WorldWideScience
 
 
1

Abstract algebra, projective geometry and time encoding of quantum information  

CERN Document Server

Algebraic geometrical concepts are playing an increasing role in quantum applications such as coding, cryptography, tomography and computing. We point out here the prominent role played by Galois fields viewed as cyclotomic extensions of the integers modulo a prime characteristic $p$. They can be used to generate efficient cyclic encoding, for transmitting secrete quantum keys, for quantum state recovery and for error correction in quantum computing. Finite projective planes and their generalization are the geometric counterpart to cyclotomic concepts, their coordinatization involves Galois fields, and they have been used repetitively for enciphering and coding. Finally the characters over Galois fields are fundamental for generating complete sets of mutually unbiased bases, a generic concept of quantum information processing and quantum entanglement. Gauss sums over Galois fields ensure minimum uncertainty under such protocols. Some Galois rings which are cyclotomic extensions of the integers modulo 4 are al...

Planat, M R P; Planat, Michel R. P.; Saniga, Metod

2005-01-01

2

Secure quantum private information retrieval using phase-encoded queries  

CERN Document Server

We propose a quantum solution to the classical private information retrieval (PIR) problem, which allows one to query a database in a private manner. The protocol offers privacy thresholds and allows the user to obtain information from a database in a way that offers the potential adversary, in this model the database owner, no possibility of deterministically establishing the query contents. This protocol may also be viewed as a solution to the symmetrically private information retrieval problem in that it can offer database security (inability for a querying user to steal its contents). Compared to classical solutions, the protocol offers substantial improvement in terms of communication complexity. In comparison with the recent quantum private queries {[}Phys. Rev. Lett. 100, 230502 (2008)] protocol, it is more efficient in terms of communication complexity and the number of rounds, while offering a clear privacy parameter. We discuss the security of the protocol and analyze its strengths and conclude that...

Olejnik, L

2011-01-01

3

Deterministically Encoding Quantum Information Using 100-Photon Schrodinger Cat States.  

UK PubMed Central (United Kingdom)

In contrast to a single quantum bit, an oscillator can store multiple excitations and coherences, provided one has the ability to generate and manipulate complex multiphoton states. We demonstrate multiphoton control using a superconducting transmon qubit coupled to a waveguide cavity resonator with a highly ideal off-resonant coupling. This dispersive interaction is much greater than decoherence rates and higher-order nonlinearities to allow simultaneous manipulation of hundreds of photons. With a toolset of conditional qubit-photon logic, we map an arbitrary qubit state to a superposition of coherent states, known as a "cat state." We create cat states as large as 111 photons and extend this protocol to create superpositions of up to four coherent states. This control creates a powerful interface between discrete and continuous variable quantum computation and could enable applications in metrology and quantum information processing.

Vlastakis B; Kirchmair G; Leghtas Z; Nigg SE; Frunzio L; Girvin SM; Mirrahimi M; Devoret MH; Schoelkopf RJ

2013-10-01

4

Secure quantum private information retrieval using phase-encoded queries  

Energy Technology Data Exchange (ETDEWEB)

We propose a quantum solution to the classical private information retrieval (PIR) problem, which allows one to query a database in a private manner. The protocol offers privacy thresholds and allows the user to obtain information from a database in a way that offers the potential adversary, in this model the database owner, no possibility of deterministically establishing the query contents. This protocol may also be viewed as a solution to the symmetrically private information retrieval problem in that it can offer database security (inability for a querying user to steal its contents). Compared to classical solutions, the protocol offers substantial improvement in terms of communication complexity. In comparison with the recent quantum private queries [Phys. Rev. Lett. 100, 230502 (2008)] protocol, it is more efficient in terms of communication complexity and the number of rounds, while offering a clear privacy parameter. We discuss the security of the protocol and analyze its strengths and conclude that using this technique makes it challenging to obtain the unconditional (in the information-theoretic sense) privacy degree; nevertheless, in addition to being simple, the protocol still offers a privacy level. The oracle used in the protocol is inspired both by the classical computational PIR solutions as well as the Deutsch-Jozsa oracle.

Olejnik, Lukasz [CERN, 1211 Geneva 23, Switzerland and Poznan Supercomputing and Networking Center, Noskowskiego 12/14, PL-61-704 Poznan (Poland)

2011-08-15

5

Secure quantum private information retrieval using phase-encoded queries  

Science.gov (United States)

We propose a quantum solution to the classical private information retrieval (PIR) problem, which allows one to query a database in a private manner. The protocol offers privacy thresholds and allows the user to obtain information from a database in a way that offers the potential adversary, in this model the database owner, no possibility of deterministically establishing the query contents. This protocol may also be viewed as a solution to the symmetrically private information retrieval problem in that it can offer database security (inability for a querying user to steal its contents). Compared to classical solutions, the protocol offers substantial improvement in terms of communication complexity. In comparison with the recent quantum private queries [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.100.230502 100, 230502 (2008)] protocol, it is more efficient in terms of communication complexity and the number of rounds, while offering a clear privacy parameter. We discuss the security of the protocol and analyze its strengths and conclude that using this technique makes it challenging to obtain the unconditional (in the information-theoretic sense) privacy degree; nevertheless, in addition to being simple, the protocol still offers a privacy level. The oracle used in the protocol is inspired both by the classical computational PIR solutions as well as the Deutsch-Jozsa oracle.

Olejnik, Lukasz

2011-08-01

6

Multi-party quantum secret sharing with the single-particle quantum state to encode the information  

Science.gov (United States)

We present a three-party quantum secret sharing (QSS) scheme via the entangled Greenberger-Horne-Zeilinger state. In this scheme, the sender Alice encodes her arbitrary secret information by means of preparing a single-particle quantum state. The agent Bob obtains his shared information according to his hobby, while Charlie can easily calculate his shared information. The proposed scheme is secure. It is shown that even a dishonest agent, who may avoid the security checking, cannot obtain any useful information. Moreover, we further investigate the multi-party QSS scheme which allows most agents to predetermine their information.

Chen, Xiu-Bo; Niu, Xin-Xin; Zhou, Xin-Jie; Yang, Yi-Xian

2013-01-01

7

Abstract algebra, projective geometry and time encoding of quantum information  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Algebraic geometrical concepts are playing an increasing role in quantum applications such as coding, cryptography, tomography and computing. We point out here the prominent role played by Galois fields viewed as cyclotomic extensions of the integers modulo a prime characteristic $p$. They can be us...

Planat, Michel; Saniga, Metod

8

Quantum Repeater with Encoding  

CERN Document Server

We propose a new approach to implement quantum repeaters for long distance quantum communication. Our protocol generates a backbone of encoded Bell pairs and uses the procedure of classical error correction during simultaneous entanglement connection. We illustrate that the repeater protocol with simple Calderbank-Shor-Steane (CSS) encoding can significantly extend the communication distance, while still maintaining a fast key generation rate.

Jiang, Liang; Nemoto, Kae; Munro, William J; Van Meter, Rodney; Lukin, Mikhail D

2008-01-01

9

Decoherence of encoded quantum registers  

CERN Document Server

In order to eliminate disturbing effects of decoherence, encoding of quantum information in decoherence-free subspaces has been suggested. We analyze the benefits of this concept for a quantum register that is realized in a spin chain in contact with a common bosonic bath. Within a dissipation-less model we provide explicit analytical results for the average fidelity of plain and encoded quantum registers. For the investigation of dissipative spin-boson couplings we employ a master equation of Bloch-Redfield type.

Borghoff, Stefan

2007-01-01

10

Relativistically invariant quantum information  

CERN Document Server

We show that quantum information can be encoded into entangled states of multiple indistinguishable particles in such a way that any inertial observer can prepare, manipulate, or measure the encoded state independent of their reference frame. Such relativistically invariant quantum information is free of the difficulties associated with encoding into spin or other degrees of freedom in a relativistic context.

Bartlett, S D; Bartlett, Stephen D.; Terno, Daniel R.

2005-01-01

11

Quantum information  

Energy Technology Data Exchange (ETDEWEB)

A new research direction known as quantum information is a multidisciplinary subject which involves quantum mechanics, optics, information theory, programming, discrete mathematics, laser physics and spectroscopy, and depends heavily on contributions from such areas as quantum computing, quantum teleportation and quantum cryptography, decoherence studies, and single-molecule and impurity spectroscopy. Some new results achieved in this rapidly growing field are discussed. (reviews of topical problems)

Kilin, Sergei Ya [B.I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, Minsk (Belarus)

1999-05-31

12

Quantum Information  

CERN Document Server

Quantum information- the subject- is a new and exciting area of science, which brings together physics, information theory, computer science and mathematics. "Quantum Information"- the book- is based on two successful lecture courses given to advanced undergraduate and beginning postgraduate students in physics. The intention is to introduce readers at this level to the fundamental, but offer rather simple, ideas behind ground-breaking developments including quantum cryptography,teleportation and quantum computing. The text is necessarily rather mathematical in style, but the mathema

Barnett, Stephen

2009-01-01

13

Quantum information  

Energy Technology Data Exchange (ETDEWEB)

There is more to information than a string of ones and zeroes the ability of ''quantum bits'' to be in two states at the same time could revolutionize information technology. In the mid-1930s two influential but seemingly unrelated papers were published. In 1935 Einstein, Podolsky and Rosen proposed the famous EPR paradox that has come to symbolize the mysteries of quantum mechanics. Two years later, Alan Turing introduced the universal Turing machine in an enigmatically titled paper, On computable numbers, and laid the foundations of the computer industry one of the biggest industries in the world today. Although quantum physics is essential to understand the operation of transistors and other solid-state devices in computers, computation itself has remained a resolutely classical process. Indeed it seems only natural that computation and quantum theory should be kept as far apart as possible surely the uncertainty associated with quantum theory is anathema to the reliability expected from computers? Wrong. In 1985 David Deutsch introduced the universal quantum computer and showed that quantum theory can actually allow computers to do more rather than less. The ability of particles to be in a superposition of more than one quantum state naturally introduces a form of parallelism that can, in principle, perform some traditional computing tasks faster than is possible with classical computers. Moreover, quantum computers are capable of other tasks that are not conceivable with their classical counterparts. Similar breakthroughs in cryptography and communication followed. (author)

Rodgers, P

1998-03-01

14

Classical and Quantum Information  

CERN Document Server

A new discipline, Quantum Information Science, has emerged in the last two decades of the twentieth century at the intersection of Physics, Mathematics, and Computer Science. Quantum Information Processing is an application of Quantum Information Science which covers the transformation, storage, and transmission of quantum information; it represents a revolutionary approach to information processing. This book covers topics in quantum computing, quantum information theory, and quantum error correction, three important areas of quantum information processing. Quantum information theory and qua

Marinescu, Dan C

2011-01-01

15

Minimal-memory, non-catastrophic, polynomial-depth quantum convolutional encoders  

CERN Document Server

Quantum convolutional coding is a technique for encoding a stream of quantum information before transmitting it over a noisy quantum communication channel. Two important goals in the design of quantum convolutional encoders are to minimize the memory required by them and to avoid the catastrophic propagation of errors. In a previous companion paper, we determined minimal-memory, non-catastrophic, polynomial-depth encoders for a few exemplary quantum convolutional codes. In this paper, we elucidate a general technique for finding an encoder of an arbitrary quantum convolutional code such that the encoder possesses these desirable properties. Additionally, we apply our technique to many quantum convolutional codes from the literature.

Houshmand, Monireh; Wilde, Mark M

2011-01-01

16

Encoded Universality in Physical Implementations of a Quantum Computer  

CERN Multimedia

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

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

2001-01-01

17

Quantum teleportation and quantum information  

International Nuclear Information System (INIS)

The scheme of quantum teleportation is described in a mathematically rigorous way, including analysis of the role and importance of quantum entanglement. The experiments with quantum teleportation performed in Innsbruck and in Rome are described in detail, and some differences between the two approaches are discussed. The elements of quantum information theory are introduced and compared with Shannon's classical information theory. The phenomenon of quantum teleportation is placed into a wider context of the developing quantum information theory, which enables quantum teleportation to be described by using the particle physics language. (Z.J.)

2000-01-01

18

Quantum Logical Operations on Encoded Qubits  

Energy Technology Data Exchange (ETDEWEB)

We show how to carry out quantum logical operations (controlled-not and Toffoli gates) on encoded qubits for several encodings which protect against various 1-bit errors. This improves the reliability of these operations by allowing one to correct for 1-bit errors which either preexisted or occurred in the course of operation. The logical operations we consider allow one to carry out the vast majority of the steps in the quantum factoring algorithm. {copyright} {ital 1996 The American Physical Society.}

Zurek, W.H.; Laflamme, R. [Theoretical Astrophysics, T-6, MS B288, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

1996-11-01

19

Decoherence-Insensitive Quantum Communication by Optimal C^*-Encoding  

CERN Document Server

The central issue in this article is to transmit a quantum state in such a way that after some decoherence occurs, most of the information can be restored by a suitable decoding operation. For this purpose, we incorporate redundancy by mapping a given initial quantum state to a messenger state on a larger-dimensional Hilbert space via a $C^*$-algebra embedding. Our noise model for the transmission is a phase damping channel which admits a noiseless or decoherence-free subspace or subsystem. More precisely, the transmission channel is obtained from convex combinations of a set of lowest rank yes/no measurements that leave a component of the messenger state unchanged. The objective of our encoding is to distribute quantum information optimally across the noise-susceptible component of the transmission when the noiseless component is not large enough to contain all the quantum information to be transmitted. We derive simple geometric conditions for optimal encoding and construct examples.

Bodmann, B G; Paulsen, V I; Bodmann, Bernhard G.; Kribs, David W.; Paulsen, Vern I.

2006-01-01

20

Quantum information to the home  

International Nuclear Information System (INIS)

Information encoded on individual quanta will play an important role in our future lives, much as classically encoded digital information does today. Combining quantum information carried by single photons with classical signals encoded on strong laser pulses in modern fibre-to-the-home (FTTH) networks is a significant challenge, the solution to which will facilitate the global distribution of quantum information to the home and with it a quantum internet. In real-world networks, spontaneous Raman scattering in the optical fibre would induce crosstalk between the high-power classical channels and a single-photon quantum channel, such that the latter is unable to operate. Here, we show that the integration of quantum and classical information on an FTTH network is possible by performing quantum key distribution (QKD) on a network while simultaneously transferring realistic levels of classical data. Our novel scheme involves synchronously interleaving a channel of quantum data with the Raman scattered photons from a classical channel, exploiting the periodic minima in the instantaneous crosstalk and thereby enabling secure QKD to be performed.

2011-01-01

 
 
 
 
21

Quantum information to the home  

Energy Technology Data Exchange (ETDEWEB)

Information encoded on individual quanta will play an important role in our future lives, much as classically encoded digital information does today. Combining quantum information carried by single photons with classical signals encoded on strong laser pulses in modern fibre-to-the-home (FTTH) networks is a significant challenge, the solution to which will facilitate the global distribution of quantum information to the home and with it a quantum internet. In real-world networks, spontaneous Raman scattering in the optical fibre would induce crosstalk between the high-power classical channels and a single-photon quantum channel, such that the latter is unable to operate. Here, we show that the integration of quantum and classical information on an FTTH network is possible by performing quantum key distribution (QKD) on a network while simultaneously transferring realistic levels of classical data. Our novel scheme involves synchronously interleaving a channel of quantum data with the Raman scattered photons from a classical channel, exploiting the periodic minima in the instantaneous crosstalk and thereby enabling secure QKD to be performed.

Choi, Iris; Young, Robert J; Townsend, Paul D, E-mail: paul.townsend@tyndall.ie [Photonic Systems Group, Tyndall National Institute and Department of Physics, University College Cork, Cork (Ireland)

2011-06-15

22

Quantum information to the home  

Science.gov (United States)

Information encoded on individual quanta will play an important role in our future lives, much as classically encoded digital information does today. Combining quantum information carried by single photons with classical signals encoded on strong laser pulses in modern fibre-to-the-home (FTTH) networks is a significant challenge, the solution to which will facilitate the global distribution of quantum information to the home and with it a quantum internet [1]. In real-world networks, spontaneous Raman scattering in the optical fibre would induce crosstalk between the high-power classical channels and a single-photon quantum channel, such that the latter is unable to operate. Here, we show that the integration of quantum and classical information on an FTTH network is possible by performing quantum key distribution (QKD) on a network while simultaneously transferring realistic levels of classical data. Our novel scheme involves synchronously interleaving a channel of quantum data with the Raman scattered photons from a classical channel, exploiting the periodic minima in the instantaneous crosstalk and thereby enabling secure QKD to be performed.

