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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 quantumcomputer, which would dramatically improve computational power for particular tasks. A number of physical systems, spanning much of modern physics, are being developed for quantumcomputation. 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

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

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 quantumcomputer. In this talk I will review several basic concepts of a quantumcomputer. Why quantumcomputing and how do we do it? What is the status of several (but not all) approaches towards building a quantumcomputer, including IBM's approach using superconducting qubits? And what will it take to build a functional machine? The promise is that a quantumcomputer could solve certain interesting computational problems such as factoring using exponentially fewer computational steps than classical systems. Although the most sophisticated modern quantumcomputing 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 quantumcomputing aspects. At the minimum, future demonstrations will shed much light on what lies ahead.

Quantumcomputation is an excercise in quantum control: for a quantum system to compute, its dynamics must be controlled to a high degree of precision. Quantum control, in turn, is an excercise in quantumcomputation: control can be thought of in terms of how information is represented and processed. This talk reviews recent developments in quantumcomputation and quantum control

Superconductive technology is one of the most promising approaches to quantumcomputing because it offers devices with little dissipation, ultrasensitive magnetometers, and electrometers for state readout, large-scale-integration, and a family of classical electronics that could be used for quantum bit (qubit) control. The challenges this technology faces, however, are substantial: for example, control of the qubit to a part in

This episode of the PBS program Closer to the Truth provides some insight into quantumcomputingtechnology. The program summary discusses some of the potential uses for quantumcomputing 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.

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

Quantumcomputation is an excercise in quantum control: for a quantum system to compute, its dynamics must be controlled to a high degree of precision. Quantum control, in turn, is an excercise in quantumcomputation: control can be thought of in terms of how information is represented and processed. This talk reviews recent developments in quantumcomputation and quantum control with an emphasis on their theoretical and experimental overlap.

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

From the research laboratories of Hewlett Packard, Quantum Information Technology provides an informative look at current work in quantum information processing and communication (QIPC). The report, published in November 2002, recognizes the potential applications of QIPC and how it could revolutionize conventional information technology. It cites cryptography, quantumcomputers, and quantum teleportation as motivational factors for development of this technology, offering a basic introduction to each discipline. The paper concludes with an analysis of the direction current research is taking and what the future may hold. Several links to further sources of information are also included.

A quantumcomputer comprising a semiconductor substrate into which donor atoms are introduced to produce an array of donor nuclear spin electron systems having large electron wave functions at the nucleus of the donor atoms, where the donor electrons only occupy the nondegenerate lowest spin energy level. An insulating layer above the substrate. Conducting A-gates on the insulating layer above respective donor atoms to control strength of the hyperfine interactions between the donated electrons and the donor atoms' nuclear spins, and hence the resonance frequency of the nuclear spins of the donor atoms. Conducting J-gates on the Insulating layer between the A-gates to turn on and off electron mediated coupling between the nuclear spins or adjacent donor atoms. Where the nuclear spins of the donor atoms are the quantum states or "qubits" in which binary information is stored and manipulated by selective application of voltage to the A- and J-gates and selective application of an alternating magnetic field to the substrate.

The theory of quantumcomputational networks is the quantum generalization of the theory of logic circuits used in classical computing machines. Quantum gates are the generalization of classical logic gates. A single type of gate, the univeral quantum gate, together with quantum 'unit wires', is adequate for constructing networks with any possible quantumcomputational property.

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 u...

C. Monroe F. Jelezko R. Laflamme T. D. Ladd Y. Nakamura

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

Our time at the Computing Beyond Silicon Summer School, hosted by Caltech, gave us a unique opportunity to explore new concepts and learn about advances in modern information processing that interest us. We chose to study quantumcomputation using quantum dot systems because of their potential for bringing forth a solid-sate quantum information processing system. Specifically we chose to investigate

Joon Ho Baek; Happy Hsin; Joshua LaForge; Daniel Nedelcu

The paper is intended to be a survey of all the important aspects and results that have shaped the field of quantumcomputation and quantum information. The reader is first familiarized with those features and principles of quantum mechanics providing a more efficient and secure information processing. Their applications to the general theory of information, cryptography, algorithms, computational complexity and

Students will learn the history of computers as well as how computers work. COMPUTERTECHNOLOGY (9-12) - 52.0417 ComputerTechnology is an introduction to computer application software that includes word processing, spreadsheet, database, and telecommunications. An awareness of career opportunities, business ethics, and trends is included. Everything is done with computers. Your job will most likely have a computer to save files, write ...

We describe a QuantumComputer Emulator for a generic, general purpose QuantumComputer. This emulator consists of a simulator of the physical realization of the quantumcomputer and a graphical user interface to program and control the simulator. We illustrate the use of the quantumcomputer emulator through various implementations of the Deutsch–Jozsa and Grover's database search algorithm.

Hans De Raedt; Anthony H. Hams; Kristel Michielsen; Koen De Raedt

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 quantumcomputers 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 quantumcomputers 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.

A quantumcomputer, if built, will be to an ordinary computer as a hydrogen bomb is to gunpowder, at least for some types of computations. Today no quantumcomputer exists, beyond laboratory prototypes capable of solving only tiny problems, and many practical problems remain to be solved. Yet the theory of quantumcomputing has advanced significantly in the past decade,

We propose an implementation of a universal set of one- and two-quantum-bit gates for quantumcomputation using the spin states of coupled single-electron quantum dots. Desired operations are effected by the gating of the tunneling barrier between neighboring dots. Several measures of the gate quality are computed within a recently derived spin master equation incorporating decoherence caused by a prototypical

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 quantumcomputation,

We briefly review what a quantumcomputer 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 quantumcomputation is an extension of classical digital computation, quantum simulation differs fundamentally in how the data are encoded in the quantumcomputer. 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 quantumcomputer. 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 quantumcomputers, 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

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 quantumcomputer, which is a device that uses quantum systems themselves to store and process data. Here we report the application of the latest photonic quantumcomputertechnology 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

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

We discuss possible applications of the 1-D direct and inverse scattering problem to design of universal quantum gates for quantumcomputation. The potentials generating some universal gates are described. In this article we propose a theory of quantum scattering and notion of unitary scattering matrix to formulate quantum input-output rela- tions. This differs from standard approach to this subject in

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

A new quantum theory of communication and computation is emerging, in which the stuff transmitted or processed is not classical information, but arbitrary superpositions of quantum states. {copyright} 1995 {ital American} {ital Institute} {ital of} {ital Physics}.

We analyse dissipation in quantumcomputation and its destructive impact on\\u000aefficiency of quantum algorithms. Using a general model of decoherence, we\\u000astudy the time evolution of a quantum register of arbitrary length coupled with\\u000aan environment of arbitrary coherence length. We discuss relations between\\u000adecoherence and computational complexity and show that the quantum\\u000afactorization algorithm must be modified in

G. Massimo Palma; Kalle-Antti Suominen; Artur K. Ekert

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

Emanuel Knill; Raymond Laflamme; Wojciech H. Zurek

Blind quantumcomputation is a secure delegated quantumcomputing protocol where Alice, who does not have sufficient quantumtechnology at her disposal, delegates her computation to Bob, who has a fully fledged quantumcomputer, in such a way that Bob cannot learn anything about Alice’s input, output, and algorithm. Protocols of blind quantumcomputation 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 quantumcomputation for the continuous-variable measurement-based model. We show that blind quantumcomputation 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 quantumcomputation.

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

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

We show that in quantumcomputation almost every gate that operates on two or more bits is a universal gate. We discuss various physical considerations bearing on the proper definition of universality for computational components such as logic gates.

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

Present information technology is based on the laws of classical physics. However, advances in quantum physics have stimulated interest in its potential impact on such technology. This article is an introductory review of three aspects of quantum information processing, cryptography, computation, and teleportation. The author serves up hors d'oeuvres on the relevant parts of quantum physics and the sorts of

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 quantumcomputer, the program is a carefully prepared wave packet that propagates through different computational states. Deutsch presented a quantumcomputer 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.

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 quantumcomputer, the program is a carefully prepared wave packet that propagates through different computational states. Deutsch presented a quantumcomputer 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.

Quantumcomputational 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 quantumcomputation that has been recently taken up and developed by our research group.

Entanglement of two Aharonov-Bohm (AB) rings, or two artificial atoms, is similar to the entanglement of spins from two electrons. The directions of the angular momentum of two AB rings serve as the inputs for a basic two-bit computing in the quantum network. The question is whether the read-out is to be performed under a short and weak external perturbation? We found that a stronger entanglement than the situation needed for a quantum superposition combines with a strong external terminal connections is the only solution for robust classical readouts. A ``half-adder'' example will be presented. There has to be an inter-relation between internal and external coupling strengths. They are so adjusted for each other so that read-outs are possible.

Quantum Information Technology (QIT) is a relatively new area of research whose purpose is to take advantage of the quantum nature of matter and energy to design and build quantumcomputers which have the potential of improved performance over classical a...

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

Gross, D. [Institute for Theoretical Physics, Leibniz University Hannover, D-30167 Hannover (Germany); Eisert, J. [Institute for Physics and Astronomy, University of Potsdam, D-14476 Potsdam (Germany); Institute for Advanced Study Berlin, D-14193 Berlin (Germany)

It has recently been realized that use of the properties of quantum mechanics might speed up certain compu- tations dramatically. Interest in quantumcomputation has since been growing. One of the main difficulties in realizing quantumcomputation is that decoherence tends to destroy the information in a superposition of states in a quantumcomputer, making long compu- tations impossible. A

The theory for topologically configured two state systems immersed in a monochromatic field is generated in terms of the Monte Carlo Wave Function method. Specifically, I model one and two two-level atom(s) in a detuned laser field ("Laser Physics" by Sargent, Scully and Lamb). Allowing for spontaneous emission via quantum jumps, I use the density matrix to formulate the vacuum modes in the reservoir. It is the quantum jumps causing dephasing that lead to steady state superpositions of the atom and on resonance depictions give exotic non-linear predictions for state probabilities that exist in quantumcomputing.

Because the subject of relativistic quantum field theory (QFT) contains all\\u000aof non-relativistic quantum mechanics, we expect quantum field computation to\\u000acontain (non-relativistic) quantumcomputation. Although we do not yet have a\\u000aquantum theory of the gravitational field, and are far from a practical\\u000aimplementation of a quantum field computer, some pieces of the puzzle (without\\u000agravity) are now available.

Blind quantumcomputation is a novel secure quantum-computing protocol that enables Alice, who does not have sufficient quantumtechnology at her disposal, to delegate her quantumcomputation to Bob, who has a fully fledged quantumcomputer, in such a way that Bob cannot learn anything about Alice's input, output and algorithm. A recent proof-of-principle experiment demonstrating blind quantumcomputation in an optical system has raised new challenges regarding the scalability of blind quantumcomputation in realistic noisy conditions. Here we show that fault-tolerant blind quantumcomputation 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 quantumcomputation. As the error per gate of the order 10(-3) was already achieved in some experimental systems, our result implies that secure cloud quantumcomputation is within reach. PMID:22948818

Quantumcomputers, besides offering substantial computational speedups, are also expected to preserve the privacy of a computation. We present an experimental demonstration of blind quantumcomputing in which the input, computation, and output all remain unknown to the computer. We exploit the conceptual framework of measurement-based quantumcomputation 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 quantumcomputers widely available. PMID:22267806

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

Adiabatic quantumcomputation has recently attracted attention in the physics and computer science communities, but its computational power has been unknown. We settle this question and describe an efficient adiabatic simulation of any given quantum algorit hm, which implies that the adiabatic com- putation model and the conventional quantum circuit model are polynomially equivalent. Our result can be extended to

Dorit Aharonov; Wim Van Dam; Julia Kempe; Zeph Landau; Seth Lloyd; Oded Regev

Building on the work of Deutsch and Jozsa, we construct oracles relative to which (1) there is a decision problem that can be solved with certainty in worst-case polynomial time on the quantumcomputer, yet it cannot be solved classically in probabilistic expected polynomial time if errors are not tolerated, nor even in nondeterministic polynomial time, and (2) there is

This paper examines the notion of quantum neural computing in thecontext of several new directions in neural network research. In particular,we consider new neuron and network models that lead to rapidtraining; chaotic dynamics in neuron assemblies; models of attention andawareness; cytoskeletal microtubule information processing; and quantummodels. Recent discoveries in neuroscience that cannot be placed in the reductionistmodels of biological information

Physical mechanism of the time resolved four-wave mixing (TRFWM) has been investigated for further implication in optical information processing. It was found that photon echo physical and optical characteristics allow to use it for parallel optical data processing. We show that one can elaborate existing nonlinear optical technology in application to the one-way quantumcomputer scheme. Time resolved four-wave mixing

The DiVincenzo criteria for implementing a quantumcomputer have been seminal in focusing both experimental and theoretical research in quantum-information processing. These criteria were formulated specifically for the circuit model of quantumcomputing. However, several new models for quantumcomputing (paradigms) have been proposed that do not seem to fit the criteria well. Therefore, the question is what are the general criteria for implementing quantumcomputers. To this end, a formal operational definition of a quantumcomputer is introduced. It is then shown that, according to this definition, a device is a quantumcomputer if it obeys the following criteria: Any quantumcomputer 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 quantumcomputing paradigms and how they fit within this framework. Finally, we present a decision tree for selecting an avenue toward building a quantumcomputer. This is intended to help experimentalists determine the most natural paradigm given a particular physical implementation.

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

Sehrawat, Arun; Englert, Berthold-Georg [Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, 117543 Singapore (Singapore); Department of Physics, National University of Singapore, 2 Science Drive 3, 117542 Singapore (Singapore); Zemann, Daniel [Institut fuer Quantenoptik und Quanteninformation, Technikerstrasse 21a, A-6020 Innsbruck (Austria)

The physics of quantum walks on graphs is formulated in Hamiltonian language, both for simple quantum walks and for composite walks, where extra discrete degrees of freedom live at each node of the graph. It is shown how to map between quantum walk Hamiltonians and Hamiltonians for qubit systems and quantum circuits; this is done for both single-excitation and multiexcitation encodings. Specific examples of spin chains, as well as static and dynamic systems of qubits, are mapped to quantum walks, and walks on hyperlattices and hypercubes are mapped to various gate systems. We also show how to map a quantum circuit performing the quantum Fourier transform, the key element of Shor's algorithm, to a quantum walk system doing the same. The results herein are an essential preliminary to a Hamiltonian formulation of quantum walks in which coupling to a dynamic quantum environment is included.

Hines, Andrew P. [Pacific Institute of Theoretical Physics and Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, British Columbia, V6T 1Z1 (Canada); Pacific Institute for the Mathematical Sciences, 1933 West Mall, University of British Columbia, Vancouver, British Columbia, V6T 1Z2 (Canada); Stamp, P. C. E. [Pacific Institute of Theoretical Physics and Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, British Columbia, V6T 1Z1 (Canada)

The theory of quantumcomputation can be constructed from the abstract study\\u000aof anyonic systems. In mathematical terms, these are unitary topological\\u000amodular functors. They underlie the Jones polynomial and arise in\\u000aWitten-Chern-Simons theory. The braiding and fusion of anyonic excitations in\\u000aquantum Hall electron liquids and 2D-magnets are modeled by modular functors,\\u000aopening a new possibility for the realization

Michael H. Freedman; Alexei Kitaev; Michael J. Larsen; Zhenghan Wang; L. D. Landau; Michael H. Freedman

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.; Wood, Christopher J.

Quantumcomputation offers a promising new kind of information processing, where the non-classical features of quantum mechanics are harnessed and exploited. A number of models of quantumcomputation exist. These models have been shown to be formally equivalent, but their underlying elementary concepts and the requirements for their practical realization can differ significantly. A particularly exciting paradigm is that of

D. E. Browne; R. Raussendorf; M. Van den Nest; H. J. Briegel

Identifying and designing physical systems for use as qubits, the basic units of quantum information, are critical steps in the development of a quantumcomputer. 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

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

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

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 quantumcomputer. Some researchers in discrete complexity theory believe that quantumcomputation is not effective for eigenvalue problems. One of our goals in this paper is to explain this dissonance.

We present a scheme to use external quantum devices using the universal quantumcomputer previously constructed. We thereby show how the universal quantumcomputer can utilize networked quantum information resources to carry out local computations. Such information may come from specialized quantum devices or even from remote universal quantumcomputers. We show how to accomplish this by devising universal quantumcomputer 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 quantumcomputer. PMID:22216276

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

The Wigner-Araki-Yanase theorem shows that conservation laws limit the accuracy of measurement. Here, we generalize the argument to show that conservation laws limit the accuracy of quantum logic operations. A rigorous lower bound is obtained of the error probability of any physical realization of the controlled-NOT gate under the constraint that the computational basis is represented by a component of spin, and that physical implementations obey the angular momentum conservation law. The lower bound is shown to be inversely proportional to the number of ancilla qubits or the strength of the external control field. PMID:12144465

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 quantumcomputation 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 quantumcomputation.

Cai Jianming; Briegel, Hans J. [Institut fuer Quantenoptik und Quanteninformation der Oesterreichischen Akademie der Wissenschaften, Innsbruck (Austria); Institut fuer Theoretische Physik, Universitaet Innsbruck, Technikerstrasse 25, A-6020 Innsbruck (Austria); Miyake, Akimasa [Perimeter Institute for Theoretical Physics, 31 Caroline Street North, Waterloo, Ontario N2L 2Y5 (Canada); Duer, Wolfgang [Institut fuer Theoretische Physik, Universitaet Innsbruck, Technikerstrasse 25, A-6020 Innsbruck (Austria)

One of the motivating ideas of quantumcomputation 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 quantumcomputer, 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.

Quantum states of matter can be exploited as high performance sensors for measuring time, gravity, rotation, and electromagnetic fields, and quantum states of light provide powerful new tools for imaging and communication. Much attention is being paid to the ultimate limits of this quantumtechnology. For example, it has already been shown that exotic quantum states can be used to

Malcolm Boshier; Dana Berkeland; Tr Govindan; Jamil Abo-Shaeer

In this thesis, I investigate aspects of local Hamiltonians in quantumcomputing. First, I focus on the Adiabatic QuantumComputing model, based on evolution with a time dependent Hamiltonian. I show that to succeed using AQC, the Hamiltonian involved must have local structure, which leads to a result about eigenvalue gaps from information theory. I also improve results about simulating

Arrays of weakly coupled quantum systems might compute if subjected to a sequence of electromagnetic pulses of well-defined frequency and length. Such pulsed arrays are true quantumcomputers: bits can be placed in superpositions of 0 and 1, logical operations take place coherently, and dissipation is required only for error correction. Operated with frequent error correction, such a system functions

Encoding quantum information in spins embedded in semiconductors (electronic, ionic, or nuclear) offers several potential\\u000a approaches towards solid-state quantumcomputation. Electronic spin transport, persistence and manipulation in nonmagnetic\\u000a semiconductor materials, as well as the interaction of electronic spins with optics, are the fundamental properties reviewed\\u000a here. The presentation focuses on the material properties important for implementing quantumcomputation, and on

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

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

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

Rossini, Davide [Center for Nonlinear and Complex Systems, Universita degli Studi dell'Insubria, Via Valleggio 11, 22100 Como (Italy); Benenti, Giuliano [Center for Nonlinear and Complex Systems, Universita degli Studi dell'Insubria, Via Valleggio 11, 22100 Como (Italy); Istituto Nazionale per la Fisica della Materia, Unita di Como, Via Valleggio 11, 22100 Como (Italy); Casati, Giulio [Center for Nonlinear and Complex Systems, Universita degli Studi dell'Insubria, Via Valleggio 11, 22100 Como (Italy); Istituto Nazionale per la Fisica della Materia, Unita di Como, Via Valleggio 11, 22100 Como (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Milano, Via Celoria 16, 20133 Milan (Italy)

Compilers and computer-aided design tools will be essential for quantumcomput- ing. We present a computer-aided design flow that transforms a high-level language program representing a quantumcomputing algorithm into a technology-specific im- plementation. We trace the significant steps in this flow and illustrate the transfor- mations to the representation of the quantum program. The focus of this paper is

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

Standard quantumcomputation is based on sequences of unitary quantum logic gates that process qubits. The one-way quantumcomputer proposed by Raussendorf and Briegel is entirely different. It has changed our understanding of the requirements for quantumcomputation and more generally how we think about quantum physics. This new model requires qubits to be initialized in a highly entangled cluster

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

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

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

Due to the rapid advances made in Nano-Biotechnology, optical control of molecular dynamics and quantumcomputation, there is an increasing need to understand the fundamental structure, from the systems theoretical point of view, of the control and observation of quantum mechanical systems for designing advanced sensors and actuators. In this presentation we start with a discussion of the design, synthesis,

We use the powerful tools of counting complexity and generic oracles to help understand the lim- itations of the complexity of quantumcomputation. We show several results for the probabilistic quantum class BQP. BQP is low for PP, i.e., PPBQP = PP. There exists a relativized world where P = BQP and the polynomial-time hierarchy is innite. There exists a

Despite the obvious practical considerations (e.g., stability, controllability), certain quantum mechanical systems seem to naturally lend themselves in a theoretical sense to the task of performing computations. The purpose of this report is to describe ...

Proposals for adiabatic quantumcomputation generated renewed interest and questions about the adiabatic approximation. We presented a simple proof of the adiabatic theorem in which we showed that the first order correction has the expected dependence on ...

We show how it is possible to realize quantumcomputations on a system in which most of the parameters are practically unknown. We illustrate our results with a novel implementation of a quantumcomputer by means of bosonic atoms in an optical lattice. In particular, we show how a universal set of gates can be carried out even if the number of atoms per site is uncertain.

The goal of this research was to explore the use of superconducting circuits as components for quantumcomputingQuantumcomputers are devices that store information on quantum variables and process that information by making those variables interact in a...

The focus of this research was on developing quantum algorithms for continuous problems, complexity analysis of these algorithms, and their simulation and implementation. Continuous problems are a focus because much of physics, chemistry, and engineering ...

In photosynthesis, the Sun's energy is harvested and converted into biomass, greening the planet. Evidence is growing that quantum mechanics plays a part in that process. But exactly how, and why, remains to be explored.

In a quantumcomputer any superposition of inputs evolves unitarily into the correspond- ing superposition of outputs. It has been recently demonstrated that such computers can dramatically speed up the task of finding factors of large numbers - a problem of great practical significance because of its cryptographic applications. Instead of the nearly ex- ponential (? exp L1\\/3, for a

This article is concerned with the construction of a quantum-mechanical Hamiltonian describing a computer. This Hamiltonian generates a dynamical evolution which mimics a sequence of elementary logical steps. This can be achieved if each logical step is locally reversible (global reversibility is insufficient). Computational errors due to noise can be corrected by means of redundancy. In particular, reversible error-correcting codes

Classical and quantum information are very different. Together they can perform feats that neither could achieve alone. These include quantumcomputing, quantum cryptography and quantum teleportation. This paper surveys some of the most striking new applications of quantum mechanics to computer science. Some of these applications are still theoretical but others have been implemented.

Quantum information based on ion-trap technology is well regarded for its stability, high detection fidelity, and ease of manipulation. Here we demonstrate a proof of principle experiment for scaling this technology to large numbers of ions in separate traps by linking the ions via photons. We give results for entanglement between distant ions via probabilistic photonic gates that is then swapped between ions in the same trap via deterministic Coulombic gates. We report fidelities above 65% and show encouraging preliminary results for the next stage of experimental improvement. Such a system could be used for quantumcomputing requiring large numbers of qubits or for quantum repeaters requiring the qubits to be separated by large distances.

Clark, Susan; Hayes, David; Hucul, David; Inlek, I. Volkan; Monroe, Christopher

The focus of this project was the theoretical study of quantumcomputation based on controlled transfer of individual quasiparticles in systems of quantum antidots in the regime of the Fractional Quantum Hall Effect (FQHE). The work addressed the basic is...

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

Cryptology and information security are set to play a more prominent role in the near future. In this regard, quantum communication and cryptography offer new opportunities to tackle ICT security. Quantum Information Processing and Communication (QIPC) is a scientific field where new conceptual foundations and techniques are being developed. They promise to play an important role in the future of information Security. It is therefore essential to have a cross-fertilizing development between quantumtechnology and cryptology in order to address the security challenges of the emerging quantum era. In this article, we discuss the impact of quantumtechnology on the current as well as future crypto-techniques. We then analyse the assumptions on which quantumcomputers may operate. Then we present our vision for the distribution of security attributes using a novel form of trust based on Heisenberg's uncertainty; and, building highly secure quantum networks based on the clear transmission of single photons and/or bundles of photons able to withstand unauthorized reading as a result of secure protocols based on the observations of quantum mechanics. We argue how quantum cryptographic systems need to be developed that can take advantage of the laws of physics to provide long-term security based on solid assumptions. This requires a structured integration effort to deploy quantumtechnologies within the existing security infrastructure. Finally, we conclude that classical cryptographic techniques need to be redesigned and upgraded in view of the growing threat of cryptanalytic attacks posed by quantum information processing devices leading to the development of post-quantum cryptography.

This paper addresses foundational issues related to quantumcomputing. The need for a universally valid theory such as quantum mechanics to describe to some extent its own validation is noted. This includes quantum mechanical descriptions of systems that do theoretical calculations (i.e. quantumcomputers) and systems that perform experiments. Quantum robots interacting with an environment are a small first step in this direction. Quantum robots are described here as mobile quantum systems with on-board quantumcomputers that interact with environments. Included are discussions on the carrying out of tasks and the division of tasks into computation and action phases. Specific models based on quantum Turing machines are described. Differences and similarities between quantum robots plus environments and quantumcomputers are discussed.

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

Shrivastava, Keshav N. [Department of Physics, University of Malaya, Kuala Lumpur 50603 (Malaysia)

The effect of the inevitable coupling to external degrees of freedom of a\\u000aquantum computer are examined. It is found that for quantum calculations (in\\u000awhich the maintenance of coherence over a large number of states is important),\\u000anot only must the coupling be small but the time taken in the quantum\\u000acalculation must be less than the thermal time

Quantum states of matter can be exploited as high performance sensors for measuring time, gravity, rotation, and electromagnetic fields, and quantum states of light provide powerful new tools for imaging and communication. Much attention is being paid to the ultimate limits of this quantumtechnology. For example, it has already been shown that exotic quantum states can be used to measure or image with higher precision or higher resolution or lower radiated power than any conventional technologies, and proof-of-principle experiments demonstrating measurement precision below the standard quantum limit (shot noise) are just starting to appear. However, quantumtechnologies have another powerful advantage beyond pure sensing performance that may turn out to be more important in practical applications: the potential for building devices with lower size/weight/power (SWaP) and cost requirements than existing instruments. The organizers of QuantumTechnology Applications Workshop (QTAW) have several goals: (1) Bring together sponsors, researchers, engineers and end users to help build a stronger quantumtechnology community; (2) Identify how quantum systems might improve the performance of practical devices in the near- to mid-term; and (3) Identify applications for which more long term investment is necessary to realize improved performance for realistic applications. To realize these goals, the QTAW II workshop included fifty scientists, engineers, managers and sponsors from academia, national laboratories, government and the private-sector. The agenda included twelve presentations, a panel discussion, several breaks for informal exchanges, and a written survey of participants. Topics included photon sources, optics and detectors, squeezed light, matter waves, atomic clocks and atom magnetometry. Corresponding applications included communication, imaging, optical interferometry, navigation, gravimetry, geodesy, biomagnetism, and explosives detection. Participants considered the physics and engineering of quantum and conventional technologies, and how quantum techniques could (or could not) overcome limitations of conventional systems. They identified several auxiliary technologies that needed to be further developed in order to make quantumtechnology more accessible. Much of the discussion also focused on specific applications of quantumtechnology and how to push the technology into broader communities, which would in turn identify new uses of the technology. Since our main interest is practical improvement of devices and techniques, we take a liberal definition of 'quantumtechnology': a system that utilizes preparation and measurement of a well-defined coherent quantum state. This nomenclature encompasses features broader than entanglement, squeezing or quantum correlations, which are often more difficult to utilize outside of a laboratory environment. Still, some applications discussed in the workshop do take advantage of these 'quantum-enhanced' features. They build on the more established quantumtechnologies that are amenable to manipulation at the quantum level, such as atom magnetometers and atomic clocks. Understanding and developing those technologies through traditional engineering will clarify where quantum-enhanced features can be used most effectively, in addition to providing end users with improved devices in the near-term.

