Science.gov

Sample records for quantum computing technologies

  1. Quantum computing

    PubMed Central

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

    2001-01-01

    Quantum computing is a quickly growing research field. This article introduces the basic concepts of quantum computing, recent developments in quantum searching, and decoherence in a possible quantum dot realization. PMID:11562459

  2. Enabling Technologies for Scalable Trapped Ion Quantum Computing

    NASA Astrophysics Data System (ADS)

    Crain, Stephen; Gaultney, Daniel; Mount, Emily; Knoernschild, Caleb; Baek, Soyoung; Maunz, Peter; Kim, Jungsang

    2013-05-01

    Scalability is one of the main challenges of trapped ion based quantum computation, mainly limited by the lack of enabling technologies needed to trap, manipulate and process the increasing number of qubits. Microelectromechanical systems (MEMS) technology allows one to design movable micromirrors to focus laser beams on individual ions in a chain and steer the focal point in two dimensions. Our current MEMS system is designed to steer 355 nm pulsed laser beams to carry out logic gates on a chain of Yb ions with a waist of 1.5 μm across a 20 μm range. In order to read the state of the qubit chain we developed a 32-channel PMT with a custom read-out circuit operating near the thermal noise limit of the readout amplifier which increases state detection fidelity. We also developed a set of digital to analog converters (DACs) used to supply analog DC voltages to the electrodes of an ion trap. We designed asynchronous DACs to avoid added noise injection at the update rate commonly found in synchronous DACs. Effective noise filtering is expected to reduce the heating rate of a surface trap, thus improving multi-qubit logic gate fidelities. Our DAC system features 96 channels and an integrated FPGA that allows the system to be controlled in real time. This work was supported by IARPA/ARO.

  3. Quantum computing with trapped ions

    SciTech Connect

    Hughes, R.J.

    1998-01-01

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

  4. Quantum entanglement, quantum communication and the limits of quantum computing

    NASA Astrophysics Data System (ADS)

    Ambainis, Andris

    Quantum entanglement is a term describing the quantum correlations between different parts of a quantum system. Quantum information theory has developed sophisticated techniques to quantify and study quantum entanglement. In this thesis, we show how to apply those techniques to problems in quantum algorithms, complexity theory, communication and cryptography. The main results are: (1) quantum communication protocols that are exponentially more efficient that conventional (classical) communication protocols, (2) unconditionally secure quantum protocols for cryptographic problems, (3) a new "quantum adversary" method for proving lower bounds on quantum algorithms, (4) a study of "one clean qubit computation", a model related to the experimental implementation of quantum computers using NMR (nucleo-magnetic resonance) technology.

  5. Quantum walk computation

    SciTech Connect

    Kendon, Viv

    2014-12-04

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

  6. Type-II Quantum Computers

    NASA Astrophysics Data System (ADS)

    Yepez, Jeffrey

    This paper discusses a computing architecture that uses both classical parallelism and quantum parallelism. We consider a large parallel array of small quantum computers, connected together by classical communication channels. This kind of computer is called a type-II quantum computer, to differentiate it from a globally phase-coherent quantum computer, which is the first type of quantum computer that has received nearly exclusive attention in the literature. Although a hybrid, a type-II quantum computer retains the crucial advantage allowed by quantum mechanical superposition that its computational power grows exponentially in the number of phase-coherent qubits per node, only short-range and short time phase-coherence is needed, which significantly reduces the level of engineering facility required to achieve its construction. Therefore, the primary factor limiting its computational power is an economic one and not a technological one, since the volume of its computational medium can in principle scale indefinitely.

  7. Quantum Computer Games: Quantum Minesweeper

    ERIC Educational Resources Information Center

    Gordon, Michal; Gordon, Goren

    2010-01-01

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

  8. Quantum Computing's Classical Problem, Classical Computing's Quantum Problem

    NASA Astrophysics Data System (ADS)

    Van Meter, Rodney

    2014-08-01

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

  9. Verifiable Quantum Computing

    NASA Astrophysics Data System (ADS)

    Kashefi, Elham

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

  10. Cryptography, quantum computation and trapped ions

    SciTech Connect

    Hughes, Richard J.

    1998-03-01

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

  11. Introduction to Quantum Computation

    NASA Astrophysics Data System (ADS)

    Ekert, A.

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

  12. Quantum computing and probability.

    PubMed

    Ferry, David K

    2009-11-25

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

  13. Quantum analogue computing.

    PubMed

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

    2010-08-13

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

  14. Scalable optical quantum computer

    SciTech Connect

    Manykin, E A; Mel'nichenko, E V

    2014-12-31

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

  15. Towards quantum chemistry on a quantum computer.

    PubMed

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

    2010-02-01

    Exact first-principles calculations of molecular properties are currently intractable because their computational cost grows exponentially with both the number of atoms and basis set size. A solution is to move to a radically different model of computing by building a quantum computer, which is a device that uses quantum systems themselves to store and process data. Here we report the application of the latest photonic quantum computer technology to calculate properties of the smallest molecular system: the hydrogen molecule in a minimal basis. We calculate the complete energy spectrum to 20 bits of precision and discuss how the technique can be expanded to solve large-scale chemical problems that lie beyond the reach of modern supercomputers. These results represent an early practical step toward a powerful tool with a broad range of quantum-chemical applications. PMID:21124400

  16. Photonic quantum technologies

    NASA Astrophysics Data System (ADS)

    O'Brien, Jeremy

    2013-03-01

    Of the approaches to quantum computing, photons are appealing for their low-noise properties and ease of manipulation, and relevance to other quantum technologies, including communication, metrology and measurement. We report an integrated waveguide approach to photonic quantum circuits for high performance, miniaturization and scalability [6-10]. We address the challenges of scaling up quantum circuits using new insights into how controlled operations can be efficiently realised, demonstrating Shor's algorithm with consecutive CNOT gates and the iterative phase estimation algorithm. We have shown how quantum circuits can be reconfigured, using thermo-optic phase shifters to realise a highly reconfigurable quantum circuit, and electro-optic phase shifters in lithium niobate to rapidly manipulate the path and polarisation of telecomm wavelength single photons. We have addressed miniaturisation using multimode interference architectures to directly implement NxN Hadamard operations, and by using high refractive index contrast materials such as SiOxNy, in which we have implemented quantum walks of correlated photons, and Si, in which we have demonstrated generation of orbital angular momentum states of light. We have incorporated microfluidic channels for the delivery of samples to measure the concentration of a blood protein with entangled states of light. We have begun to address the integration of superconducting single photon detectors and diamond and non-linear single photon sources. Finally, we give an overview of recent work on fundamental aspects of quantum measurement, including a quantum version of Wheeler's delayed choice experiment.

  17. Adiabatic topological quantum computing

    NASA Astrophysics Data System (ADS)

    Cesare, Chris; Landahl, Andrew J.; Bacon, Dave; Flammia, Steven T.; Neels, Alice

    2015-07-01

    Topological quantum computing promises error-resistant quantum computation without active error correction. However, there is a worry that during the process of executing quantum gates by braiding anyons around each other, extra anyonic excitations will be created that will disorder the encoded quantum information. Here, we explore this question in detail by studying adiabatic code deformations on Hamiltonians based on topological codes, notably Kitaev's surface codes and the more recently discovered color codes. We develop protocols that enable universal quantum computing by adiabatic evolution in a way that keeps the energy gap of the system constant with respect to the computation size and introduces only simple local Hamiltonian interactions. This allows one to perform holonomic quantum computing with these topological quantum computing systems. The tools we develop allow one to go beyond numerical simulations and understand these processes analytically.

  18. Quantum information and computation

    SciTech Connect

    Bennett, C.H.

    1995-10-01

    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}.

  19. Quantum computing classical physics.

    PubMed

    Meyer, David A

    2002-03-15

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

  20. ASCR Workshop on Quantum Computing for Science

    SciTech Connect

    Aspuru-Guzik, Alan; Van Dam, Wim; Farhi, Edward; Gaitan, Frank; Humble, Travis; Jordan, Stephen; Landahl, Andrew J; Love, Peter; Lucas, Robert; Preskill, John; Muller, Richard P.; Svore, Krysta; Wiebe, Nathan; Williams, Carl

    2015-06-01

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

  1. Dissipative quantum computing with open quantum walks

    SciTech Connect

    Sinayskiy, Ilya; Petruccione, Francesco

    2014-12-04

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

  2. Probabilistic Cloning and Quantum Computation

    NASA Astrophysics Data System (ADS)

    Gao, Ting; Yan, Feng-Li; Wang, Zhi-Xi

    2004-06-01

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

  3. Photonic quantum technologies (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    O'Brien, Jeremy L.

    2015-09-01

    The impact of quantum technology will be profound and far-reaching: secure communication networks for consumers, corporations and government; precision sensors for biomedical technology and environmental monitoring; quantum simulators for the design of new materials, pharmaceuticals and clean energy devices; and ultra-powerful quantum computers for addressing otherwise impossibly large datasets for machine learning and artificial intelligence applications. However, engineering quantum systems and controlling them is an immense technological challenge: they are inherently fragile; and information extracted from a quantum system necessarily disturbs the system itself. Of the various approaches to quantum technologies, photons are particularly appealing for their low-noise properties and ease of manipulation at the single qubit level. We have developed an integrated waveguide approach to photonic quantum circuits for high performance, miniaturization and scalability. We will described our latest progress in generating, manipulating and interacting single photons in waveguide circuits on silicon chips.

  4. Experimental quantum computing without entanglement.

    PubMed

    Lanyon, B P; Barbieri, M; Almeida, M P; White, A G

    2008-11-14

    Deterministic quantum computation with one pure qubit (DQC1) is an efficient model of computation that uses highly mixed states. Unlike pure-state models, its power is not derived from the generation of a large amount of entanglement. Instead it has been proposed that other nonclassical correlations are responsible for the computational speedup, and that these can be captured by the quantum discord. In this Letter we implement DQC1 in an all-optical architecture, and experimentally observe the generated correlations. We find no entanglement, but large amounts of quantum discord-except in three cases where an efficient classical simulation is always possible. Our results show that even fully separable, highly mixed, states can contain intrinsically quantum mechanical correlations and that these could offer a valuable resource for quantum information technologies.

  5. Continuous-Variable Blind Quantum Computation

    NASA Astrophysics Data System (ADS)

    Morimae, Tomoyuki

    2012-12-01

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

  6. Quantum Analog Computing

    NASA Technical Reports Server (NTRS)

    Zak, M.

    1998-01-01

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

  7. Quantum steady computation

    SciTech Connect

    Castagnoli, G. )

    1991-08-10

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

  8. Experimental verification of quantum computation

    NASA Astrophysics Data System (ADS)

    Barz, Stefanie; Fitzsimons, Joseph F.; Kashefi, Elham; Walther, Philip

    2013-11-01

    Quantum computers are expected to offer substantial speed-ups over their classical counterparts and to solve problems intractable for classical computers. Beyond such practical significance, the concept of quantum computation opens up fundamental questions, among them the issue of whether quantum computations can be certified by entities that are inherently unable to compute the results themselves. Here we present the first experimental verification of quantum computation. We show, in theory and experiment, how a verifier with minimal quantum resources can test a significantly more powerful quantum computer. The new verification protocol introduced here uses the framework of blind quantum computing and is independent of the experimental quantum-computation platform used. In our scheme, the verifier is required only to generate single qubits and transmit them to the quantum computer. We experimentally demonstrate this protocol using four photonic qubits and show how the verifier can test the computer's ability to perform quantum computation.

  9. Entanglement and adiabatic quantum computation

    NASA Astrophysics Data System (ADS)

    Ahrensmeier, D.

    2006-06-01

    Adiabatic quantum computation provides an alternative approach to quantum computation using a time-dependent Hamiltonian. The time evolution of entanglement during the adiabatic quantum search algorithm is studied, and its relevance as a resource is discussed.

  10. Layered Architectures for Quantum Computers and Quantum Repeaters

    NASA Astrophysics Data System (ADS)

    Jones, Nathan C.

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

  11. Quantum computational webs

    SciTech Connect

    Gross, D.; Eisert, J.

    2010-10-15

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

  12. Optical quantum computing.

    PubMed

    O'Brien, Jeremy L

    2007-12-01

    In 2001, all-optical quantum computing became feasible with the discovery that scalable quantum computing is possible using only single-photon sources, linear optical elements, and single-photon detectors. Although it was in principle scalable, the massive resource overhead made the scheme practically daunting. However, several simplifications were followed by proof-of-principle demonstrations, and recent approaches based on cluster states or error encoding have dramatically reduced this worrying resource overhead, making an all-optical architecture a serious contender for the ultimate goal of a large-scale quantum computer. Key challenges will be the realization of high-efficiency sources of indistinguishable single photons, low-loss, scalable optical circuits, high-efficiency single-photon detectors, and low-loss interfacing of these components.

  13. Computational quantum chemistry website

    SciTech Connect

    1997-08-22

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

  14. Abstract quantum computing machines and quantum computational logics

    NASA Astrophysics Data System (ADS)

    Chiara, Maria Luisa Dalla; Giuntini, Roberto; Sergioli, Giuseppe; Leporini, Roberto

    2016-06-01

    Classical and quantum parallelism are deeply different, although it is sometimes claimed that quantum Turing machines are nothing but special examples of classical probabilistic machines. We introduce the concepts of deterministic state machine, classical probabilistic state machine and quantum state machine. On this basis, we discuss the question: To what extent can quantum state machines be simulated by classical probabilistic state machines? Each state machine is devoted to a single task determined by its program. Real computers, however, behave differently, being able to solve different kinds of problems. This capacity can be modeled, in the quantum case, by the mathematical notion of abstract quantum computing machine, whose different programs determine different quantum state machines. The computations of abstract quantum computing machines can be linguistically described by the formulas of a particular form of quantum logic, termed quantum computational logic.

  15. Performing quantum computing experiments in the cloud

    NASA Astrophysics Data System (ADS)

    Devitt, Simon J.

    2016-09-01

    Quantum computing technology has reached a second renaissance in the past five years. Increased interest from both the private and public sector combined with extraordinary theoretical and experimental progress has solidified this technology as a major advancement in the 21st century. As anticipated my many, some of the first realizations of quantum computing technology has occured over the cloud, with users logging onto dedicated hardware over the classical internet. Recently, IBM has released the Quantum Experience, which allows users to access a five-qubit quantum processor. In this paper we take advantage of this online availability of actual quantum hardware and present four quantum information experiments. We utilize the IBM chip to realize protocols in quantum error correction, quantum arithmetic, quantum graph theory, and fault-tolerant quantum computation by accessing the device remotely through the cloud. While the results are subject to significant noise, the correct results are returned from the chip. This demonstrates the power of experimental groups opening up their technology to a wider audience and will hopefully allow for the next stage of development in quantum information technology.

  16. Demonstration of blind quantum computing.

    PubMed

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

    2012-01-20

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

  17. Blind topological measurement-based quantum computation

    NASA Astrophysics Data System (ADS)

    Morimae, Tomoyuki; Fujii, Keisuke

    2012-09-01

    Blind quantum computation is a novel secure quantum-computing protocol that enables Alice, who does not have sufficient quantum technology at her disposal, to delegate her quantum computation to Bob, who has a fully fledged quantum computer, in such a way that Bob cannot learn anything about Alice's input, output and algorithm. A recent proof-of-principle experiment demonstrating blind quantum computation in an optical system has raised new challenges regarding the scalability of blind quantum computation in realistic noisy conditions. Here we show that fault-tolerant blind quantum computation is possible in a topologically protected manner using the Raussendorf-Harrington-Goyal scheme. The error threshold of our scheme is 4.3×10-3, which is comparable to that (7.5×10-3) of non-blind topological quantum computation. As the error per gate of the order 10-3 was already achieved in some experimental systems, our result implies that secure cloud quantum computation is within reach.

  18. Holographic quantum computing.

    PubMed

    Tordrup, Karl; Negretti, Antonio; Mølmer, Klaus

    2008-07-25

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

  19. Investigating photonic quantum computation

    NASA Astrophysics Data System (ADS)

    Myers, Casey Robert

    The use of photons as qubits is a promising implementation for quantum computation. The inability of photons to interact, especially with the environment, makes them an ideal physical candidate. However, this also makes them a difficult system to perform two qubit gates on. Recent breakthroughs in photonic quantum computing have shown methods around the requirement of direct photon-photon interaction. In this thesis we study three recently discovered schemes for optical quantum computation. We first investigate the so called linear optical quantum computing (LOQC) scheme, exploring a method to improve the original proposal by constructing a photon-number QND detector that succeeds with a high probability. In doing this we present a new type of LOQC teleporter, one that can detect the presence of a single photon in an arbitrary polarisation state when the input state is a sum of vacuum and multi-photon terms. This new type of teleporter is an improvement on the original scheme in that the entangled states required can be made offline with fewer entangling operations. We next investigate the so called quantum bus (qubus) scheme for photonic quantum computing. We show a scheme to measure the party of n qubit states by using a single qubus mode, controlled rotations and displacements. This allows for the syndrome measurements of any stabilizer quantum error correcting code. We extend these results to a fault tolerant scheme to measure an arbitrary Pauli operator of weight n, incorporating so called single bit teleportations. We investigate the construction of a Toffoli gate by using a single qubus mode, controlled rotations and displacements that works with a success probability of at least 25%. We also investigate the use of single bit teleportations to construct a universal set of gates on coherent state type logic and in the construction of cluster states. We finally investigate the optical Zeno gate, a gate that uses the Zeno effect in the form of two photon

  20. Quantum computers: Definition and implementations

    SciTech Connect

    Perez-Delgado, Carlos A.; Kok, Pieter

    2011-01-15

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

  1. Quantum computers: Definition and implementations

    NASA Astrophysics Data System (ADS)

    Pérez-Delgado, Carlos A.; Kok, Pieter

    2011-01-01

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

  2. Some Thoughts Regarding Practical Quantum Computing

    NASA Astrophysics Data System (ADS)

    Ghoshal, Debabrata; Gomez, Richard; Lanzagorta, Marco; Uhlmann, Jeffrey

    2006-03-01

    Quantum computing has become an important area of research in computer science because of its potential to provide more efficient algorithmic solutions to certain problems than are possible with classical computing. The ability of performing parallel operations over an exponentially large computational space has proved to be the main advantage of the quantum computing model. In this regard, we are particularly interested in the potential applications of quantum computers to enhance real software systems of interest to the defense, industrial, scientific and financial communities. However, while much has been written in popular and scientific literature about the benefits of the quantum computational model, several of the problems associated to the practical implementation of real-life complex software systems in quantum computers are often ignored. In this presentation we will argue that practical quantum computation is not as straightforward as commonly advertised, even if the technological problems associated to the manufacturing and engineering of large-scale quantum registers were solved overnight. We will discuss some of the frequently overlooked difficulties that plague quantum computing in the areas of memories, I/O, addressing schemes, compilers, oracles, approximate information copying, logical debugging, error correction and fault-tolerant computing protocols.

  3. Quantum Walk Schemes for Universal Quantum Computation

    NASA Astrophysics Data System (ADS)

    Underwood, Michael S.

    Random walks are a powerful tool for the efficient implementation of algorithms in classical computation. Their quantum-mechanical analogues, called quantum walks, hold similar promise. Quantum walks provide a model of quantum computation that has recently been shown to be equivalent in power to the standard circuit model. As in the classical case, quantum walks take place on graphs and can undergo discrete or continuous evolution, though quantum evolution is unitary and therefore deterministic until a measurement is made. This thesis considers the usefulness of continuous-time quantum walks to quantum computation from the perspectives of both their fundamental power under various formulations, and their applicability in practical experiments. In one extant scheme, logical gates are effected by scattering processes. The results of an exhaustive search for single-qubit operations in this model are presented. It is shown that the number of distinct operations increases exponentially with the number of vertices in the scattering graph. A catalogue of all graphs on up to nine vertices that implement single-qubit unitaries at a specific set of momenta is included in an appendix. I develop a novel scheme for universal quantum computation called the discontinuous quantum walk, in which a continuous-time quantum walker takes discrete steps of evolution via perfect quantum state transfer through small 'widget' graphs. The discontinuous quantum-walk scheme requires an exponentially sized graph, as do prior discrete and continuous schemes. To eliminate the inefficient vertex resource requirement, a computation scheme based on multiple discontinuous walkers is presented. In this model, n interacting walkers inhabiting a graph with 2n vertices can implement an arbitrary quantum computation on an input of length n, an exponential savings over previous universal quantum walk schemes. This is the first quantum walk scheme that allows for the application of quantum error correction

  4. Quantum computation vs. firewalls

    NASA Astrophysics Data System (ADS)

    Harlow, Daniel; Hayden, Patrick

    2013-06-01

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

  5. Quantum computing of semiclassical formulas.

    PubMed

    Georgeot, B; Giraud, O

    2008-04-01

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

  6. Secure Quantum Technologies

    NASA Astrophysics Data System (ADS)

    Malik, Mehul

    Over the past three decades, quantum mechanics has allowed the development of technologies that provide unconditionally secure communication. In parallel, the quantum nature of the transverse electromagnetic field has spawned the field of quantum imaging that encompasses technologies such as quantum lithography, quantum ghost imaging, and high-dimensional quantum key distribution (QKD). The emergence of such quantum technologies also highlights the need for the development of accurate and efficient methods of measuring and characterizing the elusive quantum state itself. In this thesis, I present new technologies that use the quantum properties of light for security. The first of these is a technique that extends the principles behind QKD to the field of imaging and optical ranging. By applying the polarization-based BB84 protocol to individual photons in an active imaging system, we obtained images that were secure against any intercept-resend jamming attacks. The second technology presented in this thesis is based on an extension of quantum ghost imaging, a technique that uses position-momentum entangled photons to create an image of an object without directly gaining any spatial information from it. We used a holographic filtering technique to build a quantum ghost image identification system that uses a few pairs of photons to identify an object from a set of known objects. The third technology addressed in this thesis is a high-dimensional QKD system that uses orbital-angular-momentum (OAM) modes of light for encoding. Moving to a high-dimensional state space in QKD allows one to impress more information on each photon, as well as introduce higher levels of security. I discuss the development of two OAM-QKD protocols based on the BB84 and Ekert protocols of QKD. In addition, I present a study characterizing the effects of turbulence on a communication system using OAM modes for encoding. The fourth and final technology presented in this thesis is a relatively

  7. Quantum computing on encrypted data.

    PubMed

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

    2014-01-01

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

  8. Quantum computing with defects.

    PubMed

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

    2010-05-11

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

  9. Quantum computing with defects

    PubMed Central

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

    2010-01-01

    Identifying and designing physical systems for use as qubits, the basic units of quantum information, are critical steps in the development of a quantum computer. Among the possibilities in the solid state, a defect in diamond known as the nitrogen-vacancy (NV-1) center stands out for its robustness—its quantum state can be initialized, manipulated, and measured with high fidelity at room temperature. Here we describe how to systematically identify other deep center defects with similar 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

  10. Universal quantum computation by discontinuous quantum walk

    SciTech Connect

    Underwood, Michael S.; Feder, David L.

    2010-10-15

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

  11. Welcome to Quantum Science and Technology

    NASA Astrophysics Data System (ADS)

    Thew, Rob

    2016-03-01

    Quantum information science and related technologies now involve thousands of researchers worldwide, cutting across physics, chemistry, engineering, bioscience, applied mathematics and computer science, extending from fundamental science to novel applications and industry. This situation defines the scope and mission of Quantum Science and Technology, a new IOP journal serving the interests of this multidisciplinary field by publishing research of the highest quality and impact.

  12. Universal quantum computation with weakly integral anyons

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  13. Quantum Computation Using Optically Coupled Quantum Dot Arrays

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

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

  14. Intermediate quantum maps for quantum computation

    SciTech Connect

    Giraud, O.; Georgeot, B.

    2005-10-15

    We study quantum maps displaying spectral statistics intermediate between Poisson and Wigner-Dyson. It is shown that they can be simulated on a quantum computer with a small number of gates, and efficiently yield information about fidelity decay or spectral statistics. We study their matrix elements and entanglement production and show that they converge with time to distributions which differ from random matrix predictions. A randomized version of these maps can be implemented even more economically and yields pseudorandom operators with original properties, enabling, for example, one to produce fractal random vectors. These algorithms are within reach of present-day quantum computers.

  15. Entanglement and Quantum Computation: An Overview

    SciTech Connect

    Perez, R.B.

    2000-06-27

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

  16. Quasicrystals and Quantum Computing

    NASA Astrophysics Data System (ADS)

    Berezin, Alexander A.

    1997-03-01

    In Quantum (Q) Computing qubits form Q-superpositions for macroscopic times. One scheme for ultra-fast (Q) computing can be based on quasicrystals. Ultrafast processing in Q-coherent structures (and the very existence of durable Q-superpositions) may be 'consequence' of presence of entire manifold of integer arithmetic (A0, aleph-naught of Georg Cantor) at any 4-point of space-time, furthermore, at any point of any multidimensional phase space of (any) N-particle Q-system. The latter, apart from quasicrystals, can include dispersed and/or diluted systems (Berezin, 1994). In such systems such alleged centrepieces of Q-Computing as ability for fast factorization of long integers can be processed by sheer virtue of the fact that entire infinite pattern of prime numbers is instantaneously available as 'free lunch' at any instant/point. Infinitely rich pattern of A0 (including pattern of primes and almost primes) acts as 'independent' physical effect which directly generates Q-dynamics (and physical world) 'out of nothing'. Thus Q-nonlocality can be ultimately based on instantaneous interconnectedness through ever- the-same structure of A0 ('Platonic field' of integers).

  17. Quantum Computing: Solving Complex Problems

    ScienceCinema

    DiVincenzo, David [IBM Watson Research Center

    2016-07-12

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

  18. The Physics of Quantum Computation

    NASA Astrophysics Data System (ADS)

    Falci, Giuseppe; Paladino, Elisabette

    2015-10-01

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

  19. Conceptual aspects of geometric quantum computation

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  20. Conceptual aspects of geometric quantum computation

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  1. Duality quantum computer and the efficient quantum simulations

    NASA Astrophysics Data System (ADS)

    Wei, Shi-Jie; Long, Gui-Lu

    2016-03-01

    Duality quantum computing is a new mode of a quantum computer to simulate a moving quantum computer passing through a multi-slit. It exploits the particle wave duality property for computing. A quantum computer with n qubits and a qudit simulates a moving quantum computer with n qubits passing through a d-slit. Duality quantum computing can realize an arbitrary sum of unitaries and therefore a general quantum operator, which is called a generalized quantum gate. All linear bounded operators can be realized by the generalized quantum gates, and unitary operators are just the extreme points of the set of generalized quantum gates. Duality quantum computing provides flexibility and a clear physical picture in designing quantum algorithms, and serves as a powerful bridge between quantum and classical algorithms. In this paper, after a brief review of the theory of duality quantum computing, we will concentrate on the applications of duality quantum computing in simulations of Hamiltonian systems. We will show that duality quantum computing can efficiently simulate quantum systems by providing descriptions of the recent efficient quantum simulation algorithm of Childs and Wiebe (Quantum Inf Comput 12(11-12):901-924, 2012) for the fast simulation of quantum systems with a sparse Hamiltonian, and the quantum simulation algorithm by Berry et al. (Phys Rev Lett 114:090502, 2015), which provides exponential improvement in precision for simulating systems with a sparse Hamiltonian.

  2. Efficient Universal Blind Quantum Computation

    NASA Astrophysics Data System (ADS)

    Giovannetti, Vittorio; Maccone, Lorenzo; Morimae, Tomoyuki; Rudolph, Terry G.

    2013-12-01

    We give a cheat sensitive protocol for blind universal quantum computation that is efficient in terms of computational and communication resources: it allows one party to perform an arbitrary computation on a second party’s quantum computer without revealing either which computation is performed, or its input and output. The first party’s computational capabilities can be extremely limited: she must only be able to create and measure single-qubit superposition states. The second party is not required to use measurement-based quantum computation. The protocol requires the (optimal) exchange of O(Jlog⁡2(N)) single-qubit states, where J is the computational depth and N is the number of qubits needed for the computation.

  3. Toward a superconducting quantum computer

    PubMed Central

    Tsai, Jaw-Shen

    2010-01-01

    Intensive research on the construction of superconducting quantum computers has produced numerous important achievements. The quantum bit (qubit), based on the Josephson junction, is at the heart of this research. This macroscopic system has the ability to control quantum coherence. This article reviews the current state of quantum computing as well as its history, and discusses its future. Although progress has been rapid, the field remains beset with unsolved issues, and there are still many new research opportunities open to physicists and engineers. PMID:20431256

  4. Quantum Information and Computing

    NASA Astrophysics Data System (ADS)

    Accardi, L.; Ohya, Masanori; Watanabe, N.

    2006-03-01

    Preface -- Coherent quantum control of [symbol]-atoms through the stochastic limit / L. Accardi, S. V. Kozyrev and A. N. Pechen -- Recent advances in quantum white noise calculus / L. Accardi and A. Boukas -- Control of quantum states by decoherence / L. Accardi and K. Imafuku -- Logical operations realized on the Ising chain of N qubits / M. Asano, N. Tateda and C. Ishii -- Joint extension of states of fermion subsystems / H. Araki -- Quantum filtering and optimal feedback control of a Gaussian quantum free particle / S. C. Edwards and V. P. Belavkin -- On existence of quantum zeno dynamics / P. Exner and T. Ichinose -- Invariant subspaces and control of decoherence / P. Facchi, V. L. Lepore and S. Pascazio -- Clauser-Horner inequality for electron counting statistics in multiterminal mesoscopic conductors / L. Faoro, F. Taddei and R. Fazio -- Fidelity of quantum teleportation model using beam splittings / K.-H. Fichtner, T. Miyadera and M. Ohya -- Quantum logical gates realized by beam splittings / W. Freudenberg ... [et al.] -- Information divergence for quantum channels / S. J. Hammersley and V. P. Belavkin -- On the uniqueness theorem in quantum information geometry / H. Hasegawa -- Noncanonical representations of a multi-dimensional Brownian motion / Y. Hibino -- Some of future directions of white noise theory / T. Hida -- Information, innovation and elemental random field / T. Hida -- Generalized quantum turing machine and its application to the SAT chaos algorithm / S. Iriyama, M. Ohya and I. Volovich -- A Stroboscopic approach to quantum tomography / A. Jamiolkowski -- Positive maps and separable states in matrix algebras / A. Kossakowski -- Simulating open quantum systems with trapped ions / S. Maniscalco -- A purification scheme and entanglement distillations / H. Nakazato, M. Unoki and K. Yuasa -- Generalized sectors and adjunctions to control micro-macro transitions / I. Ojima -- Saturation of an entropy bound and quantum Markov states / D. Petz -- An

  5. Quantum computation and hidden variables

    NASA Astrophysics Data System (ADS)

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

    2008-03-01

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

  6. PERTURBATION APPROACH FOR QUANTUM COMPUTATION

    SciTech Connect

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

    2001-04-01

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

  7. Quantum chromodynamics with advanced computing

    SciTech Connect

    Kronfeld, Andreas S.; /Fermilab

    2008-07-01

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

  8. Accelerating commutation circuits in quantum computer networks

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  9. Quantum Compiling for Topological Quantum Computing

    NASA Astrophysics Data System (ADS)

    Svore, Krysta

    2014-03-01

    In a topological quantum computer, universality is achieved by braiding and quantum information is natively protected from small local errors. We address the problem of compiling single-qubit quantum operations into braid representations for non-abelian quasiparticles described by the Fibonacci anyon model. We develop a probabilistically polynomial algorithm that outputs a braid pattern to approximate a given single-qubit unitary to a desired precision. We also classify the single-qubit unitaries that can be implemented exactly by a Fibonacci anyon braid pattern and present an efficient algorithm to produce their braid patterns. Our techniques produce braid patterns that meet the uniform asymptotic lower bound on the compiled circuit depth and thus are depth-optimal asymptotically. Our compiled circuits are significantly shorter than those output by prior state-of-the-art methods, resulting in improvements in depth by factors ranging from 20 to 1000 for precisions ranging between 10-10 and 10-30.

  10. Symmetrically private information retrieval based on blind quantum computing

    NASA Astrophysics Data System (ADS)

    Sun, Zhiwei; Yu, Jianping; Wang, Ping; Xu, Lingling

    2015-05-01

    Universal blind quantum computation (UBQC) is a new secure quantum computing protocol which allows a user Alice who does not have any sophisticated quantum technology to delegate her computing to a server Bob without leaking any privacy. Using the features of UBQC, we propose a protocol to achieve symmetrically private information retrieval, which allows a quantum limited Alice to query an item from Bob with a fully fledged quantum computer; meanwhile, the privacy of both parties is preserved. The security of our protocol is based on the assumption that malicious Alice has no quantum computer, which avoids the impossibility proof of Lo. For the honest Alice, she is almost classical and only requires minimal quantum resources to carry out the proposed protocol. Therefore, she does not need any expensive laboratory which can maintain the coherence of complicated quantum experimental setups.

  11. Measurement-only verifiable blind quantum computing with quantum input verification

    NASA Astrophysics Data System (ADS)

    Morimae, Tomoyuki

    2016-10-01

    Verifiable blind quantum computing is a secure delegated quantum computing where a client with a limited quantum technology delegates her quantum computing to a server who has a universal quantum computer. The client's privacy is protected (blindness), and the correctness of the computation is verifiable by the client despite her limited quantum technology (verifiability). There are mainly two types of protocols for verifiable blind quantum computing: the protocol where the client has only to generate single-qubit states and the protocol where the client needs only the ability of single-qubit measurements. The latter is called the measurement-only verifiable blind quantum computing. If the input of the client's quantum computing is a quantum state, whose classical efficient description is not known to the client, there was no way for the measurement-only client to verify the correctness of the input. Here we introduce a protocol of measurement-only verifiable blind quantum computing where the correctness of the quantum input is also verifiable.

  12. Quantumness, Randomness and Computability

    NASA Astrophysics Data System (ADS)

    Solis, Aldo; Hirsch, Jorge G.

    2015-06-01

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

  13. Quantum Computing: Theoretical versus Practical Possibility

    NASA Astrophysics Data System (ADS)

    Paraoanu, G. S.

    2011-09-01

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

  14. Semiquantum key distribution with secure delegated quantum computation

    PubMed Central

    Li, Qin; Chan, Wai Hong; Zhang, Shengyu

    2016-01-01

    Semiquantum key distribution allows a quantum party to share a random key with a “classical” party who only can prepare and measure qubits in the computational basis or reorder some qubits when he has access to a quantum channel. In this work, we present a protocol where a secret key can be established between a quantum user and an almost classical user who only needs the quantum ability to access quantum channels, by securely delegating quantum computation to a quantum server. We show the proposed protocol is robust even when the delegated quantum server is a powerful adversary, and is experimentally feasible with current technology. As one party of our protocol is the most quantum-resource efficient, it can be more practical and significantly widen the applicability scope of quantum key distribution. PMID:26813384

  15. Semiquantum key distribution with secure delegated quantum computation.

    PubMed

    Li, Qin; Chan, Wai Hong; Zhang, Shengyu

    2016-01-01

    Semiquantum key distribution allows a quantum party to share a random key with a "classical" party who only can prepare and measure qubits in the computational basis or reorder some qubits when he has access to a quantum channel. In this work, we present a protocol where a secret key can be established between a quantum user and an almost classical user who only needs the quantum ability to access quantum channels, by securely delegating quantum computation to a quantum server. We show the proposed protocol is robust even when the delegated quantum server is a powerful adversary, and is experimentally feasible with current technology. As one party of our protocol is the most quantum-resource efficient, it can be more practical and significantly widen the applicability scope of quantum key distribution. PMID:26813384

  16. Semiquantum key distribution with secure delegated quantum computation

    NASA Astrophysics Data System (ADS)

    Li, Qin; Chan, Wai Hong; Zhang, Shengyu

    2016-01-01

    Semiquantum key distribution allows a quantum party to share a random key with a “classical” party who only can prepare and measure qubits in the computational basis or reorder some qubits when he has access to a quantum channel. In this work, we present a protocol where a secret key can be established between a quantum user and an almost classical user who only needs the quantum ability to access quantum channels, by securely delegating quantum computation to a quantum server. We show the proposed protocol is robust even when the delegated quantum server is a powerful adversary, and is experimentally feasible with current technology. As one party of our protocol is the most quantum-resource efficient, it can be more practical and significantly widen the applicability scope of quantum key distribution.

  17. Atomic physics: A milestone in quantum computing

    NASA Astrophysics Data System (ADS)

    Bartlett, Stephen D.

    2016-08-01

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

  18. Realizing universal Majorana fermionic quantum computation

    NASA Astrophysics Data System (ADS)

    Wu, Ya-Jie; He, Jing; Kou, Su-Peng

    2014-08-01

    Majorana fermionic quantum computation (MFQC) was proposed by S. B. Bravyi and A. Yu. Kitaev [Ann. Phys. (NY) 298, 210 (2002), 10.1006/aphy.2002.6254], who indicated that a (nontopological) fault-tolerant quantum computer built from Majorana fermions may be more efficient than that built from distinguishable two-state systems. However, until now scientists have not known how to realize a MFQC in a physical system. In this paper we propose a possible realization of MFQC. We find that the end of a line defect of a p-wave superconductor or superfluid in a honeycomb lattice traps a Majorana zero mode, which becomes the starting point of MFQC. Then we show how to manipulate Majorana fermions to perform universal MFQC, which possesses possibilities for high-level local controllability through individually addressing the quantum states of individual constituent elements by using timely cold-atom technology.

  19. Artificial Life in Quantum Technologies

    NASA Astrophysics Data System (ADS)

    Alvarez-Rodriguez, Unai; Sanz, Mikel; Lamata, Lucas; Solano, Enrique

    2016-02-01

    We develop a quantum information protocol that models the biological behaviours of individuals living in a natural selection scenario. The artificially engineered evolution of the quantum living units shows the fundamental features of life in a common environment, such as self-replication, mutation, interaction of individuals, and death. We propose how to mimic these bio-inspired features in a quantum-mechanical formalism, which allows for an experimental implementation achievable with current quantum platforms. This study paves the way for the realization of artificial life and embodied evolution with quantum technologies.

  20. Artificial Life in Quantum Technologies

    PubMed Central

    Alvarez-Rodriguez, Unai; Sanz, Mikel; Lamata, Lucas; Solano, Enrique

    2016-01-01

    We develop a quantum information protocol that models the biological behaviours of individuals living in a natural selection scenario. The artificially engineered evolution of the quantum living units shows the fundamental features of life in a common environment, such as self-replication, mutation, interaction of individuals, and death. We propose how to mimic these bio-inspired features in a quantum-mechanical formalism, which allows for an experimental implementation achievable with current quantum platforms. This study paves the way for the realization of artificial life and embodied evolution with quantum technologies. PMID:26853918

  1. Course 10: Basic Concepts in Quantum Computation

    NASA Astrophysics Data System (ADS)

    Ekert, A.; Hayden, P. M.; Inamori, H.