Choi, Iris; Young, Robert J.; Townsend, Paul D.

2011-06-01

23

Cavity quantum electrodynamics based quantum low-density parity-check encoders and decoders  

Science.gov (United States)

Quantum information processing (QIP) relies on delicate superposition states that are sensitive to interactions with environment. The quantum gates are imperfect and the use of quantum error correction coding (QECC) is essential to enable the fault-tolerant computing and to deal with quantum errors. The most critical gate, CNOT-gate, has been implemented as a probabilistic device by using integrated optics. CNOT-gates from linear optics provide only probabilistic outcomes and as such are not suitable for large-scale computation. In this paper, we show that arbitrary set of universal quantum gates and gates from Clifford group, needed in QECC, can be implemented based on cavity quantum electrodynamics (CQED). We further show that encoders/decoders for quantum LDPC codes can be implemented based on Hadamard and CNOT gates using CQED. Finally, we perform simulations and evaluate performance of several classes of quantum LDPC codes suitable for implementation in CQED technology.

Djordjevic, Ivan B.

2011-02-01

24

Protected realizations of quantum information  

International Nuclear Information System (INIS)

There are two complementary approaches to realizing quantum information so that it is protected from a given set of error operators. Both involve encoding information by means of subsystems. One is initialization-based error protection, which involves a quantum operation that is applied before error events occur. The other is operator quantum error correction, which uses a recovery operation applied after the errors have occurred. Together, the two approaches make it clear how quantum information can be stored at all stages of a process involving alternating error and quantum operations. In particular, there is always a subsystem that faithfully represents the desired quantum information. We give a definition of faithful realization of quantum information and show that it always involves subsystems. This supports the 'subsystems principle' for realizing quantum information. In the presence of errors, one can make use of noiseless (initialization) protectable, or error-correcting subsystems. We give an explicit algorithm for finding optimal noiseless subsystems. Finding optimal protectable or error-correcting subsystems is in general difficult. Verifying that a subsystem is error correcting is known to involve only linear algebra. We discuss the verification problem for protectable subsystems and reduce it to a simpler version of the problem of finding error-detecting codes.

2006-01-01

25

Continuous-variable quantum information processing  

DEFF Research Database (Denmark)

Observables of quantum systems can possess either a discrete or a continuous spectrum. For example, upon measurements of the photon number of a light state, discrete outcomes will result whereas measurements of the light's quadrature amplitudes result in continuous outcomes. If one uses the continuous degree of freedom of a quantum system for encoding, processing or detecting information, one enters the field of continuous-variable (CV) quantum information processing. In this paper we review the basic principles of CV quantum information processing with main focus on recent developments in the field. We will be addressing the three main stages of a quantum information system; the preparation stage where quantum information is encoded into CVs of coherent states and single-photon states, the processing stage where CV information is manipulated to carry out a specified protocol and a detection stage where CV information is measured using homodyne detection or photon counting.

Andersen, Ulrik Lund; Leuchs, G.

2010-01-01

26

Quantum gloves: Quantum states that encode as much as possible chirality and nothing else  

International Nuclear Information System (INIS)

Communicating a physical quantity cannot be done using information only - i.e., using abstract cbits and/or qubits. Rather one needs appropriate physical realizations of cbits and/or qubits. We illustrate this by considering the problem of communicating chirality. We discuss in detail the physical resources this necessitates and introduce the natural concept of quantum gloves - i.e., rotationally invariant quantum states that encode as much as possible the concept of chirality and nothing more.

2005-01-01

27

Non-catastrophic Encoders and Encoder Inverses for Quantum Convolutional Codes  

CERN Document Server

We present an algorithm to construct quantum circuits for encoding and inverse encoding of quantum convolutional codes. We show that any quantum convolutional code contains a subcode of finite index which has a non-catastrophic encoding circuit. Our work generalizes the conditions for non-catastrophic encoders derived in a paper by Ollivier and Tillich (quant-ph/0401134) which are applicable only for a restricted class of quantum convolutional codes. We also show that the encoders and their inverses constructed by our method naturally can be applied online, i.e., qubits can be sent and received with constant delay.

Grassl, M; Grassl, Markus; Roetteler, Martin

2006-01-01

28

Quantum Information Science.  

Science.gov (United States)

This is the final report for the AFRL/RI in-house project Quantum Information Science. Under this project we constructed a six qubit (quantum bit) capable photon-based experimental testbed for the development of photon- based quantum gates and circuits an...

M. L. Fanto P. M. Alsing

2012-01-01

29

Quantum information processing with trapped Ca(+) ions.  

UK PubMed Central (United Kingdom)

Quantum information processing is performed with single trapped Ca(+) ions, stored in a linear Paul trap and laser-cooled to the ground state of their harmonic quantum motion. Composite laser-pulse sequences were used to implement SWAP gate, phase gate and controlled-NOT gate operations. Stark shifts on the quantum-bit transitions were precisely measured and compensated. For a demonstration of quantum information processing, a Deutsch-Jozsa algorithm has been implemented using two quantum bits encoded on a single ion.

Gulde S; Häffner H; Riebe M; Lancaster G; Becher C; Eschner J; Schmidt-Kaler F; Chuang IL; Blatt R

2003-07-01

30

Quantum Information is Physical  

CERN Multimedia

We discuss a few current developments in the use of quantum mechanically coherent systems for information processing. In each of these developments, Rolf Landauer has played a crucial role in nudging us and other workers in the field into asking the right questions, some of which we have been lucky enough to answer. A general overview of the key ideas of quantum error correction is given. We discuss how quantum entanglement is the key to protecting quantum states from decoherence in a manner which, in a theoretical sense, is as effective as the protection of digital data from bit noise. We also discuss five general criteria which must be satisfied to implement a quantum computer in the laboratory, and we illustrate the application of these criteria by discussing our ideas for creating a quantum computer out of the spin states of coupled quantum dots.

Di Vincenzo, D P; Vincenzo, David P. Di; Loss, Daniel

1998-01-01

31

Types of quantum information  

CERN Document Server

Quantum, in contrast to classical, information theory, allows for different incompatible types (or species) of information which cannot be combined with each other. Distinguishing these incompatible types is useful in understanding the role of the two classical bits in teleportation (or one bit in one-bit teleportation), for discussing decoherence in information-theoretic terms, and for giving a proper definition, in quantum terms, of ``classical information.'' Various examples (some updating earlier work) are given of theorems which relate different incompatible kinds of information, and thus have no counterparts in classical information theory.

Griffiths, Robert B

2007-01-01

32

Exploiting the quantum Zeno effect to beat photon loss in linear optical quantum information processors  

CERN Multimedia

We devise a new technique to enhance transmission of quantum information through linear optical quantum information processors. The idea is based on applying the Quantum Zeno effect to the process of photon absorption. By frequently monitoring the presence of the photon through a QND (quantum non-demolition) measurement the absorption is suppressed. Quantum information is encoded in the polarization degrees of freedom and is therefore not affected by the measurement. Some implementations of the QND measurement are proposed.

Spedalieri, F M; Florescu, M; Kapale, K T; Yurtsever, U; Dowling, J P; Spedalieri, Federico M.; Lee, Hwang; Florescu, Marian; Kapale, Kishore T.; Yurtsever, Ulvi; Dowling, Jonathan P.

2004-01-01

33

NMR Quantum Information Processing  

CERN Multimedia

Nuclear Magnetic Resonance (NMR) has provided a valuable experimental testbed for quantum information processing (QIP). Here, we briefly review the use of nuclear spins as qubits, and discuss the current status of NMR-QIP. Advances in the techniques available for control are described along with the various implementations of quantum algorithms and quantum simulations that have been performed using NMR. The recent application of NMR control techniques to other quantum computing systems are reviewed before concluding with a description of the efforts currently underway to transition to solid state NMR systems that hold promise for scalable architectures.

Ramanathan, C; Chen, Z; Cory, D G; Chuang, I; Steffen, M; Ramanathan, Chandrasekhar; Boulant, Nicolas; Chen, Zhiying; Cory, David G.; Chuang, Isaac; Steffen, Matthias

2004-01-01

34

Quantum holographic encoding in a two-dimensional electron gas  

Energy Technology Data Exchange (ETDEWEB)

The advent of bottom-up atomic manipulation heralded a new horizon for attainable information density, as it allowed a bit of information to be represented by a single atom. The discrete spacing between atoms in condensed matter has thus set a rigid limit on the maximum possible information density. While modern technologies are still far from this scale, all theoretical downscaling of devices terminates at this spatial limit. Here, however, we break this barrier with electronic quantum encoding scaled to subatomic densities. We use atomic manipulation to first construct open nanostructures - 'molecular holograms' - which in turn concentrate information into a medium free of lattice constraints: the quantum states of a two-dimensional degenerate Fermi gas of electrons. The information embedded in the holograms is transcoded at even smaller length scales into an atomically uniform area of a copper surface, where it is densely projected into both two spatial degrees of freedom and a third holographic dimension mapped to energy. In analogy to optical volume holography, this requires precise amplitude and phase engineering of electron wavefunctions to assemble pages of information volumetrically. This data is read out by mapping the energy-resolved electron density of states with a scanning tunnelling microscope. As the projection and readout are both extremely near-field, and because we use native quantum states rather than an external beam, we are not limited by lensing or collimation and can create electronically projected objects with features as small as {approx}0.3 nm. These techniques reach unprecedented densities exceeding 20 bits/nm{sup 2} and place tens of bits into a single fermionic state.

Moon, Christopher

2010-05-26

35

Introduction to Quantum Information Processing  

CERN Document Server

As a result of the capabilities of quantum information, the science of quantum information processing is now a prospering, interdisciplinary field focused on better understanding the possibilities and limitations of the underlying theory, on developing new applications of quantum information and on physically realizing controllable quantum devices. The purpose of this primer is to provide an elementary introduction to quantum information processing, and then to briefly explain how we hope to exploit the advantages of quantum information. These two sections can be read independently. For reference, we have included a glossary of the main terms of quantum information.

Knill, E H; Barnum, H; Dalvit, D A R; Dziarmaga, J; Gubernatis, J E; Gurvits, L I; Ortiz, G; Viola, L; Zurek, W H

2002-01-01

36

Gravity from Quantum Information  

CERN Multimedia

It is suggested that classical Einstein gravity can be derived by using the Landauer's principle applied to an information erasure at causal horizons and Jacobson's idea linking the Einstein equation to thermodynamics. Our result implies that gravity has a quantum informational origin.

Lee, Jae-Weon; Lee, Jungjai

2010-01-01

37

Quantum Information Science Workshop  

Science.gov (United States)

This report is the result of a workshop hosted by the National Science Foundation with the purpose of reviewing the present state of Quantum Information Science (QIS), exploring the potential impact of QIS, and making recomendations to NSF for the long term support of QIS research programs. The report is an accessible and comprehensive introduction to QIS.

Bennett, Charles H.; Divincenzo, David; Gershenfeld, Neil; Gibbs, Hyatt; Vazirani, Umesh; Wineland, David

2005-11-20

38

Quantum information and computation  

International Nuclear Information System (INIS)

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

2001-09-07

39

Quantum information and computation  

Energy Technology Data Exchange (ETDEWEB)

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

Popescu, Sandu; Linden, Noah; Jozsa, Richard

2001-09-07

40

Information encoding of a qubit into a multilevel environment  

Science.gov (United States)

I consider the interaction of a small quantum system (a qubit) with a structured environment consisting of many levels. The qubit will experience a decoherence process, which implies that part of its initial information will be encoded into correlations between system and environment. I investigate how this information is distributed on a given subset of levels as a function of its size, using the mutual information between both entities, in the spirit of the partial-information plots studied by Zurek and co-workers. In this case we can observe some differences, which arise from the fact that I am partitioning just one quantum system and not a collection of them. However, some similar features, like redundancy (in the sense that a given amount of information is shared by many subsets), which increases with the size of the environment, are also found here.

Pérez, A.

2010-05-01

 
 
 
 
41

Reducing constraints on quantum computer design by encoded selective recoupling.  

UK PubMed Central (United Kingdom)

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

Lidar DA; Wu LA

2002-01-01

42

Reducing constraints on quantum computer design by encoded selective recoupling  

International Nuclear Information System (INIS)

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

2002-01-07

43

Spatially encoded multiple-quantum excitation.  

UK PubMed Central (United Kingdom)

In this work, we present a simple method to spatially encode the transition frequencies of nuclear spin transitions and to read out these frequencies within a single scan. The experiment works by combining pulsed field gradients with an excitation sequence that selectively excites spin transitions within certain sample regions. After the initial excitation, imaging the resulting z?-magnetization is used to determine the locations where the excitations occurred, from which the corresponding transition frequencies are determined. Simple experimental demonstrations of this technique on one- and two-spin systems are presented.

Ridge CD; Borvayeh L; Walls JD

2013-05-01

44

Utilizing encoding in scalable linear optics quantum computing  

Energy Technology Data Exchange (ETDEWEB)

We present a scheme which offers a significant reduction in the resources required to implement linear optics quantum computing. The scheme is a variation of the proposal of Knill, Laflamme and Milburn, and makes use of an incremental approach to the error encoding to boost probability of success.

Hayes, A J F [Centre for Quantum Computer Technology and Physics Department, University of Queensland, QLD 4072, Brisbane (Australia); Gilchrist, A [Centre for Quantum Computer Technology and Physics Department, University of Queensland, QLD 4072, Brisbane (Australia); Myers, C R [Institute for Quantum Computing, University of Waterloo, ON, N2L 3G1 (Canada); Ralph, T C [Centre for Quantum Computer Technology and Physics Department, University of Queensland, QLD 4072, Brisbane (Australia)

2004-12-01

45

Recycling of quantum information: Multiple observations of quantum systems  

CERN Multimedia

Given a finite number of copies of an unknown qubit state that have already been measured optimally, can one still extract any information about the original unknown state? We give a positive answer to this question and quantify the information obtainable by a given observer as a function of the number of copies in the ensemble, and of the number of independent observers that, one after the other, have independently measured the same ensemble of qubits before him. The optimality of the protocol is proven and extensions to other states and encodings are also studied. According to the general lore, the state after a measurement has no information about the state before the measurement. Our results manifestly show that this statement has to be taken with a grain of salt, specially in situations where the quantum states encode confidential information.

Rapcan, Peter; Munoz-Tapia, Ramon; Bagan, Emilio; Buzek, Vladimir

2007-01-01

46

Quantum VQ Inequality Iteration and Quantum VQ Encoding Algorithm of Image Compression  

CERN Document Server

Many classical encoding algorithms of Vector Quantization (VQ) that can obtain global optimal solution have computational complexity O(N). In this paper, a quantum VQ encoding algorithm with computational complexity less than sqrt(N)that for most images is presented.

Pang, C Y; Guo, G C; Pang, Chao-Yang; Zhou, Zheng-Wei; Guo, Guang-Can

2006-01-01

47

Quantum encodings in spin systems and harmonic oscillators  

International Nuclear Information System (INIS)

We show that higher-dimensional versions of qubits, or qudits, can be encoded into spin systems and into harmonic oscillators, yielding important advantages for quantum computation. Whereas qubit-based quantum computation is adequate for analyses of quantum vs classical computation, in practice qubits are often realized in higher-dimensional systems by truncating all but two levels, thereby reducing the size of the precious Hilbert space. We develop natural qudit gates for universal quantum computation, and exploit the entire accessible Hilbert space. Mathematically, we give representations of the generalized Pauli group for qudits in coupled spin systems and harmonic oscillators, and include analyses of the qubit and the infinite-dimensional limits.

