubMed Central (United Kingdom)

Determining the quantum circuit complexity of a unitary operation is an important problem in quantum computation. By using the mathematical techniques of Riemannian geometry, we investigate the efficient quantum circuits in quantum computation with n qutrits. We show that the optimal quantum circuits are essentially equivalent to the shortest path between two points in a certain curved geometry of SU(3(n)). As an example, three-qutrit systems are investigated in detail.

Li B; Yu ZH; Fei SM

2013-09-01

168

Quantum chemistry simulation on quantum computers: theories and experiments.  

UK PubMed Central (United Kingdom)

It has been claimed that quantum computers can mimic quantum systems efficiently in the polynomial scale. Traditionally, those simulations are carried out numerically on classical computers, which are inevitably confronted with the exponential growth of required resources, with the increasing size of quantum systems. Quantum computers avoid this problem, and thus provide a possible solution for large quantum systems. In this paper, we first discuss the ideas of quantum simulation, the background of quantum simulators, their categories, and the development in both theories and experiments. We then present a brief introduction to quantum chemistry evaluated via classical computers followed by typical procedures of quantum simulation towards quantum chemistry. Reviewed are not only theoretical proposals but also proof-of-principle experimental implementations, via a small quantum computer, which include the evaluation of the static molecular eigenenergy and the simulation of chemical reaction dynamics. Although the experimental development is still behind the theory, we give prospects and suggestions for future experiments. We anticipate that in the near future quantum simulation will become a powerful tool for quantum chemistry over classical computations.

Lu D; Xu B; Xu N; Li Z; Chen H; Peng X; Xu R; Du J

2012-07-01

169

Quantum chemistry simulation on quantum computers: theories and experiments.  

Science.gov (United States)

It has been claimed that quantum computers can mimic quantum systems efficiently in the polynomial scale. Traditionally, those simulations are carried out numerically on classical computers, which are inevitably confronted with the exponential growth of required resources, with the increasing size of quantum systems. Quantum computers avoid this problem, and thus provide a possible solution for large quantum systems. In this paper, we first discuss the ideas of quantum simulation, the background of quantum simulators, their categories, and the development in both theories and experiments. We then present a brief introduction to quantum chemistry evaluated via classical computers followed by typical procedures of quantum simulation towards quantum chemistry. Reviewed are not only theoretical proposals but also proof-of-principle experimental implementations, via a small quantum computer, which include the evaluation of the static molecular eigenenergy and the simulation of chemical reaction dynamics. Although the experimental development is still behind the theory, we give prospects and suggestions for future experiments. We anticipate that in the near future quantum simulation will become a powerful tool for quantum chemistry over classical computations. PMID:22652702

Lu, Dawei; Xu, Boruo; Xu, Nanyang; Li, Zhaokai; Chen, Hongwei; Peng, Xinhua; Xu, Ruixue; Du, Jiangfeng

2012-05-31

170

Development and Application of Semiconductor Quantum Dots to Quantum Computing.  

Science.gov (United States)

This work focuses on developing and applying the necessary methodology for the understanding and application of semiconductor quantum dots for quantum computing. Several major milestones were achieved during the present program including the demonstration...

D. G. Steel

2002-01-01

171

All-silicon quantum computer.  

UK PubMed Central (United Kingdom)

A solid-state implementation of a quantum computer composed entirely of silicon is proposed. Qubits are 29Si nuclear spins arranged as chains in a 28Si (spin-0) matrix with Larmor frequencies separated by a large magnetic field gradient. No impurity dopants or electrical contacts are needed. Initialization is accomplished by optical pumping, algorithmic cooling, and pseudo-pure state techniques. Magnetic resonance force microscopy is used for ensemble measurement.

Ladd TD; Goldman JR; Yamaguchi F; Yamamoto Y; Abe E; Itoh KM

2002-07-01

172

Superconducting circuits for quantum computing  

Energy Technology Data Exchange (ETDEWEB)

Superconducting circuits provide one of the numerous current candidate routes for the realization of quantum computing (QC) technology. In this paper I review the basic physics behind this candidature and outline some superconducting QC proposals currently on the table demonstrating their common origins. More detailed discussion of the proposals follows, assessing how they measure up to the ''DiVincenzo checklist'' for QC realizations and the current status of experiments. (author)

Spiller, T.P

2000-05-01

173

Toward a superconducting quantum computer. Harnessing macroscopic quantum coherence.  

UK PubMed Central (United Kingdom)

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 many new research opportunities open to physicists and engineers.

Tsai JS

2010-01-01

174

Suppression of quantum chaos in a quantum computer hardware  

International Nuclear Information System (INIS)

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

2006-01-01

175

Suppression of quantum chaos in a quantum computer hardware.  

UK PubMed Central (United Kingdom)

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

Lages J; Shepelyansky DL

2006-08-01

176

Efficient One-way Quantum Computations for Quantum Error Correction  

CERN Multimedia

We show how to explicitly construct an $O(nd)$ size and constant quantum depth circuit which encodes any given $n$-qubit stabilizer code with $d$ generators. Our construction is derived using the graphic description for stabilizer codes and the one-way quantum computation model. Our result demonstrates how to use cluster states as scalable resources for many multi-qubit entangled states and how to use the one-way quantum computation model to improve design of quantum algorithms.

Huang, Wei

2007-01-01

177

Universal computation by multiparticle quantum walk.  

Science.gov (United States)

A quantum walk is a time-homogeneous quantum-mechanical process on a graph defined by analogy to classical random walk. The quantum walker is a particle that moves from a given vertex to adjacent vertices in quantum superposition. We consider a generalization to interacting systems with more than one walker, such as the Bose-Hubbard model and systems of fermions or distinguishable particles with nearest-neighbor interactions, and show that multiparticle quantum walk is capable of universal quantum computation. Our construction could, in principle, be used as an architecture for building a scalable quantum computer with no need for time-dependent control. PMID:23413349

Childs, Andrew M; Gosset, David; Webb, Zak

2013-02-15

178

Universal quantum computation using the discrete-time quantum walk  

International Nuclear Information System (INIS)

A proof that continuous-time quantum walks are universal for quantum computation, using unweighted graphs of low degree, has recently been presented by A. M. Childs [Phys. Rev. Lett. 102, 180501 (2009)]. We present a version based instead on the discrete-time quantum walk. We show that the discrete-time quantum walk is able to implement the same universal gate set and thus both discrete and continuous-time quantum walks are computational primitives. Additionally, we give a set of components on which the discrete-time quantum walk provides perfect state transfer.

2010-01-01

179

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; Shirish Pathania

2010-01-01

180

Quantum Computer Circuit Analysis and Design.  

Science.gov (United States)

Recent developments in the Riemannian geometry of quantum computation offer a new approach to the analysis of quantum computation. A geodesic equation defined on the SU(2n) group manifold, representing quantum gate operations on n qubits, may be used to d...

H. E. Brandt

2009-01-01

 
 
 
 
181

An unsharp logic from quantum computation  

CERN Document Server

Logical gates studied in quantum computation suggest a natural logical abstraction that gives rise to a new form of unsharp quantum logic. We study the logical connectives corresponding to the following gates: the Toffoli gate, the NOT and the squareroot of NOT (which admit of natural physical models). This leads to a semantic characterization of a logic that we call computational quantum logic CQL.

Cattaneo, G; Giuntini, R; Leporini, R

2002-01-01

182

Quantum computational logics and possible applications  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In quantum computational logics meanings of formulas are identified with quantum information quantities: systems of qubits or, more generally, mixtures of systems of qubits. We consider two kinds of quantum computational semantics: 1) a compositional semantics, where the meaning of a compound formul...

DALLA CHIARA, MARIA LUISA; GIUNTINI, ROBERTO; TORALDO DI FRANCIA, GIULIANO; LEPORINI, ROBERTO

183

Parallel computing and quantum chromodynamics  

CERN Multimedia

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

184

Embracing the quantum limit in silicon computing.  

UK PubMed Central (United Kingdom)

Quantum computers hold the promise of massive performance enhancements across a range of applications, from cryptography and databases to revolutionary scientific simulation tools. Such computers would make use of the same quantum mechanical phenomena that pose limitations on the continued shrinking of conventional information processing devices. Many of the key requirements for quantum computing differ markedly from those of conventional computers. However, silicon, which plays a central part in conventional information processing, has many properties that make it a superb platform around which to build a quantum computer.

Morton JJ; McCamey DR; Eriksson MA; Lyon SA

2011-11-01

185

Embracing the quantum limit in silicon computing.  

Science.gov (United States)

Quantum computers hold the promise of massive performance enhancements across a range of applications, from cryptography and databases to revolutionary scientific simulation tools. Such computers would make use of the same quantum mechanical phenomena that pose limitations on the continued shrinking of conventional information processing devices. Many of the key requirements for quantum computing differ markedly from those of conventional computers. However, silicon, which plays a central part in conventional information processing, has many properties that make it a superb platform around which to build a quantum computer. PMID:22094695

Morton, John J L; McCamey, Dane R; Eriksson, Mark A; Lyon, Stephen A

2011-11-16

186

Polynomial simulations of decohered quantum computers  

Energy Technology Data Exchange (ETDEWEB)

Recently it has become clear, that a key issue in quantum computation is understanding how interaction with the environment, or {open_quote}decoherence{close_quotes}, effects the computational power of quantum computers. We adopt the standard physical method of describing systems which are interwound with their environment by {open_quotes}density matrices{close_quotes}, and within this framework define a model of decoherence in quantum computation. Our results show that the computational power of decohered quantum computers depends strongly on the amount of parallelism in the computation. We first present a simulation of decohered sequential quantum computers, on a classical probabilistic Turing machine, and prove that the expected slowdown of this simulation is polynomial in time and space of the quantum computation, for any non zero decoherence rate. Similar results hold for Quantum computers that are allowed to operate on logarithmic number of qubits at a time. For decohered quantum circuits (with local gates), the situation is more subtle and depends on the decoherence rate, {eta}. We find that our simulation is efficient for circuits with decoherence rate {eta} higher than some constant {eta}{sub 1}, but exponential for a general (random) circuit subjected to decoherence rate lower than some constant {eta}{sub 2}. The transition from exponential cost to polynomial cost happens in a short range of decoherence rates. We use computer experiments to exhibit the phase transitions in various quantum circuits.

Aharonov, D.; Ben-Or, M. [Hebrew Univ., Jerusalem (Israel)

1996-12-31

187

Decoherence, Control, and Symmetry in Quantum Computers  

CERN Multimedia

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

188

Zeno effect for quantum computation and control  

CERN Document Server

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

Paz-Silva, G A; Lidar, D A

2011-01-01

189

Zeno effect for quantum computation and control.  

UK PubMed Central (United Kingdom)

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

Paz-Silva GA; Rezakhani AT; Dominy JM; Lidar DA

2012-02-01

190

Blind topological measurement-based quantum computation.  

Science.gov (United States)

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

191

Blind topological measurement-based quantum computation.  

UK PubMed Central (United Kingdom)

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.

Morimae T; Fujii K

2012-01-01

192

On the computation of quantum characteristic exponents  

CERN Document Server

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

193

Physics and computer science: quantum computation and other approaches  

CERN Multimedia

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

Venegas-Andraca, Salvador E

2011-01-01

194

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 rev...

Tsai, Jaw-Shen

195

Quantum simulation of pairing models on an NMR quantum computer  

Energy Technology Data Exchange (ETDEWEB)

We give out a scheme of quantum simulation of pairing models on an NMR quantum computer. We show that it can obtain the spectrum of paring model in principle, and present a simple example. Similarly, it is possible to discuss the quantum simulation to obtain more differences of energy levels.

Wang Anmin [Department of Modern Physics and Institute for Theoretical Physics, University of Science and Technology of China, Hefei 230026 (China)]. E-mail: anmwang@ustc.edu.cn; Yang Xiaodong [Department of Modern Physics and Institute for Theoretical Physics, University of Science and Technology of China, Hefei 230026 (China)

2006-04-03

196

Quantum simulation of pairing models on an NMR quantum computer  

International Nuclear Information System (INIS)

[en] We give out a scheme of quantum simulation of pairing models on an NMR quantum computer. We show that it can obtain the spectrum of paring model in principle, and present a simple example. Similarly, it is possible to discuss the quantum simulation to obtain more differences of energy levels

2006-04-03

197

Assumptions for fault tolerant quantum computing  

Energy Technology Data Exchange (ETDEWEB)

Assumptions useful for fault tolerant quantum computing are stated and briefly discussed. We focus on assumptions related to properties of the computational system. The strongest form of the assumptions seems to be sufficient for achieving highly fault tolerant quantum computation. We discuss weakenings which are also likely to suffice.

Knill, E.; Laflamme, R.

1996-06-01

198

The Halting Problem for Quantum Computers  

CERN Document Server

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

Linden, N

1998-01-01

199

Quantum fields on the computer  

CERN Multimedia

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

1992-01-01

200

Blind quantum computation with AKLT chains  

CERN Document Server

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

 
 
 
 
201

Helping Students Learn Quantum Mechanics for Quantum Computing  

Science.gov (United States)

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

202

Photon echo quantum RAM integration in quantum computer  

CERN Document Server

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

203

An introduction to reliable quantum computation  

CERN Multimedia

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

Aliferis, Panos

2011-01-01

204

A Quantum Neural Network Computes Entanglement  

CERN Document Server

An outstanding problem in quantum computing is the calculation of entanglement, for which no closed-form algorithm exists. Here we solve that problem, and demonstrate the utility of a quantum neural computer, by showing, in simulation, that such a device can be trained to calculate the entanglement of an input state, something neither an algorithmic quantum computer nor a classical neural net can do.

Behrman, E C; Wang, Z; Belur, C K; Steck, J E; Skinner, S R

2002-01-01

205

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

206

Prospects for quantum computation with trapped ions  

Energy Technology Data Exchange (ETDEWEB)

Over the past decade information theory has been generalized to allow binary data to be represented by two-state quantum mechanical systems. (A single two-level system has come to be known as a qubit in this context.) The additional freedom introduced into information physics with quantum systems has opened up a variety of capabilities that go well beyond those of conventional information. For example, quantum cryptography allows two parties to generate a secret key even in the presence of eavesdropping. But perhaps the most remarkable capabilities have been predicted in the field of quantum computation. Here, a brief survey of the requirements for quantum computational hardware, and an overview of the in trap quantum computation project at Los Alamos are presented. The physical limitations to quantum computation with trapped ions are discussed.