    Contents 1 Qubits, gates and networks 2 Quantum arithmetic and function evaluations 3 Algorithms and their complexity 4 From interferometers to computers 5 The first quantum algorithms 6 Quantum search 7 Optimal phase estimation 8 Periodicity and quantum factoring 9 Cryptography 10 Conditional quantum dynamics 11 Decoherence and recoherence 12 Concluding remarks

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

    PubMed

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

    2012-10-13

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

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

    PubMed Central

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

    2012-01-01

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

  4. Quantum technology and its applications

    SciTech Connect

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

    2010-12-10

    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 quantum technology. 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, quantum technologies 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 Quantum Technology Applications Workshop (QTAW) have several goals: (1) Bring together sponsors, researchers, engineers and end users to help build a stronger quantum technology 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

  5. Topics in linear optical quantum computation

    NASA Astrophysics Data System (ADS)

    Glancy, Scott Charles

    This thesis covers several topics in optical quantum computation. A quantum computer is a computational device which is able to manipulate information by performing unitary operations on some physical system whose state can be described as a vector (or mixture of vectors) in a Hilbert space. The basic unit of information, called the qubit, is considered to be a system with two orthogonal states, which are assigned logical values of 0 and 1. Photons make excellent candidates to serve as qubits. They have little interactions with the environment. Many operations can be performed using very simple linear optical devices such as beam splitters and phase shifters. Photons can easily be processed through circuit-like networks. Operations can be performed in very short times. Photons are ideally suited for the long-distance communication of quantum information. The great difficulty in constructing an optical quantum computer is that photons naturally interact weakly with one another. This thesis first gives a brief review of two early approaches to optical quantum computation. It will describe how any discrete unitary operation can be performed using a single photon and a network of beam splitters, and how the Kerr effect can be used to construct a two photon logic gate. Second, this work provides a thorough introduction to the linear optical quantum computer developed by Knill, Laflamme, and Milburn. It then presents this author's results on the reliability of this scheme when implemented using imperfect photon detectors. This author finds that quantum computers of this sort cannot be built using current technology. Third, this dissertation describes a method for constructing a linear optical quantum computer using nearly orthogonal coherent states of light as the qubits. It shows how a universal set of logic operations can be performed, including calculations of the fidelity with which these operations may be accomplished. It discusses methods for reducing and

  6. Europe plans quantum technology flagship

    NASA Astrophysics Data System (ADS)

    Allen, Michael

    2016-06-01

    The European Commission (EC) looks set to fund a €1bn flagship programme in quantum technologies starting in 2018. Similar to the EC's 10-year €1bn graphene flagship that began in 2013, the project was initiated by a group of researchers from across Europe in a “quantum manifesto” that was published in March and presented at the Quantum Europe 2016 conference in Amsterdam last month.

  7. General Quantum Interference Principle and Duality Computer

    NASA Astrophysics Data System (ADS)

    Long, Gui-Lu

    2006-05-01

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

  8. Efficient quantum computing using coherent photon conversion.

    PubMed

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

    2011-10-12

    Single photons are excellent quantum information carriers: they were used in the earliest demonstrations of entanglement and in the production of the highest-quality entanglement reported so far. However, current schemes for preparing, processing and measuring them are inefficient. For example, down-conversion provides heralded, but randomly timed, single photons, and linear optics gates are inherently probabilistic. Here we introduce a deterministic process--coherent photon conversion (CPC)--that provides a new way to generate and process complex, multiquanta states for photonic quantum information applications. The technique uses classically pumped nonlinearities to induce coherent oscillations between orthogonal states of multiple quantum excitations. One example of CPC, based on a pumped four-wave-mixing interaction, is shown to yield a single, versatile process that provides a full set of photonic quantum processing tools. This set satisfies the DiVincenzo criteria for a scalable quantum computing architecture, including deterministic multiqubit entanglement gates (based on a novel form of photon-photon interaction), high-quality heralded single- and multiphoton states free from higher-order imperfections, and robust, high-efficiency detection. It can also be used to produce heralded multiphoton entanglement, create optically switchable quantum circuits and implement an improved form of down-conversion with reduced higher-order effects. Such tools are valuable building blocks for many quantum-enabled technologies. Finally, using photonic crystal fibres we experimentally demonstrate quantum correlations arising from a four-colour nonlinear process suitable for CPC and use these measurements to study the feasibility of reaching the deterministic regime with current technology. Our scheme, which is based on interacting bosonic fields, is not restricted to optical systems but could also be implemented in optomechanical, electromechanical and superconducting

  9. Demonstration of measurement-only blind quantum computing

    NASA Astrophysics Data System (ADS)

    Greganti, Chiara; Roehsner, Marie-Christine; Barz, Stefanie; Morimae, Tomoyuki; Walther, Philip

    2016-01-01

    Blind quantum computing allows for secure cloud networks of quasi-classical clients and a fully fledged quantum server. Recently, a new protocol has been proposed, which requires a client to perform only measurements. We demonstrate a proof-of-principle implementation of this measurement-only blind quantum computing, exploiting a photonic setup to generate four-qubit cluster states for computation and verification. Feasible technological requirements for the client and the device-independent blindness make this scheme very applicable for future secure quantum networks.

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

    SciTech Connect

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

    2003-12-01

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

  11. Brain Neurons as Quantum Computers:

    NASA Astrophysics Data System (ADS)

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

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

  12. Quantum computing with parafermions

    NASA Astrophysics Data System (ADS)

    Hutter, Adrian; Loss, Daniel

    2016-03-01

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

  13. Quantum technologies with hybrid systems

    PubMed Central

    Kurizki, Gershon; Bertet, Patrice; Kubo, Yuimaru; Mølmer, Klaus; Petrosyan, David; Rabl, Peter; Schmiedmayer, Jörg

    2015-01-01

    An extensively pursued current direction of research in physics aims at the development of practical technologies that exploit the effects of quantum mechanics. As part of this ongoing effort, devices for quantum information processing, secure communication, and high-precision sensing are being implemented with diverse systems, ranging from photons, atoms, and spins to mesoscopic superconducting and nanomechanical structures. Their physical properties make some of these systems better suited than others for specific tasks; thus, photons are well suited for transmitting quantum information, weakly interacting spins can serve as long-lived quantum memories, and superconducting elements can rapidly process information encoded in their quantum states. A central goal of the envisaged quantum technologies is to develop devices that can simultaneously perform several of these tasks, namely, reliably store, process, and transmit quantum information. Hybrid quantum systems composed of different physical components with complementary functionalities may provide precisely such multitasking capabilities. This article reviews some of the driving theoretical ideas and first experimental realizations of hybrid quantum systems and the opportunities and challenges they present and offers a glance at the near- and long-term perspectives of this fascinating and rapidly expanding field. PMID:25737558

  14. Quantum technologies with hybrid systems.

    PubMed

    Kurizki, Gershon; Bertet, Patrice; Kubo, Yuimaru; Mølmer, Klaus; Petrosyan, David; Rabl, Peter; Schmiedmayer, Jörg

    2015-03-31

    An extensively pursued current direction of research in physics aims at the development of practical technologies that exploit the effects of quantum mechanics. As part of this ongoing effort, devices for quantum information processing, secure communication, and high-precision sensing are being implemented with diverse systems, ranging from photons, atoms, and spins to mesoscopic superconducting and nanomechanical structures. Their physical properties make some of these systems better suited than others for specific tasks; thus, photons are well suited for transmitting quantum information, weakly interacting spins can serve as long-lived quantum memories, and superconducting elements can rapidly process information encoded in their quantum states. A central goal of the envisaged quantum technologies is to develop devices that can simultaneously perform several of these tasks, namely, reliably store, process, and transmit quantum information. Hybrid quantum systems composed of different physical components with complementary functionalities may provide precisely such multitasking capabilities. This article reviews some of the driving theoretical ideas and first experimental realizations of hybrid quantum systems and the opportunities and challenges they present and offers a glance at the near- and long-term perspectives of this fascinating and rapidly expanding field.

  15. Geometry of discrete quantum computing

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

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

  16. Exploiting Locality in Quantum Computation for Quantum Chemistry.

    PubMed

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

    2014-12-18

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

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

    SciTech Connect

    Yang, W. L.; Feng, M.; Yin, Z. Q.; Hu, Y.; Du, J. F.

    2011-07-15

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

  18. A scheme for efficient quantum computation with linear optics

    NASA Astrophysics Data System (ADS)

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

    2001-01-01

    Quantum computers 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 quantum computation is based on implementing a quantum bit with two optical modes containing one photon. The proposal is appealing because of the ease with which photon interference can be observed. Until now, it suffered from the requirement for non-linear couplings between optical modes containing few photons. Here we show that efficient quantum computation is possible using only beam splitters, phase shifters, single photon sources and photo-detectors. Our methods exploit feedback from photo-detectors and are robust against errors from photon loss and detector inefficiency. The basic elements are accessible to experimental investigation with current technology.

  19. Universal computation by multiparticle quantum walk.

    PubMed

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

    2013-02-15

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

  20. Computational multiqubit tunnelling in programmable quantum annealers.

    PubMed

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

    2016-01-07

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

  1. Computational multiqubit tunnelling in programmable quantum annealers

    PubMed Central

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

    2016-01-01

    Quantum tunnelling is a phenomenon in which a quantum state traverses energy barriers higher than the energy of the state itself. Quantum tunnelling has been hypothesized as an advantageous physical resource for optimization in quantum annealing. However, computational multiqubit tunnelling has not yet been observed, and a theory of co-tunnelling under high- and low-frequency noises is lacking. Here we show that 8-qubit tunnelling plays a computational role in a currently available programmable quantum annealer. We devise a probe for tunnelling, a computational primitive where classical paths are trapped in a false minimum. In support of the design of quantum annealers we develop a nonperturbative theory of open quantum dynamics under realistic noise characteristics. This theory accurately predicts the rate of many-body dissipative quantum tunnelling subject to the polaron effect. Furthermore, we experimentally demonstrate that quantum tunnelling outperforms thermal hopping along classical paths for problems with up to 200 qubits containing the computational primitive. PMID:26739797

  2. Computational multiqubit tunnelling in programmable quantum annealers

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  3. Experimental one-way quantum computing.

    PubMed

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

    2005-03-10

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

  4. Ensemble quantum computing by NMR spectroscopy

    PubMed Central

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

    1997-01-01

    A quantum computer (QC) can operate in parallel on all its possible inputs at once, but the amount of information that can be extracted from the result is limited by the phenomenon of wave function collapse. We present a new computational model, which differs from a QC only in that the result of a measurement is the expectation value of the observable, rather than a random eigenvalue thereof. Such an expectation value QC can solve nondeterministic polynomial-time complete problems in polynomial time. This observation is significant precisely because the computational model can be realized, to a certain extent, by NMR spectroscopy on macroscopic ensembles of quantum spins, namely molecules in a test tube. This is made possible by identifying a manifold of statistical spin states, called pseudo-pure states, the mathematical description of which is isomorphic to that of an isolated spin system. The result is a novel NMR computer that can be programmed much like a QC, but in other respects more closely resembles a DNA computer. Most notably, when applied to intractable combinatorial problems, an NMR computer can use an amount of sample, rather than time, which grows exponentially with the size of the problem. Although NMR computers will be limited by current technology to exhaustive searches over only 15 to 20 bits, searches over as much as 50 bits are in principle possible, and more advanced algorithms could greatly extend the range of applicability of such machines. PMID:9050830

  5. Universal quantum computation using the discrete-time quantum walk

    SciTech Connect

    Lovett, Neil B.; Cooper, Sally; Everitt, Matthew; Trevers, Matthew; Kendon, Viv

    2010-04-15

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

  6. The Quantum Human Computer (QHC) Hypothesis

    ERIC Educational Resources Information Center

    Salmani-Nodoushan, Mohammad Ali

    2008-01-01

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

  7. Universal quantum computation with qudits

    NASA Astrophysics Data System (ADS)

    Luo, MingXing; Wang, XiaoJun

    2014-09-01

    Quantum circuit model has been widely explored for various quantum applications such as Shors algorithm and Grovers searching algorithm. Most of previous algorithms are based on the qubit systems. Herein a proposal for a universal circuit is given based on the qudit system, which is larger and can store more information. In order to prove its universality for quantum applications, an explicit set of one-qudit and two-qudit gates is provided for the universal qudit computation. The one-qudit gates are general rotation for each two-dimensional subspace while the two-qudit gates are their controlled extensions. In comparison to previous quantum qudit logical gates, each primitive qudit gate is only dependent on two free parameters and may be easily implemented. In experimental implementation, multilevel ions with the linear ion trap model are used to build the qudit systems and use the coupling of neighbored levels for qudit gates. The controlled qudit gates may be realized with the interactions of internal and external coordinates of the ion.

  8. Innovative quantum technologies for microgravity fundamental physics and biological research

    NASA Technical Reports Server (NTRS)

    Kierk, I.; Israelsson, U.; Lee, M.

    2001-01-01

    This paper presents a new technology program, within the fundamental physics research program, focusing on four quantum technology areas: quantum atomics, quantum optics, space superconductivity and quantum sensor technology, and quantum fluid based sensor and modeling technology.

  9. Innovative quantum technologies for microgravity fundamental physics and biological research

    NASA Technical Reports Server (NTRS)

    Kierk, I. K.

    2002-01-01

    This paper presents a new technology program, within the fundamental physics, focusing on four quantum technology areas: quantum atomics, quantum optics, space superconductivity and quantum sensor technology, and quantum field based sensor and modeling technology.

  10. Computer Technology for Industry

    NASA Technical Reports Server (NTRS)

    1979-01-01

    In this age of the computer, more and more business firms are automating their operations for increased efficiency in a great variety of jobs, from simple accounting to managing inventories, from precise machining to analyzing complex structures. In the interest of national productivity, NASA is providing assistance both to longtime computer users and newcomers to automated operations. Through a special technology utilization service, NASA saves industry time and money by making available already developed computer programs which have secondary utility. A computer program is essentially a set of instructions which tells the computer how to produce desired information or effect by drawing upon its stored input. Developing a new program from scratch can be costly and time-consuming. Very often, however, a program developed for one purpose can readily be adapted to a totally different application. To help industry take advantage of existing computer technology, NASA operates the Computer Software Management and Information Center (COSMIC)(registered TradeMark),located at the University of Georgia. COSMIC maintains a large library of computer programs developed for NASA, the Department of Defense, the Department of Energy and other technology-generating agencies of the government. The Center gets a continual flow of software packages, screens them for adaptability to private sector usage, stores them and informs potential customers of their availability.

  11. Non-unitary probabilistic quantum computing

    NASA Technical Reports Server (NTRS)

    Gingrich, Robert M.; Williams, Colin P.

    2004-01-01

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

  12. Embracing the quantum limit in silicon computing.

    PubMed

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

    2011-11-17

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

  13. Embracing the quantum limit in silicon computing.

    PubMed

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

    2011-11-16

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

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

    PubMed

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

    2014-06-19

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

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

    PubMed

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

    2014-06-19

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

  16. Contextuality supplies the `magic' for quantum computation

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

  17. Quantum computing with steady state spin currents

    NASA Astrophysics Data System (ADS)

    Sutton, Brian M.

    Many approaches to quantum computing use spatially confined qubits in the presence of dynamic fields to perform computation. These approaches are contrasted with proposals using mobile qubits in the presence of static fields. In this thesis, steady state quantum computing using mobile electrons is explored using numerical modeling. Firstly, a foundational introduction to the case of spatially confined qubits embodied via quantum dots is provided. A collection of universal gates implemented with dynamic fields is described using simulations. These gates are combined to implement a five-qubit Grover search to provide further insight on the time-dependent field approach. Secondly, the quantum dot description is contrasted with quantum computing using steady state spin currents. Leveraging the Non-Equilibrium Greens Function formalism to perform numerical simulations, the quantum aspects of steady state spin currents are explored by revisiting the Stern-Gerlach experiment using spin-polarized contacts on a one-dimensional channel. After demonstrating the quantum nature of mobile electrons at steady state, arbitrary single qubit operations using static fields are explored. The model is further extended to incorporate two-qubit interactions to realize the square root of SWAP gate. The two-qubit CNOT gate is used to prepare a Bell state, which is read via quantum state tomography. Finally, Grover's search is revisited to explore the performance benefits of steady state quantum computing. The described multi-particle model is applicable to mobile qubit quantum computing proposals leveraging synchronized electron transport in static fields to perform quantum computing.

  18. Computers boost structural technology

    NASA Technical Reports Server (NTRS)

    Noor, Ahmed K.; Venneri, Samuel L.

    1989-01-01

    Derived from matrix methods of structural analysis and finite element methods developed over the last three decades, computational structures technology (CST) blends computer science, numerical analysis, and approximation theory into structural analysis and synthesis. Recent significant advances in CST include stochastic-based modeling, strategies for performing large-scale structural calculations on new computing systems, and the integration of CST with other disciplinary modules for multidisciplinary analysis and design. New methodologies have been developed at NASA for integrated fluid-thermal structural analysis and integrated aerodynamic-structure-control design. The need for multiple views of data for different modules also led to the development of a number of sophisticated data-base management systems. For CST to play a role in the future development of structures technology and in the multidisciplinary design of future flight vehicles, major advances and computational tools are needed in a number of key areas.

  19. Assumptions for fault tolerant quantum computing

    SciTech Connect

    Knill, E.; Laflamme, R.

    1996-06-01

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

  20. Quantum computing. Defining and detecting quantum speedup.

    PubMed

    Rønnow, Troels F; Wang, Zhihui; Job, Joshua; Boixo, Sergio; Isakov, Sergei V; Wecker, David; Martinis, John M; Lidar, Daniel A; Troyer, Matthias

    2014-07-25

    The development of small-scale quantum devices raises the question of how to fairly assess and detect quantum speedup. Here, we show how to define and measure quantum speedup and how to avoid pitfalls that might mask or fake such a speedup. We illustrate our discussion with data from tests run on a D-Wave Two device with up to 503 qubits. By using random spin glass instances as a benchmark, we found no evidence of quantum speedup when the entire data set is considered and obtained inconclusive results when comparing subsets of instances on an instance-by-instance basis. Our results do not rule out the possibility of speedup for other classes of problems and illustrate the subtle nature of the quantum speedup question.

  1. Molecular Realizations of Quantum Computing 2007

    NASA Astrophysics Data System (ADS)

    Nakahara, Mikio; Ota, Yukihiro; Rahimi, Robabeh; Kondo, Yasushi; Tada-Umezaki, Masahito

    2009-06-01

    Liquid-state NMR quantum computer: working principle and some examples / Y. Kondo -- Flux qubits, tunable coupling and beyond / A. O. Niskanen -- Josephson phase qubits, and quantum communication via a resonant cavity / M. A. Sillanpää -- Quantum computing using pulse-based electron-nuclear double resonance (ENDOR): molecular spin-qubits / K. Sato ... [et al.] -- Fullerene C[symbol]: a possible molecular quantum computer / T. Wakabayashi -- Molecular magnets for quantum computation / T. Kuroda -- Errors in a plausible scheme of quantum gates in Kane's model / Y. Ota -- Yet another formulation for quantum simultaneous noncooperative bimatrix games / A. SaiToh, R. Rahimi, M. Nakahara -- Continuous-variable teleportation of single-photon states and an accidental cloning of a photonic qubit in two-channel teleportation / T. Ide.

  2. Quantum Computational Logics and Possible Applications

    NASA Astrophysics Data System (ADS)

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

    2008-01-01

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

  3. Prospects for quantum computation with trapped ions

    SciTech Connect

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

    1997-12-31

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

  4. Quantum computing with incoherent resources and quantum jumps.

    PubMed

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

    2012-04-27

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

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

    PubMed

    Lenhard, Johannes

    2014-12-01

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

  6. Quantum technology: from research to application

    NASA Astrophysics Data System (ADS)

    Schleich, Wolfgang P.; Ranade, Kedar S.; Anton, Christian; Arndt, Markus; Aspelmeyer, Markus; Bayer, Manfred; Berg, Gunnar; Calarco, Tommaso; Fuchs, Harald; Giacobino, Elisabeth; Grassl, Markus; Hänggi, Peter; Heckl, Wolfgang M.; Hertel, Ingolf-Volker; Huelga, Susana; Jelezko, Fedor; Keimer, Bernhard; Kotthaus, Jörg P.; Leuchs, Gerd; Lütkenhaus, Norbert; Maurer, Ueli; Pfau, Tilman; Plenio, Martin B.; Rasel, Ernst Maria; Renn, Ortwin; Silberhorn, Christine; Schiedmayer, Jörg; Schmitt-Landsiedel, Doris; Schönhammer, Kurt; Ustinov, Alexey; Walther, Philip; Weinfurter, Harald; Welzl, Emo; Wiesendanger, Roland; Wolf, Stefan; Zeilinger, Anton; Zoller, Peter

    2016-05-01

    The term quantum physics refers to the phenomena and characteristics of atomic and subatomic systems which cannot be explained by classical physics. Quantum physics has had a long tradition in Germany, going back nearly 100 years. Quantum physics is the foundation of many modern technologies. The first generation of quantum technology provides the basis for key areas such as semiconductor and laser technology. The "new" quantum technology, based on influencing individual quantum systems, has been the subject of research for about the last 20 years. Quantum technology has great economic potential due to its extensive research programs conducted in specialized quantum technology centres throughout the world. To be a viable and active participant in the economic potential of this field, the research infrastructure in Germany should be improved to facilitate more investigations in quantum technology research.

  7. The Heisenberg representation of quantum computers

    SciTech Connect

    Gottesman, D.

    1998-06-24

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

  8. Quantum computing with realistically noisy devices.

    PubMed

    Knill, E

    2005-03-01

    In theory, quantum computers offer a means of solving problems that would be intractable on conventional computers. Assuming that a quantum computer could be constructed, it would in practice be required to function with noisy devices called 'gates'. These gates cause decoherence of the fragile quantum states that are central to the computer's operation. The goal of so-called 'fault-tolerant quantum computing' is therefore to compute accurately even when the error probability per gate (EPG) is high. Here we report a simple architecture for fault-tolerant quantum computing, providing evidence that accurate quantum computing is possible for EPGs as high as three per cent. Such EPGs have been experimentally demonstrated, but to avoid excessive resource overheads required by the necessary architecture, lower EPGs are needed. Assuming the availability of quantum resources comparable to the digital resources available in today's computers, we show that non-trivial quantum computations at EPGs of as high as one per cent could be implemented.

  9. Quantum Computer Games: Schrodinger Cat and Hounds

    ERIC Educational Resources Information Center

    Gordon, Michal; Gordon, Goren

    2012-01-01

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

  10. Pattern recognition on a quantum computer

    SciTech Connect

    Schuetzhold, Ralf

    2003-06-01

    By means of a simple example, it is demonstrated that the task of finding and identifying certain patterns in an otherwise (macroscopically) unstructured picture (dataset) can be accomplished efficiently by a quantum computer. Employing the powerful tool of the quantum Fourier transform, the proposed quantum algorithm exhibits an exponential speedup in comparison with its classical counterpart.

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

    PubMed

    Fujii, Keisuke; Tamate, Shuhei

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Fujii, Keisuke; Tamate, Shuhei

    2016-05-01

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

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

    PubMed Central

    Fujii, Keisuke; Tamate, Shuhei

    2016-01-01

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

  14. Nonlinear optics quantum computing with circuit QED.

    PubMed

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

    2013-02-01

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

  15. Quantum and classical dynamics in adiabatic computation

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    Adiabatic transport provides a powerful way to manipulate quantum states. By preparing a system in a readily initialized state and then slowly changing its Hamiltonian, one may achieve quantum states that would otherwise be inaccessible. Moreover, a judicious choice of final Hamiltonian whose ground state encodes the solution to a problem allows adiabatic transport to be used for universal quantum computation. However, the dephasing effects of the environment limit the quantum correlations that an open system can support and degrade the power of such adiabatic computation. We quantify this effect by allowing the system to evolve over a restricted set of quantum states, providing a link between physically inspired classical optimization algorithms and quantum adiabatic optimization. This perspective allows us to develop benchmarks to bound the quantum correlations harnessed by an adiabatic computation. We apply these to the D-Wave Vesuvius machine with revealing—though inconclusive—results.

  16. Functional quantum computing: An optical approach

    NASA Astrophysics Data System (ADS)

    Rambo, Timothy M.; Altepeter, Joseph B.; Kumar, Prem; D'Ariano, G. Mauro

    2016-05-01

    Recent theoretical investigations treat quantum computations as functions, quantum processes which operate on other quantum processes, rather than circuits. Much attention has been given to the N -switch function which takes N black-box quantum operators as input, coherently permutes their ordering, and applies the result to a target quantum state. This is something which cannot be equivalently done using a quantum circuit. Here, we propose an all-optical system design which implements coherent operator permutation for an arbitrary number of input operators.

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

    NASA Astrophysics Data System (ADS)

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

    2007-07-01

    The application of quantum mechanics to information related fields such as communication, computation and cryptography is a fast growing line of research that has been witnessing an outburst of theoretical and experimental results, with possible practical applications. On the one hand, quantum cryptography with its impact on secrecy of transmission is having its first important actual implementations; on the other hand, the recent advances in quantum optics, ion trapping, BEC manipulation, spin and quantum dot technologies allow us to put to direct test a great deal of theoretical ideas and results. These achievements have stimulated a reborn interest in various aspects of quantum mechanics, creating a unique interplay between physics, both theoretical and experimental, mathematics, information theory and computer science. In view of all these developments, it appeared timely to organize a meeting where graduate students and young researchers could be exposed to the fundamentals of the theory, while senior experts could exchange their latest results. The activity was structured as a school followed by a workshop, and took place at The Abdus Salam International Center for Theoretical Physics (ICTP) and The International School for Advanced Studies (SISSA) in Trieste, Italy, from 12-23 June 2006. The meeting was part of the activity of the Joint European Master Curriculum Development Programme in Quantum Information, Communication, Cryptography and Computation, involving the Universities of Cergy-Pontoise (France), Chania (Greece), Leuven (Belgium), Rennes1 (France) and Trieste (Italy). This special issue of Journal of Physics A: Mathematical and Theoretical collects 22 contributions from well known experts who took part in the workshop. They summarize the present day status of the research in the manifold aspects of quantum information. The issue is opened by two review articles, the first by G Adesso and F Illuminati discussing entanglement in continuous variable

  18. Embedding quantum simulators for quantum computation of entanglement.

    PubMed

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

    2013-12-13

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

  19. Quantum error correction and fault-tolerant quantum computation

    NASA Astrophysics Data System (ADS)

    Lai, Ching-Yi

    Quantum computers need to be protected by quantum error-correcting codes against decoherence. One of the most interesting and useful classes of quantum codes is the class of quantum stabilizer codes. Entanglement-assisted (EA) quantum codes are a class of stabilizer codes that make use of preshared entanglement between the sender and the receiver. We provide several code constructions for entanglement-assisted quantum codes. The MacWilliams identity for quantum codes leads to linear programming bounds on the minimum distance. We find new constraints on the simplified stabilizer group and the logical group, which help improve the linear programming bounds on entanglement-assisted quantum codes. The results also can be applied to standard stabilizer codes. In the real world, quantum gates are faulty. To implement quantum computation fault-tolerantly, quantum codes with certain properties are needed. We first analyze Knill's postselection scheme in a two-dimensional architecture. The error performance of this scheme is better than other known concatenated codes. Then we propose several methods to protect syndrome extraction against measurement errors.

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

    SciTech Connect

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

    2010-01-15

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

  1. Adiabatic Quantum Computation and the Theory of Quantum Phase Transitions

    NASA Astrophysics Data System (ADS)

    Kaminsky, William; Lloyd, Seth

    2007-03-01

    We present a general approach to determining the asymptotic scaling of adiabatic quantum computational resources (space, time, energy, and precision) on random instances of NP-complete graph theory problems. By utilizing the isomorphisms between certain NP-complete graph theory problems and certain frustrated spin models, we demonstrate that the asymptotic scaling of the minimum spectral gap that determines the asymptotic running time of adiabatic algorithms is itself determined by the presence and character of quantum phase transitions in these frustrated models. Most notably, we draw the conclusion that adiabatic quantum computers based on quantum Ising models are much less likely to be efficient than those based on quantum rotor or Heisenberg models. We then exhibit practical rotor and Heisenberg model based architectures using Josephson junction and quantum dot circuits.

  2. Cavity QED Deutsch quantum computer

    NASA Astrophysics Data System (ADS)

    Hollenberg, Lloyd C. L.; Salgueiro, A. N.; Nemes, M. C.

    2001-10-01

    The two-atom correlation scheme originally proposed by Davidovich, Brune, Raimond, and Haroche for measuring the decoherence of a mesoscopic superposition of coherent states of a QED cavity field is shown to be equivalent to a quantum computer solving Deutsch's problem. Using the existing analysis of decoherence in the Master equation formalism, and other important losses in this system, the final probability for obtaining the correct result for the computation is found in terms of the time period between atom traversals, the number of photons in the cavity, and the precision of the atomic velocity. The error due to decoherence in this system amounts to a phase error, and in the Master equation approach is a linear effect at small time scales. By explicitly considering the dynamics of the decoherence process when the system is coupled to a bath of oscillators with finite mode cutoff the error due to decoherence is found to decrease significantly and becomes a quadratic effect at short-time scales.

  3. Universal quantum computation with little entanglement.

    PubMed

    Van den Nest, Maarten

    2013-02-01

    We show that universal quantum computation 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 quantum computation 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 quantum computers.

  4. The case for biological quantum computer elements

    NASA Astrophysics Data System (ADS)

    Baer, Wolfgang; Pizzi, Rita

    2009-05-01

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

  5. Technology study of quantum remote sensing imaging

    NASA Astrophysics Data System (ADS)

    Bi, Siwen; Lin, Xuling; Yang, Song; Wu, Zhiqiang

    2016-02-01

    According to remote sensing science and technology development and application requirements, quantum remote sensing is proposed. First on the background of quantum remote sensing, quantum remote sensing theory, information mechanism, imaging experiments and prototype principle prototype research situation, related research at home and abroad are briefly introduced. Then we expounds compress operator of the quantum remote sensing radiation field and the basic principles of single-mode compression operator, quantum quantum light field of remote sensing image compression experiment preparation and optical imaging, the quantum remote sensing imaging principle prototype, Quantum remote sensing spaceborne active imaging technology is brought forward, mainly including quantum remote sensing spaceborne active imaging system composition and working principle, preparation and injection compression light active imaging device and quantum noise amplification device. Finally, the summary of quantum remote sensing research in the past 15 years work and future development are introduced.

  6. Graph isomorphism and adiabatic quantum computing

    NASA Astrophysics Data System (ADS)

    Gaitan, Frank; Clark, Lane

    2014-02-01

    In the graph isomorphism (GI) problem two N-vertex graphs G and G' are given and the task is to determine whether there exists a permutation of the vertices of G that preserves adjacency and transforms G →G'. If yes, then G and G' are said to be isomorphic; otherwise they are nonisomorphic. The GI problem is an important problem in computer science and is thought to be of comparable difficulty to integer factorization. In this paper we present a quantum algorithm that solves arbitrary instances of GI and which also provides an approach to determining all automorphisms of a given graph. We show how the GI problem can be converted to a combinatorial optimization problem that can be solved using adiabatic quantum evolution. We numerically simulate the algorithm's quantum dynamics and show that it correctly (i) distinguishes nonisomorphic graphs; (ii) recognizes isomorphic graphs and determines the permutation(s) that connect them; and (iii) finds the automorphism group of a given graph G. We then discuss the GI quantum algorithm's experimental implementation, and close by showing how it can be leveraged to give a quantum algorithm that solves arbitrary instances of the NP-complete subgraph isomorphism problem. The computational complexity of an adiabatic quantum algorithm is largely determined by the minimum energy gap Δ (N) separating the ground and first-excited states in the limit of large problem size N ≫1. Calculating Δ (N) in this limit is a fundamental open problem in adiabatic quantum computing, and so it is not possible to determine the computational complexity of adiabatic quantum algorithms in general, nor consequently, of the specific adiabatic quantum algorithms presented here. Adiabatic quantum computing has been shown to be equivalent to the circuit model of quantum computing, and so development of adiabatic quantum algorithms continues to be of great interest.

  7. Video Encryption and Decryption on Quantum Computers

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  8. Exponential rise of dynamical complexity in quantum computing through projections.

    PubMed

    Burgarth, Daniel Klaus; Facchi, Paolo; Giovannetti, Vittorio; Nakazato, Hiromichi; Pascazio, Saverio; Yuasa, Kazuya

    2014-10-10

    The ability of quantum systems to host exponentially complex dynamics has the potential to revolutionize science and technology. Therefore, much effort has been devoted to developing of protocols for computation, communication and metrology, which exploit this scaling, despite formidable technical difficulties. Here we show that the mere frequent observation of a small part of a quantum system can turn its dynamics from a very simple one into an exponentially complex one, capable of universal quantum computation. After discussing examples, we go on to show that this effect is generally to be expected: almost any quantum dynamics becomes universal once 'observed' as outlined above. Conversely, we show that any complex quantum dynamics can be 'purified' into a simpler one in larger dimensions. We conclude by demonstrating that even local noise can lead to an exponentially complex dynamics.

  9. Exponential rise of dynamical complexity in quantum computing through projections

    PubMed Central

    Burgarth, Daniel Klaus; Facchi, Paolo; Giovannetti, Vittorio; Nakazato, Hiromichi; Pascazio, Saverio; Yuasa, Kazuya

    2014-01-01

    The ability of quantum systems to host exponentially complex dynamics has the potential to revolutionize science and technology. Therefore, much effort has been devoted to developing of protocols for computation, communication and metrology, which exploit this scaling, despite formidable technical difficulties. Here we show that the mere frequent observation of a small part of a quantum system can turn its dynamics from a very simple one into an exponentially complex one, capable of universal quantum computation. After discussing examples, we go on to show that this effect is generally to be expected: almost any quantum dynamics becomes universal once ‘observed’ as outlined above. Conversely, we show that any complex quantum dynamics can be ‘purified’ into a simpler one in larger dimensions. We conclude by demonstrating that even local noise can lead to an exponentially complex dynamics. PMID:25300692

  10. Secure Entanglement Distillation for Double-Server Blind Quantum Computation

    NASA Astrophysics Data System (ADS)

    Morimae, Tomoyuki; Fujii, Keisuke

    2013-07-01

    Blind quantum computation is a new secure quantum computing protocol where a client, who does not have enough quantum technologies at her disposal, can delegate her quantum computation to a server, who has a fully fledged quantum computer, 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 quantum computing.

  11. Secure entanglement distillation for double-server blind quantum computation.

    PubMed

    Morimae, Tomoyuki; Fujii, Keisuke

    2013-07-12

    Blind quantum computation is a new secure quantum computing protocol where a client, who does not have enough quantum technologies at her disposal, can delegate her quantum computation to a server, who has a fully fledged quantum computer, 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 quantum computing.

  12. Race begins to secure quantum technology investment

    NASA Astrophysics Data System (ADS)

    Lavender, Gemma

    2014-06-01

    Lancaster University in the UK opened a new £6m Quantum Technology Centre last month, which it hopes will become part of a new £270m national network of quantum-technology hubs that will seek to turn quantum-physics research into commercial products.

  13. Relativistic Quantum Metrology: Exploiting relativity to improve quantum measurement technologies

    PubMed Central

    Ahmadi, Mehdi; Bruschi, David Edward; Sabín, Carlos; Adesso, Gerardo; Fuentes, Ivette

    2014-01-01

    We present a framework for relativistic quantum metrology that is useful for both Earth-based and space-based technologies. Quantum metrology has been so far successfully applied to design precision instruments such as clocks and sensors which outperform classical devices by exploiting quantum properties. There are advanced plans to implement these and other quantum technologies in space, for instance Space-QUEST and Space Optical Clock projects intend to implement quantum communications and quantum clocks at regimes where relativity starts to kick in. However, typical setups do not take into account the effects of relativity on quantum properties. To include and exploit these effects, we introduce techniques for the application of metrology to quantum field theory. Quantum field theory properly incorporates quantum theory and relativity, in particular, at regimes where space-based experiments take place. This framework allows for high precision estimation of parameters that appear in quantum field theory including proper times and accelerations. Indeed, the techniques can be applied to develop a novel generation of relativistic quantum technologies for gravimeters, clocks and sensors. As an example, we present a high precision device which in principle improves the state-of-the-art in quantum accelerometers by exploiting relativistic effects. PMID:24851858

  14. Relativistic quantum metrology: exploiting relativity to improve quantum measurement technologies.

    PubMed

    Ahmadi, Mehdi; Bruschi, David Edward; Sabín, Carlos; Adesso, Gerardo; Fuentes, Ivette

    2014-05-22

    We present a framework for relativistic quantum metrology that is useful for both Earth-based and space-based technologies. Quantum metrology has been so far successfully applied to design precision instruments such as clocks and sensors which outperform classical devices by exploiting quantum properties. There are advanced plans to implement these and other quantum technologies in space, for instance Space-QUEST and Space Optical Clock projects intend to implement quantum communications and quantum clocks at regimes where relativity starts to kick in. However, typical setups do not take into account the effects of relativity on quantum properties. To include and exploit these effects, we introduce techniques for the application of metrology to quantum field theory. Quantum field theory properly incorporates quantum theory and relativity, in particular, at regimes where space-based experiments take place. This framework allows for high precision estimation of parameters that appear in quantum field theory including proper times and accelerations. Indeed, the techniques can be applied to develop a novel generation of relativistic quantum technologies for gravimeters, clocks and sensors. As an example, we present a high precision device which in principle improves the state-of-the-art in quantum accelerometers by exploiting relativistic effects.

  15. Relativistic quantum metrology: exploiting relativity to improve quantum measurement technologies.

    PubMed

    Ahmadi, Mehdi; Bruschi, David Edward; Sabín, Carlos; Adesso, Gerardo; Fuentes, Ivette

    2014-01-01

    We present a framework for relativistic quantum metrology that is useful for both Earth-based and space-based technologies. Quantum metrology has been so far successfully applied to design precision instruments such as clocks and sensors which outperform classical devices by exploiting quantum properties. There are advanced plans to implement these and other quantum technologies in space, for instance Space-QUEST and Space Optical Clock projects intend to implement quantum communications and quantum clocks at regimes where relativity starts to kick in. However, typical setups do not take into account the effects of relativity on quantum properties. To include and exploit these effects, we introduce techniques for the application of metrology to quantum field theory. Quantum field theory properly incorporates quantum theory and relativity, in particular, at regimes where space-based experiments take place. This framework allows for high precision estimation of parameters that appear in quantum field theory including proper times and accelerations. Indeed, the techniques can be applied to develop a novel generation of relativistic quantum technologies for gravimeters, clocks and sensors. As an example, we present a high precision device which in principle improves the state-of-the-art in quantum accelerometers by exploiting relativistic effects. PMID:24851858

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

    PubMed

    Ren, Bao-Cang; Deng, Fu-Guo

    2014-04-11

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

  17. One-way quantum computation with circuit quantum electrodynamics

    SciTech Connect

    Wu Chunwang; Han Yang; Chen Pingxing; Li Chengzu; Zhong Xiaojun

    2010-03-15

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

  18. Materials Frontiers to Empower Quantum Computing

    SciTech Connect

    Taylor, Antoinette Jane; Sarrao, John Louis; Richardson, Christopher

    2015-06-11

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

  19. Ramsey numbers and adiabatic quantum computing.

    PubMed

    Gaitan, Frank; Clark, Lane

    2012-01-01

    The graph-theoretic Ramsey numbers are notoriously difficult to calculate. In fact, for the two-color Ramsey numbers R(m,n) with m, n≥3, only nine are currently known. We present a quantum algorithm for the computation of the Ramsey numbers R(m,n). We show how the computation of R(m,n) can be mapped to a combinatorial optimization problem whose solution can be found using adiabatic quantum evolution. We numerically simulate this adiabatic quantum algorithm and show that it correctly determines the Ramsey numbers R(3,3) and R(2,s) for 5≤s≤7. We then discuss the algorithm's experimental implementation, and close by showing that Ramsey number computation belongs to the quantum complexity class quantum Merlin Arthur.