2002-01-01

48

Inequalities for quantum skew information  

DEFF Research Database (Denmark)

We study quantum information inequalities and show that the basic inequality between the quantum variance and the metric adjusted skew information generates all the multi-operator matrix inequalities or Robertson type determinant inequalities studied by a number of authors. We introduce an order relation on the set of functions representing quantum Fisher information that renders the set into a lattice with an involution. This order structure generates new inequalities for the metric adjusted skew informations. In particular, the Wigner-Yanase skew information is the maximal skew information with respect to this order structure in the set of Wigner-Yanase-Dyson skew informations.

Audenaert, Koenraad; Cai, Liang

2008-01-01

49

Quantum information and precision measurement  

CERN Multimedia

We describe some applications of quantum information theory to the analysis of quantum limits on measurement sensitivity. A measurement of a weak force acting on a quantum system is a determination of a classical parameter appearing in the master equation that governs the evolution of the system; limitations on measurement accuracy arise because it is not possible to distinguish perfectly among the different possible values of this parameter. Tools developed in the study of quantum information and computation can be exploited to improve the precision of physics experiments; examples include superdense coding, fast database search, and the quantum Fourier transform.

Childs, A M; Renes, J M; Childs, Andrew M.; Preskill, John; Renes, Joseph

2000-01-01

50

Physics as Quantum Information Processing: Quantum Fields as Quantum Automata  

CERN Multimedia

Can we reduce Quantum Field Theory (QFT) to a quantum computation? Can physics be simulated by a quantum computer? Do we believe that a quantum field is ultimately made of a numerable set of quantum systems that are unitarily interacting? A positive answer to these questions corresponds to substituting QFT with a theory of quantum cellular automata (QCA), and the present work is examining this hypothesis. These investigations are part of a large research program on a "quantum-digitalization" of physics, with Quantum Theory as a special theory of information, and Physics as emergent from the same quantum-information processing. A QCA-based QFT has tremendous potential advantages compared to QFT, being quantum "ab-initio" and free from the problems plaguing QFT due to the continuum hypothesis. Here I will show how dynamics emerges from the quantum processing, how the QCA can reproduce the Dirac-field phenomenology at large scales, and the kind of departures from QFT that that should be expected at a Planck-scal...

D'Ariano, Giacomo Mauro

2011-01-01

51

Block synchronization for quantum information  

CERN Multimedia

We develop a coding theoretic method for properly locating boundaries of quantum information without relying on external synchronization. The method also protects qubits from decoherence in a manner similar to conventional quantum error-correcting codes, seamlessly achieving synchronization recovery and error correction. Infinitely many examples of quantum codes that are simultaneously synchronizable and error-correcting are given. The unified approach to synchronization and quantum error correction may simplify requirements on hardware.

Fujiwara, Yuichiro

2012-01-01

52

Informational power of quantum measurements  

International Nuclear Information System (INIS)

[en] We introduce the informational power of a quantum measurement as the maximum amount of classical information that the measurement can extract from any ensemble of quantum states. We prove the additivity by showing that the informational power corresponds to the classical capacity of a quantum-classical channel. We restate the problem of evaluating the informational power as the maximization of the accessible information of a suitable ensemble. We provide a numerical algorithm to find an optimal ensemble and quantify the informational power.

2011-01-01

53

Efficient Phase-Encoding Quantum Key Generation with Narrow-Band Single Photons  

CERN Multimedia

We propose an efficient phase-encoding quantum secret key generation scheme with heralded narrow-band single photons. The key information is carried by the phase modulation directly on the single-photon temporal waveform without using any passive beam splitters or optical switches. We show that, when the technique is applied to the conventional fiber-based phase-encoding BB84 and differential phase shift (DPS) quantum key distribution schemes, the key generation efficiencies can be improved by a factor of 2 and 3, respectively. For N(>3)-period DPS systems, the key generation efficiency can be improved by a factor of N. The technique is suitable for quantum memory-based long-distance fiber communication system.

Yan, Hui; Du, Shengwang

2010-01-01

54

On quantum information  

CERN Multimedia

We investigate the following generalisation of the entropy of quantum measurement. Let H be an infinite-dimensional separable Hilbert space with a 'density' operator {\\rho}, tr {\\rho}=1. Let I(P)\\in R be defined for any partition P = (P_1,...,P_m), P_1+ ... +P_m=1_H, P_i \\in proj H$ and let I(P_i Qj, i \\leq m, j \\leq n) = I(P) + I(Q) for Q =(Q_1,..., Q_n), \\sum Q_j = 1_H and P_iQ_j = Q_j P_i, tr {\\rho} P_iQ_j = tr {\\rho} P_i tr {\\rho} Q_j (P, Q are physically independent). Assuming some continuity properties we give a general form of generalised information I.

Paszkiewicz, Adam

2012-01-01

55

Environment-assisted quantum-information correction for continuous variables  

DEFF Research Database (Denmark)

Quantum-information protocols are inevitably affected by decoherence which is associated with the leakage of quantum information into an environment. In this article we address the possibility of recovering the quantum information from an environmental measurement. We investigate continuous-variable quantum information, and we propose a simple environmental measurement that under certain circumstances fully restores the quantum information of the signal state although the state is not reconstructed with unit fidelity. We implement the protocol for which information is encoded into conjugate quadratures of coherent states of light and the noise added under the decoherence process is of Gaussian nature. The correction protocol is tested using both a deterministic as well as a probabilistic strategy. The potential use of the protocol in a continuous-variable quantum-key distribution scheme as a means to combat excess noise is also investigated.

Sabuncu, Metin; Filip, R.

2010-01-01

56

Environmental Assisted Quantum Information Correction for Continuous Variables  

CERN Multimedia

Quantum information protocols are inevitably affected by decoherence which is associated with the leakage of quantum information into an environment. In this paper we address the possibility of recovering the quantum information from an environmental measurement. We investigate continuous variable quantum information, and we propose a simple environmental measurement that under certain circumstances fully restores the quantum information of the signal state although the state is not reconstructed with unit fidelity. We implement the protocol for which information is encoded into conjugate quadratures of coherent states of light and the noise added under the decoherence process is of Gaussian nature. The correction protocol is tested using both a deterministic as well as a probabilistic strategy. The potential use of the protocol in a continuous variable quantum key distribution scheme as a means to combat excess noise is also investigated.

Sabuncu, Metin; Leuchs, Gerd; Andersen, Ulrik L

2009-01-01

57

Time, Quantum and Information  

International Nuclear Information System (INIS)

Time, Quantum and Information, a paean to Professor Carl Friedrich von Weizsaecker, commemorates his 90th birthday. The range of Professor Weizsaecker's endeavours is an exhilarating example of what can be accomplished by one freely-soaring human spirit, who is at the same time a physicist, a philosopher, and a humanitarian. The editors, Lutz Castell and Otfried Ischebeck, have assembled an admirable collection of essays and articles written by Weizsaecker?s past students, collaborators, colleagues and acquaintances. Time, Quantum and Information offers the reader a panoply of unique insights into twentieth century science and history. Entangled with the stories about Weizsaecker?s influence on the lives of some of the contributors are discussions of the activities of German scientists during and following World War II, emphasizing their reluctance to work on atomic weapons following the war. By outlining Weizsaecker?s role in the early development of numerous tributaries of physical science, the book gives us a new glimpse into the origins of some of its disparate domains, such as nuclear physics, the physics of stellar nucleosynthesis, cosmic ray physics, fluid turbulence, and the formation of the solar system. We physicists have all studied Weizsaecker?s semi-empirical mass formula describing the binding energy of nuclei. We are aware too that both he and Hans Bethe independently discovered the nuclear cycles that provide stars with their enduring energy output. We have studied the Weizsaecker--Williams technique of calculating the bremsstrahlung of relativistic electrons. But how many of us know of Weizsaecker's work in fluid turbulence that he, like Werner Heisenberg under whom he had earned his doctorate, pursued while holed up in Farm Hall? And how many of us are aware of his introduction of turbulent viscosity to account for the origin of planetary orbits, involving the migration of mass inwards and angular momentum outwards? Moreover, before finally turning his attention to philosophy in 1957, Weizsaecker became interested in nuclear fusion research and educated a generation of postwar German physicists in both plasma physics and astrophysics. Michael Frayn's play 'Copenhagen' has ignited worldwide interest in the mysterious meeting of Niels Bohr with Werner Heisenberg in September 1941. However, an article by R Luest indicates that in 1951 Bohr enjoyed a friendly visit with Heisenberg in Goettingen. This 1941 meeting of Heisenberg and Bohr is discussed further in an article by Goetz Neuneck, who also details the World War II and post-war research and interests of the Uranium Club, a group of 70--100 German physicists and chemists. Neuneck also discusses the resistance of individual scientists, such as Hahn, Heisenberg, and Bothe, to the Nazi regime. We learn that, unlike Wernher von Braun, no member of the Uranium Club was ever granted an audience with Hitler. After the war, German scientists renounced any role for German development of nuclear weapons in various manifestos, such as the Mainau and Goettingen Declarations that were both influenced by Weizsaecker. Time, Quantum and Information contains much anecdotal material. Examples include a touching quotation in a letter from Edward Teller to Weizsaecker: 'If I could share your religious belief, I would wish that you will one day come from a higher heaven and visit me in purgatory.' Another example, less complimentary, is a comment from Pauli after hearing from Weisskopf that Weizsaecker had made numerous errors in his habilitation thesis and realizing that Weizsaecker had accepted an offer from Peter Debye at Berlin: 'The measure of sloppiness in Weizsaecker's work exceeds altogether and by far the tolerable measure, and my pain of not having had him as an assistant has been alleviated by this.' Two-thirds of this compendium also explores the philosophical interests of Weizsaecker. This portion discusses his attempt to reconstruct quantum mechanics and build up a 'theory of everything' based on his 'ur' hypothesis. As stated by the mathematician G G Emch in

2004-04-09

58

Manipulating quantum information via quantum cloning  

International Nuclear Information System (INIS)

An extensive characterization of the information flux underlying the 1 ?2 universal cloning process is presented together with the realization of several cloning and measurement tasks. The restoration of both the quantum and classical information associated to the input qubit was theoretically analysed and experimentally accomplished. At the same time the extension of the 1 ?2 cloning to the 1 ?3 universal and covariant processes is reported with the first experimental optical realizations.

2005-12-01

59

Bohmian Mechanics and Quantum Information  

CERN Multimedia

Many recent results suggest that quantum theory is about information, and that quantum theory is best understood as arising from principles concerning information and information processing. At the same time, by far the simplest version of quantum mechanics, Bohmian mechanics, is concerned, not with information but with the behavior of an objective microscopic reality given by particles and their positions. What I would like to do here is to examine whether, and to what extent, the importance of information, observation, and the like in quantum theory can be understood from a Bohmian perspective. I would like to explore the hypothesis that the idea that information plays a special role in physics naturally emerges in a Bohmian universe.

Goldstein, Sheldon

2009-01-01

60

Bohmian Mechanics and Quantum Information  

Science.gov (United States)

Many recent results suggest that quantum theory is about information, and that quantum theory is best understood as arising from principles concerning information and information processing. At the same time, by far the simplest version of quantum mechanics, Bohmian mechanics, is concerned, not with information but with the behavior of an objective microscopic reality given by particles and their positions. What I would like to do here is to examine whether, and to what extent, the importance of information, observation, and the like in quantum theory can be understood from a Bohmian perspective. I would like to explore the hypothesis that the idea that information plays a special role in physics naturally emerges in a Bohmian universe.

Goldstein, Sheldon

2010-04-01

 
 
 
 
61

Certainty and Uncertainty in Quantum Information Processing  

CERN Multimedia

This survey, aimed at information processing researchers, highlights intriguing but lesser known results, corrects misconceptions, and suggests research areas. Themes include: certainty in quantum algorithms; the "fewer worlds" theory of quantum mechanics; quantum learning; probability theory versus quantum mechanics.

Rieffel, E G

2007-01-01

62

From Geometric Quantum Mechanics to Quantum Information  

CERN Multimedia

We consider the geometrization of quantum mechanics. We then focus on the pull-back of the Fubini-Study metric tensor field from the projective Hibert space to the orbits of the local unitary groups. An inner product on these tensor fields allows us to obtain functions which are invariant under the considered local unitary groups. This procedure paves the way to an algorithmic approach to the identification of entanglement monotone candidates. Finally, a link between the Fubini-Study metric and a quantum version of the Fisher information metric is discussed.

Aniello, P; Marmo, G; Volkert, G F

2011-01-01

63

Experimental implementation of encoded logical qubit operations in a perfect quantum error correcting code.  

UK PubMed Central (United Kingdom)

Large-scale universal quantum computing requires the implementation of quantum error correction (QEC). While the implementation of QEC has already been demonstrated for quantum memories, reliable quantum computing requires also the application of nontrivial logical gate operations to the encoded qubits. Here, we present examples of such operations by implementing, in addition to the identity operation, the NOT and the Hadamard gate to a logical qubit encoded in a five qubit system that allows correction of arbitrary single-qubit errors. We perform quantum process tomography of the encoded gate operations, demonstrate the successful correction of all possible single-qubit errors, and measure the fidelity of the encoded logical gate operations.

Zhang J; Laflamme R; Suter D

2012-09-01

64

Optimal strategies for sending information through A quantum channel  

UK PubMed Central (United Kingdom)

Quantum states can be used to encode the information contained in a direction, i.e., in a unit vector. We present the best encoding procedure when the quantum state is made up of N spins (qubits). We find that the quality of this optimal procedure, which we quantify in terms of the fidelity, depends solely on the dimension of the encoding space. We also investigate the use of spatial rotations on a quantum state, which provide a natural and less demanding encoding. In this case we prove that the fidelity is directly related to the largest zeros of the Legendre and Jacobi polynomials. We also discuss our results in terms of the information gain.

Bagan E; Baig M; Brey A; Munoz-Tapia R; Tarrach R

2000-12-01

65

Quantum: information theory: technological challenge  

International Nuclear Information System (INIS)

[en] The new Quantum Information Theory augurs powerful machines that obey the entangled logic of the subatomic world. Parallelism, entanglement, teleportation, no-cloning and quantum cryptography are typical peculiarities of this novel way of understanding computation. (Author) 24 refs

2001-01-01

66

Quantum information and convex optimization  

International Nuclear Information System (INIS)

[en] This thesis is concerned with convex optimization problems in quantum information theory. It features an iterative algorithm for optimal quantum error correcting codes, a postprocessing method for incomplete tomography data, a method to estimate the amount of entanglement in witness experiments, and it gives necessary and sufficient criteria for the existence of retrodiction strategies for a generalized mean king problem. (orig.)

2008-01-01

67

High-fidelity linear optical quantum computing with polarization encoding  

International Nuclear Information System (INIS)

We show that the KLM scheme [Knill, Laflamme, and Milburn, Nature 409, 46 (2001)] can be implemented using polarization encoding, thus reducing the number of path modes required by half. One of the main advantages of this new implementation is that it naturally incorporates a loss detection mechanism that makes the probability of a gate introducing a non-detected error, when non-ideal detectors are considered, dependent only on the detector dark-count rate and independent of its efficiency. Since very low dark-count rate detectors are currently available, a high-fidelity gate (probability of error of order 10-6 conditional on the gate being successful) can be implemented using polarization encoding. The detector efficiency determines the overall success probability of the gate but does not affect its fidelity. This can be applied to the efficient construction of optical cluster states with very high fidelity for quantum computing.

2006-01-01

68

Quantum information. Teleporation - cryptography - quantum computer  

International Nuclear Information System (INIS)

[en] The following topics are dealt with: Reality in the test house, quantum teleportation, 100 years of quantum theory, the reality of quanta, interactionless quantum measurement, rules for quantum computers, quantum computers with ions, spintronics with diamond, the limits of the quantum computers, a view into the future of quantum optics. (HSI)

2010-01-01

69

Quantum Information Science and Nanotechnology  

CERN Document Server

In this note is touched upon an application of quantum information science (QIS) in nanotechnology area. The laws of quantum mechanics may be very important for nano-scale objects. A problem with simulating of quantum systems is well known and quantum computer was initially suggested by R. Feynman just as the way to overcome such difficulties. Mathematical methods developed in QIS also may be applied for description of nano-devices. Few illustrative examples are mentioned and they may be related with so-called fourth generation of nanotechnology products.