Boshier, Malcolm [Los Alamos National Laboratory; Berkeland, Dana [USG; Govindan, Tr [ARO; Abo - Shaeer, Jamil [DARPA

In a topological quantumcomputer, universal quantumcomputation is performed by dragging quasiparticle excitations of certain two dimensional systems around each other to form braids of their world lines in 2+1 dimensional space-time. We show that any such quantumcomputation that can be done by braiding n identical quasiparticles can also be done by moving a single quasiparticle around n-1 other identical quasiparticles whose positions remain fixed. This result may greatly reduce the technological challenge of realizing topological quantumcomputation.

Single photons make very good quantum information carriers, but current schemes for photonic quantum information processing (QIP) are inefficient. We describe a new scheme, coherent photon conversion (CPC), using classically pumped nonlinearities to generate and process complex multiquanta statesootnotetextPublished in Nature 478, 360 (2011). One example based on four-wave mixing provides a full suite of QIP tools for scalable quantumcomputing from a single, versatile process, including: deterministic multiqubit entanglement gates based on a novel photon-photon interaction, high-quality heralded multiphoton states without higher-order imperfections, and robust, high-efficiency detection. Using photonic crystal fibres, we present observations of quantum correlations from a four-colour nonlinear process suitable for CPC and study the feasibility of reaching the deterministic regime with current technology. The scheme could also be implemented in optomechanical, electromechanical and superconducting systems.

Langford, Nathan K.; Ramelow, Sven; Prevedel, Robert; Munro, William J.; Milburn, Gerard J.; Zeilinger, Anton

Since Shor's discovery of an algorithm to factor numbers on a quantumcomputer in polynomial time, quantumcomputation has become a subject of immense interest. Unfortunately, one of the key features of quantumcomputers - the difficulty of describing them on classical computers - also makes it difficult to describe and understand precisely what can be done with them. A

Quantumcomputation is a subject of much recent interest. In much of the work in the literature quantumcomputers are described as built up from a sequence of unitary operators where each unitary operator carries out a stage of the overall quantumcomputation. The sequence and connection of the different unitary operators is provided presumably by some external agent which

Technological developments sparked by quantum mechanics and wave–particle duality are still gaining ground over a hundred years after the theories were devised. While the impact of the theories in fundamental research, philosophy and even art and literature is widely appreciated, the implications in device innovations continue to breed potential. Applications inspired by these concepts include quantumcomputation and quantum cryptography

Is the notion of a quantumcomputer (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.

As NASA spacecraft explore deeper into the cosmos, speed-of-light-limited signal delays make it increasingly impractical to command missions from Earth. Future spacecraft will need greater onboard computing capacity to mimic human-level intelligence and autonomy. The solution might come from quantumcomputers, which offer properties of size, power, and robustness that are ideally suited to the space environment. The potential of

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

Individually trapped {sup 137}Ba{sup +} in an RF Paul trap is proposed as a qubit candidate, and its various benefits are compared to other ionic qubits. We report the current experimental status of using this ion for quantumcomputation. Future plans and prospects are discussed.

Dietrich, M. R.; Avril, A.; Bowler, R.; Kurz, N.; Salacka, J. S.; Shu, G.; Blinov, B. B. [University of Washington Department of Physics, Seattle, Washington, 98195 (United States)

The main development has been the invention of the holographic method for deriving polynomial time algorithms where none were known before. The method is heavily inspired by the quantumcomputational model, but the algorithms we have derived to date can a...

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 level from the root. We devise a quantum-mechanical algorithm that evolves a state, initially localized at the root, through the tree.

Recent experimental advances have demonstrated technologies capable of supporting scalable quantumcomputation. A critical next step is how to put those technologies together into a scalable, fault-tolerant system that is also feasible. We propose a Quantum Logic Array (QLA) microarchitecture that forms the foundation of such a system. The QLA focuses on the communication resources necessary to efficiently support fault-tolerant

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

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, quantumcomputers consisting of 4 to 7 qubits in a 'quantumcomputing register' have been built. Innovative algorithms suited to quantumcomputing 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 'quantumcomputing 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 'quantumcomputing 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.

We study a hybrid quantumcomputing 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 quantumcomputing 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)

We show that the Knill Laflamme Milburn method of quantumcomputation with linear optics gates can be interpreted as a one-way, measurement based quantumcomputation 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 quantumcomputation.

Determining the quantum circuit complexity of a unitary operation is an important problem in quantumcomputation. By using the mathematical techniques of Riemannian geometry, we investigate the efficient quantum circuits in quantumcomputation 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.

It has been claimed that quantumcomputers 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. Quantumcomputers 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 quantumcomputer, 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

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

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

The successful implementation of a scalable, fault-tolerant quantumcomputer would introduce a type of information processing more powerful than any available today. Reciprocally, the discovery of a fundamental obstacle to such a system would be an important advance in the foundations of quantum theory. No such fundamental obstacles are currently known, but neither has any architecture been shown to be experimentally scalable. Many technologies have been considered for finding such an architecture; in this work I focus on nuclear spins in semiconductors. Semiconductors provide promising optical means for polarizing and measuring small nuclear spin ensembles, which are tasks that pose critical challenges to quantumcomputers based on nuclear magnetic resonance (NMR). At the same time, semiconductor nuclei are sufficiently coherent quantum oscillators to allow complex information processing using resonant radio-frequency pulse sequences. In particular, the isotopically clean and magnetically quiet environment of pure, high quality, bulk single-crystal silicon provides a nuclear environment allowing what may be the longest absolute coherence time of any solid-state qubit currently under consideration. I have experimentally tested this claim using high-power NMR pulse sequences to eliminate inhomogeneous dephasing and dipolar evolution among an ensemble of 29Si nuclei in isotopically modified silicon crystals. Intrinsic decoherence processes are only observed in polycrystalline silicon, where 1/f charging noise processes are likely to blame. In high-quality single crystal samples, nuclear coherence persists for over 25 seconds, a timescale limited only by pulse sequence imperfections. I will discuss an architecture that takes advantage of this clean nuclear environment, but I will also address its scalability limitations due to silicon's poor optical characteristics. These limitations will suggest new experiments employing nuclear spins in optically controlled semiconductor quantum dots, which may hold more promise for future scalable quantumcomputer architectures.

The parametric deformations of quasienergies and eigenvectors of unitary operators are applied to the design of quantum adiabatic algorithms. The conventional, standard adiabatic quantumcomputation proceeds along eigenenergies of parameter-dependent Hamiltonians. By contrast, discrete adiabatic computation utilizes adiabatic passage along the quasienergies of parameter-dependent unitary operators. For example, such computation can be realized by a concatenation of parameterized quantum circuits, with an adiabatic though inevitably discrete change of the parameter. A design principle of adiabatic passage along quasienergy was recently proposed: Cheon's quasienergy and eigenspace anholonomies on unitary operators is available to realize anholonomic adiabatic algorithms [A. Tanaka and M. Miyamoto, Phys. Rev. Lett. 98, 160407 (2007)], which compose a nontrivial family of discrete adiabatic algorithms. It is straightforward to port a standard adiabatic algorithm to an anholonomic adiabatic one, except an introduction of a parameter |v>, which is available to adjust the gaps of the quasienergies to control the running time steps. In Grover's database search problem, the costs to prepare |v> for the qualitatively different (i.e., power or exponential) running time steps are shown to be qualitatively different.

Tanaka, Atushi; Nemoto, Kae [Department of Physics, Tokyo Metropolitan University, Minami-Osawa, Hachioji, Tokyo 192-0397 (Japan); National Institute of Informatics, 2-1-2 Hitotsubashi, Chiyoda ku, Tokyo 101-8430 (Japan)

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

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

A proof that continuous-time quantum walks are universal for quantumcomputation, 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.

Lovett, Neil B.; Cooper, Sally; Everitt, Matthew; Trevers, Matthew; Kendon, Viv [School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom)

Information is something that can be encoded in the state of a physical system, and a computation is a task that can be performed with a physically realizable device. Therefore, since the physical world is fundamentally quantum mechanical, the foundations of information theory and computer science should be sought in quantum physics. In fact, quantum information has weird properties that

Information is something that can be encoded in the state of a physical system, and a computation is a task that can be performed with a physically realizable device. Therefore, since the physical world is fundamentally quantum mechanical, the foundations of information theory and computer science should be sought in quantum physics. In fact, quantum information has weird properties that

Information is something that can be encoded in the state of a physical system, and a computation is a task that can be performed with a physically realizable device. Therefore, since the physical world is fundamentally quantum mechanical, the foundations of information theory and computer science should be sought in quantum physics. In fact, quantum information has weird properties that

We argue that computation via quantum mechanical processes is irrelevant to explaining how brains produce thought, contrary to the ongoing speculations of many theorists. First, quantum effects do not have the temporal properties required for neural information processing. Second, there are substantial physical obstacles to any organic instantiation of quantumcomputation. Third, there is no psychological evidence that such mental

Abninder Litt; Chris Eliasmith; Frederick W. Kroon

We present a scheme of quantumcomputation that consists entirely of one-qubit measurements on a particular class of entangled states, the cluster states. The measurements are used to imprint a quantum logic circuit on the state, thereby destroying its entanglement at the same time. Cluster states are thus one-way quantumcomputers and the measurements form the program.

An event advertised as the first demonstration of a commercial quantumcomputer raises the question of how far one can go with a 'do not care' attitude towards imperfections, without losing the quantum advantage.

We develop a multivalued logic for quantumcomputing for use in multi-level quantum systems, and discuss the practical advantages of this approach for scaling up a quantumcomputer. Generalizing the methods of binary quantum logic, we establish that arbitrary unitary operations on any number of d-level systems (d>2) can be decomposed into logic gates that operate on only two systems

Quantumcomputers hold the promise of solving problems that would otherwise be intractable with conventional computers. Some prototypes of the simplest elements needed to build a quantumcomputer have already been implemented in the laboratory. The efforts now concentrate on combining these elements into scalable systems. In addition, alternative routes to creating large scale quantumcomputers are continuously being developed. This volume gives a cross-section of recent achievements in both the theory and the practical realization of quantumcomputing devices. Samuel L. Braunstein (Reader, University of Wales, Bangor, and editor of the book "QuantumComputing - Where do we want to go tomorrow") and Hoi-Kwong Lo (Chief Scientist, MagiQ Technologies, Inc., NY) invited experts across many disciplines involved in the development of quantumcomputers to review their proposals in a manner accessible to the non-expert. Breaking with tradition, this book not only contains proposals, but a set of independent expert evaluations of these ideas as well. As a by-product this volume facilitates a comparison between the widely varying disciplines covered, including: ion traps, cavity quantum electrodynamics, nuclear magnetic resonance, optical lattices, quantum dots, silicon systems, superconductivity and electrons on helium.

A Knill-Laflamme-Milburn (KLM) type quantumcomputation with bosonic neutral atoms or bosonic ions is suggested. Crucially, as opposite to other quantumcomputation 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

Recent research has demonstrated that quantumcomput- ers can solve certain types of problems substantially faster than the known classical algorithms. These problems include factoring integers and certain physics simulations. Practical quantumcomputation requires overcoming the problems of environmental noise and operational errors, problems which appear to be much more severe than in classical computation due to the inherent fragility

Emanuel Knill; Raymond Laflamme; Wojciech H. Zurek

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

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

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

In quantumcomputational 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 quantumcomputational semantics: (1) a compositional semantics, where the meaning of a compound formula is determined by the meanings of its parts; (2) a holistic semantics, which makes essential use of the characteristic “holistic” features of the quantum-theoretic formalism. The compositional and the holistic semantics turn out to characterize the same logic. In this framework, one can introduce the notion of quantum-classical truth table, which corresponds to the most natural way for a quantumcomputer to calculate classical tautologies. Quantumcomputational logics can be applied to investigate different kinds of semantic phenomena where holistic, contextual and gestaltic patterns play an essential role (from natural languages to musical compositions).

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

In the quantum optics group at Caltech, we are attempting to lay the foundations for quantum information science by way of advances on several fronts in optical physics. Within the setting of cavity QED, single atoms are strongly coupled to the field of a high finesse optical cavity at the single photon level, with current work directed toward trapping and

H. J. Kimble; J. Buck; C. Fuchs; A. Furusawa; C. Hood; H. Mabuchi; T. Lynn; J. Sorensen; Q. Turchette; S. Van Enk; D. Vernooy; J. Ye

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

Because of its geometric nature, holonomic quantumcomputation is fault tolerant against certain types of control errors. Although proposed more than a decade ago, the experimental realization of holonomic quantumcomputation is still an open challenge. In this Letter, we report the first experimental demonstration of nonadiabatic holonomic quantumcomputation 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 quantumcomputation demonstrates the experimental feasibility of this quantumcomputing paradigm. PMID:23705695

|The quantumcomputer 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…

A quantumcomputer can be implemented with cold ions confined in a linear trap and interacting with laser beams. Quantum gates involving any pair, triplet, or subset of ions can be realized by coupling the ions through the collective quantized motion. In this system decoherence is negligible, and the measurement (readout of the quantum register) can be carried out with

Quantum chemistry is concerned with solving the Schrodinger equation for chemically relevant systems. This is typically done by making useful and systematic approximations which form the basis for model chemistries. A primary contribution of this dissertation, is taking concrete steps toward establishing a new model chemistry based on quantumcomputation. Electronic energies of the system can be efficiently obtained to fixed accuracy using quantum algorithms exploiting the ability of quantumcomputers to efficiently simulate the time evolution of quantum systems. The quantum circuits for simulation of arbitrary electronic Hamiltonians are given using quantum bits associated with single particle basis functions. This model chemistry is applied to hydrogen molecule as a case study where all necessary quantum circuits are clearly laid out. Furthermore, our collaboration to experimentally realize a simplified version of the hydrogen molecule quantum circuit is also included in this thesis. Finally, alternatives to the gate model of quantumcomputation are pursued by exploring models based on the quantum adiabatic theorem and on the generalization of random walks.

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 quantumcomputing. Here, we suggest a circuit-QED approach to nonlinear optics quantumcomputing 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

Though attractive from scalability aspects, optical approaches to quantumcomputing are highly prone to decoherence and rapid population loss due to nonradiative processes such as vibrational redistribution. We show that such effects can be reduced by adiabatic coherent control, in which quantum interference between multiple excitation pathways is used to cancel coupling to the unwanted, non-radiative channels. We focus on experimentally demonstrated adiabatic controlled population transfer experiments wherein the details on the coherence aspects are yet to be explored theoretically but are important for quantumcomputation. Such quantumcomputing schemes also form a back-action connection to coherent control developments.

Intensive research on the construction of superconducting quantumcomputers 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 quantumcomputing 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

We investigate the boundary between classical and quantumcomputational power. This work consists of two parts. First we develop new classical simulation algorithms that are centered on sampling methods. Using these techniques we generate new classes of classically simulatable quantum circuits where standard techniques relying on the exact computation of measurement probabilities fail to provide efficient simulations. For example, we

We show, under natural assumptions for qubit systems, that measurement-based quantumcomputations (MBQCs) which compute a nonlinear Boolean function with a high probability are contextual. The class of contextual MBQCs includes an example which is of practical interest and has a superpolynomial speedup over the best-known classical algorithm, namely, the quantum algorithm that solves the “discrete log” problem.

A two-dimensional quantum system with anyonic excitations can be considered as a quantumcomputer. Unitary transformations can be performed by moving the excitations around each other. Measurements can be performed by joining excitations in pairs and observing the result of fusion. Such computation is fault-tolerant by its physical nature.

To facilitate numerical study of noise and decoherence in QC algorithms,and of the efficacy of error correction schemes, we have developed a Fortran 90 quantumcomputer simulator with parallel processing capabilities. It permits rapid evaluation of quantum algorithms for a large number of qubits and for various ``noise'' scenarios. State vectors are distributed over many processors, to employ a large number of qubits. Parallel processing is implemented by the Message-Passing Interface protocol. A description of how to spread the wave function components over many processors, along with how to efficiently describe the action of general one- and two-qubit operators on these state vectors will be delineated.Grover's search and Shor's factoring algorithms with noise will be discussed as examples. A major feature of this work is that concurrent versions of the algorithms can be evaluated with each version subject to diverse noise effects, corresponding to solving a stochastic Schrodinger equation. The density matrix for the ensemble of such noise cases is constructed using parallel distribution methods to evaluate its associated entropy. Applications of this powerful tool is made to delineate the stability and correction of QC processes using Hamiltonian based dynamics.

The applications of photonic entanglement manifold and reach from quantum communication [1] to quantum metrology [2] and optical quantumcomputing [3]. The advantage of the photon's mobility makes optical quantumcomputing unprecedented in speed, including feed-forward operations with high fidelity [4]. During the last few years the degree of control over photonic multi-particle entanglement has improved substantially and allows for not only overcoming the random nature of spontaneous emission sources [5], but also for the quantum simulation of other quantum systems. Here, I will also present the simulation of four spin-1/2 particles interacting via any Heisenberg-type Hamiltonian [6]. Moreover, recent experimental and theoretical progress, using the concepts of measurement-based quantumcomputation, indicates that photons are best suited for quantum networks. I will also present present results for the realization for such a client-server environment, where quantum information is communicated and computed using the same physical system [7]. References: [1] PRL 103, 020503 (2009); [2] Nature 429, 158 (2004); [3] Nature 434, 169 (2005); [4] Nature 445, 65 (2007); [5] Nature Photon 4, 553 (2010); [6] Nature Physics 7, 399 (2011); [7] in press.

We propose a magnetic resonance force microscopy (MRFM)-based nuclear spin quantumcomputer using tellurium impurities in silicon. This approach to quantumcomputing combines well-developed silicon technology and expected advances in MRFM. Our proposal does not use electrostatic gates to realize quantum logic operations.

Berman, G. P.; Doolen, G. D.; Hammel, P. C.; Tsifrinovich, V. I.

We propose a magnetic resonance force microscopy (MRFM)-based nuclear spin quantumcomputer using tellurium impurities in silicon. This approach to quantumcomputing combines well-developed silicon technology and expected advances in MRFM. Our proposal does not use electrostatic gates to realize quantum logic operations. PMID:11290066

Berman, G P; Doolen, G D; Hammel, P C; Tsifrinovich, V I

|This publication provides materials to help adult educators use computertechnology in their teaching. Section 1, Computer Basics, contains activities and materials on these topics: increasing computer literacy, computer glossary, parts of a computer, keyboard, disk care, highlighting text, scrolling and wrap-around text, setting up text,…

Slider, Patty; Hodges, Kathy; Carter, Cea; White, Barbara

We show that universal quantumcomputation can be achieved in the standard pure-state circuit model while the entanglement entropy of every bipartition is small in each step of the computation. The entanglement entropy required for large-scale quantumcomputation even tends to zero. Moreover we show that the same conclusion applies to many entanglement measures commonly used in the literature. This includes e.g., the geometric measure, localizable entanglement, multipartite concurrence, squashed entanglement, witness-based measures, and more generally any entanglement measure which is continuous in a certain natural sense. These results demonstrate that many entanglement measures are unsuitable tools to assess the power of quantumcomputers.

We analyze the ground-state entanglement in a quantum adiabatic evolution algorithm designed to solve the NP-complete Exact Cover problem. The entropy of entanglement seems to obey linear and universal scaling at the point where the energy gap becomes small, suggesting that the system passes near a quantum phase transition. Such a large scaling of entanglement suggests that the effective connectivity of the system diverges as the number of qubits goes to infinity and that this algorithm cannot be efficiently simulated by classical means. On the other hand, entanglement in Grover's algorithm is bounded by a constant.

Latorre, Jose Ignacio; Orus, Roman [Department d'Estructura i Constituents de la Materia, Universitat de Barcelona, 08028, Barcelona (Spain)

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

Blind quantumcomputation is a new secure quantumcomputing protocol where a client, who does not have enough quantumtechnologies at her disposal, can delegate her quantumcomputation to a server, who has a fully fledged quantumcomputer, in such a way that the server cannot learn anything about the client's input, output, and program. If the client interacts with only a single server, the client has to have some minimum quantum power, such as the ability of emitting randomly rotated single-qubit states or the ability of measuring states. If the client interacts with two servers who share Bell pairs but cannot communicate with each other, the client can be completely classical. For such a double-server scheme, two servers have to share clean Bell pairs, and therefore the entanglement distillation is necessary in a realistic noisy environment. In this Letter, we show that it is possible to perform entanglement distillation in the double-server scheme without degrading the security of blind quantumcomputing. PMID:23889375

We describe an array of quantum gates implementing Shor's algorithm [in Proceedings of the 35th Annual Symposium on Foundations of Computer Science, edited by S. Goldwasser (IEEE Computer Society, Los Alamitos, CA, 1994), p. 116; (unpublished); Phys. Rev. A 53, R2493 (1995)] for prime factorization in a quantumcomputer. The array includes a circuit for modular exponentiation with several subcomponents (such as controlled multipliers and adders) that are described in terms of elementary Toffoli gates. We present a simple analysis of the impact of losses and decoherence on the performance of this quantum factoring circuit. For that purpose, we simulate a quantumcomputer that is running the program to factor N=15 while interacting with a dissipative environment. As a consequence of this interaction, randomly selected quantum bits (qubits) may spontaneously decay. Using the results of our numerical simulations, we analyze the efficiency of some simple error correction techniques.

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...

Presented is a quantum lattice gas for Navier-Stokes fluid dynamics simulation. The quantum lattice-gas transport equation at the microscopic scale is presented as a generalization of the classical lattice-gas transport equation. A special type of quantum...

We investigate relations between computational power and correlation in resource states for quantumcomputational tensor network, which is a general framework for measurement-based quantumcomputation. We find that if the size of resource states is finite, not all resource states allow correct projective measurements in the correlation space, which is related to non-vanishing two-point correlations in the resource states. On

Matchgates are a group of two-qubit gates associated with free fermions. They are classically simulatable if restricted to act between nearest neighbors on a one-dimensional chain, but become universal for quantumcomputation with longer-range interactions. We describe various alternative geometries with nearest-neighbor interactions that result in universal quantumcomputation with matchgates only, including subtle departures from the chain. Our results pave the way for new quantumcomputer architectures that rely solely on the simple interactions associated with matchgates.

In certain approaches to quantumcomputing the operations between qubits are nondeterministic and likely to fail. For example, a distributed quantum processor would achieve scalability by networking together many small components; operations between components should be assumed to be failure prone. In the ultimate limit of this architecture each component contains only one qubit. Here we derive thresholds for fault-tolerant quantumcomputation under this extreme paradigm. We find that computation is supported for remarkably high failure rates (exceeding 90%) providing that failures are heralded; meanwhile the rate of unknown errors should not exceed 2 in 104 operations.

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

The application of concatenated codes to fault tolerant quantumcomputing 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.

Contents §0. Introduction §1. Abelian problem on the stabilizer §2. Classical models of computations2.1. Boolean schemes and sequences of operations2.2. Reversible computations §3. Quantum formalism3.1. Basic notions and notation3.2. Transformations of mixed states3.3. Accuracy §4. Quantum models of computations4.1. Definitions and basic properties4.2. Construction of various operators from the elements of a basis4.3. Generalized quantum control and universal schemes §5.

Schemes for the construction of quantumcomputers on multiatomic ensembles in quantum electrodynamic cavity are considered. With that, both encoding of physical qubits on each separate multiatomic ensemble and logical encoding of qubits on the pairs of ensembles are introduced. Possible constructions of swapping ( SWAP, sqrt {SWAP} ) and controlled swapping gates ( CSWAP) are analyzed. Mechanism of collective blockade and dynamical elimination procedure are proposed for realization of these gates. The comparison of the scheme solutions is carried out for the construction of quantumcomputer at using of physical and logical qubits.

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

For several years now quantumcomputing has been viewed as a new paradigm for certain computing applications. Of particular importance to this burgeoning field is the development of an algorithm for factoring large numbers which obviously has deep implications for cryptography and national security. Implementation of these theoretical ideas faces extraordinary challenges in preparing and manipulating quantum states. The quantum transport group at Sandia has demonstrated world-leading, unique double quantum wires devices where we have unprecedented control over the coupling strength, number of 1 D channels, overlap and interaction strength in this nanoelectronic system. In this project, we study 1D-1D tunneling with the ultimate aim of preparing and detecting quantum states of the coupled wires. In a region of strong tunneling, electrons can coherently oscillate from one wire to the other. By controlling the velocity of the electrons, length of the coupling region and tunneling strength we will attempt to observe tunneling oscillations. This first step is critical for further development double quantum wires into the basic building block for a quantumcomputer, and indeed for other coupled nanoelectronic devices that will rely on coherent transport. If successful, this project will have important implications for nanoelectronics, quantumcomputing and information technology.

Lyo, Sungkwun Kenneth; Dunn, Roberto G.; Lilly, Michael Patrick; Tibbetts, Denise R. (.; )); Stephenson, Larry L.; Seamons, John Andrew; Reno, John Louis; Bielejec, Edward Salvador; Simmons, Jerry Alvon

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

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

Quantum information science involves exploration of fundamental laws of quantum mechanics for information processing tasks. This thesis presents several new approaches towards scalable quantum information processing. First, we consider a hybrid approach to scalable quantumcomputation, based on an optically connected network of few-qubit quantum registers. Specifically, we develop a novel scheme for scalable quantumcomputation that is robust against

We introduce stochastic and quantum finite-state transducers as computation-theoretic models of classical stochastic and quantum finitary processes. Formal process languages, representing the distribution over a process’ behaviors, are recognized and generated by suitable specializations. We characterize and compare deterministic and nondeterministic versions, summarizing their relative computational power in a hierarchy of finitary process languages. Quantum finite-state transducers and generators are a first step toward a computation-theoretic analysis of individual, repeatedly measured quantum dynamical systems. They are explored via several physical systems, including an iterated-beam-splitter, an atom in a magnetic field, and atoms in an ion trap—a special case of which implements the Deutsch quantum algorithm. We show that these systems’ behaviors, and so their information processing capacity, depends sensitively on the measurement protocol.

After a brief introduction to the principles and promise of quantum\\u000ainformation processing, the requirements for the physical implementation of\\u000aquantum computation are discussed. These five requirements, plus two relating\\u000ato the communication of quantum information, are extensively explored and\\u000arelated to the many schemes in atomic physics, quantum optics, nuclear and\\u000aelectron magnetic resonance spectroscopy, superconducting electronics, and\\u000aquantum-dot

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

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

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

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

We show how the measurement induced model of quantumcomputation proposed by Raussendorf and Briegel (2001, Phys. Rev. Letts., 86, 5188) can be adapted to a nonlinear optical interaction. This optical implementation requires a Kerr nonlinearity, a single photon source, a single photon detector and fast feed forward. Although nondeterministic optical quantum information proposals such as that suggested by KLM

We solve a problem, which while not fitting into the usual paradigm, can be viewed as a quantumcomputation. Suppose we are given a quantum system with a Hamiltonian of the form E\\\\|w> is an unknown (normalized) state. The problem is to produce \\\\|w> by adding a Hamiltonian (independent of \\\\|w>) and evolving the system. If \\\\|w> is chosen uniformly

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

We show that quantumcomputation circuits using coherent states as the logical qubits can be constructed from simple linear networks, conditional photon measurements, and 'small' coherent superposition resource states.