  20. Superadiabatic Controlled Evolutions and Universal Quantum Computation

    PubMed Central

    Santos, Alan C.; Sarandy, Marcelo S.

    2015-01-01

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

  1. From transistor to trapped-ion computers for quantum chemistry.

    PubMed

    Yung, M-H; Casanova, J; Mezzacapo, A; McClean, J; Lamata, L; Aspuru-Guzik, A; Solano, E

    2014-01-01

    Over the last few decades, quantum chemistry has progressed through the development of computational methods based on modern digital computers. However, these methods can hardly fulfill the exponentially-growing resource requirements when applied to large quantum systems. As pointed out by Feynman, this restriction is intrinsic to all computational models based on classical physics. Recently, the rapid advancement of trapped-ion technologies has opened new possibilities for quantum control and quantum simulations. Here, we present an efficient toolkit that exploits both the internal and motional degrees of freedom of trapped ions for solving problems in quantum chemistry, including molecular electronic structure, molecular dynamics, and vibronic coupling. We focus on applications that go beyond the capacity of classical computers, but may be realizable on state-of-the-art trapped-ion systems. These results allow us to envision a new paradigm of quantum chemistry that shifts from the current transistor to a near-future trapped-ion-based technology. PMID:24395054

  2. Reducing computational complexity of quantum correlations

    NASA Astrophysics Data System (ADS)

    Chanda, Titas; Das, Tamoghna; Sadhukhan, Debasis; Pal, Amit Kumar; SenDe, Aditi; Sen, Ujjwal

    2015-12-01

    We address the issue of reducing the resource required to compute information-theoretic quantum correlation measures such as quantum discord and quantum work deficit in two qubits and higher-dimensional systems. We show that determination of the quantum correlation measure is possible even if we utilize a restricted set of local measurements. We find that the determination allows us to obtain a closed form of quantum discord and quantum work deficit for several classes of states, with a low error. We show that the computational error caused by the constraint over the complete set of local measurements reduces fast with an increase in the size of the restricted set, implying usefulness of constrained optimization, especially with the increase of dimensions. We perform quantitative analysis to investigate how the error scales with the system size, taking into account a set of plausible constructions of the constrained set. Carrying out a comparative study, we show that the resource required to optimize quantum work deficit is usually higher than that required for quantum discord. We also demonstrate that minimization of quantum discord and quantum work deficit is easier in the case of two-qubit mixed states of fixed ranks and with positive partial transpose in comparison to the corresponding states having nonpositive partial transpose. Applying the methodology to quantum spin models, we show that the constrained optimization can be used with advantage in analyzing such systems in quantum information-theoretic language. For bound entangled states, we show that the error is significantly low when the measurements correspond to the spin observables along the three Cartesian coordinates, and thereby we obtain expressions of quantum discord and quantum work deficit for these bound entangled states.

  3. Is the Brain a Quantum Computer?

    ERIC Educational Resources Information Center

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

    2006-01-01

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

  4. Directional coupling for quantum computing and communication.

    PubMed

    Nikolopoulos, Georgios M

    2008-11-14

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

  5. Grating chips for quantum technologies

    NASA Astrophysics Data System (ADS)

    McGilligan, James Patrick; Ingleby, Stuart; Griffin, Paul Francis; Riis, Erling; Arnold, Aidan

    2015-05-01

    Laser cooled atomic samples have resulted in profound advances in frequency metrology, however the technology is typically complex and bulky. In the cover story of the May 2013 issue of Nature Nanotechnology we describe a micro-fabricated optical element that greatly facilitates miniaturisation of ultra-cold atom technology. Portable devices should be feasible with accuracy vastly exceeding that of equivalent room-temperature technology, with a minimal footprint. Laser cooled samples will be ideal for measurement devices e.g. portable atomic clocks and magnetometers and, moreover, they hold great potential for longer-term breakthroughs exploiting e.g. optical lattices for all-optical clocks and Bose-Einstein condensates for atom interferometry. Here we will discuss next generation diffractive optical elements (DOE) and demonstrate quantum based measurements on samples of ultra-cold atoms created using our miniaturised optical setup.

  6. LDRD final report on quantum computing using interacting semiconductor quantum wires.

    SciTech Connect

    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

    2006-01-01

    For several years now quantum computing 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 quantum computer, and indeed for other coupled nanoelectronic devices that will rely on coherent transport. If successful, this project will have important implications for nanoelectronics, quantum computing and information technology.

  7. Quantum computation with optical coherent states

    SciTech Connect

    Ralph, T.C.; Gilchrist, A.; Milburn, G.J.; Munro, W.J.; Glancy, S.

    2003-10-01

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

  8. Quantum computing Hyper Terahertz Facility opens

    NASA Astrophysics Data System (ADS)

    Singh Chadha, Kulvinder

    2016-01-01

    A new facility has opened at the University of Surrey to use terahertz radiation for quantum computing. The Hyper Terahertz Facility (HTF) is a joint collaboration between the University of Surrey and the National Physical Laboratory (NPL).

  9. Iterated Gate Teleportation and Blind Quantum Computation.

    PubMed

    Pérez-Delgado, Carlos A; Fitzsimons, Joseph F

    2015-06-01

    Blind quantum computation allows a user to delegate a computation to an untrusted server while keeping the computation hidden. A number of recent works have sought to establish bounds on the communication requirements necessary to implement blind computation, and a bound based on the no-programming theorem of Nielsen and Chuang has emerged as a natural limiting factor. Here we show that this constraint only holds in limited scenarios, and show how to overcome it using a novel method of iterated gate teleportations. This technique enables drastic reductions in the communication required for distributed quantum protocols, extending beyond the blind computation setting. Applied to blind quantum computation, this technique offers significant efficiency improvements, and in some scenarios offers an exponential reduction in communication requirements. PMID:26196609

  10. Iterated Gate Teleportation and Blind Quantum Computation.

    PubMed

    Pérez-Delgado, Carlos A; Fitzsimons, Joseph F

    2015-06-01

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

  11. Braid group representation on quantum computation

    SciTech Connect

    Aziz, Ryan Kasyfil; Muchtadi-Alamsyah, Intan

    2015-09-30

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

  12. Computer Technology in Adult Education.

    ERIC Educational Resources Information Center

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

    This publication provides materials to help adult educators use computer technology 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,…

  13. Acausal measurement-based quantum computing

    NASA Astrophysics Data System (ADS)

    Morimae, Tomoyuki

    2014-07-01

    In measurement-based quantum computing, there is a natural "causal cone" among qubits of the resource state, since the measurement angle on a qubit has to depend on previous measurement results in order to correct the effect of by-product operators. If we respect the no-signaling principle, by-product operators cannot be avoided. Here we study the possibility of acausal measurement-based quantum computing by using the process matrix framework [Oreshkov, Costa, and Brukner, Nat. Commun. 3, 1092 (2012), 10.1038/ncomms2076]. We construct a resource process matrix for acausal measurement-based quantum computing restricting local operations to projective measurements. The resource process matrix is an analog of the resource state of the standard causal measurement-based quantum computing. We find that if we restrict local operations to projective measurements the resource process matrix is (up to a normalization factor and trivial ancilla qubits) equivalent to the decorated graph state created from the graph state of the corresponding causal measurement-based quantum computing. We also show that it is possible to consider a causal game whose causal inequality is violated by acausal measurement-based quantum computing.

  14. Cat-qubits for quantum computation

    NASA Astrophysics Data System (ADS)

    Mirrahimi, Mazyar

    2016-08-01

    The development of quantum Josephson circuits has created a strong expectation for reliable processing of quantum information. While this progress has already led to various proof-of-principle experiments on small-scale quantum systems, a major scaling step is required towards many-qubit protocols. Fault-tolerant computation with protected logical qubits usually comes at the expense of a significant overhead in the hardware. Each of the involved physical qubits still needs to satisfy the best achieved properties (coherence times, coupling strengths and tunability). Here, and in the aim of addressing alternative approaches to deal with these obstacles, I overview a series of recent theoretical proposals, and the experimental developments following these proposals, to enable a hardware-efficient paradigm for quantum memory protection and universal quantum computation.

  15. Computing technology in the 1980's. [computers

    NASA Technical Reports Server (NTRS)

    Stone, H. S.

    1978-01-01

    Advances in computing technology have been led by consistently improving semiconductor technology. The semiconductor industry has turned out ever faster, smaller, and less expensive devices since transistorized computers were first introduced 20 years ago. For the next decade, there appear to be new advances possible, with the rate of introduction of improved devices at least equal to the historic trends. The implication of these projections is that computers will enter new markets and will truly be pervasive in business, home, and factory as their cost diminishes and their computational power expands to new levels. The computer industry as we know it today will be greatly altered in the next decade, primarily because the raw computer system will give way to computer-based turn-key information and control systems.

  16. Progress in silicon-based quantum computing.

    PubMed

    Clark, R G; Brenner, R; Buehler, T M; Chan, V; Curson, N J; Dzurak, A S; Gauja, E; Goan, H S; Greentree, A D; Hallam, T; Hamilton, A R; Hollenberg, L C L; Jamieson, D N; McCallum, J C; Milburn, G J; O'Brien, J L; Oberbeck, L; Pakes, C I; Prawer, S D; Reilly, D J; Ruess, F J; Schofield, S R; Simmons, M Y; Stanley, F E; Starrett, R P; Wellard, C; Yang, C

    2003-07-15

    We review progress at the Australian Centre for Quantum Computer Technology towards the fabrication and demonstration of spin qubits and charge qubits based on phosphorus donor atoms embedded in intrinsic silicon. Fabrication is being pursued via two complementary pathways: a 'top-down' approach for near-term production of few-qubit demonstration devices and a 'bottom-up' approach for large-scale qubit arrays with sub-nanometre precision. The 'top-down' approach employs a low-energy (keV) ion beam to implant the phosphorus atoms. Single-atom control during implantation is achieved by monitoring on-chip detector electrodes, integrated within the device structure. In contrast, the 'bottom-up' approach uses scanning tunnelling microscope lithography and epitaxial silicon overgrowth to construct devices at an atomic scale. In both cases, surface electrodes control the qubit using voltage pulses, and dual single-electron transistors operating near the quantum limit provide fast read-out with spurious-signal rejection.

  17. Robust dynamical decoupling for quantum computing and quantum memory.

    PubMed

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

    2011-06-17

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

  18. Irreconcilable difference between quantum walks and adiabatic quantum computing

    NASA Astrophysics Data System (ADS)

    Wong, Thomas G.; Meyer, David A.

    2016-06-01

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

  19. Efficient quantum circuits for one-way quantum computing.

    PubMed

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

    2009-03-13

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

  20. Nondissipative decoherence bounds on quantum computation

    NASA Astrophysics Data System (ADS)

    Mancini, Stefano; Bonifacio, Rodolfo

    2001-03-01

    We investigate the capabilities of a quantum computer based on cold trapped ions in the presence of nondissipative decoherence. The latter is accounted by using the evolution time as a random variable and then averaging on a properly defined probability distribution. Severe bounds on computational performances are found.

  1. Qubus ancilla-driven quantum computation

    NASA Astrophysics Data System (ADS)

    Brown, Katherine Louise; De, Suvabrata; Kendon, Viv; Munro, Bill

    2014-12-01

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

  2. Qubus ancilla-driven quantum computation

    SciTech Connect

    Brown, Katherine Louise; De, Suvabrata; Kendon, Viv; Munro, Bill

    2014-12-04

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

  3. Computer Viruses. Technology Update.

    ERIC Educational Resources Information Center

    Ponder, Tim, Comp.; Ropog, Marty, Comp.; Keating, Joseph, Comp.

    This document provides general information on computer viruses, how to help protect a computer network from them, measures to take if a computer becomes infected. Highlights include the origins of computer viruses; virus contraction; a description of some common virus types (File Virus, Boot Sector/Partition Table Viruses, Trojan Horses, and…

  4. Nursing Education Update: Computer Technology.

    ERIC Educational Resources Information Center

    Gothler, Ann M.

    1985-01-01

    A survey of nursing faculty showed that 91 percent of nursing education programs had faculty members who had attended or participated in a conference on computers during 1983 and 1984. Other survey responses concerned computer applications integrated into nursing courses, required courses in computer technology, and computer-assisted instruction.…

  5. Biologically inspired path to quantum computer

    NASA Astrophysics Data System (ADS)

    Ogryzko, Vasily; Ozhigov, Yuri

    2014-12-01

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

  6. Photonic quantum information: science and technology.

    PubMed

    Takeuchi, Shigeki

    2016-01-01

    Recent technological progress in the generation, manipulation and detection of individual single photons has opened a new scientific field of photonic quantum information. This progress includes the realization of single photon switches, photonic quantum circuits with specific functions, and the application of novel photonic states to novel optical metrology beyond the limits of standard optics. In this review article, the recent developments and current status of photonic quantum information technology are overviewed based on the author's past and recent works.

  7. Power of one qumode for quantum computation

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  8. Scalable quantum computing based on stationary spin qubits in coupled quantum dots inside double-sided optical microcavities

    NASA Astrophysics Data System (ADS)

    Wei, Hai-Rui; Deng, Fu-Guo

    2014-12-01

    Quantum logic gates are the key elements in quantum computing. Here we investigate the possibility of achieving a scalable and compact quantum computing based on stationary electron-spin qubits, by using the giant optical circular birefringence induced by quantum-dot spins in double-sided optical microcavities as a result of cavity quantum electrodynamics. We design the compact quantum circuits for implementing universal and deterministic quantum gates for electron-spin systems, including the two-qubit CNOT gate and the three-qubit Toffoli gate. They are compact and economic, and they do not require additional electron-spin qubits. Moreover, our devices have good scalability and are attractive as they both are based on solid-state quantum systems and the qubits are stationary. They are feasible with the current experimental technology, and both high fidelity and high efficiency can be achieved when the ratio of the side leakage to the cavity decay is low.

  9. Scalable quantum computing based on stationary spin qubits in coupled quantum dots inside double-sided optical microcavities.

    PubMed

    Wei, Hai-Rui; Deng, Fu-Guo

    2014-12-18

    Quantum logic gates are the key elements in quantum computing. Here we investigate the possibility of achieving a scalable and compact quantum computing based on stationary electron-spin qubits, by using the giant optical circular birefringence induced by quantum-dot spins in double-sided optical microcavities as a result of cavity quantum electrodynamics. We design the compact quantum circuits for implementing universal and deterministic quantum gates for electron-spin systems, including the two-qubit CNOT gate and the three-qubit Toffoli gate. They are compact and economic, and they do not require additional electron-spin qubits. Moreover, our devices have good scalability and are attractive as they both are based on solid-state quantum systems and the qubits are stationary. They are feasible with the current experimental technology, and both high fidelity and high efficiency can be achieved when the ratio of the side leakage to the cavity decay is low.

  10. Scalable quantum computing based on stationary spin qubits in coupled quantum dots inside double-sided optical microcavities

    PubMed Central

    Wei, Hai-Rui; Deng, Fu-Guo

    2014-01-01

    Quantum logic gates are the key elements in quantum computing. Here we investigate the possibility of achieving a scalable and compact quantum computing based on stationary electron-spin qubits, by using the giant optical circular birefringence induced by quantum-dot spins in double-sided optical microcavities as a result of cavity quantum electrodynamics. We design the compact quantum circuits for implementing universal and deterministic quantum gates for electron-spin systems, including the two-qubit CNOT gate and the three-qubit Toffoli gate. They are compact and economic, and they do not require additional electron-spin qubits. Moreover, our devices have good scalability and are attractive as they both are based on solid-state quantum systems and the qubits are stationary. They are feasible with the current experimental technology, and both high fidelity and high efficiency can be achieved when the ratio of the side leakage to the cavity decay is low. PMID:25518899

  11. Information-theoretic temporal Bell inequality and quantum computation

    SciTech Connect

    Morikoshi, Fumiaki

    2006-05-15

    An information-theoretic temporal Bell inequality is formulated to contrast classical and quantum computations. 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 quantum computation.

  12. Quantum computation with ions in microscopic traps

    NASA Astrophysics Data System (ADS)

    Šašura, Marek; Steane, Andrew M.

    2002-12-01

    We discuss a possible experimental realization of fast quantum gates with high fidelity with ions confined in microscopic traps. The original proposal of this physical system for quantum computation comes from Cirac and Zoller (Nature 404, 579 (2000)). In this paper we analyse a sensitivity of the ion-trap quantum gate on various experimental parameters which was omitted in the original proposal. We address imprecision of laser pulses, impact of photon scattering, nonzero temperature effects and influence of laser intensity fluctuations on the total fidelity of the two-qubit phase gate.

  13. Computations in quantum mechanics made easy

    NASA Astrophysics Data System (ADS)

    Korsch, H. J.; Rapedius, K.

    2016-09-01

    Convenient and simple numerical techniques for performing quantum computations based on matrix representations of Hilbert space operators are presented and illustrated by various examples. The applications include the calculations of spectral and dynamical properties for one-dimensional and two-dimensional single-particle systems as well as bosonic many-particle and open quantum systems. Due to their technical simplicity these methods are well suited as a tool for teaching quantum mechanics to undergraduates and graduates. Explicit implementations of the presented numerical methods in Matlab are given.

  14. Quantum computation with ``hot`` trapped ions

    SciTech Connect

    James, D.F.V.; Schneider, S. |; Milburn, G.J.

    1998-12-31

    The authors describe two methods that have been proposed to circumvent the problem of heating by external electromagnetic fields in ion trap quantum computers. 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.

  15. Universal dephasing control during quantum computation

    SciTech Connect

    Gordon, Goren; Kurizki, Gershon

    2007-10-15

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

  16. Can the human brain do quantum computing?

    PubMed

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

    2004-01-01

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

  17. Silicon enhancement mode nanostructures for quantum computing.

    SciTech Connect

    Carroll, Malcolm S.

    2010-03-01

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

  18. Trading Classical and Quantum Computational Resources

    NASA Astrophysics Data System (ADS)

    Bravyi, Sergey; Smith, Graeme; Smolin, John A.

    2016-04-01

    We propose examples of a hybrid quantum-classical simulation where a classical computer assisted by a small quantum processor can efficiently simulate a larger quantum system. First, we consider sparse quantum circuits such that each qubit participates in O (1 ) two-qubit gates. It is shown that any sparse circuit on n +k qubits can be simulated by sparse circuits on n qubits and a classical processing that takes time 2O (k )poly (n ) . Second, we study Pauli-based computation (PBC), where allowed operations are nondestructive eigenvalue measurements of n -qubit Pauli operators. The computation begins by initializing each qubit in the so-called magic state. This model is known to be equivalent to the universal quantum computer. We show that any PBC on n +k qubits can be simulated by PBCs on n qubits and a classical processing that takes time 2O (k )poly (n ). Finally, we propose a purely classical algorithm that can simulate a PBC on n qubits in a time 2α npoly (n ) , where α ≈0.94 . This improves upon the brute-force simulation method, which takes time 2npoly (n ). Our algorithm exploits the fact that n -fold tensor products of magic states admit a low-rank decomposition into n -qubit stabilizer states.

  19. [Earth Science Technology Office's Computational Technologies Project

    NASA Technical Reports Server (NTRS)

    Fischer, James (Technical Monitor); Merkey, Phillip

    2005-01-01

    This grant supported the effort to characterize the problem domain of the Earth Science Technology Office's Computational Technologies Project, to engage the Beowulf Cluster Computing Community as well as the High Performance Computing Research Community so that we can predict the applicability of said technologies to the scientific community represented by the CT project and formulate long term strategies to provide the computational resources necessary to attain the anticipated scientific objectives of the CT project. Specifically, the goal of the evaluation effort is to use the information gathered over the course of the Round-3 investigations to quantify the trends in scientific expectations, the algorithmic requirements and capabilities of high-performance computers to satisfy this anticipated need.

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

    PubMed

    Tempel, David G; Aspuru-Guzik, Alán

    2012-01-01

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

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

    PubMed Central

    Tempel, David G.; Aspuru-Guzik, Alán

    2012-01-01

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

  2. Computer and information technology: hardware.

    PubMed

    O'Brien, D

    1998-02-01

    Computers open the door to an ever-expanding arena of knowledge and technology. Most nurses practicing in perianesthesia setting were educated before the computer era, and many fear computers and the associated technology. Frequently, the greatest difficulty is finding the resources and knowing what questions to ask. The following is the first in a series of articles on computers and information technology. This article discusses computer hardware to get the novice started or the experienced user upgraded to access new technologies and the Internet. Future articles will discuss start up and usual software applications, getting up to speed on the information superhighway, and other technologies that will broaden our knowledge and expand our personal and professional world. PMID:9543967

  3. Towards universal quantum computation through relativistic motion

    PubMed Central

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

    2016-01-01

    We show how to use relativistic motion to generate continuous variable Gaussian cluster states within cavity modes. Our results can be demonstrated experimentally using superconducting circuits where tuneable boundary conditions correspond to mirrors moving with velocities close to the speed of light. In particular, we propose the generation of a quadripartite square cluster state as a first example that can be readily implemented in the laboratory. Since cluster states are universal resources for universal one-way quantum computation, our results pave the way for relativistic quantum computation schemes. PMID:26860584

  4. Towards universal quantum computation through relativistic motion

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  5. Processor core model for quantum computing.

    PubMed

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

    2006-06-01

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

  6. Random Numbers and Quantum Computers

    ERIC Educational Resources Information Center

    McCartney, Mark; Glass, David

    2002-01-01

    The topic of random numbers is investigated in such a way as to illustrate links between mathematics, physics and computer science. First, the generation of random numbers by a classical computer using the linear congruential generator and logistic map is considered. It is noted that these procedures yield only pseudo-random numbers since…

  7. Mimicking time evolution within a quantum ground state: Ground-state quantum computation, cloning, and teleportation

    SciTech Connect

    Mizel, Ari

    2004-07-01

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

  8. Designing defect spins for wafer-scale quantum technologies

    SciTech Connect

    Koehl, William F.; Seo, Hosung; Galli, Giulia; Awschalom, David D.

    2015-11-27

    The past decade has seen remarkable progress in the development of the nitrogen-vacancy (NV) defect center in diamond, which is one of the leading candidates for quantum information technologies. The success of the NV center as a solid-state qubit has stimulated an active search for similar defect spins in other technologically important and mature semiconductors, such as silicon carbide. If successfully combined with the advanced microfabrication techniques available to such materials, coherent quantum control of defect spins could potentially lead to semiconductor-based, wafer-scale quantum technologies that make use of exotic quantum mechanical phenomena like entanglement. In this article, we describe the robust spin property of the NV center and the current status of NV center research for quantum information technologies. We then outline first-principles computational modeling techniques based on density functional theory to efficiently search for potential spin defects in nondiamond hosts suitable for quantum information applications. The combination of computational modeling and experimentation has proven invaluable in this area, and we describe the successful interplay between theory and experiment achieved with the divacancy spin qubit in silicon carbide.

  9. Decoding Technology: Computer Shortcuts

    ERIC Educational Resources Information Center

    Walker, Tim; Donohue, Chip

    2008-01-01

    For the typical early childhood administrator, there will never be enough hours in a day to finish the work that needs to be done. This includes numerous hours spent on a computer tracking enrollment, managing the budget, researching curriculum ideas online, and many other administrative tasks. Improving an administrator's computer efficiency can…

  10. Research on Quantum Authentication Methods for the Secure Access Control Among Three Elements of Cloud Computing

    NASA Astrophysics Data System (ADS)

    Dong, Yumin; Xiao, Shufen; Ma, Hongyang; Chen, Libo

    2016-08-01

    Cloud computing and big data have become the developing engine of current information technology (IT) as a result of the rapid development of IT. However, security protection has become increasingly important for cloud computing and big data, and has become a problem that must be solved to develop cloud computing. The theft of identity authentication information remains a serious threat to the security of cloud computing. In this process, attackers intrude into cloud computing services through identity authentication information, thereby threatening the security of data from multiple perspectives. Therefore, this study proposes a model for cloud computing protection and management based on quantum authentication, introduces the principle of quantum authentication, and deduces the quantum authentication process. In theory, quantum authentication technology can be applied in cloud computing for security protection. This technology cannot be cloned; thus, it is more secure and reliable than classical methods.

  11. Computers, Technology, and Disability. [Update.

    ERIC Educational Resources Information Center

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

    This paper describes programs and resources that focus on access of postsecondary students with disabilities to computers and other forms of technology. Increased access to technological devices and services is provided to students with disabilities under the Technology-Related Assistance for Individuals with Disabilities Act (Tech Act). Section…

  12. A surface code quantum computer in silicon

    PubMed Central

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

    2015-01-01

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

  13. A surface code quantum computer in silicon.

    PubMed

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

    2015-10-01

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

  14. A surface code quantum computer in silicon.

    PubMed

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

    2015-10-01

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

  15. The quantum cryptograpy: Communication and computation

    NASA Astrophysics Data System (ADS)

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

    2005-07-01

    Nowadays there are two secure ways of encrypting information, the public key cryptography (PKC), and the symmetric cryptography (SC). With the arrival of the quantum computation, 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.

  16. Computers: Educational Technology Paradox?

    ERIC Educational Resources Information Center

    Hashim, Hajah Rugayah Hj.; Mustapha, Wan Narita

    2005-01-01

    As we move further into the new millennium, the need to involve and adapt learners with new technology have been the main aim of many institutions of higher learning in Malaysia. The involvement of the government in huge technology-based projects like the Multimedia Super Corridor Highway (MSC) and one of its flagships, the Smart Schools have…

  17. Industrial Superconducting Quantum Computer Development in Canada

    NASA Astrophysics Data System (ADS)

    Rose, Geordie

    2002-05-01

    Quantum computation 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 quantum computer 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.

  18. Universality of computation in real quantum theory

    NASA Astrophysics Data System (ADS)

    Belenchia, A.; D'Ariano, G. M.; Perinotti, P.

    2013-10-01

    Recently de la Torre et al. (Phys. Rev. Lett., 109 (2012) 090403) reconstructed Quantum Theory from its local structure on the basis of local discriminability and the existence of a one-parameter group of bipartite transformations containing an entangling gate. This result relies on universality of any entangling gate for quantum computation. Here we prove universality of C-NOT with local gates for Real Quantum Theory (RQT), showing that the universality requirement would not be sufficient for the result, whereas local discriminability and the local qubit structure play a crucial role. For reversible computation, generally an extra rebit is needed for RQT. As a by-product we also provide a short proof of universality of C-NOT for CQT.

  19. Hybrid quantum computing: semicloning for general database retrieval

    NASA Astrophysics Data System (ADS)

    Lanzagorta, Marco; Uhlmann, Jeffrey K.

    2005-05-01

    Quantum computing (QC) has become an important area of research in computer science because of its potential to provide more efficient algorithmic solutions to certain problems than are possible with classical computing (CC). In particular, QC is able to exploit the special properties of quantum superposition to achieve computational parallelism beyond what can be achieved with parallel CC computers. However, these special properties are not applicable for general computation. Therefore, we propose the use of "hybrid quantum computers" (HQCs) that combine both classical and quantum computing architectures in order to leverage the benefits of both. We demonstrate how an HQC can exploit quantum search to support general database operations more efficiently than is possible with CC. Our solution is based on new quantum results that are of independent significance to the field of quantum computing. More specifically, we demonstrate that the most restrictive implications of the quantum No-Cloning Theorem can be avoided through the use of semiclones.

  20. Adiabatic quantum computing with spin qubits hosted by molecules.

    PubMed

    Yamamoto, Satoru; Nakazawa, Shigeaki; Sugisaki, Kenji; Sato, Kazunobu; Toyota, Kazuo; Shiomi, Daisuke; Takui, Takeji

    2015-01-28

    A molecular spin quantum computer (MSQC) requires electron spin qubits, which pulse-based electron spin/magnetic resonance (ESR/MR) techniques can afford to manipulate for implementing quantum gate operations in open shell molecular entities. Importantly, nuclear spins, which are topologically connected, particularly in organic molecular spin systems, are client qubits, while electron spins play a role of bus qubits. Here, we introduce the implementation for an adiabatic quantum algorithm, suggesting the possible utilization of molecular spins with optimized spin structures for MSQCs. We exemplify the utilization of an adiabatic factorization problem of 21, compared with the corresponding nuclear magnetic resonance (NMR) case. Two molecular spins are selected: one is a molecular spin composed of three exchange-coupled electrons as electron-only qubits and the other an electron-bus qubit with two client nuclear spin qubits. Their electronic spin structures are well characterized in terms of the quantum mechanical behaviour in the spin Hamiltonian. The implementation of adiabatic quantum computing/computation (AQC) has, for the first time, been achieved by establishing ESR/MR pulse sequences for effective spin Hamiltonians in a fully controlled manner of spin manipulation. The conquered pulse sequences have been compared with the NMR experiments and shown much faster CPU times corresponding to the interaction strength between the spins. Significant differences are shown in rotational operations and pulse intervals for ESR/MR operations. As a result, we suggest the advantages and possible utilization of the time-evolution based AQC approach for molecular spin quantum computers and molecular spin quantum simulators underlain by sophisticated ESR/MR pulsed spin technology.

  1. The quantum computer game: citizen science

    NASA Astrophysics Data System (ADS)

    Damgaard, Sidse; Mølmer, Klaus; Sherson, Jacob

    2013-05-01

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

  2. Towards fault tolerant adiabatic quantum computation.

    PubMed

    Lidar, Daniel A

    2008-04-25

    I show how to protect adiabatic quantum computation (AQC) against decoherence and certain control errors, using a hybrid methodology involving dynamical decoupling, subsystem and stabilizer codes, and energy gaps. Corresponding error bounds are derived. As an example, I show how to perform decoherence-protected AQC against local noise using at most two-body interactions.

  3. Blind quantum computing with weak coherent pulses.

    PubMed

    Dunjko, Vedran; Kashefi, Elham; Leverrier, Anthony

    2012-05-18

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

  4. Simulations of Probabilities for Quantum Computing

    NASA Technical Reports Server (NTRS)

    Zak, M.

    1996-01-01

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

  5. Computer Technology for Industry

    NASA Technical Reports Server (NTRS)

    1982-01-01

    Shell Oil Company used a COSMIC program, called VISCEL to insure the accuracy of the company's new computer code for analyzing polymers, and chemical compounds. Shell reported that there were no other programs available that could provide the necessary calculations. Shell produces chemicals for plastic products used in the manufacture of automobiles, housewares, appliances, film, textiles, electronic equipment and furniture.

  6. Quantum optics: science and technology in a new light.

    PubMed

    Walmsley, I A

    2015-05-01

    Light facilitates exploration of quantum phenomena that illuminate the basic properties of nature and also enables radical new technologies based on these phenomena. The critical features of quantum light that underpin the opportunities for discovery and application are exceptionally low noise and strong correlations. Rapid progress in both science and technology has been stimulated by adopting components developed for optical telecommunications and networking, such as highly efficient detectors, integrated photonic circuits, and waveguide- or nanostructure-based nonlinear optical devices. These provide the means to generate new quantum states of light and matter of unprecedented scale, containing many photons with quantum correlations across space and time. Notably, networks with only several tens of photons are already beyond what can be efficiently analyzed by current computers. PMID:25931550

  7. Quantum optics: Science and technology in a new light

    NASA Astrophysics Data System (ADS)

    Walmsley, I. A.

    2015-05-01

    Light facilitates exploration of quantum phenomena that illuminate the basic properties of nature and also enables radical new technologies based on these phenomena. The critical features of quantum light that underpin the opportunities for discovery and application are exceptionally low noise and strong correlations. Rapid progress in both science and technology has been stimulated by adopting components developed for optical telecommunications and networking, such as highly efficient detectors, integrated photonic circuits, and waveguide- or nanostructure-based nonlinear optical devices. These provide the means to generate new quantum states of light and matter of unprecedented scale, containing many photons with quantum correlations across space and time. Notably, networks with only several tens of photons are already beyond what can be efficiently analyzed by current computers.

  8. Deterministic quantum computation with one photonic qubit

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

  9. Optical technologies for quantum information science

    NASA Astrophysics Data System (ADS)

    Kwiat, Paul G.; Altepeter, Joseph; Barreiro, Julio; Branning, David A.; Jeffrey, Evan R.; Peters, Nicholas; VanDevender, Aaron P.

    2004-02-01

    A number of optical technologies remain to be developed and optimized for various applications in quantum information processing, especially quantum communication. We will give an overview of our approach to some of these, including periodic heralded single-photon sources based on spontaneous parametric down-conversion, ultrabright sources of tunable entangled photons, near unit efficiency single- and multi-photon detectors based on an atomic vapor interaction, quantum state transducers based on high efficiency frequency up-conversion, and low-loss optical quantum memories.

  10. Scheme for Quantum Computing Immune to Decoherence

    NASA Technical Reports Server (NTRS)

    Williams, Colin; Vatan, Farrokh

    2008-01-01

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

  11. Quantum information processing : science & technology.

    SciTech Connect

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

    2010-09-01

    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.

  12. Photonic quantum information: science and technology

    PubMed Central

    TAKEUCHI, Shigeki

    2016-01-01

    Recent technological progress in the generation, manipulation and detection of individual single photons has opened a new scientific field of photonic quantum information. This progress includes the realization of single photon switches, photonic quantum circuits with specific functions, and the application of novel photonic states to novel optical metrology beyond the limits of standard optics. In this review article, the recent developments and current status of photonic quantum information technology are overviewed based on the author’s past and recent works. PMID:26755398

  13. Ubiquitous Computing Technologies in Education

    ERIC Educational Resources Information Center

    Hwang, Gwo-Jen; Wu, Ting-Ting; Chen, Yen-Jung

    2007-01-01

    The prosperous development of wireless communication and sensor technologies has attracted the attention of researchers from both computer and education fields. Various investigations have been made for applying the new technologies to education purposes, such that more active and adaptive learning activities can be conducted in the real world.…

  14. Non-abelian fractional quantum hall effect for fault-resistant topological quantum computation.

    SciTech Connect

    Pan, Wei; Thalakulam, Madhu; Shi, Xiaoyan; Crawford, Matthew; Nielsen, Erik; Cederberg, Jeffrey George

    2013-10-01

    Topological quantum computation (TQC) has emerged as one of the most promising approaches to quantum computation. Under this approach, the topological properties of a non-Abelian quantum system, which are insensitive to local perturbations, are utilized to process and transport quantum information. The encoded information can be protected and rendered immune from nearly all environmental decoherence processes without additional error-correction. It is believed that the low energy excitations of the so-called =5/2 fractional quantum Hall (FQH) state may obey non-Abelian statistics. Our goal is to explore this novel FQH state and to understand and create a scientific foundation of this quantum matter state for the emerging TQC technology. We present in this report the results from a coherent study that focused on obtaining a knowledge base of the physics that underpins TQC. We first present the results of bulk transport properties, including the nature of disorder on the 5/2 state and spin transitions in the second Landau level. We then describe the development and application of edge tunneling techniques to quantify and understand the quasiparticle physics of the 5/2 state.

  15. Measurement and Information Extraction in Complex Dynamics Quantum Computation

    NASA Astrophysics Data System (ADS)

    Casati, Giulio; Montangero, Simone

    Quantum Information processing has several di.erent applications: some of them can be performed controlling only few qubits simultaneously (e.g. quantum teleportation or quantum cryptography) [1]. Usually, the transmission of large amount of information is performed repeating several times the scheme implemented for few qubits. However, to exploit the advantages of quantum computation, the simultaneous control of many qubits is unavoidable [2]. This situation increases the experimental di.culties of quantum computing: maintaining quantum coherence in a large quantum system is a di.cult task. Indeed a quantum computer is a many-body complex system and decoherence, due to the interaction with the external world, will eventually corrupt any quantum computation. Moreover, internal static imperfections can lead to quantum chaos in the quantum register thus destroying computer operability [3]. Indeed, as it has been shown in [4], a critical imperfection strength exists above which the quantum register thermalizes and quantum computation becomes impossible. We showed such e.ects on a quantum computer performing an e.cient algorithm to simulate complex quantum dynamics [5,6].

  16. Quantum computation: algorithms and implementation in quantum dot devices

    NASA Astrophysics Data System (ADS)

    Gamble, John King

    In this thesis, we explore several aspects of both the software and hardware of quantum computation. First, we examine the computational power of multi-particle quantum random walks in terms of distinguishing mathematical graphs. We study both interacting and non-interacting multi-particle walks on strongly regular graphs, proving some limitations on distinguishing powers and presenting extensive numerical evidence indicative of interactions providing more distinguishing power. We then study the recently proposed adiabatic quantum algorithm for Google PageRank, and show that it exhibits power-law scaling for realistic WWW-like graphs. Turning to hardware, we next analyze the thermal physics of two nearby 2D electron gas (2DEG), and show that an analogue of the Coulomb drag effect exists for heat transfer. In some distance and temperature, this heat transfer is more significant than phonon dissipation channels. After that, we study the dephasing of two-electron states in a single silicon quantum dot. Specifically, we consider dephasing due to the electron-phonon coupling and charge noise, separately treating orbital and valley excitations. In an ideal system, dephasing due to charge noise is strongly suppressed due to a vanishing dipole moment. However, introduction of disorder or anharmonicity leads to large effective dipole moments, and hence possibly strong dephasing. Building on this work, we next consider more realistic systems, including structural disorder systems. We present experiment and theory, which demonstrate energy levels that vary with quantum dot translation, implying a structurally disordered system. Finally, we turn to the issues of valley mixing and valley-orbit hybridization, which occurs due to atomic-scale disorder at quantum well interfaces. We develop a new theoretical approach to study these effects, which we name the disorder-expansion technique. We demonstrate that this method successfully reproduces atomistic tight-binding techniques

  17. Scalable Quantum Computing Over the Rainbow

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

    The physical implementation of nontrivial quantum computing is an experimental challenge due to decoherence and the need for scalability. Recently we proved a novel theoretical scheme for realizing a scalable quantum register of very large size, entangled in a cluster state, in the optical frequency comb (OFC) defined by the eigenmodes of a single optical parametric oscillator (OPO). The classical OFC is well known as implemented by the femtosecond, carrier-envelope-phase- and mode-locked lasers which have redefined frequency metrology in recent years. The quantum OFC is a set of harmonic oscillators, or Qmodes, whose amplitude and phase quadratures are continuous variables, the manipulation of which is a mature field for one or two Qmodes. We have shown that the nonlinear optical medium of a single OPO can be engineered, in a sophisticated but already demonstrated manner, so as to entangle in constant time the OPO's OFC into a finitely squeezed, Gaussian cluster state suitable for universal quantum computing over continuous variables. Here we summarize our theoretical result and survey the ongoing experimental efforts in this direction.