Vlasov, Alexander Yu

2009-01-01

70

Quantum Tomograms and Their Application in Quantum Information Science  

Science.gov (United States)

This note is devoted to quantum tomograms application in quantum information science. Representation for quantum tomograms of continuous variables via Feynman path integrals is considered. Due to this construction quantum tomograms of harmonic oscillator are obtained. Application tomograms in causal analysis of quantum states is presented. Two qubit maximum entangled and "quantum-classical" states have been analyzed by tomographic causal analysis of quantum states.

Fedorov, Aleksey K.; Yurchenko, Stanislav O.

2013-02-01

71

Information security: from classical to quantum  

Science.gov (United States)

Quantum cryptography was designed to provide a new approach to the problem of distributing keys for private-key cryptography. The principal idea is that security can be ensured by exploiting the laws of quantum physics and, in particular, by the fact that any attempt to measure a quantum state will change it uncontrollably. This change can be detected by the legitimate users of the communication channel and so reveal to them the presence of an eavesdropper. In this paper I explain (briefly) how quantum key distribution works and some of the progress that has been made towards making this a viable technology. With the principles of quantum communication and quantum key distribution firmly established, it is perhaps time to consider how efficient it can be made. It is interesting to ask, in particular, how many bits of information might reasonably be encoded securely on each photon. The use of photons entangled in their time of arrival might make it possible to achieve data rates in excess of 10 bits per photon.

Barnett, Stephen M.; Brougham, Thomas

2012-09-01

72

Quantum information processing with atoms  

Energy Technology Data Exchange (ETDEWEB)

A brief review is given of the recent progress in theoretical and experimental studies of quantum information, with emphasis on the role played by atomic physics. Specific topics discussed are generation of atomic entanglement and teleportation of atomic states.

Lee, Hai Woong [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of)

2004-07-01

73

Quantum gloves: Physics and Information  

CERN Document Server

The slogan information is physical has been so successful that it led to some excess. Classical and quantum information can be thought of independently of any physical implementation. Pure information tasks can be realized using such abstract c- and qu-bits, but physical tasks require appropriate physical realizations of c- or qu-bits. As illustration we consider the problem of communicating chirality.

Gisin, Nicolas

2004-01-01

74

Evaluating standard terminologies for encoding allergy information.  

UK PubMed Central (United Kingdom)

OBJECTIVE: Allergy documentation and exchange are vital to ensuring patient safety. This study aims to analyze and compare various existing standard terminologies for representing allergy information. METHODS: Five terminologies were identified, including the Systemized Nomenclature of Medical Clinical Terms (SNOMED CT), National Drug File-Reference Terminology (NDF-RT), Medication Dictionary for Regulatory Activities (MedDRA), Unique Ingredient Identifier (UNII), and RxNorm. A qualitative analysis was conducted to compare desirable characteristics of each terminology, including content coverage, concept orientation, formal definitions, multiple granularities, vocabulary structure, subset capability, and maintainability. A quantitative analysis was also performed to compare the content coverage of each terminology for (1) common food, drug, and environmental allergens and (2) descriptive concepts for common drug allergies, adverse reactions (AR), and no known allergies. RESULTS: Our qualitative results show that SNOMED CT fulfilled the greatest number of desirable characteristics, followed by NDF-RT, RxNorm, UNII, and MedDRA. Our quantitative results demonstrate that RxNorm had the highest concept coverage for representing drug allergens, followed by UNII, SNOMED CT, NDF-RT, and MedDRA. For food and environmental allergens, UNII demonstrated the highest concept coverage, followed by SNOMED CT. For representing descriptive allergy concepts and adverse reactions, SNOMED CT and NDF-RT showed the highest coverage. Only SNOMED CT was capable of representing unique concepts for encoding no known allergies. CONCLUSIONS: The proper terminology for encoding a patient's allergy is complex, as multiple elements need to be captured to form a fully structured clinical finding. Our results suggest that while gaps still exist, a combination of SNOMED CT and RxNorm can satisfy most criteria for encoding common allergies and provide sufficient content coverage.

Goss FR; Zhou L; Plasek JM; Broverman C; Robinson G; Middleton B; Rocha RA

2013-09-01

75

Quantum information. Teleportation - cryptography - quantum computer  

International Nuclear Information System (INIS)

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

2012-01-01

76

On the photonic implementation of universal quantum gates, bell states preparation circuit and quantum LDPC encoders and decoders based on directional couplers and HNLF.  

Science.gov (United States)

The Bell states preparation circuit is a basic circuit required in quantum teleportation. We describe how to implement it in all-fiber technology. The basic building blocks for its implementation are directional couplers and highly nonlinear optical fiber (HNLF). Because the quantum information processing is based on delicate superposition states, it is sensitive to quantum errors. In order to enable fault-tolerant quantum computing the use of quantum error correction is unavoidable. We show how to implement in all-fiber technology encoders and decoders for sparse-graph quantum codes, and provide an illustrative example to demonstrate this implementation. We also show that arbitrary set of universal quantum gates can be implemented based on directional couplers and HNLFs. PMID:20588656

Djordjevic, Ivan B

2010-04-12

77

On the photonic implementation of universal quantum gates, bell states preparation circuit and quantum LDPC encoders and decoders based on directional couplers and HNLF.  

UK PubMed Central (United Kingdom)

The Bell states preparation circuit is a basic circuit required in quantum teleportation. We describe how to implement it in all-fiber technology. The basic building blocks for its implementation are directional couplers and highly nonlinear optical fiber (HNLF). Because the quantum information processing is based on delicate superposition states, it is sensitive to quantum errors. In order to enable fault-tolerant quantum computing the use of quantum error correction is unavoidable. We show how to implement in all-fiber technology encoders and decoders for sparse-graph quantum codes, and provide an illustrative example to demonstrate this implementation. We also show that arbitrary set of universal quantum gates can be implemented based on directional couplers and HNLFs.

Djordjevic IB

2010-04-01

78

Information transfer through quantum channels  

International Nuclear Information System (INIS)

This PhD thesis represents work done between Aug. 2003 and Dec. 2006 in Reinhard F. Werner's quantum information theory group at Technische Universitaet Braunschweig, and Artur Ekert's Centre for Quantum Computation at the University of Cambridge. My thesis falls into the field of abstract quantum information theory. This work investigates both fundamental properties of quantum channels and their asymptotic capacities for classical as well as quantum information transfer. Stinespring's theorem is the basic structure theorem for quantum channels. It implies that every quantum channel can be represented as a unitary evolution on an enlarged system. In Ch. 3 we present a continuity theorem for Stinespring's representation: two quantum channels are similar if and only if it is possible to find unitary implementations that are likewise similar, with dimension-independent norm bounds. The continuity theorem allows to derive a formulation of the information-disturbance tradeoff in terms of quantum channels, and a continuity estimate for the no-broadcasting principle. In Ch. 4 we then apply the continuity theorem to give a strengthened no-go proof for quantum bit commitment, an important cryptographic primitive. This result also provides a natural characterization of those protocols that fall outside the standard setting of unconditional security, and thus may allow secure bit commitment. We present a new such protocol whose security relies on decoherence in the receiver's lab. Ch. 5 reviews the capacities of quantum channels for the transfer of both classical and quantum information, and investigates several variations in the notion of channel capacity. Memory effects are then investigated in detail in Ch. 6. We advertise a model which is sufficiently general to encompass all causal automata: every quantum process in which the outputs up to any given time t do not depend on the inputs at times t'>t can be represented as a concatenated memory channel. We then explain how all known coding theorems can be generalized from memoryless channels to forgetful memory channels. We also present examples for non-forgetful channels, and derive generic entropic upper bounds on their capacities for (private) classical and quantum information transfer. Ch. 7 provides a brief introduction to quantum information spectrum methods as a promising approach to coding theorems for completely general quantum sources and channels. We present a data compression theorem for general quantum sources and apply these results to ergodic as well as mixed sources. Finally we investigate the continuity of distillable entanglement - another key notion of the field, which characterizes the optimal asymptotic rate at which maximally entangled states can be generated from many copies of a less entangled state. We derive uniform norm bounds for all states with full support, and we extend some of these results to quantum channel capacities. (orig.)

2007-01-01

79

Information transfer through quantum channels  

Energy Technology Data Exchange (ETDEWEB)

This PhD thesis represents work done between Aug. 2003 and Dec. 2006 in Reinhard F. Werner's quantum information theory group at Technische Universitaet Braunschweig, and Artur Ekert's Centre for Quantum Computation at the University of Cambridge. My thesis falls into the field of abstract quantum information theory. This work investigates both fundamental properties of quantum channels and their asymptotic capacities for classical as well as quantum information transfer. Stinespring's theorem is the basic structure theorem for quantum channels. It implies that every quantum channel can be represented as a unitary evolution on an enlarged system. In Ch. 3 we present a continuity theorem for Stinespring's representation: two quantum channels are similar if and only if it is possible to find unitary implementations that are likewise similar, with dimension-independent norm bounds. The continuity theorem allows to derive a formulation of the information-disturbance tradeoff in terms of quantum channels, and a continuity estimate for the no-broadcasting principle. In Ch. 4 we then apply the continuity theorem to give a strengthened no-go proof for quantum bit commitment, an important cryptographic primitive. This result also provides a natural characterization of those protocols that fall outside the standard setting of unconditional security, and thus may allow secure bit commitment. We present a new such protocol whose security relies on decoherence in the receiver's lab. Ch. 5 reviews the capacities of quantum channels for the transfer of both classical and quantum information, and investigates several variations in the notion of channel capacity. Memory effects are then investigated in detail in Ch. 6. We advertise a model which is sufficiently general to encompass all causal automata: every quantum process in which the outputs up to any given time t do not depend on the inputs at times t'>t can be represented as a concatenated memory channel. We then explain how all known coding theorems can be generalized from memoryless channels to forgetful memory channels. We also present examples for non-forgetful channels, and derive generic entropic upper bounds on their capacities for (private) classical and quantum information transfer. Ch. 7 provides a brief introduction to quantum information spectrum methods as a promising approach to coding theorems for completely general quantum sources and channels. We present a data compression theorem for general quantum sources and apply these results to ergodic as well as mixed sources. Finally we investigate the continuity of distillable entanglement - another key notion of the field, which characterizes the optimal asymptotic rate at which maximally entangled states can be generated from many copies of a less entangled state. We derive uniform norm bounds for all states with full support, and we extend some of these results to quantum channel capacities. (orig.)

Kretschmann, D.

2007-03-12

80

Temporal compression of quantum information-carrying photons using a photon-echo quantum memory approach  

CERN Multimedia

We study quantum compression and decompression of light pulses that carry quantum information using a photon-echo quantum memory technique with controllable inhomogeneous broadening of an isolated atomic absorption line. We investigate media with differently broadened absorption profiles, transverse and longitudinal, finding that the recall efficiency can be as large as unity and that the quantum information encoded into the photonic qubits can remain unperturbed. Our results provide new insight into reversible light-atom interaction, and are interesting in view of future quantum communication networks, where pulse compression and decompression may play an important role to increase the qubit rate, or to map quantum information from photonic carriers with large optical bandwidth into atomic memories with smaller bandwidth.

Moiseev, S A

2010-01-01

 
 
 
 
81

Temporal compression of quantum-information-carrying photons using a photon-echo quantum memory approach  

International Nuclear Information System (INIS)

We study quantum compression and decompression of light pulses that carry quantum information using a photon-echo quantum memory technique with controllable inhomogeneous broadening of an isolated atomic absorption line. We investigate media with differently broadened absorption profiles, transverse and longitudinal, finding that the recall efficiency can be as large as unity and that the quantum information encoded into the photonic qubits can remain unperturbed. Our results provide insight into reversible light-atom interaction and are interesting in view of future quantum communication networks, where pulse compression and decompression may play an important role in increasing the qubit rate or in mapping quantum information from photonic carriers with large optical bandwidth into atomic memories with smaller bandwidth.

2010-01-01

82

Encoding multiple quantum coherences in non-commuting bases  

CERN Multimedia

Multiple quantum coherences are typically characterised by their coherence number and the number of spins that make up the state, though only the coherence number is normally measured. We present a simple set of measurements that extend our knowledge of the multiple quantum state by recording the coherences in both the $x$ basis and the usual $z$ basis. The coherences in the two bases are related by a similarity transformation. We characterize the growth of the multiple quantum coherences via measurements in the two bases, and show that the rate varies with the coefficient of the driving term in the Hamiltonian. Such measurements in non-commuting bases provides additional information over the 1D method about the state of the spin system. In particular the measurement of coherences in a basis other than the usual $z$ basis allows us to study the dynamics of the spin system under Hamiltonians, such as the secular dipolar Hamiltonian, that conserve $z$ basis coherence number.

Ramanathan, C; Cappellaro, P; Boutis, G S; Cory, D G; Ramanathan, Chandrasekhar; Cho, Hyungjoon; Cappellaro, Paola; Boutis, Gregory S.; Cory, David G.

2003-01-01

83

Experimental demonstration of quantum digital signatures using phase-encoded coherent states of light  

Science.gov (United States)

Digital signatures are frequently used in data transfer to prevent impersonation, repudiation and message tampering. Currently used classical digital signature schemes rely on public key encryption techniques, where the complexity of so-called `one-way' mathematical functions is used to provide security over sufficiently long timescales. No mathematical proofs are known for the long-term security of such techniques. Quantum digital signatures offer a means of sending a message, which cannot be forged or repudiated, with security verified by information-theoretical limits and quantum mechanics. Here we demonstrate an experimental system, which distributes quantum signatures from one sender to two receivers and enables message sending ensured against forging and repudiation. Additionally, we analyse the security of the system in some typical scenarios. Our system is based on the interference of phase-encoded coherent states of light and our implementation utilizes polarization-maintaining optical fibre and photons with a wavelength of 850nm.

Clarke, Patrick J.; Collins, Robert J.; Dunjko, Vedran; Andersson, Erika; Jeffers, John; Buller, Gerald S.

2012-11-01

84

Experimental polarization encoded quantum key distribution over optical fibres with real-time continuous birefringence compensation  

CERN Document Server

In this paper we demonstrate an active polarization drift compensation scheme for optical fibres employed in a quantum key distribution experiment with polarization encoded qubits. The quantum signals are wavelength multiplexed in one fibre along with two classical optical side channels that provide the control information for the polarization compensation scheme. This set-up allows us to continuously track any polarization change without the need to interrupt the key exchange. The results obtained show that fast polarization rotations of the order of 40*pi rad/s are effectively compensated for. We demonstrate that our set-up allows continuous quantum key distribution even in a fibre stressed by random polarization fluctuations. Our results pave the way for Bell-state measurements using only linear optics with parties separated by long-distance optical fibres.

Xavier, G B; de Faria, G Vilela; Temporao, G P; Gisin, N; Zbinden, H; von der Weid, J P; 10.1088/1367-2630/11/4/045015

2009-01-01

85

Experimental polarization encoded quantum key distribution over optical fibres with real-time continuous birefringence compensation  

International Nuclear Information System (INIS)

[en] In this paper we demonstrate an active polarization drift compensation scheme for optical fibres employed in a quantum key distribution experiment with polarization encoded qubits. The quantum signals are wavelength multiplexed in one fibre along with two classical optical side channels that provide the control information for the polarization compensation scheme. This set-up allows us to continuously track any polarization change without the need to interrupt the key exchange. The results obtained show that fast polarization rotations of the order of 40? rad s-1 are effectively compensated for. We demonstrate that our set-up allows continuous quantum key distribution even in a fibre stressed by random polarization fluctuations. Our results pave the way for Bell-state measurements using only linear optics with parties separated by long-distance optical fibres.

2009-01-01

86

Immunity of information encoded in decoherence-free subspaces to particle loss  

International Nuclear Information System (INIS)

[en] We demonstrate that for an ensemble of qudits, subjected to collective decoherence in the form of perfectly correlated random SU(d) unitaries, quantum superpositions stored in the decoherence-free subspace are fully immune against the removal of one particle. This provides a feasible scheme to protect quantum information encoded in the polarization state of a sequence of photons against both collective depolarization and one-photon loss and can be demonstrated with photon quadruplets using currently available technology.