We investigate the boundary between classical and quantumcomputational\\u000apower. This work consists of two parts. First we develop new classical\\u000asimulation algorithms that are centered on sampling methods. Using these\\u000atechniques we generate new classes of classically simulatable quantum circuits\\u000awhere standard techniques relying on the exact computation of measurement\\u000aprobabilities fail to provide efficient simulations. For example, we

It is sometimes saidthat Everett's formulation of Quantum Mechanics dispenses us with the need of a theory of consciousness in the foundation of physics. This is false as Everett himself clearly recognized in his paper. Ind eedhe has buildits quantum mechanics formulation by us- ing explicitly the mechanist or computationalist hypothesis in psychology. Everett andhis followers have then d erivedthe

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

Edward Farhi; Jeffrey Goldstone; Sam Gutmann; Michael Sipser

We give a detailed account of the one-way quantumcomputer, a scheme of quantumcomputation that consists entirely of one-qubit measurements on a particular class of entangled states, the cluster states. We prove its universality, describe why its underlying computational model is different from the network model of quantumcomputation, and relate quantum algorithms to mathematical graphs. Further we investigate

Robert Raussendorf; Daniel E. Browne; Hans J. Briegel

We study various aspects of the topological quantumcomputation scheme based on the non-Abelian anyons corresponding to fractional\\u000a quantum hall effect states at filling fraction 5\\/2 using the Temperley-Lieb recoupling theory. Unitary braiding matrices are\\u000a obtained by a normalization of the degenerate ground states of a system of anyons, which is equivalent to a modification of\\u000a the definition of the

Universal quantumcomputation (UQC) using Majorana fermions on a two-dimensional 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 no 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, by constructing topologically protected two-qubit gates and any arbitrary single-qubit phase gate in a topologically unprotected manner, which can be error corrected using magic-state distillation. Thus our strategy, using a judicious combination of topologically protected and unprotected gate operations, realizes UQC on a quantum wire network with a remarkably high error threshold of 0.14 as compared to 10{sup -3} to 10{sup -4} in ordinary unprotected quantumcomputation.

Sau, Jay D.; Das Sarma, S. [Condensed Matter Theory Center and Joint Quantum Institute, Department of Physics, University of Maryland, College Park, Maryland 20742-4111 (United States); Tewari, Sumanta [Condensed Matter Theory Center and Joint Quantum Institute, Department of Physics, University of Maryland, College Park, Maryland 20742-4111 (United States); Department of Physics and Astronomy, Clemson University, Clemson, South Carolina 29634 (United States)

We construct a universal quantumcomputer 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 quantumcomputationally 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.

Lagana, Antonio A.; Lohe, M. A.; Smekal, Lorenz von [Department of Physics, University of Adelaide, South Australia 5005 (Australia)

We present a linear optics quantumcomputation scheme with a greatly reduced cost in resources compared to that proposed by Knill, Laflamme, and Milburn (KLM). The scheme makes use of elements from cluster state computation but retains the circuit based approach of KLM.

We present a linear optics quantumcomputation scheme with a greatly reduced cost in resources compared to that proposed by Knill, Laflamme, and Milburn (KLM). The scheme makes use of elements from cluster state computation but retains the circuit based approach of KLM.

Gilchrist, Alexei; Hayes, A. J. F.; Ralph, T. C. [Centre for Quantum Computer Technology and Physics Department, University of Queensland, QLD 4072, Brisbane (Australia)

A significant development in computing has been the discovery that the computational power of quantumcomputers exceeds that of Turing machines. Central to the experimental realization of quantum information processing is the construction of fault-tolerant quantum logic gates. Their operation requires conditional quantum dynamics, in which one sub-system undergoes a coherent evolution that depends on the quantum state of another sub-system; in particular, the evolving sub-system may acquire a conditional phase shift. Although conventionally dynamic in origin, phase shifts can also be geometric. Conditional geometric (or 'Berry') phases depend only on the geometry of the path executed, and are therefore resilient to certain types of errors; this suggests the possibility of an intrinsically fault-tolerant way of performing quantum gate operations. Nuclear magnetic resonance techniques have already been used to demonstrate both simple quantum information processing and geometric phase shifts. Here we combine these ideas by performing a nuclear magnetic resonance experiment in which a conditional Berry phase is implemented, demonstrating a controlled phase shift gate. PMID:10706278

Quantum-computing ideas are applied to the practical and ubiquitous problem of fluid dynamics simulation. Hence, this paper addresses two separate areas of physics: quantum mechanics and fluid dynamics (or specially, the computational simulation of fluid dynamics). The quantum algorithm is called a quantum lattice gas. An analytical treatment of the microscopic quantum lattice-gas system is carried out to predict its

A quantum algorithm is presented for modeling the time evolution of density and flow fields governed by classical equations, such as the diffusion equation, the nonlinear Burgers equation, and the damped wave equation. The algorithm is intended to run on a type-II quantumcomputer, a parallel quantumcomputer consisting of a lattice of small type I quantumcomputers undergoing unitary

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

An information-theoretic temporal Bell inequality is formulated to contrast classical and quantumcomputations. Any classical algorithm satisfies the inequality, while quantum ones can violate it. Therefore, the violation of the inequality is an immediate consequence of the quantumness in the computation. Furthermore, this approach suggests a notion of temporal nonlocality in quantumcomputation.

Quantumcomputers promise to increase greatly the efficiency of solving problems such as factoring large integers, combinatorial optimization and quantum physics simulation. One of the greatest challenges now is to implement the basic quantum-computational elements in a physical system and to demonstrate that they can be reliably and scalably controlled. One of the earliest proposals for quantumcomputation is based

The research is aimed at applying computer science and technology to problem areas of high DoD/military impact. The ISI program consists of eight research areas: Program Verification -- logical proof of program validity; Programming Research Instrument --...

This report summarizes the research performed by USC/Information Sciences Institute from July 1, 1986, to November 30, 1987, for the Defense Advanced Research Projects Agency. The research is focused on the development of computer science and technology, ...

We show how the measurement induced model of quantumcomputation proposed by\\u000aRaussendorf and Briegel [Phys. Rev. Letts. 86, 5188 (2001)] can be adapted to a\\u000anonlinear optical interaction. This optical implementation requires a Kerr\\u000anonlinearity, a single photon source, a single photon detector and fast feed\\u000aforward. Although nondeterministic optical quantum information proposals such\\u000aas that suggested by KLM

In order to use quantum error-correcting codes to improve the performance of a quantumcomputer, it is necessary to be able to perform operations fault-tolerantly on encoded states. I present a theory of fault-tolerant operations on stabilizer codes based on symmetries of the code stabilizer. This allows a straightforward determination of which operations can be performed fault-tolerantly on a given

The history of modern computing is a truly fascinating subject, and the folks at the Internet Archive have created this delightful collection of videos that document many recent developments in the field. The backbone of the 2,100 item collection is the inclusion of Computer Chronicles and Net Cafe. Computer Chronicles was a program hosted by Stewart Cheifet, broadcast from 1983 to 2002. Visitors can watch over 560 episodes of the program, which covers everything from color printers to trade shows. Moving on, visitors can view past episodes of Net Cafe, which was broadcast from 1996 to 2002. This weekly program went behind the scenes of what used to be known as the World Wide Web, and it was produced on location at Internet cafes around the Bay Area and Silicon Valley. The site is rounded out by other programs on internet governance and documentaries on Bulletin Board Services (BBS).

We have previously [11] shown that for quantum memories andquantum communication, a state can be transmitted over arbitrarydistances with error ffl provided each gate has error at most cffl. Wediscuss a similar concatenation technique which can be used with faulttolerant networks to achieve any desired accuracy when computingwith classical initial states, provided a minimum gate accuracy can beachieved. The technique

The authors describe two methods that have been proposed to circumvent the problem of heating by external electromagnetic fields in ion trap quantumcomputers. Firstly the higher order modes of ion oscillation (i.e., modes other than the center-of-mass mode) have much slower heating rates, and can therefore be employed as a reliable quantum information bus. Secondly they discuss a recently proposed method combining adiabatic passage and a number-state dependent phase shift which allows quantum gates to be performed using the center-of-mass mode as the information bus, regardless of its initial state.

James, D.F.V. [Los Alamos National Lab., NM (United States); Schneider, S. [Los Alamos National Lab., NM (United States)]|[Univ. of Queensland, St. Lucia, Queensland (Australia); Milburn, G.J. [Univ. of Queensland, St. Lucia, Queensland (Australia)

Computing involves social issues and political choices. Issues such as privacy, computer crime, gender inequity, disemployment, and electronic democracy versus "Big Brother" are addressed in the context of efforts to develop a national public policy for information technology. A broad range of research and case studies are examined in an attempt…

We propose a way of universal quantumcomputation by doing joint measurements on distributed singlets. We show how these joint measurements become local measurements when the singlets are interpreted as the virtual components of a large valence-bond state. This proves the equivalence of the cluster-state-based quantumcomputational model and the teleportation-based model, and we discuss several features and possible extensions. We show that all stabilizer states have a very simple interpretation in terms of valence-bond solids, which allows to understand their entanglement properties in a transparent way.

Information is something that can be encoded in the state of a physical system, and a computation is a task that can be performed with a physically realizable device. Therefore, since the physical world is fundamentally quantum mechanical, the foundations of information theory and computer science should be sought in quantum physics. In fact, quantum information has weird properties that contrast sharply with the familiar properties of classical information. A quantumcomputer -- a new type of machine that exploits the quantum properties of information -- could perform certain types of calculations far more efficiently than any foreseeable classical computer. To build a functional quantumcomputer will be an enormous technical challenge; in particular, a quantumcomputer is far more susceptible to errors than a conventional digital computer. New methods for quantum error correction are now being developed that can help to prevent a quantumcomputer from crashing.

We study an architecture for implementing adiabatic quantumcomputation with trapped neutral atoms. Ground-state atoms are dressed by laser fields in a manner conditional on the Rydberg blockade mechanism, thereby providing the requisite entangling interactions. As a benchmark, we study the performance of quantum annealing to the ground state of an Ising spin lattice. We model a proof-of-principle experiment in a realistic architecture, including details of the atomic implementation, with qubits encoded in the clock states of 133Cs. Numerical simulation yields fidelities >0.98 for up to four qubits, and implementations of 10–20 qubits are within the range of current technology.

Keating, Tyler; Goyal, Krittika; Jau, Yuan-Yu; Biedermann, Grant W.; Landahl, Andrew J.; Deutsch, Ivan H.

We discuss the fundamental limits of computing using a new paradigm for quantumcomputation, cellular automata composed of arrays of coulombically coupled quantum dot molecules, which we term quantum cellular automata (QCA). Any logical or arithmetic operation can be performed in this scheme. QCA's provide a valuable concrete example of quantumcomputation in which a number of fundamental issues come

We investigate the connection between local minima in the problem Hamiltonian and first-order quantum phase transitions during adiabatic quantumcomputation. We demonstrate how some properties of the local minima can lead to an extremely small gap that is exponentially sensitive to the Hamiltonian parameters. Using perturbation expansion, we derive an analytical formula that cannot only predict the behavior of the gap, but also provide insight on how to controllably vary the gap size by changing the parameters. We show agreement with numerical calculations for a weighted maximum independent set problem instance.

Amin, M. H. S. [D-Wave Systems Inc., 100-4401 Still Creek Drive, Burnaby, British Columbia, V5C 6G9 (Canada); Choi, V. [D-Wave Systems Inc., 100-4401 Still Creek Drive, Burnaby, British Columbia, V5C 6G9 (Canada); Department of Computer Science, Virginia Tech, Falls Church, Virginia 22043 (United States)

Qubits demonstrated using GaAs double quantum dots (DQD). The qubit basis states are the (1) singlet and (2) triplet stationary states. Long spin decoherence times in silicon spurs translation of GaAs qubit in to silicon. In the near term the goals are: (1) Develop surface gate enhancement mode double quantum dots (MOS & strained-Si/SiGe) to demonstrate few electrons and spin read-out and to examine impurity doped quantum-dots as an alternative architecture; (2) Use mobility, C-V, ESR, quantum dot performance & modeling to feedback and improve upon processing, this includes development of atomic precision fabrication at SNL; (3) Examine integrated electronics approaches to RF-SET; (4) Use combinations of numerical packages for multi-scale simulation of quantum dot systems (NEMO3D, EMT, TCAD, SPICE); and (5) Continue micro-architecture evaluation for different device and transport architectures.

Horton, Rebecca; Carroll, Malcolm S.; Tarman, Thomas David

Nowadays there are two secure ways of encrypting information, the public key cryptography (PKC), and the symmetric cryptography (SC). With the arrival of the quantumcomputation, both methods become vulnerable, thanks to its exponential-growing calculation capacity. To solve this lack of security, quantum physics nowadays offers us two satisfactory methods which have been proposed successfully from a theoretical point of view: the two non-commuting observables, based on the Bennet and Brassard protocol, and the quantum entanglement combined with the Bell's inequality theorem, based on the Ekert protocol. Since some experiments have demonstrated the viability of the conduction of free space quantum cryptography at the surface of the Earth, we propose that this could be a boost for secure ground-to-satellite or satellite-to-satellite communications.

Delicado, Raquel Fernandez; Cabello, David Bellver; Boada, Ivan Lloro

Quantumcomputation is one of the most active areas of research in academia. Nearly every university in the world that has a science department has researchers who are working on either trying to build hardware or develop algorithms for these machines. In this talk I will describe D-Wave's goals and achievements in assembling a global research network, centered in Canada, whose purpose is the development of superconducting quantumcomputer hardware. In addition I will describe the technical approach that we are concentrating on, involving cuprate-based flux qubits and niobium RSFQ control circuitry. Finally I will introduce a very important application of these machines, namely their use as simulators of other quantum systems, in the context of human pharmaceutical drug and vaccine design.

For a 3-manifold with triangulated boundary, the Turaev-Viro topological invariant can be interpreted as a quantum error-correcting code. The code has local stabilizers, identified by Levin and Wen, on a qudit lattice. Kitaev’s toric code arises as a special case. The toric code corresponds to an abelian anyon model, and therefore requires out-of-code operations to obtain universal quantumcomputation. In contrast, for many categories, such as the Fibonacci category, the Turaev-Viro code realizes a non-abelian anyon model. A universal set of fault-tolerant operations can be implemented by deforming the code with local gates, in order to implement anyon braiding. We identify the anyons in the code space, and present schemes for initialization, computation and measurement. This provides a family of constructions for fault-tolerant quantumcomputation that are closely related to topological quantumcomputation, but for which the fault tolerance is implemented in software rather than coming from a physical medium.

Koenig, Robert; Kuperberg, Greg; Reichardt, Ben W.

Nuclear magnetic resonance (NMR) quantumcomputation in a crystal lattice holds more promise for scalability than its solution NMR counterpart, but dephasing is a severe concern. Pulse sequence refocusing can help bring the qubit dephasing time closer to the limit of the intrinsic decoherence time, but the intrinsic transverse relaxation time (T2) and the longitudinal relaxation time (T1) of the

T. D. Ladd; J. R. Goldman; F. Yamaguchi; Y. Yamamoto

This article presents a new approach to quantumcomputing based on using bulk samples rather than isolated degrees of freedom. The problem, of course, is that such samples microscopically are in a thermal distribution of states, and it is impractical to hope to cool macroscopic materials to their ground state; furthermore, bulk samples are macroscopic ensembles whose members cannot be

It is shown that the Fourier transform preceding the final measurement in Shor's algorithm for factorization on a quantumcomputer can be carried out in a semiclassical way by using the ``classical'' (macroscopic) signal resulting from measuring one bit to determine the type of measurement carried out on the next bit, and so forth. In this way all the two-bit

For a 3-manifold with triangulated boundary, the Turaev-Viro topological invariant can be interpreted as a quantum error-correcting code. The code has local stabilizers, identified by Levin and Wen, on a qudit lattice. Kitaev's toric code arises as a special case. The toric code corresponds to an abelian anyon model, and therefore requires out-of-code operations to obtain universal quantumcomputation. In contrast, for many categories, such as the Fibonacci category, the Turaev-Viro code realizes a non-abelian anyon model. A universal set of fault-tolerant operations can be implemented by deforming the code with local gates, in order to implement anyon braiding. We identify the anyons in the code space, and present schemes for initialization, computation and measurement. This provides a family of constructions for fault-tolerant quantumcomputation that are closely related to topological quantumcomputation, but for which the fault tolerance is implemented in software rather than coming from a physical medium.

Koenig, Robert, E-mail: rkoenig@caltech.ed [Institute for Quantum Information, California Institute of Technology, Pasadena, CA 91125 (United States); Kuperberg, Greg [Department of Mathematics, University of California, Davis, CA 95616 (United States); Reichardt, Ben W. [School of Computer Science, Institute for Quantum Computing, University of Waterloo, Waterloo, ON, N2L 3G1 (Canada)

We give a detailed account of the one-way quantumcomputer, a scheme of quantumcomputation that consists entirely of one-qubit measurements on a particular class of entangled states, the cluster states. We prove its universality, describe why its underlying computational model is different from the network model of quantumcomputation, and relate quantum algorithms to mathematical graphs. Further we investigate the scaling of required resources and give a number of examples for circuits of practical interest such as the circuit for quantum Fourier transformation and for the quantum adder. Finally, we describe computation with clusters of finite size.

Raussendorf, Robert; Browne, Daniel E.; Briegel, Hans J. [Theoretische Physik, Ludwig-Maximilians-Universitaet Muenchen, Muenchen, (Germany)

Advances in quantum devices have brought scalable quantumcomputation closer to reality. We focus on the system-level issues of how quantum devices can be brought together to form a scalable architecture. In particular, we examine promising silicon-based proposals. We discover that communication of quantum data is a critical resource in such proposals. We find that traditional techniques using quantum SWAP

Dean Copsey; Mark Oskin; Francois Impens; Tzvetan Metodiev; A. Cross; F. T. Chong; I. L. Chuang; J. Kubiatowicz

New conceptual models for solid state fermionic interactions have been investigated for quantumcomputational atomic-level systems. The effects of decoherence in general as well as adiabatic decoherence upon coherent states of quantumcomputational elemen...

Improvements in the speed and accuracy of computed tomography (CT) systems, together with new developments in software, are changing the ways CT technology supports manufacturing operations. In addition to providing quantitative nondestructive inspection at the end of the manufacturing line, CT images are now also being compiled for reverse engineering and first-article characterization and certification. The enhanced performance of a state-of-the-art CT system makes it an effective complement to other digital data-based manufacturing technologies such as computer-aided design (CAD), computer-aided manufacturing (CAM), and computer-aided engineering (CAE). Furthermore, CT capabilities may be combined with those of rapid prototyping such as stereolithography, selective laser sintering, and direct metal deposition, to support the rapid, cost-efficient production of parts in small lots. This article describes how the system works, how it is used for inspection, and how it may assist with reverse engineering.

Armistead, R.A.; Stanley, J.H. [Advanced Research and Applications Corp. , Sunnyvale, CA (United States)

Computational Information Technology is a research group of the Laboratory of Computational Engineering at the Helsinki University of Technology in Finland. This section of the website introduces visitors to the group's work on modelling and analyzing complex physical, technical and economic processes and systems. Researchers "carry out method development and application oriented research on advanced probabilistic and information theoretic methods." Some applications include statistical modelling of financial markets, pattern recognition in neural networks, machine vision for microscope image processing, data mining, and intelligent human-machine interfaces. The Research Projects section describes the group's work in these areas and highlights the mathematical and statistical methods used, such as Bayesian methods, vision geometry, Turing's reaction-diffusion systems, and time-frequency analysis. Each research area has its own website, where the overall project and theoretical framework is described along with images and diagrams. Publications, such as theses and journal articles are listed and some conference proceedings and articles are available to download.

The interference has been measured by the visibility in two-level systems, which, however, does not work for multi-level systems. We generalize a measure of the interference based on decoherence process, consistent with the visibility in qubit systems. By taking cluster states as examples, we show in the one-way quantumcomputation that the gate fidelity is proportional to the interference of the measured qubit and is inversely proportional to the interference of all register qubits. We also find that the interference increases with the number of the computing steps. So we conjecture that the interference may be the source of the speedup of the one-way quantumcomputation.

Quantumcomputers promise to exceed the computational efficiency of ordinary classical machines because quantum algorithms allow the execution of certain tasks in fewer steps. But practical implementation of these machines poses a formidable challenge. Here I present a scheme for implementing a quantum-mechanical computer. Information is encoded onto the nuclear spins of donor atoms in doped silicon electronic devices. Logical

"The Stanford Persuasive Technology Lab creates insight into how computing products -- from websites to mobile phone software -- can be designed to change what people believe and what they do." This unusual field of study is called captology, and the subject is explored in detail on the lab's homepage. The Key Concepts section provides a brief overview of captology and links to another page with nine topic papers published by researchers at the lab. In a series of examples demonstrating how computers can be used to influence a person, the site's creators separate instances into macrosuasion and microsuasion. Specific websites and computer programs are highlighted to reveal these interesting marketing or motivational tactics.

The study of computer forensics technology signify much to attacking computer crime, invasion hunting, patch safety-bug, perfect safety system of network. This text makes a thorough and compact study on advancing computer forensics technology both at home and abroad; make an introduction of advancing technology, such as, dynamic computer forensics based on data mining, dynamic computer forensics based on Multi-agent,

Models of quantumcomputation (QC) are important because they change the physical requirements for achieving universal QC. For example, one-way QC requires the preparation of an entangled ''cluster'' state, followed by adaptive measurement on this state, a set of requirements which is different from the standard quantum-circuit model. Here we introduce a model based on one-way QC but without measurements (except for the final readout), instead using adiabatic deformation of a Hamiltonian whose initial ground state is the cluster state. Our results could help increase the feasibility of adiabatic schemes by using tools from one-way QC.

Bacon, Dave [Department of Computer Science and Engineering, University of Washington, Seattle, Washington 98195 (United States); Department of Physics, University of Washington, Seattle, Washington 98195 (United States); Flammia, Steven T. [Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2L 2Y5 (Canada)

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

We investigate relationships between computational power and correlation in resource states for quantumcomputational tensor network, which is a general framework for measurement-based quantumcomputation. We find that if the size of resource states is finite, not all resource states allow correct projective measurements in the correlation space, which is related to nonvanishing two-point correlations in the resource states. On the other hand, for infinite-size resource states, we can always implement correct projective measurements if the resource state can simulate arbitrary single-qubit rotations, since such a resource state exhibits exponentially decaying two-point correlations. This implies that a many-body state whose two-point correlation cannot be upper bounded by an exponentially decaying function cannot simulate arbitrary single-qubit rotations.

The curriculum guide is designed to provide students with realistic training in computertechnology theory and practice within the secondary educational framework and to prepare them for entry into an occupation or continuing postsecondary education. Each unit plan consists of a description of the area under consideration, estimated hours of…

Dependents Schools (DOD), Washington, DC. European Area.

This Mathematica 6.0 package is a simulation of a QuantumComputer. The program provides a modular, instructive approach for generating the basic elements that make up a quantum circuit. The main emphasis is on using the density matrix, although an approach using state vectors is also implemented in the package. The package commands are defined in Qdensity.m which contains the tools needed in quantum circuits, e.g., multiqubit kets, projectors, gates, etc.New version program summaryProgram title: QDENSITY 2.0 Catalogue identifier: ADXH_v2_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADXH_v2_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 26?055 No. of bytes in distributed program, including test data, etc.: 227?540 Distribution format: tar.gz Programming language: Mathematica 6.0 Operating system: Any which supports Mathematica; tested under Microsoft Windows XP, Macintosh OS X, and Linux FC4 Catalogue identifier of previous version: ADXH_v1_0 Journal reference of previous version: Comput. Phys. Comm. 174 (2006) 914 Classification: 4.15 Does the new version supersede the previous version?: Offers an alternative, more up to date, implementation Nature of problem: Analysis and design of quantum circuits, quantum algorithms and quantum clusters. Solution method: A Mathematica package is provided which contains commands to create and analyze quantum circuits. Several Mathematica notebooks containing relevant examples: Teleportation, Shor's Algorithm and Grover's search are explained in detail. A tutorial, Tutorial.nb is also enclosed. Reasons for new version: The package has been updated to make it fully compatible with Mathematica 6.0 Summary of revisions: The package has been updated to make it fully compatible with Mathematica 6.0 Running time: Most examples included in the package, e.g., the tutorial, Shor's examples, Teleportation examples and Grover's search, run in less than a minute on a Pentium 4 processor (2.6 GHz). The running time for a quantumcomputation depends crucially on the number of qubits employed.

Juliá-Díaz, Bruno; Burdis, Joseph M.; Tabakin, Frank

Nature intrinsically computes. It has been suggested that the entire universe is a computer, in particular, a quantumcomputer. 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 quantumcomputation 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

Quantumcomputation promises solution to problems that are hard to solve by classical computers. The efficient construction of quantum circuits that can solve interesting tasks is a fundamental challenge in the field. Such efficient construction also reduces decoherence losses in physical implementations of quantum algorithms by reducing interaction time with the environment. Therefore, finding time-optimal ways to synthesize unitary transformations from available physical resources is a problem of both fundamental and practical interest in quantum information processing. In this thesis, we study these problems in general mathematical frame as well as in some concrete real physical settings. We give a complete characterization of all the unitary transformations that can be synthesized in a given time for a two-qubit system in presence of general time varying coupling tensor, assuming that the local unitary transformation on two qubits can be performed arbitrarily fast (on a time scale governed by the strength of couplings). A generalization of this result on general Lie group is also presented. We then give the time optimal ways for coherence transfer on three linearly coupled spin chain, and an efficient way of constructing a CNOT gate between two indirectly coupled spins.

The rapid growth of data processing speed in computers has been sustained by the advances in cooling technology. This article first presents a review of the published data of heat loads in recent Japanese large-scale computers. The survey indicates that, since around 1980, the high-level integration of microelectronic circuits has brought about almost four fold increase in the power dissipation from logic chips. The integration also has invited the evolutions of multichip modules and new schemes of electronic interconnections. Forced convection air-cooling and liquid cooling coupled with thermal connectors are discussed with reference to the designs employed in actual computers. More advanced cooling schemes are also discussed. Finally, the importance of thermal environmental control of computer rooms is emphasized.

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

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

Highlights: > Our model is the 2D valence bond solid phase of a quantum antiferromagnet. > Universal quantumcomputation is processed by measurements of quantum correlations. > An intrinsic complexity of strongly-correlated quantum systems could be a resource. - Abstract: Quantum phases of naturally-occurring systems exhibit distinctive collective phenomena as manifestation of their many-body correlations, in contrast to our persistent technological challenge to engineer at will such strong correlations artificially. Here we show theoretically that quantum correlations exhibited in the 2D valence bond solid phase of a quantum antiferromagnet, modeled by Affleck, Kennedy, Lieb, and Tasaki (AKLT) as a precursor of spin liquids and topological orders, are sufficiently complex yet structured enough to simulate universal quantumcomputation when every single spin can be measured individually. This unveils that an intrinsic complexity of naturally-occurring 2D quantum systems-which has been a long-standing challenge for traditional computers-could be tamed as a computationally valuable resource, even if we are limited not to create newly entanglement during computation. Our constructive protocol leverages a novel way to herald the correlations suitable for deterministic quantumcomputation through a random sampling, and may be extensible to other ground states of various 2D valence bond phases beyond the AKLT state.