  18. Dual field theories of quantum computation

    NASA Astrophysics Data System (ADS)

    Vanchurin, Vitaly

    2016-06-01

    Given two quantum states of N q-bits we are interested to find the shortest quantum circuit consisting of only one- and two- q-bit gates that would transfer one state into another. We call it the quantum maze problem for the reasons described in the paper. We argue that in a large N limit the quantum maze problem is equivalent to the problem of finding a semiclassical trajectory of some lattice field theory (the dual theory) on an N +1 dimensional space-time with geometrically flat, but topologically compact spatial slices. The spatial fundamental domain is an N dimensional hyper-rhombohedron, and the temporal direction describes transitions from an arbitrary initial state to an arbitrary target state and so the initial and final dual field theory conditions are described by these two quantum computational states. We first consider a complex Klein-Gordon field theory and argue that it can only be used to study the shortest quantum circuits which do not involve generators composed of tensor products of multiple Pauli Z matrices. Since such situation is not generic we call it the Z-problem. On the dual field theory side the Z-problem corresponds to massless excitations of the phase (Goldstone modes) that we attempt to fix using Higgs mechanism. The simplest dual theory which does not suffer from the massless excitation (or from the Z-problem) is the Abelian-Higgs model which we argue can be used for finding the shortest quantum circuits. Since every trajectory of the field theory is mapped directly to a quantum circuit, the shortest quantum circuits are identified with semiclassical trajectories. We also discuss the complexity of an actual algorithm that uses a dual theory prospective for solving the quantum maze problem and compare it with a geometric approach. We argue that it might be possible to solve the problem in sub-exponential time in 2 N , but for that we must consider the Klein-Gordon theory on curved spatial geometry and/or more complicated (than N -torus

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

    DOEpatents

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

    2014-08-26

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

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

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

  1. Non-unitary probabilistic quantum computing circuit and method

    NASA Technical Reports Server (NTRS)

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

    2009-01-01

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

  2. Atomic Fock states and quantum computing

    NASA Astrophysics Data System (ADS)

    Wan, Shoupu

    The potential impact of quantum computing has stimulated a world-wide effort to develop the necessary experimental and theoretical resources. In the race for the quantum computer, several candidate systems have emerged, but the ultimate system is still unclear. We study theoretically how to realize atomic Fock states both for fermionic and bosonic atoms, mainly in one-dimensional optical traps. We demonstrate a new approach of quantum computing based on ultracold fermionic atomic Fock states in optical traps. With the Pauli exclusion principle, producing fermionic atomic Fock states in optical traps is straightforward. We find that laser culling of fermionic atoms in optical traps can produce a scalable number of ultra-high fidelity qubits. We show how each qubit can be independently prepared, and how to perform the required entanglement operations and detect the qubit states with spatially resolved, single-atom detection with adiabatic trap-splitting and fluorescence imaging. On the other hand, bosonic atoms have a strong tendency to stay together. One must rely on strong repulsive interactions to produce bosonic atomic Fock states. To simulate the physical conditions of producing Fock states with ultracold bosonic atoms, we study a many-boson system with arbitrary interaction strength using the Bethe ansatz method. This approach provides a general framework, enabling the study of Fock state production over a wide range of realistic experimental parameters.

  3. Universal quantum computation with metaplectic anyons

    NASA Astrophysics Data System (ADS)

    Cui, Shawn X.; Wang, Zhenghan

    2015-03-01

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

  4. Universal quantum computation with metaplectic anyons

    SciTech Connect

    Cui, Shawn X.; Wang, Zhenghan E-mail: zhenghwa@microsoft.com

    2015-03-15

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

  5. EDITORIAL: Quantum science and technology at the nanoscale Quantum science and technology at the nanoscale

    NASA Astrophysics Data System (ADS)

    Demming, Anna

    2010-07-01

    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

  6. Hard chaos, quantum billiards, and quantum dot computers

    SciTech Connect

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

    1996-07-01

    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.

  7. Hybrid optomechanics for Quantum Technologies

    NASA Astrophysics Data System (ADS)

    Rogers, B.; Lo Gullo, N.; De Chiara, G.; Palma, G. M.; Paternostro, M.

    2014-06-01

    We review the physics of hybrid optomechanical systems consisting of a mechanical oscillator interacting with both a radiation mode and an additional matterlike system. We concentrate on the cases embodied by either a single or a multi-atom system (a Bose-Einstein condensate, in particular) and discuss a wide range of physical effects, from passive mechanical cooling to the set-up of multipartite entanglement, from optomechanical nonlocality to the achievement of non-classical states of a single mechanical mode. The reviewed material showcases the viability of hybridised cavity optomechanical systems as basic building blocks for quantum communication networks and quantum state-engineering devices, possibly empowered by the use of quantum and optimal control techniques. The results that we discuss are instrumental to the promotion of hybrid optomechanical devices as promising experimental platforms for the study of nonclassicality at the genuine mesoscopic level.

  8. Trusted Computing Technologies, Intel Trusted Execution Technology.

    SciTech Connect

    Guise, Max Joseph; Wendt, Jeremy Daniel

    2011-01-01

    We describe the current state-of-the-art in Trusted Computing Technologies - focusing mainly on Intel's Trusted Execution Technology (TXT). This document is based on existing documentation and tests of two existing TXT-based systems: Intel's Trusted Boot and Invisible Things Lab's Qubes OS. We describe what features are lacking in current implementations, describe what a mature system could provide, and present a list of developments to watch. Critical systems perform operation-critical computations on high importance data. In such systems, the inputs, computation steps, and outputs may be highly sensitive. Sensitive components must be protected from both unauthorized release, and unauthorized alteration: Unauthorized users should not access the sensitive input and sensitive output data, nor be able to alter them; the computation contains intermediate data with the same requirements, and executes algorithms that the unauthorized should not be able to know or alter. Due to various system requirements, such critical systems are frequently built from commercial hardware, employ commercial software, and require network access. These hardware, software, and network system components increase the risk that sensitive input data, computation, and output data may be compromised.

  9. Compact quantum circuits from one-way quantum computation

    NASA Astrophysics Data System (ADS)

    Dias da Silva, Raphael; Galvão, Ernesto F.

    2013-07-01

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

  10. Novel systems and methods for quantum communication, quantum computation, and quantum simulation

    NASA Astrophysics Data System (ADS)

    Gorshkov, Alexey Vyacheslavovich

    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 quantum computation and communication tasks. In contrast to photon storage, many quantum computation 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 quantum computing 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

  11. Applicability of Rydberg atoms to quantum computers

    NASA Astrophysics Data System (ADS)

    Ryabtsev, Igor I.; Tretyakov, Denis B.; Beterov, Ilya I.

    2005-01-01

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

  12. Software Systems for High-performance Quantum Computing

    SciTech Connect

    Humble, Travis S; Britt, Keith A

    2016-01-01

    Quantum computing promises new opportunities for solving hard computational problems, but harnessing this novelty requires breakthrough concepts in the design, operation, and application of computing systems. We define some of the challenges facing the development of quantum computing systems as well as software-based approaches that can be used to overcome these challenges. Following a brief overview of the state of the art, we present models for the quantum programming and execution models, the development of architectures for hybrid high-performance computing systems, and the realization of software stacks for quantum networking. This leads to a discussion of the role that conventional computing plays in the quantum paradigm and how some of the current challenges for exascale computing overlap with those facing quantum computing.

  13. Universal fault-tolerant adiabatic quantum computing with quantum dots or donors

    NASA Astrophysics Data System (ADS)

    Landahl, Andrew

    I will present a conceptual design for an adiabatic quantum computer that can achieve arbitrarily accurate universal fault-tolerant quantum computations with a constant energy gap and nearest-neighbor interactions. This machine can run any quantum algorithm known today or discovered in the future, in principle. The key theoretical idea is adiabatic deformation of degenerate ground spaces formed by topological quantum error-correcting codes. An open problem with the design is making the four-body interactions and measurements it uses more technologically accessible. I will present some partial solutions, including one in which interactions between quantum dots or donors in a two-dimensional array can emulate the desired interactions in second-order perturbation theory. I will conclude with some open problems, including the challenge of reformulating Kitaev's gadget perturbation theory technique so that it preserves fault tolerance. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  14. Quantum computation over the butterfly network

    SciTech Connect

    Soeda, Akihito; Kinjo, Yoshiyuki; Turner, Peter S.; Murao, Mio

    2011-07-15

    In order to investigate distributed quantum computation under restricted network resources, we introduce a quantum computation task over the butterfly network where both quantum and classical communications are limited. We consider deterministically performing a two-qubit global unitary operation on two unknown inputs given at different nodes, with outputs at two distinct nodes. By using a particular resource setting introduced by M. Hayashi [Phys. Rev. A 76, 040301(R) (2007)], which is capable of performing a swap operation by adding two maximally entangled qubits (ebits) between the two input nodes, we show that unitary operations can be performed without adding any entanglement resource, if and only if the unitary operations are locally unitary equivalent to controlled unitary operations. Our protocol is optimal in the sense that the unitary operations cannot be implemented if we relax the specifications of any of the channels. We also construct protocols for performing controlled traceless unitary operations with a 1-ebit resource and for performing global Clifford operations with a 2-ebit resource.

  15. Multiple-server Flexible Blind Quantum Computation in Networks

    NASA Astrophysics Data System (ADS)

    Kong, Xiaoqin; Li, Qin; Wu, Chunhui; Yu, Fang; He, Jinjun; Sun, Zhiyuan

    2016-06-01

    Blind quantum computation (BQC) can allow a client with limited quantum power to delegate his quantum computation to a powerful server and still keep his own data private. In this paper, we present a multiple-server flexible BQC protocol, where a client who only needs the ability of accessing qua ntum channels can delegate the computational task to a number of servers. Especially, the client's quantum computation also can be achieved even when one or more delegated quantum servers break down in networks. In other words, when connections to certain quantum servers are lost, clients can adjust flexibly and delegate their quantum computation to other servers. Obviously it is trivial that the computation will be unsuccessful if all servers are interrupted.

  16. Milestones Toward Majorana-Based Quantum Computing

    NASA Astrophysics Data System (ADS)

    Aasen, David; Hell, Michael; Mishmash, Ryan V.; Higginbotham, Andrew; Danon, Jeroen; Leijnse, Martin; Jespersen, Thomas S.; Folk, Joshua A.; Marcus, Charles M.; Flensberg, Karsten; Alicea, Jason

    2016-07-01

    We introduce a scheme for preparation, manipulation, and read out of Majorana zero modes in semiconducting wires with mesoscopic superconducting islands. Our approach synthesizes recent advances in materials growth with tools commonly used in quantum-dot experiments, including gate control of tunnel barriers and Coulomb effects, charge sensing, and charge pumping. We outline a sequence of milestones interpolating between zero-mode detection and quantum computing that includes (1) detection of fusion rules for non-Abelian anyons using either proximal charge sensors or pumped current, (2) validation of a prototype topological qubit, and (3) demonstration of non-Abelian statistics by braiding in a branched geometry. The first two milestones require only a single wire with two islands, and additionally enable sensitive measurements of the system's excitation gap, quasiparticle poisoning rates, residual Majorana zero-mode splittings, and topological-qubit coherence times. These pre-braiding experiments can be adapted to other manipulation and read out schemes as well.

  17. Teacher Teams and Computer Technology.

    ERIC Educational Resources Information Center

    Hecht, Jeffrey B.; Roberts, Nicole K.; Schoon, Perry L.; Fansler, Gigi

    This research used three groups in a quasi-experimental approach to assess the combined impact of teacher teaming and computer technology on student grade point averages (GPAs). Ninth-grade students' academic achievement in each of four different subject areas (algebra, biology, world cultures, and English) was studied. Two separate treatments…

  18. Computer Technology. Career Education Guide.

    ERIC Educational Resources Information Center

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

    The curriculum guide is designed to provide students with realistic training in computer technology 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…

  19. Minimal computational-space implementation of multiround quantum protocols

    SciTech Connect

    Bisio, Alessandro; D'Ariano, Giacomo Mauro; Perinotti, Paolo; Chiribella, Giulio

    2011-02-15

    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.

  20. Optical Computers and Space Technology

    NASA Technical Reports Server (NTRS)

    Abdeldayem, Hossin A.; Frazier, Donald O.; Penn, Benjamin; Paley, Mark S.; Witherow, William K.; Banks, Curtis; Hicks, Rosilen; Shields, Angela

    1995-01-01

    The rapidly increasing demand for greater speed and efficiency on the information superhighway requires significant improvements over conventional electronic logic circuits. Optical interconnections and optical integrated circuits are strong candidates to provide the way out of the extreme limitations imposed on the growth of speed and complexity of nowadays computations by the conventional electronic logic circuits. The new optical technology has increased the demand for high quality optical materials. NASA's recent involvement in processing optical materials in space has demonstrated that a new and unique class of high quality optical materials are processible in a microgravity environment. Microgravity processing can induce improved orders in these materials and could have a significant impact on the development of optical computers. We will discuss NASA's role in processing these materials and report on some of the associated nonlinear optical properties which are quite useful for optical computers technology.

  1. High-speed linear optics quantum computing using active feed-forward.

    PubMed

    Prevedel, Robert; Walther, Philip; Tiefenbacher, Felix; Böhi, Pascal; Kaltenbaek, Rainer; Jennewein, Thomas; Zeilinger, Anton

    2007-01-01

    As information carriers in quantum computing, photonic qubits have the advantage of undergoing negligible decoherence. However, the absence of any significant photon-photon interaction is problematic for the realization of non-trivial two-qubit gates. One solution is to introduce an effective nonlinearity by measurements resulting in probabilistic gate operations. In one-way quantum computation, the random quantum measurement error can be overcome by applying a feed-forward technique, such that the future measurement basis depends on earlier measurement results. This technique is crucial for achieving deterministic quantum computation once a cluster state (the highly entangled multiparticle state on which one-way quantum computation is based) is prepared. Here we realize a concatenated scheme of measurement and active feed-forward in a one-way quantum computing experiment. We demonstrate that, for a perfect cluster state and no photon loss, our quantum computation scheme would operate with good fidelity and that our feed-forward components function with very high speed and low error for detected photons. With present technology, the individual computational step (in our case the individual feed-forward cycle) can be operated in less than 150 ns using electro-optical modulators. This is an important result for the future development of one-way quantum computers, whose large-scale implementation will depend on advances in the production and detection of the required highly entangled cluster states.

  2. One-way quantum computing in the optical frequency comb.

    PubMed

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

    2008-09-26

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

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

    SciTech Connect

    Das Sarma, Sankar

    2012-10-03

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

  4. Fast graph operations in quantum computation

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    The connection between certain entangled states and graphs has been heavily studied in the context of measurement-based quantum computation as a tool for understanding entanglement. Here we show that this correspondence can be harnessed in the reverse direction to yield a graph data structure, which allows for more efficient manipulation and comparison of graphs than any possible classical structure. We introduce efficient algorithms for many transformation and comparison operations on graphs represented as graph states, and prove that no classical data structure can have similar performance for the full set of operations studied.

  5. Do multipartite correlations speed up adiabatic quantum computation or quantum annealing?

    NASA Astrophysics Data System (ADS)

    Batle, J.; Ooi, C. H. Raymond; Farouk, Ahmed; Abutalib, M.; Abdalla, S.

    2016-08-01

    Quantum correlations are thought to be the reason why certain quantum algorithms overcome their classical counterparts. Since the nature of this resource is still not fully understood, we shall investigate how multipartite entanglement and non-locality among qubits vary as the quantum computation runs. We shall encounter that quantum measures on the whole system cannot account for their corresponding speedup.

  6. The Potential for Quantum Technology Gravity Sensors

    NASA Astrophysics Data System (ADS)

    Boddice, Daniel; Metje, Nicole; Tuckwell, George

    2016-04-01

    Gravity measurements are widely used in geophysics for the detection of subsurface cavities such as sinkhole and past mine workings. The chief advantage of gravity compared to other geophysical techniques is that it is passive method which cannot be shielded by intervening features or ground giving it no theoretical limitations on penetration depth beyond the resolution of the instrument, and that it responds to an absence of mass as opposed to a proxy ground property like other techniques. However, current instruments are limited both by their resolution and by sources of environmental noise. This can be overcome with the imminent arrival of gravity sensors using quantum technology (QT) currently developed and constructed by the QT-Hub in Sensors and Metrology, which promise a far greater resolution. The QT sensor uses a technique called atom interferometry, where cold atoms are used as ideal test-masses to create a gravity sensor which can measure a gravity gradient rather than an absolute value. This suppresses several noise sources and creates a sensor useful in everyday applications. The paper will present computer simulations of buried targets and noise sources to explore the potential uses of these new sensors for a range of applications including pipes, tunnels and mine shafts. This will provide information on the required resolution and sensitivity of any new sensor if it is to deliver the promised step change in geophysical detection capability.

  7. Center for Advanced Computational Technology

    NASA Technical Reports Server (NTRS)

    Noor, Ahmed K.

    2000-01-01

    The Center for Advanced Computational Technology (ACT) was established to serve as a focal point for diverse research activities pertaining to application of advanced computational technology to future aerospace systems. These activities include the use of numerical simulations, artificial intelligence methods, multimedia and synthetic environments, and computational intelligence, in the modeling, analysis, sensitivity studies, optimization, design and operation of future aerospace systems. The Center is located at NASA Langley and is an integral part of the School of Engineering and Applied Science of the University of Virginia. The Center has four specific objectives: 1) conduct innovative research on applications of advanced computational technology to aerospace systems; 2) act as pathfinder by demonstrating to the research community what can be done (high-potential, high-risk research); 3) help in identifying future directions of research in support of the aeronautical and space missions of the twenty-first century; and 4) help in the rapid transfer of research results to industry and in broadening awareness among researchers and engineers of the state-of-the-art in applications of advanced computational technology to the analysis, design prototyping and operations of aerospace and other high-performance engineering systems. In addition to research, Center activities include helping in the planning and coordination of the activities of a multi-center team of NASA and JPL researchers who are developing an intelligent synthesis environment for future aerospace systems; organizing workshops and national symposia; as well as writing state-of-the-art monographs and NASA special publications on timely topics.

  8. Graph isomorphism and adiabatic quantum computing

    NASA Astrophysics Data System (ADS)

    Gaitan, Frank; Clark, Lane

    2014-03-01

    In the Graph Isomorphism (GI) problem two N-vertex graphs G and G' are given and the task is to determine whether there exists a permutation of the vertices of G that preserves adjacency and maps G --> G'. If yes (no), then G and G' are said to be isomorphic (non-isomorphic). The GI problem is an important problem in computer science and is thought to be of comparable difficulty to integer factorization. We present a quantum algorithm that solves arbitrary instances of GI, and which provides a novel approach to determining all automorphisms of a graph. The algorithm converts a GI instance to a combinatorial optimization problem that can be solved using adiabatic quantum evolution. Numerical simulation of the algorithm's quantum dynamics shows that it correctly distinguishes non-isomorphic graphs; recognizes isomorphic graphs; and finds the automorphism group of a graph. We also discuss the algorithm's experimental implementation and show how it can be leveraged to solve arbitrary instances of the NP-Complete Sub-Graph Isomorphism problem.

  9. Parallelism for quantum computation with qudits

    SciTech Connect

    O'Leary, Dianne P.; Brennen, Gavin K.; Bullock, Stephen S.

    2006-09-15

    Robust quantum computation 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.

  10. Topological quantum computing with only one mobile quasiparticle.

    PubMed

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

    2006-02-24

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

  11. Multiple network alignment on quantum computers

    NASA Astrophysics Data System (ADS)

    Daskin, Anmer; Grama, Ananth; Kais, Sabre

    2014-12-01

    Comparative analyses of graph-structured datasets underly diverse problems. Examples of these problems include identification of conserved functional components (biochemical interactions) across species, structural similarity of large biomolecules, and recurring patterns of interactions in social networks. A large class of such analyses methods quantify the topological similarity of nodes across networks. The resulting correspondence of nodes across networks, also called node alignment, can be used to identify invariant subgraphs across the input graphs. Given graphs as input, alignment algorithms use topological information to assign a similarity score to each -tuple of nodes, with elements (nodes) drawn from each of the input graphs. Nodes are considered similar if their neighbors are also similar. An alternate, equivalent view of these network alignment algorithms is to consider the Kronecker product of the input graphs and to identify high-ranked nodes in the Kronecker product graph. Conventional methods such as PageRank and HITS (Hypertext-Induced Topic Selection) can be used for this purpose. These methods typically require computation of the principal eigenvector of a suitably modified Kronecker product matrix of the input graphs. We adopt this alternate view of the problem to address the problem of multiple network alignment. Using the phase estimation algorithm, we show that the multiple network alignment problem can be efficiently solved on quantum computers. We characterize the accuracy and performance of our method and show that it can deliver exponential speedups over conventional (non-quantum) methods.

  12. Measurement-only topological quantum computation via anyonic interferometry

    SciTech Connect

    Bonderson, Parsa Freedman, Michael Nayak, Chetan

    2009-04-15

    We describe measurement-only topological quantum computation 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 quantum computation, and hence that the physical transportation of computational anyons is unnecessary. We give a detailed discussion of the anyonics for implementation of topological quantum computation (particularly, using the measurement-only approach) in fractional quantum Hall systems.

  13. Quantum computation of multifractal exponents through the quantum wavelet transform

    SciTech Connect

    Garcia-Mata, Ignacio; Giraud, Olivier; Georgeot, Bertrand

    2009-05-15

    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.

  14. Infinite possibilities: Computational structures technology

    NASA Astrophysics Data System (ADS)

    Beam, Sherilee F.

    1994-12-01

    Computational Fluid Dynamics (or CFD) methods are very familiar to the research community. Even the general public has had some exposure to CFD images, primarily through the news media. However, very little attention has been paid to CST--Computational Structures Technology. Yet, no important design can be completed without it. During the first half of this century, researchers only dreamed of designing and building structures on a computer. Today their dreams have become practical realities as computational methods are used in all phases of design, fabrication and testing of engineering systems. Increasingly complex structures can now be built in even shorter periods of time. Over the past four decades, computer technology has been developing, and early finite element methods have grown from small in-house programs to numerous commercial software programs. When coupled with advanced computing systems, they help engineers make dramatic leaps in designing and testing concepts. The goals of CST include: predicting how a structure will behave under actual operating conditions; designing and complementing other experiments conducted on a structure; investigating microstructural damage or chaotic, unpredictable behavior; helping material developers in improving material systems; and being a useful tool in design systems optimization and sensitivity techniques. Applying CST to a structure problem requires five steps: (1) observe the specific problem; (2) develop a computational model for numerical simulation; (3) develop and assemble software and hardware for running the codes; (4) post-process and interpret the results; and (5) use the model to analyze and design the actual structure. Researchers in both industry and academia continue to make significant contributions to advance this technology with improvements in software, collaborative computing environments and supercomputing systems. As these environments and systems evolve, computational structures technology will

  15. Infinite possibilities: Computational structures technology

    NASA Technical Reports Server (NTRS)

    Beam, Sherilee F.

    1994-01-01

    Computational Fluid Dynamics (or CFD) methods are very familiar to the research community. Even the general public has had some exposure to CFD images, primarily through the news media. However, very little attention has been paid to CST--Computational Structures Technology. Yet, no important design can be completed without it. During the first half of this century, researchers only dreamed of designing and building structures on a computer. Today their dreams have become practical realities as computational methods are used in all phases of design, fabrication and testing of engineering systems. Increasingly complex structures can now be built in even shorter periods of time. Over the past four decades, computer technology has been developing, and early finite element methods have grown from small in-house programs to numerous commercial software programs. When coupled with advanced computing systems, they help engineers make dramatic leaps in designing and testing concepts. The goals of CST include: predicting how a structure will behave under actual operating conditions; designing and complementing other experiments conducted on a structure; investigating microstructural damage or chaotic, unpredictable behavior; helping material developers in improving material systems; and being a useful tool in design systems optimization and sensitivity techniques. Applying CST to a structure problem requires five steps: (1) observe the specific problem; (2) develop a computational model for numerical simulation; (3) develop and assemble software and hardware for running the codes; (4) post-process and interpret the results; and (5) use the model to analyze and design the actual structure. Researchers in both industry and academia continue to make significant contributions to advance this technology with improvements in software, collaborative computing environments and supercomputing systems. As these environments and systems evolve, computational structures technology will

  16. Computer Visualization of Many-Particle Quantum Dynamics

    SciTech Connect

    Ozhigov, A. Y.

    2009-03-10

    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.

  17. Computer Visualization of Many-Particle Quantum Dynamics

    NASA Astrophysics Data System (ADS)

    Ozhigov, A. Y.

    2009-03-01

    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.

  18. Heterotic quantum and classical computing on convergence spaces

    NASA Astrophysics Data System (ADS)

    Patten, D. R.; Jakel, D. W.; Irwin, R. J.; Blair, H. A.

    2015-05-01

    Category-theoretic characterizations of heterotic models of computation, introduced by Stepney et al., combine computational models such as classical/quantum, digital/analog, synchronous/asynchronous, etc. to obtain increased computational power. A highly informative classical/quantum heterotic model of computation is represented by Abramsky's simple sequential imperative quantum programming language which extends the classical simple imperative programming language to encompass quantum computation. The mathematical (denotational) semantics of this classical language serves as a basic foundation upon which formal verification methods can be developed. We present a more comprehensive heterotic classical/quantum model of computation based on heterotic dynamical systems on convergence spaces. Convergence spaces subsume topological spaces but admit finer structure from which, in prior work, we obtained differential calculi in the cartesian closed category of convergence spaces allowing us to define heterotic dynamical systems, given by coupled systems of first order differential equations whose variables are functions from the reals to convergence spaces.

  19. QCMPI: A parallel environment for quantum computing

    NASA Astrophysics Data System (ADS)

    Tabakin, Frank; Juliá-Díaz, Bruno

    2009-06-01

    QCMPI is a quantum computer (QC) simulation package written in Fortran 90 with parallel processing capabilities. It is an accessible research tool that permits rapid evaluation of quantum algorithms for a large number of qubits and for various "noise" scenarios. The prime motivation for developing QCMPI is to facilitate numerical examination of not only how QC algorithms work, but also to include noise, decoherence, and attenuation effects and to evaluate the efficacy of error correction schemes. The present work builds on an earlier Mathematica code QDENSITY, which is mainly a pedagogic tool. In that earlier work, although the density matrix formulation was featured, the description using state vectors was also provided. In QCMPI, the stress is on state vectors, in order to employ a large number of qubits. The parallel processing feature is implemented by using the Message-Passing Interface (MPI) protocol. A description of how to spread the wave function components over many processors is provided, along with how to efficiently describe the action of general one- and two-qubit operators on these state vectors. These operators include the standard Pauli, Hadamard, CNOT and CPHASE gates and also Quantum Fourier transformation. These operators make up the actions needed in QC. Codes for Grover's search and Shor's factoring algorithms are provided as examples. A major feature of this work is that concurrent versions of the algorithms can be evaluated with each version subject to alternate noise effects, which corresponds to the idea of solving a stochastic Schrödinger equation. The density matrix for the ensemble of such noise cases is constructed using parallel distribution methods to evaluate its eigenvalues and associated entropy. Potential applications of this powerful tool include studies of the stability and correction of QC processes using Hamiltonian based dynamics. Program summaryProgram title: QCMPI Catalogue identifier: AECS_v1_0 Program summary URL

  20. Computer Access. Tech Use Guide: Using Computer Technology.

    ERIC Educational Resources Information Center

    Council for Exceptional Children, Reston, VA. Center for Special Education Technology.

    One of nine brief guides for special educators on using computer technology, this guide focuses on access including adaptations in input devices, output devices, and computer interfaces. Low technology devices include "no-technology" devices (usually modifications to existing devices), simple switches, and multiple switches. High technology input…

  1. Experimental test of Mermin inequalities on a five-qubit quantum computer

    NASA Astrophysics Data System (ADS)

    Alsina, Daniel; Latorre, José Ignacio

    2016-07-01

    Violation of Mermin inequalities is tested on the five-qubit IBM quantum computer. For three, four, and five parties, quantum states that violate the corresponding Mermin inequalities are constructed using quantum circuits on superconducting qubits. Measurements on different bases are included as additional final gates in the circuits. The experimental results obtained using the quantum computer show violation of all Mermin inequalities, with a clear degradation of the results in the five-qubit case. Though this quantum computer is not competitive to test Mermin inequalities as compared to other techniques when applied to a few qubits, it does offer the opportunity to explore multipartite entanglement for four and five qubits beyond the reach of other alternative technologies.

  2. Random matrix model of adiabatic quantum computing

    SciTech Connect

    Mitchell, David R.; Adami, Christoph; Lue, Waynn; Williams, Colin P.

    2005-05-15

    We present an analysis of the quantum adiabatic algorithm for solving hard instances of 3-SAT (an NP-complete problem) in terms of random matrix theory (RMT). We determine the global regularity of the spectral fluctuations of the instantaneous Hamiltonians encountered during the interpolation between the starting Hamiltonians and the ones whose ground states encode the solutions to the computational problems of interest. At each interpolation point, we quantify the degree of regularity of the average spectral distribution via its Brody parameter, a measure that distinguishes regular (i.e., Poissonian) from chaotic (i.e., Wigner-type) distributions of normalized nearest-neighbor spacings. We find that for hard problem instances - i.e., those having a critical ratio of clauses to variables - the spectral fluctuations typically become irregular across a contiguous region of the interpolation parameter, while the spectrum is regular for easy instances. Within the hard region, RMT may be applied to obtain a mathematical model of the probability of avoided level crossings and concomitant failure rate of the adiabatic algorithm due to nonadiabatic Landau-Zener-type transitions. Our model predicts that if the interpolation is performed at a uniform rate, the average failure rate of the quantum adiabatic algorithm, when averaged over hard problem instances, scales exponentially with increasing problem size.

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

    NASA Astrophysics Data System (ADS)

    Poulin, David

    2009-03-01

    The simulation of quantum many-body systems is a notoriously hard problem in condensed matter physics, but it could easily be handled by a quantum computer [4,1]. There is however one catch: while a quantum computer can naturally implement the dynamics of a quantum system --- i.e. solve Schr"odinger's equation --- there was until now no general method to initialize the computer in a low-energy state of the simulated system. We present a quantum algorithm [5] that can prepare the ground state and thermal states of a quantum many-body system in a time proportional to the square-root of its Hilbert space dimension. This is the same scaling as required by the best known algorithm to prepare the ground state of a classical many-body system on a quantum computer [3,2]. This provides strong evidence that for a quantum computer, preparing the ground state of a quantum system is in the worst case no more difficult than preparing the ground state of a classical system. 1 D. Aharonov and A. Ta-Shma, Adiabatic quantum state generation and statistical zero knowledge, Proc. 35th Annual ACM Symp. on Theo. Comp., (2003), p. 20. F. Barahona, On the computational complexity of ising spin glass models, J. Phys. A. Math. Gen., 15 (1982), p. 3241. C. H. Bennett, E. Bernstein, G. Brassard, and U. Vazirani, Strengths and weaknessess of quantum computing, SIAM J. Comput., 26 (1997), pp. 1510--1523, quant-ph/9701001. S. Lloyd, Universal quantum simulators, Science, 273 (1996), pp. 1073--1078. D. Poulin and P. Wocjan, Preparing ground states of quantum many-body systems on a quantum computer, 2008, arXiv:0809.2705.

  4. Number Partitioning via Quantum Adiabatic Computation

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

  5. Trapped Ion Quantum Computation by Adiabatic Passage

    SciTech Connect

    Feng Xuni; Wu Chunfeng; Lai, C. H.; Oh, C. H.

    2008-11-07

    We propose a new universal quantum computation 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.

  6. Scalable quantum computation via local control of only two qubits

    SciTech Connect

    Burgarth, Daniel; Maruyama, Koji; Murphy, Michael; Montangero, Simone; Calarco, Tommaso; Nori, Franco; Plenio, Martin B.

    2010-04-15

    We apply quantum control techniques to a long spin chain by acting only on two qubits at one of its ends, thereby implementing universal quantum computation by a combination of quantum gates on these qubits and indirect swap operations across the chain. It is shown that the control sequences can be computed and implemented efficiently. We discuss the application of these ideas to physical systems such as superconducting qubits in which full control of long chains is challenging.

  7. The Brain Is both Neurocomputer and Quantum Computer

    ERIC Educational Resources Information Center

    Hameroff, Stuart R.

    2007-01-01

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

  8. Transitions in the computational power of thermal states for measurement-based quantum computation

    SciTech Connect

    Barrett, Sean D.; Bartlett, Stephen D.; Jennings, David; Doherty, Andrew C.; Rudolph, Terry

    2009-12-15

    We show that the usefulness of the thermal state of a specific spin-lattice model for measurement-based quantum computing exhibits a transition between two distinct 'phases' - one in which every state is a universal resource for quantum computation, and another in which any local measurement sequence can be simulated efficiently on a classical computer. Remarkably, this transition in computational power does not coincide with any phase transition, classical, or quantum in the underlying spin-lattice model.

  9. Military engine computational structures technology

    NASA Technical Reports Server (NTRS)

    Thomson, Daniel E.

    1992-01-01

    Integrated High Performance Turbine Engine Technology Initiative (IHPTET) goals require a strong analytical base. Effective analysis of composite materials is critical to life analysis and structural optimization. Accurate life prediction for all material systems is critical. User friendly systems are also desirable. Post processing of results is very important. The IHPTET goal is to double turbine engine propulsion capability by the year 2003. Fifty percent of the goal will come from advanced materials and structures, the other 50 percent will come from increasing performance. Computer programs are listed.

  10. Computer technologies and institutional memory

    NASA Technical Reports Server (NTRS)

    Bell, Christopher; Lachman, Roy

    1989-01-01

    NASA programs for manned space flight are in their 27th year. Scientists and engineers who worked continuously on the development of aerospace technology during that period are approaching retirement. The resulting loss to the organization will be considerable. Although this problem is general to the NASA community, the problem was explored in terms of the institutional memory and technical expertise of a single individual in the Man-Systems division. The main domain of the expert was spacecraft lighting, which became the subject area for analysis in these studies. The report starts with an analysis of the cumulative expertise and institutional memory of technical employees of organizations such as NASA. A set of solutions to this problem are examined and found inadequate. Two solutions were investigated at length: hypertext and expert systems. Illustrative examples were provided of hypertext and expert system representation of spacecraft lighting. These computer technologies can be used to ameliorate the problem of the loss of invaluable personnel.

  11. EDITORIAL: Progress in quantum technology: one photon at a time Progress in quantum technology: one photon at a time

    NASA Astrophysics Data System (ADS)

    Demming, Anna

    2012-07-01

    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 quantum computation and quantum cryptography protocols based on single photons, among many others. In this issue, researchers in Germany and the US report a step towards precisely triggered single-photon sources driven by surface acoustic waves (SAWs) [1]. The work brings technology based on quantum mechanics yet another step closer to practical device reality. Generation of single 'antibunched' photons has been one of the key challenges to progress in quantum information processing and communication. Researchers from Toshiba and Cambridge University in the UK recently reported what they described as 'the first electrically driven single-photon source capable of emitting indistinguishable photons' [2]. Single-photon sources have been reported previously [3]. However the approach demonstrated by Shields and colleagues allows electrical control, which is particularly useful for implementing in compact devices. The researchers used a layer of InAs quantum dots embedded in the intrinsic region of a p-i-n diode to demonstrate interference between single photons. They also present a complete theory based on the interference of photons with a Lorentzian spectrum, which they compare with both continuous-wave and pulsed experiments. The application of SAWs in achieving precisely triggered single-photon sources develops the work of researchers in Germany in the late 1990s [4]. Surface acoustic waves travel like sound waves, but are characterized by an amplitude that typically decays exponentially with depth into the substrate. As Rocke and colleagues demonstrated, they can be used to

  12. Demonstration of a small programmable quantum computer with atomic qubits

    NASA Astrophysics Data System (ADS)

    Debnath, S.; Linke, N. M.; Figgatt, C.; Landsman, K. A.; Wright, K.; Monroe, C.

    2016-08-01

    Quantum computers can solve certain problems more efficiently than any possible conventional computer. Small quantum algorithms have been demonstrated on multiple quantum computing platforms, many specifically tailored in hardware to implement a particular algorithm or execute a limited number of computational paths. Here we demonstrate a five-qubit trapped-ion quantum computer that can be programmed in software to implement arbitrary quantum algorithms by executing any sequence of universal quantum logic gates. We compile algorithms into a fully connected set of gate operations that are native to the hardware and have a mean fidelity of 98 per cent. Reconfiguring these gate sequences provides the flexibility to implement a variety of algorithms without altering the hardware. As examples, we implement the Deutsch–Jozsa and Bernstein–Vazirani algorithms with average success rates of 95 and 90 per cent, respectively. We also perform a coherent quantum Fourier transform on five trapped-ion qubits for phase estimation and period finding with average fidelities of 62 and 84 per cent, respectively. This small quantum computer can be scaled to larger numbers of qubits within a single register, and can be further expanded by connecting several such modules through ion shuttling or photonic quantum channels.

  13. Demonstration of a small programmable quantum computer with atomic qubits.

    PubMed

    Debnath, S; Linke, N M; Figgatt, C; Landsman, K A; Wright, K; Monroe, C

    2016-08-01

    Quantum computers can solve certain problems more efficiently than any possible conventional computer. Small quantum algorithms have been demonstrated on multiple quantum computing platforms, many specifically tailored in hardware to implement a particular algorithm or execute a limited number of computational paths. Here we demonstrate a five-qubit trapped-ion quantum computer that can be programmed in software to implement arbitrary quantum algorithms by executing any sequence of universal quantum logic gates. We compile algorithms into a fully connected set of gate operations that are native to the hardware and have a mean fidelity of 98 per cent. Reconfiguring these gate sequences provides the flexibility to implement a variety of algorithms without altering the hardware. As examples, we implement the Deutsch-Jozsa and Bernstein-Vazirani algorithms with average success rates of 95 and 90 per cent, respectively. We also perform a coherent quantum Fourier transform on five trapped-ion qubits for phase estimation and period finding with average fidelities of 62 and 84 per cent, respectively. This small quantum computer can be scaled to larger numbers of qubits within a single register, and can be further expanded by connecting several such modules through ion shuttling or photonic quantum channels. PMID:27488798

  14. Demonstration of a small programmable quantum computer with atomic qubits.

    PubMed

    Debnath, S; Linke, N M; Figgatt, C; Landsman, K A; Wright, K; Monroe, C

    2016-08-03

    Quantum computers can solve certain problems more efficiently than any possible conventional computer. Small quantum algorithms have been demonstrated on multiple quantum computing platforms, many specifically tailored in hardware to implement a particular algorithm or execute a limited number of computational paths. Here we demonstrate a five-qubit trapped-ion quantum computer that can be programmed in software to implement arbitrary quantum algorithms by executing any sequence of universal quantum logic gates. We compile algorithms into a fully connected set of gate operations that are native to the hardware and have a mean fidelity of 98 per cent. Reconfiguring these gate sequences provides the flexibility to implement a variety of algorithms without altering the hardware. As examples, we implement the Deutsch-Jozsa and Bernstein-Vazirani algorithms with average success rates of 95 and 90 per cent, respectively. We also perform a coherent quantum Fourier transform on five trapped-ion qubits for phase estimation and period finding with average fidelities of 62 and 84 per cent, respectively. This small quantum computer can be scaled to larger numbers of qubits within a single register, and can be further expanded by connecting several such modules through ion shuttling or photonic quantum channels.

  15. Demonstration of a small programmable quantum computer with atomic qubits

    NASA Astrophysics Data System (ADS)

    Debnath, S.; Linke, N. M.; Figgatt, C.; Landsman, K. A.; Wright, K.; Monroe, C.

    2016-08-01

    Quantum computers can solve certain problems more efficiently than any possible conventional computer. Small quantum algorithms have been demonstrated on multiple quantum computing platforms, many specifically tailored in hardware to implement a particular algorithm or execute a limited number of computational paths. Here we demonstrate a five-qubit trapped-ion quantum computer that can be programmed in software to implement arbitrary quantum algorithms by executing any sequence of universal quantum logic gates. We compile algorithms into a fully connected set of gate operations that are native to the hardware and have a mean fidelity of 98 per cent. Reconfiguring these gate sequences provides the flexibility to implement a variety of algorithms without altering the hardware. As examples, we implement the Deutsch-Jozsa and Bernstein-Vazirani algorithms with average success rates of 95 and 90 per cent, respectively. We also perform a coherent quantum Fourier transform on five trapped-ion qubits for phase estimation and period finding with average fidelities of 62 and 84 per cent, respectively. This small quantum computer can be scaled to larger numbers of qubits within a single register, and can be further expanded by connecting several such modules through ion shuttling or photonic quantum channels.