Hughes, R.J.; James, D.F.V.

1997-12-31

207

Centre for Quantum Computation & Communication Technology  

Science.gov (United States)

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.

208

Difficulties in the Implementation of Quantum Computers  

CERN Document Server

This paper reviews various engineering hurdles facing the field of quantum computing. Specifically, problems related to decoherence, state preparation, error correction, and implementability of gates are considered.

Ponnath, A

2006-01-01

209

Quantum-mechanical computers and uncomputability  

International Nuclear Information System (INIS)

The time evolution operator for any quantum-mechanical computer is diagonalizable, but to obtain the diagonal decomposition of a program state of the computer is as hard as actually performing the computation corresponding to the program. In particular, if a quantum-mechanical system is capable of universal computation, then the diagonal decomposition of program states is uncomputable. As a result, in a universe in which local variables support universal computation, a quantum-mechanical theory for that universe that supplies its spectrum cannot supply the spectral decomposition of the computational variables. A ''theory of everything'' can be simultaneously correct and fundamentally incomplete.

1993-01-01

210

Quantum Computing with Incoherent Resources and Quantum Jumps  

Science.gov (United States)

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.

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

2012-04-01

211

Quantum computing with incoherent resources and quantum jumps.  

Science.gov (United States)

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

2012-04-24

212

Experimental realization of nonadiabatic holonomic quantum computation.  

Science.gov (United States)

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

2013-05-06

213

Treatment of sound on quantum computers  

CERN Multimedia

We study numerically how a sound signal stored in a quantum computer can be recognized and restored with a minimal number of measurements in presence of random quantum gate errors. A method developed uses elements of MP3 sound compression and allows to recover human speech and sound of complex quantum wavefunctions.

Lee, J W; Shepelyansky, D; Lee, Jae Weon; Chepelianskii, Alexei; Shepelyansky, Dima

2003-01-01

214

NMR quantum computation with indirectly coupled gates  

CERN Document Server

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

215

Quantum Computer Games: Schrodinger Cat and Hounds  

Science.gov (United States)

|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

216

Teleportation in a nuclear spin quantum computer  

International Nuclear Information System (INIS)

[en] We present a procedure for quantum teleportation in a nuclear spin quantum computer in which quantum logic gates are implemented by using selective electromagnetic pulses. A sequence of pulses is combined with single-spin measurements in the ?z basis for fast transfer of information in a spin quantum computer. We simulated this procedure for quantum teleportation in a nuclear spin chain with a large number (201) of spins. The systematic errors generated in the process of teleportation due to the non-resonant effects are analyzed in detail. We demonstrate that a '2?k' method provides a significant reduction of errors

2002-01-01

217

Nonlinear optics quantum computing with circuit QED.  

Science.gov (United States)

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

2013-02-05

218

Parallel Quantum Computation and Quantum Codes  

CERN Multimedia

We propose a definition of QNC, the quantum analog of the efficient parallel class NC. We exhibit several useful gadgets and prove that various classes of circuits can be parallelized to logarithmic depth, including circuits for encoding and decoding standard quantum error-correcting codes, or more generally any circuit consisting of controlled-not gates, controlled pi-shifts, and Hadamard gates. Finally, while we note the Quantum Fourier Transform can be parallelized to linear depth, we conjecture that an even simpler `staircase' circuit cannot be parallelized to less than linear depth, and might be used to prove that QNC < QP.

Moore, Cristopher; Moore, Cristopher; Nilsson, Martin

1998-01-01

219

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

220

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.

2009-01-01

 
 
 
 
221

Quantum computing in a piece of glass  

CERN Document Server

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

222

Quantum Fuzzy Sets: Blending Fuzzy Set Theory and Quantum Computation  

CERN Multimedia

In this article we investigate a way in which quantum computing can be used to extend the class of fuzzy sets. The core idea is to see states of a quantum register as characteristic functions of quantum fuzzy subsets of a given set. As the real unit interval is embedded in the Bloch sphere, every fuzzy set is automatically a quantum fuzzy set. However, a generic quantum fuzzy set can be seen as a (possibly entangled) superposition of many fuzzy sets at once, offering new opportunities for modeling uncertainty. After introducing the main framework of quantum fuzzy set theory, we analyze the standard operations of fuzzification and defuzzification from our viewpoint. We conclude this preliminary paper with a list of possible applications of quantum fuzzy sets to pattern recognition, as well as future directions of pure research in quantum fuzzy set theory.

Mannucci, M A

2006-01-01

223

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

2011-01-01

224

The potential of the quantum computer  

CERN Multimedia

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

225

Toward a superconducting quantum computer. Harnessing macroscopic quantum coherence.  

Science.gov (United States)

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 many new research opportunities open to physicists and engineers. PMID:20431256

Tsai, Jaw-Shen

2010-01-01

226

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

227

Fault-tolerant holonomic quantum computation  

CERN Multimedia

We explain how to combine holonomic quantum computation (HQC) with fault tolerant quantum error correction. This establishes the scalability of HQC, putting it on equal footing with other models of computation, while retaining the inherent robustness the method derives from its geometric nature.

Oreshkov, Ognyan; Lidar, Daniel A

2008-01-01

228

Clifford quantum computer and the Mathieu groups  

Digital Repository Infrastructure Vision for European Research (DRIVER)

One learned from Gottesman-Knill theorem that the Clifford model of quantum computing \\cite{Clark07} may be generated from a few quantum gates, the Hadamard, Phase and Controlled-Z gates, and efficiently simulated on a classical computer. We employ the group theoretical package GAP\\cite{GAP} for sim...

Planat, Michel

229

How fast can a quantum computer search?  

CERN Multimedia

This paper gives a simple proof of why a quantum computer, despite being in all possible states simultaneously, needs at least 0.707*sqrt(N) queries to retrieve a desired item from an unsorted list. The proof is refined to show that a quantum computer would need at least 0.785*sqrt(N) queries. The quantum search algorithm needs precisely this many queries. The proofs in this paper are simpler than that in other related papers.

Grover, L K

1998-01-01

230

Non-adiabatic holonomic quantum computation  

CERN Document Server

We develop a non-adiabatic generalization of holonomic quantum computation in which high-speed universal quantum gates can be realized by using non-Abelian geometric phases. We show how a universal non-adiabatic holonomic one-qubit gate can be implemented by utilizing optical transitions in a generic three-level $\\Lambda$ configuration. Our scheme opens up for the possibility to perform holonomic quantum computation on qubits characterized by short coherence times.

Sjöqvist, Erik; Hessmo, Björn; Johansson, Markus; Singh, Kuldip

2011-01-01

231

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

International Nuclear Information System (INIS)

[en] One-way quantum computing is an important and novel approach to quantum computation. By exploiting the existing particle-particle interactions, we report an 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.

2010-01-01

232

No quantum advantage for nonlocal computation  

CERN Multimedia

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

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

2006-01-01

233

Secure Multi-party Quantum Computation  

UK PubMed Central (United Kingdom)

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

Claude Cr Epeau; Daniel Gottesman; Adam Smith

234

Quantum computing using shortcuts through higher dimensions  

CERN Multimedia

Quantum computation offers the potential to solve fundamental yet otherwise intractable problems across a range of active fields of research. Recently, universal quantum-logic gate sets - the building blocks for a quantum computer - have been demonstrated in several physical architectures. A serious obstacle to a full-scale implementation is the sheer number of these gates required to implement even small quantum algorithms. Here we present and demonstrate a general technique that harnesses higher dimensions of quantum systems to significantly reduce this number, allowing the construction of key quantum circuits with existing technology. We are thereby able to present the first implementation of two key quantum circuits: the three-qubit Toffoli and the two-qubit controlled-unitary. The gates are realised in a linear optical architecture, which would otherwise be absolutely infeasible with current technology.

Lanyon, B P; Almeida, M P; Jennewein, T; Ralph, T C; Resch, K J; Pryde, G J; O'Brien, J L; Gilchrist, A; White, A G

2008-01-01

235

Quantum state diffusion, localization and computation  

International Nuclear Information System (INIS)

[en] 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 wavepackets occupying small regions of classical phase space. Following and extending the original proposal of Percival, Alber and Steimle (1995), 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 generation in quantum optics. Potential applications in atomic and molecular dynamics, quantum circuits and quantum computation are suggested. (author)

1995-09-21

236

Quantum computing and the entanglement frontier  

Science.gov (United States)

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

Preskill, John

2013-04-01

237

Quantum computer elements based on coupled quantum waveguides  

International Nuclear Information System (INIS)

[en] Possible applications of two weakly coupled quantum waveguides for quantum computation are considered. The approach is based on the resonance phenomena in the system. Two different qubits interpretations are described. Some single-qubit and two-qubits operations are realized in the framework of these interpretations

2005-07-03

238

KLM quantum computation with bosonic atoms  

CERN Multimedia

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

Popescu, S

2006-01-01

239

Molecular Realizations of Quantum Computing 2007  

CERN Multimedia

This book provides an overview on physical realizations of quantum computing by means of molecular systems. It will be useful for graduate students and researchers interested in quantum computing from different areas of physics, physical chemistry, informatics and computer science. Each chapter is written in a self-contained manner and hence can be accessible for researchers and graduate students with even less background in the topics.

Nakahara, Mikio

2009-01-01

240

Quantum Computer for Shor's Algorithm.  

Science.gov (United States)

We employ learning algorithms, optical and terahertz pulse shaping and ultrafast laser techniques to control quantum coherence in Rydberg atom wave packet quantum data registers. Our goals are to discover efficient ways to limit decoherence in these syste...

P. H. Bucksbaum

2004-01-01

 
 
 
 
241

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)

2005-01-01

242

Quantum computation with doped silicon cavities  

CERN Multimedia

We propose a quantum computer architecture involving substitutional donors in photonic-crystal silicon cavities and the optical initialization, manipulation, and detection processes already demonstrated in ion traps and other atomic systems. Our scheme considerably simplifies the implementation of the building blocks for the successful operation of silicon-based solid-state quantum computers, including positioning of the donors, realization of one- and two-qubit gates, initialization and readout of the qubits. Detailed consideration of the processes involved, using state-of-the-art values for the relevant parameters, indicates that this architecture might lead to errors per gate compatible with scalable quantum computation.

Abanto, M; Koiller, Belita; Filho, R L de Matos

2008-01-01

243

Concatenated codes for fault tolerant quantum computing  

Energy Technology Data Exchange (ETDEWEB)

The application of concatenated codes to fault tolerant quantum computing is discussed. We have previously shown that for quantum memories and quantum communication, a state can be transmitted with error {epsilon} provided each gate has error at most c{epsilon}. We show how this can be used with Shor`s fault tolerant operations to reduce the accuracy requirements when maintaining states not currently participating in the computation. Viewing Shor`s fault tolerant operations as a method for reducing the error of operations, we give a concatenated implementation which promises to propagate the reduction hierarchically. This has the potential of reducing the accuracy requirements in long computations.

Knill, E.; Laflamme, R.; Zurek, W.

1995-05-01

244

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.

2010-01-01

245

A Paraconsistent Approach to Quantum Computing  

CERN Document Server

We propose a method to define axiomatic theories for deterministic Turing machine computations. This method, when applied to axiomatizing computations in non-deterministic Turing machines, produces (in some cases) contradictory theories, therefore trivial theories (considering classical logic as the underlying logic). Substituting in such theories the underlying logic by the paraconsistent logic LFI1* permits us to define a new model of computation which we call paraconsistent Turing machine. We show that this initial model of computation allows the simulation of important quantum computing features. In particular, it allows to simulate the quantum solution of the well-known Deutsch's and Deutsch-Jozsa problems. However, we show that this initial model of computation does not adequately represent the notion of entangled states, a key feature in quantum computing. In this way, the construction is refined by defining a paraconsistent logic with a connective expressing entangled states in a logical fashion, and ...

Agudelo, Juan C

2008-01-01

246

Development and production of two explosive components using SCB technology  

Energy Technology Data Exchange (ETDEWEB)

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

Tarbell, W.W.; Sanchez, D.H. [Sandia National Labs., Albuquerque, NM (United States); Oestreich, M.L.; Prentice, J.W. [Pacific Scientific, Inc., Chandler, AZ (United States). Energy Dynamics Div.

1995-05-01

247

Quantum Field Symbolic Analog Computation Relativity Model  

CERN Document Server

It is natural to consider a quantum system in the continuum limit ofspace-time configuration. Incorporating also, Einstein's special relativity,leads to the quantum theory of fields. Non-relativistic quantum mechanics andclassical mechanics are special cases. By studying vacuum expectation values(Wightman functions W(n; z) where z denotes the set of n complex variables) ofproducts of quantum field operators in a separable Hilbert space, one is led tocomputation of holomorphy domains for these functions over the space of severalcomplex variables, C^n. Quantum fields were reconstructed from these functionsby Wightman. Computer automation has been accomplished as deterministic exactanalog computation (computation over "cells" in the continuum of C^n) forobtaining primitive extended tube domains of holomorphy. This is done in a onedimensional space plus one dimensional time model. By considering boundaryrelated semi-algebraic sets, some analytic extensions of these domains areobtained by non-deterministic methods...

Manoharan, A C

2000-01-01

248

Ramsey numbers and adiabatic quantum computing.  

UK PubMed Central (United Kingdom)

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 F; Clark L

2012-01-01

249

Pattern recognition on a quantum computer  

CERN Document Server

By means of a simple example it is demonstrated that the task of finding certain patterns in an otherwise random data set can be accomplished efficiently by a quantum computer. Employing the powerful tool of the quantum Fourier transform the quantum algorithm exhibits an exponential speed-up in comparison with its classical counterpart. PACS: 03.67.Lx, 03.67.-a, 42.30.Sy, 89.70.+c.

Schützhold, R

2003-01-01

250

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.

MIHAI OCTAVIAN DIMA; MARIAN PETRE; DORINA ARANGHEL; BOGDAN MITRICA; MIHNEA DULEA; CARMELIA PETRE; MIHAELA STOICA; MIRCEA UDREA; RODICA STERIAN; PAUL STERIAN; CHIVUTA RAMONA BADITA

2010-01-01

251

Quantum computing and the chaotic amplifier  

Energy Technology Data Exchange (ETDEWEB)

A new model for computations is considered which combines the quantum computer with the chaotic dynamics amplifier, based on the logistic map. We discuss the satisfiability problem and argue that the problem can, in principle, be solved in polynomial time if one uses the new model for computations.