2011-01-01

87

Immunity of information encoded in decoherence-free subspaces to particle loss  

Energy Technology Data Exchange (ETDEWEB)

We demonstrate that for an ensemble of qudits, subjected to collective decoherence in the form of perfectly correlated random SU(d) unitaries, quantum superpositions stored in the decoherence-free subspace are fully immune against the removal of one particle. This provides a feasible scheme to protect quantum information encoded in the polarization state of a sequence of photons against both collective depolarization and one-photon loss and can be demonstrated with photon quadruplets using currently available technology.

Migdal, Piotr [Instytut Fizyki Teoretycznej, Wydzial Fizyki, Uniwersytet Warszawski, Hoza 69, PL-00-681 Warszawa (Poland); ICFO-Institut de Ciencies Fotoniques, Castelldefels, ES-08860 Barcelona (Spain); Banaszek, Konrad [Instytut Fizyki Teoretycznej, Wydzial Fizyki, Uniwersytet Warszawski, Hoza 69, PL-00-681 Warszawa (Poland)

2011-11-15

88

Symmetric Informationally Complete Quantum Measurements  

CERN Multimedia

We consider the existence in arbitrary finite dimensions d of a POVM comprised of d^2 rank-one operators all of whose operator inner products are equal. Such a set is called a ``symmetric, informationally complete'' POVM (SIC-POVM) and is equivalent to a set of d^2 equiangular lines in C^d. SIC-POVMs are relevant for quantum state tomography, quantum cryptography, and foundational issues in quantum mechanics. We construct SIC-POVMs in dimensions two, three, and four. We further conjecture that a particular kind of group-covariant SIC-POVM exists in arbitrary dimensions, providing numerical results up to dimension 45 to bolster this claim.

Renes, J M; Scott, A J; Caves, C M; Renes, Joseph M.; Blume-Kohout, Robin; Caves, Carlton M.

2004-01-01

89

Quantum Information Processing:  

UK PubMed Central (United Kingdom)

Quantum mechanics has the potential to play a major rolein the future of cryptology. On the one hand, it could bring to its kneesmost of the current trends in contemporary cryptography. On the otherhand, it offers an alternative for the protection of privacy whose securitycannot be matched by classical means.

Gilles Brassard

90

Contract Signature Using Quantum Information  

CERN Document Server

This paper describes how to perform contract signature in a fair way using quantum information. The protocol proposed permits two partners, users of a communication network, to exchange their signatures with non-repudiation. For this, we assume that there is a trustable arbitrator, responsible for the authentication of the signers and that performs a central task in a quantum teleportation protocol of the XOR function between two classical bits.

De Sousa, P B M; Ramos, Rubens Viana; Sousa, Paulo Benicio Melo de

2006-01-01

91

Quantum Mechanics as Information Fusion  

CERN Multimedia

We provide evidence that quantum mechanics can be interpreted as a rational algorithm for finding the least complex description for the correlations in the outputs of sensors in a large array. In particular, by comparing the self-organization approach to solving the Traveling Salesman Problem with a solution based on taking the classical limit of a Feynman path integral, we are led to a connection between the quantum mechanics of motion in a magnetic field and self-organized information fusion.

Chapline, G

1999-01-01

92

Location of quantum information in additive graph codes  

CERN Multimedia

The location of quantum information in various subsets of the qudit carriers of an additive graph code is discussed using a collection of operators on the coding space which form what we call the information group. It represents the input information through an encoding operation constructed as an explicit quantum circuit. Partial traces of these operators down to a particular subset of carriers provide an isomorphism of a subgroup of the information group, and this gives a precise characterization of what kinds of information they contain. All carriers are assumed to have the same dimension D, an arbitrary integer greater than 1.

Gheorghiu, Vlad; Griffiths, Robert B

2009-01-01

93

On the Automation of Encoding Processes in the Quantum IO Monad  

Directory of Open Access Journals (Sweden)

Full Text Available It is now clear that the use of resilient encoding schemes will be required for any quantum computing device to be realised. However, quantum programmers of the future will not wish to be tied up in the particulars of such encoding schemes. Quantum programming languages and libraries are already being developed, one of which is the Quantum IO Monad. QIO, as it is often abbreviated to, provides an interface to define and simulate quantum computations via a library of functions written in Haskell, a purely functional programming language. A solution is presented that takes an arbitrary QIO program and returns an equivalent program incorporating some specified quantum error correction techniques.

James Barratt

2012-01-01

94

Analysis of SM quantum information  

CERN Document Server

Morozova and Chentsov (Morozova and Chentsov 90) studied Riemannian metrics on the set of probability measures. They showed that, up to a constant factor, the Fisher information is the only Riemannian metric which is monotone under stochastic transformation. Sarovar and Milburn (Sarovar and Milburn 06) computed an upper bound on the Fisher information for one-parameter channels. In (O'Loan 07) we extended their bound to an upper bound on the Fisher information of multi-parameter families of states; we call this the SM quantum information. Petz and Sud\\'ar (Petz 95) characterized fully the set of monotone metrics on the space of all density matrices. We analyse the SM quantum information in light of their work. We show that the SM quantum information is not a well-defined metric on the space of density matrices: different choices of phase of the eigenvectors lead to different metrics. We define a new metric C_L as a lower bound among the SM quantum informations. We look at properties of C_L and show that it is...

O'Loan, Caleb J

2008-01-01

95

Problems and solutions in quantum computing and quantum information  

CERN Multimedia

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

Steeb, Willi-Hans

2012-01-01

96

Quantum information processing and quantum logic toward mutual illumination  

CERN Document Server

Quantum information and computation may serve as a source of useful axioms and ideas for the quantum logic/quantum structures project of characterizing and classifying types of physical theories, including quantum mechanics and classical mechanics. The axiomatic approach of quantum structures may help isolate what aspects of quantum mechanics are responsible for what aspects of its greater-than-classical information processing power, and whether more general physical theories may escape some common limitations of classical and quantum theories. Also, by by helping us understand how existing quantum algorithms work, quantum structures analyses may suggest new quantum protocols exploiting general features of quantum mechanics. I stress the importance, for these matters, of understanding open and closed-system dynamics, and the structure of composite systems in general frameworks for operational theories, such as effect algebras, convex sets, and related structures.

Barnum, H

2002-01-01

97

No-partial erasure of quantum information  

International Nuclear Information System (INIS)

[en] In complete erasure any arbitrary pure quantum state is transformed to a fixed pure state by irreversible operation. Here we ask if the process of partial erasure of quantum information is possible by general quantum operations, where partial erasure refers to reducing the dimension of the parameter space that specifies the quantum state. We prove that quantum information stored in qubits and qudits cannot be partially erased, even by irreversible operations. The 'no-partial erasure' theorem applies to spin and bosonic coherent states, and continuous variable quantum information schemes as well. Our theorem suggests an integrity principle that quantum information is indivisible

2006-11-06

98

Centre for Quantum Information and Foundations  

Science.gov (United States)

The Centre for Quantum Information and Foundations (formerly the Centre for Quantum Computation), part of the University of Cambridge, and based within the Department for Applied Maths and Theoretical Physics, conducts theoretical research into all aspects of quantum information processing, and into the implications of the quantum theory of computation for physics itself. This site contains links to current research, journal articles, educational materials (including lecture notes, puzzles and quizzes), and extensive links to the greater quantum information and computing community.

2005-11-21

99

Some Charicteristics and Applications for Quantum Information  

Directory of Open Access Journals (Sweden)

Full Text Available In this work some charicteristics and applications for quantum information is revealed. The various dynamical equations of quantum information density have been investigated, transmission characteristics of the dynamical mutual information have been studied, and the decoherence-free controlling procedure has been considered, which exposes that quantum information is holographic through the similarity structure of subdynamic kinetic equations for quantum information density.

Bi Qiao; Jinqing Fang; Harry E. Ruda

2012-01-01

100

Quantum Cloning and Deletion in Quantum Information Theory  

CERN Document Server

Quantum mechanics put restriction on performing some task which we can do classically. One such restriction is that we cannot copy an arbitrary quantum state. This is known as No-cloning theorem. Although quantum mechanics forbid us to construct a perfect cloner, there is no restriction to construct an imperfect cloner. Therefore, we have constructed and studied a special kind of quantum cloning machine named as Hybrid quantum cloning machine which is nothing but a different combination of pre-existing quantum cloning machines. We showed that this hybrid quantum cloning machine sometime gives better quality copy than the pre-existing quantum cloners. Quantum entanglement is a very astonishing property in a multi-partite system and it is a very useful ingredient of quantum information theory. Therefore broadcasting (cloning) of entanglement is a very important subject to study. In this regard we have studied the broadcasting of entanglement using state dependent quantum cloning machine. Further, we have invest...

Adhikari, Satyabrata

2006-01-01

 
 
 
 
101

Quantum Information Science Workshop: Proceedings  

Science.gov (United States)

Proceedings from an October 28-29, 1999 workshop in Arlington, Virginia on the emerging field of Quantum Information Science are now online at this National Science Foundation page. The workshop proceedings include text and color figures and provide a substantial overview of the emerging field of "interdisciplinary research and education in science and engineering."

102

The decoupling approach to quantum information theory  

CERN Multimedia

Quantum information theory studies the fundamental limits that physical laws impose on information processing tasks such as data compression and data transmission on noisy channels. This thesis presents general techniques that allow one to solve many fundamental problems of quantum information theory in a unified framework. The central theorem of this thesis proves the existence of a protocol that transmits quantum data that is partially known to the receiver through a single use of an arbitrary noisy quantum channel. In addition to the intrinsic interest of this problem, this theorem has as immediate corollaries several central theorems of quantum information theory. The following chapters use this theorem to prove the existence of new protocols for two other types of quantum channels, namely quantum broadcast channels and quantum channels with side information at the transmitter. These protocols also involve sending quantum information partially known by the receiver with a single use of the channel, and ha...

Dupuis, Frédéric

2010-01-01

103

Scalable quantum information processing with atomic ensembles and flying photons  

CERN Multimedia

We present a scheme for scalable quantum information processing (QIP) with atomic ensembles and flying photons. Using the Rydberg blockade, we encode the qubits in the collective atomic states, which could be manipulated fast and easily due to the enhanced interaction, in comparison to the single-atom case. We demonstrate that our proposed gating could be applied to generation of two-dimensional cluster states for measurement-based quantum computation. Moreover, the atomic ensembles also function as quantum repeaters useful for long distance quantum state transfer. We show the possibility of our scheme to work in bad cavity or in weak coupling regime, which could much relax the experimental requirement. The efficient coherent operations on the ensemble qubits enable our scheme to be switchable between quantum computation and quantum communication using atomic ensembles.

Mei, Feng; Yu, Ya-Fei; Zhang, Zhi-Ming

2009-01-01

104

Information-preserving structures: A general framework for quantum zero-error information  

International Nuclear Information System (INIS)

Quantum systems carry information. Quantum theory supports at least two distinct kinds of information (classical and quantum), and a variety of different ways to encode and preserve information in physical systems. A system's ability to carry information is constrained and defined by the noise in its dynamics. This paper introduces an operational framework, using information-preserving structures, to classify all the kinds of information that can be perfectly (i.e., with zero error) preserved by quantum dynamics. We prove that every perfectly preserved code has the same structure as a matrix algebra, and that preserved information can always be corrected. We also classify distinct operational criteria for preservation (e.g., 'noiseless','unitarily correctible', etc.) and introduce two natural criteria for measurement-stabilized and unconditionally preserved codes. Finally, for several of these operational criteria, we present efficient (polynomial in the state-space dimension) algorithms to find all of a channel's information-preserving structures.

2010-01-01

105

Minimal-memory realization of pearl-necklace encoders of general quantum convolutional codes  

CERN Document Server

Quantum convolutional codes, like their classical counterparts, promise to offer higher error correction performance than block codes of equivalent encoding complexity, and are expected to find important applications in reliable quantum communication where a continuous stream of qubits is transmitted. Grassl and Roetteler devised an algorithm to encode a quantum convolutional code with a "pearl-necklace encoder." Despite their theoretical significance as a neat way of representing quantum convolutional codes, they are not well-suited to practical realization. In fact, there is no straightforward way to implement any given pearl-necklace structure. This paper closes the gap between theoretical representation and practical implementation. In our previous work, we presented an efficient algorithm for finding a minimal-memory realization of a pearl-necklace encoder for Calderbank-Shor-Steane (CSS) convolutional codes. This work extends our previous work and presents an algorithm for turning a pearl-necklace encod...

Houshmand, Monireh

2010-01-01

106

Philosophy of Quantum Information and Entanglement  

Science.gov (United States)

Preface; Introduction; Part I. Quantum Entanglement and Nonlocality: 1. Nonlocality beyond quantum mechanics Sandu Popescu; 2. Entanglement and subsystems, entanglement beyond subsystems, and all that Lorenza Viola and Howard Barnum; 3. Formalism locality in quantum theory and quantum gravity Lucien Hardy; Part II. Quantum Probability: 4. Bell's inequality from the contextual probabilistic viewpoint Andrei Khrennikov; 5. Probabilistic theories: what is special about quantum mechanics? Giacomo Mauro D'Ariano; 6. What probabilities tell about quantum systems, with application to entropy and entanglement John Myers and Hadi Madjid; 7. Bayesian updating and information gain in quantum measurements Leah Henderson; Part III. Quantum Information: 8. Schumacher information and the philosophy of physics Arnold Duwell; 9. From physics to information theory and back Wayne Myrvold; 10. Information, immaterialism, and instrumentalism: old and new in quantum information Chris Timpson; Part IV. Quantum Communication and Computing: 11. Quantum computation: where does the speed-up come from? Jeff Bub; 12. Quantum mechanics, quantum computing and quantum cryptography Tai Wu.

Bokulich, Alisa; Jaeger, Gregg

2010-06-01

107

No-compressing of quantum phase information  

CERN Multimedia

We raise a general question of quantum information theory whether the quantum phase information can be compressed and retrieved. A general qubit contains both amplitude and phase information, while an equatorial qubit contains only a phase information. We study whether it is possible to compress the phase information of n equatorial qubits into m general qubits with m being less than n, and still those information can be retrieved perfectly. We prove that this process is not allowed by quantum mechanics.

Wang, Yi-Nan; Jing, Li; Xiong, Zhao-Xi; Lei, Jin; Mu, Liang-Zhu; Fan, Heng

2011-01-01

108

Non-compression of quantum phase information  

International Nuclear Information System (INIS)

We raise a general question of quantum information theory: whether quantum phase information can be compressed and retrieved. A general qubit contains both amplitude and phase information, while an equatorial qubit contains only phase information. We study whether it is possible to compress the phase information of n equatorial qubits into m general qubits, with m being less than n, and still perfectly retrieve that information. We prove that this process is not allowed by quantum mechanics. (paper)

2012-01-20

109

Quantum information processing A linear systems perspective  

CERN Document Server

In this paper a system-oriented formalism of Quantum Information Processing is presented. Its form resembles that of standard signal processing, although further complexity is added in order to describe pure quantum-mechanical effects and operations. Examples of the application of the formalism to quantum time evolution and quantum measurement are given.

Curty, M; Curty, Marcos; Santos, David J.

2001-01-01

110

Bayesian updating of a probability distribution encoded on a quantum register  

International Nuclear Information System (INIS)

We investigate the problem of Bayesian updating of a probability distribution encoded in the quantum state of n qubits. The updating procedure takes the form of a quantum algorithm that prepares the quantum register in the state representing the posterior distribution. Depending on how the prior distribution is given, we describe two implementations, one probabilistic and one deterministic, of such an algorithm in the standard model of a quantum computer.

2006-01-01

111

Information-theoretic characterization of quantum chaos  

CERN Multimedia

Hypersensitivity to perturbation is a criterion for chaos based on the question of how much information about a perturbing environment is needed to keep the entropy of a Hamiltonian system from increasing. We demonstrate numerically that hypersensitivity to perturbation is present in the following quantum maps: the quantum kicked top, the quantum baker's map, the quantum lazy baker's map, and the quantum sawtooth and cat maps.