  16. Universal Quantum Computing with Arbitrary Continuous-Variable Encoding.

    PubMed

    Lau, Hoi-Kwan; Plenio, Martin B

    2016-09-01

    Implementing a qubit quantum computer in continuous-variable systems conventionally requires the engineering of specific interactions according to the encoding basis states. In this work, we present a unified formalism to conduct universal quantum computation with a fixed set of operations but arbitrary encoding. By storing a qubit in the parity of two or four qumodes, all computing processes can be implemented by basis state preparations, continuous-variable exponential-swap operations, and swap tests. Our formalism inherits the advantages that the quantum information is decoupled from collective noise, and logical qubits with different encodings can be brought to interact without decoding. We also propose a possible implementation of the required operations by using interactions that are available in a variety of continuous-variable systems. Our work separates the "hardware" problem of engineering quantum-computing-universal interactions, from the "software" problem of designing encodings for specific purposes. The development of quantum computer architecture could hence be simplified.

  17. Universal Quantum Computing with Arbitrary Continuous-Variable Encoding

    NASA Astrophysics Data System (ADS)

    Lau, Hoi-Kwan; Plenio, Martin B.

    2016-09-01

    Implementing a qubit quantum computer in continuous-variable systems conventionally requires the engineering of specific interactions according to the encoding basis states. In this work, we present a unified formalism to conduct universal quantum computation with a fixed set of operations but arbitrary encoding. By storing a qubit in the parity of two or four qumodes, all computing processes can be implemented by basis state preparations, continuous-variable exponential-swap operations, and swap tests. Our formalism inherits the advantages that the quantum information is decoupled from collective noise, and logical qubits with different encodings can be brought to interact without decoding. We also propose a possible implementation of the required operations by using interactions that are available in a variety of continuous-variable systems. Our work separates the "hardware" problem of engineering quantum-computing-universal interactions, from the "software" problem of designing encodings for specific purposes. The development of quantum computer architecture could hence be simplified.

  18. Popescu-Rohrlich correlations imply efficient instantaneous nonlocal quantum computation

    NASA Astrophysics Data System (ADS)

    Broadbent, Anne

    2016-08-01

    In instantaneous nonlocal quantum computation, two parties cooperate in order to perform a quantum computation on their joint inputs, while being restricted to a single round of simultaneous communication. Previous results showed that instantaneous nonlocal quantum computation is possible, at the cost of an exponential amount of prior shared entanglement (in the size of the input). Here, we show that a linear amount of entanglement suffices, (in the size of the computation), as long as the parties share nonlocal correlations as given by the Popescu-Rohrlich box. This means that communication is not required for efficient instantaneous nonlocal quantum computation. Exploiting the well-known relation to position-based cryptography, our result also implies the impossibility of secure position-based cryptography against adversaries with nonsignaling correlations. Furthermore, our construction establishes a quantum analog of the classical communication complexity collapse under nonsignaling correlations.

  19. Universal Quantum Computing with Arbitrary Continuous-Variable Encoding.

    PubMed

    Lau, Hoi-Kwan; Plenio, Martin B

    2016-09-01

    Implementing a qubit quantum computer in continuous-variable systems conventionally requires the engineering of specific interactions according to the encoding basis states. In this work, we present a unified formalism to conduct universal quantum computation with a fixed set of operations but arbitrary encoding. By storing a qubit in the parity of two or four qumodes, all computing processes can be implemented by basis state preparations, continuous-variable exponential-swap operations, and swap tests. Our formalism inherits the advantages that the quantum information is decoupled from collective noise, and logical qubits with different encodings can be brought to interact without decoding. We also propose a possible implementation of the required operations by using interactions that are available in a variety of continuous-variable systems. Our work separates the "hardware" problem of engineering quantum-computing-universal interactions, from the "software" problem of designing encodings for specific purposes. The development of quantum computer architecture could hence be simplified. PMID:27636459

  20. Cluster State Quantum Computation and the Repeat-Until Scheme

    NASA Astrophysics Data System (ADS)

    Kwek, L. C.

    Cluster state computation or the one way quantum computation (1WQC) relies on an initially highly entangled state (called a cluster state) and an appropriate sequence of single qubit measurements along different directions, together with feed-forward based on the measurement results, to realize a quantum computation process. The final result of the computation is obtained by measuring the last remaining qubits in the computational basis. In this short tutorial on cluster state quantum computation, we will also describe the basic ideas of a cluster state and proceed to describe how a single qubit operation can be done on a cluster state. Recently, we proposed a repeat-until-success (RUS) scheme that could effectively be used to realize one-way quantum computer on a hybrid system of photons and atoms. We will briefly describe this RUS scheme and show how it can be used to entangled two distant stationary qubits.

  1. An Atomic Abacus: Trapped ion quantum computing experiments at NIST

    NASA Astrophysics Data System (ADS)

    Demarco, Brian

    2003-03-01

    Trapped atomic ions are an ideal system for exploring quantum information science because deterministic state preparation and efficient state detection are possible and coherent manipulation of atomic systems is relatively advanced. In our experiment, a few singly charged Be ions are confined by static and radio-frequency electric fields in a micro-machined linear Paul trap. The internal and motional states of the ions are coherently manipulated using applied laser light. Our current work focuses on demonstrating the necessary ingredients to produce a scalable quantum computing scheme and on simplifying and improving quantum logic gates. I will speak about a new set of experiments that was made possible by recent improvements in trap technology. A novel trap with multiple trapping regions was used to demonstrate the first steps towards a fully scalable quantum computing scheme. Single ions were ``shuttled" between trapping regions without disturbing the ion's motional and internal state, and two ions were separated from a single to two different trapping zones. Improvements in the trap manufacturing process has led to a reduction of nearly two orders of magnitude in the ion's motional heating rate, making possible two new improved logic gates. The first gate utilizes the wave-packet nature of the ions to tune the laser-atom interaction and achieve a controlled-NOT gate between a single ion's spin and motional states. The second, a two-ion phase gate, uses phase-space dynamics to produce a state-sensitive geometric phase. I will end with a quick look at experiments using a Mg ion to sympathetically cool a simultaneously trapped Be ion and a glimpse of the next generation of ions traps currently under construction.

  2. Experimental magic state distillation for fault-tolerant quantum computing.

    PubMed

    Souza, Alexandre M; Zhang, Jingfu; Ryan, Colm A; Laflamme, Raymond

    2011-01-25

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

  3. Quantum Monte Carlo Endstation for Petascale Computing

    SciTech Connect

    Lubos Mitas

    2011-01-26

    NCSU research group has been focused on accomplising the key goals of this initiative: establishing new generation of quantum Monte Carlo (QMC) computational tools as a part of Endstation petaflop initiative for use at the DOE ORNL computational facilities and for use by computational electronic structure community at large; carrying out high accuracy quantum Monte Carlo demonstration projects in application of these tools to the forefront electronic structure problems in molecular and solid systems; expanding the impact of QMC methods and approaches; explaining and enhancing the impact of these advanced computational approaches. In particular, we have developed quantum Monte Carlo code (QWalk, www.qwalk.org) which was significantly expanded and optimized using funds from this support and at present became an actively used tool in the petascale regime by ORNL researchers and beyond. These developments have been built upon efforts undertaken by the PI's group and collaborators over the period of the last decade. The code was optimized and tested extensively on a number of parallel architectures including petaflop ORNL Jaguar machine. We have developed and redesigned a number of code modules such as evaluation of wave functions and orbitals, calculations of pfaffians and introduction of backflow coordinates together with overall organization of the code and random walker distribution over multicore architectures. We have addressed several bottlenecks such as load balancing and verified efficiency and accuracy of the calculations with the other groups of the Endstation team. The QWalk package contains about 50,000 lines of high quality object-oriented C++ and includes also interfaces to data files from other conventional electronic structure codes such as Gamess, Gaussian, Crystal and others. This grant supported PI for one month during summers, a full-time postdoc and partially three graduate students over the period of the grant duration, it has resulted in 13

  4. Secure Multiparty Quantum Computation for Summation and Multiplication.

    PubMed

    Shi, Run-hua; Mu, Yi; Zhong, Hong; Cui, Jie; Zhang, Shun

    2016-01-01

    As a fundamental primitive, Secure Multiparty Summation and Multiplication can be used to build complex secure protocols for other multiparty computations, specially, numerical computations. However, there is still lack of systematical and efficient quantum methods to compute Secure Multiparty Summation and Multiplication. In this paper, we present a novel and efficient quantum approach to securely compute the summation and multiplication of multiparty private inputs, respectively. Compared to classical solutions, our proposed approach can ensure the unconditional security and the perfect privacy protection based on the physical principle of quantum mechanics. PMID:26792197

  5. Secure Multiparty Quantum Computation for Summation and Multiplication

    PubMed Central

    Shi, Run-hua; Mu, Yi; Zhong, Hong; Cui, Jie; Zhang, Shun

    2016-01-01

    As a fundamental primitive, Secure Multiparty Summation and Multiplication can be used to build complex secure protocols for other multiparty computations, specially, numerical computations. However, there is still lack of systematical and efficient quantum methods to compute Secure Multiparty Summation and Multiplication. In this paper, we present a novel and efficient quantum approach to securely compute the summation and multiplication of multiparty private inputs, respectively. Compared to classical solutions, our proposed approach can ensure the unconditional security and the perfect privacy protection based on the physical principle of quantum mechanics. PMID:26792197

  6. Secure Multiparty Quantum Computation for Summation and Multiplication

    NASA Astrophysics Data System (ADS)

    Shi, Run-Hua; Mu, Yi; Zhong, Hong; Cui, Jie; Zhang, Shun

    2016-01-01

    As a fundamental primitive, Secure Multiparty Summation and Multiplication can be used to build complex secure protocols for other multiparty computations, specially, numerical computations. However, there is still lack of systematical and efficient quantum methods to compute Secure Multiparty Summation and Multiplication. In this paper, we present a novel and efficient quantum approach to securely compute the summation and multiplication of multiparty private inputs, respectively. Compared to classical solutions, our proposed approach can ensure the unconditional security and the perfect privacy protection based on the physical principle of quantum mechanics.

  7. Computable measure of total quantum correlations of multipartite systems

    NASA Astrophysics Data System (ADS)

    Behdani, Javad; Akhtarshenas, Seyed Javad; Sarbishaei, Mohsen

    2016-04-01

    Quantum discord as a measure of the quantum correlations cannot be easily computed for most of density operators. In this paper, we present a measure of the total quantum correlations that is operationally simple and can be computed effectively for an arbitrary mixed state of a multipartite system. The measure is based on the coherence vector of the party whose quantumness is investigated as well as the correlation matrix of this part with the remainder of the system. Being able to detect the quantumness of multipartite systems, such as detecting the quantum critical points in spin chains, alongside with the computability characteristic of the measure, makes it a useful indicator to be exploited in the cases which are out of the scope of the other known measures.

  8. Continuous-variable quantum computing in optical time-frequency modes using quantum memories.

    PubMed

    Humphreys, Peter C; Kolthammer, W Steven; Nunn, Joshua; Barbieri, Marco; Datta, Animesh; Walmsley, Ian A

    2014-09-26

    We develop a scheme for time-frequency encoded continuous-variable cluster-state quantum computing using quantum memories. In particular, we propose a method to produce, manipulate, and measure two-dimensional cluster states in a single spatial mode by exploiting the intrinsic time-frequency selectivity of Raman quantum memories. Time-frequency encoding enables the scheme to be extremely compact, requiring a number of memories that are a linear function of only the number of different frequencies in which the computational state is encoded, independent of its temporal duration. We therefore show that quantum memories can be a powerful component for scalable photonic quantum information processing architectures.

  9. Noisy one-way quantum computations: The role of correlations

    SciTech Connect

    Chaves, Rafael; Melo, Fernando de

    2011-08-15

    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 quantum computations. 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.

  10. Optimizing qubit resources for quantum chemistry simulations in second quantization on a quantum computer

    NASA Astrophysics Data System (ADS)

    Moll, Nikolaj; Fuhrer, Andreas; Staar, Peter; Tavernelli, Ivano

    2016-07-01

    Quantum chemistry simulations on a quantum computer suffer from the overhead needed for encoding the Fermionic problem in a system of qubits. By exploiting the block diagonality of a Fermionic Hamiltonian, we show that the number of required qubits can be reduced while the number of terms in the Hamiltonian will increase. All operations for this reduction can be performed in operator space. The scheme is conceived as a pre-computational step that would be performed prior to the actual quantum simulation. We apply this scheme to reduce the number of qubits necessary to simulate both the Hamiltonian of the two-site Fermi-Hubbard model and the hydrogen molecule. Both quantum systems can then be simulated with a two-qubit quantum computer. Despite the increase in the number of Hamiltonian terms, the scheme still remains a useful tool to reduce the dimensionality of specific quantum systems for quantum simulators with a limited number of resources.

  11. Optimizing qubit resources for quantum chemistry simulations in second quantization on a quantum computer

    NASA Astrophysics Data System (ADS)

    Moll, Nikolaj; Fuhrer, Andreas; Staar, Peter; Tavernelli, Ivano

    2016-07-01

    Quantum chemistry simulations on a quantum computer suffer from the overhead needed for encoding the Fermionic problem in a system of qubits. By exploiting the block diagonality of a Fermionic Hamiltonian, we show that the number of required qubits can be reduced while the number of terms in the Hamiltonian will increase. All operations for this reduction can be performed in operator space. The scheme is conceived as a pre-computational step that would be performed prior to the actual quantum simulation. We apply this scheme to reduce the number of qubits necessary to simulate both the Hamiltonian of the two-site Fermi–Hubbard model and the hydrogen molecule. Both quantum systems can then be simulated with a two-qubit quantum computer. Despite the increase in the number of Hamiltonian terms, the scheme still remains a useful tool to reduce the dimensionality of specific quantum systems for quantum simulators with a limited number of resources.

  12. Quantum computing with acceptor spins in silicon.

    PubMed

    Salfi, Joe; Tong, Mengyang; Rogge, Sven; Culcer, Dimitrie

    2016-06-17

    The states of a boron acceptor near a Si/SiO2 interface, which bind two low-energy Kramers pairs, have exceptional properties for encoding quantum information and, with the aid of strain, both heavy hole and light hole-based spin qubits can be designed. Whereas a light-hole spin qubit was introduced recently (arXiv:1508.04259), here we present analytical and numerical results proving that a heavy-hole spin qubit can be reliably initialised, rotated and entangled by electrical means alone. This is due to strong Rashba-like spin-orbit interaction terms enabled by the interface inversion asymmetry. Single qubit rotations rely on electric-dipole spin resonance (EDSR), which is strongly enhanced by interface-induced spin-orbit terms. Entanglement can be accomplished by Coulomb exchange, coupling to a resonator, or spin-orbit induced dipole-dipole interactions. By analysing the qubit sensitivity to charge noise, we demonstrate that interface-induced spin-orbit terms are responsible for sweet spots in the dephasing time [Formula: see text] as a function of the top gate electric field, which are close to maxima in the EDSR strength, where the EDSR gate has high fidelity. We show that both qubits can be described using the same starting Hamiltonian, and by comparing their properties we show that the complex interplay of bulk and interface-induced spin-orbit terms allows a high degree of electrical control and makes acceptors potential candidates for scalable quantum computation in Si. PMID:27171901

  13. Quantum computing with acceptor spins in silicon.

    PubMed

    Salfi, Joe; Tong, Mengyang; Rogge, Sven; Culcer, Dimitrie

    2016-06-17

    The states of a boron acceptor near a Si/SiO2 interface, which bind two low-energy Kramers pairs, have exceptional properties for encoding quantum information and, with the aid of strain, both heavy hole and light hole-based spin qubits can be designed. Whereas a light-hole spin qubit was introduced recently (arXiv:1508.04259), here we present analytical and numerical results proving that a heavy-hole spin qubit can be reliably initialised, rotated and entangled by electrical means alone. This is due to strong Rashba-like spin-orbit interaction terms enabled by the interface inversion asymmetry. Single qubit rotations rely on electric-dipole spin resonance (EDSR), which is strongly enhanced by interface-induced spin-orbit terms. Entanglement can be accomplished by Coulomb exchange, coupling to a resonator, or spin-orbit induced dipole-dipole interactions. By analysing the qubit sensitivity to charge noise, we demonstrate that interface-induced spin-orbit terms are responsible for sweet spots in the dephasing time [Formula: see text] as a function of the top gate electric field, which are close to maxima in the EDSR strength, where the EDSR gate has high fidelity. We show that both qubits can be described using the same starting Hamiltonian, and by comparing their properties we show that the complex interplay of bulk and interface-induced spin-orbit terms allows a high degree of electrical control and makes acceptors potential candidates for scalable quantum computation in Si.

  14. Quantum computing with acceptor spins in silicon

    NASA Astrophysics Data System (ADS)

    Salfi, Joe; Tong, Mengyang; Rogge, Sven; Culcer, Dimitrie

    2016-06-01

    The states of a boron acceptor near a Si/SiO2 interface, which bind two low-energy Kramers pairs, have exceptional properties for encoding quantum information and, with the aid of strain, both heavy hole and light hole-based spin qubits can be designed. Whereas a light-hole spin qubit was introduced recently (arXiv:1508.04259), here we present analytical and numerical results proving that a heavy-hole spin qubit can be reliably initialised, rotated and entangled by electrical means alone. This is due to strong Rashba-like spin-orbit interaction terms enabled by the interface inversion asymmetry. Single qubit rotations rely on electric-dipole spin resonance (EDSR), which is strongly enhanced by interface-induced spin-orbit terms. Entanglement can be accomplished by Coulomb exchange, coupling to a resonator, or spin-orbit induced dipole-dipole interactions. By analysing the qubit sensitivity to charge noise, we demonstrate that interface-induced spin-orbit terms are responsible for sweet spots in the dephasing time {T}2* as a function of the top gate electric field, which are close to maxima in the EDSR strength, where the EDSR gate has high fidelity. We show that both qubits can be described using the same starting Hamiltonian, and by comparing their properties we show that the complex interplay of bulk and interface-induced spin-orbit terms allows a high degree of electrical control and makes acceptors potential candidates for scalable quantum computation in Si.

  15. Digitized adiabatic quantum computing with a superconducting circuit

    NASA Astrophysics Data System (ADS)

    Barends, R.; Shabani, A.; Lamata, L.; Kelly, J.; Mezzacapo, A.; Heras, U. Las; Babbush, R.; Fowler, A. G.; Campbell, B.; Chen, Yu; Chen, Z.; Chiaro, B.; Dunsworth, A.; Jeffrey, E.; Lucero, E.; Megrant, A.; Mutus, J. Y.; Neeley, M.; Neill, C.; O'Malley, P. J. J.; Quintana, C.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; White, T. C.; Solano, E.; Neven, H.; Martinis, John M.

    2016-06-01

    Quantum mechanics can help to solve complex problems in physics and chemistry, provided they can be programmed in a physical device. In adiabatic quantum computing, a system is slowly evolved from the ground state of a simple initial Hamiltonian to a final Hamiltonian that encodes a computational problem. The appeal of this approach lies in the combination of simplicity and generality; in principle, any problem can be encoded. In practice, applications are restricted by limited connectivity, available interactions and noise. A complementary approach is digital quantum computing, which enables the construction of arbitrary interactions and is compatible with error correction, but uses quantum circuit algorithms that are problem-specific. Here we combine the advantages of both approaches by implementing digitized adiabatic quantum computing in a superconducting system. We tomographically probe the system during the digitized evolution and explore the scaling of errors with system size. We then let the full system find the solution to random instances of the one-dimensional Ising problem as well as problem Hamiltonians that involve more complex interactions. This digital quantum simulation of the adiabatic algorithm consists of up to nine qubits and up to 1,000 quantum logic gates. The demonstration of digitized adiabatic quantum computing in the solid state opens a path to synthesizing long-range correlations and solving complex computational problems. When combined with fault-tolerance, our approach becomes a general-purpose algorithm that is scalable.

  16. Digitized adiabatic quantum computing with a superconducting circuit.

    PubMed

    Barends, R; Shabani, A; Lamata, L; Kelly, J; Mezzacapo, A; Las Heras, U; Babbush, R; Fowler, A G; Campbell, B; Chen, Yu; Chen, Z; Chiaro, B; Dunsworth, A; Jeffrey, E; Lucero, E; Megrant, A; Mutus, J Y; Neeley, M; Neill, C; O'Malley, P J J; Quintana, C; Roushan, P; Sank, D; Vainsencher, A; Wenner, J; White, T C; Solano, E; Neven, H; Martinis, John M

    2016-06-01

    Quantum mechanics can help to solve complex problems in physics and chemistry, provided they can be programmed in a physical device. In adiabatic quantum computing, a system is slowly evolved from the ground state of a simple initial Hamiltonian to a final Hamiltonian that encodes a computational problem. The appeal of this approach lies in the combination of simplicity and generality; in principle, any problem can be encoded. In practice, applications are restricted by limited connectivity, available interactions and noise. A complementary approach is digital quantum computing, which enables the construction of arbitrary interactions and is compatible with error correction, but uses quantum circuit algorithms that are problem-specific. Here we combine the advantages of both approaches by implementing digitized adiabatic quantum computing in a superconducting system. We tomographically probe the system during the digitized evolution and explore the scaling of errors with system size. We then let the full system find the solution to random instances of the one-dimensional Ising problem as well as problem Hamiltonians that involve more complex interactions. This digital quantum simulation of the adiabatic algorithm consists of up to nine qubits and up to 1,000 quantum logic gates. The demonstration of digitized adiabatic quantum computing in the solid state opens a path to synthesizing long-range correlations and solving complex computational problems. When combined with fault-tolerance, our approach becomes a general-purpose algorithm that is scalable. PMID:27279216

  17. Digitized adiabatic quantum computing with a superconducting circuit.

    PubMed

    Barends, R; Shabani, A; Lamata, L; Kelly, J; Mezzacapo, A; Las Heras, U; Babbush, R; Fowler, A G; Campbell, B; Chen, Yu; Chen, Z; Chiaro, B; Dunsworth, A; Jeffrey, E; Lucero, E; Megrant, A; Mutus, J Y; Neeley, M; Neill, C; O'Malley, P J J; Quintana, C; Roushan, P; Sank, D; Vainsencher, A; Wenner, J; White, T C; Solano, E; Neven, H; Martinis, John M

    2016-06-08

    Quantum mechanics can help to solve complex problems in physics and chemistry, provided they can be programmed in a physical device. In adiabatic quantum computing, a system is slowly evolved from the ground state of a simple initial Hamiltonian to a final Hamiltonian that encodes a computational problem. The appeal of this approach lies in the combination of simplicity and generality; in principle, any problem can be encoded. In practice, applications are restricted by limited connectivity, available interactions and noise. A complementary approach is digital quantum computing, which enables the construction of arbitrary interactions and is compatible with error correction, but uses quantum circuit algorithms that are problem-specific. Here we combine the advantages of both approaches by implementing digitized adiabatic quantum computing in a superconducting system. We tomographically probe the system during the digitized evolution and explore the scaling of errors with system size. We then let the full system find the solution to random instances of the one-dimensional Ising problem as well as problem Hamiltonians that involve more complex interactions. This digital quantum simulation of the adiabatic algorithm consists of up to nine qubits and up to 1,000 quantum logic gates. The demonstration of digitized adiabatic quantum computing in the solid state opens a path to synthesizing long-range correlations and solving complex computational problems. When combined with fault-tolerance, our approach becomes a general-purpose algorithm that is scalable.

  18. Holonomic quantum computation on microwave photons with all resonant interactions

    NASA Astrophysics Data System (ADS)

    Dong, Ping; Yu, Long-Bao; Zhou, Jian

    2016-08-01

    The intrinsic difficulties of holonomic quantum computation on superconducting circuits are originated from the use of three levels in superconducting transmon qubits and the complicated dispersive interaction between them. Due to the limited anharmonicity of transmon qubits, the experimental realization seems to be very challenging. However, with recent experimental progress, coherent control over microwave photons in superconducting circuit cavities is well achieved, and thus provides a promising platform for quantum information processing with photonic qubits. Here, with all resonant inter-cavity photon-photon interactions, we propose a scheme for implementing scalable holonomic quantum computation on a circuit QED lattice. In our proposal, three cavities, connected by a SQUID, are used to encode a logical qubit. By tuning the inter-cavity photon-photon interaction, we can construct all the holonomies needed for universal quantum computation in a non-adiabatic way. Therefore, our scheme presents a promising alternative for robust quantum computation with microwave photons.

  19. Holonomic quantum computation on microwave photons with all resonant interactions

    NASA Astrophysics Data System (ADS)

    Dong, Ping; Yu, Long-Bao; Zhou, Jian

    2016-08-01

    The intrinsic difficulties of holonomic quantum computation on superconducting circuits are originated from the use of three levels in superconducting transmon qubits and the complicated dispersive interaction between them. Due to the limited anharmonicity of transmon qubits, the experimental realization seems to be very challenging. However, with recent experimental progress, coherent control over microwave photons in superconducting circuit cavities is well achieved, and thus provides a promising platform for quantum information processing with photonic qubits. Here, with all resonant inter-cavity photon–photon interactions, we propose a scheme for implementing scalable holonomic quantum computation on a circuit QED lattice. In our proposal, three cavities, connected by a SQUID, are used to encode a logical qubit. By tuning the inter-cavity photon–photon interaction, we can construct all the holonomies needed for universal quantum computation in a non-adiabatic way. Therefore, our scheme presents a promising alternative for robust quantum computation with microwave photons.

  20. Universal quantum computation with a nonlinear oscillator network

    NASA Astrophysics Data System (ADS)

    Goto, Hayato

    2016-05-01

    We theoretically show that a nonlinear oscillator network with controllable parameters can be used for universal quantum computation. The initialization is achieved by a quantum-mechanical bifurcation based on quantum adiabatic evolution, which yields a Schrödinger cat state. All the elementary quantum gates are also achieved by quantum adiabatic evolution, in which dynamical phases accompanying the adiabatic evolutions are controlled by the system parameters. Numerical simulation results indicate that high gate fidelities can be achieved, where no dissipation is assumed.

  1. Center for Computational Structures Technology

    NASA Technical Reports Server (NTRS)

    Noor, Ahmed K.; Perry, Ferman W.

    1995-01-01

    The Center for Computational Structures Technology (CST) is intended to serve as a focal point for the diverse CST research activities. The CST activities include the use of numerical simulation and artificial intelligence methods in modeling, analysis, sensitivity studies, and optimization of flight-vehicle structures. The Center is located at NASA Langley and is an integral part of the School of Engineering and Applied Science of the University of Virginia. The key elements of the Center are: (1) conducting innovative research on advanced topics of CST; (2) acting as pathfinder by demonstrating to the research community what can be done (high-potential, high-risk research); (3) strong collaboration with NASA scientists and researchers from universities and other government laboratories; and (4) rapid dissemination of CST to industry, through integration of industrial personnel into the ongoing research efforts.

  2. Symbolic Quantum Computation Simulation in SymPy

    NASA Astrophysics Data System (ADS)

    Cugini, Addison; Curry, Matt; Granger, Brian

    2010-10-01

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

  3. Stabilizer quantum error correction with quantum bus computation

    SciTech Connect

    Myers, Casey R.; Silva, Marcus; Nemoto, Kae; Munro, William J.

    2007-07-15

    In this paper we investigate stabilizer quantum error correction codes using controlled phase rotations of strong coherent probe states. We explicitly describe two methods to measure the Pauli operators that generate the stabilizer group of a quantum code. First, we show how to measure a Pauli operator acting on physical qubits using a single coherent state with large average photon number, displacement operations, and photon detection. Second, we show how to measure the stabilizer operators fault-tolerantly by the deterministic preparation of coherent quantum superposition ('cat') states along with one-bit teleportations between a qubitlike encoding of coherent states and physical qubits.

  4. Trapped Ion Quantum Computing with Microwaves

    NASA Astrophysics Data System (ADS)

    Randall, Joe; Weidt, Sebastian; Standing, Eamon; Webster, Simon; Lake, Kim; Murgia, David; Navickas, Tomas; Lekitsch, Bjoern; Hughes, Marcus; Sterling, Robin; de Motte, Darren; Giri, Gouri; Rodriguez, Andrea; Webb, Anna; Rattanasonti, Hwanjit; Srinivasan, Prasanna; Kraft, Michael; Maclean, Jessica; Mellor, Chris; Hensinger, Winfried

    2015-03-01

    To this point, entanglement operations in trapped ion qubits have been predominantly performed with lasers. However, this becomes problematic when scaling to large numbers of qubits due to the challenging engineering required. The use of stable and easily controllable microwaves to drive entanglement gates can overcome this problem. We will present our work towards implementing multi-qubit entanglement gates using microwaves in an experimental setup that produces a static magnetic field gradient of 24 T/m over an ion string. We will first present a scheme for preparing and manipulating dressed-state qubits and qutrits that are highly robust to decoherence from magnetic field fluctuations. We will also present our work experimentally demonstrating motional sideband transitions and Schrödinger cat states using microwaves in conjunction with the magnetic field gradient, as well as sideband cooling to the ground state of motion using dressed-states. Furthermore, we will show our latest results in creating microfabricated ion trap chips towards large scale quantum computing and simulation.

  5. Consciousness and Logic in a Quantum-Computing Universe

    NASA Astrophysics Data System (ADS)

    Zizzi, Paola

    The early inflationary universe can be described in terms of quantum information. More specifically, the inflationary universe can be viewed as a superposed state of quantum registers. Actually, during inflation, one can speak of a quantum superposition of universes. At the end of inflation, only one universe is selected, by a mechanism called self-reduction, which is consistent with Penrose's objective reduction (OR) model. The quantum gravity threshold of (OR) is reached at the end of inflation, and corresponds to a superposed state of 109 quantum registers. This is also the number of superposed tubulins — qubits in our brain, which undergo the Penrose-Hameroff orchestrated objective reduction, (Orch OR), leading to a conscious event. Then, an analogy naturally arises between the very early quantum-computing universe, and our mind. In fact, we argue that at the end of in- flation, the universe underwent a cosmic conscious event, the so-called "Big Wow", which acted as an imprinting for the future minds to come, with future modes of computation, consciousness and logic. The postinflationary universe organized itself as a cellular automaton (CA) with two computational modes: quantum and classical, like the two conformations assumed by the cellular automaton of tubulins in our brain, as in Hameroff's model. In the quantum configuration, the universe quantum-evaluates recursive functions, which are the laws of physics in their most abstract form. To do so in a very efficient way, the universe uses, as subroutines, black holes - quantum computers and quantum minds, which operate in parallel. The outcomes of the overall quantum computation are the universals, the attributes of things in themselves. These universals are partially obtained also by the quantum minds, and are endowed with subjective meaning. The units of the subjective universals are qualia, which are strictly related to the (virtual) existence of Planckian black holes. Further, we consider two aspects

  6. Towards scalable quantum communication and computation: Novel approaches and realizations

    NASA Astrophysics Data System (ADS)

    Jiang, Liang

    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 quantum computation, based on an optically connected network of few-qubit quantum registers. Specifically, we develop a novel scheme for scalable quantum computation that is robust against various imperfections. To justify that nitrogen-vacancy (NV) color centers in diamond can be a promising realization of the few-qubit quantum register, we show how to isolate a few proximal nuclear spins from the rest of the environment and use them for the quantum register. We also demonstrate experimentally that the nuclear spin coherence is only weakly perturbed under optical illumination, which allows us to implement quantum logical operations that use the nuclear spins to assist the repetitive-readout of the electronic spin. Using this technique, we demonstrate more than two-fold improvement in signal-to-noise ratio. Apart from direct application to enhance the sensitivity of the NV-based nano-magnetometer, this experiment represents an important step towards the realization of robust quantum information processors using electronic and nuclear spin qubits. We then study realizations of quantum repeaters for long distance quantum communication. Specifically, we develop an efficient scheme for quantum repeaters based on atomic ensembles. We use dynamic programming to optimize various quantum repeater protocols. In addition, we propose a new protocol of quantum repeater with encoding, which efficiently uses local resources (about 100 qubits) to identify and correct errors, to achieve fast one-way quantum communication over long distances. Finally, we explore quantum systems with topological order. Such systems can exhibit remarkable phenomena such as quasiparticles with anyonic statistics and have been proposed as

  7. Faculty Computer Expertise and Use of Instructional Technology. Technology Survey.

    ERIC Educational Resources Information Center

    Gabriner, Robert; Mery, Pamela

    This report shows the findings of a 1997 technology survey used to assess degrees of faculty computer expertise and the use of instructional technology. Part 1 reviews general findings of the fall 1997 technology survey: (1) the level of computer expertise among faculty, staff and administrators appears to be increasing; (2) in comparison with the…

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

    SciTech Connect

    Poulin, David; Wocjan, Pawel

    2009-04-03

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

  9. Experimental quantum computing to solve systems of linear equations.

    PubMed

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

    2013-06-01

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

  10. Computer Technology: State of the Art.

    ERIC Educational Resources Information Center

    Withington, Frederic G.

    1981-01-01

    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)

  11. Computing protein infrared spectroscopy with quantum chemistry.

    PubMed

    Besley, Nicholas A

    2007-12-15

    Quantum chemistry is a field of science that has undergone unprecedented advances in the last 50 years. From the pioneering work of Boys in the 1950s, quantum chemistry has evolved from being regarded as a specialized and esoteric discipline to a widely used tool that underpins much of the current research in chemistry today. This achievement was recognized with the award of the 1998 Nobel Prize in Chemistry to John Pople and Walter Kohn. As the new millennium unfolds, quantum chemistry stands at the forefront of an exciting new era. Quantitative calculations on systems of the magnitude of proteins are becoming a realistic possibility, an achievement that would have been unimaginable to the early pioneers of quantum chemistry. In this article we will describe ongoing work towards this goal, focusing on the calculation of protein infrared amide bands directly with quantum chemical methods.

  12. Integrated System Technologies for Modular Trapped Ion Quantum Information Processing

    NASA Astrophysics Data System (ADS)

    Crain, Stephen G.

    Although trapped ion technology is well-suited for quantum information science, scalability of the system remains one of the main challenges. One of the challenges associated with scaling the ion trap quantum computer is the ability to individually manipulate the increasing number of qubits. Using micro-mirrors fabricated with micro-electromechanical systems (MEMS) technology, laser beams are focused on individual ions in a linear chain and steer the focal point in two dimensions. Multiple single qubit gates are demonstrated on trapped 171Yb+ qubits and the gate performance is characterized using quantum state tomography. The system features negligible crosstalk to neighboring ions (< 3e-4), and switching speeds comparable to typical single qubit gate times (< 2 mus). In a separate experiment, photons scattered from the 171Yb+ ion are coupled into an optical fiber with 63% efficiency using a high numerical aperture lens (0.6 NA). The coupled photons are directed to superconducting nanowire single photon detectors (SNSPD), which provide a higher detector efficiency (69%) compared to traditional photomultiplier tubes (35%). The total system photon collection efficiency is increased from 2.2% to 3.4%, which allows for fast state detection of the qubit. For a detection beam intensity of 11 mW/cm 2, the average detection time is 23.7 mus with 99.885(7)% detection fidelity. The technologies demonstrated in this thesis can be integrated to form a single quantum register with all of the necessary resources to perform local gates as well as high fidelity readout and provide a photon link to other systems.

  13. Time independent universal computing with spin chains: quantum plinko machine

    NASA Astrophysics Data System (ADS)

    Thompson, K. F.; Gokler, C.; Lloyd, S.; Shor, P. W.

    2016-07-01

    We present a scheme for universal quantum computing using XY Heisenberg spin chains. Information is encoded into packets propagating down these chains, and they interact with each other to perform universal quantum computation. A circuit using g gate blocks on m qubits can be encoded into chains of length O({g}3+δ {m}3+δ ) for all δ \\gt 0 with vanishingly small error.

  14. Some generalizations of fuzzy structures in quantum computational logic

    NASA Astrophysics Data System (ADS)

    Giuntini, Roberto; Ledda, Antonio; Sergioli, Giuseppe; Paoli, Francesco

    2011-01-01

    Quantum computational logics provide a fertile common ground for a unified treatment of vagueness and uncertainty. In this paper, we describe an approach to the logic of quantum computation that has been recently taken up and developed. After reporting on the state of the art, we explore some future research perspectives in the light of some recent limitative results whose general significance will be duly assessed.

  15. Quantum computation for large-scale image classification

    NASA Astrophysics Data System (ADS)

    Ruan, Yue; Chen, Hanwu; Tan, Jianing; Li, Xi

    2016-10-01

    Due to the lack of an effective quantum feature extraction method, there is currently no effective way to perform quantum image classification or recognition. In this paper, for the first time, a global quantum feature extraction method based on Schmidt decomposition is proposed. A revised quantum learning algorithm is also proposed that will classify images by computing the Hamming distance of these features. From the experimental results derived from the benchmark database Caltech 101, and an analysis of the algorithm, an effective approach to large-scale image classification is derived and proposed against the background of big data.

  16. Quantum computation for large-scale image classification

    NASA Astrophysics Data System (ADS)

    Ruan, Yue; Chen, Hanwu; Tan, Jianing; Li, Xi

    2016-07-01

    Due to the lack of an effective quantum feature extraction method, there is currently no effective way to perform quantum image classification or recognition. In this paper, for the first time, a global quantum feature extraction method based on Schmidt decomposition is proposed. A revised quantum learning algorithm is also proposed that will classify images by computing the Hamming distance of these features. From the experimental results derived from the benchmark database Caltech 101, and an analysis of the algorithm, an effective approach to large-scale image classification is derived and proposed against the background of big data.

  17. Algorithm-based analysis of collective decoherence in quantum computation

    NASA Astrophysics Data System (ADS)

    Utsunomiya, Shoko; Master, Cyrus P.; Yamamoto, Yoshihisa

    2007-02-01

    In a quantum computer, 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 algorithms and propose a simple alternative of implementing quantum algorithms using a quantum trajectory that is close to a decoherence-free subspace that avoids unstable Dicke's superradiant states and Schrödinger's cat state.

  18. Universal linear Bogoliubov transformations through one-way quantum computation

    SciTech Connect

    Ukai, Ryuji; Yoshikawa, Jun-ichi; Iwata, Noriaki; Furusawa, Akira; Loock, Peter van

    2010-03-15

    We show explicitly how to realize an arbitrary linear unitary Bogoliubov (LUBO) transformation on a multimode quantum state through homodyne-based one-way quantum computation. 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.

  19. ONSET OF CHAOS IN A MODEL OF QUANTUM COMPUTATION

    SciTech Connect

    G. BERMAN; ET AL

    2001-02-01

    Recently, the question of a relevance of the so-called quantum chaos has been raised in applications to quantum computation [2,3]. Indeed, according to the general approach to closed systems of finite number of interacting Fermi-particles (see, e.g. [4,5]), with an increase of an interaction between qubits a kind of chaos is expected to emerge in the energy spectra and structure of many-body states. Specifically, the fluctuations of energy levels and components of the eigenstates turn out to be very strong and described by the Random Matrix Theory. Clearly, if this happens in a quantum computer, it may lead to a destruction of the coherence of quantum computations due to internal decoherence inside many-body states. It is important to stress that quantum chaos occurs not only in the systems with random interaction, but also for purely dynamical interaction. In the latter case, the mechanism of chaos is due to a complex (non-linear) form of a two-body interaction represented in the basis of non-interacting particles. Numerical analysis [2] of a simplest model of quantum computer (2D model of 1/2-spins with a random interqubit interaction J) shows that with an increase of the number L of qubits, the chaos threshold J{sub cr} decreases as J{sub cr} {infinity} 1/L. On this ground, it was claimed that the onset of quantum chaos could be dangerous for quantum computers, since their effectiveness requires L >> 1. On the other hand, in [3] it was argued that in order to treat this problem properly, one needs to distinguish between chaotic properties of stationary states, and the dynamical process of quantum computation.