Ohya, Masanori [Department of Information Sciences, Science University of Tokyo, Noda City, Chiba 278-8510 (Japan); Volovich, Igor V [Steklov Mathematical Institute, Gubkin Street 8, GSP-1, 117966, Moscow (Russian Federation)

2003-12-01

252

Decoherence and a simple quantum computer  

Energy Technology Data Exchange (ETDEWEB)

The authors analyze the effect of decoherence on the operation of part of a simple quantum computer. The results indicate that quantum bit coding techniques may be used to mitigate the effects of two sources of decoherence - amplitude damping and phase randomization.

Chuang, I.L.; Yamamoto, Y. [Stanford Univ., CA (United States); Laflamme, R. [Los Alamos National Lab., NM (United States)

1995-10-01

253

On non-adiabatic holonomic quantum computer  

Energy Technology Data Exchange (ETDEWEB)

Non-adiabatic non-Abelian geometric phase of spin-3/2 system in the rotating magnetic field is considered. Explicit expression for the corresponding effective non-Abelian gauge potential is obtained. This formula can be used for construction of quantum gates in quantum computations.

Margolin, A.E.; Strazhev, V.I.; Tregubovich, A.Ya

2003-06-16

254

Quantum Computing for Molecular Energy Simulations  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Over the last century, a large number of physical and mathematical developments paired with rapidly advancing technology have allowed the field of quantum chemistry to advance dramatically. However, the lack of computationally efficient methods for the exact simulation of quantum systems on classica...

Biamonte, Jacob; Whitfield, James D.; Aspuru-Guzik, Alan

255

Solid-State NMR Quantum Computer.  

Science.gov (United States)

We have obtained experimental evidence confirming each component of our proposed scheme for nuclear spin-based large scale quantum computation. Long decoherence time, individual accessibility and optical initialization/readout of nuclear spins are promisi...

Y. Yamamoto

2005-01-01

256

Investigation of Quantum Computing With Laughlin Quasiparticles.  

Science.gov (United States)

Laughlin quasiparticles of a gapped fractional quantum Hall (FQH) fluid, have been demonstrated to have fractional electric charge and anyonic braiding statistics. Topological computation with anyons has been proposed as the physical implementation of int...

V. J. Goldman

2007-01-01

257

Type II Quantum Computing With Superconductors.  

Science.gov (United States)

The results of this research centered on the experimental studies of a single superconducting persistent current qubit, the implementation of type-II algorithms using these qubits, and the proposal for adiabatic quantum computing using these qubits. The m...

T. P. Orlando

2004-01-01

258

Limitations of silicon devices for quantum computing  

Energy Technology Data Exchange (ETDEWEB)

There is considerable interest in the use of silicon devices as qubits for quantum computing. The existence of nuclear spin in a silicon isotope and the complex band structure of silicon are unfavourable for this application of silicon devices. (viewpoint)

Keyes, Robert W [IBM Research Division, Yorktown, NY 10598 (United States)

2004-04-28

259

Hidden symmetry detection on a quantum computer  

CERN Document Server

The fastest quantum algorithms (for the solution of classical computational problems) known so far are basically variations of the hidden subgroup problem f(U[x])=f(x). By means of some simple examples it is demonstrated that the detection of more general hidden (two-point) symmetries V{f(x),f(U[x])}=0 by a quantum computer can also admit an exponential speed-up. PACS: 03.67.Lx, 03.67.-a, 89.70.+c.

Schützhold, R

2003-01-01

260

2D cavity grid quantum computing  

Energy Technology Data Exchange (ETDEWEB)

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.

Helmer, Ferdinand; Delft, Jan von; Solano, Enrique; Marquardt, Florian [Arnold-Sommerfeld Center for Theoretical Physics, Center for NanoScience and Department of Physics, Ludwig-Maximilians Universitaet Muenchen (Germany); Mariantoni, Matteo [Walther-Meissner Institut, Bayerische Akademie der Wissenschaften, Garching b. Muenchen (Germany); Fowler, Austin [Institute for Quantum Computing, University of Waterloo, Waterloo, ON (Canada)

2008-07-01

 
 
 
 
261

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

262

Geometric Control Methods for Quantum Computations  

CERN Multimedia

The applications of geometric control theory methods on Lie groups and homogeneous spaces to the theory of quantum computations are investigated. These methods are shown to be very useful for the problem of constructing an universal set of gates for quantum computations: the well-known result that the set of all one-bit gates together with almost any one two-bit gate is universal is considered from the control theory viewpoint.

Giunashvili, Z

2004-01-01

263

Halting in quantum Turing computation  

CERN Document Server

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

264

Scaling considerations in ground state quantum computation  

Energy Technology Data Exchange (ETDEWEB)

We study design challenges associated with realizing a ground-state quantum computer. In such a computer, it is necessary that the energy gap between the ground state and first excited state be sufficiently large to prevent disruptive excitations. Here, an estimate of this gap is provided as a function of computer size. We then address the problem of detecting the output of a ground-state quantum computer. It is shown that the exponential detection difficulties that appear to be present at first can be overcome by small design changes.

Mizel, Ari; Mitchell, M.W.; Cohen, Marvin L.

1999-08-31

265

Decoherence Free Subspaces for Quantum Computation  

CERN Multimedia

Decoherence in quantum computers is formulated within the Semigroup approach. The error generators are identified with the generators of a Lie algebra. This allows for a comprehensive description which includes as a special case the frequently assumed spin-boson model. A general condition is presented for error-less quantum computation: decoherence-free subspaces are spanned by those states which are annihilated by all the generators. It is shown that these subspaces are stable to perturbations and moreover, that universal quantum oomputation is possible within them.

Lidar, D A; Whaley, K B

1998-01-01

266

Universal Blind Quantum Computing with Coherent States  

CERN Multimedia

The recently proposed Universal Blind Quantum Computation (UBQC) protocol allows a client to perform an arbitrary quantum computation on a remote server such that perfect privacy is guaranteed if the client is capable of producing random separable single qubit states. While from a theoretical point of view, this arguably constitutes the lowest possible quantum requirement, from a pragmatic point of view, generation of random single qubits which can be sent along long distances without loss is quite challenging and can never be achieved perfectly. In analogy to the concept of \\epsilon -security developed for other cryptographic protocols, we introduce here the concept of \\epsilon -blindness for UBQC, allowing us to characterize the robustness of the protocol to possible imperfections. Following this, we present a remote blind single qubit preparation protocol, by which a client with access to realistic quantum devices (such as coherent laser light) can in a delegated fashion prepare quantum states arbitrarily ...

Dunjko, Vedran; Leverrier, Anthony

2011-01-01

267

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 ba...

Nilesh BARDE; Deepak THAKUR; Pranav BARDAPURKAR; Sanjaykumar DALVI

268

Universal quantum computation on a semiconductor quantum wire network  

CERN Multimedia

Universal quantum computation (UQC) using Majorana fermions on a 2D topological superconducting (TS) medium remains an outstanding open problem. This is because the quantum gate set that can be generated by braiding of the Majorana fermions does not include any two-qubit gate and also the single-qubit $\\pi/8$ phase gate. In principle, it is possible to create these crucial extra gates using quantum interference of Majorana fermion currents. However, it is not clear if the motion of the various order parameter defects (vortices, domain walls, etc.), to which the Majorana fermions are bound in a TS medium, can be quantum coherent. We show that these obstacles can be overcome using a semiconductor quantum wire network in the vicinity of an $s$-wave superconductor, which renders UQC possible in principle.

Sau, Jay D; Sarma, S Das

2010-01-01

269

Demonstrating quantum algorithm acceleration with NMR quantum computer  

International Nuclear Information System (INIS)

[en] In general, a quantum circuit is constructed with elementary gates, such as one-qubit gates and CNOT gates. It is possible, however, to speed up the execution time of a given circuit by merging those elementary gates together into larger modules, such that the desired unitary matrix expressing the algorithm is directly implemented. We demonstrate this experimentally by taking the two-qubit Grover's algorithm implemented in NMR quantum computations, whose pseudopure state is generated by cyclic permutations of the state populations. This is the first exact time-optimal solution, to our knowledge, obtained for a self-contained quantum algorithm

2004-01-01

270

Robust dynamical decoupling for quantum computing and quantum memory.  

UK PubMed Central (United Kingdom)

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.

Souza AM; Alvarez GA; Suter D

2011-06-01

271

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.

2003-01-01

272

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

Science.gov (United States)

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

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

2010-03-01

273

Construction of a universal quantum computer  

International Nuclear Information System (INIS)

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

2009-01-01

274

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

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 informati...

Tempel, David Gabriel; Aspuru-Guzik, Alan

275

Computational Studies of Quantum Spin Systems  

CERN Multimedia

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

276

Simulated Quantum Computation of Global Minima  

CERN Multimedia

Finding the optimal solution to a complex optimization problem is of great importance in practically all fields of science, technology, technical design and econometrics. We demonstrate that a modified Grover's quantum algorithm can be applied to real problems of finding a global minimum using modest numbers of quantum bits. Calculations of the global minimum of simple test functions and Lennard-Jones clusters have been carried out on a quantum computer simulator using a modified Grover's algorithm. The number of function evaluations $N$ reduced from O(N) in classical simulation to $O(\\sqrt{N})$ in quantum simulation. We also show how the Grover's quantum algorithm can be combined with the classical Pivot method for global optimization to treat larger systems.

Zhu, Jing; Kais, Sabre

2009-01-01

277

Accelerating commutation circuits in quantum computer networks  

Science.gov (United States)

In a high speed and packet-switched quantum computer network, a packet routing delay often leads to traffic jams, becoming a severe bottleneck for speeding up the transmission rate. Based on the delayed commutation circuit proposed in Phys. Rev. Lett. 97, 110502 (2006), we present an improved scheme for accelerating network transmission. For two more realistic scenarios, we utilize the characteristic of a quantum state to simultaneously implement a data switch and transmission that makes it possible to reduce the packet delay and route a qubit packet even before its address is determined. This circuit is further extended to the quantum network for the transmission of the unknown quantum information. The analysis demonstrates that quantum communication technology can considerably reduce the processing delay time and build faster and more efficient packet-switched networks.

Jiang, Min; Huang, Xu; Chen, Xiaoping; Zhang, Zeng-ke

2012-12-01

278

Molecular quantum computer of neuron.  

UK PubMed Central (United Kingdom)

Living cells are controlled by quantum regulators in which the price of action of elementary operations approaches Planck's constant. The description of such systems is based on four principles: (1) minimal price of action principle for control; (2) principle of optimality; (3) minimum irreversibility principle; and (4) the principle of causality.

Liberman EA; Minina SV

1995-01-01

279

Universal dephasing control during quantum computation  

International Nuclear Information System (INIS)

[en] 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

2007-01-01

280

Quantum Computation with Vibrationally Excited Molecules  

CERN Multimedia

A new physical implementation for quantum computation is proposed. The vibrational modes of molecules are used to encode qubit systems. Global quantum logic gates are realized using shaped femtosecond laser pulses which are calculated applying optimal control theory. The scaling of the system is favourable, sources for decoherence can be eliminated. A complete set of one and two quantum gates is presented for a specific molecule. Detailed analysis regarding experimental realization shows that the structural resolution of today's pulse shapers is easiliy sufficient for pulse formation.

Tesch, C M; Tesch, Carmen M.; Vivie-Riedle, Regina de

2002-01-01

 
 
 
 
281

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.

2005-01-01

282

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.

2010-01-01

283

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

284

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

Science.gov (United States)

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

Tempel, David G.; Aspuru-Guzik, Alan

2012-01-01

285

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

UK PubMed Central (United Kingdom)

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

Tempel DG; Aspuru-Guzik A

2012-01-01

286

Mimicking Time Evolution within a Quantum Ground State: Ground-State Quantum Computation, Cloning, and Teleportation  

CERN Document Server

Ground-state quantum computers mimic quantum mechanical time evolution within the amplitudes of a time-independent quantum state. We explore the principles that constrain this mimicking. A no-cloning argument is found to impose strong restrictions. It is shown, however, that there is flexibility that can be exploited using quantum teleportation methods to improve ground-state quantum computer design.

Mizel, A

2003-01-01

287

Quantum computation with trapped polar molecules.  

UK PubMed Central (United Kingdom)

We propose a novel physical realization of a quantum computer. The qubits are electric dipole moments of ultracold diatomic molecules, oriented along or against an external electric field. Individual molecules are held in a 1D trap array, with an electric field gradient allowing spectroscopic addressing of each site. Bits are coupled via the electric dipole-dipole interaction. Using technologies similar to those already demonstrated, this design can plausibly lead to a quantum computer with greater, approximately > or = 10(4) qubits, which can perform approximately 10(5) CNOT gates in the anticipated decoherence time of approximately 5 s.

DeMille D

2002-02-01

288

Quantum computing of molecular magnet Mn12  

International Nuclear Information System (INIS)

Quantum computation in molecular magnets is studied by solving the time-dependent Schroedinger equation numerically. Following Leuenberger and Loss [Nature (London) 410, 789 (2001)], an external alternating magnetic field is applied to populate and manipulate a superposition of single-spin states in molecular magnet Mn12. The conditions to realize parallel recording and reading databases of Grover algorithms in molecular magnets are discussed in detail. It is found that an accurate time duration of the magnetic pulse as well as the discrete frequency spectrum and the amplitudes are required to design a quantum computing device.

2002-01-01

289

Quantum Computation by Adiabatic Evolution  

CERN Multimedia

We give a quantum algorithm for solving instances of the satisfiability problem, based on adiabatic evolution. The evolution of the quantum state is governed by a time-dependent Hamiltonian that interpolates between an initial Hamiltonian, whose ground state is easy to construct, and a final Hamiltonian, whose ground state encodes the satisfying assignment. To ensure that the system evolves to the desired final ground state, the evolution time must be big enough. The time required depends on the minimum energy difference between the two lowest states of the interpolating Hamiltonian. We are unable to estimate this gap in general. We give some special symmetric cases of the satisfiability problem where the symmetry allows us to estimate the gap and we show that, in these cases, our algorithm runs in polynomial time.

Farhi, E; Gutmann, S; Sipser, M; Farhi, Edward; Goldstone, Jeffrey; Gutmann, Sam; Sipser, Michael

2000-01-01

290

Computational studies of semiconductor quantum dots.  