Schack, R

1995-01-01

112

Quantum Information Theoretical Analysis of Quantum Secret Sharing  

Science.gov (United States)

Quantum secret sharing (QSS) schemes are analyzed from an information theoretical perspective centered on the Araki—Lieb inequality. Based on this inequality, mathematical characterizations of QSS schemes and quantum error-correcting codes (QECCs) are given. Furthermore, we present a proof of the relation between QSS schemes and QECCs. This information theoretic description of QSS schemes is used to derive the quantum Singleton bound.

Xiao, He-Ling; Guo, Wang-Mei; Wang, Xiao

2012-11-01

113

Gaussian states in continuous variable quantum information  

CERN Document Server

These notes originated out of a set of lectures in Quantum Optics and Quantum Information given by one of us (MGAP) at the University of Napoli and the University of Milano. A quite broad set of issues are covered, ranging from elementary concepts to current research topics, and from fundamental concepts to applications. A special emphasis has been given to the phase space analysis of quantum dynamics and to the role of Gaussian states in continuous variable quantum information.

Ferraro, A; Paris, M G A; Ferraro, Alessandro; Olivares, Stefano; Paris, Matteo G. A

2005-01-01

114

Lest we remember a quantum: quantum information shredding  

CERN Multimedia

Given a bipartite quantum system, correlation between subsystems can be understood as information that each subsystem carries about the other. Here we introduce and analyze the task of quantum information shredding, corresponding to locally reducing correlations in a given bipartite state without transferring them to the environment. Such a constraint prevents adversaries from gaining information by accessing the environment left after the decoupling process. Remarkably, information carried by separable correlations is always perfectly shreddable.

Buscemi, Francesco

2009-01-01

115

Quantum hierarchic models for information processing  

CERN Multimedia

Both classical and quantum computations operate with the registers of bits. At nanometer scale the quantum fluctuations at the position of a given bit, say, a quantum dot, not only lead to the decoherence of quantum state of this bit, but also affect the quantum states of the neighboring bits, and therefore affect the state of the whole register. That is why the requirement of reliable separate access to each bit poses the limit on miniaturization, i.e, constrains the memory capacity and the speed of computation. In the present paper we suggest an algorithmic way to tackle the problem of constructing reliable and compact registers of quantum bits. We suggest to access the states of quantum register hierarchically, descending from the state of the whole register to the states of its parts. Our method is similar to quantum wavelet transform, and can be applied to information compression, quantum memory, quantum computations.

Altaisky, Mikhail V

2011-01-01

116

Fisher Information of Wavefunctions: Classical and Quantum  

Science.gov (United States)

A parametric quantum mechanical wavefunction naturally induces parametric probability distributions by taking absolute square, and we can consider its classical Fisher information. On the other hand, it also induces parametric rank-one projections which may be viewed as density operators, and we can talk about its quantum Fisher information. Among many versions of quantum Fisher information, there are two prominent ones. The first, defined via a quantum score function, was introduced by Helstrom in 1967 and is well known. The second, defined via the square root of the density operator, has its origin in the skew information introduced by Wigner and Yanase in 1963 and remains relatively unnoticed. This study is devoted to investigating the relationships between the classical Fisher information and these two versions of quantum Fisher information for wavefunctions. It is shown that the two versions of quantum Fisher information differ by a factor 2 and that they dominate the classical Fisher information. The non-coincidence of these two versions of quantum Fisher information may be interpreted as a manifestation of quantum discord. We further calculate the difference between the Helstrom quantum Fisher information and the classical Fisher information, and show that it is precisely the instantaneous phase fluctuation of the wavefunctions.

Luo, Shun-Long

2006-12-01

117

Information transmission through a noisy quantum channel  

CERN Document Server

Noisy quantum channels may be used in many information carrying applications. We show that different applications may result in different channel capacities. Upper bounds on several of these capacities are proved. These bounds are based on the coherent information, which plays a role in quantum information theory analogous to that played by the mutual information in classical information theory. Many new properties of the coherent information and entanglement fidelity are proved. Two non-classical features of the coherent information are demonstrated: the failure of subadditivity, and the failure of the pipelining inequality. Both properties arise as a consequence of quantum entanglement, and give quantum information new features not found in classical information theory. The problem of a noisy quantum channel with a classical observer measuring the environment is introduced, and bounds on the corresponding channel capacity proved. These bounds are always greater than for the unobserved channel. We conclude w...

Barnum, H N; Schumacher, B; Barnum, Howard; Schumacher, Benjamin

1997-01-01

118

Information propagation through disordered quantum spin chains  

Digital Repository Infrastructure Vision for European Research (DRIVER)

One of the central aims of quantum information theory is to exploit quantum mechanical phenomena such as superposition and entanglement to build a quantum computer — a device capable of effciently performing computational tasks which are not feasible on a classical computer. In order to achieve this...

Burrell, Christian

119

Holography, Quantum Geometry, and Quantum Information Theory  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract: We interpret the Holographic Conjecture in terms of quantum bits (qubits). N-qubit states are associated with surfaces that are punctured in N points by spin networks' edges labelled by the spin-½ representation of SU(2), which are in a superposed quantum state of spin "up" and spin "down". The formalism is applied in particular to de Sitter horizons, and leads to a picture of the early inflationary universe in terms of quantum computation. A discrete micro-causality emerges, where the time parameter is being defined by the discrete increase of entropy. Then, the model is analysed in the framework of the theory of presheaves (varying sets on a causal set) and we get a quantum history. A (bosonic) Fock space of the whole history is considered. The Fock space wavefunction, which resembles a Bose-Einstein condensate, undergoes decoherence at the end of inflation. This fact seems to be responsible for the rather low entropy of our universe.

P. A. Zizzi

2000-01-01

120

Manipulating quantum information on the controllable systems or subspaces  

CERN Multimedia

In this paper, we explore how to constructively manipulate quantum information on the controllable systems or subspaces. It is revealed that one can make full use of distinguished properties of Pauli operators to design control Hamiltonian based on the geometric parametrization of quantum states. It is demonstrated in this research that Bang-Bang controls, triangle-function controls and square-function control can be utilized to manipulate controllable qubits or encoded qubits on controllable subspace for both open quantum dynamical systems and uncontrollable closed quantum dynamical systems. Furthermore, we propose a new kind of time-energy performance index to trade-off time and energy resource cost, and comprehensively discuss how to design control magnitude to minimize a kind of time-energy performance. A comparison has been made among these three kind of optimal control. It is underlined in this research that the optimal time performance can be always expressed as J^{*} =\\lamda{\\cdot}t^{*}_{f} +E^{*} for...

Zhang, Ming

2010-01-01

 
 
 
 
121

Enhanced optical property of Au coated polystyrene beads for multi-color quantum dots encoding.  

UK PubMed Central (United Kingdom)

A novel quantum dots (QDs) fluorescent encoding method was demonstrated in this paper by using Au coated polystyrene (Au @ PS) beads. In the experiments, Au nanoparticles were deposited onto the polystyrene bead to form a stable Au coating through Layer-by-Layer assembly, and the surface morphology of the Au @ PS beads was studied by Scanning Electronic Microscope (SEM). Furthermore, the QDs encoding abilities, including the loading of QDs, the anti-photo bleaching ability and the multi-color encoding feasibility were studied using Au @ PS beads. The QDs leakage from doped QDs encoded Au @ PS was also studied. This study shows that Au particles improve the QDs encoding performance and the QD-encoded Au @ PS beads are the ideal material for the optical encoding.

Cao YC; Wang Z; Wang HQ; Wang JH; Hua XF; Jin X; Yang L; Huang ZL; Liu MX; Zhao YD

2009-03-01

122

Quantum Bertrand duopoly of incomplete information  

Energy Technology Data Exchange (ETDEWEB)

We study Bertrand's duopoly of incomplete information. It is found that the effect of quantum entanglement on the outcome of the game is dramatically changed by the uncertainty of information. In contrast with the case of complete information where the outcome increases with entanglement, when information is incomplete the outcome is maximized at some finite entanglement. As a consequence, information and entanglement are both crucial factors that determine the properties of a quantum oligopoly.

Qin Gan [Hefei National Laboratory for Physical Science at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, 230026 (China); Chen Xi [Hefei National Laboratory for Physical Science at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, 230026 (China); Sun Min [Hefei National Laboratory for Physical Science at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, 230026 (China); Du Jiangfeng [Hefei National Laboratory for Physical Science at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, 230026 (China)

2005-05-13

123

Encoding Frequency Information in Lexicalized Grammars  

CERN Document Server

We address the issue of how to associate frequency information with lexicalized grammar formalisms, using Lexicalized Tree Adjoining Grammar as a representative framework. We consider systematically a number of alternative probabilistic frameworks, evaluating their adequacy from both a theoretical and empirical perspective using data from existing large treebanks. We also propose three orthogonal approaches for backing off probability estimates to cope with the large number of parameters involved.

Carroll, J; Carroll, John; Weir, David

1997-01-01

124

Encoded Recoupling and Decoupling An Alternative to Quantum Error Correcting Codes, Applied to Trapped Ion Quantum Computation  

CERN Document Server

A recently developed theory for eliminating decoherence and design constraints in quantum computers, ``encoded recoupling and decoupling'', is shown to be fully compatible with a promising proposal for an architecture enabling scalable ion-trap quantum computation [D. Kielpinski et al., Nature 417, 709 (2002)]. Logical qubits are encoded into pairs of ions. Logic gates are implemented using the Sorensen-Molmer (SM) scheme applied to pairs of ions at a time. The encoding offers continuous protection against collective dephasing. Decoupling pulses, that are also implemented using the SM scheme directly to the encoded qubits, are capable of further reducing various other sources of qubit decoherence, such as due to differential dephasing and due to decohered vibrational modes. The feasibility of using the relatively slow SM pulses in a decoupling scheme quenching the latter source of decoherence follows from the observed 1/f spectrum of the vibrational bath.

Lidar, D A

2003-01-01

125

Quantum nondemolition measurements for quantum information  

International Nuclear Information System (INIS)

We discuss the characterization and properties of quantum nondemolition (QND) measurements on qubit systems. We introduce figures of merit which can be applied to systems of any Hilbert space dimension, thus providing universal criteria for characterizing QND measurements. The controlled-NOT gate and an optical implementation are examined as examples of QND devices for qubits. We also consider the QND measurement of weak values.

2006-01-01

126

Distinguishability and accessible information in quantum theory  

CERN Multimedia

This document focuses on translating various information-theoretic measures of distinguishability for probability distributions into measures of distin- guishability for quantum states. These measures should have important appli- cations in quantum cryptography and quantum computation theory. The results reported include the following. An exact expression for the quantum fidelity between two mixed states is derived. The optimal measurement that gives rise to it is studied in detail. Several upper and lower bounds on the quantum mutual information are derived via similar techniques and compared to each other. Of note is a simple derivation of the important upper bound first proved by Holevo and an explicit expression for another (tighter) upper bound that appears implicitly in the same derivation. Several upper and lower bounds to the quan- tum Kullback relative information are derived. The measures developed are also applied to ferreting out the extent to which quantum systems must be disturbed by information...

Fuchs, C

1996-01-01

127

Basic Elements of Quantum Information Technology  

UK PubMed Central (United Kingdom)

The marriage of quantum physics and information technology has the potentialto generate radically new information processing devices. Examples arequantum cryptosystems, which provide guaranteed secure communication, andquantum computers, which manipulate data quantum mechanically and couldthus solve some problems currently intractable to conventional (classical) computation.This introductory chapter serves two purposes. Firstly, I discuss someof the basic aspects of quantum physics which underpin quantum informationtechnology (QIT). These will be used (and in somes cases further expanded upon)in subsequent chapters. Secondly, and as a lead into the whole book, I outlinesome of the ideas of QIT and its possible uses.To appear as Chapter 1 of Introduction to Quantum Computation and Information, eds. H.-K.Lo, S. Popescu and T. P. Spiller, (World Scientific Press 1998), http://www.wspc.com.sg/.11 IntroductionInformation technology (IT) can feed off quantum physic...

Timothy P. Spiller

128

Quantum Stackelberg duopoly with incomplete information  

International Nuclear Information System (INIS)

We investigate the quantum version of the Stackelberg duopoly with incomplete information, especially how the quantum entanglement affects the first-mover advantage in the classical form. It is found that while positive entanglement enhances the first-mover advantage beyond the classical limit, the advantage is dramatically suppressed by negative entanglement. Moreover, despite that positive quantum entanglement improves the first-mover's tolerance for the informational incompleteness, the quantum effect does not change the basic fact that Firm A's lack of complete information of Firm B's unit cost is eradicating the first-mover advantage.

2005-10-10

129

Quantum Causality, Stochastics, Trajectories and Information  

CERN Document Server

A history of the discovery of quantum mechanics and paradoxes of its interpretation is reconsidered from the modern point of view of quantum stochastics and information. It is argued that in the orthodox quantum mechanics there is no place for quantum phenomenology such as events. The development of quantum measurement theory, initiated by von Neumann, and Bell's conceptual critics of hidden variable theories indicated a possibility for resolution of this crisis. This can be done by divorcing the algebra of the dynamical generators and an extended algebra of the potential (quantum) and the actual (classical) observables. The latter, called beables, form the center of the algebra of all observables, as the only visible (macroscopic) observables must be compatible with any hidden (microscopic) observable. It is shown that within this approach quantum causality can be rehabilitated within an extended quantum mechanics (eventum mechanics) in the form of a superselection rule for compatibility of the consistent hi...

Belavkin, V P

2002-01-01

130

Information quality measurement of medical encoding support based on usability.  

Science.gov (United States)

Medical encoding support systems for diagnoses and medical procedures are an emerging technology that begins to play a key role in billing, reimbursement, and health policies decisions. A significant problem to exploit these systems is how to measure the appropriateness of any automatically generated list of codes, in terms of fitness for use, i.e. their quality. Until now, only information retrieval performance measurements have been applied to estimate the accuracy of codes lists as quality indicator. Such measurements do not give the value of codes lists for practical medical encoding, and cannot be used to globally compare the quality of multiple codes lists. This paper defines and validates a new encoding information quality measure that addresses the problem of measuring medical codes lists quality. It is based on a usability study of how expert coders and physicians apply computer-assisted medical encoding. The proposed measure, named ADN, evaluates codes Accuracy, Dispersion and Noise, and is adapted to the variable length and content of generated codes lists, coping with limitations of previous measures. According to the ADN measure, the information quality of a codes list is fully represented by a single point, within a suitably constrained feature space. Using one scheme, our approach is reliable to measure and compare the information quality of hundreds of codes lists, showing their practical value for medical encoding. Its pertinence is demonstrated by simulation and application to real data corresponding to 502 inpatient stays in four clinic departments. Results are compared to the consensus of three expert coders who also coded this anonymized database of discharge summaries, and to five information retrieval measures. Information quality assessment applying the ADN measure showed the degree of encoding-support system variability from one clinic department to another, providing a global evaluation of quality measurement trends. PMID:23958646

Puentes, John; Montagner, Julien; Lecornu, Laurent; Cauvin, Jean-Michel

2013-08-16

131

Information quality measurement of medical encoding support based on usability.  

UK PubMed Central (United Kingdom)

Medical encoding support systems for diagnoses and medical procedures are an emerging technology that begins to play a key role in billing, reimbursement, and health policies decisions. A significant problem to exploit these systems is how to measure the appropriateness of any automatically generated list of codes, in terms of fitness for use, i.e. their quality. Until now, only information retrieval performance measurements have been applied to estimate the accuracy of codes lists as quality indicator. Such measurements do not give the value of codes lists for practical medical encoding, and cannot be used to globally compare the quality of multiple codes lists. This paper defines and validates a new encoding information quality measure that addresses the problem of measuring medical codes lists quality. It is based on a usability study of how expert coders and physicians apply computer-assisted medical encoding. The proposed measure, named ADN, evaluates codes Accuracy, Dispersion and Noise, and is adapted to the variable length and content of generated codes lists, coping with limitations of previous measures. According to the ADN measure, the information quality of a codes list is fully represented by a single point, within a suitably constrained feature space. Using one scheme, our approach is reliable to measure and compare the information quality of hundreds of codes lists, showing their practical value for medical encoding. Its pertinence is demonstrated by simulation and application to real data corresponding to 502 inpatient stays in four clinic departments. Results are compared to the consensus of three expert coders who also coded this anonymized database of discharge summaries, and to five information retrieval measures. Information quality assessment applying the ADN measure showed the degree of encoding-support system variability from one clinic department to another, providing a global evaluation of quality measurement trends.