  20. Continuous-Variable Quantum Computation of Oracle Decision Problems

    NASA Astrophysics Data System (ADS)

    Adcock, Mark R. A.

    Quantum information processing is appealing due its ability to solve certain problems quantitatively faster than classical information processing. Most quantum algorithms have been studied in discretely parameterized systems, but many quantum systems are continuously parameterized. The field of quantum optics in particular has sophisticated techniques for manipulating continuously parameterized quantum states of light, but the lack of a code-state formalism has hindered the study of quantum algorithms in these systems. To address this situation, a code-state formalism for the solution of oracle decision problems in continuously-parameterized quantum systems is developed. Quantum information processing is appealing due its ability to solve certain problems quantitatively faster than classical information processing. Most quantum algorithms have been studied in discretely parameterized systems, but many quantum systems are continuously parameterized. The field of quantum optics in particular has sophisticated techniques for manipulating continuously parameterized quantum states of light, but the lack of a code-state formalism has hindered the study of quantum algorithms in these systems. To address this situation, a code-state formalism for the solution of oracle decision problems in continuously-parameterized quantum systems is developed. In the infinite-dimensional case, we study continuous-variable quantum algorithms for the solution of the Deutsch--Jozsa oracle decision problem implemented within a single harmonic-oscillator. Orthogonal states are used as the computational bases, and we show that, contrary to a previous claim in the literature, this implementation of quantum information processing has limitations due to a position-momentum trade-off of the Fourier transform. We further demonstrate that orthogonal encoding bases are not unique, and using the coherent states of the harmonic oscillator as the computational bases, our formalism enables quantifying

  1. Spin Glass a Bridge Between Quantum Computation and Statistical Mechanics

    NASA Astrophysics Data System (ADS)

    Ohzeki, Masayuki

    2013-09-01

    In this chapter, we show two fascinating topics lying between quantum information processing and statistical mechanics. First, we introduce an elaborated technique, the surface code, to prepare the particular quantum state with robustness against decoherence. Interestingly, the theoretical limitation of the surface code, accuracy threshold, to restore the quantum state has a close connection with the problem on the phase transition in a special model known as spin glasses, which is one of the most active researches in statistical mechanics. The phase transition in spin glasses is an intractable problem, since we must strive many-body system with complicated interactions with change of their signs depending on the distance between spins. Fortunately, recent progress in spin-glass theory enables us to predict the precise location of the critical point, at which the phase transition occurs. It means that statistical mechanics is available for revealing one of the most interesting parts in quantum information processing. We show how to import the special tool in statistical mechanics into the problem on the accuracy threshold in quantum computation. Second, we show another interesting technique to employ quantum nature, quantum annealing. The purpose of quantum annealing is to search for the most favored solution of a multivariable function, namely optimization problem. The most typical instance is the traveling salesman problem to find the minimum tour while visiting all the cities. In quantum annealing, we introduce quantum fluctuation to drive a particular system with the artificial Hamiltonian, in which the ground state represents the optimal solution of the specific problem we desire to solve. Induction of the quantum fluctuation gives rise to the quantum tunneling effect, which allows nontrivial hopping from state to state. We then sketch a strategy to control the quantum fluctuation efficiently reaching the ground state. Such a generic framework is called

  2. Scalable digital hardware for a trapped ion quantum computer

    NASA Astrophysics Data System (ADS)

    Mount, Emily; Gaultney, Daniel; Vrijsen, Geert; Adams, Michael; Baek, So-Young; Hudek, Kai; Isabella, Louis; Crain, Stephen; van Rynbach, Andre; Maunz, Peter; Kim, Jungsang

    2015-09-01

    Many of the challenges of scaling quantum computer hardware lie at the interface between the qubits and the classical control signals used to manipulate them. Modular ion trap quantum computer architectures address scalability by constructing individual quantum processors interconnected via a network of quantum communication channels. Successful operation of such quantum hardware requires a fully programmable classical control system capable of frequency stabilizing the continuous wave lasers necessary for loading, cooling, initialization, and detection of the ion qubits, stabilizing the optical frequency combs used to drive logic gate operations on the ion qubits, providing a large number of analog voltage sources to drive the trap electrodes, and a scheme for maintaining phase coherence among all the controllers that manipulate the qubits. In this work, we describe scalable solutions to these hardware development challenges.

  3. Nonadiabatic holonomic quantum computation with all-resonant control

    NASA Astrophysics Data System (ADS)

    Xue, Zheng-Yuan; Zhou, Jian; Chu, Yao-Ming; Hu, Yong

    2016-08-01

    The implementation of holonomic quantum computation on superconducting quantum circuits is challenging due to the general requirement of controllable complicated coupling between multilevel systems. Here we solve this problem by proposing a scalable circuit QED lattice with simple realization of a universal set of nonadiabatic holonomic quantum gates. Compared with the existing proposals, we can achieve both the single and two logical qubit gates in a tunable and all-resonant way through a hybrid transmon-transmission-line encoding of the logical qubits in the decoherence-free subspaces. This distinct advantage thus leads to quantum gates with very fast speeds and consequently very high fidelities. Therefore, our scheme paves a promising way towards the practical realization of high-fidelity nonadiabatic holonomic quantum computation.

  4. Quantum perceptron over a field and neural network architecture selection in a quantum computer.

    PubMed

    da Silva, Adenilton José; Ludermir, Teresa Bernarda; de Oliveira, Wilson Rosa

    2016-04-01

    In this work, we propose a quantum neural network named quantum perceptron over a field (QPF). Quantum computers are not yet a reality and the models and algorithms proposed in this work cannot be simulated in actual (or classical) computers. QPF is a direct generalization of a classical perceptron and solves some drawbacks found in previous models of quantum perceptrons. We also present a learning algorithm named Superposition based Architecture Learning algorithm (SAL) that optimizes the neural network weights and architectures. SAL searches for the best architecture in a finite set of neural network architectures with linear time over the number of patterns in the training set. SAL is the first learning algorithm to determine neural network architectures in polynomial time. This speedup is obtained by the use of quantum parallelism and a non-linear quantum operator. PMID:26878722

  5. Quantum perceptron over a field and neural network architecture selection in a quantum computer.

    PubMed

    da Silva, Adenilton José; Ludermir, Teresa Bernarda; de Oliveira, Wilson Rosa

    2016-04-01

    In this work, we propose a quantum neural network named quantum perceptron over a field (QPF). Quantum computers are not yet a reality and the models and algorithms proposed in this work cannot be simulated in actual (or classical) computers. QPF is a direct generalization of a classical perceptron and solves some drawbacks found in previous models of quantum perceptrons. We also present a learning algorithm named Superposition based Architecture Learning algorithm (SAL) that optimizes the neural network weights and architectures. SAL searches for the best architecture in a finite set of neural network architectures with linear time over the number of patterns in the training set. SAL is the first learning algorithm to determine neural network architectures in polynomial time. This speedup is obtained by the use of quantum parallelism and a non-linear quantum operator.

  6. Unitary R-matrices for topological quantum computing

    NASA Astrophysics Data System (ADS)

    Burton, P. J.; Gould, M. D.

    2006-02-01

    The main problem with current approaches to quantum computing is the difficulty of establishing and maintaining entanglement. A Topological Quantum Computer (TQC) aims to overcome this by using different physical processes that are topological in nature and which are less susceptible to disturbance by the environment. In a (2+1)-dimensional system, pseudoparticles called anyons have statistics that fall somewhere between bosons and fermions. The exchange of two anyons, an effect called braiding from knot theory, can occur in two different ways. The quantum states corresponding to the two elementary braids constitute a two-state system allowing the definition of a computational basis. Quantum gates can be built up from patterns of braids and for quantum computing it is essential that the operator describing the braiding—the R-matrix—be described by a unitary operator. The physics of anyonic systems is governed by quantum groups, in particular the quasi-triangular Hopf algebras obtained from finite groups by the application of the Drinfeld quantum double construction. Their representation theory has been described in detail by Gould and Tsohantjis, and in this review article we relate the work of Gould to TQC schemes, particularly that of Kauffman.

  7. Quantum Computation Based on Photons with Three Degrees of Freedom.

    PubMed

    Luo, Ming-Xing; Li, Hui-Ran; Lai, Hong; Wang, Xiaojun

    2016-01-01

    Quantum systems are important resources for quantum computer. Different from previous encoding forms using quantum systems with one degree of freedom (DoF) or two DoFs, we investigate the possibility of photon systems encoding with three DoFs consisting of the polarization DoF and two spatial DoFs. By exploring the optical circular birefringence induced by an NV center in a diamond embedded in the photonic crystal cavity, we propose several hybrid controlled-NOT (hybrid CNOT) gates operating on the two-photon or one-photon system. These hybrid CNOT gates show that three DoFs may be encoded as independent qubits without auxiliary DoFs. Our result provides a useful way to reduce quantum simulation resources by exploring complex quantum systems for quantum applications requiring large qubit systems. PMID:27174302

  8. Quantum Computation Based on Photons with Three Degrees of Freedom

    PubMed Central

    Luo, Ming-Xing; Li, Hui-Ran; Lai, Hong; Wang, Xiaojun

    2016-01-01

    Quantum systems are important resources for quantum computer. Different from previous encoding forms using quantum systems with one degree of freedom (DoF) or two DoFs, we investigate the possibility of photon systems encoding with three DoFs consisting of the polarization DoF and two spatial DoFs. By exploring the optical circular birefringence induced by an NV center in a diamond embedded in the photonic crystal cavity, we propose several hybrid controlled-NOT (hybrid CNOT) gates operating on the two-photon or one-photon system. These hybrid CNOT gates show that three DoFs may be encoded as independent qubits without auxiliary DoFs. Our result provides a useful way to reduce quantum simulation resources by exploring complex quantum systems for quantum applications requiring large qubit systems. PMID:27174302

  9. Quantum Computation Based on Photons with Three Degrees of Freedom

    NASA Astrophysics Data System (ADS)

    Luo, Ming-Xing; Li, Hui-Ran; Lai, Hong; Wang, Xiaojun

    2016-05-01

    Quantum systems are important resources for quantum computer. Different from previous encoding forms using quantum systems with one degree of freedom (DoF) or two DoFs, we investigate the possibility of photon systems encoding with three DoFs consisting of the polarization DoF and two spatial DoFs. By exploring the optical circular birefringence induced by an NV center in a diamond embedded in the photonic crystal cavity, we propose several hybrid controlled-NOT (hybrid CNOT) gates operating on the two-photon or one-photon system. These hybrid CNOT gates show that three DoFs may be encoded as independent qubits without auxiliary DoFs. Our result provides a useful way to reduce quantum simulation resources by exploring complex quantum systems for quantum applications requiring large qubit systems.

  10. Quantum Computing: Selected Internet Resources for Librarians, Researchers, and the Casually Curious

    ERIC Educational Resources Information Center

    Cirasella, Jill

    2009-01-01

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

  11. Quantum Monte Carlo Endstation for Petascale Computing

    SciTech Connect

    David Ceperley

    2011-03-02

    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

  12. Theory-Guided Technology in Computer Science.

    ERIC Educational Resources Information Center

    Ben-Ari, Mordechai

    2001-01-01

    Examines the history of major achievements in computer science as portrayed by 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. Discusses reasons why TGT is practical in computer science and…

  13. Prior Computer Experience and Technology Acceptance

    ERIC Educational Resources Information Center

    Varma, Sonali

    2010-01-01

    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 computer technology. The lack of a theory driven approach to measuring prior experience has however led to conceptually different factors being used interchangeably in…

  14. Computer technology for autistic students.

    PubMed

    Panyan, M V

    1984-12-01

    The first purpose of this article is to review the literature related to the use of computers with autistic individuals. Although only a limited number of applications have been reported, the potential of the computer to facilitate the progress of autistic persons is promising. The second purpose is to identify specific learning problems or styles associated with autism from the research literature and link these with the unique aspects of computer-based instruction. For example, the computer's role in improving the motivation of autistic individuals is related to its capacity to analyze the reinforcing qualities of a particular event interactively and immediately for each user. Finally, recommendations that may enable computers to be maximally beneficial in assessing the learning process and remediating learning problems are offered. Two such recommendations are selecting appropriate software and integrating computer instruction within the classroom environment. PMID:6549182

  15. Computer technology for autistic students.

    PubMed

    Panyan, M V

    1984-12-01

    The first purpose of this article is to review the literature related to the use of computers with autistic individuals. Although only a limited number of applications have been reported, the potential of the computer to facilitate the progress of autistic persons is promising. The second purpose is to identify specific learning problems or styles associated with autism from the research literature and link these with the unique aspects of computer-based instruction. For example, the computer's role in improving the motivation of autistic individuals is related to its capacity to analyze the reinforcing qualities of a particular event interactively and immediately for each user. Finally, recommendations that may enable computers to be maximally beneficial in assessing the learning process and remediating learning problems are offered. Two such recommendations are selecting appropriate software and integrating computer instruction within the classroom environment.

  16. Blind quantum computation over a collective-noise channel

    NASA Astrophysics Data System (ADS)

    Takeuchi, Yuki; Fujii, Keisuke; Ikuta, Rikizo; Yamamoto, Takashi; Imoto, Nobuyuki

    2016-05-01

    Blind quantum computation (BQC) allows a client (Alice), who only possesses relatively poor quantum devices, to delegate universal quantum computation to a server (Bob) in such a way that Bob cannot know Alice's inputs, algorithm, and outputs. The quantum channel between Alice and Bob is noisy, and the loss over the long-distance quantum communication should also be taken into account. Here we propose to use decoherence-free subspace (DFS) to overcome the collective noise in the quantum channel for BQC, which we call DFS-BQC. We propose three variations of DFS-BQC protocols. One of them, a coherent-light-assisted DFS-BQC protocol, allows Alice to faithfully send the signal photons with a probability proportional to a transmission rate of the quantum channel. In all cases, we combine the ideas based on DFS and the Broadbent-Fitzsimons-Kashefi protocol, which is one of the BQC protocols, without degrading unconditional security. The proposed DFS-based schemes are generic and hence can be applied to other BQC protocols where Alice sends quantum states to Bob.

  17. Center for Computer Sciences and Technology.

    ERIC Educational Resources Information Center

    National Bureau of Standards (DOC), Washington, DC.

    Functions of the Center for Computer Sciences and Technology (CCST), a national center for computer research and development for the United States government, are described. CCST provides computer and related services to the National Bureau of Standards of which it is a part and to other government agencies on a cost-reimbursable basis. The Office…

  18. Computer Service Technology (An Associate Degree Program).

    ERIC Educational Resources Information Center

    McQuay, Paul L.; Bronk, Carol G.

    Delaware County College's (DCC's) computer service technology program is described in this paper, along with job market needs for computer personnel in Delaware County and nationwide. First, the type of work performed by computer service technicians and the areas in which they are employed are outlined. Next, the objectives of DCC's program are…

  19. SLJ Special Section: Computer Technology and Libraries.

    ERIC Educational Resources Information Center

    School Library Journal, 1984

    1984-01-01

    This 5-article section provides an annotated bibliography of 39 books about computer technology; describes peripheral equipment essential for building computer systems; suggests an approach to software evaluation and selection; describes the implementation of a computer program for elementary/secondary students and teachers; and reviews 34…

  20. Computer Technology Resources for Literacy Projects.

    ERIC Educational Resources Information Center

    Florida State Council on Aging, Tallahassee.

    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…

  1. Slow phase relaxation as a route to quantum computing beyond the quantum chaos border

    NASA Astrophysics Data System (ADS)

    Flores, J.; Kun, S. Yu.; Seligman, T. H.

    2005-07-01

    We reveal that phase memory can be much longer than energy relaxation in systems with exponentially large dimensions of Hilbert space; this finding is documented by 50 years of nuclear experiments, though the information is somewhat hidden. For quantum computers Hilbert spaces of dimension 2100 or larger will be typical and therefore this effect may contribute significantly to reduce the problems of scaling of quantum computers to a useful number of qubits.

  2. From computational quantum chemistry to computational biology: experiments and computations are (full) partners.

    PubMed

    Ma, Buyong; Nussinov, Ruth

    2004-12-01

    Computations are being integrated into biological research at an increasingly fast pace. This has not only changed the way in which biological information is managed; it has also changed the way in which experiments are planned in order to obtain information from nature. Can experiments and computations be full partners? Computational chemistry has expanded over the years, proceeding from computations of a hydrogen molecule toward the challenging goal of systems biology, which attempts to handle the entire living cell. Applying theories from ab initio quantum mechanics to simplified models, the virtual worlds explored by computations provide replicas of real-world phenomena. At the same time, the virtual worlds can affect our perception of the real world. Computational biology targets a world of complex organization, for which a unified theory is unlikely to exist. A computational biology model, even if it has a clear physical or chemical basis, may not reduce to physics and chemistry. At the molecular level, computational biology and experimental biology have already been partners, mutually benefiting from each other. For the perception to become reality, computation and experiment should be united as full partners in biological research.

  3. PERSPECTIVE: From computational quantum chemistry to computational biology: experiments and computations are (full) partners

    NASA Astrophysics Data System (ADS)

    Ma, Buyong; Nussinov, Ruth

    2004-12-01

    Computations are being integrated into biological research at an increasingly fast pace. This has not only changed the way in which biological information is managed; it has also changed the way in which experiments are planned in order to obtain information from nature. Can experiments and computations be full partners? Computational chemistry has expanded over the years, proceeding from computations of a hydrogen molecule toward the challenging goal of systems biology, which attempts to handle the entire living cell. Applying theories from ab initio quantum mechanics to simplified models, the virtual worlds explored by computations provide replicas of real-world phenomena. At the same time, the virtual worlds can affect our perception of the real world. Computational biology targets a world of complex organization, for which a unified theory is unlikely to exist. A computational biology model, even if it has a clear physical or chemical basis, may not reduce to physics and chemistry. At the molecular level, computational biology and experimental biology have already been partners, mutually benefiting from each other. For the perception to become reality, computation and experiment should be united as full partners in biological research.

  4. Adiabatic pipelining: a key to ternary computing with quantum dots.

    PubMed

    Pečar, P; Ramšak, A; Zimic, N; Mraz, M; Lebar Bajec, I

    2008-12-10

    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.

  5. Entanglement-based machine learning on a quantum computer.

    PubMed

    Cai, X-D; Wu, D; Su, Z-E; Chen, M-C; Wang, X-L; Li, Li; Liu, N-L; Lu, C-Y; Pan, J-W

    2015-03-20

    Machine learning, a branch of artificial intelligence, learns from previous experience to optimize performance, which is ubiquitous in various fields such as computer sciences, financial analysis, robotics, and bioinformatics. A challenge is that machine learning with the rapidly growing "big data" could become intractable for classical computers. Recently, quantum machine learning algorithms [Lloyd, Mohseni, and Rebentrost, arXiv.1307.0411] were proposed which could offer an exponential speedup over classical algorithms. Here, we report the first experimental entanglement-based classification of two-, four-, and eight-dimensional vectors to different clusters using a small-scale photonic quantum computer, which are then used to implement supervised and unsupervised machine learning. The results demonstrate the working principle of using quantum computers to manipulate and classify high-dimensional vectors, the core mathematical routine in machine learning. The method can, in principle, be scaled to larger numbers of qubits, and may provide a new route to accelerate machine learning. PMID:25839250

  6. Entanglement-based machine learning on a quantum computer.

    PubMed

    Cai, X-D; Wu, D; Su, Z-E; Chen, M-C; Wang, X-L; Li, Li; Liu, N-L; Lu, C-Y; Pan, J-W

    2015-03-20

    Machine learning, a branch of artificial intelligence, learns from previous experience to optimize performance, which is ubiquitous in various fields such as computer sciences, financial analysis, robotics, and bioinformatics. A challenge is that machine learning with the rapidly growing "big data" could become intractable for classical computers. Recently, quantum machine learning algorithms [Lloyd, Mohseni, and Rebentrost, arXiv.1307.0411] were proposed which could offer an exponential speedup over classical algorithms. Here, we report the first experimental entanglement-based classification of two-, four-, and eight-dimensional vectors to different clusters using a small-scale photonic quantum computer, which are then used to implement supervised and unsupervised machine learning. The results demonstrate the working principle of using quantum computers to manipulate and classify high-dimensional vectors, the core mathematical routine in machine learning. The method can, in principle, be scaled to larger numbers of qubits, and may provide a new route to accelerate machine learning.

  7. Entanglement-Based Machine Learning on a Quantum Computer

    NASA Astrophysics Data System (ADS)

    Cai, X.-D.; Wu, D.; Su, Z.-E.; Chen, M.-C.; Wang, X.-L.; Li, Li; Liu, N.-L.; Lu, C.-Y.; Pan, J.-W.

    2015-03-01

    Machine learning, a branch of artificial intelligence, learns from previous experience to optimize performance, which is ubiquitous in various fields such as computer sciences, financial analysis, robotics, and bioinformatics. A challenge is that machine learning with the rapidly growing "big data" could become intractable for classical computers. Recently, quantum machine learning algorithms [Lloyd, Mohseni, and Rebentrost, arXiv.1307.0411] were proposed which could offer an exponential speedup over classical algorithms. Here, we report the first experimental entanglement-based classification of two-, four-, and eight-dimensional vectors to different clusters using a small-scale photonic quantum computer, which are then used to implement supervised and unsupervised machine learning. The results demonstrate the working principle of using quantum computers to manipulate and classify high-dimensional vectors, the core mathematical routine in machine learning. The method can, in principle, be scaled to larger numbers of qubits, and may provide a new route to accelerate machine learning.

  8. Kochen-Specker Theorem as a Precondition for Quantum Computing

    NASA Astrophysics Data System (ADS)

    Nagata, Koji; Nakamura, Tadao

    2016-08-01

    We study the relation between the Kochen-Specker theorem (the KS theorem) and quantum computing. The KS theorem rules out a realistic theory of the KS type. We consider the realistic theory of the KS type that the results of measurements are either +1 or -1. We discuss an inconsistency between the realistic theory of the KS type and the controllability of quantum computing. We have to give up the controllability if we accept the realistic theory of the KS type. We discuss an inconsistency between the realistic theory of the KS type and the observability of quantum computing. We discuss the inconsistency by using the double-slit experiment as the most basic experiment in quantum mechanics. This experiment can be for an easy detector to a Pauli observable. We cannot accept the realistic theory of the KS type to simulate the double-slit experiment in a significant specific case. The realistic theory of the KS type can not depicture quantum detector. In short, we have to give up both the observability and the controllability if we accept the realistic theory of the KS type. Therefore, the KS theorem is a precondition for quantum computing, i.e., the realistic theory of the KS type should be ruled out.

  9. EDITORIAL: Progress in quantum technology: one photon at a time Progress in quantum technology: one photon at a time

    NASA Astrophysics Data System (ADS)

    Demming, Anna

    2012-07-01

    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 quantum computation and quantum cryptography protocols based on single photons, among many others. In this issue, researchers in Germany and the US report a step towards precisely triggered single-photon sources driven by surface acoustic waves (SAWs) [1]. The work brings technology based on quantum mechanics yet another step closer to practical device reality. Generation of single 'antibunched' photons has been one of the key challenges to progress in quantum information processing and communication. Researchers from Toshiba and Cambridge University in the UK recently reported what they described as 'the first electrically driven single-photon source capable of emitting indistinguishable photons' [2]. Single-photon sources have been reported previously [3]. However the approach demonstrated by Shields and colleagues allows electrical control, which is particularly useful for implementing in compact devices. The researchers used a layer of InAs quantum dots embedded in the intrinsic region of a p-i-n diode to demonstrate interference between single photons. They also present a complete theory based on the interference of photons with a Lorentzian spectrum, which they compare with both continuous-wave and pulsed experiments. The application of SAWs in achieving precisely triggered single-photon sources develops the work of researchers in Germany in the late 1990s [4]. Surface acoustic waves travel like sound waves, but are characterized by an amplitude that typically decays exponentially with depth into the substrate. As Rocke and colleagues demonstrated, they can be used to

  10. Bifurcation-based adiabatic quantum computation with a nonlinear oscillator network.

    PubMed

    Goto, Hayato

    2016-01-01

    The dynamics of nonlinear systems qualitatively change depending on their parameters, which is called bifurcation. A quantum-mechanical nonlinear oscillator can yield a quantum superposition of two oscillation states, known as a Schrödinger cat state, via quantum adiabatic evolution through its bifurcation point. Here we propose a quantum computer comprising such quantum nonlinear oscillators, instead of quantum bits, to solve hard combinatorial optimization problems. The nonlinear oscillator network finds optimal solutions via quantum adiabatic evolution, where nonlinear terms are increased slowly, in contrast to conventional adiabatic quantum computation or quantum annealing, where quantum fluctuation terms are decreased slowly. As a result of numerical simulations, it is concluded that quantum superposition and quantum fluctuation work effectively to find optimal solutions. It is also notable that the present computer is analogous to neural computers, which are also networks of nonlinear components. Thus, the present scheme will open new possibilities for quantum computation, nonlinear science, and artificial intelligence. PMID:26899997

  11. Bifurcation-based adiabatic quantum computation with a nonlinear oscillator network

    PubMed Central

    Goto, Hayato

    2016-01-01

    The dynamics of nonlinear systems qualitatively change depending on their parameters, which is called bifurcation. A quantum-mechanical nonlinear oscillator can yield a quantum superposition of two oscillation states, known as a Schrödinger cat state, via quantum adiabatic evolution through its bifurcation point. Here we propose a quantum computer comprising such quantum nonlinear oscillators, instead of quantum bits, to solve hard combinatorial optimization problems. The nonlinear oscillator network finds optimal solutions via quantum adiabatic evolution, where nonlinear terms are increased slowly, in contrast to conventional adiabatic quantum computation or quantum annealing, where quantum fluctuation terms are decreased slowly. As a result of numerical simulations, it is concluded that quantum superposition and quantum fluctuation work effectively to find optimal solutions. It is also notable that the present computer is analogous to neural computers, which are also networks of nonlinear components. Thus, the present scheme will open new possibilities for quantum computation, nonlinear science, and artificial intelligence. PMID:26899997

  12. Bifurcation-based adiabatic quantum computation with a nonlinear oscillator network

    NASA Astrophysics Data System (ADS)

    Goto, Hayato

    2016-02-01

    The dynamics of nonlinear systems qualitatively change depending on their parameters, which is called bifurcation. A quantum-mechanical nonlinear oscillator can yield a quantum superposition of two oscillation states, known as a Schrödinger cat state, via quantum adiabatic evolution through its bifurcation point. Here we propose a quantum computer comprising such quantum nonlinear oscillators, instead of quantum bits, to solve hard combinatorial optimization problems. The nonlinear oscillator network finds optimal solutions via quantum adiabatic evolution, where nonlinear terms are increased slowly, in contrast to conventional adiabatic quantum computation or quantum annealing, where quantum fluctuation terms are decreased slowly. As a result of numerical simulations, it is concluded that quantum superposition and quantum fluctuation work effectively to find optimal solutions. It is also notable that the present computer is analogous to neural computers, which are also networks of nonlinear components. Thus, the present scheme will open new possibilities for quantum computation, nonlinear science, and artificial intelligence.

  13. Bifurcation-based adiabatic quantum computation with a nonlinear oscillator network.

    PubMed

    Goto, Hayato

    2016-02-22

    The dynamics of nonlinear systems qualitatively change depending on their parameters, which is called bifurcation. A quantum-mechanical nonlinear oscillator can yield a quantum superposition of two oscillation states, known as a Schrödinger cat state, via quantum adiabatic evolution through its bifurcation point. Here we propose a quantum computer comprising such quantum nonlinear oscillators, instead of quantum bits, to solve hard combinatorial optimization problems. The nonlinear oscillator network finds optimal solutions via quantum adiabatic evolution, where nonlinear terms are increased slowly, in contrast to conventional adiabatic quantum computation or quantum annealing, where quantum fluctuation terms are decreased slowly. As a result of numerical simulations, it is concluded that quantum superposition and quantum fluctuation work effectively to find optimal solutions. It is also notable that the present computer is analogous to neural computers, which are also networks of nonlinear components. Thus, the present scheme will open new possibilities for quantum computation, nonlinear science, and artificial intelligence.

  14. Optimal control, geometry, and quantum computing

    NASA Astrophysics Data System (ADS)

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

    2006-06-01

    We prove upper and lower bounds relating the quantum gate complexity of a unitary operation, U , to the optimal control cost associated to the synthesis of U . These bounds apply for any optimal control problem, and can be used to show that the quantum gate complexity is essentially equivalent to the optimal control cost for a wide range of problems, including time-optimal control and finding minimal distances on certain Riemannian, sub-Riemannian, and Finslerian manifolds. These results generalize the results of [Nielsen, Dowling, Gu, and Doherty, Science 311, 1133 (2006)], which showed that the gate complexity can be related to distances on a Riemannian manifold.

  15. On the ``principle of the quantumness,'' the quantumness of Relativity, and the computational grand-unification

    NASA Astrophysics Data System (ADS)

    D'Ariano, Giacomo Mauro

    2010-05-01

    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 quantum computer," 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.

  16. On the 'principle of the quantumness', the quantumness of Relativity, and the computational grand-unification

    SciTech Connect

    D'Ariano, Giacomo Mauro

    2010-05-04

    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 quantum computer', 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.

  17. Requirements for fault-tolerant factoring on an atom-optics quantum computer

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

    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 quantum computer 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.

  18. From Computer Lab to Technology Class.

    ERIC Educational Resources Information Center

    Sherwood, Sandra

    1999-01-01

    Discussion of integrating technology into elementary school classrooms focuses on teacher training that is based on a three-year plan developed at an elementary school in Marathon, New York. Describes the role of a technology teacher who facilitates technology integration by running the computer lab, offering workshops, and developing inservice…

  19. Art Therapists and Computer Technology

    ERIC Educational Resources Information Center

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

    2005-01-01

    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…

  20. a Computable Framework for Loop Quantum Gravity

    NASA Astrophysics Data System (ADS)

    Husain, Viqar; Pawłowski, Tomasz

    2015-01-01

    We present a non-perturbative quantization of general relativity coupled to dust and other matter fields. The dust provides a natural time variable, leading to a physical Hamiltonian with spatial diffeomorphism symmetry. The methods of loop quantum gravity applied to this model lead to a physical Hilbert space and Hamiltonian. This provides a framework for physical calculations in the theory.

  1. Quantum computation in the analysis of hyperspectral data

    NASA Astrophysics Data System (ADS)

    Gomez, Richard B.; Ghoshal, Debabrata; Jayanna, Anil

    2004-08-01

    Recent research on the topic of quantum computation provides us with some quantum algorithms with higher efficiency and speedup compared to their classical counterparts. In this paper, it is our intent to provide the results of our investigation of several applications of such quantum algorithms - especially the Grover's Search algorithm - in the analysis of Hyperspectral Data. We found many parallels with Grover's method in existing data processing work that make use of classical spectral matching algorithms. Our efforts also included the study of several methods dealing with hyperspectral image analysis work where classical computation methods involving large data sets could be replaced with quantum computation methods. The crux of the problem in computation involving a hyperspectral image data cube is to convert the large amount of data in high dimensional space to real information. Currently, using the classical model, different time consuming methods and steps are necessary to analyze these data including: Animation, Minimum Noise Fraction Transform, Pixel Purity Index algorithm, N-dimensional scatter plot, Identification of Endmember spectra - are such steps. If a quantum model of computation involving hyperspectral image data can be developed and formalized - it is highly likely that information retrieval from hyperspectral image data cubes would be a much easier process and the final information content would be much more meaningful and timely. In this case, dimensionality would not be a curse, but a blessing.

  2. Combining dynamical decoupling with fault-tolerant quantum computation

    SciTech Connect

    Ng, Hui Khoon; Preskill, John; Lidar, Daniel A.

    2011-07-15

    We study how dynamical decoupling (DD) pulse sequences can improve the reliability of quantum computers. 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 quantum computer 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.

  3. Linear optical quantum computing in a single spatial mode.

    PubMed

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

    2013-10-11

    We present a scheme for linear optical quantum computing 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 quantum computing 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.

  4. Scheme for Entering Binary Data Into a Quantum Computer

    NASA Technical Reports Server (NTRS)

    Williams, Colin

    2005-01-01

    A quantum algorithm provides for the encoding of an exponentially large number of classical data bits by use of a smaller (polynomially large) number of quantum bits (qubits). The development of this algorithm was prompted by the need, heretofore not satisfied, for a means of entering real-world binary data into a quantum computer. The data format provided by this algorithm is suitable for subsequent ultrafast quantum processing of the entered data. Potential applications lie in disciplines (e.g., genomics) in which one needs to search for matches between parts of very long sequences of data. For example, the algorithm could be used to encode the N-bit-long human genome in only log2N qubits. The resulting log2N-qubit state could then be used for subsequent quantum data processing - for example, to perform rapid comparisons of sequences.

  5. Universal quantum computation with hybrid spin-Majorana qubits

    NASA Astrophysics Data System (ADS)

    Hoffman, Silas; Schrade, Constantin; Klinovaja, Jelena; Loss, Daniel

    2016-07-01

    We theoretically propose a set of universal quantum gates acting on a hybrid qubit formed by coupling a quantum-dot spin qubit and Majorana fermion qubit. First, we consider a quantum dot that is tunnel coupled to two topological superconductors. The effective spin-Majorana exchange facilitates a hybrid cnot gate for which either qubit can be the control or target. The second setup is a modular scalable network of topological superconductors and quantum dots. As a result of the exchange interaction between adjacent spin qubits, a cnot gate is implemented that acts on neighboring Majorana qubits and eliminates the necessity of interqubit braiding. In both setups, the spin-Majorana exchange interaction allows for a phase gate, acting on either the spin or the Majorana qubit, and for a swap or hybrid swap gate which is sufficient for universal quantum computation without projective measurements.

  6. Computational studies of quantum spin systems

    NASA Astrophysics Data System (ADS)

    Wang, Ling

    Quantum spin models are important for studying the magnetic behavior of strongly correlated electronic insulators. Specifically, the 2D S = 1/2 Heisenberg model closely captures the antiferromagnetic state of CuO2 layers of the high-Tc superconductor parent compounds at half band filling. Introducing competing interactions or disorder can drive quantum phase transitions to other new states. I use the stochastic series expansion (SSE) quantum Monte Carlo (QMC) method and finite-size scaling to study the quantum critical points of two Heisenberg bilayers, each with intra- and inter-plane couplings J and J⊥. Tuning the inter- to intra-layer coupling constant ratio g = J⊥ /J drives a quantum phase transition between the Neel ordered state and a quantum disordered state. I discuss the ground-state finite-size scaling properties of three different quantities and extract the critical value of the coupling ratio gc. The results improve gc by more than an order of magnitude over the previous best estimates. Upon doping with static non-magnetic impurities, (e.g., substituting Cu with Zn), the cuprate layer is driven through a percolation phase transition. While the static properties are described by 2D classical percolation, the dynamical properties are quantum mechanical. I use exact diagonalization to calculate the lowest excitation gap Delta and use SSE to study an upper bound for Delta obtained from sum rules. Scaling the gap distribution with the cluster length L, a dynamic exponent z ≈ 2Df is obtained, where Df is the fractal dimensionality of the percolating cluster. I present several arguments showing that the low-energy excitations are due to weakly coupled effective moments formed owing to local imbalance in sublattice occupation. Many interesting quantum spin models lead to negative signs in the importance weight used in QMC sampling, and thus this method cannot be used. Matrix product states (MPSs) and tensor product states (TPSs) have recently been

  7. Quantum algorithms for spin models and simulable gate sets for quantum computation

    NASA Astrophysics Data System (ADS)

    van den Nest, M.; Dür, W.; Raussendorf, R.; Briegel, H. J.

    2009-11-01

    We present simple mappings between classical lattice models and quantum circuits, which provide a systematic formalism to obtain quantum algorithms to approximate partition functions of lattice models in certain complex-parameter regimes. We, e.g., present an efficient quantum algorithm for the six-vertex model as well as a two-dimensional Ising-type model. We show that classically simulating these (complex-parameter) spin models is as hard as simulating universal quantum computation, i.e., BQP complete (BQP denotes bounded-error quantum polynomial time). Furthermore, our mappings provide a framework to obtain efficiently simulable quantum gate sets from exactly solvable classical models. We, e.g., show that the simulability of Valiant’s match gates can be recovered by using the solvability of the free-fermion eight-vertex model.

  8. An Invitation to the Mathematics of Topological Quantum Computation

    NASA Astrophysics Data System (ADS)

    Rowell, E. C.

    2016-03-01

    Two-dimensional topological states of matter offer a route to quantum computation that would be topologically protected against the nemesis of the quantum circuit model: decoherence. Research groups in industry, government and academic institutions are pursuing this approach. We give a mathematician's perspective on some of the advantages and challenges of this model, highlighting some recent advances. We then give a short description of how we might extend the theory to three-dimensional materials.

  9. Computers and Writing. Tech Use Guide: Using Computer Technology.

    ERIC Educational Resources Information Center

    Dalton, Bridget

    One of nine brief guides for special educators on using computer technology, this guide focuses on the use of computers to improve skills and attitudes in writing instruction. Pre-writing tools such as group brainstorming, story webs, free-writing, journal entries, and prewriting guides help generate ideas and can be carried out either on or off…

  10. Information-Technology Approach to Quantum Feedback Control

    NASA Astrophysics Data System (ADS)

    Dong, Dao-Yi; Zhang, Chen-Bin; Chen, Zong-Hai; Chen, Chun-Lin

    Quantum control theory is profitably reexamined from the perspective of quantum information, two results on the role of quantum information technology in quantum feedback control are presented and two quantum feedback control schemes, teleportation-based distant quantum feedback control and quantum feedback control with quantum cloning, are proposed. In the first feedback scheme, the output from the quantum system to be controlled is fed back into the distant actuator via teleportation to alter the dynamics of system. The result theoretically shows that it can accomplish some tasks such as distant feedback quantum control that Markovian or Bayesian quantum feedback can not complete. In the second feedback strategy, the design of quantum feedback control algorithms is separated into a state recognition step, which gives "on-off" signal to the actuator through recognizing some copies from the cloning machine, and a feedback (control) step using another copies of cloning machine. A compromise between information acquisition and measurement disturbance is established, and this strategy can perform some quantum control tasks with coherent feedback.

  11. Individual addressing in quantum computation through spatial refocusing

    NASA Astrophysics Data System (ADS)

    Shen, C.; Gong, Z.-X.; Duan, L.-M.

    2013-11-01

    Separate addressing of individual qubits is a challenging requirement for scalable quantum computation, and crosstalk between operations on neighboring qubits remains a significant source of error for current experimental implementations of multiqubit platforms. We propose a scheme based on spatial refocusing from interference of several coherent laser beams to significantly reduce the crosstalk error for any type of quantum gate. A general framework is developed for the spatial refocusing technique, in particular with practical Gaussian beams, and we show that the crosstalk-induced infidelity of quantum gates can be reduced by several orders of magnitude with a moderate cost of a few correction laser beams under typical experimental conditions.