Miyake, Akimasa, E-mail: amiyake@perimeterinstitute.ca [Perimeter Institute for Theoretical Physics, 31 Caroline Street North, Waterloo Ontario, N2L 2Y5 (Canada)

We are developing, both theoretically and experimentally, a neutral atom qubit approach to adiabatic quantumcomputation. 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.

A new quantumcomputing architecture, quantum cellular automata, is studied. Quantum cellular automata (QCA's) are composed of interacting quantum dot molecules, each of which contains two electrons. Repulsion between these two electrons causes these molecules to exhibit bistable behavior, which allows the encoding of binary information directly in the quantum state of each cell. QCA's take advantage of "computing with the ground state", in which dissipation acts to drive the system to the ground state corresponding to the applied boundary conditions. By carefully designing the geometric layout of arrays of these quantum dot molecules, it is possible to perform useful calculations with these ground state alignments. The logic primitive of such a system is a majority logic gate, which can be reduced to act as either an AND gate or an OR gate. Due to the local nature of the Coulombic interaction between cells, it is possible to use hierarchical design rules to combine these elements into more complicated logic devices. Since the interactions between cells are purely Coulombic, no direct interconnections are necessary between QCA cells. In addition, energy is only supplied at the edge of the system when an input cell is switched, so QCA's can be said to be truly edge-driven. Such an edge-driven system will eliminate many of the fabrication challenges present in systems with complicated interconnection requirements. Although the results of a ground-state calculation do not rely on the exact nature of the system dynamics, these dynamics do provide an estimate of the switching speed of QCA devices. We have developed several approximate techniques for the modeling of this very complicated system and have obtained estimates on the intrinsic switching speed of both semiconductor-based cells and macro-molecular cells. As expected, the macro-molecular cells exhibit greatly improved performance over the larger semiconductor cells. An alternative to abrupt switching of QCA arrays takes advantage of the adiabatic theorem to guarantee that the system will always remain in its instantaneous ground state. Such adiabatic switching has several advantages over abrupt switching, the most important of which is avoidance of metastable states.

Single flux quantum (SFQ) electronics is extremely fast and has very low on-chip power dissipation. SFQ VLSI is an excellent candidate for high-performance computing and other applications requiring extremely high-speed signal processing. Despite this, SFQ technology has generally not been accepted for system implementation. We argue that this is due, at least in part, to the use of outdated tools

Arnold Silver; Paul Bunyk; Alan Kleinsasser; John Spargo

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

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.

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

Mao Wenjin [Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794, USA and 20 Hearthstone Drive, Edison, New Jersey 08820 (United States)

We present a quantum algorithm that additively approximates the value of a tensor network to a certain scale. When combined with existing results, this provides a complete problem for quantumcomputation. The result is a simple new way of looking at quantumcomputation in which unitary gates are replaced by tensors and time is replaced by the order in which

In the past year many developments had taken place in the area of quantum error corrections. Recently Shor showed how to perform fault tolerant quantumcomputation when, ?, the probability for a fault in one time step per qubit or per gate, is logarithmically small. This paper improves this bound and shows how to perform fault tolerant quantumcomputation when

Quantumcomputation 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 quantumcomputation in decoherence-free subspaces have been proposed in the past few years. However, nonadiabatic holonomic quantumcomputation 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 quantumcomputation 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, G. F.; Zhang, J.; Tong, D. M.; Sjöqvist, Erik; Kwek, L. C.

Precise control over quantum systems can enable the realization of fascinating applications such as powerful computers, secure communication devices, and simulators that can elucidate the physics of complex condensed matter systems. However, the fragility of quantum effects makes it very difficult to harness the power of quantum mechanics. In this thesis, we present novel systems and tools for gaining fundamental insights into the complex quantum world and for bringing practical applications of quantum mechanics closer to reality. We first optimize and show equivalence between a wide range of techniques for storage of photons in atomic ensembles. We describe experiments demonstrating the potential of our optimization algorithms for quantum communication and computation applications. Next, we combine the technique of photon storage with strong atom-atom interactions to propose a robust protocol for implementing the two-qubit photonic phase gate, which is an important ingredient in many quantumcomputation and communication tasks. In contrast to photon storage, many quantumcomputation and simulation applications require individual addressing of closely-spaced atoms, ions, quantum dots, or solid state defects. To meet this requirement, we propose a method for coherent optical far-field manipulation of quantum systems with a resolution that is not limited by the wavelength of radiation. While alkali atoms are currently the system of choice for photon storage and many other applications, we develop new methods for quantum information processing and quantum simulation with ultracold alkaline-earth atoms in optical lattices. We show how multiple qubits can be encoded in individual alkaline-earth atoms and harnessed for quantumcomputing and precision measurements applications. We also demonstrate that alkaline-earth atoms can be used to simulate highly symmetric systems exhibiting spin-orbital interactions and capable of providing valuable insights into strongly correlated physics of transition metal oxides, heavy fermion materials, and spin liquid phases. While ultracold atoms typically exhibit only short-range interactions, numerous exotic phenomena and practical applications require long-range interactions, which can be achieved with ultracold polar molecules. We demonstrate the possibility to engineer a repulsive interaction between polar molecules, which allows for the suppression of inelastic collisions, efficient evaporative cooling, and the creation of novel phases of polar molecules.

A single-party strategy in a multiround quantum protocol can be implemented by sequential networks of quantum operations connected by internal memories. Here, we provide an efficient realization in terms of computational-space resources.

Bisio, Alessandro; D'Ariano, Giacomo Mauro; Perinotti, Paolo; Chiribella, Giulio [QUIT group, Dipartimento di Fisica ''A. Volta'', and INFN Sezione di Pavia, via Bassi 6, IT-27100 Pavia (Italy); Perimeter Institute for Theoretical Physics, 31 Caroline Street North, Waterloo, Ontario N2L 2Y5 (Canada)

We present a quantumcomputing 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.

Tian Lin; Zoller, P. [Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck (Austria)

A quantumcomputer has a clear advantage over a classical computer for\\u000aexhaustive search. The quantum mechanical algorithm for exhaustive search was\\u000aoriginally derived by using subtle properties of a particular quantum\\u000amechanical operation called the Walsh-Hadamard (W-H) transform. This paper\\u000ashows that this algorithm can be implemented by replacing the W-H transform by\\u000aalmost any quantum mechanical operation. This

This Mathematica 7.0/8.0 package upgrades and extends the quantumcomputer simulation code called QDENSITY. Use of the density matrix was emphasized in QDENSITY, although that code was also applicable to a quantum state description. In the present version, the quantum state version is stressed and made amenable to future extensions to parallel computer simulations. The add-on QCWAVE extends QDENSITY in several ways. The first way is to describe the action of one, two and three-qubit quantum gates as a set of small (2×2, 4×4 or 8×8) matrices acting on the 2n amplitudes for a system of n qubits. This procedure was described in our parallel computer simulation QCMPI and is reviewed here. The advantage is that smaller storage demands are made, without loss of speed, and that the procedure can take advantage of message passing interface (MPI) techniques, which will hopefully be generally available in future Mathematica versions.Another extension of QDENSITY provided here is a multiverse approach, as described in our QCMPI paper. This multiverse approach involves using the present slave-master parallel processing capabilities of Mathematica 7.0/8.0 to simulate errors and error correction. The basic idea is that parallel versions of QCWAVE run simultaneously with random errors introduced on some of the processors, with an ensemble average used to represent the real world situation. Within this approach, error correction steps can be simulated and their efficacy tested. This capability allows one to examine the detrimental effects of errors and the benefits of error correction on particular quantum algorithms.Other upgrades provided in this version include circuit-diagram drawing commands, better Dirac form and amplitude display features. These are included in the add-ons QCWave.m and Circuits.m, and are illustrated in tutorial notebooks.In separate notebooks, QCWAVE is applied to sample algorithms in which the parallel multiverse setup is illustrated and error correction is simulated. These extensions and upgrades will hopefully help in both instruction and in application to QC dynamics and error correction studies.

In this bimonthly series, the author examines how nurse educators can use Internet and Web-based computertechnologies such as search, communication, and collaborative writing tools, social networking and social bookmarking sites, virtual worlds, and Web-based teaching and learning programs. This article describes approaches to finding information on the Web. Web-based search tools including Internet search engines, organizational databases, and those at the library will be discussed. Techniques to evaluate the validity, usefulness, and applicability of search outcomes are included. PMID:19104333

In a distributed quantumcomputer, scalability is accomplished by networking together many elementary nodes. Typically the network is optical and internode entanglement involves photon detection. In complex networks the entanglement fidelity may be degraded by the twin problems of photon loss and dark counts. Here we describe an entanglement protocol which can achieve high fidelity even when these issues are arbitrarily severe; indeed the method succeeds with finite probability even if the photon detectors are entirely removed from the network. An experimental demonstration should be possible with existing technologies.

Matsuzaki, Yuichiro [Department of Materials, University of Oxford, OX1 3PH (United Kingdom); Benjamin, Simon C. [Department of Materials, University of Oxford, OX1 3PH (United Kingdom); Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, Singapore 117543 (Singapore); Fitzsimons, Joseph [Department of Materials, University of Oxford, OX1 3PH (United Kingdom); Institute for Quantum Computing, University of Waterloo, Waterloo, Ontario (Canada)

We are implementing a new platform for adiabatic quantumcomputation (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.

Robust quantumcomputation with d-level quantum systems (qudits) poses two requirements: fast, parallel quantum gates and high-fidelity two-qudit gates. We first describe how to implement parallel single-qudit operations. It is by now well known that any single-qudit unitary can be decomposed into a sequence of Givens rotations on two-dimensional subspaces of the qudit state space. Using a coupling graph to represent physically allowed couplings between pairs of qudit states, we then show that the logical depth (time) of the parallel gate sequence is equal to the height of an associated tree. The implementation of a given unitary can then optimize the tradeoff between gate time and resources used. These ideas are illustrated for qudits encoded in the ground hyperfine states of the alkali-metal atoms {sup 87}Rb and {sup 133}Cs. Second, we provide a protocol for implementing parallelized nonlocal two-qudit gates using the assistance of entangled qubit pairs. Using known protocols for qubit entanglement purification, this offers the possibility of high-fidelity two-qudit gates.

O'Leary, Dianne P. [Department of Computer Science and Institute for Advanced Computer Studies, University of Maryland, College Park, Maryland 20742, USA and Mathematical and Computational Sciences Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); IDA Center for Computing Sciences, 17100 Science Drive, Bowie, Maryland 20715-4300 (United States); Brennen, Gavin K. [Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020, Innsbruck (Austria); Bullock, Stephen S. [IDA Center for Computing Sciences, 17100 Science Drive, Bowie, Maryland 20715-4300 (United States)

We describe measurement-only topological quantumcomputation using both projective and interferometrical measurement of topological charge. We demonstrate how anyonic teleportation can be achieved using 'forced measurement' protocols for both types of measurement. Using this, it is shown how topological charge measurements can be used to generate the braiding transformations used in topological quantumcomputation, and hence that the physical transportation of computational anyons is unnecessary. We give a detailed discussion of the anyonics for implementation of topological quantumcomputation (particularly, using the measurement-only approach) in fractional quantum Hall systems.

Bonderson, Parsa [Microsoft Research, Station Q, Elings Hall, University of California, Santa Barbara, CA 93106 (United States)], E-mail: parsab@microsoft.com; Freedman, Michael [Microsoft Research, Station Q, Elings Hall, University of California, Santa Barbara, CA 93106 (United States)], E-mail: michaelf@microsoft.com; Nayak, Chetan [Microsoft Research, Station Q, Elings Hall, University of California, Santa Barbara, CA 93106 (United States); Department of Physics, University of California, Santa Barbara, CA 93106 (United States)], E-mail: nayak@kitp.ucsb.edu

Quantum spin models are of great interest because they describe the behavior of real magnetic materials and provide a simple context for understanding exotic quantum phases. Experimental results on the triangular lattice antiferromagnet NiGa2S4 in particular have motivated the study of S = 1 models having strong biquadratic interactions that favor a spin nematic ground state. We describe a scenario where the presence of such interactions in NiGa2S4 could be responsible for tuning it into the vicinity of a zero temperature critical point such that two distinct temperature scales emerge in its thermodynamic properties. We also observe that the likely presence of strong third-neighbor exchange interactions in this material leads to a finite temperature phase transition into a classical spin disordered phase that breaks lattice rotational symmetry. To confirm these predictions, we devise an approach in which the model is treated in a semi-classical approximation amenable to Monte Carlo simulations. Unlike a standard classical approximation, our method retains all of the symmetries of the quantum Hamiltonian and succeeds in correctly capturing the effects of biquadratic interactions. However, it is not able to make quantitatively accurate predictions. In order to address this shortcoming, we turn to a second method that is able to fully treat both quantum and classical thermal effects. In this method, thermal averages are computed by sampling a set of wave-functions known as minimally entangled typical thermal states, or METTS. We describe each step of the sampling process in detail and present efficient algorithms for working with matrix product states and matrix product operators. The METTS themselves can be studied to observe characteristic order and excitations of a system, and their properties reveal that they make an especially efficient basis for sampling. Finally, we explore the extent to which the average entanglement of a METTS ensemble is minimal. Future possibilities for both the semi-classical and METTS methods are discussed.

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 using a set of rapidly thermal-relaxing bits. Such auxiliary bits could be implemented by using spins that rapidly get into thermal equilibrium with the environment, e.g., electron spins. Interestingly, the interaction with the environment, usually a most undesired interaction, is used here to our benefit, allowing a cooling mechanism. Cooling spins to a very low temperature without cooling the environment could lead to a breakthrough in NMR experiments, and our “spin-refrigerating” method suggests that this is possible. The scaling of NMR ensemble computers is currently one of the main obstacles to building larger-scale quantumcomputing devices, and our spin-refrigerating method suggests that this problem can be resolved.

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 using a set of rapidly thermal-relaxing bits. Such auxiliary bits could be implemented by using spins that rapidly get into thermal equilibrium with the environment, e.g., electron spins. Interestingly, the interaction with the environment, usually a most undesired interaction, is used here to our benefit, allowing a cooling mechanism. Cooling spins to a very low temperature without cooling the environment could lead to a breakthrough in NMR experiments, and our "spin-refrigerating" method suggests that this is possible. The scaling of NMR ensemble computers is currently one of the main obstacles to building larger-scale quantumcomputing devices, and our spin-refrigerating method suggests that this problem can be resolved.

Figures of merit connecting processing capabilities with power dissipated (OpS\\/Watt, Joule\\/bit, etc.) are becoming dominant factors in choosing technologies for implementing the next generation of computing and communication network systems. Superconductivity is viewed as a technology capable of achieving higher energy efficiencies than other technologies. Static power dissipation of standard RSFQ logic, associated with dc bias resistors, is responsible for

The (meta)logic underlying classical theory of computation is Boolean (two- valued) logic. Quantum logic was proposed by Birkhoff and von Neumann as a logic of quantum mechanics more than sixty years ago. It is currently under- stood as a logic whose truth values are taken from an orthomodular lattice. The major difference between Boolean logic and quantum logic is that

In this paper I show the importance of computer visualization in researching of many-particle quantum dynamics. Such a visualization becomes an indispensable illustrative tool for understanding the behavior of dynamic swarm-based quantum systems. It is also an important component of the corresponding simulation framework, and can simplify the studies of underlying algorithms for multi-particle quantum systems.

Ozhigov, A. Y. [Moscow State Institute of Electronics and Mathematics (Russian Federation)

We present a quantum algorithm to prepare injective projected entangled pair states (PEPS) on a quantumcomputer, 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

We present a quantum algorithm to prepare injective projected entangled pair states (PEPS) on a quantumcomputer, 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, Martin; Temme, Kristan; Verstraete, Frank

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

Horsman, Clare; Fowler, Austin G.; Devitt, Simon; Van Meter, Rodney

We study the use of the quantum wavelet transform to extract efficiently information about the multifractal exponents for multifractal quantum states. We show that, combined with quantum simulation algorithms, it enables to build quantum algorithms for multifractal exponents with a polynomial gain compared to classical simulations. Numerical results indicate that a rough estimate of fractality could be obtained exponentially fast. Our findings are relevant, e.g., for quantum simulations of multifractal quantum maps and of the Anderson model at the metal-insulator transition.

In this chapter, we have presented an overview of various nanoscale and molecular computing architectures. We have given a brief tutorial on various existing nanoscale and molecular devices. These include molecular switches, resonant tunnel diodes, tunnel diodes, single electron transistors, carbon nanotube field-effect transistors, quantum dots, and spin systems. We have next discussed a set of nanoscale computing modules, such

Mary M. Eshaghian-Wilner; Amar H. Flood; Alex Khitun; J. Fraser Stoddart; Kang Wang

Quantumcomputation has the potential to provide an efficient means of solving certain problems which are intractable on classical machines. Superconducting electronics may enable a solid state quantumcomputer of macroscopic dimensions. The first step is to demonstrate macroscopic quantum coherence in a single superconducting rf-SQUID qubit, manifest as the tunneling of magnetic flux in and out of the SQUID loop, or equivalently, the phase across the junction alternately increasing and decreasing by 2pi. This will likely require improvements in the current fabrication technology, as it will require submicron junctions with extremely low leakage current. We propose a scheme to experimentally demonstrate macroscopic quantum coherence in the rf-SQUID qubit by speeding up the time evolution of the system by momentarily suppressing the junction critical current through the application of a series of single flux quantum (SFQ) pulses. The precise timing of the perturbing pulses and the subsequent measurement of the qubit state would be performed using rapid single flux quantum (RSFQ) circuitry. Conventional digital electronics based on the single flux quantum offers very low power dissipation and high operating frequency. These same features, however, make timing of clock and data signals difficult. Circuits with recurrent data paths, such as the circular shift register (CSR) have the most stringent timing requirements. A 64-bit CSR composed of approximately 425 Josephson junctions was designed and successfully demonstrated. The CSR has an area of 0.8 mm2 and consumes approximately 80 muW of power. The circuit showed correct operation at low speed with a critical margin of +/-7.5%, and operated correctly at frequencies up to 18 GHz. The bit-error rate (BER) of the 64-bit CSR, i.e. the probability that an error in circuit operation will occur during any single circulation of the data through all 64 register stages, was measured as a function of clock frequency, and the currents supplied to the clock and data paths. The error-rate curves thus obtained suggest an effective operating temperature of 8--9 K and timing jitter of approximately 290 fs per Josephson transmission line (JTL) stage.

|Because the graphic industry demands graduates with computer skills, art students want college programs that include complex computertechnologies. However, students can produce good computer art only if they have mastered traditional drawing and design skills. Discusses designing an art curriculum including both technology and traditional course…

Quantumcomputers offer the promise of formidable computational power for certain tasks. Of the various possible physical implementations of such a device, silicon based architectures are attractive for their scalability and ease of integration with existing silicon technology. These designs use either the electron or nuclear spin state of single donor atoms to store quantum information. Here we describe a strategy to fabricate an array of single phosphorus atoms in silicon for the construction of such a silicon based quantumcomputer. We demonstrate the controlled placement of single phosphorus bearing molecules on a silicon surface. This has been achieved by patterning a hydrogen mono-layer 'resist' with a scanning tunneling microscope (STM) tip and exposing the patterned surface to phosphine (PH3) molecules. We also describe preliminary studies into a process to incorporate these surface phosphorus atoms into the silicon crystal at the array sites. Keywords: Quantumcomputing, nanotechriology scanning turincling microscopy, hydrogen lithography

O'Brien, J. L. (Jeremy L.); Schofield, S. R. (Steven R.); Simmons, M. Y. (Michelle Y.); Clark, R. G. (Robert G.); Dzurak, A. S. (Andrew S.); Curson, N. J. (Neil J.); Kane, B. E. (Bruce E.); McAlpine, N. S. (Neal S.); Hawley, M. E. (Marilyn E.); Brown, G. W. (Geoffrey W.)

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

In the framework of quantumcomputational tensor network [D. Gross and J. Eisert, Phys. Rev. Lett. {\\\\bf98}, 220503 (2007)], which is a general framework of measurement-based quantumcomputation, the resource many-body state is represented in a tensor-network form, and universal quantumcomputation is performed in a virtual linear space, which is called a correlation space, where tensors live. Since any

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

Peter W. ShorAT&T Bell LabsRoom 2D-149600 Mountain Ave.Murray Hill, NJ 07974 USAemail: shor@research.att.comAbstractThis paper gives algorithms for the discrete log and the factoring problems thattake random polynomial time on a quantumcomputer (thus giving the first examplesof quantum cryptanalysis).1 IntroductionSince the discovery of quantum mechanics, people have found the behavior of the laws ofprobability in quantum mechanics counterintuitive. Because of

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

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 nontraditional programming techniques. The aim of this paper is to guide computer scientists through

We present a quantum algorithm that additively approximates the value of a\\u000atensor network to a certain scale. When combined with existing results, this\\u000aprovides a complete problem for quantumcomputation. The result is a simple new\\u000away of looking at quantumcomputation in which unitary gates are replaced by\\u000atensors and time is replaced by the order in which

Fock space system (FSS) has unfixed number (N) of particles and/or degrees of freedom. In quantumcomputing (QC) main requirement is sustainability of coherent Q-superpositions. This normally favoured by low noise environment. High excitation/high temperature (T) limit is hence discarded as unfeasible for QC. Conversely, if N is itself a quantized variable, the dimensionality of Hilbert basis for qubits may increase faster (say, N-exponentially) than thermal noise (likely, in powers of N and T). Hence coherency may win over T-randomization. For this type of QC speed (S) of factorization of long integers (with D digits) may increase with D (for 'ordinary' QC speed polynomially decreases with D). This (apparent) paradox rests on non-monotonic bijectivity (cf. Georg Cantor's diagonal counting of rational numbers). This brings entire aleph-null structurality ("Babylonian Library" of infinite informational content of integer field) to superposition determining state of quantum analogue of Turing machine head. Structure of integer infinititude (e.g. distribution of primes) results in direct "Platonic pressure" resembling semi-virtual Casimir efect (presure of cut-off vibrational modes). This "effect", the embodiment of Pythagorean "Number is everything", renders Godelian barrier arbitrary thin and hence FSS-based QC can in principle be unlimitedly efficient (e.g. D/S may tend to zero when D tends to infinity).

The interpretation of quantum mechanics is an area of increasing interest to many working physicists. In particular, interest has come from those involved in quantumcomputing 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 quantumcomputation. 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 quantumcomputation are investigated, and common objections to using many worlds to describe quantumcomputing are answered. We find that using this particular many-worlds theory as a physical foundation for quantumcomputation gives several distinct advantages over other interpretations, and over not interpreting quantum theory at all.

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 nonuniform 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-metals are on the order of milliseconds, much faster then the anticipated decoherence times. Single qubit operations take about 10 {mu}s. 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 metastable alkaline-earth atoms with larger magnetic moments.

Derevianko, Andrei; Cannon, Caleb C. [Department of Physics, University of Nevada, Reno, Nevada 89557 (United States)

We propose a new universal quantumcomputation scheme for trapped ions in thermal motion via the technique of adiabatic passage, which incorporates the advantages of both the adiabatic passage and the model of trapped ions in thermal motion. Our scheme is immune from the decoherence due to spontaneous emission from excited states as the system in our scheme evolves along a dark state. In our scheme the vibrational degrees of freedom are not required to be cooled to their ground states because they are only virtually excited. It is shown that the fidelity of the resultant gate operation is still high even when the magnitude of the effective Rabi frequency moderately deviates from the desired value.

Feng Xuni; Wu Chunfeng; Lai, C. H.; Oh, C. H. [Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542 (Singapore) and Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, Singapore 117543 (Singapore)

We discuss the possibility of performing single spin measurements in Si-based quantumcomputers through electric field control of electrons bound to double donors near a barrier interface[1]. In particular, we investigate the feasibility of shuttling donor-bound electrons between the double donor impurity in the bulk and the Si/SiO2 interface by tuning an external electric field. We find that both the required electric fields and the tunneling times involved are probably too large for practical implementations. We also investigate operations with double donors in their first excited state: In this case ionization fields are smaller and tunneling times are faster, as required in spin-to-charge conversion measurements. This work is supported by LPS and NSA. [1] M.J. Calderon, B. Koiller, and S. Das Sarma, cond- mat/0610089.

Calderon, Maria J.; Koiller, Belita; Das Sarma, Sankar

We consider how the ability to control quantum effects might give rise to entirely new technologies, present an overview of potential applications and consider some of the key challenges facing quantum control. A general overview of the main techniques that have been employed successfully so far in controlling various quantum phenomena is given and their applications, advantages and shortcomings are discussed. We conclude with an outlook on the future challenges to be overcome to make quantumtechnologies a reality. PMID:17090468

The electronic computer, mainstay of an advanced information processing technology, is described as being central to the solution of information management and control problems in education. Current applications of computer and information system technolo...

|Describes the nature of modern general-purpose computer systems, including hardware, semiconductor electronics, microprocessors, computer architecture, input output technology, and system control programs. Seven suggested readings are cited. (FM)|

A scheme to evaluate computation fidelities within the one-way model is developed and explored to understand the role of correlations in the quality of noisy quantumcomputations. The formalism is promptly applied to many computation instances and unveils that a higher amount of entanglement in the noisy resource state does not necessarily imply a better computation.

Chaves, Rafael [ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, 08860 Castelldefels (Barcelona) (Spain); Instituto de Fisica, Universidade Federal do Rio de Janeiro, Rio de Janeiro (Brazil); Physikalisches Institut der Albert-Ludwigs-Universitaet, Freiburg (Germany); Melo, Fernando de [Instituut voor Theoretische Fysica, Katholieke Universiteit Leuven, Leuven (Belgium); Physikalisches Institut der Albert-Ludwigs-Universitaet, Freiburg (Germany)

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.

For several years now quantumcomputing has been viewed as a new paradigm for certain computing applications. Of particular importance to this burgeoning field is the development of an algorithm for factoring large numbers which obviously has deep implica...

E. Bielejec M. P. Lilly J. A. Seamons D. R. Tibbetts R. G. Dunn S. K. Lyo J. L. Reno

The purpose was to identify AAAE members' computer anxiety levels, attitudes toward computers and perceptions of Web-based survey methods. A total of 389 AAAE members participated in this experimental study. Respondents were assigned randomly to Web- and paper- based data collection method subgroups. AAAE members perceived that they did not suffer from computer anxiety, held positive attitudes toward computers and

Gary J. Wingenbach; M. Damon Ladner; Michael E. Newman; Matt R. Raven

We discuss novel nanoelectronic architecture paradigms based on cells composed of coupled quantum-dots. Boolean logic functions may be implemented in speci® c arrays of cells representing binary information, the so-called quantum-dot cellular automata (QCA). Cells may also be viewed as carrying analogue information and we outline a network-theoretic description of such quantum-dot nonlinear net- works (Q-CNN). In addition, we discuss

WOLFGANG POROD; CRAIG S. LENT; GARY H. BERNSTEIN; ALEXEI O. ORLOV; ISLAMSHAH AMLANI; GREGORY L. SNIDER; JAMES L. MERZ

Quantumcomputation 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 quantumcomputation in decoherence-free subspaces have been proposed in the past few years. However, nonadiabatic holonomic quantumcomputation 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 quantumcomputation 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. PMID:23215167

Xu, G F; Zhang, J; Tong, D M; Sjöqvist, Erik; Kwek, L C

A Knill-Laflamme-Milburn (KLM) type quantumcomputation with bosonic neutral atoms or bosonic ions is suggested. Crucially, as opposite to other quantumcomputation 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. PMID:17930567

A Knill-Laflamme-Milburn (KLM) type quantumcomputation with bosonic neutral atoms or bosonic ions is suggested. Crucially, as opposite to other quantumcomputation 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.