Puentes J; Montagner J; Lecornu L; Cauvin JM

2013-08-01

132

Multiple Access Channels with Cooperative Encoders and Channel State Information  

CERN Document Server

The two-user Multiple Access Channel (MAC) with cooperative encoders and Channel State Information (CSI) is considered where two different scenarios are investigated: A two-user MAC with common message (MACCM) and a two-user MAC with conferencing encoders (MACCE). For both situations, the two cases where the CSI is known to the encoders either non-causally or causally are studied. Achievable rate regions are established for both discrete memoryless channels and Gaussian channels with additive interference. The achievable rate regions derived for the Gaussian models with additive interference known non-causally to the encoders are shown to coincide with the capacity region of the same channel with no interference. Therefore, the capacity region for such channels is established.

Khosravi-Farsani, Reza

2010-01-01

133

Quantum information-flow, concretely, and axiomatically  

CERN Multimedia

These lecture notes survey some joint work with Samson Abramsky. Somewhat informally I will discuss the main results in a pedestrian not too technical way. These include: (1) `The logic of entanglement', that is, the identification and abstract axiomatization of the `quantum information-flow' which enables protocols such as quantum teleportation. To this means we define strongly compact closed categories which abstractly capture the behavioral properties of quantum entanglement. (2) `Postulates for an abstract quantum formalism' in which classical information-flow (e.g. token exchange) is part of the formalism. As an example, we provide a purely formal description of quantum teleportation and prove correctness in abstract generality. In this formalism types reflect kinds, contra the essentially typeless von Neumann formalism. Hence even concretely this formalism manifestly improves on the usual one. (3) `A high-level approach to quantum informatics'.

Coecke, B

2005-01-01

134

Thermodynamical cost of accessing quantum information  

International Nuclear Information System (INIS)

Thermodynamics is a macroscopic physical theory whose two very general laws are independent of any underlying dynamical laws and structures. Nevertheless, its generality enables us to understand a broad spectrum of phenomena in physics, information science and biology. Does thermodynamics then imply any results in quantum information theory? Taking accessible information in a system as an example, we show that thermodynamics implies a weaker bound on it than the quantum mechanical one (the Holevo bound). In other words, if any post-quantum physics should allow more information storage it could still be under the umbrella of thermodynamics.

2005-08-12

135

Relativistic Quantum Information: developments in Quantum Information in general relativistic scenarios  

CERN Multimedia

Recently, there has been increased interest in understanding entanglement and quantum communication in black hole spacetimes and in using quantum information techniques to address questions in gravity. Studies on relativistic entanglement show the emergence of conceptually important qualitative differences to a non-relativistic treatment. For instance, entanglement was found to be an observer-dependent property that changes from the perspective of accelerated observers moving in flat spacetime. Relativisitic quantum information theory uses well-known tools coming from quantum information and quantum optics to study quantum effects provoked by gravity to learn information about the spacetime. We can take advantage of our knowledge about quantum correlations and effects produced by the gravitational interaction to set the basis for experimental proposals ultimately aiming at finding corrections due to quantum gravity effects, too mild to be directly observed. This doctoral thesis dissertation summarises most of...

Martin-Martinez, E

2011-01-01

136

Photonic Communications and Quantum Information Storage Capacities  

Directory of Open Access Journals (Sweden)

Full Text Available This paper presents photonic communications and data storage capacitates for classical and quantum communications over a quantum channel. These capacities represent a generalization of Shannon’s classical channel capacity and coding theorem in two ways. First, it extends classical results for bit communication transport to all frequencies in the electromagnetic spectrum. Second, it extends the results to quantum bit (qubit) transport as well as a hybrid of classical and quantum communications. Nature’s limits on the rate at which classical and/or quantum information can be sent error-free over a quantum channel using classical and/or quantum error-correcting codes are presented as a function of the thermal background light level and Einstein zero-point energy. Graphical results are given as well as numerical results regarding communication rate limits using Planck’s natural frequency and time-interval units!

William C. Lindsey

2013-01-01

137

Quantum technology and cryptology for information security  

Science.gov (United States)

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

Naqvi, Syed; Riguidel, Michel

2007-05-01

138

Quantum information processing with circuit quantum electrodynamics  

CERN Multimedia

We theoretically study single and two-qubit dynamics in the circuit QED architecture. We focus on the current experimental design [Wallraff et al., Nature 431, 162 (2004); Schuster et al., cond-mat/0608693 (2006)] in which superconducting charge qubits are capacitively coupled to a single high-Q superconducting coplanar resonator. In this system, logical gates are realized by driving the resonator with microwave fields. Advantages of this architecture are that it allows for multi-qubit gates between non-nearest qubits and for the realization of gates in parallel, opening the possibility of fault-tolerant quantum computation with superconduting circuits. In this paper, we focus on one and two-qubit gates that do not require moving away from the charge-degeneracy `sweet spot'. This is advantageous as it helps to increase the qubit dephasing time and does not require modification of the original circuit QED. However these gates can, in some cases, be slower than those that do not use this constraint. Five types ...

Blais, A; Wallraff, A; Schuster, D I; Girvin, S M; Devoret, M H; Schölkopf, R J; Blais, Alexandre; Gambetta, Jay

2006-01-01

139

Photonic entanglement-assisted quantum low-density parity-check encoders and decoders.  

UK PubMed Central (United Kingdom)

I propose encoder and decoder architectures for entanglement-assisted (EA) quantum low-density parity-check (LDPC) codes suitable for all-optical implementation. I show that two basic gates needed for EA quantum error correction, namely, controlled-NOT (CNOT) and Hadamard gates can be implemented based on Mach-Zehnder interferometer. In addition, I show that EA quantum LDPC codes from balanced incomplete block designs of unitary index require only one entanglement qubit to be shared between source and destination.

Djordjevic IB

2010-05-01

140

Photonic entanglement-assisted quantum low-density parity-check encoders and decoders.  

Science.gov (United States)

I propose encoder and decoder architectures for entanglement-assisted (EA) quantum low-density parity-check (LDPC) codes suitable for all-optical implementation. I show that two basic gates needed for EA quantum error correction, namely, controlled-NOT (CNOT) and Hadamard gates can be implemented based on Mach-Zehnder interferometer. In addition, I show that EA quantum LDPC codes from balanced incomplete block designs of unitary index require only one entanglement qubit to be shared between source and destination. PMID:20436604

Djordjevic, Ivan B

2010-05-01

 
 
 
 
141

Quantum information and entanglement transfer for qutrits  

Energy Technology Data Exchange (ETDEWEB)

We propose a scheme for the transfer of quantum information among distant qutrits. We apply this scheme to the distribution of entanglement of qutrits states among distant nodes and to the generation of multipartite antisymmetric states. We also discuss applications to quantum secret sharing.

Delgado, A. [Center for Quantum Optics and Quantum Information, Departamento de Fisica, Universidad de Concepcion, Casilla 160-C, Concepcion (Chile); Saavedra, C. [Center for Quantum Optics and Quantum Information, Departamento de Fisica, Universidad de Concepcion, Casilla 160-C, Concepcion (Chile)], E-mail: carlos.saavedra@udec.cl; Retamal, J.C. [Departamento de Fisica, Universidad de Santiago de Chile, Casilla 307, Correo 2, Santiago (Chile)

2007-10-08

142

Quantum information theory with Gaussian systems  

International Nuclear Information System (INIS)

This thesis applies ideas and concepts from quantum information theory to systems of continuous-variables such as the quantum harmonic oscillator. The focus is on three topics: the cloning of coherent states, Gaussian quantum cellular automata and Gaussian private channels. Cloning was investigated both for finite-dimensional and for continuous-variable systems. We construct a private quantum channel for the sequential encryption of coherent states with a classical key, where the key elements have finite precision. For the case of independent one-mode input states, we explicitly estimate this precision, i.e. the number of key bits needed per input state, in terms of these parameters. (orig.)

2006-01-01

143

Quantum information theory with Gaussian systems  

Energy Technology Data Exchange (ETDEWEB)

This thesis applies ideas and concepts from quantum information theory to systems of continuous-variables such as the quantum harmonic oscillator. The focus is on three topics: the cloning of coherent states, Gaussian quantum cellular automata and Gaussian private channels. Cloning was investigated both for finite-dimensional and for continuous-variable systems. We construct a private quantum channel for the sequential encryption of coherent states with a classical key, where the key elements have finite precision. For the case of independent one-mode input states, we explicitly estimate this precision, i.e. the number of key bits needed per input state, in terms of these parameters. (orig.)

Krueger, O.

2006-04-06

144

The information-carrying capacity of certain quantum channels  

CERN Document Server

In this thesis we analyse the type of states and ensembles which achieve the capacity for certain quantum channels carrying classical information. We first concentrate on the product-state capacity of a particular quantum channel, that is, the capacity which is achieved by encoding the output states from a source into codewords comprised of states taken from ensembles of non-entangled states and sending them over copies of the quantum channel. Using the "single-letter" formula proved independently by Holevo and by Schumacher and Westmoreland we obtain the product-state capacity of the qubit quantum amplitude-damping channel, which is determined by a transcendental equation in a single real variable and can be solved numerically. We demonstrate that the product-state capacity of this channel can be achieved using a minimal ensemble of non-orthogonal pure states. Next we consider the classical capacity of two quantum channels with memory, namely a periodic channel with quantum depolarising channel branches and ...

Morgan, Ciara

2010-01-01

145

Quantum information processing and nuclear magnetic resonance  

CERN Multimedia

as spectrometer pulse sequence programs. Quantum computers are information processing devices which operate by and exploit the laws of quantum mechanics, potentially allowing them to solve problems which are intractable using classical computers. This dissertation considers the practical issues involved in one of the more successful implementations to date, nuclear magnetic resonance (NMR). Techniques for dealing with systematic errors are presented, and a quantum protocol is implemented. Chapter 1 is a brief introduction to quantum computation. The physical basis of its efficiency and issues involved in its implementation are discussed. NMR quantum information processing is reviewed in more detail in Chapter 2. Chapter 3 considers some of the errors that may be introduced in the process of implementing an algorithm, and high-level ways of reducing the impact of these errors by using composite rotations. Novel general expressions for stabilising composite rotations are presented in Chapter 4 and a new class o...

Cummins, H K

2001-01-01

146

Why Genetic Information Processing could be Quantum  

CERN Multimedia

Living organisms are not just random collections of organic molecules. There is continuous information processing going on in the apparent bouncing around of molecules of life. Optimisation criteria in this information processing can be searched for using the laws of physics. Quantum dynamics can explain why living organisms have 4 nucleotide bases and 20 amino acids, as optimal solutions of the molecular assembly process. Experiments should be able to tell whether evolution indeed took advantage of quantum dynamics or not.

Patel, A

2001-01-01

147

Quantum contextuality in classical information retrieval  

CERN Document Server

Document ranking based on probabilistic evaluations of relevance is known to exhibit non-classical correlations, which may be explained by admitting a complex structure of the event space, namely, by assuming the events to emerge from multiple sample spaces. The structure of event space formed by overlapping sample spaces is known in quantum mechanics, they may exhibit some counter-intuitive features, called quantum contextuality. In this Note I observe that from the structural point of view quantum contextuality looks similar to personalization of information retrieval scenarios. Along these lines, Knowledge Revision is treated as operationalistic measurement and a way to quantify the rate of personalization of Information Retrieval scenarios is suggested.

Zapatrin, Roman

2012-01-01

148

Quantum probabilities: an information-theoretic interpretation  

CERN Document Server

This Chapter develops a realist information-theoretic interpretation of the nonclassical features of quantum probabilities. On this view, what is fundamental in the transition from classical to quantum physics is the recognition that \\emph{information in the physical sense has new structural features}, just as the transition from classical to relativistic physics rests on the recognition that space-time is structurally different than we thought. Hilbert space, the event space of quantum systems, is interpreted as a kinematic (i.e., pre-dynamic) framework for an indeterministic physics, in the sense that the geometric structure of Hilbert space imposes objective probabilistic or information-theoretic constraints on correlations between events, just as the geometric structure of Minkowski space in special relativity imposes spatio-temporal kinematic constraints on events. The interpretation of quantum probabilities is more subjectivist in spirit than other discussions in this book (e.g., the chapter by Timpson)...

Bub, Jeffrey

2010-01-01

149

Manipulating quantum information by propagation  

International Nuclear Information System (INIS)

[en] We study the creation of bipartite and multipartite continuous variable entanglement in structures of coupled quantum harmonic oscillators. By adjusting the interaction strengths between nearest neighbours we show how to maximize the entanglement production between the arms in a Y-shaped structure where an initial single mode squeezed state is created in the first oscillator of the input arm. We also consider the action of the same structure as an approximate quantum cloner. For a specific time in the system dynamics the last oscillators in the output arms can be considered as imperfect copies of the initial state. By increasing the number of arms in the structure, multipartite entanglement is obtained, as well as 1 ?M cloning. Finally, we consider configurations that implement the symmetric splitting of an initial entangled state. All calculations are carried out within the framework of the rotating wave approximation in quantum optics, and our predictions could be tested with current available experimental techniques

2005-12-01

150

Manipulating quantum information by propagation  

CERN Multimedia

We study creation of bi- and multipartite continuous variable entanglement in structures of coupled quantum harmonic oscillators. By adjusting the interaction strengths between nearest neighbors we show how to maximize the entanglement production between the arms in a Y-shaped structure where an initial single mode squeezed state is created in the first oscillator of the input arm. We also consider the action of the same structure as an approximate quantum cloner. For a specific time in the system dynamics the last oscillators in the output arms can be considered as imperfect copies of the initial state. By increasing the number of arms in the structure, multipartite entanglement is obtained, as well as 1 to M cloning. Finally, we are considering configurations that implement the symmetric splitting of an initial entangled state. All calculations are carried out within the framework of the rotating wave approximation in quantum optics, and our predictions could be tested with current available experimental te...

Perales, A; Perales, Alvaro; Plenio, Martin B.

2005-01-01

151

Manipulating quantum information by propagation  

Energy Technology Data Exchange (ETDEWEB)

We study the creation of bipartite and multipartite continuous variable entanglement in structures of coupled quantum harmonic oscillators. By adjusting the interaction strengths between nearest neighbours we show how to maximize the entanglement production between the arms in a Y-shaped structure where an initial single mode squeezed state is created in the first oscillator of the input arm. We also consider the action of the same structure as an approximate quantum cloner. For a specific time in the system dynamics the last oscillators in the output arms can be considered as imperfect copies of the initial state. By increasing the number of arms in the structure, multipartite entanglement is obtained, as well as 1 {yields}M cloning. Finally, we consider configurations that implement the symmetric splitting of an initial entangled state. All calculations are carried out within the framework of the rotating wave approximation in quantum optics, and our predictions could be tested with current available experimental techniques.

Perales, Alvaro [Departmento de Automatica, Escuela Politecnica, Universidad de Alcala, 28871 Alcala de Henares, Madrid (Spain); Plenio, Martin B [Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2BW (United Kingdom); Institute for Mathematical Sciences, Imperial College London, 53 Exhibition Road, London SW7 2AZ (United Kingdom)

2005-12-01

152

The Nature and Location of Quantum Information  

CERN Document Server

Quantum information is defined by applying the concepts of ordinary (Shannon) information theory to a quantum sample space consisting of a single framework or consistent family. A classical analogy for a spin-half particle and other arguments show that the infinite amount of information needed to specify a precise vector in its Hilbert space is not a measure of the information carried by a quantum entity with a $d$-dimensional Hilbert space; the latter is, instead, bounded by log d bits (1 bit per qubit). The two bits of information transmitted in dense coding are located not in one but in the correlation between two qubits, consistent with this bound. A quantum channel can be thought of as a "structure" or collection of frameworks, and the physical location of the information in the individual frameworks can be used to identify the location of the channel. Analysis of a quantum circuit used as a model of teleportation shows that the location of the channel depends upon which structure is employed; for ordina...