  12. Topological quantum computing with Read-Rezayi states.

    PubMed

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

    2009-10-16

    Read-Rezayi fractional quantum Hall states are among the prime candidates for realizing non-Abelian anyons which, in principle, can be used for topological quantum computation. We present a prescription for efficiently finding braids which can be used to carry out a universal set of quantum gates on encoded qubits based on anyons of the Read-Rezayi states with k>2, k not equal 4. This work extends previous results which only applied to the case k=3 (Fibonacci) and clarifies why, in that case, gate constructions are simpler than for a generic Read-Rezayi state.

  13. Computer studies of multiple-quantum spin dynamics

    SciTech Connect

    Murdoch, J.B.

    1982-11-01

    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.

  14. Limitations of quantum computing with Gaussian cluster states

    SciTech Connect

    Ohliger, M.; Kieling, K.; Eisert, J.

    2010-10-15

    We discuss the potential and limitations of Gaussian cluster states for measurement-based quantum computing. 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 quantum computing. The results can equally be viewed as referring to Gaussian quantum repeater networks.

  15. Advancing colloidal quantum dot photovoltaic technology

    NASA Astrophysics Data System (ADS)

    Cheng, Yan; Arinze, Ebuka S.; Palmquist, Nathan; Thon, Susanna M.

    2016-06-01

    Colloidal quantum dots (CQDs) are attractive materials for solar cells due to their low cost, ease of fabrication and spectral tunability. Progress in CQD photovoltaic technology over the past decade has resulted in power conversion efficiencies approaching 10%. In this review, we give an overview of this progress, and discuss limiting mechanisms and paths for future improvement in CQD solar cell technology.We briefly summarize nanoparticle synthesis and film processing methods and evaluate the optoelectronic properties of CQD films, including the crucial role that surface ligands play in materials performance. We give an overview of device architecture engineering in CQD solar cells. The compromise between carrier extraction and photon absorption in CQD photovoltaics is analyzed along with different strategies for overcoming this trade-off. We then focus on recent advances in absorption enhancement through innovative device design and the use of nanophotonics. Several light-trapping schemes, which have resulted in large increases in cell photocurrent, are described in detail. In particular, integrating plasmonic elements into CQD devices has emerged as a promising approach to enhance photon absorption through both near-field coupling and far-field scattering effects. We also discuss strategies for overcoming the single junction efficiency limits in CQD solar cells, including tandem architectures, multiple exciton generation and hybrid materials schemes. Finally, we offer a perspective on future directions for the field and the most promising paths for achieving higher device efficiencies.

  16. Theory-Guided Technology in Computer Science

    NASA Astrophysics Data System (ADS)

    Ben-Ari, Mordechai

    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.

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

    NASA Astrophysics Data System (ADS)

    Poulsen Nautrup, Hendrik; Wei, Tzu-Chieh

    Measurement-based quantum computation (MBQC) is a model for quantum information processing utilizing only local measurements on suitably entangled resource states for the implementation of quantum gates. A complete characterization for universal resource states is still missing. It has been shown that symmetry-protected topological order (SPTO) in one dimension can be exploited for the protection of certain quantum gates in MBQC. Here we investigate whether any 2D nontrivial SPTO states can serve as resource for MBQC. In particular, we show that the nontrivial SPTO ground state of the CZX model on the square lattice by Chen et al. [Phys. Rev. B 84, 235141 (2011)] can be reduced to a 2D cluster state by local measurement, hence a universal resource state. Such ground states have been generalized to qudits with symmetry action described by three cocycles of a finite group G of order d and shown to exhibit nontrivial SPTO. We also extend these to arbitary lattices and show that the generalized two-dimensional plaquette states on arbitrary lattices exhibit nontrivial SPTO in terms of symmetry fractionalization and that they are universal resource states for quantum computation. SPTO states therefore can provide a new playground for measurement-based quantum computation. This work was supported in part by the National Science Foundation.

  18. Computing, Information and Communications Technology (CICT) Website

    NASA Technical Reports Server (NTRS)

    Hardman, John; Tu, Eugene (Technical Monitor)

    2002-01-01

    The Computing, Information and Communications Technology Program (CICT) was established in 2001 to ensure NASA's Continuing leadership in emerging technologies. It is a coordinated, Agency-wide effort to develop and deploy key enabling technologies for a broad range of mission-critical tasks. The NASA CICT program is designed to address Agency-specific computing, information, and communications technology requirements beyond the projected capabilities of commercially available solutions. The areas of technical focus have been chosen for their impact on NASA's missions, their national importance, and the technical challenge they provide to the Program. In order to meet its objectives, the CICT Program is organized into the following four technology focused projects: 1) Computing, Networking and Information Systems (CNIS); 2) Intelligent Systems (IS); 3) Space Communications (SC); 4) Information Technology Strategic Research (ITSR).

  19. Advances and trends in computational structures technology

    NASA Technical Reports Server (NTRS)

    Noor, A. K.; Venneri, S. L.

    1990-01-01

    The major goals of computational structures technology (CST) are outlined, and recent advances in CST are examined. These include computational material modeling, stochastic-based modeling, computational methods for articulated structural dynamics, strategies and numerical algorithms for new computing systems, multidisciplinary analysis and optimization. The role of CST in the future development of structures technology and the multidisciplinary design of future flight vehicles is addressed, and the future directions of CST research in the prediction of failures of structural components, the solution of large-scale structural problems, and quality assessment and control of numerical simulations are discussed.

  20. Positive Wigner Functions Render Classical Simulation of Quantum Computation Efficient

    NASA Astrophysics Data System (ADS)

    Mari, A.; Eisert, J.

    2012-12-01

    We show that quantum circuits where the initial state and all the following quantum operations can be represented by positive Wigner functions can be classically efficiently simulated. This is true both for continuous-variable as well as discrete variable systems in odd prime dimensions, two cases which will be treated on entirely the same footing. Noting the fact that Clifford and Gaussian operations preserve the positivity of the Wigner function, our result generalizes the Gottesman-Knill theorem. Our algorithm provides a way of sampling from the output distribution of a computation or a simulation, including the efficient sampling from an approximate output distribution in the case of sampling imperfections for initial states, gates, or measurements. In this sense, this work highlights the role of the positive Wigner function as separating classically efficiently simulable systems from those that are potentially universal for quantum computing and simulation, and it emphasizes the role of negativity of the Wigner function as a computational resource.

  1. Ground-state geometric quantum computing in superconducting systems

    SciTech Connect

    Solinas, P.; Moettoenen, M.

    2010-11-15

    We present a theoretical proposal for the implementation of geometric quantum computing 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 quantum computing. The introduced paradigm for the implementation of geometric quantum computing is expected to be robust against environmental effects.

  2. Randomized benchmarking in measurement-based quantum computing

    NASA Astrophysics Data System (ADS)

    Alexander, Rafael N.; Turner, Peter S.; Bartlett, Stephen D.

    2016-09-01

    Randomized benchmarking is routinely used as an efficient method for characterizing the performance of sets of elementary logic gates in small quantum devices. In the measurement-based model of quantum computation, logic gates are implemented via single-site measurements on a fixed universal resource state. Here we adapt the randomized benchmarking protocol for a single qubit to a linear cluster state computation, which provides partial, yet efficient characterization of the noise associated with the target gate set. Applying randomized benchmarking to measurement-based quantum computation exhibits an interesting interplay between the inherent randomness associated with logic gates in the measurement-based model and the random gate sequences used in benchmarking. We consider two different approaches: the first makes use of the standard single-qubit Clifford group, while the second uses recently introduced (non-Clifford) measurement-based 2-designs, which harness inherent randomness to implement gate sequences.

  3. Exploring quantum computing application to satellite data assimilation

    NASA Astrophysics Data System (ADS)

    Cheung, S.; Zhang, S. Q.

    2015-12-01

    This is an exploring work on potential application of quantum computing to a scientific data optimization problem. On classical computational platforms, the physical domain of a satellite data assimilation problem is represented by a discrete variable transform, and classical minimization algorithms are employed to find optimal solution of the analysis cost function. The computation becomes intensive and time-consuming when the problem involves large number of variables and data. The new quantum computer opens a very different approach both in conceptual programming and in hardware architecture for solving optimization problem. In order to explore if we can utilize the quantum computing machine architecture, we formulate a satellite data assimilation experimental case in the form of quadratic programming optimization problem. We find a transformation of the problem to map it into Quadratic Unconstrained Binary Optimization (QUBO) framework. Binary Wavelet Transform (BWT) will be applied to the data assimilation variables for its invertible decomposition and all calculations in BWT are performed by Boolean operations. The transformed problem will be experimented as to solve for a solution of QUBO instances defined on Chimera graphs of the quantum computer.

  4. (CICT) Computing, Information, and Communications Technology Overview

    NASA Technical Reports Server (NTRS)

    VanDalsem, William R.

    2003-01-01

    The goal of the Computing, Information, and Communications Technology (CICT) program is to enable NASA's Scientific Research, Space Exploration, and Aerospace Technology Missions with greater mission assurance, for less cost, with increased science return through the development and use of advanced computing, information and communications technologies. This viewgraph presentation includes diagrams of how the political guidance behind CICT is structured. The presentation profiles each part of the NASA Mission in detail, and relates the Mission to the activities of CICT. CICT's Integrated Capability Goal is illustrated, and hypothetical missions which could be enabled by CICT are profiled. CICT technology development is profiled.

  5. Robust and scalable optical one-way quantum computation

    SciTech Connect

    Wang Hefeng; Yang Chuiping; Nori, Franco

    2010-05-15

    We propose an efficient approach for deterministically generating scalable cluster states with photons. This approach involves unitary transformations performed on atoms coupled to optical cavities. Its operation cost scales linearly with the number of qubits in the cluster state, and photon qubits are encoded such that single-qubit operations can be easily implemented by using linear optics. Robust optical one-way quantum computation can be performed since cluster states can be stored in atoms and then transferred to photons that can be easily operated and measured. Therefore, this proposal could help in performing robust large-scale optical one-way quantum computation.

  6. Closed timelike curves in measurement-based quantum computation

    NASA Astrophysics Data System (ADS)

    Dias da Silva, Raphael; Galvão, Ernesto F.; Kashefi, Elham

    2011-01-01

    Many results have been recently obtained regarding the power of hypothetical closed timelike curves (CTCs) in quantum computation. Here we show that the one-way model of measurement-based quantum computation encompasses in a natural way the CTC model proposed by Bennett, Schumacher, and Svetlichny. We identify a class of CTCs in this model that can be simulated deterministically and point to a fundamental limitation of Deutsch’s CTC model which leads to predictions conflicting with those of the one-way model.

  7. Closed timelike curves in measurement-based quantum computation

    SciTech Connect

    Dias da Silva, Raphael; Galvao, Ernesto F.; Kashefi, Elham

    2011-01-15

    Many results have been recently obtained regarding the power of hypothetical closed timelike curves (CTCs) in quantum computation. Here we show that the one-way model of measurement-based quantum computation encompasses in a natural way the CTC model proposed by Bennett, Schumacher, and Svetlichny. We identify a class of CTCs in this model that can be simulated deterministically and point to a fundamental limitation of Deutsch's CTC model which leads to predictions conflicting with those of the one-way model.

  8. Efficient computations of quantum canonical Gibbs state in phase space

    NASA Astrophysics Data System (ADS)

    Bondar, Denys I.; Campos, Andre G.; Cabrera, Renan; Rabitz, Herschel A.

    2016-06-01

    The Gibbs canonical state, as a maximum entropy density matrix, represents a quantum system in equilibrium with a thermostat. This state plays an essential role in thermodynamics and serves as the initial condition for nonequilibrium dynamical simulations. We solve a long standing problem for computing the Gibbs state Wigner function with nearly machine accuracy by solving the Bloch equation directly in the phase space. Furthermore, the algorithms are provided yielding high quality Wigner distributions for pure stationary states as well as for Thomas-Fermi and Bose-Einstein distributions. The developed numerical methods furnish a long-sought efficient computation framework for nonequilibrium quantum simulations directly in the Wigner representation.

  9. Efficient computations of quantum canonical Gibbs state in phase space.

    PubMed

    Bondar, Denys I; Campos, Andre G; Cabrera, Renan; Rabitz, Herschel A

    2016-06-01

    The Gibbs canonical state, as a maximum entropy density matrix, represents a quantum system in equilibrium with a thermostat. This state plays an essential role in thermodynamics and serves as the initial condition for nonequilibrium dynamical simulations. We solve a long standing problem for computing the Gibbs state Wigner function with nearly machine accuracy by solving the Bloch equation directly in the phase space. Furthermore, the algorithms are provided yielding high quality Wigner distributions for pure stationary states as well as for Thomas-Fermi and Bose-Einstein distributions. The developed numerical methods furnish a long-sought efficient computation framework for nonequilibrium quantum simulations directly in the Wigner representation. PMID:27415384

  10. Computer Programming Projects in Technology Courses.

    ERIC Educational Resources Information Center

    Thomas, Charles R.

    1985-01-01

    Discusses programming projects in applied technology courses, examining documentation, formal reports, and implementation. Includes recommendations based on experience with a sophomore machine elements course which provided computers for problem solving exercises. (DH)

  11. Ultimate computing. Biomolecular consciousness and nano Technology

    SciTech Connect

    Hameroff, S.R.

    1987-01-01

    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.

  12. Quantum annealing: The fastest route to quantum computation?

    NASA Astrophysics Data System (ADS)

    Smorra, C.; Blaum, K.; Bojtar, L.; Borchert, M.; Franke, K. A.; Higuchi, T.; Leefer, N.; Nagahama, H.; Matsuda, Y.; Mooser, A.; Niemann, M.; Ospelkaus, C.; Quint, W.; Schneider, G.; Sellner, S.; Tanaka, T.; Van Gorp, S.; Walz, J.; Yamazaki, Y.; Ulmer, S.

    2015-11-01

    The Baryon Antibaryon Symmetry Experiment (BASE) aims at performing a stringent test of the combined charge parity and time reversal (CPT) symmetry by comparing the magnetic moments of the proton and the antiproton with high precision. Using single particles in a Penning trap, the proton/antiproton g-factors, i.e. the magnetic moment in units of the nuclear magneton, are determined by measuring the respective ratio of the spin-precession frequency to the cyclotron frequency. The spin precession frequency is measured by non-destructive detection of spin quantum transitions using the continuous Stern-Gerlach effect, and the cyclotron frequency is determined from the particle*s motional eigenfrequencies in the Penning trap using the invariance theorem. By application of the double Penning-trap method we expect that in our measurements a fractional precision of δ g/ g 10-9 can be achieved. The successful application of this method to the antiproton will consist a factor 1000 improvement in the fractional precision of its magnetic moment. The BASE collaboration has constructed and commissioned a new experiment at the Antiproton Decelerator (AD) of CERN. This article describes and summarizes the physical and technical aspects of this new experiment.

  13. Computer technology forecast study for general aviation

    NASA Technical Reports Server (NTRS)

    Seacord, C. L.; Vaughn, D.

    1976-01-01

    A multi-year, multi-faceted program is underway to investigate and develop potential improvements in airframes, engines, and avionics for general aviation aircraft. The objective of this study was to assemble information that will allow the government to assess the trends in computer and computer/operator interface technology that may have application to general aviation in the 1980's and beyond. The current state of the art of computer hardware is assessed, technical developments in computer hardware are predicted, and nonaviation large volume users of computer hardware are identified.

  14. Magnetic resonance force microscopy and a solid state quantum computer.

    SciTech Connect

    Pelekhov, D. V.; Martin, I.; Suter, A.; Reagor, D. W.; Hammel, P. C.

    2001-01-01

    A Quantum Computer (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 Quantum Computer (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.

  15. Quantum computing with an electron spin ensemble.

    PubMed

    Wesenberg, J H; Ardavan, A; Briggs, G A D; Morton, J J L; Schoelkopf, R J; Schuster, D I; Mølmer, K

    2009-08-14

    We propose to encode a register of quantum bits in different collective electron spin wave excitations in a solid medium. Coupling to spins is enabled by locating them in the vicinity of a superconducting transmission line cavity, and making use of their strong collective coupling to the quantized radiation field. The transformation between different spin waves is achieved by applying gradient magnetic fields across the sample, while a Cooper pair box, resonant with the cavity field, may be used to carry out one- and two-qubit gate operations.

  16. Vision for single flux quantum very large scale integrated technology

    NASA Astrophysics Data System (ADS)

    Silver, Arnold; Bunyk, Paul; Kleinsasser, Alan; Spargo, John

    2006-05-01

    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 to produce SFQ circuits and chips. Assuming the use of tools equivalent to those employed in the semiconductor industry, we estimate the density of Josephson junctions, circuit speed, and power dissipation that could be achieved with SFQ technology. Today, CMOS lithography is at 90-65 nm with about 20 layers. Assuming equivalent technology, aggressively increasing the current density above 100 kA cm-2 to achieve junction speeds approximately 1000 GHz, and reducing device footprints by converting device profiles from planar to vertical, one could expect to integrate about 250 M Josephson junctions cm-2 into SFQ digital circuits. This should enable circuit operation with clock frequencies above 200 GHz and place approximately 20 K gates within a radius of one clock period. As a result, complete microprocessors, including integrated memory registers, could be fabricated on a single chip. This technology was exported from the United States in accordance with the US Department of Commerce Export Administration Regulations (EAR) for ultimate destination in the United Kingdom. Diversion contrary to US law prohibited.

  17. [Computer technologies in teaching pathological anatomy].

    PubMed

    Ponomarev, A B; Fedorov, D N

    2015-01-01

    The paper gives experience with personal computers used at the Academician A.L. Strukov Department of Pathological Anatomy for more than 20 years. It shows the objective necessity of introducing computer technologies at all stages of acquiring skills in anatomical pathology, including lectures, students' free work, test check, etc.

  18. Applications of Computer Technology in Intercollegiate Debate.

    ERIC Educational Resources Information Center

    Kay, Jack, Ed.

    1986-01-01

    Focusing on how computers can and should be used in intercollegiate forensics, this journal issue offers the perspectives of a number of forensics instructors. The lead article, "Applications of Computer Technology in Intercollegiate Debate" by Theodore F. Sheckels, Jr., discusses five areas in which forensics educators might use computer…

  19. Page Recognition: Quantum Leap In Recognition Technology

    NASA Astrophysics Data System (ADS)

    Miller, Larry

    1989-07-01

    No milestone has proven as elusive as the always-approaching "year of the LAN," but the "year of the scanner" might claim the silver medal. Desktop scanners have been around almost as long as personal computers. And everyone thinks they are used for obvious desktop-publishing and business tasks like scanning business documents, magazine articles and other pages, and translating those words into files your computer understands. But, until now, the reality fell far short of the promise. Because it's true that scanners deliver an accurate image of the page to your computer, but the software to recognize this text has been woefully disappointing. Old optical-character recognition (OCR) software recognized such a limited range of pages as to be virtually useless to real users. (For example, one OCR vendor specified 12-point Courier font from an IBM Selectric typewriter: the same font in 10-point, or from a Diablo printer, was unrecognizable!) Computer dealers have told me the chasm between OCR expectations and reality is so broad and deep that nine out of ten prospects leave their stores in disgust when they learn the limitations. And this is a very important, very unfortunate gap. Because the promise of recognition -- what people want it to do -- carries with it tremendous improvements in our productivity and ability to get tons of written documents into our computers where we can do real work with it. The good news is that a revolutionary new development effort has led to the new technology of "page recognition," which actually does deliver the promise we've always wanted from OCR. I'm sure every reader appreciates the breakthrough represented by the laser printer and page-makeup software, a combination so powerful it created new reasons for buying a computer. A similar breakthrough is happening right now in page recognition: the Macintosh (and, I must admit, other personal computers) equipped with a moderately priced scanner and OmniPage software (from Caere

  20. Deterministic entanglement distillation for secure double-server blind quantum computation

    PubMed Central

    Sheng, Yu-Bo; Zhou, Lan

    2015-01-01

    Blind quantum computation (BQC) provides an efficient method for the client who does not have enough sophisticated technology and knowledge to perform universal quantum computation. The single-server BQC protocol requires the client to have some minimum quantum ability, while the double-server BQC protocol makes the client's device completely classical, resorting to the pure and clean Bell state shared by two servers. Here, we provide a deterministic entanglement distillation protocol in a practical noisy environment for the double-server BQC protocol. This protocol can get the pure maximally entangled Bell state. The success probability can reach 100% in principle. The distilled maximally entangled states can be remaind to perform the BQC protocol subsequently. The parties who perform the distillation protocol do not need to exchange the classical information and they learn nothing from the client. It makes this protocol unconditionally secure and suitable for the future BQC protocol. PMID:25588565

  1. Computer Technology: For Better or Worse?

    ERIC Educational Resources Information Center

    Ware, Willis H.

    Computer technology ought to be among the most helpful and useful of any technology, but if it is not treated with care, the society will be worse off for it. The Federal Privacy Act of 1974 established the Privacy Protection Study Commission whose business started in June, 1975. In examination of the private sector, the commission's…

  2. Crystal gazing v. computer system technology projections.

    NASA Astrophysics Data System (ADS)

    Wells, Donald C.

    The following sections are included: * INTRODUCTION * PREDICTIONS FOR THE EARLY NINETIES * EVOLUTION OF COMPUTER CAPACITIES * UNIX IS COMING! * GRAPHICS TECHNOLOGY * MASSIVE ARCHIVAL STORAGE * ADA AND PROJECT MANAGEMENT * ARTIFICIAL INTELLIGENCE TECHNOLOGY * FILLING IN THE DETAILS * UNIX DESIDERATA * ICON-DRIVEN COMMAND LANGUAGES? * AI AGAIN * DISCUSSION * REFERENCES * BIBLIOGRAPHY—FOR FURTHER READING

  3. Quantum computing with collective ensembles of multilevel systems.

    PubMed

    Brion, E; Mølmer, K; Saffman, M

    2007-12-31

    We propose a new physical approach for encoding and processing of quantum information in ensembles of multilevel quantum systems, where the different bits are not carried by individual particles but associated with the collective population of different internal levels. One- and two-bit gates are implemented by collective internal state transitions taking place in the presence of an excitation blockade mechanism, which restricts the population of each internal state to the values zero and unity. Quantum computers with 10-20 bits can be built via this scheme in single trapped clouds of ground state atoms subject to the Rydberg excitation blockade mechanism, and the linear dependence between register size and the number of internal quantum states in atoms offers realistic means to reach larger registers.

  4. Computational nuclear quantum many-body problem: The UNEDF project

    SciTech Connect

    Fann, George I

    2013-01-01

    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.

  5. Nano-Bio Quantum Technology for Device-Specific Materials

    NASA Technical Reports Server (NTRS)

    Choi, Sang H.

    2009-01-01

    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. Quantum technology for optical devices: a) Quantum apertures; b) Smart optical materials; c) Micro spectrometer. III. Bio-template oriented materials: a) Bionanobattery; b) Bio-fuel cells; c) Energetic materials.

  6. Sequential measurement-based quantum computing with memories

    SciTech Connect

    Roncaglia, Augusto J.; Aolita, Leandro; Ferraro, Alessandro; Acin, Antonio

    2011-06-15

    We introduce a general scheme for sequential one-way quantum computation 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.

  7. Architecture Framework for Trapped-Ion Quantum Computer based on Performance Simulation Tool

    NASA Astrophysics Data System (ADS)

    Ahsan, Muhammad

    The challenge of building scalable quantum computer lies in striking appropriate balance between designing a reliable system architecture from large number of faulty computational resources and improving the physical quality of system components. The detailed investigation of performance variation with physics of the components and the system architecture requires adequate performance simulation tool. In this thesis we demonstrate a software tool capable of (1) mapping and scheduling the quantum circuit on a realistic quantum hardware architecture with physical resource constraints, (2) evaluating the performance metrics such as the execution time and the success probability of the algorithm execution, and (3) analyzing the constituents of these metrics and visualizing resource utilization to identify system components which crucially define the overall performance. Using this versatile tool, we explore vast design space for modular quantum computer architecture based on trapped ions. We find that while success probability is uniformly determined by the fidelity of physical quantum operation, the execution time is a function of system resources invested at various layers of design hierarchy. At physical level, the number of lasers performing quantum gates, impact the latency of the fault-tolerant circuit blocks execution. When these blocks are used to construct meaningful arithmetic circuit such as quantum adders, the number of ancilla qubits for complicated non-clifford gates and entanglement resources to establish long-distance communication channels, become major performance limiting factors. Next, in order to factorize large integers, these adders are assembled into modular exponentiation circuit comprising bulk of Shor's algorithm. At this stage, the overall scaling of resource-constraint performance with the size of problem, describes the effectiveness of chosen design. By matching the resource investment with the pace of advancement in hardware technology

  8. Research on Key Technologies of Cloud Computing

    NASA Astrophysics Data System (ADS)

    Zhang, Shufen; Yan, Hongcan; Chen, Xuebin

    With the development of multi-core processors, virtualization, distributed storage, broadband Internet and automatic management, a new type of computing mode named cloud computing is produced. It distributes computation task on the resource pool which consists of massive computers, so the application systems can obtain the computing power, the storage space and software service according to its demand. It can concentrate all the computing resources and manage them automatically by the software without intervene. This makes application offers not to annoy for tedious details and more absorbed in his business. It will be advantageous to innovation and reduce cost. It's the ultimate goal of cloud computing to provide calculation, services and applications as a public facility for the public, So that people can use the computer resources just like using water, electricity, gas and telephone. Currently, the understanding of cloud computing is developing and changing constantly, cloud computing still has no unanimous definition. This paper describes three main service forms of cloud computing: SAAS, PAAS, IAAS, compared the definition of cloud computing which is given by Google, Amazon, IBM and other companies, summarized the basic characteristics of cloud computing, and emphasized on the key technologies such as data storage, data management, virtualization and programming model.

  9. Culture Computing: Interactive Technology to Explore Culture

    NASA Astrophysics Data System (ADS)

    Cheok, Adrian David

    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 computer technology 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.

  10. High threshold distributed quantum computing with three-qubit nodes

    NASA Astrophysics Data System (ADS)

    Li, Ying; Benjamin, Simon C.

    2012-09-01

    In the distributed quantum computing 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.

  11. Philosophical and metamathematical considerations of quantum mechanical computers

    NASA Astrophysics Data System (ADS)

    Caulfield, H. John; Shamir, Joseph

    1990-07-01

    We ask and give only very preliminary answers to two questions which must arise when we consider quantum mechanical computers with significant quantunt indeterminacy. First, how does this impact our belief in Church's thesis? Second, how does this impact our belief in freedom of thought?

  12. Adapting the traveling salesman problem to an adiabatic quantum computer

    NASA Astrophysics Data System (ADS)

    Warren, Richard H.

    2013-04-01

    We show how to guide a quantum computer 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.

  13. Cloud Computing Technologies and Applications

    NASA Astrophysics Data System (ADS)

    Zhu, Jinzy

    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.

  14. Using weak nonlinearity under decoherence for macroscopic entanglement generation and quantum computation

    SciTech Connect

    Jeong, Hyunseok

    2005-09-15

    Recently, there have been several suggestions that weak Kerr nonlinearity can be used for generation of macroscopic superpositions and entanglement and for linear optics quantum computation. However, it is not immediately clear that this approach can overcome decoherence effects. Our numerical study shows that nonlinearity of weak strength could be useful for macroscopic entanglement generation and quantum gate operations in the presence of decoherence. We suggest specific values for real experiments based on our analysis. Our discussion shows that the generation of macroscopic entanglement using this approach is within the reach of current technology.

  15. Human-competitive evolution of quantum computing artefacts by Genetic Programming.

    PubMed

    Massey, Paul; Clark, John A; Stepney, Susan

    2006-01-01

    We show how Genetic Programming (GP) can be used to evolve useful quantum computing artefacts of increasing sophistication and usefulness: firstly specific quantum circuits, then quantum programs, and finally system-independent quantum algorithms. We conclude the paper by presenting a human-competitive Quantum Fourier Transform (QFT) algorithm evolved by GP.

  16. Computational and Mathematical Modeling of Coupled Superconducting Quantum Interference Devices

    NASA Astrophysics Data System (ADS)

    Berggren, Susan Anne Elizabeth

    This research focuses on conducting an extensive computational investigation and mathematical analysis into the average voltage response of arrays of Superconducting Quantum Interference Devices (SQUIDs). These arrays will serve as the basis for the development of a sensitive, low noise, significantly lower Size, Weight and Power (SWaP) antenna integrated with Low-Noise Amplifier (LNA) using the SQUID technology. The goal for this antenna is to be capable of meeting all requirements for Guided Missile Destroyers (DDG) 1000 class ships for Information Operations/Signals Intelligence (IO/SIGINT) applications in Very High Frequency/Ultra High Frequency (V/UHF) bands. The device will increase the listening capability of receivers by moving technology into a new regime of energy detection allowing wider band, smaller size, more sensitive, stealthier systems. The smaller size and greater sensitivity will allow for ships to be “de-cluttered” of their current large dishes and devices, replacing everything with fewer and smaller SQUID antenna devices. The fewer devices present on the deck of a ship, the more invisible the ship will be to enemy forces. We invent new arrays of SQUIDs, optimized for signal detection with very high dynamic range and excellent spur-free dynamic range, while maintaining extreme small size (and low radar cross section), wide bandwidth, and environmentally noise limited sensitivity, effectively shifting the bottle neck of receiver systems forever away from the antenna itself deeper into the receiver chain. To accomplish these goals we develop and validate mathematical models for different designs of SQUID arrays and use them to invent a new device and systems design. This design is capable of significantly exceeding, per size weight and power, state-of-the-art receiver system measures of performance, such as bandwidth, sensitivity, dynamic range, and spurious-free dynamic range.

  17. Interplay between computable measures of entanglement and other quantum correlations

    SciTech Connect

    Girolami, Davide; Adesso, Gerardo

    2011-11-15

    Composite quantum systems can be in generic states characterized not only by entanglement but also by more general quantum correlations. The interplay between these two signatures of nonclassicality is still not completely understood. In this work we investigate this issue, focusing on computable and observable measures of such correlations: entanglement is quantified by the negativity N, while general quantum correlations are measured by the (normalized) geometric quantum discord D{sub G}. For two-qubit systems, we find that the geometric discord reduces to the squared negativity on pure states, while the relationship D{sub G}{>=}N{sup 2} holds for arbitrary mixed states. The latter result is rigorously extended to pure, Werner, and isotropic states of two-qudit systems for arbitrary d, and numerical evidence of its validity for arbitrary states of a qubit and a qutrit is provided as well. Our results establish an interesting hierarchy, which we conjecture to be universal, between two relevant and experimentally friendly nonclassicality indicators. This ties in with the intuition that general quantum correlations should at least contain and in general exceed entanglement on mixed states of composite quantum systems.

  18. Quantum computation mediated by ancillary qudits and spin coherent states

    NASA Astrophysics Data System (ADS)

    Proctor, Timothy J.; Dooley, Shane; Kendon, Viv

    2015-01-01

    Models of universal quantum computation in which the required interactions between register (computational) qubits are mediated by some ancillary system are highly relevant to experimental realizations of a quantum computer. We introduce such a universal model that employs a d -dimensional ancillary qudit. The ancilla-register interactions take the form of controlled displacements operators, with a displacement operator defined on the periodic and discrete lattice phase space of a qudit. We show that these interactions can implement controlled phase gates on the register by utilizing geometric phases that are created when closed loops are traversed in this phase space. The extra degrees of freedom of the ancilla can be harnessed to reduce the number of operations required for certain gate sequences. In particular, we see that the computational advantages of the quantum bus (qubus) architecture, which employs a field-mode ancilla, are also applicable to this model. We then explore an alternative ancilla-mediated model which employs a spin ensemble as the ancillary system and again the interactions with the register qubits are via controlled displacement operators, with a displacement operator defined on the Bloch sphere phase space of the spin coherent states of the ensemble. We discuss the computational advantages of this model and its relationship with the qubus architecture.

  19. Computational complexity of nonequilibrium steady states of quantum spin chains

    NASA Astrophysics Data System (ADS)

    Marzolino, Ugo; Prosen, Tomaž

    2016-03-01

    We study nonequilibrium steady states (NESS) of spin chains with boundary Markovian dissipation from the computational complexity point of view. We focus on X X chains whose NESS are matrix product operators, i.e., with coefficients of a tensor operator basis described by transition amplitudes in an auxiliary space. Encoding quantum algorithms in the auxiliary space, we show that estimating expectations of operators, being local in the sense that each acts on disjoint sets of few spins covering all the system, provides the answers of problems at least as hard as, and believed by many computer scientists to be much harder than, those solved by quantum computers. We draw conclusions on the hardness of the above estimations.

  20. Simulating Ising spin glasses on a quantum computer

    NASA Astrophysics Data System (ADS)

    Lidar, Daniel A.; Biham, Ofer

    1997-09-01

    A linear-time algorithm is presented for the construction of the Gibbs distribution of configurations in the Ising model, on a quantum computer. The algorithm is designed so that each run provides one configuration with a quantum probability equal to the corresponding thermodynamic weight. The partition function is thus approximated efficiently. The algorithm neither suffers from critical slowing down nor gets stuck in local minima. The algorithm can be applied in any dimension, to a class of spin-glass Ising models with a finite portion of frustrated plaquettes, diluted Ising models, and models with a magnetic field.

  1. Efficient quantum algorithm for computing n-time correlation functions.

    PubMed

    Pedernales, J S; Di Candia, R; Egusquiza, I L; Casanova, J; Solano, E

    2014-07-11

    We propose a method for computing n-time correlation functions of arbitrary spinorial, fermionic, and bosonic operators, consisting of an efficient quantum algorithm that encodes these correlations in an initially added ancillary qubit for probe and control tasks. For spinorial and fermionic systems, the reconstruction of arbitrary n-time correlation functions requires the measurement of two ancilla observables, while for bosonic variables time derivatives of the same observables are needed. Finally, we provide examples applicable to different quantum platforms in the frame of the linear response theory.

  2. Quantum computation using weak nonlinearities: Robustness against decoherence

    SciTech Connect

    Jeong, Hyunseok

    2006-05-15

    We investigate decoherence effects in the recently suggested quantum-computation scheme using weak nonlinearities, strong probe coherent fields, detection, and feedforward methods. It is shown that in the weak-nonlinearity-based quantum gates, decoherence in nonlinear media can be made arbitrarily small simply by using arbitrarily strong probe fields, if photon-number-resolving detection is used. On the contrary, we find that homodyne detection with feedforward is not appropriate for this scheme because in this case decoherence rapidly increases as the probe field gets larger.

  3. Controllable coherent population transfers in superconducting qubits for quantum computing.

    PubMed

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

    2008-03-21

    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 quantum computing. 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.

  4. Scalable photonic quantum computing assisted by quantum-dot spin in double-sided optical microcavity.

    PubMed

    Wei, Hai-Rui; Deng, Fu-Guo

    2013-07-29

    We investigate the possibility of achieving scalable photonic quantum computing by the giant optical circular birefringence induced by a quantum-dot spin in a double-sided optical microcavity as a result of cavity quantum electrodynamics. We construct a deterministic controlled-not gate on two photonic qubits by two single-photon input-output processes and the readout on an electron-medium spin confined in an optical resonant microcavity. This idea could be applied to multi-qubit gates on photonic qubits and we give the quantum circuit for a three-photon Toffoli gate. High fidelities and high efficiencies could be achieved when the side leakage to the cavity loss rate is low. It is worth pointing out that our devices work in both the strong and the weak coupling regimes. PMID:23938640

  5. Scalable photonic quantum computing assisted by quantum-dot spin in double-sided optical microcavity.

    PubMed

    Wei, Hai-Rui; Deng, Fu-Guo

    2013-07-29

    We investigate the possibility of achieving scalable photonic quantum computing by the giant optical circular birefringence induced by a quantum-dot spin in a double-sided optical microcavity as a result of cavity quantum electrodynamics. We construct a deterministic controlled-not gate on two photonic qubits by two single-photon input-output processes and the readout on an electron-medium spin confined in an optical resonant microcavity. This idea could be applied to multi-qubit gates on photonic qubits and we give the quantum circuit for a three-photon Toffoli gate. High fidelities and high efficiencies could be achieved when the side leakage to the cavity loss rate is low. It is worth pointing out that our devices work in both the strong and the weak coupling regimes.

  6. Prediction by linear regression on a quantum computer

    NASA Astrophysics Data System (ADS)

    Schuld, Maria; Sinayskiy, Ilya; Petruccione, Francesco

    2016-08-01

    We give an algorithm for prediction on a quantum computer which is based on a linear regression model with least-squares optimization. In contrast to related previous contributions suffering from the problem of reading out the optimal parameters of the fit, our scheme focuses on the machine-learning task of guessing the output corresponding to a new input given examples of data points. Furthermore, we adapt the algorithm to process nonsparse data matrices that can be represented by low-rank approximations, and significantly improve the dependency on its condition number. The prediction result can be accessed through a single-qubit measurement or used for further quantum information processing routines. The algorithm's runtime is logarithmic in the dimension of the input space provided the data is given as quantum information as an input to the routine.

  7. Adaptive quantum computation in changing environments using projective simulation

    PubMed Central

    Tiersch, M.; Ganahl, E. J.; Briegel, H. J.

    2015-01-01

    Quantum information processing devices need to be robust and stable against external noise and internal imperfections to ensure correct operation. In a setting of measurement-based quantum computation, we explore how an intelligent agent endowed with a projective simulator can act as controller to adapt measurement directions to an external stray field of unknown magnitude in a fixed direction. We assess the agent’s learning behavior in static and time-varying fields and explore composition strategies in the projective simulator to improve the agent’s performance. We demonstrate the applicability by correcting for stray fields in a measurement-based algorithm for Grover’s search. Thereby, we lay out a path for adaptive controllers based on intelligent agents for quantum information tasks. PMID:26260263

  8. Adaptive quantum computation in changing environments using projective simulation

    NASA Astrophysics Data System (ADS)

    Tiersch, M.; Ganahl, E. J.; Briegel, H. J.

    2015-08-01

    Quantum information processing devices need to be robust and stable against external noise and internal imperfections to ensure correct operation. In a setting of measurement-based quantum computation, we explore how an intelligent agent endowed with a projective simulator can act as controller to adapt measurement directions to an external stray field of unknown magnitude in a fixed direction. We assess the agent’s learning behavior in static and time-varying fields and explore composition strategies in the projective simulator to improve the agent’s performance. We demonstrate the applicability by correcting for stray fields in a measurement-based algorithm for Grover’s search. Thereby, we lay out a path for adaptive controllers based on intelligent agents for quantum information tasks.

  9. Semiconductor-inspired design principles for superconducting quantum computing.

    PubMed

    Shim, Yun-Pil; Tahan, Charles

    2016-01-01

    Superconducting circuits offer tremendous design flexibility in the quantum regime culminating most recently in the demonstration of few qubit systems supposedly approaching the threshold for fault-tolerant quantum information processing. Competition in the solid-state comes from semiconductor qubits, where nature has bestowed some very useful properties which can be utilized for spin qubit-based quantum computing. Here we begin to explore how selective design principles deduced from spin-based systems could be used to advance superconducting qubit science. We take an initial step along this path proposing an encoded qubit approach realizable with state-of-the-art tunable Josephson junction qubits. Our results show that this design philosophy holds promise, enables microwave-free control, and offers a pathway to future qubit designs with new capabilities such as with higher fidelity or, perhaps, operation at higher temperature. The approach is also especially suited to qubits on the basis of variable super-semi junctions. PMID:26983379

  10. Semiconductor-inspired design principles for superconducting quantum computing.

    PubMed

    Shim, Yun-Pil; Tahan, Charles

    2016-03-17

    Superconducting circuits offer tremendous design flexibility in the quantum regime culminating most recently in the demonstration of few qubit systems supposedly approaching the threshold for fault-tolerant quantum information processing. Competition in the solid-state comes from semiconductor qubits, where nature has bestowed some very useful properties which can be utilized for spin qubit-based quantum computing. Here we begin to explore how selective design principles deduced from spin-based systems could be used to advance superconducting qubit science. We take an initial step along this path proposing an encoded qubit approach realizable with state-of-the-art tunable Josephson junction qubits. Our results show that this design philosophy holds promise, enables microwave-free control, and offers a pathway to future qubit designs with new capabilities such as with higher fidelity or, perhaps, operation at higher temperature. The approach is also especially suited to qubits on the basis of variable super-semi junctions.