We show that the topological modular functor from Witten-Chern-Simons theory is universal for quantumcomputation in the sense a quantum circuit computation can be efficiently approximated by an intertwining action of a braid on the functor's state space. A computational model based on Chern-Simons theory at a fifth root of unity is defined and shown to be polynomially equivalent to

Michael Freedman; Michael Larsen; Zhenghan Wang; Michael H. Freedman

Quantum logic operations can he performed using linear optical elements ancilla photons, and corrections based on the results of measurements made on the ancilla. We have recently demonstrated several basic quantum logic operations using single photons, a...

J. D. Franson M. M. Donegan M. J. Fitch B. C. Jacobs T. B. Pittman

It is natural to consider a quantum system in the continuum limit of\\u000aspace-time configuration. Incorporating also, Einstein's special relativity,\\u000aleads to the quantum theory of fields. Non-relativistic quantum mechanics and\\u000aclassical mechanics are special cases. By studying vacuum expectation values\\u000a(Wightman functions W(n; z) where z denotes the set of n complex variables) of\\u000aproducts of quantum field operators

DNA computing is a new method of simulating biomolecular structure of DNA and computing by means of molecular biology technologicalcomputation. It introduces a fire-new data structure and calculating method, providing a new way for solving the NP-complete problem. It is a new computational method by harnessing the enormous parallel computing ability and high memory density of bio-molecules, which brings

Computertechnology is one of the new automation innovations impacting health care today. There are no neatly packaged courses which provide nurses with state-of-the-art information in computertechnology. The purpose of this publication is to provide nur...

Similar to human persuaders in our society, persuasive computingtechnologies can influence people's attitudes and bring some constructive changes in many domains such as marketing, health, safety, environment and so on. Since the study of computers as persuasive technologies was introduced at CHI 97 as a new research area, more valuable studies have been done in this relatively unexplored area.

|Prior computer experience with information technology has been identified as a key variable (Lee, Kozar, & Larsen, 2003) that can influence an individual's future use of newer computertechnology. The lack of a theory driven approach to measuring prior experience has however led to conceptually different factors being used interchangeably in…

The experience and the expectations of a large scientific society publisher of chemical and chemical engineering information tools provide a broad context for considering the history and probable future impact of computertechnology on information dissemination. Chemical Abstracts Service (CAS) was in good health for half a century before computertechnology was available in practical application to the production of

Noting a recent increase in the number of cases of computer crime and computer piracy, this paper takes up the question, "How can understanding the social context of computing help us--as parents, educators, and members of government and industry--to educate young people to become morally responsible members of an electronic information…

A review is given of some aspects of the Riemannian geometry of quantumcomputation in which the quantum evolution is represented in the tangent space manifold of the special unitary unimodular group SU(2n) for n qubits. The Riemannian right-invariant metric, connection, curvature, geodesic equation for minimal complexity quantum circuits, Jacobi equation and the lifted Jacobi equation for varying penalty parameter are reviewed. Sharpened tools for calculating the geodesic derivative are presented. The geodesic derivative may facilitate the numerical investigation of conjugate points and the global characteristics of geodesic paths in the group manifold, the determination of optimal quantum circuits for carrying out a quantumcomputation, and the determination of the complexity of particular quantum algorithms.

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 - quantumcomputers and quantum minds, which operate in parallel. The outcomes of the overall quantumcomputation 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.

This paper surveys 3D measurement technologies for computer animation and considers unsolved problems on this subject. 3D measurement technologies are actually very important for converting various 3D objects in the real world to 3D models in the virtual world for computer animation. Current 3D measurement technologies have been developed mainly for measuring objects in industrial or scientific fields, such as

Assistive technology that can help disabled computer users is described, and a resource guide to computer help for the disabled is presented. The Americans with Disabilities Act of 1990 has broad implications for higher education, in that it mandates that colleges and universities give disabled students equal access to computers on public…

Adaptive technology offers people with disabilities the opportunity not just to use computers, but to use computers to complete tasks that were previously not possible for them. Computers can be used to assist individuals with speech or writing impairments, physical or mobility impairments, visual impairments, and learning disabilities. (Author/JL)

This resource booklet was prepared to assist literacy projects and community adult education programs in determining the technology they need to serve more older persons. Section 1 contains the following reprinted articles: "The Human Touch in the Computer Age: Seniors Learn Computer Skills from Schoolkids" (Suzanne Kashuba); "Computer Instruction…

This article explores how insights from the learning sciences can guide the effective use of computertechnologies to promote learning and how these technologies make new types of learning opportunities possible. The discussion is organized to provide three illustrations of how the introduction of new technologies can have “ripple effects” that influence many different aspects of the teaching and learning

The development of quantum theory was an archetypal scientific revolution in early twentieth-century physics. In many ways, the probabilities and uncertainties that replaced the ubiquitous application of classical mechanics may have seemed a violent assault on logic and reason. 'Something unknown is doing we don't know what-that is what our theory amounts to,' Sir Arthur Eddington famously remarked, adding, 'It does not sound a particularly illuminating theory. I have read something like it elsewhere: the slithy toves, did gyre and gimble in the wabe' [1]. Today, quantum mechanics no longer seems a dark art best confined to the boundaries of physics and philosophy. Scanning probe micrographs have captured actual images of quantum-mechanical interference patterns [2], and familiarity has made the claims of quantum theory more palatable. An understanding of quantum effects is essential for nanoscale science and technology research. This special issue on quantum science and technology at the nanoscale collates some of the latest research that is extending the boundaries of our knowledge and understanding in the field. Quantum phenomena have become particularly significant in attempts to further reduce the size of electronic devices, the trend widely referred to as Moore's law. In this issue, researchers in Switzerland report results from transport studies on graphene. The researchers investigate the conductance variance in systems with superconducting contacts [3]. Also in this issue, researchers in Germany calculate the effects of spin-orbit coupling in a molecular dimer and predict nonlinear transport. They also explain how ferromagnetic electrodes can be used to probe these interactions [4]. Our understanding of spin and the ability to manipulate it has advanced greatly since the notion of spin was first proposed. However, it remains the case that little is known about local coherent fluctuations of spin polarizations, the scale on which they occur, how they are correlated, and how they influence spin currents and their fluctuations, as well as the mechanisms behind current-induced spin polarizations in chaotic ballistic systems. In a theoretical report on current-induced spin polarization from the University of Arizona, progress is made in filling in some of these gaps, and a 'spin-probe' model is proposed [5]. Spin is also an important element in quantum information research. With electron spin coherence lifetimes exceeding 1 ms at room temperature, as well as the added benefit of being optically addressable, nitrogen-vacancy defects in diamond have been identified as having considerable potential for quantum information applications. Now researchers in the US describe the fabrication and low-temperature characterization of silica microdisk cavities coupled to diamond nanoparticles, and present theoretical and experimental studies of gallium phosphide structures coupled to nitrogen-vacancy centers in bulk diamond [6]. Double quantum dots have been considered as prospective candidates for charge qubits for quantum information processors. The application of a bias voltage can be used to control tunnelling between the double quantum dots, allowing the energy states to be tuned. Researchers in Switzerland investigate experimentally the effect of ohmic heating of the phonon bath on decoherence, and find that the system can be considered as a thermoelectric generator [7]. This progress has only been made possible by advances in our understanding of the fundamental science behind quantum mechanics, and work exploring this territory is still a hotbed of activity and progress. Increasingly sophisticated tools, both numerical and experimental, have facilitated engagement with quantum phenomena in nanoscale systems. Molecular spin clusters represent an ideal setting within solid-state systems to test concepts in quantum mechanics, as highlighted in this issue by researchers in Italy, who report their work on controlling entanglement between molecular spins [8]. Nanofabrication techniques have seen tremendous advances that have en

We propose a scalable neutral atom quantumcomputer with an on- demand interaction. Artificial lattice of near field optical traps is employed to trap atom qubits. Interactions between atoms can be turned off if the atoms are separated by a high enough potential barrier so that the size of the atomic wave function is much less than the interatomic distance. One-qubit gate operation is implemented by a gate control laser beam which is attached to an individual atom. Two-qubit gate operation between a particular pair of atoms is introduced by leaving these atoms in an optical lattice and making them collide so that a particular two-qubit state acquires a dynamical phase. Our proposal is feasible within existing technology developed in cold atom gas, MEMS, nanolithography, and various areas in optics.

A number of questions associated with practical implementations of quantum cryp- tography systems having to do with unconditional secrecy, computational loads and effective secrecy rates in the presence of perfect and imperfect sources are discussed. The different types of unconditional secrecy, and their relationship to general com- munications security, are discussed in the context of quantum cryptography. In order to

Many algorithmic developments in quantum com- plexity theory, including Shor's celebrated algorithms for factoring and discrete logs, have made use of Fourier transforms over abelian groups. That is, at some point in the computation, the macline is in a superposition of states corresponding to elements of a finite abelian group G, and in quantum polynomial time (i.e., poly- nomial in

Modeling noisy discrete systems utilizing conserva- tive reversible elementary cellular automata (CRECA) is presented. The new method results in adding variable redundancy to incorporate noise. Since noise is an inte- gral part of any real process and since the reduction of power consumption is a main requirement for circuit de- sign of future technologies such as in quantumcomputing (QC),

The many advanced technology requirements dictated by the demanding low-Earth orbit research environment can only be satisfied through the adaptation of innovative methods and technologies. The fundamental physics research program in microgravity sponsors research that explores the physics governing matter, space, and time and that seeks to discover and understand the organizing principles of nature, including the emergence of complex structures. The fundamental physics research program currently supports research in four areas: gravitational and relativistic physics, laser cooling and atomic physics, low temperature and condensed matter physics, and biological physics. The microgravity fundamental physics is one of the science disciplines within the new NASA Office of Biological and Physical Sciences Research, where quantumtechnology plays a major role. Quantumtechnology, based on controlled manipulation of fundamentally quantum processes of atoms, molecules, or soft matter, enables novel and significantly extended capabilities. This paper presents a new technology program, within the fundamental physics research program, focusing on four quantumtechnology areas: quantum atomics, quantum optics, space superconductivity and quantum sensor technology, and quantum fluid based sensor and modeling technology.

We present straightforward proofs of estimates used in the adiabatic approximation. The gap dependence is analyzed explicitly. We apply the result to interpolating Hamiltonians of interest in quantumcomputing.

Jansen, Sabine; Ruskai, Mary-Beth; Seiler, Ruedi [Institut fuer Mathematik, TU Berlin, MA 7-2, Strasse des 17, Juni 136, D-10623 Berlin (Germany); Department of Mathematics, Tufts University, Medford, Massachusetts 02155 (United States); Institut fuer Mathematik, TU Berlin, MA 7-2, Strasse des 17, Juni 136, D-10623 Berlin (Germany)

One of the earliest proposals for implementing quantumcomputation was based on encoding each qubit in two optical modes, each containing exactly one photon. However, it is extremely difficult to unitarily couple two optical modes containing few photons. ...

We demonstrate process characterization of basic gates of an optical cluster-state quantumcomputing. We present complete process tomography of a single-qubit gate and evaluate the bounds on the process fidelity of a two-qubit gate.

This document describes and forecasts computer peripheral memory technologies as displayed by U.S. research and manufacturing facilities. Specifically, both technical and economic criteria are discussed. The presented peripheral memories include contempor...

TTI provides a unique cluster computing service accessible online from anywhere. TTI is committed to providing up-to-date, industry recognized, high performance computing (HPC) systems and services to companies and academia with the absolute best in customer service and support. And, because it is affordable, our services are even within reach of the individual scientist.

The purpose of this study was to understand the impact of technology on art therapists by exploring how art therapists own and use technology and to determine barriers to ownership and use. A survey was conducted at the 2002 annual conference of the American Art Therapy Association in Washington, DC. Of the 250 surveys distributed, 195 were…

Peterson, Brent C.; Stovall, Kay; Elkins, David E.; Parker-Bell, Barbara

Researches in technology diffusion is popular in economics; however most papers focus on geographical pattern. In this research, we examined the international technology diffusion by using patent citations and focused on Computers and Communications field to investigate technology in-flow and out-flow between countries. The results indicate that technology diffusion of this field is more significant intra-field, differing by countries. It

Scientists usually identify themselves as either theoreticians or experimentalists, while technology - the application of science in practice - is done by engineers. In computer science, these distinctions are often blurred. This paper examines the history of major achievements in computer science as portrayed by the winners of the prestigious Turing Award and identifies a possibly unique activity called Theory-Guided Technology (TGT). Researchers develop TGT by using theoretical results to create practical technology. The reasons why TGT is practical in computer science are discussed, as is the cool reception that TGT has been received by software engineers.

We introduce the concept of directional coupling, i.e., the selective\\u000atransfer of a state between adjacent quantum wires, in the context of quantum\\u000acomputing and short-distance communication. Our analysis rests upon a\\u000amathematical analogy between a dual-channel directional coupler and a composite\\u000aspin system.

In this work, we show how Gibbs or thermal states appear dynamically in closed quantum many-body systems, building on the program of dynamical typicality. We introduce a novel perturbation theorem for physically relevant weak system-bath couplings that is applicable even in the thermodynamic limit. We identify conditions under which thermalization happens and discuss the underlying physics. Based on these results, we also present a fully general quantum algorithm for preparing Gibbs states on a quantumcomputer with a certified runtime and error bound. This complements quantum Metropolis algorithms, which are expected to be efficient but have no known runtime estimates and only work for local Hamiltonians. PMID:22463502

We show explicitly how to realize an arbitrary linear unitary Bogoliubov (LUBO) transformation on a multimode quantum state through homodyne-based one-way quantumcomputation. Any LUBO transformation can be approximated by means of a fixed, finite-sized, sufficiently squeezed Gaussian cluster state that allows for the implementation of beam splitters (in form of three-mode connection gates) and general one-mode LUBO transformations. In particular, we demonstrate that a linear four-mode cluster state is a sufficient resource for an arbitrary one-mode LUBO transformation. Arbitrary-input quantum states including non-Gaussian states could be efficiently attached to the cluster through quantum teleportation.

Ukai, Ryuji; Yoshikawa, Jun-ichi; Iwata, Noriaki; Furusawa, Akira [Department of Applied Physics and Quantum-Phase Electronics Center, School of Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Loock, Peter van [Optical Quantum Information Theory Group, Max Planck Institute for the Science of Light, Institute of Theoretical Physics I, Universitaet Erlangen-Nuernberg, Staudtstrasse 7/B2, D-91058 Erlangen (Germany)

We propose a modified metric based on the Hilbert-Schmidt norm and adopt it to define a rescaled version of the geometric measure of quantum discord. Such a measure is found not to suffer from pathological dependence on state purity. Although the employed metric is still non-contractive under quantum operations, we show that the resulting indicator of quantum correlations is in agreement with other bona fide discord measures in a number of physical examples. We present a critical assessment of the requirements of reliability versus computability when approaching the task of quantifying, or measuring, general quantum correlations in a bipartite state.

|This article presents an annotated selection of the most important and informative Internet resources for learning about quantumcomputing, finding quantumcomputing literature, and tracking quantumcomputing news. All of the quantumcomputing resources described in this article are freely available, English-language web sites that fall into one…

How well the computer site manager avoids future dangers and takes advantage of future opportunities depends to a considerable degree on how much anticipatory information he has available. People who rise in management are expected with each successive pr...

The requirement of performing both single-qubit and two-qubit operations in the implementation of universal quantum logic often leads to very demanding constraints on quantumcomputer design. We show here how to eliminate the need for single-qubit operations in a large subset of quantumcomputer proposals: those governed by isotropic and XXZ, XY-type anisotropic exchange interactions. Our method employs an encoding of one logical qubit into two physical qubits, while logic operations are performed using an analogue of the NMR selective recoupling method. PMID:11800990

The power of a quantumcomputer (QC) relies on the fundamental concept of the superposition in quantum mechanics and thus allowing an inherent large-scale parallelization of computation. In a QC, binary information embodied in a quantum system, such as spin degrees of freedom of a spin-1/2 particle forms the qubits (quantum mechanical bits), over which appropriate logical gates perform the computation. In classical computers, the basic unit of information is the bit, which can take a value of either 0 or 1. Bits are connected together by logic gates to form logic circuits to implement complex logical operations. The expansion of modern computers has been driven by the developments of faster, smaller and cheaper logic gates. As the size of the logic gates become smaller toward the level of atomic dimensions, the performance of such a system is no longer considered classical but is rather governed by quantum mechanics. Quantumcomputers offer the potentially superior prospect of solving computational problems that are intractable to classical computers such as efficient database searches and cryptography. A variety of algorithms have been developed recently, most notably Shor's algorithm for factorizing long numbers into prime factors in polynomial time and Grover's quantum search algorithm. The algorithms that were of only theoretical interest as recently, until several methods were proposed to build an experimental QC. These methods include, trapped ions, cavity-QED, coupled quantum dots, Josephson junctions, spin resonance transistors, linear optics and nuclear magnetic resonance. Nuclear magnetic resonance (NMR) is uniquely capable of constructing small QCs and several algorithms have been implemented successfully. NMR-QC differs from other implementations in one important way that it is not a single QC, but a statistical ensemble of them. Thus, quantumcomputing based on NMR is considered as ensemble quantumcomputing. In NMR quantumcomputing, the spins with non-zero nuclear moments (spin 1/2 nuclei such as {sup 1}H or {sup 13}C) in an organic molecule dissolved in a solvent constitute the required qubits. The logic gates and algorithms correspond to set of instructions containing radio frequency (r.f) pulses and delays that manipulate the qubits and the final spectrum reflects the outcome of the algorithm. Three years ago, when we initiated proposal on NMR-QC, the foremost of the aim is to develop quantumcomputing as part of LLNL research programs and hence cultivate an interdisciplinary working group in the area of quantumcomputing. Our success in the proposal is in part responsible for the formation of the laboratory-wide exploratory group on ''quantumcomputing and information''. The PI's play an integral role in promoting the work performed using the LDRD funded project and hence acquire the attention within the lab as well outside. In specific goals of the project were to (a) develop experimental and sample based methods to improve the performance of NMR-QC, (b) define and estimate actual time cost or efficiency of a QCs, and (c) construct a comprehensive simulator of QC based on the principles of ensemble quantumcomputing. We were able to accomplish these goals and in particular we have reached some significant milestones in defining the QC efficiency and development of the QC-simulator. These developments have resulted to three publications.

Progress in molecular electronics is beginning to yield the technology for creating structures that incorporate myriads of nanoscale computationally active units. These could be fabricated at almost no cost, provided (1) the individual units need not all ...

Recent developments of surface codes now place superconducting quantumcomputing at an important crossroad, where ``proof of concept'' experiments involving small numbers of qubits can be transitioned to more challenging and systematic approaches that could actually lead to building a quantumcomputer. Although the integrated circuit nature of these qubits helps with the design of a complex architecture and control system, it also presents a serious challenge for coherence since the quantum wavefunctions are in contact with a variety of materials defects. I will review both logic gate design and recent developments in coherence in superconducting qubits, and argue that state-of-the-art devices are now near the fault tolerant threshold. Future progress looks promising for fidelity ten times better than threshold, as needed for scalable quantum error correction and computation.

Measurement based quantumcomputation, which requires only single particle measurements on a universal resource state to achieve the full power of quantumcomputing, has been recognized as one of the most promising models for the physical realization of quantumcomputers. Despite considerable progress in the past decade, it remains a great challenge to search for new universal resource states with naturally occurring Hamiltonians and to better understand the entanglement structure of these kinds of states. Here we show that most of the resource states currently known can be reduced to the cluster state, the first known universal resource state, via adaptive local measurements at a constant cost. This new quantum state reduction scheme provides simpler proofs of universality of resource states and opens up plenty of space to the search of new resource states.

The book advances the premise that the cytoskeleton is the cell's nervous system, the biological controller/computer. If indeed cytoskeletal dynamics in the nanoscale (billionth meter, billionth second) are the texture of intracellular information processing, emerging ''NanoTechnologies'' (scanning tunneling microscopy, Feynman machines, von Neumann replicators, etc.) should enable direct monitoring, decoding and interfacing between biological and technological information devices. This in turn could result in important biomedical applications and perhaps a merger of mind and machine: Ultimate Computing.

Quantum information processing and its associated technologies have reached a pivotal stage in their development, with many experiments having established the basic building blocks. Moving forward, the challenge is to scale up to larger machines capable of performing computational tasks not possible today. This raises questions that need to be urgently addressed, such as what resources these machines will consume and how large will they be. Here we estimate the resources required to execute Shor’s factoring algorithm on an atom-optics quantumcomputer architecture. We determine the runtime and size of the computer as a function of the problem size and physical error rate. Our results suggest that once the physical error rate is low enough to allow quantum error correction, optimization to reduce resources and increase performance will come mostly from integrating algorithms and circuits within the error correction environment, rather than from improving the physical hardware.

Devitt, Simon J.; Stephens, Ashley M.; Munro, William J.; Nemoto, Kae

We show that quantum theory allows for transformations of black boxes that cannot be realized by inserting the input black boxes within a circuit in a predefined causal order. The simplest example of such a transformation is the classical switch of black boxes, where two input black boxes are arranged in two different orders conditionally on the value of a classical bit. The quantum version of this transformation—the quantum switch—produces an output circuit where the order of the connections is controlled by a quantum bit, which becomes entangled with the circuit structure. Simulating these transformations in a circuit with fixed causal structure requires either postselection or an extra query to the input black boxes.

The following topics are discussed: the physical and chemical processes inside operating internal combustion engines which are being studied to improve IC engine performance; the CHEMKIN computer code for theoretical modeling studies of combustion kinetics; an acoustic thermometer capable of measuring temperatures to 3000Â°C and which can be used in reactor safety studies; and the new application of inertial navigational

Computer network reliability testing is an important technology for network reliability evaluation. Focused on reliability testing for computer network applications, the testing profile building method, the sample selection method, the failure criterions setting method and the index evaluation method are researched. Finally, the testing process is explained with a testing case.

Ruiying Li; Ning Huang; Shuo Li; Rui Kang; Shuo Chang

The citizen of tomorrow needs to understand the role of information in political systems; computertechnology and information storage, retrieval, and use; the implications of information systems for individual rights; and the impact of computer crime, databanks, and systems analysis on the social, economic, and political spheres. (QKR)

This work presents a review of the development and application of computers. It traces the highlights of emergent computingtechnologies shaping our world. Recent trends in hardware and software deployment are chronicled as well as their impact on various segments of the society. The expectations for the future are also discussed along with…

This article discusses the design and development of a program to integrate computertechnology into two Nurse Wellness Centers located in low-income minority high-rise facilities. The goal of the program is to teach residents how to use the computers and the Internet to locate health information and to take a more active role in their own health care. Previous research

The major achievements enabled by QMC Endstation grant include * Performance improvement on clusters of x86 multi-core systems, especially on Cray XT systems * New and improved methods for the wavefunction optimizations * New forms of trial wavefunctions * Implementation of the full application on NVIDIA GPUs using CUDA The scaling studies of QMCPACK on large-scale systems show excellent parallel efficiency up to 216K cores on Jaguarpf (Cray XT5). The GPU implementation shows speedups of 10-15x over the CPU implementation on older generation of x86. We have implemented hybrid OpenMP/MPI scheme in QMC to take advantage of multi-core shared memory processors of petascale systems. Our hybrid scheme has several advantages over the standard MPI-only scheme. * Memory optimized: large read-only data to store one-body orbitals and other shared properties to represent the trial wave function and many-body Hamiltonian can be shared among threads, which reduces the memory footprint of a large-scale problem. * Cache optimized: the data associated with an active Walker are in cache during the compute-intensive drift-diffusion process and the operations on an Walker are optimized for cache reuse. Thread-local objects are used to ensure the data affinity to a thread. * Load balanced: Walkers in an ensemble are evenly distributed among threads and MPI tasks. The two-level parallelism reduces the population imbalance among MPI tasks and reduces the number of point-to-point communications of large messages (serialized objects) for the Walker exchange. * Communication optimized: the communication overhead, especially for the collective operations necessary to determine ET and measure the properties of an ensemble, is significantly lowered by using less MPI tasks. The multiple forms of parallelism afforded by QMC algorithms make them ideal candidates for acceleration in the many-core paradigm. We presented the results of our effort to port the QMCPACK simulation code to the NVIDIA CUDA GPU platform. We restructured the CPU algorithms to express additional parallelism, minimize GPU-CPU communication, and efficiently utilize the GPU memory hierarchy. Using mixed precision on GT200 GPUs and MPI for intercommunication and load balancing, we observe typical full-application speedups of approximately 10x to 15x relative to quad-core Xeon CPUs alone, while reproducing the double-precision CPU results within statistical error. We developed an all-electron quantum Monte Carlo (QMC) method for solids that does not rely on pseudopotentials, and used it to construct a primary ultra-high-pressure calibration based on the equation of state of cubic boron nitride. We computed the static contribution to the free energy with the QMC method and obtained the phonon contribution from density functional theory, yielding a high-accuracy calibration up to 900 GPa usable directly in experiment. We computed the anharmonic Raman frequency shift with QMC simulations as a function of pressure and temperature, allowing optical pressure calibration. In contrast to present experimental approaches, small systematic errors in the theoretical EOS do not increase with pressure, and no extrapolation is needed. This all-electron method is applicable to first-row solids, providing a new reference for ab initio calculations of solids and benchmarks for pseudopotential accuracy. We compared experimental and theoretical results on the momentum distribution and the quasiparticle renormalization factor in sodium. From an x-ray Compton-profile measurement of the valence-electron momentum density, we derived its discontinuity at the Fermi wavevector finding an accurate measure of the renormalization factor that we compared with quantum-Monte-Carlo and G0W0 calculations performed both on crystalline sodium and on the homogeneous electron gas. Our calculated results are in good agreement with the experiment. We have been studying the heat of formation for various Kubas complexes of molecular hydrogen on Ti(1,2)ethylene-nH2 using Diffusion Monte Carlo. This work has been started and is o

The quantum-dot cellular automaton (QCA), a processing platform based on interacting quantum dots, was introduced by Lent in the mid-1990s. What followed was an exhilarating period with the development of the line, the functionally complete set of logic functions, as well as more complex processing structures, however all in the realm of binary logic. Regardless of these achievements, it has to be acknowledged that the use of binary logic is in computing systems mainly the end result of the technological limitations, which the designers had to cope with in the early days of their design. The first advancement of QCAs to multi-valued (ternary) processing was performed by Lebar Bajec et al, with the argument that processing platforms of the future should not disregard the clear advantages of multi-valued logic. Some of the elementary ternary QCAs, necessary for the construction of more complex processing entities, however, lead to a remarkable increase in size when compared to their binary counterparts. This somewhat negates the advantages gained by entering the ternary computing domain. As it turned out, even the binary QCA had its initial hiccups, which have been solved by the introduction of adiabatic switching and the application of adiabatic pipeline approaches. We present here a study that introduces adiabatic switching into the ternary QCA and employs the adiabatic pipeline approach to successfully solve the issues of elementary ternary QCAs. What is more, the ternary QCAs presented here are sizewise comparable to binary QCAs. This in our view might serve towards their faster adoption.

Pe?ar, P.; Ramšak, A.; Zimic, N.; Mraz, M.; Lebar Bajec, I.