UK PubMed Central (United Kingdom)

Light-absorption and luminescence processes in nano-sized materials can be modelled either by using computational approaches developed for quantum chemical calculations or by applying computational methods in the effective mass approximation (EMA) originally intended for solid-state theory studies. An overview of the theory and implementation of an ab initio correlation EMA method for studies of luminescence properties of embedded semiconductor quantum dots is presented. The applicability of the method and the importance of correlation effects are demonstrated by calculations on InGaAs/GaAs quantum-dot and quantum-ring samples. Ab initio and density functional theory (DFT) quantum chemical studies of optical transitions in freestanding silicon nanoclusters are also discussed. The accuracy of the optical gaps and oscillator strengths for silicon nanoclusters obtained using different computational methods is addressed. Changes in the cluster structures, excitation energies and band strengths upon excitation are reported. The role of the surface termination and functional groups on the silicon nanocluster surfaces is discussed.

Lehtonen O; Sundholm D; Vänskä T

2008-08-01

291

Theory of measurement-based quantum computing  

CERN Multimedia

In the study of quantum computation, data is represented in terms of linear operators which form a generalized model of probability, and computations are most commonly described as products of unitary transformations, which are the transformations which preserve the quality of the data in a precise sense. This naturally leads to "unitary circuit models", which are models of computation in which unitary operators are expressed as a product of "elementary" unitary transformations. However, unitary transformations can also be effected as a composition of operations which are not all unitary themselves: the "one-way measurement model" is one such model of quantum computation. In this thesis, we examine the relationship between representations of unitary operators and decompositions of those operators in the one-way measurement model. In particular, we consider different circumstances under which a procedure in the one-way measurement model can be described as simulating a unitary circuit, by considering the combi...

de Beaudrap, Jonathan Robert Niel

2008-01-01

292

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.

2010-01-01

293

Efficient quantum computing using coherent photon conversion  

CERN Multimedia

Single photons provide excellent quantum information carriers, but current schemes for preparing, processing and measuring them are inefficient. For example, down-conversion provides heralded, but randomly timed single photons, while linear-optics gates are inherently probabilistic. Here, we introduce a deterministic scheme for photonic quantum information. Our single, versatile process---coherent photon conversion---provides a full suite of photonic quantum processing tools, from creating high-quality heralded single- and multiphoton states free of higher-order imperfections to implementing deterministic multiqubit entanglement gates and high-efficiency detection. It fulfils all requirements for a scalable photonic quantum computing architecture. Using photonic crystal fibres, we experimentally demonstrate a four-colour nonlinear process usable for coherent photon conversion and show that current technology provides a feasible path towards deterministic operation. Our scheme, based on interacting bosonic fie...

Langford, N K; Prevedel, R; Munro, W J; Milburn, G J; Zeilinger, A

2011-01-01

294

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.

2003-01-01

295

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.

2011-01-01

296

Efficient quantum computing with weak measurements  

Energy Technology Data Exchange (ETDEWEB)

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.

Lund, A P, E-mail: a.lund@griffith.edu.au [Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland 4111 (Australia)

2011-05-15

297

Blind topological measurement-based quantum computation  

CERN Multimedia

We propose a protocol of blind topological measurement-based quantum computation. It is fault-tolerant, and the threshold is $4.3\\times10^{-3}$ for erroneous preparation of initial states, erroneous CZ gates, and erroneous local measurements. Our protocol is also fault-tolerant against the detectable qubit loss.

Morimae, Tomoyuki

2011-01-01

298

Adiabatic quantum computation and Deutsch's algorithm  

International Nuclear Information System (INIS)

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

2002-01-01

299

Quantum computation perspectives in medical image processing  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The need to increase the complexity of computational methods to produce improvements in functional performance, particularly in medical image processing applications, leads to find suitable physical devices. This chapter describes two ways of adapting the techniques of image processing to quantum de...

Rodrigues, Pedro; Ferreira, Manuel; Monteiro, João

300

Blind quantum computing with weak coherent pulses.  

UK PubMed Central (United Kingdom)

The universal blind quantum computation (UBQC) protocol [A. Broadbent, J. Fitzsimons, and E. Kashefi, in Proceedings of the 50th Annual IEEE Symposiumon Foundations of Computer Science (IEEE Computer Society, Los Alamitos, CA, USA, 2009), pp. 517-526.] allows a client to perform quantum computation on a remote server. In an ideal setting, perfect privacy is guaranteed if the client is capable of producing specific, randomly chosen single qubit states. While from a theoretical point of view, this may constitute the lowest possible quantum requirement, from a pragmatic point of view, generation of such states to be sent along long distances can never be achieved perfectly. We introduce the concept of ? blindness for UBQC, in analogy to the concept of ? security developed for other cryptographic protocols, allowing us to characterize the robustness and security properties of the protocol under possible imperfections. We also present a remote blind single qubit preparation protocol with weak coherent pulses for the client to prepare, in a delegated fashion, quantum states arbitrarily close to perfect random single qubit states. This allows us to efficiently achieve ?-blind UBQC for any ?>0, even if the channel between the client and the server is arbitrarily lossy.

Dunjko V; Kashefi E; Leverrier A

2012-05-01

 
 
 
 
301

Blind quantum computing with weak coherent pulses.  

Science.gov (United States)

The universal blind quantum computation (UBQC) protocol [A. Broadbent, J. Fitzsimons, and E. Kashefi, in Proceedings of the 50th Annual IEEE Symposiumon Foundations of Computer Science (IEEE Computer Society, Los Alamitos, CA, USA, 2009), pp. 517-526.] allows a client to perform quantum computation on a remote server. In an ideal setting, perfect privacy is guaranteed if the client is capable of producing specific, randomly chosen single qubit states. While from a theoretical point of view, this may constitute the lowest possible quantum requirement, from a pragmatic point of view, generation of such states to be sent along long distances can never be achieved perfectly. We introduce the concept of ? blindness for UBQC, in analogy to the concept of ? security developed for other cryptographic protocols, allowing us to characterize the robustness and security properties of the protocol under possible imperfections. We also present a remote blind single qubit preparation protocol with weak coherent pulses for the client to prepare, in a delegated fashion, quantum states arbitrarily close to perfect random single qubit states. This allows us to efficiently achieve ?-blind UBQC for any ?>0, even if the channel between the client and the server is arbitrarily lossy. PMID:23003133

Dunjko, Vedran; Kashefi, Elham; Leverrier, Anthony

2012-05-18

302

Distributed Quantum Computation Based-on Small Quantum Registers  

CERN Multimedia

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

303

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.

2002-01-01

304

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

305

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

306

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

307

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.

2007-01-01

308

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

309

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)

2002-01-01

310

Design constraints for nanometer scale quantum computers  

CERN Document Server

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

311

Some Notes on Quantum Information Theory and Emerging Computing Technologies  

CERN Multimedia

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

312

Epistemic quantum computational structures in a Hilbert-space environment  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Quantum computation and quantum computational logics are intrinsically connected with some puzzling epistemic problems. In the framework of a quantum computational approach to epistemic logic we investigate the following question: is it possible to interpret the basic epistemic operations (having in...

BELTRAMETTI, ENRICO; DALLA CHIARA, MARIA LUISA; GIUNTINI, ROBERTO; LEPORINI, ROBERTO; SERGIOLI, GIUSEPPE

313

Accuracy threshold for postselected quantum computation  

CERN Document Server

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

Aliferis, Panos; Preskill, John

2007-01-01

314

Quantum computation with phase drift errors  

CERN Document Server

We present results of numerical simulations of the evolution of an ion trap quantum computer made out of 18 ions which are subject to a sequence of nearly 15000 laser pulses in order to find the prime factors of N=15. We analyze the effect of random and systematic phase drift errors arising from inaccuracies in the laser pulses which induce over (under) rotation of the quantum state. Simple analytic estimates of the tolerance for the quality of driving pulses are presented. We examine the use of watchdog stabilization to partially correct phase drift errors concluding that, in the regime investigated, it is rather inefficient.

Miquel, C; Zurek, W H; Miquel, Cesar; Paz, Juan Pablo; Zurek, Wojciech Hubert

1997-01-01

315

An Introduction to Quantum Computing for Non-Physicists  

CERN Document Server

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

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

1998-01-01

316

Ensemble quantum computing by NMR spectroscopy  

Science.gov (United States)

A quantum computer (QC) can operate in parallel on all its possible inputs at once, but the amount of information that can be extracted from the result is limited by the phenomenon of wave function collapse. We present a new computational model, which differs from a QC only in that the result of a measurement is the expectation value of the observable, rather than a random eigenvalue thereof. Such an expectation value QC can solve nondeterministic polynomial-time complete problems in polynomial time. This observation is significant precisely because the computational model can be realized, to a certain extent, by NMR spectroscopy on macroscopic ensembles of quantum spins, namely molecules in a test tube. This is made possible by identifying a manifold of statistical spin states, called pseudo-pure states, the mathematical description of which is isomorphic to that of an isolated spin system. The result is a novel NMR computer that can be programmed much like a QC, but in other respects more closely resembles a DNA computer. Most notably, when applied to intractable combinatorial problems, an NMR computer can use an amount of sample, rather than time, which grows exponentially with the size of the problem. Although NMR computers will be limited by current technology to exhaustive searches over only 15 to 20 bits, searches over as much as 50 bits are in principle possible, and more advanced algorithms could greatly extend the range of applicability of such machines.

Cory, David G.; Fahmy, Amr F.; Havel, Timothy F.

1997-01-01

317

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

318

Nature computes: information processing in quantum dynamical systems.  

Science.gov (United States)

Nature intrinsically computes. It has been suggested that the entire universe is a computer, in particular, a quantum computer. To corroborate this idea we require tools to quantify the information processing. Here we review a theoretical framework for quantifying information processing in a quantum dynamical system. So-called intrinsic quantum computation combines tools from dynamical systems theory, information theory, quantum mechanics, and computation theory. We will review how far the framework has been developed and what some of the main open questions are. On the basis of this framework we discuss upper and lower bounds for intrinsic information storage in a quantum dynamical system. PMID:20887080

Wiesner, Karoline

2010-09-01

319

Nature computes: information processing in quantum dynamical systems.  

UK PubMed Central (United Kingdom)

Nature intrinsically computes. It has been suggested that the entire universe is a computer, in particular, a quantum computer. To corroborate this idea we require tools to quantify the information processing. Here we review a theoretical framework for quantifying information processing in a quantum dynamical system. So-called intrinsic quantum computation combines tools from dynamical systems theory, information theory, quantum mechanics, and computation theory. We will review how far the framework has been developed and what some of the main open questions are. On the basis of this framework we discuss upper and lower bounds for intrinsic information storage in a quantum dynamical system.

Wiesner K

2010-09-01

320

Decoherence in the Kane quantum computer  

International Nuclear Information System (INIS)

[en] Full text: The Kane design for a quantum computer in the solid-state has recently received a great deal of attention, and is the main area of study in the Special Research Centre for Quantum Computer Technology. In this paper, the adiabatic CNOT gate, as proposed by Goan and Milburn, is simulated exactly for a range of pulse sequence profiles. In the absence of de-phasing, the CNOT gate operation time (semi-optimized) was found to be 26 micro-seconds with error probability of 5 x 10-5. Simulation of the CNOT gate in the presence of a coherence destroying environmental coupling as well as gate noise was subsequently carried out for a range of de-coherence rates, and the effect on gate fidelity determined

2002-01-01

 
 
 
 
321

A quantum computation architecture using optical tweezers  

CERN Multimedia

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

322

Algorithmic Cooling and Scalable NMR Quantum Computers  

CERN Document Server

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

323

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

CERN Multimedia

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

324

Adiabatic Quantum Computing with Neutral Atoms  

Science.gov (United States)

We are developing, both theoretically and experimentally, a neutral atom qubit approach to adiabatic quantum computation. Using our microfabricated diffractive optical elements, we plan to implement an array of optical traps for cesium atoms and use Rydberg-dressed ground states to provide a controlled atom-atom interaction. We will develop this experimental capability to generate a two-qubit adiabatic evolution aimed specifically toward demonstrating the two-qubit quadratic unconstrained binary optimization (QUBO) routine.

Hankin, Aaron; Biedermann, Grant; Burns, George; Jau, Yuan-Yu; Johnson, Cort; Kemme, Shanalyn; Landahl, Andrew; Mangan, Michael; Parazzoli, L. Paul; Schwindt, Peter; Armstrong, Darrell

2012-06-01

325

Nuclear spin quantum computing with trapped ions  

CERN Document Server

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

326

The clock of a quantum computer  

International Nuclear Information System (INIS)

[en] If the physical agent (the 'pointer', or 'cursor', or 'clocking mechanism') that sequentially scans the T lines of a long computer program is a microscopic system, two quantum phenomena become relevant: spreading of the probability distribution of the pointer along the program lines, and scattering of the probability amplitude at the two endpoints of the physical space allowed for its motion. We show that the first effect determines an upper bound O(T-2/3) on the probability of finding the pointer exactly at the END line. By adding an adequate number ? of further empty lines ('telomers'), one can store the result of the computation up to the moment in which the pointer is scattered back into the active region. This leads to a less severe upper bound O(??/T) on the probability of finding the pointer either at the END line or within the additional empty lines. Our analysis is performed in the context of Feynman's model of quantum computation, the only model, to our knowledge, that explicitly includes a physically plausible quantum clocking mechanism in its considerations

2002-11-29

327

Analog analogue of a digital quantum computation  

International Nuclear Information System (INIS)

We solve a problem, which while not fitting into the usual paradigm, can be viewed as a quantum computation. Suppose we are given a quantum system with a Hamiltonian of the form Evertical strokew> is an unknown (normalized) state. The problem is to produce vertical strokew> by adding a Hamiltonian (independent of vertical strokew>) and evolving the system. If vertical strokew> is chosen uniformly at random we can (with high probability) produce vertical strokew> in a time proportional to N1/2/E. If vertical strokew> is instead chosen from a fixed, known orthonormal basis we can also produce vertical strokew> in a time proportional to N1/2/E and we show that this time is optimally short. This restricted problem is an analog analogue to Grover's algorithm, a computation on a conventional (exclamation) quantum computer that locates a marked item from an unsorted list of N items in a number of steps proportional to N1/2. copyright 1998 The American Physical Society.