  11. Semiconductor-inspired design principles for superconducting quantum computing

    PubMed Central

    Shim, Yun-Pil; Tahan, Charles

    2016-01-01

    Superconducting circuits offer tremendous design flexibility in the quantum regime culminating most recently in the demonstration of few qubit systems supposedly approaching the threshold for fault-tolerant quantum information processing. Competition in the solid-state comes from semiconductor qubits, where nature has bestowed some very useful properties which can be utilized for spin qubit-based quantum computing. Here we begin to explore how selective design principles deduced from spin-based systems could be used to advance superconducting qubit science. We take an initial step along this path proposing an encoded qubit approach realizable with state-of-the-art tunable Josephson junction qubits. Our results show that this design philosophy holds promise, enables microwave-free control, and offers a pathway to future qubit designs with new capabilities such as with higher fidelity or, perhaps, operation at higher temperature. The approach is also especially suited to qubits on the basis of variable super-semi junctions. PMID:26983379

  12. Semiconductor-inspired design principles for superconducting quantum computing

    NASA Astrophysics Data System (ADS)

    Shim, Yun-Pil; Tahan, Charles

    2016-03-01

    Superconducting circuits offer tremendous design flexibility in the quantum regime culminating most recently in the demonstration of few qubit systems supposedly approaching the threshold for fault-tolerant quantum information processing. Competition in the solid-state comes from semiconductor qubits, where nature has bestowed some very useful properties which can be utilized for spin qubit-based quantum computing. Here we begin to explore how selective design principles deduced from spin-based systems could be used to advance superconducting qubit science. We take an initial step along this path proposing an encoded qubit approach realizable with state-of-the-art tunable Josephson junction qubits. Our results show that this design philosophy holds promise, enables microwave-free control, and offers a pathway to future qubit designs with new capabilities such as with higher fidelity or, perhaps, operation at higher temperature. The approach is also especially suited to qubits on the basis of variable super-semi junctions.

  13. Quantum computation of the electromagnetic cross section of dielectric targets

    NASA Astrophysics Data System (ADS)

    Lanzagorta, Marco; Uhlmann, Jeffrey; Jitrik, Oliverio; Venegas-Andraca, Salvador E.; Wiesman, Seth

    2016-05-01

    The Radar Cross Section (RCS) is a crucial element for assessing target visibility and target characterization, and it depends not only on the target's geometry but also on its composition. However, the calculation of the RCS is a challenging task due to the mathematical description of electromagnetic phenomena as well as the computational resources needed. In this paper, we will introduce two ideas for the use of quantum information processing techniques to calculate the RCS of dielectric targets. The first is to use toolboxes of quantum functions to determine the geometric component of the RCS. The second idea is to use quantum walks, expressed in terms of scattering processes, to model radar absorbing materials.

  14. Is the brain a Clifford algebra quantum computer?

    NASA Astrophysics Data System (ADS)

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

    2001-11-01

    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 O(kn log N), respectively. Our hypotheses are 1) the brain of primates calculates hypercomplex-valued invariants of an image during recognizing, 2) visual systems of animals with different evolutionary history use different hypercomplex algebras. The main goal of the paper is to show that quantum Clifford algebras can be used to solve pattern recognition in multispectral environment in a natural and effective manner.

  15. Bifurcation-based adiabatic quantum computation with a nonlinear oscillator network

    NASA Astrophysics Data System (ADS)

    Goto, Hayato

    The dynamics of nonlinear systems qualitatively change depending on their parameters, which is called bifurcation. A quantum-mechanical nonlinear oscillator can yield a quantum superposition of two oscillation states, known as a Schrödinger cat state, via its bifurcation with a slowly varying parameter. Here we propose a quantum computer comprising such quantum nonlinear oscillators, instead of quantum bits, to solve hard combinatorial optimization problems. The nonlinear oscillator network finds optimal solutions via quantum adiabatic evolution, where nonlinear terms are increased slowly, in contrast to conventional adiabatic quantum computation or quantum annealing. To distinguish them, we refer to the present approach as bifurcation-based adiabatic quantum computation. Our numerical simulation results suggest that quantum superposition and quantum fluctuation work effectively to find optimal solutions.

  16. Exploring the quantum speed limit with computer games.

    PubMed

    Sørensen, Jens Jakob W H; Pedersen, Mads Kock; Munch, Michael; Haikka, Pinja; Jensen, Jesper Halkjær; Planke, Tilo; Andreasen, Morten Ginnerup; Gajdacz, Miroslav; Mølmer, Klaus; Lieberoth, Andreas; Sherson, Jacob F

    2016-04-14

    Humans routinely solve problems of immense computational complexity by intuitively forming simple, low-dimensional heuristic strategies. Citizen science (or crowd sourcing) is a way of exploiting this ability by presenting scientific research problems to non-experts. 'Gamification'--the application of game elements in a non-game context--is an effective tool with which to enable citizen scientists to provide solutions to research problems. The citizen science games Foldit, EteRNA and EyeWire have been used successfully to study protein and RNA folding and neuron mapping, but so far gamification has not been applied to problems in quantum physics. Here we report on Quantum Moves, an online platform gamifying optimization problems in quantum physics. We show that human players are able to find solutions to difficult problems associated with the task of quantum computing. Players succeed where purely numerical optimization fails, and analyses of their solutions provide insights into the problem of optimization of a more profound and general nature. Using player strategies, we have thus developed a few-parameter heuristic optimization method that efficiently outperforms the most prominent established numerical methods. The numerical complexity associated with time-optimal solutions increases for shorter process durations. To understand this better, we produced a low-dimensional rendering of the optimization landscape. This rendering reveals why traditional optimization methods fail near the quantum speed limit (that is, the shortest process duration with perfect fidelity). Combined analyses of optimization landscapes and heuristic solution strategies may benefit wider classes of optimization problems in quantum physics and beyond. PMID:27075097

  17. Exploring the quantum speed limit with computer games

    NASA Astrophysics Data System (ADS)

    Sørensen, Jens Jakob W. H.; Pedersen, Mads Kock; Munch, Michael; Haikka, Pinja; Jensen, Jesper Halkjær; Planke, Tilo; Andreasen, Morten Ginnerup; Gajdacz, Miroslav; Mølmer, Klaus; Lieberoth, Andreas; Sherson, Jacob F.

    2016-04-01

    Humans routinely solve problems of immense computational complexity by intuitively forming simple, low-dimensional heuristic strategies. Citizen science (or crowd sourcing) is a way of exploiting this ability by presenting scientific research problems to non-experts. ‘Gamification’—the application of game elements in a non-game context—is an effective tool with which to enable citizen scientists to provide solutions to research problems. The citizen science games Foldit, EteRNA and EyeWire have been used successfully to study protein and RNA folding and neuron mapping, but so far gamification has not been applied to problems in quantum physics. Here we report on Quantum Moves, an online platform gamifying optimization problems in quantum physics. We show that human players are able to find solutions to difficult problems associated with the task of quantum computing. Players succeed where purely numerical optimization fails, and analyses of their solutions provide insights into the problem of optimization of a more profound and general nature. Using player strategies, we have thus developed a few-parameter heuristic optimization method that efficiently outperforms the most prominent established numerical methods. The numerical complexity associated with time-optimal solutions increases for shorter process durations. To understand this better, we produced a low-dimensional rendering of the optimization landscape. This rendering reveals why traditional optimization methods fail near the quantum speed limit (that is, the shortest process duration with perfect fidelity). Combined analyses of optimization landscapes and heuristic solution strategies may benefit wider classes of optimization problems in quantum physics and beyond.

  18. Exploring the quantum speed limit with computer games.

    PubMed

    Sørensen, Jens Jakob W H; Pedersen, Mads Kock; Munch, Michael; Haikka, Pinja; Jensen, Jesper Halkjær; Planke, Tilo; Andreasen, Morten Ginnerup; Gajdacz, Miroslav; Mølmer, Klaus; Lieberoth, Andreas; Sherson, Jacob F

    2016-04-14

    Humans routinely solve problems of immense computational complexity by intuitively forming simple, low-dimensional heuristic strategies. Citizen science (or crowd sourcing) is a way of exploiting this ability by presenting scientific research problems to non-experts. 'Gamification'--the application of game elements in a non-game context--is an effective tool with which to enable citizen scientists to provide solutions to research problems. The citizen science games Foldit, EteRNA and EyeWire have been used successfully to study protein and RNA folding and neuron mapping, but so far gamification has not been applied to problems in quantum physics. Here we report on Quantum Moves, an online platform gamifying optimization problems in quantum physics. We show that human players are able to find solutions to difficult problems associated with the task of quantum computing. Players succeed where purely numerical optimization fails, and analyses of their solutions provide insights into the problem of optimization of a more profound and general nature. Using player strategies, we have thus developed a few-parameter heuristic optimization method that efficiently outperforms the most prominent established numerical methods. The numerical complexity associated with time-optimal solutions increases for shorter process durations. To understand this better, we produced a low-dimensional rendering of the optimization landscape. This rendering reveals why traditional optimization methods fail near the quantum speed limit (that is, the shortest process duration with perfect fidelity). Combined analyses of optimization landscapes and heuristic solution strategies may benefit wider classes of optimization problems in quantum physics and beyond.

  19. Promoting Conceptual Coherence in Quantum Learning through Computational Models

    NASA Astrophysics Data System (ADS)

    Lee, Hee-Sun

    2012-02-01

    In order to explain phenomena at the quantum level, scientists use multiple representations in verbal, pictorial, mathematical, and computational forms. Conceptual coherence among these multiple representations is used as an analytical framework to describe student learning trajectories in quantum physics. A series of internet-based curriculum modules are designed to address topics in quantum mechanics, semiconductor physics, and nano-scale engineering applications. In these modules, students are engaged in inquiry-based activities situated in a highly interactive computational modeling environment. This study was conducted in an introductory level solid state physics course. Based on in-depth interviews with 13 students, methods for identifying conceptual coherence as a function of students' level of understanding are presented. Pre-post test comparisons of 20 students in the course indicate a statistically significant improvement in students' conceptual coherence of understanding quantum phenomena before and after the course, Effect Size = 1.29 SD. Additional analyses indicate that students who responded to the modules more coherently improved their conceptual coherence to a greater extent than those who did less to the modules after controlling for their course grades.

  20. Phonon-based scalable quantum computing and sensing (Presentation Video)

    NASA Astrophysics Data System (ADS)

    El-Kady, Ihab

    2015-04-01

    Quantum computing fundamentally depends on the ability to concurrently entangle and individually address/control a large number of qubits. In general, the primary inhibitors of large scale entanglement are qubit dependent; for example inhomogeneity in quantum dots, spectral crowding brought about by proximity-based entanglement in ions, weak interactions of neutral atoms, and the fabrication tolerances in the case of Si-vacancies or SQUIDs. We propose an inherently scalable solid-state qubit system with individually addressable qubits based on the coupling of a phonon with an acceptor impurity in a high-Q Phononic Crystal resonant cavity. Due to their unique nonlinear properties, phonons enable new opportunities for quantum devices and physics. We present a phononic crystal-based platform for observing the phonon analogy of cavity quantum electrodynamics, called phonodynamics, in a solid-state system. Practical schemes involve selective placement of a single acceptor atom in the peak of the strain field in a high-Q phononic crystal cavity that enables strong coupling of the phonon modes to the energy levels of the atom. A qubit is then created by entangling a phonon at the resonance frequency of the cavity with the atomic acceptor states. We show theoretical optimization of the cavity design and excitation waveguides, along with estimated performance figures of the phoniton system. Qubits based on this half-sound, half-matter quasi-particle, may outcompete other quantum architectures in terms of combined emission rate, coherence lifetime, and fabrication demands.

  1. Evaluation of Advanced Computing Techniques and Technologies: Reconfigurable Computing

    NASA Technical Reports Server (NTRS)

    Wells, B. Earl

    2003-01-01

    The focus of this project was to survey the technology of reconfigurable computing determine its level of maturity and suitability for NASA applications. To better understand and assess the effectiveness of the reconfigurable design paradigm that is utilized within the HAL-15 reconfigurable computer system. This system was made available to NASA MSFC for this purpose, from Star Bridge Systems, Inc. To implement on at least one application that would benefit from the performance levels that are possible with reconfigurable hardware. It was originally proposed that experiments in fault tolerance and dynamically reconfigurability would be perform but time constraints mandated that these be pursued as future research.

  2. Instructional Technology in Computer Science Education

    ERIC Educational Resources Information Center

    Jenny, Frederick J.

    2004-01-01

    The Web, the Internet, the intranet and associated resources, campus computer labs, smart classrooms, course management systems, and a plethora of software packages all offer opportunities for every classroom instructor to enrich in-class and out-of-class activities. Why should an instructor consider the integration of technology into their…

  3. Women Workers as Users of Computer Technology.

    ERIC Educational Resources Information Center

    Larwood, Laurie

    1992-01-01

    Discussion of expectations, trends, and implications of growth of computer technology and its effect on women workers argues that the experience of women is different from that of men in the nature of jobs in which women are found, their training and education, home-family conflict, and discrimination. The impact on women of increasing…

  4. Publishing a School Newspaper Using Computer Technology.

    ERIC Educational Resources Information Center

    Whitney, Jeanne; And Others

    By publishing a quarterly school and community newspaper, sixth, seventh, and eighth graders get involved in the writing of many types of articles, proofreading, communication skills, interviewing skills, investigative reporting, photography, artistic and graphic design, and computer technology. As the students work together on each issue of the…

  5. Business/Computer Technologies. State Competency Profile.

    ERIC Educational Resources Information Center

    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/computer technology 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…

  6. Competency Index. [Business/Computer Technologies Cluster.

    ERIC Educational Resources Information Center

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

    This index allows the user to scan the competencies under each title for the 28 subjects appropriate for use in a competency list for the 12 occupations within the business/computer technologies cluster. Titles of the 28 units are as follows: employability skills; professionalism; teamwork; professional and ethical standards; economic and business…

  7. Physical Architecture for a Universal Topological Quantum Computer based on a Network of Majorana Nanowires

    NASA Astrophysics Data System (ADS)

    Sau, Jay; Barkeshli, Maissam

    The idea of topological quantum computation (TQC) is to encode and manipulate quantum information in an intrinsically fault-tolerant manner by utilizing the physics of topologically ordered phases of matter. Currently, the most promising platforms for a topological qubit are either in terms of Majorana fermion zero modes (MZMs) in spin-orbit coupled superconducting nanowires or in terms of the Kitaev Z2 surface code. However, the topologically robust operations that are possible in these systems are not sufficient for realizing a universal gate set for topological quantum computation. Here, we show that an array of coupled semiconductor/superconductor nanowires with MZM edge states can be used to realize a more sophisticated type of non-Abelian defect, a genon in an Ising X Ising topological state. This leads to a possible implementation of the missing topologically protected pi/8 phase gate and thus paves a path for universal topological quantum computation based on semiconductor-superconductor nanowire technology. We provide detailed numerical estimates of the relevant energy scales, which we show to lie within accessible ranges. J. S. was supported by Microsoft Station Q, startup funds from the University of Maryland and NSF-JQI-PFC.

  8. SYMBMAT: Symbolic computation of quantum transition matrix elements

    NASA Astrophysics Data System (ADS)

    Ciappina, M. F.; Kirchner, T.

    2012-08-01

    We have developed a set of Mathematica notebooks to compute symbolically quantum transition matrices relevant for atomic ionization processes. The utilization of a symbolic language allows us to obtain analytical expressions for the transition matrix elements required in charged-particle and laser induced ionization of atoms. Additionally, by using a few simple commands, it is possible to export these symbolic expressions to standard programming languages, such as Fortran or C, for the subsequent computation of differential cross sections or other observables. One of the main drawbacks in the calculation of transition matrices is the tedious algebraic work required when initial states other than the simple hydrogenic 1s state need to be considered. Using these notebooks the work is dramatically reduced and it is possible to generate exact expressions for a large set of bound states. We present explicit examples of atomic collisions (in First Born Approximation and Distorted Wave Theory) and laser-matter interactions (within the Dipole and Strong Field Approximations and different gauges) using both hydrogenic wavefunctions and Slater-Type Orbitals with arbitrary nlm quantum numbers as initial states. Catalogue identifier: AEMI_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEMI_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC license, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 71 628 No. of bytes in distributed program, including test data, etc.: 444 195 Distribution format: tar.gz Programming language: Mathematica Computer: Single machines using Linux or Windows (with cores with any clock speed, cache memory and bits in a word) Operating system: Any OS that supports Mathematica. The notebooks have been tested under Windows and Linux and with versions 6.x, 7.x and 8.x Classification: 2.6 Nature of problem

  9. Los Alamos Quantum Dots for Solar, Display Technology

    SciTech Connect

    Klimov, Victor

    2015-04-13

    Quantum dots are ultra-small bits of semiconductor matter that can be synthesized with nearly atomic precision via modern methods of colloidal chemistry. Their emission color can be tuned by simply varying their dimensions. Color tunability is combined with high emission efficiencies approaching 100 percent. These properties have recently become the basis of a new technologyquantum dot displays – employed, for example, in the newest generation of e-readers and video monitors.

  10. Numerical simulation of NQR/NMR: Applications in quantum computing.

    PubMed

    Possa, Denimar; Gaudio, Anderson C; Freitas, Jair C C

    2011-04-01

    A numerical simulation program able to simulate nuclear quadrupole resonance (NQR) as well as nuclear magnetic resonance (NMR) experiments is presented, written using the Mathematica package, aiming especially applications in quantum computing. The program makes use of the interaction picture to compute the effect of the relevant nuclear spin interactions, without any assumption about the relative size of each interaction. This makes the program flexible and versatile, being useful in a wide range of experimental situations, going from NQR (at zero or under small applied magnetic field) to high-field NMR experiments. Some conditions specifically required for quantum computing applications are implemented in the program, such as the possibility of use of elliptically polarized radiofrequency and the inclusion of first- and second-order terms in the average Hamiltonian expansion. A number of examples dealing with simple NQR and quadrupole-perturbed NMR experiments are presented, along with the proposal of experiments to create quantum pseudopure states and logic gates using NQR. The program and the various application examples are freely available through the link http://www.profanderson.net/files/nmr_nqr.php.

  11. Quantum memristors

    PubMed Central

    Pfeiffer, P.; Egusquiza, I. L.; Di Ventra, M.; Sanz, M.; Solano, E.

    2016-01-01

    Technology based on memristors, resistors with memory whose resistance depends on the history of the crossing charges, has lately enhanced the classical paradigm of computation with neuromorphic architectures. However, in contrast to the known quantized models of passive circuit elements, such as inductors, capacitors or resistors, the design and realization of a quantum memristor is still missing. Here, we introduce the concept of a quantum memristor as a quantum dissipative device, whose decoherence mechanism is controlled by a continuous-measurement feedback scheme, which accounts for the memory. Indeed, we provide numerical simulations showing that memory effects actually persist in the quantum regime. Our quantization method, specifically designed for superconducting circuits, may be extended to other quantum platforms, allowing for memristor-type constructions in different quantum technologies. The proposed quantum memristor is then a building block for neuromorphic quantum computation and quantum simulations of non-Markovian systems. PMID:27381511

  12. Quantum memristors.

    PubMed

    Pfeiffer, P; Egusquiza, I L; Di Ventra, M; Sanz, M; Solano, E

    2016-01-01

    Technology based on memristors, resistors with memory whose resistance depends on the history of the crossing charges, has lately enhanced the classical paradigm of computation with neuromorphic architectures. However, in contrast to the known quantized models of passive circuit elements, such as inductors, capacitors or resistors, the design and realization of a quantum memristor is still missing. Here, we introduce the concept of a quantum memristor as a quantum dissipative device, whose decoherence mechanism is controlled by a continuous-measurement feedback scheme, which accounts for the memory. Indeed, we provide numerical simulations showing that memory effects actually persist in the quantum regime. Our quantization method, specifically designed for superconducting circuits, may be extended to other quantum platforms, allowing for memristor-type constructions in different quantum technologies. The proposed quantum memristor is then a building block for neuromorphic quantum computation and quantum simulations of non-Markovian systems. PMID:27381511

  13. Quantum memristors.

    PubMed

    Pfeiffer, P; Egusquiza, I L; Di Ventra, M; Sanz, M; Solano, E

    2016-07-06

    Technology based on memristors, resistors with memory whose resistance depends on the history of the crossing charges, has lately enhanced the classical paradigm of computation with neuromorphic architectures. However, in contrast to the known quantized models of passive circuit elements, such as inductors, capacitors or resistors, the design and realization of a quantum memristor is still missing. Here, we introduce the concept of a quantum memristor as a quantum dissipative device, whose decoherence mechanism is controlled by a continuous-measurement feedback scheme, which accounts for the memory. Indeed, we provide numerical simulations showing that memory effects actually persist in the quantum regime. Our quantization method, specifically designed for superconducting circuits, may be extended to other quantum platforms, allowing for memristor-type constructions in different quantum technologies. The proposed quantum memristor is then a building block for neuromorphic quantum computation and quantum simulations of non-Markovian systems.

  14. Quantum memristors

    NASA Astrophysics Data System (ADS)

    Pfeiffer, P.; Egusquiza, I. L.; di Ventra, M.; Sanz, M.; Solano, E.

    2016-07-01

    Technology based on memristors, resistors with memory whose resistance depends on the history of the crossing charges, has lately enhanced the classical paradigm of computation with neuromorphic architectures. However, in contrast to the known quantized models of passive circuit elements, such as inductors, capacitors or resistors, the design and realization of a quantum memristor is still missing. Here, we introduce the concept of a quantum memristor as a quantum dissipative device, whose decoherence mechanism is controlled by a continuous-measurement feedback scheme, which accounts for the memory. Indeed, we provide numerical simulations showing that memory effects actually persist in the quantum regime. Our quantization method, specifically designed for superconducting circuits, may be extended to other quantum platforms, allowing for memristor-type constructions in different quantum technologies. The proposed quantum memristor is then a building block for neuromorphic quantum computation and quantum simulations of non-Markovian systems.

  15. Secure multiparty computation with a dishonest majority via quantum means

    SciTech Connect

    Loukopoulos, Klearchos; Browne, Daniel E.

    2010-06-15

    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.

  16. Secure multiparty computation with a dishonest majority via quantum means

    NASA Astrophysics Data System (ADS)

    Loukopoulos, Klearchos; Browne, Daniel E.

    2010-06-01

    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.

  17. Experimental detection of nonclassical correlations in mixed-state quantum computation

    SciTech Connect

    Passante, G.; Moussa, O.; Trottier, D. A.; Laflamme, R.

    2011-10-15

    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.

  18. Quantum computation in brain microtubules: Decoherence and biological feasibility

    NASA Astrophysics Data System (ADS)

    Hagan, S.; Hameroff, S. R.; Tuszyński, J. A.

    2002-06-01

    The Penrose-Hameroff orchestrated objective reduction (orch. OR) model assigns a cognitive role to quantum computations 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

  19. Enabling computational technologies for subsurface simulations

    SciTech Connect

    Falgout, R D

    1999-02-22

    We collaborated with Environmental Programs to develop and apply advanced computational methodologies for simulating multiphase flow through heterogeneous porous media. The primary focus was on developing a fast accurate advection scheme using a new temporal subcycling technique and on the scalable and efficient solution of the nonlinear Richards' equation used to model two-phase (variably saturated) flow. The resulting algorithms can be orders-of-magnitude faster than existing methods. Our computational technologies were applied to the simulation of subsurface fluid flow and chemical transport in the context of two important applications: water resource management and groundwater remediation.

  20. Advances in computed tomography imaging technology.

    PubMed

    Ginat, Daniel Thomas; Gupta, Rajiv

    2014-07-11

    Computed tomography (CT) is an essential tool in diagnostic imaging for evaluating many clinical conditions. In recent years, there have been several notable advances in CT technology that already have had or are expected to have a significant clinical impact, including extreme multidetector CT, iterative reconstruction algorithms, dual-energy CT, cone-beam CT, portable CT, and phase-contrast CT. These techniques and their clinical applications are reviewed and illustrated in this article. In addition, emerging technologies that address deficiencies in these modalities are discussed.

  1. SYMBMAT: Symbolic computation of quantum transition matrix elements

    NASA Astrophysics Data System (ADS)

    Ciappina, M. F.; Kirchner, T.

    2012-08-01

    We have developed a set of Mathematica notebooks to compute symbolically quantum transition matrices relevant for atomic ionization processes. The utilization of a symbolic language allows us to obtain analytical expressions for the transition matrix elements required in charged-particle and laser induced ionization of atoms. Additionally, by using a few simple commands, it is possible to export these symbolic expressions to standard programming languages, such as Fortran or C, for the subsequent computation of differential cross sections or other observables. One of the main drawbacks in the calculation of transition matrices is the tedious algebraic work required when initial states other than the simple hydrogenic 1s state need to be considered. Using these notebooks the work is dramatically reduced and it is possible to generate exact expressions for a large set of bound states. We present explicit examples of atomic collisions (in First Born Approximation and Distorted Wave Theory) and laser-matter interactions (within the Dipole and Strong Field Approximations and different gauges) using both hydrogenic wavefunctions and Slater-Type Orbitals with arbitrary nlm quantum numbers as initial states. Catalogue identifier: AEMI_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEMI_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC license, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 71 628 No. of bytes in distributed program, including test data, etc.: 444 195 Distribution format: tar.gz Programming language: Mathematica Computer: Single machines using Linux or Windows (with cores with any clock speed, cache memory and bits in a word) Operating system: Any OS that supports Mathematica. The notebooks have been tested under Windows and Linux and with versions 6.x, 7.x and 8.x Classification: 2.6 Nature of problem

  2. Multilevel distillation of magic states for quantum computing

    NASA Astrophysics Data System (ADS)

    Jones, Cody

    2013-03-01

    We develop a procedure for distilling magic states used in universal quantum computing which requires substantially fewer resources than prior schemes. Our distillation circuit is based on a family of concatenated quantum codes with a transversal Hadamard operation which can distill the eigenstate of the Hadamard operator. A crucial result of this design is that low-fidelity magic states can be consumed to purify high-fidelity magic states to even higher fidelity, which we call ``multilevel distillation.'' We show numerically that there exist multilevel protocols such that the average number of magic states consumed to distill from error rate ɛin = 0 . 01 to ɛout in the range 10-5 to 10-40 is about 14log10 (1 /ɛout) - 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 quantum computing.

  3. Technologies for Achieving Field Ubiquitous Computing

    NASA Astrophysics Data System (ADS)

    Nagashima, Akira

    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.

  4. Computer Education and Instructional Technology Teacher Trainees' Opinions about Cloud Computing Technology

    ERIC Educational Resources Information Center

    Karamete, Aysen

    2015-01-01

    This study aims to show the present conditions about the usage of cloud computing in the department of Computer Education and Instructional Technology (CEIT) amongst teacher trainees in School of Necatibey Education, Balikesir University, Turkey. In this study, a questionnaire with open-ended questions was used. 17 CEIT teacher trainees…

  5. Practical aspects of security certification for commercial quantum technologies

    NASA Astrophysics Data System (ADS)

    Walenta, Nino; Soucarros, Mathilde; Stucki, Damien; Caselunghe, Dario; Domergue, Mathias; Hagerman, Michael; Hart, Randall; Hayford, Don; Houlmann, Raphaël.; Legré, Matthieu; McCandlish, Todd; Page, Jean-Benoît; Tourville, Maurice; Wolterman, Richard

    2015-10-01

    Quantum random number generation (QRNG) and quantum key distribution (QKD) are the first applications of quantum physics at the level of individual quanta that have matured into commercial products. Both have been commercially available for over 10 years and increasingly adopted in information security systems. Current efforts focus on standardization and certification of QRNG and QKD devices and their components in order to validate the technology and enable more widespread adoption. Since no official certification scheme specific to quantum devices has been devised so far, alternative options must be investigated. This paper describes our approaches and efforts to enable compliance of commercial QRNG and QKD network devices with security standards such as AIS 20/311 and FIPS 140-2.2

  6. Safeguards technology and computer security training

    SciTech Connect

    Hunteman, W.J.; Zack, N.R.

    1992-09-01

    The Los Alamos National Laboratory Safeguards Systems Group provides a variety of training services to the federal government and its contractors. The US Department of Energy sponsors a Safeguards Technology Training Program at Los Alamos in which seminars are offered concerning materials accounting for nuclear safeguards, measurement control for materials accounting, and variance propagation and systems analysis. These seminars provide guidance and techniques for accounting for nuclear material, developing and quantifying quality nuclear material measurements, and assessing overall accounting system performance. The Safeguards Systems Group also provides training in computer and data security applications; i.e., a workshop and the Los Alamos Vulnerability/Risk Assessment System (LAVA), computer system security officer training, and nuclear material safeguards for managers training, which are available on request. This paper describes the purpose, content, and expected benefits of the training activities that can be applied at nuclear materials facilities or where there are computer and/or data security concerns.

  7. Universal quantum computation with ordered spin-chain networks

    NASA Astrophysics Data System (ADS)

    Tserkovnyak, Yaroslav; Loss, Daniel

    2011-09-01

    It is shown that anisotropic spin chains with gapped bulk excitations and magnetically ordered ground states offer a promising platform for quantum computation, which bridges the conventional single-spin-based qubit concept with recently developed topological Majorana-based proposals. We show how to realize the single-qubit Hadamard, phase, and π/8 gates as well as the two-qubit controlled-not (cnot) gate, which together form a fault-tolerant universal set of quantum gates. The gates are implemented by judiciously controlling Ising exchange and magnetic fields along a network of spin chains, with each individual qubit furnished by a spin-chain segment. A subset of single-qubit operations is geometric in nature, relying on control of anisotropy of spin interactions rather than their strength. We contrast topological aspects of the anisotropic spin-chain networks to those of p-wave superconducting wires discussed in the literature.

  8. Fast and robust quantum computation with ionic Wigner crystals

    SciTech Connect

    Baltrusch, J. D.; Negretti, A.; Taylor, J. M.; Calarco, T.

    2011-04-15

    We present a detailed analysis of the modulated-carrier quantum phase gate implemented with Wigner crystals of ions confined in Penning traps. We elaborate on a recent scheme, proposed by two of the authors, to engineer two-body interactions between ions in such crystals. We analyze the situation in which the cyclotron ({omega}{sub c}) and the crystal rotation ({omega}{sub r}) frequencies do not fulfill the condition {omega}{sub c}=2{omega}{sub r}. It is shown that even in the presence of the magnetic field in the rotating frame the many-body (classical) Hamiltonian describing small oscillations from the ion equilibrium positions can be recast in canonical form. As a consequence, we are able to demonstrate that fast and robust two-qubit gates are achievable within the current experimental limitations. Moreover, we describe a realization of the state-dependent sign-changing dipole forces needed to realize the investigated quantum computing scheme.

  9. Quantum computer networks with the orbital angular momentum of light

    NASA Astrophysics Data System (ADS)

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

    2012-09-01

    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.

  10. Majorana Fermion Surface Code for Universal Quantum Computation

    NASA Astrophysics Data System (ADS)

    Vijay, Sagar; Hsieh, Tim; Fu, Liang

    We introduce an exactly solvable model of interacting Majorana fermions realizing Z2 topological order with a Z2 fermion parity grading and lattice symmetries permuting the three fundamental anyon types. We propose a concrete physical realization by utilizing quantum phase slips in an array of Josephson-coupled mesoscopic topological superconductors, which can be implemented in a wide range of solid state systems, including topological insulators, nanowires or two-dimensional electron gases, proximitized by s-wave superconductors. Our model finds a natural application as a Majorana fermion surface code for universal quantum computation, with a single-step stabilizer measurement requiring no physical ancilla qubits, increased error tolerance, and simpler logical gates than a surface code with bosonic physical qubits. We thoroughly discuss protocols for stabilizer measurements, encoding and manipulating logical qubits, and gate implementations.

  11. Majorana Fermion Surface Code for Universal Quantum Computation

    NASA Astrophysics Data System (ADS)

    Vijay, Sagar; Hsieh, Timothy H.; Fu, Liang

    2015-10-01

    We introduce an exactly solvable model of interacting Majorana fermions realizing Z2 topological order with a Z2 fermion parity grading and lattice symmetries permuting the three fundamental anyon types. We propose a concrete physical realization by utilizing quantum phase slips in an array of Josephson-coupled mesoscopic topological superconductors, which can be implemented in a wide range of solid-state systems, including topological insulators, nanowires, or two-dimensional electron gases, proximitized by s -wave superconductors. Our model finds a natural application as a Majorana fermion surface code for universal quantum computation, with a single-step stabilizer measurement requiring no physical ancilla qubits, increased error tolerance, and simpler logical gates than a surface code with bosonic physical qubits. We thoroughly discuss protocols for stabilizer measurements, encoding and manipulating logical qubits, and gate implementations.

  12. Percolation, renormalization, and quantum computing with nondeterministic gates.

    PubMed

    Kieling, K; Rudolph, T; Eisert, J

    2007-09-28

    We apply a notion of static renormalization to the preparation of entangled states for quantum computing, exploiting ideas from percolation theory. Such a strategy yields a novel way to cope with the randomness of nondeterministic quantum gates. This is most relevant in the context of optical architectures, where probabilistic gates are common, and cold atoms in optical lattices, where hole defects occur. We demonstrate how to efficiently construct cluster states without the need for rerouting, thereby avoiding a massive amount of conditional dynamics; we furthermore show that except for a single layer of gates during the preparation, all subsequent operations can be shifted to the final adapted single-qubit measurements. Remarkably, cluster state preparation is achieved using essentially the same scaling in resources as if deterministic gates were available.

  13. Radix-independent, efficient arrays for multi-level n-qudit quantum and reversible computation

    NASA Astrophysics Data System (ADS)

    Mohammadi, Majid

    2015-08-01

    Multiple-valued quantum logic allows the designers to reduce the number of cells while obtaining more functionality in the quantum circuits. Large r-valued reversible or quantum gates ( r stands for radix and is more than 2) cannot be directly realized in the current quantum technology. Therefore, we are interested in designing the large reversible and quantum controlled gates using the arrays of one-quantum digit (qudit) or two-qudit gates. In our previous work, we proposed quantum arrays to implement the r-valued quantum circuits. In this paper, we propose novel efficient structures and arrays, for r-valued quantum logic gates. The quantum costs of the developed quantum arrays are independent of the radix of calculations in the quantum circuit.

  14. Reviews of computing technology: Client-server technology

    SciTech Connect

    Johnson, S.M.

    1990-09-01

    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.

  15. Reviews of computing technology: Client-server technology

    SciTech Connect

    Johnson, S.M.

    1990-09-01

    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.

  16. Multilevel distillation of magic states for quantum computing

    NASA Astrophysics Data System (ADS)

    Jones, Cody

    2013-04-01

    We develop a procedure for distilling magic states used in universal quantum computing 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 ɛ→0 for each input magic state, the number of input magic states consumed on average to yield an output state with infidelity O(ɛ2r) 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 ɛin=0.01 to ɛout in the range 10-5-10-40 is about 14log10(1/ɛout)-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 quantum computing and provide insight into the limitations of nearly resource-optimal quantum error correction.

  17. Grid computing technology for hydrological applications

    NASA Astrophysics Data System (ADS)

    Lecca, G.; Petitdidier, M.; Hluchy, L.; Ivanovic, M.; Kussul, N.; Ray, N.; Thieron, V.

    2011-06-01

    SummaryAdvances in e-Infrastructure promise to revolutionize sensing systems and the way in which data are collected and assimilated, and complex water systems are simulated and visualized. According to the EU Infrastructure 2010 work-programme, data and compute infrastructures and their underlying technologies, either oriented to tackle scientific challenges or complex problem solving in engineering, are expected to converge together into the so-called knowledge infrastructures, leading to a more effective research, education and innovation in the next decade and beyond. Grid technology is recognized as a fundamental component of e-Infrastructures. Nevertheless, this emerging paradigm highlights several topics, including data management, algorithm optimization, security, performance (speed, throughput, bandwidth, etc.), and scientific cooperation and collaboration issues that require further examination to fully exploit it and to better inform future research policies. The paper illustrates the results of six different surface and subsurface hydrology applications that have been deployed on the Grid. All the applications aim to answer to strong requirements from the Civil Society at large, relatively to natural and anthropogenic risks. Grid technology has been successfully tested to improve flood prediction, groundwater resources management and Black Sea hydrological survey, by providing large computing resources. It is also shown that Grid technology facilitates e-cooperation among partners by means of services for authentication and authorization, seamless access to distributed data sources, data protection and access right, and standardization.

  18. Computational Support for Technology- Investment Decisions

    NASA Technical Reports Server (NTRS)

    Adumitroaie, Virgil; Hua, Hook; Lincoln, William; Block, Gary; Mrozinski, Joseph; Shelton, Kacie; Weisbin, Charles; Elfes, Alberto; Smith, Jeffrey

    2007-01-01

    Strategic Assessment of Risk and Technology (START) is a user-friendly computer program that assists human managers in making decisions regarding research-and-development investment portfolios in the presence of uncertainties and of non-technological constraints that include budgetary and time limits, restrictions related to infrastructure, and programmatic and institutional priorities. START facilitates quantitative analysis of technologies, capabilities, missions, scenarios and programs, and thereby enables the selection and scheduling of value-optimal development efforts. START incorporates features that, variously, perform or support a unique combination of functions, most of which are not systematically performed or supported by prior decision- support software. These functions include the following: Optimal portfolio selection using an expected-utility-based assessment of capabilities and technologies; Temporal investment recommendations; Distinctions between enhancing and enabling capabilities; Analysis of partial funding for enhancing capabilities; and Sensitivity and uncertainty analysis. START can run on almost any computing hardware, within Linux and related operating systems that include Mac OS X versions 10.3 and later, and can run in Windows under the Cygwin environment. START can be distributed in binary code form. START calls, as external libraries, several open-source software packages. Output is in Excel (.xls) file format.

  19. Reviews of computing technology: Object-oriented technology

    SciTech Connect

    Skeen, D.C.

    1993-03-01

    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.

  20. Two results in topology, motivated by quantum computation

    NASA Astrophysics Data System (ADS)

    Alagic, Gorjan

    2015-03-01

    The field of quantum computation is built on the foundation of physics, mathematics, and computer science. While it has taken much from these fields, there are also interesting examples where it has given back. I will discuss two new results of this kind. In both cases, we use very basic ideas from quantum computation to prove an interesting fact about low-dimensional topology. First, we use the Solovay-Kitaev universality theorem with exponential precision to give a simple proof of the #P-hardness of certain 3-manifold invariants. We then apply this result to show the existence of rather exotic 3-manifold diagrams. Second, we show a relationship between the distinguishing power of a link invariant, and the entangling power of the linear operator associated to braiding. More precisely, we show that link invariants derived from non-entangling solutions to the Yang-Baxter equation are trivial. The former is joint work with Catharine Lo (Caltech), and the latter is joint work with Stephen Jordan and Michael Jarett (UMD).