This brochure presents an overview of adaptive computingtechnology and how it can help people with disabilities participate more fully in society. It defines key terms (such as "disability" and "access barriers") and briefly summarizes provisions of major laws: the Americans with Disabilities Act of 1990, the Technology-Related Assistance Act,…

American Council on Education, Washington, DC. HEATH Resource Center.

|This study investigates personal and setting characteristics, teacher attitudes, and current computertechnology practices among 764 elementary and secondary teachers from both private and public school sectors in Quebec. Using expectancy-value theory, the Technology Implementation Questionnaire (TIQ) was developed; it consists of 33 belief…

Introduced by Fuji Photo Film Japan in the early 1980s, computed radiography (CR) technology has developed considerably since then to become the mature widely installed technology it is today (about 7500 systems worldwide). Various mammographic examinations require high performance results to which CR complies on demand or following some procedures such as geometrical magnification carried out during the examination. The

Ensemble Kalman filter (EnKF) uses a randomized ensemble of subsurface models for error and uncertainty estimation. However, the complexity of geological models and the requirement of a large number of simulation runs make routine applications extremely difficult due to expensive computation cost. Grid computingtechnologies provide a cost-efficient way to combine geographically distributed computing resources to solve large-scale data and

Xin Li; Zhou Lei; Christopher D White; Gabrielle Allen; Guan Qin; F. T.-C. Tsai

The application of computationalquantum chemistry towards the design of functional materials has been identified as one of the grand challenges in the art of high performance computing, offering substantial benefit to those who are able to make progress in the art and to those who are able to utilize the results of such techniques on a production scale economic

Quantumcomputing has been of intense interest over the last 10 years because of its promising ability to do high-speed factoring and its potential for the efficient simulation of quantum dynamics. It could be implemented in many different ways using optical techniques. A better understanding of the advantages and disadvantages of these approaches would allow the experimental groups working in this area to optimize their choice of experiment and to concentrate on the approaches that are most likely to succeed. In this thesis, we are interested in quantum logic gates based on nonlinear optical approaches and mainly focus on one of the approaches----quantum Zeno gates. We theoretically analyze two-photon absorption, which is essential to perform quantum Zeno gates for coherent light and for frequency-entangled light. We also analyze and compare quantum Zeno gates with nonlinear phase gates, which is another promising optical implementation for quantum logic. The results of our theoretical analysis will be useful for future experimental work in quantumcomputation.

Quantumcomputers require the storage of quantum information in a set of two-level systems (called qubits), the processing of this information using quantum gates and a means of final readout. So far, only a few systems have been identified as potentially viable quantumcomputer models-accurate quantum control of the coherent evolution is required in order to realize gate operations, while

Ubiquitous computing is considered as a promising technological path of innovation. Intensive R&D activities and political strategies are addressing the objective to foster marketable technologies and applications. This article explores the state-of-the-art on the way towards the “Internet of things”. Which application fields have already proved their potential for realising the vision and promises related to the new technology? What

The following topics are discussed: the physical and chemical processes inside operating internal combustion engines which are being studied to improve IC engine performance; the CHEMKIN computer code for theoretical modeling studies of combustion kinetics; an acoustic thermometer capable of measuring temperatures to 3000/sup 0/C and which can be used in reactor safety studies; and the new application of inertial navigational techniques to more accurate wellbore surveys. (LCL)

Pulsed electron nuclear double resonance (ENDOR) spin technology has been invoked for realization of a quantumcomputer (QC). Sample preparation of molecular spins, quantum operations, and measurements have been performed successfully, showing that ENDOR QC is feasible. We have employed a typical stable organic open-shell entity, malonyl radical, for pulsed ENDOR-based QC experiments. Time proportional phase incrementation (TPPI) technique was applied in order to characterize entangled states. The appearance of the entanglement between electron and nuclear spins was discussed based on the pulsed ENDOR-QC experiments with the TPPI detection. The generated entangled state was operated by both the microwave and RF pulses, demonstrating the appearance of a spinor property with four-? periodicity due to electron spin-1/2, in a straightforward manner for the first time. Interconversion from one entangled state to the other one via quantum operation was demonstrated.

I will argue that the proposal of establishing operational foundations of Quantum Theory 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 suggested operational ``principles of the quantumness,'' I address the problem on whether Quantum Theory and Special Relativity are unrelated theories, or instead, if the one implies the other. I show how Special Relativity can be indeed derived from causality of Quantum Theory, within the computational paradigm ``the universe is a huge quantumcomputer,'' reformulating QFT as a Quantum-Computational Field Theory (QCFT). In QCFT Special Relativity emerges from the fabric of the computational network, which also naturally embeds gauge invariance. In this scheme even the quantization rule and the Planck constant can in principle be derived as emergent from the underlying causal tapestry of space-time. In this way Quantum Theory remains the only theory operating the huge computer of the universe. Is the computational paradigm only a speculative tautology (theory as simulation of reality), or does it have a scientific value? The answer will come from Occam's razor, depending on the mathematical simplicity of QCFT. Here I will just start scratching the surface of QCFT, analyzing simple field theories, including Dirac's. The number of problems and unmotivated recipes that plague QFT strongly motivates us to undertake the QCFT project, since QCFT makes all such problems manifest, and forces a re-foundation of QFT.

I will argue that the proposal of establishing operational foundations of Quantum Theory 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 suggested operational 'principles of the quantumness', I address the problem on whether Quantum Theory and Special Relativity are unrelated theories, or instead, if the one implies the other. I show how Special Relativity can be indeed derived from causality of Quantum Theory, within the computational paradigm 'the universe is a huge quantumcomputer', reformulating QFT as a Quantum-Computational Field Theory (QCFT). In QCFT Special Relativity emerges from the fabric of the computational network, which also naturally embeds gauge invariance. In this scheme even the quantization rule and the Planck constant can in principle be derived as emergent from the underlying causal tapestry of space-time. In this way Quantum Theory remains the only theory operating the huge computer of the universe.Is the computational paradigm only a speculative tautology (theory as simulation of reality), or does it have a scientific value? The answer will come from Occam's razor, depending on the mathematical simplicity of QCFT. Here I will just start scratching the surface of QCFT, analyzing simple field theories, including Dirac's. The number of problems and unmotivated recipes that plague QFT strongly motivates us to undertake the QCFT project, since QCFT makes all such problems manifest, and forces a re-foundation of QFT.

D'Ariano, Giacomo Mauro [QUIT Group, Dipartimento di Fisica 'A. Volta', 27100 Pavia (Italy) and Center for Photonic Communication and Computing, Northwestern University, Evanston, IL 60208 (Italy)

The present day rapid development of media science and digital technology is offering the modern generation more opportunities as well as challenges as the new fundamental literacy. Therefore, to reach the modern generation on issues such as an appreciation of cultures, we have to find common grounds based on digital media technology. In an increasingly hybrid cultural environment, interaction and fusion of cultural factors with the computertechnology will be an investigation into the possibilities of providing an experience into the cultures of the world, operating in the environments the modern generation inhabits. Research has created novel merging of traditional cultures and literature with recent media literacy. Three cultural computing systems, Media Me, BlogWall and Confucius Computer, are presented in this chapter. Studies showed that users gave positive feedback to their experience of interacting with cultural computing systems.

The quantum key distribution technology is an emerging technology, which uses quantum mechanics properties of micro-particles. The progress of quantum key distribution can generate the quantum key which can be kept strictly confidential. The application of quantum key distribution technology in distributed space TT & C network can improve the existing communication environment and enhance communications security. This article will

In this video adapted from Pathways to Technology, learn how exploring an interest in computers can lead to a new career. After taking, and enjoying, an online course, Hilda Villavicencio decided to study computer programming and information technology (IT) at community college. Students who attend an IT program learn how computers function, so that whether they go into networking, technical support, or any other branch of IT, they bring a solid understanding of computer systems and how to maintain them. Hilda interns at the computer help-desk at her school where she uses what she's learning in the classroom to help others. She explains where she'd like to be in five years, and how her degree will take her there.The video runs 3:12 and is accompanied by a background essay, standards alignment, and discussion questions. Users who sign up for a free account can save the resource and download the video as well.

The possibility of implementing quantum reactive scattering programs on cheap platforms, originally used for graphic purposes only, has been investigated using a NVIDIA GPU. After a conversion of the code considered from Fortran to C and its deep restructuring for exploiting the GPU key features, significant speedups have been obtained for RWAVEPR, a time dependent quantum reactive scattering code propagating in time a complex wavepacket. As benchmark calculations those concerned with the evaluation of the reactive probabilities of the Cl+H2 and the N+N2 reactions have been considered.

Pacifici, Leonardo; Nalli, Danilo; Laganŕ, Antonio

We present a scheme for linear optical quantumcomputing using time-bin-encoded qubits in a single spatial mode. We show methods for single-qubit operations and heralded controlled-phase (cphase) gates, providing a sufficient set of operations for universal quantumcomputing with the Knill-Laflamme-Milburn [Nature (London) 409, 46 (2001)] scheme. Our protocol is suited to currently available photonic devices and ideally allows arbitrary numbers of qubits to be encoded in the same spatial mode, demonstrating the potential for time-frequency modes to dramatically increase the quantum information capacity of fixed spatial resources. As a test of our scheme, we demonstrate the first entirely single spatial mode implementation of a two-qubit quantum gate and show its operation with an average fidelity of 0.84±0.07. PMID:24160584

Humphreys, Peter C; Metcalf, Benjamin J; Spring, Justin B; Moore, Merritt; Jin, Xian-Min; Barbieri, Marco; Kolthammer, W Steven; Walmsley, Ian A

We assess routes to a diamond-based quantumcomputer, 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 optical control of electron spins. For some such devices, nuclear spins give additional advantages. Since there have already been demonstrations of basic initialization and readout, our emphasis is on routes to two-qubit quantum gate operations and the linking of perhaps 10-20 such gates. We analyse the dopant properties necessary, especially centres containing N and P, and give results using simple scoping calculations for the key interactions determining gate performance. Our conclusions are cautiously optimistic: it may be possible to develop a useful quantum information processor that works above cryogenic temperatures. PMID:21832328

Stoneham, A Marshall; Harker, A H; Morley, Gavin W

We present a scheme for linear optical quantumcomputing using time-bin-encoded qubits in a single spatial mode. We show methods for single-qubit operations and heralded controlled-phase (cphase) gates, providing a sufficient set of operations for universal quantumcomputing with the Knill-Laflamme-Milburn [Nature (London) 409, 46 (2001)] scheme. Our protocol is suited to currently available photonic devices and ideally allows arbitrary numbers of qubits to be encoded in the same spatial mode, demonstrating the potential for time-frequency modes to dramatically increase the quantum information capacity of fixed spatial resources. As a test of our scheme, we demonstrate the first entirely single spatial mode implementation of a two-qubit quantum gate and show its operation with an average fidelity of 0.84±0.07.

Humphreys, Peter C.; Metcalf, Benjamin J.; Spring, Justin B.; Moore, Merritt; Jin, Xian-Min; Barbieri, Marco; Kolthammer, W. Steven; Walmsley, Ian A.

We study how dynamical decoupling (DD) pulse sequences can improve the reliability of quantumcomputers. We prove upper bounds on the accuracy of DD-protected quantum gates and derive sufficient conditions for DD-protected gates to outperform unprotected gates. Under suitable conditions, fault-tolerant quantum circuits constructed from DD-protected gates can tolerate stronger noise and have a lower overhead cost than fault-tolerant circuits constructed from unprotected gates. Our accuracy estimates depend on the dynamics of the bath that couples to the quantumcomputer and can be expressed either in terms of the operator norm of the bath's Hamiltonian or in terms of the power spectrum of bath correlations; we explain in particular how the performance of recursively generated concatenated pulse sequences can be analyzed from either viewpoint. Our results apply to Hamiltonian noise models with limited spatial correlations.

Ng, Hui Khoon; Preskill, John [Institute for Quantum Information, California Institute of Technology, Pasadena, California 91125 (United States); Lidar, Daniel A. [Departments of Electrical Engineering, Chemistry, and Physics, and Center for Quantum Information Science and Technology, University of Southern California, Los Angeles, California 90089 (United States)

The areas discussed are still under development: I. Nano structured materials for TE applications a) SiGe and Be.Te; b) Nano particles and nanoshells. II. Quantumtechnology for optical devices: a) Quantum apertures; b) Smart optical materials; c) Micro s...

\\u000a We present a method for verifying measurement-based quantumcomputations, by producing a quantum circuit equivalent to a given\\u000a deterministic measurement pattern. We define a diagrammatic presentation of the pattern, and produce a circuit via a rewriting\\u000a strategy based on the generalised flow of the pattern. Unlike other methods for translating measurement patterns with generalised\\u000a flow to circuits, this method uses

\\u000a \\u000a Abstract. A number of questions associated with practical implementations of quantum cryptography systems having to do with unconditional\\u000a secrecy, computational loads and effective secrecy rates in the presence of perfect and imperfect sources are discussed. The\\u000a different types of unconditional secrecy, and their relationship to general communications security, are discussed in the\\u000a context of quantum cryptography. In order to

We propose a novel method to calculate invariants of colour and multicolour images. It employs an idea of classical and quantum hypercomplex numbers and combines it with the idea of classical and quantum number theoretical transforms over hypercomplex algebras, which reduce the computational complexity of the global recognition algorithm for nD k-multispectral images from O(knNn+1)to O(kNn log N) and to

Valeri G. Labunets; Ekaterina V. Rundblad-Labunets; Jaakko T. Astola

We present a quantum algorithm to prepare injective PEPS on a quantumcomputer, a problem raised by Verstraete, Wolf, Perez-Garcia, and Cirac [PRL 96, 220601 (2006)]. To be efficient, our algorithm requires well-conditioned PEPS projectors and, essentially, an inverse-polynomial spectral gap of the PEPS' parent Hamiltonian. Based on this algorithm, we also present a heuristic method for approximating the contraction

In a quantumcomputer, qubits are often stored in identical two-level systems separated by a distance shorter than the characteristic wavelength of the reservoirs that are responsible for decoherence. In this case the collective qubit-reservoir interaction, rather than the individual qubit-reservoir interaction, may determine the decoherence properties. We study the collective decoherence behavior in between each step in certain quantum

Shoko Utsunomiya; Cyrus P. Master; Yoshihisa Yamamoto

A proof is given, which relies on the commutator algebra of the unitary Lie\\u000agroups, that quantum gates operating on just two bits at a time are sufficient\\u000ato construct a general quantum circuit. The best previous result had shown the\\u000auniversality of three-bit gates, by analogy to the universality of the Toffoli\\u000athree-bit gate of classical reversible computing. Two-bit

A proof is given, which relies on the commutator algebra of the unitary Lie groups, that quantum gates operating on just two bits at a time are sufficient to construct a general quantum circuit. The best previous result had shown the universality of three-bit gates, by analogy to the universality of the Toffoli three-bit gate of classical reversible computing. Two-bit

In a nutshell, the existing Internet provides to us content in the forms of videos, emails and information served up in web pages. With Cloud Computing, the next generation of Internet will allow us to "buy" IT services from a web portal, drastic expanding the types of merchandise available beyond those on e-commerce sites such as eBay and Taobao. We would be able to rent from a virtual storefront the basic necessities to build a virtual data center: such as CPU, memory, storage, and add on top of that the middleware necessary: web application servers, databases, enterprise server bus, etc. as the platform(s) to support the applications we would like to either rent from an Independent Software Vendor (ISV) or develop ourselves. Together this is what we call as "IT as a Service," or ITaaS, bundled to us the end users as a virtual data center.

A method for quantumcomputation in the presence of spontaneous emission is proposed. The method combines strong and fast (dynamical decoupling) pulses and a quantum error correcting code that encodes n logical qubits into only n+1 physical qubits. Universal, fault-tolerant, quantumcomputation is shown to be possible in this scheme using Hamiltonians relevant to a range of promising proposals for the physical implementation of quantumcomputers.

Khodjasteh, K.; Lidar, D. A. [Department of Physics, University of Toronto, 60 St. George Street, Toronto, Ontario, Canada M5S 1A7 (Canada); Chemical Physics Theory Group, Chemistry Department, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada M5S 3H6 (Canada)

Composite pulses provide a simple means for constructing quantum logic gates which are robust to small errors in the control fields used to implement them. Here I describe how antisymmetric composite NOT gates can be nested to produce gates with arbitrary tolerance of errors.

The excitation and detection of multiple-quantum (MQ) transitions in Fourier transform NMR spectroscopy is an interesting problem in the quantum mechanical dynamics of spin systems as well as an important new technique for investigation of molecular structure. In particular, multiple-quantum spectroscopy can be used to simplify overly complex spectra or to separate the various interactions between a nucleus and its environment. The emphasis of this work is on computer simulation of spin-system evolution to better relate theory and experiment.

In a topological quantumcomputer, braids of non-Abelian anyons in a (2+1)-dimensional space time form quantum gates, whose fault tolerance relies on the topological, rather than geometric, properties of the braids. Here we propose to create and exploit redundant geometric degrees of freedom to improve the theoretical accuracy of topological single- and two-qubit quantum gates. We demonstrate the power of the idea using explicit constructions in the Fibonacci model. We compare its efficiency with that of the Solovay-Kitaev algorithm and explain its connection to the leakage errors reduction in an earlier construction [H. Xu and X. Wan, Phys. Rev. A 78, 042325 (2008)].

Xu Haitan [Zhejiang Institute of Modern Physics, Zhejiang University, Hangzhou 310027 (China); Wan Xin [Zhejiang Institute of Modern Physics, Zhejiang University, Hangzhou 310027 (China); Asia Pacific Center for Theoretical Physics , Pohang, Gyeongbuk 790-784 (Korea, Republic of); Department of Physics, Pohang University of Science and Technology, Pohang, Gyeongbuk 790-784 (Korea, Republic of)

Simulating exotic phases of matter that are not amenable to classical techniques is one of the most important potential applications of quantum information processing. We present an efficient algorithm for preparing a large class of topological quantum states, the G-injective projected entangled pair states (PEPS), on a quantumcomputer. Important examples include the resonant valence bond states, conjectured to be topological spin liquids. The runtime of the algorithm scales polynomially with the condition number of the PEPS projectors and inverse polynomially in the spectral gap of the PEPS parent Hamiltonian.

We discuss the potential and limitations of Gaussian cluster states for measurement-based quantumcomputing. Using a framework of Gaussian-projected entangled pair states, we show that no matter what Gaussian local measurements are performed on systems distributed on a general graph, transport and processing of quantum information are not possible beyond a certain influence region, except for exponentially suppressed corrections. We also demonstrate that even under arbitrary non-Gaussian local measurements, slabs of Gaussian cluster states of a finite width cannot carry logical quantum information, even if sophisticated encodings of qubits in continuous-variable systems are allowed for. This is proven by suitably contracting tensor networks representing infinite-dimensional quantum systems. The result can be seen as sharpening the requirements for quantum error correction and fault tolerance for Gaussian cluster states and points toward the necessity of non-Gaussian resource states for measurement-based quantumcomputing. The results can equally be viewed as referring to Gaussian quantum repeater networks.

Ohliger, M.; Kieling, K. [Institute of Physics and Astronomy, University of Potsdam, D-14476 Potsdam (Germany); Eisert, J. [Institute of Physics and Astronomy, University of Potsdam, D-14476 Potsdam (Germany); Institute for Advanced Study Berlin, D-14193 Berlin (Germany)

Alice has made a decision in her mind. While she does not want to reveal it to Bob at this moment, she would like to convince Bob that she is committed to this particular decision and that she cannot change it at a later time. Is there a way to get Bob's trust? This practical question is also one of the fundamental dilemmas of quantum cryptography, and is discussed in this fascinating and highly topical volume. In addition, experimental realizations and theoretical aspects of trapped-ion and other possible quantumcomputers are presented in detail. Still a number of years ahead, quantumcomputers will possibly shape the 21st century as much as conventional computers shaped the 20th century. This volume provides you with up-to-date information on the current state of the art in this rapidly advancing field.

We present a theoretical proposal for the implementation of geometric quantumcomputing based on a Hamiltonian which has a doubly degenerate ground state. Thus the system which is steered adiabatically, remains in the ground-state. The proposed physical implementation relies on a superconducting circuit composed of three SQUIDs and two superconducting islands with the charge states encoding the logical states. We obtain a universal set of single-qubit gates and implement a nontrivial two-qubit gate exploiting the mutual inductance between two neighboring circuits, allowing us to realize a fully geometric ground-state quantumcomputing. The introduced paradigm for the implementation of geometric quantumcomputing is expected to be robust against environmental effects.

Solinas, P. [Department of Applied Physics/COMP, Aalto University, P. O. Box 15100, FI-00076 Aalto (Finland); Pirkkalainen, J.-M. [Department of Applied Physics/COMP, Aalto University, P. O. Box 15100, FI-00076 Aalto (Finland); Low Temperature Laboratory, Aalto University, P. O. Box 13500, FI-00076 Aalto (Finland); Moettoenen, M. [Department of Applied Physics/COMP, Aalto University, P. O. Box 15100, FI-00076 Aalto (Finland); Low Temperature Laboratory, Aalto University, P. O. Box 13500, FI-00076 Aalto (Finland); Australian Research Council Centre of Excellence for Quantum Computer Technology, School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales 2052 (Australia)

Nanowires and nanotubes are promising building blocks for designing nanoscale devices for sensing warfare agents. Computer models are key to designing and improving such sensors. Due to their nanoscale size, quantum models are needed to model the transpor...

This talk will present an overview on a decade's worth of innovation and progress toward developing a quantumcomputer, and suggest future research directions. In the eleven years since Peter Shor's quantum algorithms, quantum information science has become one of the fastest growing areas of physics. The prospect of executing quantum algorithms with no classical counterparts that accomplish tasks far beyond the capabilities of classical computers is one of the grand challenges of modern physics. The quest for quantumcomputing has inspired the discovery of passive and active forms of error correction, the formulation of compelling concepts for physical quantum bits, and the construction of experimental apparatus to realize them. Steady progress on both the experimental and theoretical fronts is transforming the fundamental tenets of quantumcomputing from a theoretical notion to a proven reality. The search for suitable physical systems has promoted the cross-pollination of ideas and language between atomic, molecular, and optical physics and solid-state physics, to the advantage of both communities.

Molecular spin clusters are prototypical systems exhibiting coherent dynamics of the electronic spin. The pattern of the lowest lying spin states is well defined and controlled at the synthetic level. The chemical bottom up approach used for the synthesis of molecules also allows to reduce intrinsic sources of decoherence and to build links between clusters, thus creating entanglement of spin states. Molecular spin clusters can be deposited at surfaces, thus forming scalable networks. Different molecules and ligands may be combined to exploit different functionalities, the latter being defined at molecular level. These facts provide extraordinary motivation to attempt the implementation of molecular quantum processors that, in turns, are test bench for novel quantum algorithms. Recent achievements obtained on antiferromagnetic molecular rings will be presented.

The treewidth of a graph is a useful combinatorial measure of how close the graph is to a tree. We prove that a quantum circuit with $T$ gates whose underlying graph has treewidth $d$ can be simulated deterministically in $T^{O(1)}\\\\exp[O(d)]$ time, which, in particular, is polynomial in $T$ if $d=O(\\\\log T)$. Among many implications, we show efficient simulations for log-depth

The treewidth of a graph is a useful combinatorial measure of how close the graph is to a tree. We prove that a quantum circuit with T gates whose underlying graph has treewidth d can be simulated deterministically in T O(1) exp(O(d)) time, which, in particular, is polynomial in T if d = O(log T). Among many implications, we show

Service-Oriented Architecture (SOA) is the contemporary paradigm of choice for developing scalable, loosely-coupled applications that span organisations. However the architectural paradigm that is SOA is often confused with the implementation technology that is Web Services. In this paper we aim to clarify the fundamental tenets of SOA and their relevance to Internet-scale computing (or Grid computing). We then show how

A QuantumComputer (QC) is a device that utilizes the principles of Quantum Mechanics to perform computations. Such a machine would be capable of accomplishing tasks not achievable by means of any conventional digital computer, for instance factoring large numbers. Currently it appears that the QC architecture based on an array of spin quantum bits (qubits) embedded in a solid-state matrix is one of the most promising approaches to fabrication of a scalable QC. However, the fabrication and operation of a Solid State QuantumComputer (SSQC) presents very formidable challenges; primary amongst these are: (1) the characterization and control of the fabrication process of the device during its construction and (2) the readout of the computational result. Magnetic Resonance Force Microscopy (MRFM)--a novel scanning probe technique based on mechanical detection of magnetic resonance-provides an attractive means of addressing these requirements. The sensitivity of the MRFM significantly exceeds that of conventional magnetic resonance measurement methods, and it has the potential for single electron spin detection. Moreover, the MRFM is capable of true 3D subsurface imaging. These features will make MRFM an invaluable tool for the implementation of a spin-based QC. Here we present the general principles of MRFM operation, the current status of its development and indicate future directions for its improvement.

Pelekhov, D. V. (Denis V.); Martin, I. (Ivar); Suter, A. (Andreas); Reagor, D. W. (David W.); Hammel, P. C. (P. Chris)

The UNEDF project was a large-scale collaborative effort that applied high-performance computing to the nuclear quantum many-body problem. The primary focus of the project was on constructing, validating, and applying an optimized nuclear energy density functional, which entailed a wide range of pioneering developments in microscopic nuclear structure and reactions, algorithms, high-performance computing, and uncertainty quantification. 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, S.; Bulgac, A.; Carlson, J.; Engel, J.; Fann, G.; Furnstahl, R. J.; Gandolfi, S.; Hagen, G.; Horoi, M.; Johnson, C.; Kortelainen, M.; Lusk, E.; Maris, P.; Nam, H.; Navratil, P.; Nazarewicz, W.; Ng, E.; Nobre, G. P. A.; Ormand, E.; Papenbrock, T.; Pei, J.; Pieper, S. C.; Quaglioni, S.; Roche, K. J.; Sarich, J.; Schunck, N.; Sosonkina, M.; Terasaki, J.; Thompson, I.; Vary, J. P.; Wild, S. M.

We obtain an upper bound on the time available for quantumcomputation for a given quantumcomputer and decohering environment with quantum error correction implemented. First, we derive an explicit quantum evolution operator for the logical qubits and show that it has the same form as that for the physical qubits but with a reduced coupling strength to the environment. Using this evolution operator, we find the trace distance between the real and ideal states of the logical qubits in two cases. For a super-Ohmic bath, the trace distance saturates, while for Ohmic or sub-Ohmic baths, there is a finite time before the trace distance exceeds a value set by the user.

Novais, E. [Centro de Ciencias Naturais e Humanas, Universidade Federal do ABC, Santo Andre, Sao Paulo (Brazil); Mucciolo, Eduardo R. [Department of Physics, University of Central Florida, Box 162385, Orlando, Florida 32816 (United States); Baranger, Harold U. [Department of Physics, Duke University, Box 90305, Durham, North Carolina 27708-0305 (United States)

We obtain an upper bound on the time available for quantumcomputation for a given quantumcomputer and decohering environment with quantum error correction implemented. First, we derive an explicit quantum evolution operator for the logical qubits and show that it has the same form as that for the physical qubits but with a reduced coupling strength to the environment. Using this evolution operator, we find the trace distance between the real and ideal states of the logical qubits in two cases. For a super-Ohmic bath, the trace distance saturates, while for Ohmic or sub-Ohmic baths, there is a finite time before the trace distance exceeds a value set by the user.

Novais, E.; Mucciolo, Eduardo R.; Baranger, Harold U.