1998-01-01

328

Analog analogue of a digital quantum computation  

Energy Technology Data Exchange (ETDEWEB)

We solve a problem, which while not fitting into the usual paradigm, can be viewed as a quantum computation. Suppose we are given a quantum system with a Hamiltonian of the form E{vert_bar}w{r_angle}{l_angle}w{vert_bar} where {vert_bar}w{r_angle} is an unknown (normalized) state. The problem is to produce {vert_bar}w{r_angle} by adding a Hamiltonian (independent of {vert_bar}w{r_angle}) and evolving the system. If {vert_bar}w{r_angle} is chosen uniformly at random we can (with high probability) produce {vert_bar}w{r_angle} in a time proportional to N{sup 1/2}/E. If {vert_bar}w{r_angle} is instead chosen from a fixed, known orthonormal basis we can also produce {vert_bar}w{r_angle} in a time proportional to N{sup 1/2}/E and we show that this time is optimally short. This restricted problem is an analog analogue to Grover{close_quote}s algorithm, a computation on a conventional (!) quantum computer that locates a marked item from an unsorted list of N items in a number of steps proportional to N{sup 1/2}. {copyright} {ital 1998} {ital The American Physical Society}

Farhi, E. [Center for Theoretical Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts02139 (United States); Gutmann, S. [Department of Mathematics, Northeastern University, Boston, Massachusetts02115 (United States)

1998-04-01

329

Chow's theorem and universal holonomic quantum computation  

CERN Multimedia

A theorem from control theory relating the Lie algebra generated by vector fields on a manifold to the controllability of the dynamical system is shown to apply to Holonomic Quantum Computation. Conditions for deriving the holonomy algebra are presented by taking covariant derivatives of the curvature associated to a non-Abelian gauge connection. When applied to the Optical Holonomic Computer, these conditions determine the holonomy group of the two-qubit interaction model to be $SU(2) \\times SU(2)$. In particular, a universal two-qubit logic gate is attainable for this model.

Lucarelli, D G

2002-01-01

330

Effect of Coulomb Interaction on GaAs Quantum Computer Performance.  

Science.gov (United States)

Interaction between the quantum bits strongly limits quantum computer performance while using large quantum registers. We investigated influence of such interaction for recently proposed quantum computer based on GaAs quantum dots with built-in barrier. O...

L. Fedichkin M. Yanchenko

2001-01-01

331

Hard chaos, quantum billiards, and quantum dot computers  

Energy Technology Data Exchange (ETDEWEB)

This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Research was performed in analytic and computational techniques for dealing with hard chaos, especially the powerful tool of cycle expansions. This work has direct application to the understanding of electrons in nanodevices, such as junctions of quantum wires, or in arrays of dots or antidots. We developed a series of techniques for computing the properties of quantum systems with hard chaos, in particular the flow of electrons through nanodevices. These techniques are providing the insight and tools to design computers with nanoscale components. Recent efforts concentrated on understanding the effects of noise and orbit pruning in chaotic dynamical systems. We showed that most complicated chaotic systems (not just those equivalent to a finite shift) will develop branch points in their cycle expansion. Once the singularity is known to exist, it can be removed with a dramatic increase in the speed of convergence of quantities of physical interest.

Mainieri, R.; Cvitanovic, P.; Hasslacher, B.

1996-07-01

332

Solving satisfiability problems by the ground-state quantum computer  

International Nuclear Information System (INIS)

[en] A quantum algorithm is proposed to solve the satisfiability (SAT) problems by the ground-state quantum computer. The scale of the energy gap of the ground-state quantum computer is analyzed for the 3-bit exact cover problem. The time cost of this algorithm on the general SAT problems is discussed

2005-01-01

333

Low cost igniter utilizing an SCB and titanium sub-hydride potassium perchlorate pyrotechnic.  

Science.gov (United States)

A conventional NSI (NASA standard initiator) normally employs a hot-wire ignition element to ignite ZPP (zirconium potassium perchlorate). With minor modifications to the interior of a header similar to an NSI device to accommodate an SCB (semiconductor b...

R. W. Bickes M. C. Grubelich J. K. Hartman C. B. McCampbell J. K. Churchill

1993-01-01

334

Nonadiabatic holonomic quantum computation in decoherence-free subspaces.  

UK PubMed Central (United Kingdom)

Quantum computation that combines the coherence stabilization virtues of decoherence-free subspaces and the fault tolerance of geometric holonomic control is of great practical importance. Some schemes of adiabatic holonomic quantum computation in decoherence-free subspaces have been proposed in the past few years. However, nonadiabatic holonomic quantum computation in decoherence-free subspaces, which avoids a long run-time requirement but with all the robust advantages, remains an open problem. Here, we demonstrate how to realize nonadiabatic holonomic quantum computation in decoherence-free subspaces. By using only three neighboring physical qubits undergoing collective dephasing to encode one logical qubit, we realize a universal set of quantum gates.

Xu GF; Zhang J; Tong DM; Sjöqvist E; Kwek LC

2012-10-01

335

Quantum computation and Shor{close_quote}s factoring algorithm  

Energy Technology Data Exchange (ETDEWEB)

Current technology is beginning to allow us to manipulate rather than just observe individual quantum phenomena. This opens up the possibility of exploiting quantum effects to perform computations beyond the scope of any classical computer. Recently Peter Shor discovered an efficient algorithm for factoring whole numbers, which uses characteristically quantum effects. The algorithm illustrates the potential power of quantum computation, as there is no known efficient classical method for solving this problem. The authors give an exposition of Shor{close_quote}s algorithm together with an introduction to quantum computation and complexity theory. They discuss experiments that may contribute to its practical implementation. {copyright} {ital 1996 The American Physical Society.}

Ekert, A.; Jozsa, R. [Clarendon Laboratory, University of Oxford Oxford OX1 3PU (United Kingdom)]|[School of Mathematics and Statistics, University of Plymouth, Plymouth, Devon PL4 8AA (United Kingdom)

1996-07-01

336

Quantum computation and Shor close-quote s factoring algorithm  

International Nuclear Information System (INIS)

Current technology is beginning to allow us to manipulate rather than just observe individual quantum phenomena. This opens up the possibility of exploiting quantum effects to perform computations beyond the scope of any classical computer. Recently Peter Shor discovered an efficient algorithm for factoring whole numbers, which uses characteristically quantum effects. The algorithm illustrates the potential power of quantum computation, as there is no known efficient classical method for solving this problem. The authors give an exposition of Shor close-quote s algorithm together with an introduction to quantum computation and complexity theory. They discuss experiments that may contribute to its practical implementation. copyright 1996 The American Physical Society

1996-01-01

337

Applicability of Rydberg atoms to quantum computers  

Energy Technology Data Exchange (ETDEWEB)

The applicability of Rydberg atoms to quantum computers is examined from an experimental point of view. In many recent theoretical proposals, the excitation of atoms into highly excited Rydberg states was considered as a way to achieve quantum entanglement in cold atomic ensembles via dipole-dipole interactions that could be strong for Rydberg atoms. Appropriate conditions to realize a conditional quantum phase gate have been analysed. We also present the results of modelling experiments on microwave spectroscopy of single- and multi-atom excitations at the one-photon 37S{sub 1/2} {yields} 37P{sub 1/2} and two-photon 37S{sub 1/2} {yields} 38S{sub 1/2} transitions in an ensemble of a few sodium Rydberg atoms. The microwave spectra were investigated for various final states of the ensemble initially prepared in its ground state. The results may be applied to the studies on collective laser excitation of ground-state atoms aiming to realize quantum gates.

Ryabtsev, Igor I; Tretyakov, Denis B; Beterov, Ilya I [Institute of Semiconductor Physics, Prospekt Lavrentyeva 13, 630090 Novosibirsk (Russian Federation)

2005-01-28

338

Applicability of Rydberg atoms to quantum computers  

International Nuclear Information System (INIS)

The applicability of Rydberg atoms to quantum computers is examined from an experimental point of view. In many recent theoretical proposals, the excitation of atoms into highly excited Rydberg states was considered as a way to achieve quantum entanglement in cold atomic ensembles via dipole-dipole interactions that could be strong for Rydberg atoms. Appropriate conditions to realize a conditional quantum phase gate have been analysed. We also present the results of modelling experiments on microwave spectroscopy of single- and multi-atom excitations at the one-photon 37S1/2 ? 37P1/2 and two-photon 37S1/2 ? 38S1/2 transitions in an ensemble of a few sodium Rydberg atoms. The microwave spectra were investigated for various final states of the ensemble initially prepared in its ground state. The results may be applied to the studies on collective laser excitation of ground-state atoms aiming to realize quantum gates.

2005-01-28

339

Macroscopic models for quantum systems and computers  

International Nuclear Information System (INIS)

We present examples of macroscopic systems entailing a quantum mechanical structure. One of our examples has a structure which is isomorphic to the spin structure for a spin 1/2 and another system entails a structure isomorphic to the structure of two spin 1/2 in the entangled singlet state. We elaborate this system by showing that an arbitrary tensor product state representing two entangled qubits can be described in a complete way by a specific internal constraint between the ray or density states of the two qubits, which describes the behavior of the state of one of the spins if measurements are executed on the other spin. Since any n-qubit unitary operation can be decomposed into 2-qubit gates and unary operations, we argue that our representation of 2-qubit entanglement contributes to a better understanding of the role of n-qubit entanglement in quantum computation. We illustrate our approach on two 2-qubit algorithms proposed by Deutsch, respectively Arvind et al. One of the advantages of the 2-qubit case besides its relative simplicity is that it allows for a nice geometrical representation of entanglement, which contributes to a more intuitive grasp of what is going on in a 2-qubit quantum computation

2007-01-01

340

Macroscopic models for quantum systems and computers  

Energy Technology Data Exchange (ETDEWEB)

We present examples of macroscopic systems entailing a quantum mechanical structure. One of our examples has a structure which is isomorphic to the spin structure for a spin 1/2 and another system entails a structure isomorphic to the structure of two spin 1/2 in the entangled singlet state. We elaborate this system by showing that an arbitrary tensor product state representing two entangled qubits can be described in a complete way by a specific internal constraint between the ray or density states of the two qubits, which describes the behavior of the state of one of the spins if measurements are executed on the other spin. Since any n-qubit unitary operation can be decomposed into 2-qubit gates and unary operations, we argue that our representation of 2-qubit entanglement contributes to a better understanding of the role of n-qubit entanglement in quantum computation. We illustrate our approach on two 2-qubit algorithms proposed by Deutsch, respectively Arvind et al. One of the advantages of the 2-qubit case besides its relative simplicity is that it allows for a nice geometrical representation of entanglement, which contributes to a more intuitive grasp of what is going on in a 2-qubit quantum computation.

Aerts, Diederik [Center Leo Apostel, Vrije Universiteit Brussel, Krijgskundestraat 33, 1160 Brussels (Belgium); Czachor, Marek [Katedra Fizyki Teoretycznej i Metod Matematycznych, Politechnika Gdanska, 80-952 Gdansk (Poland); Dehaene, Jeroen [SISTA, Department of Electrical Engineering (ESAT), Faculty of Engineering, Katholieke Universiteit Leuven, 3000 Leuven (Belgium); Moor, Bart De [SISTA, Department of Electrical Engineering (ESAT), Faculty of Engineering, Katholieke Universiteit Leuven, 3000 Leuven (Belgium); D' Hooghe, Bart [Center Leo Apostel, Vrije Universiteit Brussel, Krijgskundestraat 33, 1160 Brussels (Belgium)

2007-05-15

 
 
 
 
341

An Overview of Quantum Computing for Technology Managers  

CERN Document Server

Faster algorithms, novel cryptographic mechanisms, and alternative methods of communication become possible when the model underlying information and computation changes from a classical mechanical model to a quantum mechanical one. Quantum algorithms perform a select set of tasks vastly more efficiently than any classical algorithm, but for many tasks it has been proved that quantum algorithms provide no advantage. The breadth of quantum computing applications is still being explored. Major application areas include security and the many fields that would benefit from efficient quantum simulation. The quantum information processing viewpoint provides insight into classical algorithmic issues as well as a deeper understanding of entanglement and other non-classical aspects of quantum physics. This overview is aimed at technology managers who wish to gain a high level understanding of quantum information processing, particularly quantum computing.

Rieffel, Eleanor G

2008-01-01

342

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

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 compu...

Belaga, Edward G.; Grucker, Daniel

343

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

CERN Multimedia

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

344

Quantum computing with atomic Josephson junction arrays  

International Nuclear Information System (INIS)

We present a quantum computing scheme with atomic Josephson junction arrays. The system consists of a small number of atoms with three internal states and trapped in a far-off-resonant optical lattice. Raman lasers provide the 'Josephson' tunneling, and the collision interaction between atoms represent the 'capacitive' couplings between the modes. The qubit states are collective states of the atoms with opposite persistent currents. This system is closely analogous to the superconducting flux qubit. Single-qubit quantum logic gates are performed by modulating the Raman couplings, while two-qubit gates result from a tunnel coupling between neighboring wells. Readout is achieved by tuning the Raman coupling adiabatically between the Josephson regime to the Rabi regime, followed by a detection of atoms in internal electronic states. Decoherence mechanisms are studied in detail promising a high ratio between the decoherence time and the gate operation time.

2003-01-01

345

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

346

Trapped-ion qutrit spin molecule quantum computer  

CERN Multimedia

We present a qutrit quantum computer design using trapped ions in the presence of a magnetic field gradient. The magnetic field gradient induces a "spin-spin" type coupling, similar to the J-coupling observed in molecules, between the qutrits which allows conditional quantum logic to take place. We describe in some detail, how one can execute specific one and two qutrit quantum gates, required for universal qutrit quantum computing.

McHugh, D

2005-01-01

347

One-way quantum computing in the optical frequency comb.  

Science.gov (United States)

One-way quantum computing allows any quantum algorithm to be implemented easily using just measurements. The difficult part is creating the universal resource, a cluster state, on which the measurements are made. We propose a scalable method that uses a single, multimode optical parametric oscillator (OPO). The method is very efficient and generates a continuous-variable cluster state, universal for quantum computation, with quantum information encoded in the quadratures of the optical frequency comb of the OPO. PMID:18851426

Menicucci, Nicolas C; Flammia, Steven T; Pfister, Olivier

2008-09-22

348

Trapped-ion qutrit spin molecule quantum computer  

International Nuclear Information System (INIS)

[en] We present a qutrit quantum computer design using trapped ions in the presence of a magnetic field gradient. The magnetic field gradient induces a 'spin-spin' type coupling, similar to the J-coupling observed in molecules, between the qutrits which allows conditional quantum logic to take place. We describe in some detail how one can execute specific one and two qutrit quantum gates, required for universal qutrit quantum computing

2005-01-01

349

Gate errors in solid-state quantum-computer architectures  

International Nuclear Information System (INIS)

[en] We theoretically consider possible errors in solid-state quantum computation due to the interplay of the complex solid-state environment and gate imperfections. In particular, we study two examples of gate operations in the opposite ends of the gate speed spectrum, an adiabatic gate operation in electron-spin-based quantum dot quantum computation and a sudden gate operation in Cooper-pair-box superconducting quantum computation. We evaluate quantitatively the nonadiabatic operation of a two-qubit gate in a two-electron double quantum dot. We also analyze the nonsudden pulse gate in a Cooper-pair-box-based quantum-computer model. In both cases our numerical results show strong influences of the higher excited states of the system on the gate operation, clearly demonstrating the importance of a detailed understanding of the relevant Hilbert-space structure on the quantum-computer operations

2002-01-01

350

From Cbits to Qbits Teaching computer scientists quantum mechanics  

CERN Multimedia

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

351

Computing with quantum knots: Marjorana modes, non-Abelian anyons, and topological quantum computation  

Energy Technology Data Exchange (ETDEWEB)

I will discuss the revolutionary new concept of topological quantum computation, which is fault-tolerant at the hardware level with no need, in principle, of any quantum error correction protocols. Errors simply do not occur since the physical qubits and the computation steps are protected against decoherence by non-local topological correlations in the underlying physical system. The key idea is non-Abelian statistics of the quasiparticles (called 'anyons' as opposed to fermions or bosons), where the space-time braiding of the anyons around each other, i.e. quantum 'knots', form topologically protected quantum gate operations. I will describe in detail the theoretical principles guiding the experimental search for the appropriate topological phases of matter where such non-Abelian anyons, which are low-dimensional solid state versions of the elusive and exotic Majorana fermions hypothesized seventy-five years ago, may exist. I will critically discuss the recent experimental claims of observing the Majorana modes in semiconductor nanowire structures following earlier theoretical proposals, outlining the future developments which would be necessary to eventually build a topological quantum computer.

Das Sarma, Sankar [University of Maryland

2012-10-03

352

A quantum neural network computes its own relative phase  

Science.gov (United States)

Complete characterization of the state of a quantum system made up of subsystems requires determination of relative phase, because of interference effects between the subsystems. For a system of qubits used as a quantum computer this is especially vital, because the entanglement, which is the basis for the quantum advantage in computing, depends intricately on phase. We present here a first step towards that determination, in which we use a two-qubit quantum system as a quantum neural network, which is trained to compute and output its own relative phase.

Behrman, Elizabeth

2013-03-01

353

Quantum Computation: Particle and Wave Aspects of Algorithms  

CERN Document Server

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

Patel, Apoorva

2011-01-01

354

High Fidelity Adiabatic Quantum Computation via Dynamical Decoupling  

CERN Document Server

We introduce high-order dynamical decoupling strategies for open system adiabatic quantum computation. Our numerical results demonstrate that a judicious choice of high-order dynamical decoupling method, in conjunction with an encoding which allows computation to proceed alongside decoupling, can dramatically enhance the fidelity of adiabatic quantum computation in spite of decoherence.

Quiroz, Gregory

2012-01-01

355

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.

2002-01-01

356

Procrastination in Quantum Coding and Computation  

UK PubMed Central (United Kingdom)

When storing, communicating, or processing information,we are often forced to make decisions earlier than wewould like. Perhaps we can only afford to store a subsetof our data, and must choose what to discard long beforewe know which parts are truly important. Or perhaps weonly have time to compute responses for a certain numberof scenarios, and must decide which to prepare before thesituation we face becomes into focus. This paper examineswhether quantum resources can help us to delay those decisionsuntil they can be made in an informed manner.

Paul Fitzpatrick

357

Quantum Computational Complexity in the Presence of Closed Timelike Curves  

CERN Multimedia

Quantum computation with quantum data that can traverse closed timelike curves represents a new physical model of computation. We argue that a model of quantum computation in the presence of closed timelike curves can be formulated which represents a valid quantification of resources given the ability to construct compact regions of closed timelike curves. The notion of self-consistent evolution for quantum computers whose components follow closed timelike curves, as pointed out by Deutsch [Phys. Rev. D {\\bf 44}, 3197 (1991)], implies that the evolution of the chronology respecting components which interact with the closed timelike curve components is nonlinear. We demonstrate that this nonlinearity can be used to efficiently solve computational problems which are generally thought to be intractable. In particular we demonstrate that a quantum computer which has access to closed timelike curve qubits can solve NP-complete problems with only a polynomial number of quantum gates.

Bacon, D J

2003-01-01

358

Copying quantum computer makes NP-complete problems tractable  

UK PubMed Central (United Kingdom)

Under the assumption that a quantum computer can exactly copy quantumsuperpositions, we show that NP-complete problems can be solved probabilisticallyin polynomial time. We also propose two methods that couldpotentially allow to avoid the use of a quantum copymachine.Supported by the Academy of Finland under grant 14047.To be presented at MCU'98, March 1998, Metz, France.TUCS Research GroupTheory Group: Mathematical Methods in Computer Science1 IntroductionIt was conjectured by R. Feynman [5] in 1982 that it may be impossible tosimulate quantum physical phenomena by an ordinary computer without anexponential slowdown in the efficiency of the simulation. In his work, Feynmanalso suggested that the slowdown could be avoided by allowing thecomputer run according to rules of quantum mechanics, thus introducingthe idea of quantum computer. However, quantum computation remainedquite a marginal phenomenon in the theory of computing until 1994, whenPeter W. Shor discovered ...

Mika Hirvensalo; Turku Centre; Computer Science

359

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2003-12-01

360

Quantum computing accelerator I/O : LDRD 52750 final report  

International Nuclear Information System (INIS)

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

2003-01-01

 
 
 
 
361

An introduction to many worlds in quantum computation  

CERN Multimedia

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

362

Adiabatic Quantum Computation with Neutral Atoms  

Science.gov (United States)

We are implementing a new platform for adiabatic quantum computation (AQC)footnotetext E. Farhi, et al. Science 292, 472 (2000) based on trapped neutral atoms whose coupling is mediated by the dipole-dipole interactions of Rydberg states. Ground state cesium atoms are dressed by laser fields in a manner conditional on the Rydberg blockade mechanism,footnotetextS. Rolston, et al. Phys. Rev. A, 82, 033412 (2010)^,footnotetextT. Keating, et al. arXiv:1209.4112 (2012) thereby providing the requisite entangling interactions. As a benchmark we study a Quadratic Unconstrained Binary Optimization (QUBO) problem whose solution is found in the ground state spin configuration of an Ising-like model.[4pt] In collaboration with Lambert Parazzoli, Sandia National Laboratories; Aaron Hankin, Center for Quantum Information and Control (CQuIC), University of New Mexico; James Chin-Wen Chou, Yuan-Yu Jau, Peter Schwindt, Cort Johnson, and George Burns, Sandia National Laboratories; Tyler Keating, Krittika Goyal, and Ivan Deutsch, Center for Quantum Information and Control (CQuIC), University of New Mexico; and Andrew Landahl, Sandia National Laboratories.

Biedermann, Grant

2013-03-01

363

Control aspects of quantum computing using pure and mixed states.  

Science.gov (United States)

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

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

2012-10-13

364

Control aspects of quantum computing using pure and mixed states.  

UK PubMed Central (United Kingdom)

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

Schulte-Herbrüggen T; Marx R; Fahmy A; Kauffman L; Lomonaco S; Khaneja N; Glaser SJ

2012-10-01

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  

CERN Document Server

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  

CERN Multimedia

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

Buckyball Quantum Computer: Realization of a Quantum Gate  

CERN Document Server

We have studied a system composed by two endohedral fullerene molecules. We have found that this system can be used as good candidate for the realization of Quantum Gates Each of these molecules encapsules an atom carrying a spin,therefore they interact through the spin dipole interaction. We show that a phase gate can be realized if we apply on each encased spin static and time dependent magnetic field. We have evaluated the operational time of a $\\pi$-phase gate, which is of the order of ns. We made a comparison between the theoretical estimation of the gate time and the experimental decoherence time for each spin. The comparison shows that the spin relaxation time is much larger than the $\\pi$-gate operational time. Therefore, this indicates that, during the decoherence time, it is possible to perform some thousands of quantum computational operations. Moreover, through the study of concurrence, we get very good results for the entanglement degree of the two-qubit system. This finding opens a new avenue fo...

Garelli, M S

2005-01-01

369

Quantum Computing in Condensed Matter Systems.  

Science.gov (United States)

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

370

Preparing projected entangled pair states on a quantum computer.  

Science.gov (United States)

We present a quantum algorithm to prepare injective projected entangled pair states (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's parent Hamiltonian. PMID:22540445

Schwarz, Martin; Temme, Kristan; Verstraete, Frank

2012-03-13

371

Preparing projected entangled pair states on a quantum computer.  

UK PubMed Central (United Kingdom)

We present a quantum algorithm to prepare injective projected entangled pair states (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's parent Hamiltonian.

Schwarz M; Temme K; Verstraete F

2012-03-01

372

The limits of quantum computers; Die Grenzen der Quantencomputer  

Energy Technology Data Exchange (ETDEWEB)

Future computers, which work with quantum bits, would indeed solve some special problems extremely fastly, but for the most problems the would hardly be superior to contemporary computers. This knowledge could manifest a new fundamental physical principle.

Aaronson, S. [Massachusetts Inst. of Tech., Cambridge, MA (United States)

2008-07-15

373

Topological quantum computation--from basic concepts to first experiments.  

UK PubMed Central (United Kingdom)

Quantum computation requires controlled engineering of quantum states to perform tasks that go beyond those possible with classical computers. Topological quantum computation aims to achieve this goal by using non-Abelian quantum phases of matter. Such phases allow for quantum information to be stored and manipulated in a nonlocal manner, which protects it from imperfections in the implemented protocols and from interactions with the environment. Recently, substantial progress in this field has been made on both theoretical and experimental fronts. We review the basic concepts of non-Abelian phases and their topologically protected use in quantum information processing tasks. We discuss different possible realizations of these concepts in experimentally available solid-state systems, including systems hosting Majorana fermions, their recently proposed fractional counterparts, and non-Abelian quantum Hall states.

Stern A; Lindner NH

2013-03-01

374

Algebras and universal quantum computations with higher dimensional systems  

CERN Multimedia

Here is discussed application of the Weyl pair to construction of universal set of quantum gates for high-dimensional quantum system. An application of Lie algebras (Hamiltonians) for construction of universal gates is revisited first. It is shown next, how for quantum computation with qubits can be used two-dimensional analog of this Cayley-Weyl matrix algebras, i.e. Clifford algebras, and discussed well known applications to product operator formalism in NMR, Jordan-Wigner construction in fermionic quantum computations. It is introduced universal set of quantum gates for higher dimensional system (``qudit''), as some generalization of these models. Finally it is briefly mentioned possible application of such algebraic methods to design of quantum processors (programmable gates arrays) and discussed generalization to quantum computation with continuous variables.

Vlasov, A Yu

2002-01-01

375

Quantum computer with mixed states and four-valued logic  

Energy Technology Data Exchange (ETDEWEB)

In this paper we discuss a model of quantum computer in which a state is an operator of density matrix and gates are general quantum operations, not necessarily unitary. A mixed state (operator of density matrix) of n two-level quantum systems is considered as an element of 4{sup n}-dimensional operator Hilbert space (Liouville space). It allows us to use a quantum computer model with four-valued logic. The gates of this model are general superoperators which act on n-ququat state. Ququat is a quantum state in a four-dimensional (operator) Hilbert space. Unitary two-valued logic gates and quantum operations for an n-qubit open system are considered as four-valued logic gates acting on n-ququats. We discuss properties of quantum four-valued logic gates. In the paper we study universality for quantum four-valued logic gates. (author)

Tarasov, Vasily E. [Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow (Russian Federation)]. E-mail: tarasov@theory.sinp.msu.ru

2002-06-28

376

Quantum computer with mixed states and four-valued logic  

International Nuclear Information System (INIS)

[en] In this paper we discuss a model of quantum computer in which a state is an operator of density matrix and gates are general quantum operations, not necessarily unitary. A mixed state (operator of density matrix) of n two-level quantum systems is considered as an element of 4n-dimensional operator Hilbert space (Liouville space). It allows us to use a quantum computer model with four-valued logic. The gates of this model are general superoperators which act on n-ququat state. Ququat is a quantum state in a four-dimensional (operator) Hilbert space. Unitary two-valued logic gates and quantum operations for an n-qubit open system are considered as four-valued logic gates acting on n-ququats. We discuss properties of quantum four-valued logic gates. In the paper we study universality for quantum four-valued logic gates. (author)

2002-06-28

377

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

International Nuclear Information System (INIS)

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

2001-01-01

378

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 decompositio...

Alexis De Vos; Stijn De Baerdemacker

379

A quantum computer based on recombination processes in microelectronic devices  

International Nuclear Information System (INIS)

[en] 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

2005-01-01

380

Universal Quantum Computation with Continuous-Variable Abelian Anyons  

CERN Document Server

We describe how continuous-variable abelian anyons, created on the surface of a continuous-variable analogue of Kitaev's lattice model can be utilized for quantum computation. In particular, we derive protocols for the implementation of quantum gates using topological operations. We find that the topological operations alone are insufficient for universal quantum computation which leads us to study additional non-topological operations such as offline squeezing and single-mode measurements. It is shown that these in conjunction with a non-Gaussian element allow for universal quantum computation using continuous-variable abelian anyons.

Milne, Darran F; van Loock, Peter

2011-01-01

 
 
 
 
381

Finding Matches between Two Databases on a Quantum Computer  

CERN Multimedia

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

Heiligman, M

2000-01-01

382

On the "principle of the quantumness", the quantumness of Relativity, and the computational grand-unification  

CERN Multimedia

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

383

Could one make a diamond-based quantum computer?  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We assess routes to a diamond-based quantum computer, where we specifically look towards scalable devices, with at least 10 linked quantum gates. Such a computer should satisfy the deVincenzo rules and might be used at convenient temperatures. The specific examples that we examine are based on the o...