We introduce a general scheme for sequential one-way quantumcomputation where static systems with long-living quantum coherence (memories) interact with moving systems that may possess very short coherence times. Both the generation of the cluster state needed for the computation and its consumption by measurements are carried out simultaneously. As a consequence, effective clusters of one spatial dimension fewer than in the standard approach are sufficient for computation. In particular, universal computation requires only a one-dimensional array of memories. The scheme applies to discrete-variable systems of any dimension as well as to continuous-variable ones, and both are treated equivalently under the light of local complementation of graphs. In this way our formalism introduces a general framework that encompasses and generalizes in a unified manner some previous system-dependent proposals. The procedure is intrinsically well suited for implementations with atom-photon interfaces.

Roncaglia, Augusto J.; Aolita, Leandro [ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, E-08860 Castelldefels, Barcelona (Spain); Ferraro, Alessandro [Grup d'Optica, Universitat Autonoma de Barcelona, E-08193 Bellaterra, Barcelona (Spain); Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom); Acin, Antonio [ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, E-08860 Castelldefels, Barcelona (Spain); ICREA-Institucio Catalana de Recerca i Estudis Avancats, Lluis Companys 23, E-08010 Barcelona (Spain)

In the circuit model, quantumcomputers rely on the availability of a universal quantum gate set. A particularly intriguing example is a set of two-qubit-only gates: 'matchgates', along with swap (the exchange of two qubits). In this paper, we show a simple decomposition of arbitrary matchgates into better-known elementary gates and implement a matchgate in a single-photon linear optics experiment. The gate performance is fully characterized via quantum process tomography. Moreover, we represent the resulting reconstructed quantum process in a novel way, as a fidelity map in the space of all possible non-local two-qubit unitaries. We propose the non-local distance—which is independent of local imperfections such as uncorrelated noise or uncompensated local rotations—as a new diagnostic process measure for the non-local properties of the implemented gate.

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

In the distributed quantumcomputing paradigm, well-controlled few-qubit ‘nodes’ are networked together by connections which are relatively noisy and failure prone. A practical scheme must offer high tolerance to errors while requiring only simple (i.e. few-qubit) nodes. Here we show that relatively modest, three-qubit nodes can support advanced purification techniques and so offer robust scalability: the infidelity in the entanglement channel may be permitted to approach 10% if the infidelity in local operations is of order 0.1%. Our tolerance of network noise is therefore an order of magnitude beyond prior schemes, and our architecture remains robust even in the presence of considerable decoherence rates (memory errors). We compare the performance with that of schemes involving nodes of lower and higher complexity. Ion traps, and NV-centres in diamond, are two highly relevant emerging technologies: they possess the requisite properties of good local control, rapid and reliable readout, and methods for entanglement-at-a-distance.

Terahertz computed tomographic imaging has been performed based on an imaging system which includes a terahertz quantum cascade laser as the light source and a terahertz quantum well photo-detector. The main reconstruction methods of filtered back projection, iterative analysis and the wavelet reconstruction technique are adopted and compared. The reconstructed quality has been discussed with respect to projection numbers, contrast and geometric preservation. We have applied parameter structural similarity to quantitatively analyze the image quality at the end.

The purposes of this study were to determine if computertechnology had an impact on EFL college students' reading habits and if students' online reading habits and their demographic variables, such as gender, age, CJEE scores, employment status, and online hours were related. 124 valid survey questionnaires were collected from college students in a university in southern Taiwan. The results

|This document contains 272 competencies, grouped into 36 units, for tech prep programs in the business/computertechnology cluster. The competencies were developed through collaboration of Ohio business, industry, and labor representatives and secondary and associate degree educators. The competencies are rated either "essential" (necessary to…

Ohio State Univ., Columbus. Center on Education and Training for Employment.

This document contains 272 competencies, grouped into 36 units, for tech prep programs in the business/computertechnology cluster. The competencies were developed through collaboration of Ohio business, industry, and labor representatives and secondary and associate degree educators. The competencies are rated either "essential" (necessary to…

Ohio State Univ., Columbus. Center on Education and Training for Employment.

The evolution of artificial intelligence technology over the past decade has lead to the development of a mature application area known as knowledge based systems. Knowledge base systems are computer programs capable of reasoning based on information maintained in a domain specific knowledge base. This paper describes the requirements of knowledge base system construction and discusses their relevance in the

We will report on the realisation of high-fidelity Schroedinger- Cat states with more than six qubits in a string of ^40Ca^ + ions stored in a linear ion trap. We achieved fidelities with the target states exceeding 95% for up to four ions and 88% for six ions. These high fidelities allow to investigate decoherence of highly entangled quantum states in the presence of collective dephasing, the predominant source of decoherence in ion-trap based and other physical realizations of quantumcomputation. Assuming the noise to be Gaussian and stationary, we derive and experimentally confirm a model that predicts an exponential decay of the state fidelity that scales as N^2 where N is the number of qubits. Such a scaling behaviour has severe effects on quantumcomputation and related fields, such as metrology.

Monz, Thomas; Schindler, Philipp; Barreiro, Julio T.; Chwalla, Michael; Coish, Bill; Hennrich, Markus T.; Blatt, Rainer

Whether or not neuronal signal properties can engage 'non-trivial', i.e. functionally significant, quantum properties, is the subject of an ongoing debate. Here we provide evidence that quantum coherence dynamics can play a functional role in ion conduction mechanism with consequences on the shape and associative character of classical membrane signals. In particular, these new perspectives predict that a specific neuronal topology (e.g. the connectivity pattern of cortical columns in the primate brain) is less important and not really required to explain abilities in perception and sensory-motor integration. Instead, this evidence is suggestive for a decisive role of the number and functional segregation of ion channel proteins that can be engaged in a particular neuronal constellation. We provide evidence from comparative brain studies and estimates of computational capacity behind visual flight functions suggestive for a possible role of quantumcomputation in biological systems.

We propose a scheme to implement quantum controlled SWAP gates by directing single-photon pulses to a two-sided cavity with a single trapped atom. The resultant gates can be used to realize quantum fingerprinting and universal photonic quantumcomputation. We present a theoretical model for our scheme and analyze its performance under practical noise, including spontaneous emission and randomness of atom-cavity coupling strength. It is shown that our scheme should be robust against practical imperfections in current cavity QED experiment setup.

Wang, B.; Duan, L.-M. [FOCUS Center and MCTP, Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 (United States)

Algorithms such as quantum factoring and quantum search illustrate the great theoretical promise of quantumcomputers; but the practical implementation of such devices will require careful consideration of the minimum resource requirements, together with the development of procedures to overcome inevitable residual imperfections in physical systems. Many designs have been proposed, but none allow a large quantumcomputer to be

Efficiently mapping binary functions to adiabatic quantumcomputers is an important problem because the resulting circuits can be used as oracles in Grover's algorithm. This paper presents a method for mapping binary functions to a two-dimensional grid of qubits with nearest neighbor interactions which is used in a prototype from D-Wave Systems. This is done by writing the binary function

We show how to guide a quantumcomputer to select an optimal tour for the traveling salesman. This is significant because it opens a rapid solution method for the wide range of applications of the traveling salesman problem, which include vehicle routing, job sequencing and data clustering.

Liquid crystals offer several advantages as solvents for molecules used for nuclear magnetic resonance quantumcomputing (NMRQC). The dipolar coupling between nuclear spins manifest in the NMR spectra of molecules oriented by a liquid crystal permits a significant increase in clock frequency, while short spin-lattice relaxation times permit fast recycling of algorithms, and save time in calibration and signal-enhancement experiments.

Costantino S. Yannoni; Mark H. Sherwood; Dolores C. Miller; Isaac L. Chuang; Lieven M. K. Vandersypen; Mark G. Kubinec

In linear quantum optics we consider phase shifters, beam splitters, displacement operations, squeezing operations etc. The evolution can be described by unitary operators using Bose creation and annihilation operators. This evolution can be reduced to matrix multiplication using unitary matrices. We derive these evolutions for the different unitary operators. Finally a computer algebra implementation is provided.

We prove the existence of a class of two-input, two-output gates any one of which is universal for quantumcomputation. This is done by explicitly constructing the three-bit gate introduced by Deutsch (Proc. R. Soc. Lond. A 425, 73 (1989)) as a network consisting of replicas of a single two-bit gate.

Introduced by Fuji Photo Film Japan in the early 1980s, computed radiography (CR) technology has developed considerably since then to become the mature widely installed technology it is today (about 7500 systems worldwide). Various mammographic examinations require high performance results to which CR complies on demand or following some procedures such as geometrical magnification carried out during the examination. The basic CR principles and digital image processing as well as technical improvements are detailed in this study, which also includes a synthesis of the articles on CR mammographic applications referenced in the bibliography, focusing on strong points, limits and current methods of surpassing these limits. New CR technology development perspectives in mammography and computed assisted diagnosis (CAD) algorithms will allow wider use of this method in the near future. PMID:10477094

Spins of single donor atoms are attractive candidates forlarge scale quantum information processing in silicon. Formation ofdevices with a few qubits is crucial for validation of basic ideas anddevelopment of a scalable architecture. We describe our development of asingle ion implantation technique for placement of single atoms intodevice structures. Collimated highly charged ion beams are aligned with ascanning probe microscope. Enhanced secondary electron emission due tohigh ion charge states (e.g., 31P13+, or 126Te33+) allows efficientdetection of single ion impacts. Studies of electrical activation of lowdose, low energy implants of 31P in silicon show a drastic effect ofdopant segregation to the SiO2/Si interface, while Si3N4/Si retards 31Psegregation. We discuss resolution limiting factors in ion placement, andprocess challenges for integration of single atom arrays with controlgates and single electron transistors.

Persaud, A.; Park, S.J.; Liddle, J.A.; Rangelow, I.W.; Bokor, J.; Keller, R.; Allen, F.I.; Schneider, D.H.; Schenkel, T.

A unitary operator on a quantum spin system of the form, U = e^-iH1e^-iH2, is introduced. Here, H1 and H2 are Hermitian and easily diagonalized; however, because the diagonalizing bases for H1 and H2 are quite different, the operator U is strongly interacting. The eigenvalues of U can be used to help factor products prime numbers in a manner similar, but not identical to the Shor algorithm. Indeed even approximate eigenvalues could be useful. Since U is strongly interacting, the practical usefulness of this approach hinges of finding tractable approximations. Toward this end, results of exact diagonalization of U for small systems are compared with the solution of several different approximate schemes.

With the rapid advance in computer and network technology, computer-based electronic evidence has increasingly played an important role in the courtroom over the last decade. Computer forensics, a growing discipline rooted in forensic science and computer security technology, focuses on acquiring electronic evidence from computer systems to prosecute computer crimes, national security threats, and computer abuse. It has lost its

We investigate the possibility to have electron-pairs in dephasing-free\\u000asubspace (DFS), by means of the quantum-dot cellular automata (QCA) and\\u000asingle-spin rotations, to carry out a high-fidelity and deterministic universal\\u000aquantum computation. We show that our QCA device with electrons tunneling two\\u000adimensionally is very suitable for DFS encoding, and argue that our design\\u000afavors a scalable quantumcomputation robust

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

We propose a scheme for performing universal quantumcomputation in a linear array of single electron quantum dots using spin-orbit coupling. Quantum gates are carried out by pulsing the exchange interaction between neighboring dots. While this interaction is dominated by the isotropic Heisenberg term S_1ot S_2, spin-orbit coupling introduces small anisotropic corrections. We show that control over these corrections, even if limited, is sufficient for universal quantumcomputation over qubits encoded into pairs of electron spins on neighboring dots. There is no need for additional control mechanisms. The simplicity of our scheme hinges on these corrections having rotational symmetry about a fixed axis in spin space, and we discuss the conditions for which this is the case. For example, we show that in a linear array of GaAs quantum dots lying in the [001] plane and aligned along the [110] direction, the symmetry axis is fixed along the [1\\overline 10] direction within the Hund-Mulliken approximation. Control of spin-orbit coupling either through pulse shaping, or direct control of the Dresselhaus and Rashba terms is also discussed. We find the number of voltage pulses required to carry out either single qubit rotations or CNOT gates scales as the inverse of the strength of spin-orbit coupling. Work supported by NSF NIRT Grant No. DMR-0103034.

A scheme to implement a quantumcomputer subjected to decoherence and governed by an untunable qubit-qubit interaction is presented. By concatenating dynamical decoupling through bang-bang (BB) pulse with decoherence-free subspaces (DFSs) encoding, we protect the quantumcomputer from environment-induced decoherence that results in quantum information dissipating into the environment. For the inherent qubit-qubit interaction that is untunable in the quantum system, BB control plus DFSs encoding will eliminate its undesired effect which spoils quantum information in qubits. We show how this quantum system can be used to implement universal quantumcomputation.

Zhang Yong; Zhou Zhengwei; Yu Bo; Guo Guangcan [Key Laboratory of Quantum Information, University of Science and Technology of China, Chinese Academy of Sciences, Hefei, Anhui 230026 (China)

First-principles electronic structure theory explains properties of atoms, molecules and solids from underlying physical principles without input from empirical parameters. Time-dependent density functional theory (TDDFT) has emerged as arguably the most widely used first-principles method for describing the time-dependent quantum mechanics of many-electron systems. In this thesis, we will show how the fundamental principles of TDDFT can be extended and applied in two novel directions: The theory of open quantum systems (OQS) and quantumcomputation (QC). In the first part of this thesis, we prove theorems that establish the foundations of TDDFT for open quantum systems (OQS-TDDFT). OQS-TDDFT allows for a first-principles description of non-equilibrium systems, in which the electronic degrees of freedom undergo relaxation and decoherence due to coupling with a thermal environment, such as a vibrational or photon bath. We then discuss properties of functionals in OQS-TDDFT and investigate how these differ from functionals in conventional TDDFT using an exactly solvable model system. Next, we formulate OQS-TDDFT in the linear-response regime, which gives access to environmentally broadened excitation spectra. Lastly, we present a hybrid approach in which TDDFT can be used to construct master equations from first-principles for describing energy transfer in condensed phase systems. In the second part of this thesis, we prove that the theorems of TDDFT can be extended to a class of qubit Hamiltonians that are universal for quantumcomputation. TDDFT applied to universal Hamiltonians implies that single-qubit expectation values can be used as the basic variables in quantumcomputation and information theory, rather than wavefunctions. This offers the possibility of simplifying computations by using the principles of TDDFT similar to how it is applied in electronic structure theory. Lastly, we discuss a related result; the computational complexity of TDDFT.

We propose a scheme for scalable and universal quantumcomputation using diatomic bits with conditional dipole-dipole interaction, trapped within an optical lattice. The qubit states are encoded by the scattering state and the bound heteronuclear molecular state of two ultracold atoms per site. The conditional dipole-dipole interaction appears between neighboring bits when they both occupy the molecular state. The realization of a universal set of quantum logic gates, which is composed of single-bit operations and a two-bit controlled-NOT gate, is presented. The readout method is also discussed.

Lee, Chaohong; Ostrovskaya, Elena A. [Nonlinear Physics Centre and ARC Centre of Excellence for Quantum-Atom Optics, Research School of Physical Sciences and Engineering, Australian National University, Canberra ACT 0200 (Australia)

We propose an approach to coherently transfer populations between selected quantum states in one- and two-qubit systems by using controllable Stark-chirped rapid adiabatic passages. These evolution-time insensitive transfers, assisted by easily implementable single-qubit phase-shift operations, could serve as elementary logic gates for quantumcomputing. Specifically, this proposal could be conveniently demonstrated with existing Josephson phase qubits. Our proposal can find an immediate application in the readout of these qubits. Indeed, the broken parity symmetries of the bound states in these artificial atoms provide an efficient approach to design the required adiabatic pulses. PMID:18517785

Wei, L F; Johansson, J R; Cen, L X; Ashhab, S; Nori, Franco

This paper discusses ways to implement two-qubit gate operations for quantumcomputing with cold trapped ions within one step. The proposed scheme is widely robust against parameter fluctuations and its simplicity might help to increase the number of qubits in present experiments. The basic idea is to use the quantum Zeno effect originating from continuous measurements on a common vibrational mode to realize gate operations with very high fidelities. The gate success rate can, in principle, be arbitrarily high but operation times comparable to other schemes can only be obtained by accepting success rates below 80%.

We show that a many-body system of single-electron quantum dots, whose orbital states are dressed by a global magnetic field, can be described by an effective Hamiltonian with an anisotropic XZ spin-spin interaction which is proportional to the Zeeman splitting. We show that these interaction potentials give rise to spin-dependent Hubbard models with tunable nearest neighbor two-body and three-body interactions. The two-body interactions can even be switched off via the external electric field, and hence the three-body interaction plays a dominant role. The derivation of these effective interaction potentials follows from a well-controlled and systematic expansion into many-body interaction terms. Models of this type have appeared in the recent discussion of exotic quantum phases, in particular in the context of topological quantum phases and quantumcomputing, and we show that quantum dots can be regarded as a realistic experimental route which provides the basic building blocks and techniques toward the study of these phenomena. The main application of this derived model is to develop topological quantumcomputation.

Xue Peng [Department of Physics, Southeast University, Nanjing 211189 (China)

Systems technology has been changing its targets. This paper reviews human interaction issues in systems technology and discusses human-computer interaction in plant operation. Human-centered automation in the process industry requires the fusion of computertechnology, observations in cognitive science and cooperation technology. Cooperative human-computer interaction is a solution for an intelligent manufacturing system.

A series of NASA Webcasts on Future Computing and Communications Technologies, broadcast live in April and May 2003, are now archived and viewable at this site. Each Webcast was approximately an hour in length and featured notable scientists and technology experts from NASA projects and laboratories. Originally intended for high school juniors and seniors, the presentations addressed issues such as spaceborne communications, nanotechnology, artificially evolving systems, and more. These Webcasts are an excellent resource to learn about NASA research from a high level perspective. This site is also reviewed in the September 26, 2003 NSDL MET Report.

Trapped atoms and ions are promising candidates for the construction of a quantumcomputer and the generation of multiparticle entanglement. In my talk I will present various schemes that I have developed during my Ph.d., which enables practical implementations of quantum information processing and entanglement of several particles. For trapped ions I will present a method to implement gates between the ions by using bichromaticlight. If two ions are illuminated with light detuned above and below resonance, the absorption of photon in a single ion is forbidden but the simultaneous absorption of a photon in each of the ions is allowed by the resonance condition. This process can by used to implement gates between ions in thermal motion, and by illuminating a string of ions, it can also be used to generate multiparticle entanglement. Following this proposal D. Winelands ion trapping group was able to produce maximally entangled states of four ions. For atoms in an optical lattice it has been proposed to create a quantumcomputer by moving two lattices with respect to each other. A full quantumcomputer requires the ability to address the individual atoms in the lattice which is very complicated due to the short distance between the atoms in the lattice. But even without access to the individual atoms, the atoms in the lattices can be used to perform non-trivial quantumcomputations. I'll show that by performing lattice displacements and addressing the atoms collectively, the atoms in the lattices can simulate the dynamics of a ferro-magnet. Furthermore the interaction can also by used to form multiparticle entangled spin squeezed states, which could potentially increase the precision of atomic clocks. Spin squeezed states can also be produced by the collisional interaction in a BEC. I'll show that if a single resonant pulse is shined onto the atoms in a BEC, the collisional interaction in the subsequent free evolution will prepare the atoms in a multiparticle entangled state.

This dissertation discusses mainly transmission of coherent state qubits, generation of cat states, and entanglement purification of any stabilizer state. A quantumcomputer is any device for computation that makes direct use of distinctively quantum mechanical phenomena, such as superposition and entanglement, to perform operations on data. The elementary carriers in quantumcomputation and information are the quantum bits, or qubits. In contrast to classical bits, qubits can be in every superposition of the states |0> and |1>. This means that a vector describing a qubit may be any vector in a two dimensional Hilbert space. In this dissertation, we review a method for constructing a linear optical quantumcomputer using coherent states of light as the qubits, developed by Ralph, Gilchrist, Milburn, Munro, and Clancy. We show how an universal set of logic operations can be performed using coherent states, beam splitters, photon counters, and a source of superpositions of coherent state, called "cat states". We also discuss the principal source of errors for this scheme and then present this author's analysis of the behavior of teleportation or Z gate when a non-maximally entangled Bell state is used. We describe several different schemes to generate cat states and make an analysis of these schemes in a realistic experimental environment subject to problems such as photon loss, detector inefficiency, and limited strength of nonlinear interactions. Next, we consider that photon loss is the principal decoherence mechanism that affects a coherent-state based qubit transmission though a long optical fiber, and show how the errors introduced during transmission can be corrected in two different ways to encode the qubit. Lastly, we present a method for multipartite entanglement purification of any stabilizer state shared by several parties. In this protocol, each party measures the stabilizer operators of an error correction code on his or her qubits, exchange their syndrome results, correct errors, and decode to obtain the desired purified state.

The determination of the parity of a string of N binary digits is a well-known problem in classical as well as quantum information processing, which can be formulated as an oracle problem. It has been established that quantum algorithms require at least N/2 oracle calls. We present an algorithm that reaches this lower bound and is also optimal in terms of additional gate operations required. We discuss its application to pure and mixed states. Since it can be applied directly to thermal states, it does not suffer from signal loss associated with pseudo-pure-state preparation. For ensemble quantumcomputers, the number of oracle calls can be further reduced by a factor 2{sup k}, with k is a member of {l_brace}{l_brace}1,2,...,log{sub 2}(N/2{r_brace}{r_brace}, provided the signal-to-noise ratio is sufficiently high. This additional speed-up is linked to (classical) parallelism of the ensemble quantumcomputer. Experimental realizations are demonstrated on a liquid-state NMR quantumcomputer.

Stadelhofer, Ralf [University of Dortmund Department of Computer Science, 44221 Dortmund (Germany); Suter, Dieter [University of Dortmund, Department of Physics, 44221 Dortmund (Germany); Banzhaf, Wolfgang [Memorial University of Newfoundland, Department of Computer Science, St. John's, NL, A1B 3X5 (Canada)

We investigate an integrated optical circuit on lithium niobate designed to implement a teleportation-based quantum relay scheme for one-way quantum communication at a telecom wavelength. Such an advanced quantum circuit merges for the first time both optical-optical and electro-optical nonlinear functions necessary for implementing the desired on-chip single-qubit teleportation. On the one hand, spontaneous parametric down-conversion is used to produce entangled photon pairs. On the other, we take advantage of two photon routers, consisting of electro-optically controllable couplers, to separate the paired photons and to carry out a Bell state measurement, respectively. After having validated all the individual functions in the classical regime, we performed a Hong-Ou-Mandel experiment to mimic a one-way quantum communication link. Such a quantum effect, seen as a prerequisite towards achieving teleportation, has been obtained at one of the routers when the chip was coupled to an external single-photon source. The two-photon interference pattern shows a net visibility of 80%, which validates the proof of principle of a ‘quantum relay circuit’ for qubits carried by telecom photons. In the case of optimized losses, such a chip could increase the maximal achievable distance of one-way quantum key distribution links by a factor of 1.8. Our approach and results emphasize the potential of integrated optics on lithium niobate as a key technology for future reconfigurable quantum information manipulation.

Martin, A.; Alibart, O.; De Micheli, M. P.; Ostrowsky, D. B.; Tanzilli, S.

Although the term “ubiquitous” may sound like jargon used in information appliances, ubiquitous computing is an emerging concept in industrial automation. This paper presents the author's visions of field ubiquitous computing, which is based on the novel Internet Protocol IPv6. IPv6-based instrumentation will realize the next generation manufacturing excellence. This paper focuses on the following five key issues: 1. IPv6 standardization; 2. IPv6 interfaces embedded in field devices; 3. Compatibility with FOUNDATION fieldbus; 4. Network securities for field applications; and 5. Wireless technologies to complement IP instrumentation. Furthermore, the principles of digital plant operations and ubiquitous production to support the above key technologies to achieve field ubiquitous systems are discussed.

One of the most frequently heard terms in the computer industry these days is client-server.'' There is much misinformation available on the topic, and competitive pressures on software vendors have led to a great deal of hype with little in the way of supporting products. The purpose of this document is to explain what is meant by client-server applications, why the Advanced Technology and Architecture (ATA) section of the Information Resources Management (IRM) Department sees this emerging technology as key for computer applications during the next ten years, and what ATA sees as the existing standards and products available today. Because of the relative immaturity of existing client-server products, IRM is not yet guidelining any specific client-server products, except those that are components of guidelined data communications products or database management systems.

One of the most frequently heard terms in the computer industry these days is ``client-server.`` There is much misinformation available on the topic, and competitive pressures on software vendors have led to a great deal of hype with little in the way of supporting products. The purpose of this document is to explain what is meant by client-server applications, why the Advanced Technology and Architecture (ATA) section of the Information Resources Management (IRM) Department sees this emerging technology as key for computer applications during the next ten years, and what ATA sees as the existing standards and products available today. Because of the relative immaturity of existing client-server products, IRM is not yet guidelining any specific client-server products, except those that are components of guidelined data communications products or database management systems.

This paper gives a short overview of the information technology in today's car electronics and software components, with main focus on the dramatically increasing intra-car-communication and the accumulative number of electronic control units due to the complexity of current new applications, e.g., the very new semi-autonomous car driving. It is shown how the car industry can learn from parallel computing

The purpose of this study was to provide a more in-depth analysis of the psychometric characteristics of the Principal's ComputerTechnology Survey (PCTS). The PCTS developmental process yielded a 40-item survey with groups of items comprising five subscales (i.e., curriculum integration, perceptions, acquired expertise, needs assessment, and professional development). Principals' responses to items within the five subscales was measured on

Majorana fermions hold promise for quantumcomputation, because their non-Abelian braiding statistics allows for topologically protected operations on quantum information. Topological qubits can be constructed from pairs of well-separated Majoranas in networks of nanowires. The coupling to a superconducting charge qubit in a transmission line resonator (transmon) permits braiding of Majoranas by external variation of magnetic fluxes. We show that readout operations can also be fully flux controlled, without requiring microscopic control over tunnel couplings. We identify the minimal circuit that can perform the initialization-braiding-measurement steps required to demonstrate non-Abelian statistics. We introduce the Random Access Majorana Memory (RAMM), a scalable circuit that can perform a joint parity measurement on Majoranas belonging to a selection of topological qubits. Such multiqubit measurements allow for the efficient creation of highly entangled states and simplify quantum error correction protocols by avoiding the need for ancilla qubits.

Hyart, T.; van Heck, B.; Fulga, I. C.; Burrello, M.; Akhmerov, A. R.; Beenakker, C. W. J.

Efficient ion-photon coupling is an important component for large-scale\\u000aion-trap quantumcomputing. We propose that arrays of phase Fresnel lenses\\u000a(PFLs) are a favorable optical coupling technology to match with multi-zone ion\\u000atraps. Both are scalable technologies based on conventional micro-fabrication\\u000atechniques. The large numerical apertures (NAs) possible with PFLs can reduce\\u000athe readout time for ion qubits. PFLs also

E. W. Streed; B. G. Norton; J. J. Chapman; D. Kielpinski

We discuss the use of the transverse spatial degrees of freedom of photons propagating in the paraxial approximation for continuous-variable information processing. Given the wide variety of linear optical devices available, a diverse range of operations can be performed on the spatial degrees of freedom of single photons. Here we show how to implement a set of continuous quantum logic gates which allow for universal quantumcomputation. In contrast with the usual quadratures of the electromagnetic field, the entire set of single-photon gates for spatial degrees of freedom does not require optical nonlinearity and, in principle, can be performed with a single device: the spatial light modulator. Nevertheless, nonlinear optical processes, such as four-wave mixing, are needed in the implementation of two-photon gates. The efficiency of these gates is at present very low; however, small-scale investigations of continuous-variable quantumcomputation are within the reach of current technology. In this regard, we show how novel cluster states for one-way quantumcomputing can be produced using spontaneous parametric down-conversion.

Tasca, D. S.; Gomes, R. M.; Toscano, F.; Souto Ribeiro, P. H.; Walborn, S. P. [Instituto de Fisica, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, 21941-972 Rio de Janeiro-RJ (Brazil)

A useful metaphor in introducing object-oriented concepts is the idea of a computer hardware manufacturer assembling products from an existing stock of electronic parts. In this analogy, think of the parts as pieces of computer software and of the finished products as computer applications. Like its counterpart, the object is capable of performing its specific function in a wide variety of different applications. The advantages to assembling hardware using a set of prebuilt parts are obvious. The design process is greatly simplified in this scenario, since the designer needs only to carry the design down to the chip level, rather than to the transistor level. As a result, the designer is free to develop a more reliable and feature rich product. Also, since the component parts are reused in several different products, the parts can be made more robust and subjected to more rigorous testing than would be economically feasible for a part used in only one piece of equipment. Additionally, maintenance on the resulting systems is simplified because of the part-level consistency from one type of equipment to another. The remainder of this document introduces the techniques used to develop objects, the benefits of the technology, outstanding issues that remain with the technology, industry direction for the technology, and the impact that object-oriented technology is likely to have on the organization. While going through this material, the reader will find it useful to remember the parts analogy and to keep in mind that the overall purpose of object-oriented technology is to create software parts and to construct applications using those parts.

This dissertation investigates several physical phenomena in atomic and optical physics, and quantum information science, by utilizing various types and techniques of quantum measurements. It is the deeper concepts of these measurements, and the way they are integrated into the seemingly unrelated topics investigated, which binds together the research presented here. The research comprises three different topics: Counterfactual quantumcomputation,

We report the characterization of a universal set of logic gates for one-way quantumcomputing using a four-photon ‘star’ cluster state generated by fusing photons from two independent photonic crystal fibre sources. We obtain a fidelity for the cluster state of 0.66 ± 0.01 with respect to the ideal case. We perform quantum process tomography to completely characterize a controlled-NOT, Hadamard and T gate all on the same compact entangled resource. Together, these operations make up a universal set of gates such that arbitrary quantum logic can be efficiently constructed from combinations of them. We find process fidelities with respect to the ideal cases of 0.64 ± 0.01 for the CNOT, 0.67 ± 0.03 for the Hadamard and 0.76 ± 0.04 for the T gate. The characterization of these gates enables the simulation of larger protocols and algorithms. As a basic example, we simulate a Swap gate consisting of three concatenated CNOT gates. Our work provides some pragmatic insights into the prospects for building up to a fully scalable and fault-tolerant one-way quantumcomputer with photons in realistic conditions.

Bell, B. A.; Tame, M. S.; Clark, A. S.; Nock, R. W.; Wadsworth, W. J.; Rarity, J. G.

We present unified, systematic derivations of schemes in the two known measurement-based models of quantumcomputation. The first model (introduced by Raussendorf and Briegel, [Phys. Rev. Lett. 86, 5188 (2001)]) uses a fixed entangled state, adaptive measurements on single qubits, and feedforward of the measurement results. The second model (proposed by Nielsen, [Phys. Lett. A 308, 96 (2003)] and further simplified by Leung, [Int. J. Quant. Inf. 2, 33 (2004)]) uses adaptive two-qubit measurements that can be applied to arbitrary pairs of qubits, and feedforward of the measurement results. The underlying principle of our derivations is a variant of teleportation introduced by Zhou, Leung, and Chuang, [Phys. Rev. A 62, 052316 (2000)]. Our derivations unify these two measurement-based models of quantumcomputation and provide significantly simpler schemes.

Childs, Andrew M.; Leung, Debbie W.; Nielsen, Michael A.

We propose a quantumcomputer architecture that is robust against decoherence and scalable. As a qubit we adopt rotational states of a nonpolar ionic molecule trapped in an ion trap. It is revealed that the rotational-state qubits are much more immune to decoherence than the conventional electronic-state qubits of atomic ions. A complete method set that includes state preparation, a single-qubit gate, a controlled-not gate, and qubit readout suitable for the rotational-state qubits is provided. Since the ionic molecules can be transported in an array of ion traps, the rotational-state qubits are expected to be a promising candidate to build a large-scale quantumcomputer.

We describe in detail how to perform universal fault-tolerant quantumcomputation on a two-dimensional color code, making use of only nearest neighbor interactions. Three defects (holes) in the code are used to represent logical qubits. Triple-defect logical qubits are deformed into isolated triangular sections of color code to enable transversal implementation of all single logical qubit Clifford group gates. Controlled-NOT (CNOT) is implemented between pairs of triple-defect logical qubits via braiding.

Fowler, Austin G. [Centre for Quantum Computation and Communication Technology, School of Physics, University of Melbourne, Victoria 3010 (Australia)

This chapter discusses opportunities and challenges for the creation of methods of computational intelligence (CI) and more\\u000a specifically – artificial neural networks (ANN), inspired by principles at different levels of information processing in the\\u000a brain: cognitive-, neuronal-, genetic-, and quantum, and mainly, the issues related to the integration of these principles\\u000a into more powerful and accurate CI methods. It is

A complete scientific theory that can integrate material objects with mental objects is capable of heralding the next stage of scientific revolution. Mental qualities such as experienced smell or taste has yet to be quantified in scientific domain. This chapter is devoted to this idea of subjective computation where mental qualities can be quantified. Schroedinger wave equation has been used in a recurrent quantum neural network framework to solve problems such as stochastic filtering, system identification and adaptive control.

This paper describes our programme to develop and demonstrate ultra-high performance single flux quantum (SFQ) VLSI technology that will enable superconducting digital processors for petaFLOPS-scale computing. In the hybrid technology, multi-threaded architecture, the computational engine to power a petaFLOPS machine at affordable power will consist of 4096 SFQ multi-chip processors, with 50 to 100 GHz clock frequency and associated cryogenic RAM. We present the superconducting technology requirements, progress to date and our plan to meet these requirements. We improved SFQ Nb VLSI by two generations, to a 8 kA cm-2, 1.25 µm junction process, incorporated new CAD tools into our methodology, demonstrated methods for recycling the bias current and data communication at speeds up to 60 Gb s-1, both on and between chips through passive transmission lines. FLUX-1 is the most ambitious project implemented in SFQ technology to date, a prototype general-purpose 8 bit microprocessor chip. We are testing the FLUX-1 chip (5K gates, 20 GHz clock) and designing a 32 bit floating-point SFQ multiplier with vector-register memory. We report correct operation of the complete stripline-connected gate library with large bias margins, as well as several larger functional units used in FLUX-1. The next stage will be an SFQ multi-processor machine. Important challenges include further reducing chip supply current and on-chip power dissipation, developing at least 64 kbit, sub-nanosecond cryogenic RAM chips, developing thermally and electrically efficient high data rate cryogenic-to-ambient input/output technology and improving Nb VLSI to increase gate density.

Silver, A.; Kleinsasser, A.; Kerber, G.; Herr, Q.; Dorojevets, M.; Bunyk, P.; Abelson, L.

We report on an experiment to detect nonclassical correlations in a highly mixed state. The correlations are characterized by the quantum discord and are observed using four qubits in a liquid-state nuclear magnetic resonance quantum information processor. The state analyzed is the output of a DQC1 computation, whose input is a single quantum bit accompanied by n maximally mixed qubits. This model of computation outperforms the best known classical algorithms and, although it contains vanishing entanglement, it is known to have quantum correlations characterized by the quantum discord. This experiment detects nonvanishing quantum discord, ensuring the existence of nonclassical correlations as measured by the quantum discord.

Passante, G.; Moussa, O.; Trottier, D. A. [Institute for Quantum Computing and Department of Physics, University of Waterloo, Waterloo, Ontario, N2L 3G1 (Canada); Laflamme, R. [Institute for Quantum Computing and Department of Physics, University of Waterloo, Waterloo, Ontario, N2L 3G1 (Canada); Perimeter Institute for Theoretical Physics, Waterloo, Ontario, N2J 2W9 (Canada)

We introduce a scheme for secure multiparty computation utilizing the quantum correlations of entangled states. First we present a scheme for two-party computation, exploiting the correlations of a Greenberger-Horne-Zeilinger state to provide, with the help of a third party, a near-private computation scheme. We then present a variation of this scheme which is passively secure with threshold t=2, in other words, remaining secure when pairs of players conspire together provided they faithfully follow the protocol. Furthermore, we show that the passively secure variant can be modified to be secure when cheating parties are allowed to deviate from the protocol. We show that this can be generalized to computations of n-party polynomials of degree 2 with a threshold of n-1. The threshold achieved is significantly higher than the best known classical threshold, which satisfies the bound tquantum secure multiparty computation.

Loukopoulos, Klearchos [Department of Materials, University of Oxford, Parks Road, Oxford OX1 4PH (United Kingdom); Browne, Daniel E. [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom)

Electrons with the spin quantum number 1/2, as physical qubits, have naturally been anticipated for implementing quantumcomputing and information processing (QC/QIP). Recently, electron spin-qubit systems in organic molecular frames have emerged as a hybrid spin-qubit system along with a nuclear spin-1/2 qubit. Among promising candidates for QC/QIP from the materials science side, the reasons for why electron spin-qubits such as molecular spin systems, i.e., unpaired electron spins in molecular frames, have potentialities for serving for QC/QIP will be given in the lecture (Chapter), emphasizing what their advantages or disadvantages are entertained and what technical and intrinsic issues should be dealt with for the implementation of molecular-spin quantumcomputers in terms of currently available spin manipulation technology such as pulse-based electron-nuclear double resonance (pulsed or pulse ENDOR) devoted to QC/QIP. Firstly, a general introduction and introductory remarks to pulsed ENDOR spectroscopy as electron-nuclear spin manipulation technology is given. Super dense coding (SDC) experiments by the use of pulsed ENDOR are also introduced to understand differentiating QC ENDOR from QC NMR based on modern nuclear spin technology. Direct observation of the spinor inherent in an electron spin, detected for the first time, will be shown in connection with the entanglement of an electron-nuclear hybrid system. Novel microwave spin manipulation technology enabling us to deal with genuine electron-electron spin-qubit systems in the molecular frame will be introduced, illustrating, from the synthetic strategy of matter spin-qubits, a key-role of the molecular design of g-tensor/hyperfine-(A-)tensor molecular engineering for QC/QIP. Finally, important technological achievements of recently-emerging CD ELDOR (Coherent-Dual ELectron-electron DOuble Resonance) spin technology enabling us to manipulate electron spin-qubits are described.

Over the last few decades, developments in the physical limits of computing and quantumcomputing have increasingly taught us that it can be helpful to think about physics itself in computational terms. For example, work over the last decade has shown that the energy of a quantum system limits the rate at which it can perform significant computational operations, and

Research in quantum electronics over several decades has fueled the creation and rapid growth of today's wireless communications market. Sales of electronic components into this market exceeded $25 billion in 2006. Nearly all cellular handsets sold today include integrated circuits (ICs) based on energy gap engineered transistors—high-electron mobility transistors (HEMTs) and heterojunction base transistors (HBTs). The success of these technologies

In quantum information, the qubit is not represented by a full spinor in space and in time as the z spinor below: ?0(z) = (2??20)-12e-z24?20(cos?02e-i?02sin?02ei?02) but by a simplified spinor without spatial extension ? = (cos?02e-i?02sin?02ei?02) This simplification is the basis of our first criticism of the quantumcomputer concept. Indeed, the demonstrations explaining the interest of the Deutsch, Glover and Shor algorithms are based on calculations using the factorization of entangled qubits. These factorizations are accurate for spinors without spatial extensions, but only approximate for real spinors with spatial extensions. Through the spatial extension question, we also revisit the Stern and Gerlach experiment, to explain the decoherence, the individual impacts and the quantization. We conclude in two other criticism what this spin interpretation implies for the feasibility of quantumcomputers. A second, more fundamental criticism concerns the existence of the (single) spin-based qubit itself. Indeed, we show that the variables of space and spin are not factorizable duringmeasurement. It seems that the qubit, which is a simplified spinor, does not exist as individual object, at least during the measurement. A third criticism deals with the completness of quantum mechanics. Our analysis explains very simply the negative results of the NMR technique, developed by Chuang et al, which does not use quantum objects individually. The spinor spatial extension takes into account the initial position z0 of the particle.

Quantum measurement is universal for quantumcomputation. The model of quantumcomputation introduced by Nielsen and further developed by Leung relies on a generalized form of teleportation. In order to simulate any n-qubit unitary transformation with this model, 4 auxiliary qubits are required. Moreover Leung exhibited a universal family of observables composed of 4 two-qubit measurements. We introduce a model

Among the numerous types of architecture being explored for quantumcomputers are systems utilizing ion traps, in which quantum bits (qubits) are formed from the electronic states of trapped ions and coupled through the Coulomb interaction. Although the elementary requirements for quantumcomputation have been demonstrated in this system, there exist theoretical and technical obstacles to scaling up the approach

The purpose of this research project was to improve student retention in the Computer Engineering Technology program at the Northern Alberta Institute of Technology by reducing the number of dropouts and increasing the graduation rate. This action research project utilized a mixed methods approach of a survey and face-to-face interviews. The participants were male and female, with a large majority ranging from 18 to 21 years of age. The research found that participants recognized their skills and capability, but their capacity to remain in the program was dependent on understanding and meeting the demanding pace and rigour of the program. The participants recognized that curriculum delivery along with instructor-student interaction had an impact on student retention. To be successful in the program, students required support in four domains: academic, learning management, career, and social.

We give a scheme for loss tolerantly building a linear optical quantum memory which itself is tolerant to qubit loss. We use the encoding recently introduced in Varnava et al 2006 Phys. Rev. Lett. 97 120501, and give a method for efficiently achieving this. The entire approach resides within the 'one-way' model for quantumcomputing (Raussendorf and Briegel 2001 Phys. Rev. Lett. 86 5188 91 Raussendorf et al 2003 Phys. Rev. A 68 022312). Our results suggest that it is possible to build a loss tolerant quantum memory, such that if the requirement is to keep the data stored over arbitrarily long times then this is possible with only polynomially increasing resources and logarithmically increasing individual photon life-times.

Varnava, Michael; Browne, Daniel E.; Rudolph, Terry

The Penrose-Hameroff orchestrated objective reduction (orch. OR) model assigns a cognitive role to quantumcomputations in microtubules within the neurons of the brain. Despite an apparently ``warm, wet, and noisy'' intracellular milieu, the proposal suggests that microtubules avoid environmental decoherence long enough to reach threshold for ``self-collapse'' (objective reduction) by a quantum gravity mechanism put forth by Penrose. The model has been criticized as regards the issue of environmental decoherence, and a recent report by Tegmark finds that microtubules can maintain quantum coherence for only 10-13 s, far too short to be neurophysiologically relevant. Here, we critically examine the decoherence mechanisms likely to dominate in a biological setting and find that (1) Tegmark's commentary is not aimed at an existing model in the literature but rather at a hybrid that replaces the superposed protein conformations of the orch. OR theory with a soliton in superposition along the microtubule; (2) recalculation after correcting for differences between the model on which Tegmark bases his calculations and the orch. OR model (superposition separation, charge vs dipole, dielectric constant) lengthens the decoherence time to 10-5-10-4 s (3) decoherence times on this order invalidate the assumptions of the derivation and determine the approximation regime considered by Tegmark to be inappropriate to the orch. OR superposition; (4) Tegmark's formulation yields decoherence times that increase with temperature contrary to well-established physical intuitions and the observed behavior of quantum coherent states; (5) incoherent metabolic energy supplied to the collective dynamics ordering water in the vicinity of microtubules at a rate exceeding that of decoherence can counter decoherence effects (in the same way that lasers avoid decoherence at room temperature); (6) microtubules are surrounded by a Debye layer of counterions, which can screen thermal fluctuations, and by an actin gel that might enhance the ordering of water in bundles of microtubules, further increasing the decoherence-free zone by an order of magnitude and, if the dependence on the distance between environmental ion and superposed state is accurately reflected in Tegmark's calculation, extending decoherence times by three orders of magnitude; (7) topological quantumcomputation in microtubules may be error correcting, resistant to decoherence; and (8) the decohering effect of radiative scatterers on microtubule quantum states is negligible. These considerations bring microtubule decoherence into a regime in which quantum gravity could interact with neurophysiology.

Benchmark full quantum mechanical Hartree-Fock calculation has been carried out to compute interaction energies for the streptavidin-biotin binding complex. In this report, the entire streptavidin -biotin interaction system with a total of 1775 atoms is treated by quantum mechanics. The full quantum energy calculation for this protein system is made possible by applying a recently developed MFCC approach in which

In topological quantumcomputation, quantum gates are carried out by braiding worldlines of non-Abelian anyons in 2+1 dimensional space-time. The simplest such anyons for which braiding is universal for quantumcomputation are Fibonacci anyons. Reichardt [1] has shown how to construct nontrivial braids for three Fibonacci anyons which yield 2 x2 unitary operations whose off-diagonal matrix elements (in the appropriate basis) can be made arbitrarily small through a simple and efficient iterative procedure. A great advantage of this construction is that it does not require either brute force search or the Solovay-Kitaev method. There is, however, a downside---the phases of the diagonal matrix elements cannot be directly controlled. Despite this, we show that the resulting braids can be used to construct leakage-free entangling two-qubit gates for qubits encoded using four Fibonacci anyons each. We give two explicit constructions---one based on the ``functional braid" approach of Hu and Wan [2], and another based on the ``effective qubit" approach of Hormozi et al. [3]. [1] B.W. Reichardt, Quant. Inf. and Comp. 12, 876 (2012). [2] H. Xu and X. Wan, PRA 78, 042325 (2008). [3] L. Hormozi et al., PRL 103, 160501 (2009).

Carnahan, Caitlin; Zeuch, Daniel; Bonesteel, N. E.

The energy gap between the ground and excited states of a qubit register performing an adiabatic quantumcomputation (AQC) algorithm is expected to provide additional stability against decoherence by environmental noise. However, the precise quantitative magnitude of this effect is still an open question. In this work, we show that fidelity of the ground state provides the ultimate quantitative measure of the AQC stability against decoherence. Even if the qubit register is not driven out of the ground state by the time evolution of the algorithm, the ground state is deformed by the qubit-environment interaction. The extent of this deformation can be characterized by the same noise correlators that determine the relaxation rates in the gate-model QC. We derive finite-temperature expression for the ground-state fidelity and calculate it numerically for the 16-qubit instances of adiabatic quantum optimization.

Deng, Qiang; Averin, Dmitri; Amin, Mohammad; Smith, Peter

Inside computer networks, different information processing tasks are necessary to deliver the user data efficiently. This processing can also be done in the quantum domain. We present simple optical quantum networks where the orbital angular momentum (OAM) of a single photon is used as an ancillary degree of freedom which controls decisions at the network level. Linear optical elements are enough to provide important network primitives such as multiplexing and routing. First we show how to build a simple multiplexer and demultiplexer which combine photonic qubits and separate them again at the receiver. We also give two different self-routing networks where the OAM of an input photon is enough to make it find its desired destination.

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

Threshold theorems for fault-tolerant quantumcomputing assume that errors are of certain types. But how would one detect whether errors of the “wrong” type occur in one's experiment, especially if one does not even know what type of error to look for? The problem is that for many qubits a full state description is almost impossible to analyze due to the exponentially large state space, and a full process description requires even more resources. As a result, one simply cannot detect all types of errors. Here we show through a quantum state estimation example (on up to 25 qubits) how to attack this problem using model selection. We use, in particular, the Akaike information criterion. The example indicates that the number of measurements that one has to perform before noticing errors of the wrong type scales polynomially both with the number of qubits and with the error size.

It is shown that Majorana fermions trapped in three p-wave superfluid vortices form a qubit in a topological quantumcomputing (TQC). Several similar ideas have already been proposed, in which a qubit operation is performed by braiding the world lines of these two or four Majorana fermions. Naturally the set of quantum gates thus obtained is a discrete subset of the relevant unitary group. We propose a new scheme, where three Majorana fermions form a qubit. We show that continuous qubit operations are made possible by braiding the Majorana fermions complemented with dynamical phase factors. Furthermore, it is possible to introduce entanglement between two such qubits by geometrical manipulation of some vortices involved.

We describe a fault-tolerant version of the one-way quantumcomputer using a cluster state in three spatial dimensions. Topologically protected quantum gates are realized by choosing appropriate boundary conditions on the cluster. We provide equivalence transformations for these boundary conditions that can be used to simplify fault-tolerant circuits and to derive circuit identities in a topological manner. The spatial dimensionality of the scheme can be reduced to two by converting one spatial axis of the cluster into time. The error threshold is 0.75% for each source in an error model with preparation, gate, storage and measurement errors. The operational overhead is poly-logarithmic in the circuit size.

Results have been presented on isolating rare earth atoms in small numbers in semiconductor nanoparticles so as to use their organized arrays as hardware for quantumcomputing. We have tailored atomic states of rare earths, fabricated nanoparticles where these atomic systems are incorporated in small numbers and have patterned arrays of nano-holes on semi-conducting and polymer surfaces to encapsulate these rare earth doped nanoparticles. Results are presented on fabrication, microscopy and spectroscopy of these structures.

Konjhodzic, Aras; Aly, Muhammed; Chhabria, Deepka; Hasan, Zameer U.; Wu, M.; Register, Richard A.

Quantumcomputing has been a relatively new research area in the physics and computer engineering combined fields since Feynman proposed an abstract model of quantumcomputer in 1980s. After Shor presented the algorithm for practical implementation of quantumcomputing in 1994, the research of quantumcomputing has grown quickly. However, there is a gap between the academic research and the application to industry. This survey paper attempts to fill the gap by presenting the application to the industrial needs specifically to the needs of the aerospace industry.

We develop a procedure for distilling magic states used in universal quantumcomputing that requires substantially fewer initial resources than prior schemes. Our distillation circuit is based on a family of concatenated quantum codes that possess a transversal Hadamard operation, enabling each of these codes to distill the eigenstate of the Hadamard operator. A crucial result of this design is that low-fidelity magic states can be consumed to purify other high-fidelity magic states to even higher fidelity, which we call multilevel distillation. When distilling in the asymptotic regime of infidelity ??0 for each input magic state, the number of input magic states consumed on average to yield an output state with infidelity O(?2r) approaches 2r+1, which comes close to saturating the conjectured bound in another investigation [Bravyi and Haah, Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.86.052329 86, 052329 (2012)]. We show numerically that there exist multilevel protocols such that the average number of magic states consumed to distill from error rate ?in=0.01 to ?out in the range 10-5-10-40 is about 14log10(1/?out)-40; the efficiency of multilevel distillation dominates all other reported protocols when distilling Hadamard magic states from initial infidelity 0.01 to any final infidelity below 10-7. These methods are an important advance for magic-state distillation circuits in high-performance quantumcomputing and provide insight into the limitations of nearly resource-optimal quantum error correction.

Simulation of Lattice QCD is a challenging computational problem. Currently, technological trends in computation show multiple divergent models of computation. We are witnessing homogeneous multi-core architectures, the use of accelerator on-chip or off-chip, in addition to the traditional architectural models. On the verge of this technological abundance, assessing the performance trade-offs of computing nodes based on these technologies is of

K. Ibrahim; J. Jaeger; Z. Liu; L. N. Pouchet; P. Lesnicki; L. Djoudi; D. Barthou; F. Bodin; C. Eisenbeis; G. Grosdidier; O. Pene; P. Roudeau

This paper presents a newly emerging technology called orange computing for humanistic care applications. Orange computing refers to health, happiness, and physiopsychological care computing, which focuses on designing algorithms and systems for enhancing body and mind balance. Compared with green computing, orange computing lays more emphasis on humanistic care, particularly the elderly or those who require a certain degree of

A recent proposal for modeling time-dependent quantum electron transport with Coulomb and exchange correlations using quantum (Bohm) trajectories (Oriols 2007 Phys. Rev. Lett. 98 066803) is extended towards the computation of the total (particle plus displacement) current in mesoscopic devices. In particular, two different methods for the practical computation of the total current are compared. The first method computes the particle and the displacement currents from the rate of Bohm particles crossing a particular surface and the time-dependent variations of the electric field there. The second method uses the Ramo-Shockley theorem to compute the total current on that surface from the knowledge of the Bohm particle dynamics in a 3D volume and the time-dependent variations of the electric field on the boundaries of that volume. From a computational point of view, it is shown that both methods achieve local current conservation, but the second is preferred because it is free from 'spurious' peaks. A numerical example, a Bohm trajectory crossing a double-barrier tunneling structure, is presented, supporting the conclusions.

We report an efficient quantum algorithm for estimating the local density of states (LDOS) on a quantumcomputer. The LDOS describes the redistribution of energy levels of a quantum system under the influence of a perturbation. Sometimes known as the 'strength function' from nuclear spectroscopy experiments, the shape of the LDOS is directly related to the survivial probability of unperturbed eigenstates, and has recently been related to the fidelity decay (or 'Loschmidt echo') under imperfect motion reversal. For quantum systems that can be simulated efficiently on a quantumcomputer, the LDOS estimation algorithm enables an exponential speedup over direct classical computation.

Emerson, Joseph; Cory, David [Department of Nuclear Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Lloyd, Seth [Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Poulin, David [Institute for Quantum Computing, University of Waterloo, Waterloo, ON, N2L 3G1 (Canada)

Penrose and Hameroff suggested that microtubles in living systems functioned as quantumcomputers by utilizing evanescent photons. On the basis of the theorem that the evanescent photon is a superluminal particle, the possibility of high performance computation in living systems has been studied. From the theoretical analysis, it is shown that the living system can achieve large quantum bits computation

Electron density perturbation from carbon monoxide adsorption on a multi-hundred atom gold nanoparticle. The perturbation causes significant quantum size effects in CO catalysis on gold particles. Science: Jeff Greeley and Nick Romero, Argonne National Laboratory; Jesper Kleis, Karsten Jacobsen, Jens Nřrskov, Technical University of Denmark? Visualization: Joseph Insley, Argonne National Laboratory This research used resources of the Argonne Leadership Computing Facility at Argonne National Laboratory, which is supported by the Office of Science of the U.S. Dept. of Energy under contract DE-AC02-06CH11357.

|There is a large body of research regarding computer supported education, perceptions of computer self-efficacy, computer anxiety and the technological attitudes of teachers and teacher candidates. However, no study has been conducted on the correlation between and effect of computer supported education, perceived computer self-efficacy, computer…

This guide is intended to assist industrial arts/technology education teachers in helping students in grades K-12 understand the impact of computers and computertechnology in the world. Discussed in the introductory sections are the ways in which computers have changed the face of business, industry, and education and training; the scope and…

|This guide is intended to assist industrial arts/technology education teachers in helping students in grades K-12 understand the impact of computers and computertechnology in the world. Discussed in the introductory sections are the ways in which computers have changed the face of business, industry, and education and training; the scope and…

Many improvements in computer and imaging technology have occurred since the last meeting of the American Society for Stereotactic and Functional Neurosurgery in 1987. These improvements are leading to a much wider acceptance of computerization and computer-assisted surgical procedures in the stereotactic neurosurgery field. This paper surveys the current fields of computer and imaging technology and its relationship and impact

|Analyzes concepts, technologies and challenges related to mobile computing and networking. Defines basic concepts of cellular systems. Describes the evolution of wireless technologies that constitute the foundations of mobile computing and ubiquitous networking. Presents characterization and issues of mobile computing. Analyzes economical and…