Stoneham, AM; Harker, AH; Morley, GW

384

Parallel computing and quantum simulations/011  

Energy Technology Data Exchange (ETDEWEB)

Our goal was to investigate the suitability of parallel supercomputer architectures for Quantum Monte Carlo (QMC). Because QMC allows one to study the properties of ions and electrons in a solid, it has important applications to condensed matter physics, chemistry, and materials science. research plan was to Our specific 1. Adapt quantum simulation codes which were highly optimized for vector supercomputers to run on the Intel Hypercube and Thinking Machines CM--5. 2. Identify architectural bottlenecks in communication, floating point computation, and node memory. Determine scalability with number of nodes. 3. Identify algorithmic changes required to take advantage of current and prospective architectures. We have made significant progress towards these goals. We explored implementations of the p4 parallel programming system and the Message Passing Interface (MPI) libraries to run ``world-line`` and ``determinant`` QMC and Molecular Dynamics simulations on both workstation clusters (HP, Spare, AIX, Linux) and massively parallel supercomputers (Intel iPSC1860, Meiko CS-2, BM SP-X, Intel Paragon). We addressed issues of the efficiency of parallelization as a function of distribution of the problem over the nodes and the length scale of the interactions between particles. Both choices influence he frequency of inter-node communication and the size of messages passed. We found that using the message-passing paradigm on an appropriate machine (e.g., the ntel iPSC/860) an essentially linear speedup could be obtained.

Alder, B., LLNL

1998-03-01

385

Magnetic qubits as hardware for quantum computers  

International Nuclear Information System (INIS)

[en] 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 vertical bar-0> and vertical bar-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, vertical bar-0>, and antisymmetric, vertical bar-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, ?, between the states vertical bar-0> and vertical bar-1>. The gap ? 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 hardware. (author)

2000-01-01

386

Scaling of Decoherence Effects in Quantum Computers  

CERN Document Server

The scaling of decoherence rates with the number of q-bits is studied for a simple quantum computer model. Two state q-bits are localised around well-separated positions via trapping potentials, but vibrational motion of q-bits centre of mass motion occurs. Coherent one and two q-bit gating processes are controlled by external classical fields and facilitated by a high Q cavity mode. Decoherence due to q-bit and cavity mode coupling to a bath of spontaneous emission modes, cavity decay modes and to the collective vibrational modes is treated. A non-Markovian treatment of the short time behaviour of the fidelity is presented, enabling time scales for decoherence to be determined, together with their dependence on q-bit number for the case where the q-bit/cavity mode system is in a pure state and the baths are in thermal states.

Dalton, B J

2002-01-01

387

Quantum computing with magnetically interacting atoms  

CERN Multimedia

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

Possibilities of a classical alternative to a quantum computer  

CERN Document Server

The dramatic increase in the efficiency of a quantum computer over a classical computer, raises a natural question asking, how much of this success could be attributed to its quantum nature and how much to its probabilistic content. To highlight this issue, we put forward the novel idea of a possible chemical computer driven by reaction-diffusion (RD) processes based on a probabilistic but classical approach. Such computers, obeying non-equilibrium statistical mechanics, can describe superpositions of empty and filled states with certain probabilities. With these {probit} states serving as computational basis states, such RD computers with operations satisfying a necessary semi-group property could mimic some well known quantum logic gates and carry out teleportation like procedure using entangled states, believed to be a prerogative of the quantum world. Moreover, assuming a nonlinear extension the RD computers could be used for cloning of arbitrary states, which is a famous forbidden operation in standard q...

Kundu, A

2003-01-01

389

Fundamentals of universality in one-way quantum computation  

CERN Multimedia

We build a framework allowing for a systematic investigation of the issue: "Which quantum states are universal resources for one-way quantum computation?" We start by re-examining what is exactly meant by "universality" in quantum computation, and what the implications are for universal one-way quantum computation. Given the framework of a measurement-based quantum computer, where quantum information is processed by local operations only, the most general universal one-way quantum computer is one which is capable of accepting arbitrary classical inputs and producing arbitrary quantum outputs--we refer to this property as CQ-universality. We then show that a systematic study of CQ-universality in one-way quantum computation is possible by identifying entanglement features that must be present in every universal resource. These insights are used to identify several states as being not universal, such as 1D cluster states, W states, and ground states of non-critical 1D spin systems. Our criteria are strengthened...

Van den Nest, M; Dür, W; Miyake, A

2007-01-01

390

Emergence of quantum chaos in the quantum computer core and how to manage it  

UK PubMed Central (United Kingdom)

We study the standard generic quantum computer model, which describes a realistic isolated quantum computer with fluctuations in individual qubit energies and residual short-range interqubit couplings. It is shown that in the limit where the fluctuations and couplings are small compared to the one-qubit energy spacing, the spectrum has a band structure, and a renormalized Hamiltonian is obtained which describes the eigenstate properties inside one band. Studies are concentrated on the central band of the computer ("core") with the highest density of states. We show that above a critical interqubit coupling strength, quantum chaos sets in, leading to a quantum ergodicity of the computer eigenstates. In this regime the ideal qubit structure disappears, the eigenstates become complex, and the operability of the computer is quickly destroyed. We confirm that the quantum chaos border decreases only linearly with the number of qubits n, although the spacing between multiqubit states drops exponentially with n. The investigation of time evolution in the quantum computer shows that in the quantum chaos regime, an ideal (noninteracting) state quickly disappears, and exponentially many states become mixed after a short chaotic time scale for which the dependence on system parameters is determined. Below the quantum chaos border an ideal state can survive for long times, and an be used for computation. The results show that a broad parameter region does exist where the efficient operation of a quantum computer is possible.

Georgeot B; Shepelyansky DL

2000-11-01

391

Elementary Particles as Gates for Universal Quantum Computation  

CERN Document Server

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

392

Quantum computation with quantum-dot spin qubits inside a cavity  

International Nuclear Information System (INIS)

[en] Universal set of quantum gates are realized from quantum-dot spin qubits inside a cavity via two-channel Raman interactions. Individual addressing and effective switch of the cavity mediated interaction are directly possible here. This simple realization of all wanted interaction for selective qubits makes current scenario more suitable for scalable quantum computation.

2009-04-13

393

The 2004 Latsis Symposium: Quantum optics for Communication and Computing  

CERN Multimedia

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

394

The 2004 Latsis Symposium: Quantum optics for Communication and Computing  

CERN Document Server

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

395

The 2004 Latsis Symposium: Quantum optics for Communication and Computing  

CERN Document Server

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

396

Experimental magic state distillation for fault-tolerant quantum computing.  

UK PubMed Central (United Kingdom)

Any physical quantum device for quantum information processing (QIP) 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 AM; Zhang J; Ryan CA; Laflamme R

2011-01-01

397

A no-go theorem for halting a universal quantum computer  

International Nuclear Information System (INIS)

[en] A very brief introduction to quantum computing with an emphasis on the distinction between universal quantum computers and quantum networks. It is than proved under very general and desirable assumptions, it is not possible to check for halting a universal quantum computer without losing the quantum computation. (author)

2001-01-01

398

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

CERN Document Server

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 NVEs through a common CBJJ. The experimental feasibility and challenge are justified using currently available technology.

Yang, W L; Hu, Y; Feng, M; Du, J F

2011-01-01

399

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

Energy Technology Data Exchange (ETDEWEB)

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.

Yang, W. L.; Feng, M. [State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, and Wuhan National Laboratory for Optoelectronics, Wuhan 430071 (China); Yin, Z. Q. [Key Laboratory of Quantum Information, University of Science and Technology of China, Chinese Academy of Sciences, Hefei 230026 (China); Hu, Y. [Department of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China); Du, J. F. [Hefei National Laboratory for Physics Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, 230026 (China)

2011-07-15

400

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.

2011-01-01

 
 
 
 
401

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

402

The Study of Entangled States in Quantum Computation and Quantum Information Science  

CERN Multimedia

This thesis explores the use of entangled states in quantum computation and quantum information science. Entanglement, a quantum phenomenon with no classical counterpart, has been identified as an important and quantifiable resource in many areas of theoretical quantum information science, including quantum error correction, quantum cryptography, and quantum algorithms. We first investigate the equivalence classes of a particular class of entangled states (known as graph states due to their association with mathematical graphs) under local operations. We prove that for graph states corresponding to graphs with neither cycles of length 3 nor 4, the equivalence classes can be characterized in a very simple way. We also present software for analyzing and manipulating graph states. We then study quantum error-correcting codes whose codewords are highly entangled states. An important area of investigation concerning QECCs is to determine which resources are necessary in order to carry out any computation on the co...

Chung, Hyeyoun

2008-01-01

403

Mesoporous matrices for quantum computation with improved response through redundance  

CERN Multimedia

We present a solid state implementation of quantum computation, which improves previously proposed optically driven schemes. Our proposal is based on vertical arrays of quantum dots embedded in a mesoporous material which can be fabricated with present technology. The redundant encoding typical of the chosen hardware protects the computation against gate errors and the effects of measurement induced noise. The system parameters required for quantum computation applications are calculated for II-VI and III-V materials and found to be within the experimental range. The proposed hardware may help minimize errors due to polydispersity of dot sizes, which is at present one of the main problems in relation to quantum dot-based quantum computation.

Hodgson, T; Leventis, N; D'Amico, I; 10.1063/1.2745438

2009-01-01

404

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; Alexander Vasiliev

2011-01-01

405

Photonic implementation for the topological cluster-state quantum computer  

International Nuclear Information System (INIS)

[en] An implementation of the topological cluster-state quantum computer is suggested, in which the basic elements are linear optics, measurements, and a two-dimensional array of quantum dots. This overcomes the need for nonlinear devices to create a lattice of entangled photons. Whereas the thresholds found for computational errors are quite satisfactory (above 10-3), the estimates of the minimum efficiencies needed for the detectors and quantum dots are beyond current technology's reach. This is because we rely heavily on probabilistic entangling gates, which introduces loss into the scheme irrespective of detector and quantum-dot efficiencies.

2010-01-01

406

Logical Interpretation of a Reversible Measurement in Quantum Computing  

CERN Multimedia

We give the logical description of a new kind of quantum measurement that is a reversible operation performed by an hypothetical insider observer, or, which is the same, a quantum measurement made in a quantum space background, like the fuzzy sphere. The result is that the non-contradiction and the excluded middle principles are both invalidated, leading to a paraconsistent, symmetric logic. Our conjecture is that, in this setting, one can develop the adequate logic of quantum computing. The role of standard quantum logic is then confined to describe the projective measurement scheme.

Battilotti, G; Battilotti, Giulia; Zizzi, Paola

2004-01-01

407

A silicon-based nuclear spin quantum computer  

International Nuclear Information System (INIS)

[en] Full text: Quantum mechanical computers have received significant recent attention because they have the theoretical potential to outperform conventional computers by using algorithms that exploit the superposition of quantum states. We present an architecture for a quantum computer in which information is encoded onto nuclear pins situated on donors in silicon electronic devices. Logical operations on the spins are performed using externally applied electric fields that control the spin interactions, and spin measurement is accomplished using currents of spin polarised electrons. The computer will operate at millikelvin temperatures and must be fabricated from high purity materials with device sizes of order 100 Angstroms. A silicon quantum computer, built using technologies being developed for future conventional electronics, can potentially be scaled to sizes large enough that the extraordinary promise of quantum computation can be realised. I will discuss the quantum computer initiative underway at the University of New South Wales and the strategies being pursued to fabricate a rudimentary quantum logical device at the Semiconductor Nanofabrication Facility

1998-01-01

408

Mathematical Models of Contemporary Elementary Quantum Computing Devices  

CERN Multimedia

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

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

2003-01-01

409

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

410

General-Purpose Parallel Simulator for Quantum Computing  

CERN Multimedia

With current technologies, it seems to be very difficult to implement quantum computers with many qubits. It is therefore of importance to simulate quantum algorithms and circuits on the existing computers. However, for a large-size problem, the simulation often requires more computational power than is available from sequential processing. Therefore, the simulation methods using parallel processing are required. We have developed a general-purpose simulator for quantum computing on the parallel computer (Sun, Enterprise4500). It can deal with up-to 30 qubits. We have performed Shor's factorization and Grover's database search by using the simulator, and we analyzed robustness of the corresponding quantum circuits in the presence of decoherence and operational errors. The corresponding results, statistics and analyses are presented.

Niwa, J; Imai, H; Niwa, Jumpei; Matsumoto, Keiji; Imai, Hiroshi

2002-01-01

411

State of the art and prospects for quantum computing  

CERN Document Server

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 approached, is established. Some related sociological aspects are also discussed. .

Dyakonov, M I

2012-01-01

412

Is the quantum computer a dream or a nightmare?  

International Nuclear Information System (INIS)

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

1996-01-01

413

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.

2010-01-01

414

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

415

Consciousness and Logic in a Quantum-Computing Universe  

Science.gov (United States)

The early inflationary universe can be described in terms of quantum information. More specifically, the inflationary universe can be viewed as a superposed state of quantum registers. Actually, during inflation, one can speak of a quantum superposition of universes. At the end of inflation, only one universe is selected, by a mechanism called self-reduction, which is consistent with Penrose's objective reduction (OR) model. The quantum gravity threshold of (OR) is reached at the end of inflation, and corresponds to a superposed state of 109 quantum registers. This is also the number of superposed tubulins — qubits in our brain, which undergo the Penrose-Hameroff orchestrated objective reduction, (Orch OR), leading to a conscious event. Then, an analogy naturally arises between the very early quantum-computing universe, and our mind. In fact, we argue that at the end of in- flation, the universe underwent a cosmic conscious event, the so-called "Big Wow", which acted as an imprinting for the future minds to come, with future modes of computation, consciousness and logic. The postinflationary universe organized itself as a cellular automaton (CA) with two computational modes: quantum and classical, like the two conformations assumed by the cellular automaton of tubulins in our brain, as in Hameroff's model. In the quantum configuration, the universe quantum-evaluates recursive functions, which are the laws of physics in their most abstract form. To do so in a very efficient way, the universe uses, as subroutines, black holes - quantum computers and quantum minds, which operate in parallel. The outcomes of the overall quantum computation are the universals, the attributes of things in themselves. These universals are partially obtained also by the quantum minds, and are endowed with subjective meaning. The units of the subjective universals are qualia, which are strictly related to the (virtual) existence of Planckian black holes. Further, we consider two aspects of the quantum mind, which are not algorithmic in the usual sense: the self, and mathematical intuition. The self is due to a reversible self-measurement of a quantum state of superposed tubulins. Mathematical intuition is due to the paraconsistent logic of the internal observer in a quantum-computing universe.

Zizzi, Paola

416

Group IV solid state proposals for quantum computation  

Energy Technology Data Exchange (ETDEWEB)

The discovery of the quantum factorization algorithm more than a decade ago triggered intense interest in exploring possible physical realizations of quantum computers. Among the many solid state proposals, electron and nuclear spins in Si and group IV related materials have long coherence times and the capability of state preparation, gating and read-out using electric, magnetic and optical fields. Proposals involving silicon seek to take advantage of an existing mature technology and the implicit promise of scalability from solid state materials. Nevertheless, building such quantum systems depends in many cases on the development of fabrication techniques with nearly atomic precision. Managing decoherence, initialization and read-out in any quantum computer remains a daunting task. In this review we summarize proposals and recent developments relevant to the possible realization of a quantum computer constructed out of Si (or group IV) materials.

Fodor, P S; Levy, J [Department of Physics and Astronomy, University of Pittsburgh, 3941 O' Hara Street, Pittsburgh, PA 15260 (United States)

2006-05-31

417

Encoded Universality in Physical Implementations of a Quantum Computer  

CERN Multimedia

We revisit the question of universality in quantum computing and propose a new paradigm. Instead of forcing a physical system to enact a predetermined set of universal gates (e.g., single-qubit operations and CNOT), we focus on the intrinsic ability of a system to act as a universal quantum computer using only its naturally available interactions. A key element of this approach is the realization that the fungible nature of quantum information allows for universal manipulations using quantum information encoded in a subspace of the full system Hilbert space, as an alternative to using physical qubits directly. Starting with the interactions intrinsic to the physical system, we show how to determine the possible universality resulting from these interactions over an encoded subspace. We outline a general Lie-algebraic framework which can be used to find the encoding for universality and give several examples relevant to solid-state quantum computing.

Bacon, D J; Lidar, D A; Whaley, K B; Di Vincenzo, D P

2001-01-01

418

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

CERN Document Server

We investigate an optically driven quantum computer based on electric dipole transitions within coupled single-electron quantum dots. Our quantum register consists of a freestanding n-type pillar containing a series of pair wise coupled asymmetric quantum dots, each with a slightly different energy structure, and with grounding leads at the top and bottom of the pillar. Asymmetric quantum wells confine electrons along the pillar axis and a negatively biased gate wrapped around the center of the pillar allows for electrostatic confinement in the radial direction. We self-consistently solve coupled Schrodinger and Poisson equations and develop a design for a three-qubit quantum register. Our results indicate that a single gate electrode can be used to localize a single electron in each of the quantum dots. Adjacent dots are strongly coupled by electric dipole-dipole interactions arising from the dot asymmetry, thus enabling rapid computation rates. The dots are tailored to minimize dephasing due to spontaneous ...

Sanders, G D; Holton, W C

2000-01-01

419

Efficiency of the ground-state quantum computer  

International Nuclear Information System (INIS)

[en] The energy gap is calculated for a ground-state quantum computer circuit. It is found that, when implementing a quantum algorithm by Hamiltonians containing only pairwise interaction, the inverse of energy gap is proportional to N4k, where N is the number of bits involved in the problem, and Nk is the number of control operations performed in a standard quantum paradigm

2005-01-01

420

Electron Spins in Artificial Atoms and Molecules for Quantum Computing  

CERN Multimedia

Achieving control over the electron spin in quantum dots (artificial atoms) or real atoms promises access to new technologies in conventional and in quantum information processing. Here we review our proposal for quantum computing with spins of electrons confined to quantum dots. We discuss the basic requirements for implementing spin-qubits, and describe a complete set of quantum gates for single- and two-qubit operations. We show how a quantum dot attached to leads can be used for spin filtering and spin read-out, and as a spin-memory device. Finally, we focus on the experimental characterization of the quantum dot systems, and discuss transport properties of a double-dot and show how Kondo correlations can be used to measure the Heisenberg exchange interaction between the spins of two dots.

Golovach, V N; Golovach, Vitaly N.; Loss, Daniel

2002-01-01

 
 
 
 
421

Cluster quantum computer on the basis of quasi-part  

CERN Document Server

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

Voronov, V K

2011-01-01

422

Computational Nuclear Quantum Many-Body Problem: The UNEDF Project  

CERN Multimedia

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

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

2013-01-01

423

Quantum computing by optical control of electron spins  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We review the progress and main challenges in implementing large-scale quantum computing by optical control of electron spins in quantum dots (QDs). Relevant systems include self-assembled QDs of III-V or II-VI compound semiconductors (such as InGaAs and CdSe), monolayer fluctuation QDs in compound ...

Liu, RB; Yao, W; Sham, LJ

424

Simulation of Electronic Structure Hamiltonians Using Quantum Computers  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Over the last century, a large number of physical and mathematical developments paired with rapidly advancing technology have allowed the field of quantum chemistry to advance dramatically. However, the lack of computationally efficient methods for the exact simulation of quantum systems on classica...

Whitfield, James D.; Biamonte, Jacob; Aspuru-Guzik, Alán

425

Universal quantum computing with correlated spin-charge states  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We propose a universal quantum computing scheme in which the orthogonal qubit states |0i and |1> are identical in their single-particle spin and charge properties. Each qubit is contained in a single quantum dot and gate operations are induced all-electrically by changes in the confinement potential...

Kyriakidis, Jordan; Burkard, Guido

426

Quantum computing, phase estimation and applications  

CERN Multimedia

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

427

COMPUTER TECHNOLOGIES OF TEACHING THE WAVE AND QUANTUM OPTICS ????’?????? ?????????? ???????? ????????? ? ????????? ??????  

Directory of Open Access Journals (Sweden)

Full Text Available The article is devoted to picture the main approaches of increasing the effectiveness of teaching the waves and quantum qualities of the light with application of computer technologies.?????? ?????????? ???????????? ???????? ????????? ?????????? ???????????? ??????? ???????? ????????? ? ????????? ???????????? ?????? ? ????????????? ????’??????? ??????????.

?.?. ?????????

2010-01-01

428

Experimental Quantum Computing to Solve Systems of Linear Equations  

Science.gov (United States)

Solving linear systems of equations is ubiquitous in all areas of science and engineering. With rapidly growing data sets, such a task can be intractable for classical computers, as the best known classical algorithms require a time proportional to the number of variables N. A recently proposed quantum algorithm shows that quantum computers could solve linear systems in a time scale of order log?(N), giving an exponential speedup over classical computers. Here we realize the simplest instance of this algorithm, solving 2×2 linear equations for various input vectors on a quantum computer. We use four quantum bits and four controlled logic gates to implement every subroutine required, demonstrating the working principle of this algorithm.

Cai, X.-D.; Weedbrook, C.; Su, Z.-E.; Chen, M.-C.; Gu, Mile; Zhu, M.-J.; Li, Li; Liu, Nai-Le; Lu, Chao-Yang; Pan, Jian-Wei

2013-06-01

429

Simulating chemistry efficiently on fault-tolerant quantum computers  

CERN Document Server

Quantum computers can in principle simulate quantum physics exponentially faster than their classical counterparts, but some technical hurdles remain. Here we consider methods to make proposed chemical simulation algorithms computationally fast on fault-tolerant quantum computers in the circuit model. Fault tolerance constrains the choice of available gates, so that arbitrary gates required for a simulation algorithm must be constructed from sequences of fundamental operations. We examine techniques for constructing arbitrary gates which perform substantially faster than circuits based on the conventional Solovay-Kitaev algorithm [C.M. Dawson and M.A. Nielsen, \\emph{Quantum Inf. Comput.}, \\textbf{6}:81, 2006]. For a given approximation error $\\epsilon$, arbitrary single-qubit gates can be produced fault-tolerantly and using a limited set of gates in time which is $O(\\log \\epsilon)$ or $O(\\log \\log \\epsilon)$; with sufficient parallel preparation of ancillas, constant average depth is possible using a method w...

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

2012-01-01

430

Results on two-bit gate design for quantum computers  

CERN Multimedia

We present numerical results which show how two-bit logic gates can be used in the design of a quantum computer. We show that the Toffoli gate, which is a universal gate for all classical reversible computation, can be implemented using a particular sequence of exactly five two-bit gates. An arbitrary three-bit unitary gate, which can be used to build up any arbitrary quantum computation, can be implemented exactly with six two-bit gates. The ease of implementation of any particular quantum operation is dependent upon a very non-classical feature of the operation, its exact quantum phase factor. (Submitted to: Proceedings of the Workshop on Physics and Computation, PhysComp '94 (Los Alamitos: IEEE Comp. Soc. Press, 1994). Copyright transferred to IEEE.)

Di Vincenzo, D P; DiVincenzo, David P; Smolin, John

1994-01-01

431

Effects of the magnetic field in quantum computing with silicon  

Energy Technology Data Exchange (ETDEWEB)

The effects of magnetic fields on the wavefunctions of electrons bound to donor nuclei in semiconductors will alter the properties of qubits and qubit-qubit interactions that are intended to be used for quantum computing in silicon. (viewpoint)

Keyes, R W [IBM Research Division, Yorktown, NY (United States)

2005-11-02

432

Preparing ground States of quantum many-body systems on a quantum computer.  

UK PubMed Central (United Kingdom)

Preparing the ground state of a system of interacting classical particles is an NP-hard problem. Thus, there is in general no better algorithm to solve this problem than exhaustively going through all N configurations of the system to determine the one with lowest energy, requiring a running time proportional to N. A quantum computer, if it could be built, could solve this problem in time sqrt[N]. Here, we present a powerful extension of this result to the case of interacting quantum particles, demonstrating that a quantum computer can prepare the ground state of a quantum system as efficiently as it does for classical systems.

Poulin D; Wocjan P

2009-04-01

433

Preparing Ground States of Quantum Many-Body Systems on a Quantum Computer  

International Nuclear Information System (INIS)

[en] Preparing the ground state of a system of interacting classical particles is an NP-hard problem. Thus, there is in general no better algorithm to solve this problem than exhaustively going through all N configurations of the system to determine the one with lowest energy, requiring a running time proportional to N. A quantum computer, if it could be built, could solve this problem in time ?(N). Here, we present a powerful extension of this result to the case of interacting quantum particles, demonstrating that a quantum computer can prepare the ground state of a quantum system as efficiently as it does for classical systems

2009-04-03

434

Blind quantum computation protocol in which Alice only makes measurements  

Science.gov (United States)

Blind quantum computation is a new secure quantum computing protocol which enables Alice (who does not have sufficient quantum technology) to delegate her quantum computation to Bob (who has a full-fledged quantum computer) in such a way that Bob cannot learn anything about Alice's input, output, and algorithm. In previous protocols, Alice needs to have a device which generates quantum states, such as single-photon states. Here we propose another type of blind computing protocol where Alice does only measurements, such as the polarization measurements with a threshold detector. 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 ease Alice's burden. Furthermore, the security of our protocol is based on the no-signaling principle, which is more fundamental than quantum physics. Finally, our protocols are device independent in the sense that Alice does not need to trust her measurement device in order to guarantee the security.

Morimae, Tomoyuki; Fujii, Keisuke

2013-05-01

435

Experimental realization of a quantum game on a one-way quantum computer  

Energy Technology Data Exchange (ETDEWEB)

We report the first demonstration of a quantum game on an all-optical one-way quantum computer. Following a recent theoretical proposal we implement a quantum version of Prisoner's Dilemma, where the quantum circuit is realized by a four-qubit box-cluster configuration and the player's local strategies by measurements performed on the physical qubits of the cluster. This demonstration underlines the strength and versatility of the one-way model and we expect that this will trigger further interest in designing quantum protocols and algorithms to be tested in state-of-the-art cluster resources.

Prevedel, Robert [Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna (Austria); Stefanov, Andre [Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna (Austria); Walther, Philip [Physics Department, Harvard University, Cambridge, Massachusetts 02138 (United States); Zeilinger, Anton [Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna (Austria)

2007-06-15

436

Experimental realization of a quantum game on a one-way quantum computer  

International Nuclear Information System (INIS)

We report the first demonstration of a quantum game on an all-optical one-way quantum computer. Following a recent theoretical proposal we implement a quantum version of Prisoner's Dilemma, where the quantum circuit is realized by a four-qubit box-cluster configuration and the player's local strategies by measurements performed on the physical qubits of the cluster. This demonstration underlines the strength and versatility of the one-way model and we expect that this will trigger further interest in designing quantum protocols and algorithms to be tested in state-of-the-art cluster resources

2007-01-01

437

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

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 (qu)bit, the transformation being controlled by the other w?1 (qu)bits. 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; Stijn De Baerdemacker

2011-01-01

438

Simulation of finite state machines in a quantum computer  

CERN Multimedia

A construction is given for simulating any deterministic finite state machine (FSM) on a quantum computer in a space-efficient manner. By constructing a superposition of input strings of lengths K or less, questions can be asked about the FSM, such as the inputs that reach particular nodes, and the answers can be found using a search algorithm such as Grover's. This has implications for the eventual utility of quantum computers for software validation.

Dunlavey, M R

1998-01-01

439

Solid-state quantum computer based on scanning tunneling microscopy.  

UK PubMed Central (United Kingdom)

We propose a solid-state nuclear-spin quantum computer based on application of scanning tunneling microscopy (STM) and well-developed silicon technology. It requires the measurement of tunneling-current modulation caused by the Larmor precession of a single electron spin. Our envisioned STM quantum computer would operate at the high magnetic field (approximately 10 T) and at low temperature approximately 1 K.

Berman GP; Brown GW; Hawley ME; Tsifrinovich VI

2001-08-01

440

Solid-State Quantum Computer Based on Scanning Tunneling Microscopy  

Energy Technology Data Exchange (ETDEWEB)

We propose a solid-state nuclear-spin quantum computer based on application of scanning tunneling microscopy (STM) and well-developed silicon technology. It requires the measurement of tunneling-current modulation caused by the Larmor precession of a single electron spin. Our envisioned STM quantum computer would operate at the high magnetic field ({approx}10 T) and at low temperature {approx}1 K .

Berman, G. P.; Brown, G. W.; Hawley, M. E.; Tsifrinovich, V. I.