Griffiths, R B

2002-01-01

153

Quantum Information and the PCP Theorem  

CERN Document Server

We show how to encode $2^n$ (classical) bits $a_1,...,a_{2^n}$ by a single quantum state $|\\Psi>$ of size O(n) qubits, such that: for any constant $k$ and any $i_1,...,i_k \\in \\{1,...,2^n\\}$, the values of the bits $a_{i_1},...,a_{i_k}$ can be retrieved from $|\\Psi>$ by a one-round Arthur-Merlin interactive protocol of size polynomial in $n$. This shows how to go around Holevo-Nayak's Theorem, using Arthur-Merlin proofs. We use the new representation to prove the following results: 1) Interactive proofs with quantum advice: We show that the class $QIP/qpoly$ contains ALL languages. That is, for any language $L$ (even non-recursive), the membership $x \\in L$ (for $x$ of length $n$) can be proved by a polynomial-size quantum interactive proof, where the verifier is a polynomial-size quantum circuit with working space initiated with some quantum state $|\\Psi_{L,n} >$ (depending only on $L$ and $n$). Moreover, the interactive proof that we give is of only one round, and the messages communicated are classical. 2)...

Raz, R

2005-01-01

154

A Thermodynamical Formulation of Quantum Information  

Science.gov (United States)

We show that quantum entanglement can be understood and quantified using the same axiomatic approach to thermodynamics pioneered by Caratheodory and later extended by Buchdahl and Giles. This leads to the existence of a unique measure of entanglement for pure states of systems consisting of two subsystems, analogous to the thermodynamical entropy. Thermodynamics and (quantum) information are seen to be just two different manifestations of ordering of (abstract) states connected by (abstract) processes.

Vedral, V.

2002-11-01

155

Quantum information processing with graph states  

Energy Technology Data Exchange (ETDEWEB)

Graph states are multiparticle states which are associated with graphs. Each vertex of the graph corresponds to a single system or particle. The links describe quantum correlations (entanglement) between pairs of connected particles. Graph states were initiated independently by two research groups: On the one hand, graph states were introduced by Briegel and Raussendorf as a resource for a new model of one-way quantum computing, where algorithms are implemented by a sequence of measurements at single particles. On the other hand, graph states were developed by the author of this thesis and ReinhardWerner in Braunschweig, as a tool to build quantum error correcting codes, called graph codes. The connection between the two approaches was fully realized in close cooperation of both research groups. This habilitation thesis provides a survey of the theory of graph codes, focussing mainly, but not exclusively on the author's own research work. We present the theoretical and mathematical background for the analysis of graph codes. The concept of one-way quantum computing for general graph states is discussed. We explicitly show how to realize the encoding and decoding device of a graph code on a one-way quantum computer. This kind of implementation is to be seen as a mathematical description of a quantum memory device. In addition to that, we investigate interaction processes, which enable the creation of graph states on very large systems. Particular graph states can be created, for instance, by an Ising type interaction between next neighbor particles which sits at the points of an infinitely extended cubic lattice. Based on the theory of quantum cellular automata, we give a constructive characterization of general interactions which create a translationally invariant graph state. (orig.)

Schlingemann, Dirk-Michael

2005-04-15

156

Scaling the neutral atom Rydberg gate quantum computer by collective encoding in Holmium atoms  

CERN Multimedia

We discuss a method for scaling a neutral atom Rydberg gate quantum processor to a large number of qubits. Limits are derived showing that the number of qubits that can be directly connected by entangling gates with errors at the $10^{-3}$ level using long range Rydberg interactions between sites in an optical lattice, without mechanical motion or swap chains, is about 500 in two dimensions and 7500 in three dimensions. A scaling factor of 60 at a smaller number of sites can be obtained using collective register encoding in the hyperfine ground states of the rare earth atom Holmium. We present a detailed analysis of operation of the 60 qubit register in Holmium. Combining a lattice of multi-qubit ensembles with collective encoding results in a feasible design for a 1000 qubit fully connected quantum processor.

Saffman, M

2008-01-01

157

Quantum Communication  

CERN Multimedia

Quantum communication, and indeed quantum information in general, has changed the way we think about quantum physics. In 1984 and 1991, the first protocol for quantum cryptography and the first application of quantum non-locality, respectively, attracted a diverse field of researchers in theoretical and experimental physics, mathematics and computer science. Since then we have seen a fundamental shift in how we understand information when it is encoded in quantum systems. We review the current state of research and future directions in this new field of science with special emphasis on quantum key distribution and quantum networks.

Gisin, N; Gisin, Nicolas; Thew, Rob

2007-01-01

158

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

Energy Technology Data Exchange (ETDEWEB)

The following topics are dealt with: Reality in the test house, quantum teleportation, 100 years of quantum theory, the reality of quanta, interactionless quantum measurement, rules for quantum computers, quantum computers with ions, spintronics with diamond, the limits of the quantum computers, a view into the future of quantum optics. (HSI)

Breuer, Reinhard (comp.)

2010-07-01

159

Mutual Entropy in Quantum Information and Information Genetics  

CERN Multimedia

After Shannon, entropy becomes a fundamental quantity to describe not only uncertainity or chaos of a system but also information carried by the system. Shannon's important discovery is to give a mathematical expression of the mutual entropy (information), information transmitted from an input system to an output system, by which communication processes could be analyzed on the stage of mathematical science. In this paper, first we review the quantum mutual entropy and discuss its uses in quantum information theory, and secondly we show how the classical mutual entropy can be used to analyze genomes, in particular, those of HIV.

Ohya, M

2004-01-01

160

Countering quantum noise with supplementary classical information  

International Nuclear Information System (INIS)

[en] We consider situations in which (i) Alice wishes to send quantum information to Bob via a noisy quantum channel, (ii) Alice has a classical description of the states she wishes to send, and (iii) Alice can make use of a finite amount of noiseless classical information. After setting up the problem in general, we focus attention on one specific scenario in which Alice sends a known qubit down a depolarizing channel along with a noiseless classical bit. We describe a protocol that we conjecture is optimal and calculate the average fidelity obtained. A surprising amount of structure is revealed even for this simple case, which suggests that relationships between quantum and classical information could in general be very intricate

2003-01-01

 
 
 
 
161

Calculating a maximizer for quantum mutual information  

CERN Document Server

We obtain a maximizer for the quantum mutual information for classical information sent over the quantum qubit amplitude damping channel. This is achieved by limiting the ensemble of input states to antipodal states, in the calculation of the product-state capacity for the channel, the resulting maximizing ensemble consisting of just two non-orthogonal states. We also consider the product-state capacity of a convex combination of two memoryless channels and demonstrate in particular that it is in general not given by the minimum of the capacities of the respective memoryless channels.

Dorlas, Tony

2011-01-01

162

Nonlinear coherent states for optimizing quantum information  

International Nuclear Information System (INIS)

Part of the difficulties in implementing communication in quantum information stems from the fragility of Schroedinger's cat-like superpositions. A recent experiment in quantum optics by Cook et al (2007 Nature 446 774) has proved the feasibility of a feedback-mediated quantum measurement for discriminating between optical coherent states under photodetection. Minimizing the error in receiver measurement over all possible POVMs leads to the so-called quantum error probability or 'Helstrom bound', and CMG measurements validate the theoretical prediction by Helstrom, Dolinar and Geremia concerning this bound. In this work, we present some preliminary theoretical and numerical explorations concerning the properties of the Helstrom bound in binary (or multibinary) communication involving non-Poissonian or nonlinear coherent states.

2010-01-01

163

Nonlinear coherent states for optimizing quantum information  

Energy Technology Data Exchange (ETDEWEB)

Part of the difficulties in implementing communication in quantum information stems from the fragility of Schroedinger's cat-like superpositions. A recent experiment in quantum optics by Cook et al (2007 Nature 446 774) has proved the feasibility of a feedback-mediated quantum measurement for discriminating between optical coherent states under photodetection. Minimizing the error in receiver measurement over all possible POVMs leads to the so-called quantum error probability or 'Helstrom bound', and CMG measurements validate the theoretical prediction by Helstrom, Dolinar and Geremia concerning this bound. In this work, we present some preliminary theoretical and numerical explorations concerning the properties of the Helstrom bound in binary (or multibinary) communication involving non-Poissonian or nonlinear coherent states.

Curado, E M F; Gazeau, J-P; Rodrigues, Ligia M C S, E-mail: evaldo@cbpf.b, E-mail: gazeau@apc.univ-paris7.f, E-mail: ligia@cbpf.b [Centro Brasileiro de Pesquisas Fisicas, Rua Xavier Sigaud 150, 22290-180 - Rio de Janeiro, RJ (Brazil); Laboratoire APC, Universite Paris Diderot, 10, rue A. Domon et L. Duquet 75205 Paris Cedex 13 (France); Centro Brasileiro de Pesquisas Fisicas, Rua Xavier Sigaud 150, 22290-180 - Rio de Janeiro, RJ (Brazil)

2010-09-15

164

Quantum gravity and the Information Loss Problem  

Science.gov (United States)

We review the standard picture of black hole evaporation and the ensuing Information Loss Problem. Next, we describe an alternative view of the evaporation process due to Ashtekar and Bojowald (AB) which rests on the assumption of singularity resolution in quantum gravity. To endow the AB proposal with precision as well as to test it in a quantitative setting, we consider the Callen-Giddings-Harvey-Strominger (CGHS) toy model of 2-dimensional black holes. We propose a quantum framework in which to understand this model and show that the proposed framework implies that the classical spacetime manifold acquires a quantum extension, as in the AB paradigm. We show that asymptotic analysis coupled with the quantum framework suggests a unitary picture of black hole evaporation consistent with early (on the extended null infinity) time Hawking radiation.

Varadarajan, Madhavan

2008-11-01

165

Quantum mechanics and quantum information a guide through the quantum world  

CERN Multimedia

Alongside a thorough definition of the basic concepts and their interrelations, backed by numerous examples, this textbook features a rare discussion of the quantum information theory. It also deals with other important topics hardly found in the literature, including the Robertson-Schrodinger-relation, angle and angular momentum uncertainties, interaction-free measurements, and the limitations of the no-cloning theorem With its interpretations of quantum mechanics and its discussions of quantum computing, this book is poised to become the standard textbook for advanced undergraduate and beginning graduate quantum mechanics courses and as an essential reference for physics students and physics professionals.

Fayngold, Moses

2013-01-01

166

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

CERN Multimedia

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

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

2004-01-01

167

Information-technology approach to quantum feedback control  

CERN Multimedia

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't 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 a...

Dong, D Y; Chen, Z H; Zhang, Chen-Bin; Chen, Zong-Hai

2005-01-01

168

Encoding and decoding cellular information through signaling dynamics.  

UK PubMed Central (United Kingdom)

A growing number of studies are revealing that cells can send and receive information by controlling the temporal behavior (dynamics) of their signaling molecules. In this Review, we discuss what is known about the dynamics of various signaling networks and their role in controlling cellular responses. We identify general principles that are emerging in the field, focusing specifically on how the identity and quantity of a stimulus is encoded in temporal patterns, how signaling dynamics influence cellular outcomes, and how specific dynamical patterns are both shaped and interpreted by the structure of molecular networks. We conclude by discussing potential functional roles for transmitting cellular information through the dynamics of signaling molecules and possible applications for the treatment of disease.

Purvis JE; Lahav G

2013-02-01

169

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

Energy Technology Data Exchange (ETDEWEB)

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

Koenneker, Carsten (comp.)

2012-11-01

170

Entanglement Witness for NMR Quantum Information Processing  

CERN Multimedia

We discuss the tricky issue of entanglement in NMR quantum information processing and particularly NMR implementation of superdense coding. The signal intensity is introduced as a critical experimental property and an experimental approach for detection of entanglement is proposed based on the signal intesity measurements in a single NMR experiment.

Rahimi, R; Ozawa, M; Kitagawa, M

2004-01-01

171

NIR-Emitting Quantum Dot-Encoded Microbeads through Membrane Emulsification for Multiplexed Immunoassays.  

UK PubMed Central (United Kingdom)

NIR-emitting CdSeTe/CdS/ZnS core/shell/shell QD-encoded microbeads are combined with common flow cytometry with one laser for multiplexed detection of hepatitis B virus (HBV). A facile one-pot synthetic route is developed to prepare CdSeTe/CdS/ZnS core/shell/shell QDs with high photoluminescence quantum yield and excellent stability in liquid paraffin, and a Shirasu porous glass (SPG) membrane emulsification technique is applied to incorporate the QDs into polystyrene-maleic anhydride (PSMA) microbeads to obtain highly fluorescent QD-encoded microbeads. The relatively wide NIR photoluminescence full width half maximum of the CdSeTe/CdS/ZnS QDs is used to develop a 'single wavelength' encoding method to obtain different optical codes by changing the wavelengh and emission intensity of the QDs incorporated into the microbeads. Moreover, a detection platform combining NIR-emitting CdSeTe/CdS/ZnS QD-encoded microbeads and Beckman Coulter FC 500 flow cytometry with one laser of 488 nm is successfully used to conduct a 2-plex hybridization assay for hepatitis B surface antigen (HBsAg), hepatitis B e antigen (HBeAg), and a 3-plex hybridization assay for hepatitis B surface antibody (HBsAb), hepatitis B e antibody (HBeAb), and hepatitis B core antibody (HBcAb), which suggests the promising application of NIR QD-encoded microbeads for multiplex immunoassays.

Wang X; Wang G; Li W; Zhao B; Xing B; Leng Y; Dou H; Sun K; Shen L; Yuan X; Li J; Sun K; Han J; Xiao H; Li Y; Huang P; Chen X

2013-03-01

172

NIR-Emitting Quantum Dot-Encoded Microbeads through Membrane Emulsification for Multiplexed Immunoassays.  

Science.gov (United States)

NIR-emitting CdSeTe/CdS/ZnS core/shell/shell QD-encoded microbeads are combined with common flow cytometry with one laser for multiplexed detection of hepatitis B virus (HBV). A facile one-pot synthetic route is developed to prepare CdSeTe/CdS/ZnS core/shell/shell QDs with high photoluminescence quantum yield and excellent stability in liquid paraffin, and a Shirasu porous glass (SPG) membrane emulsification technique is applied to incorporate the QDs into polystyrene-maleic anhydride (PSMA) microbeads to obtain highly fluorescent QD-encoded microbeads. The relatively wide NIR photoluminescence full width half maximum of the CdSeTe/CdS/ZnS QDs is used to develop a 'single wavelength' encoding method to obtain different optical codes by changing the wavelengh and emission intensity of the QDs incorporated into the microbeads. Moreover, a detection platform combining NIR-emitting CdSeTe/CdS/ZnS QD-encoded microbeads and Beckman Coulter FC 500 flow cytometry with one laser of 488 nm is successfully used to conduct a 2-plex hybridization assay for hepatitis B surface antigen (HBsAg), hepatitis B e antigen (HBeAg), and a 3-plex hybridization assay for hepatitis B surface antibody (HBsAb), hepatitis B e antibody (HBeAb), and hepatitis B core antibody (HBcAb), which suggests the promising application of NIR QD-encoded microbeads for multiplex immunoassays. PMID:23463727

Wang, Xiebing; Wang, Gang; Li, Wanwan; Zhao, Bingxia; Xing, Bin; Leng, Yuankui; Dou, Hongjing; Sun, Kang; Shen, Lisong; Yuan, Xiangliang; Li, Jiyu; Sun, Kun; Han, Junsong; Xiao, Huasheng; Li, Yue; Huang, Peng; Chen, Xiaoyuan

2013-03-01

173

Geometrical identification of quantum and information theories  

International Nuclear Information System (INIS)

[en] The interrelation of quantum and information theories is investigation on the base of the conception of cross-entropy. It is assumed that ''complex information geometry'' may serve as a tool for ''technological transfer'' from one research field to the other which is not connected directly with the first one. It is pointed out that the ''infinitesimal distance'' ds2 and ''infinitesimal cross-entropy'' dHsub(c) coincide

1983-01-01

174

Quantum information transport to multiple receivers  

CERN Multimedia

The importance of transporting quantum information and entanglement with high fidelity cannot be overemphasized. We present a scheme based on adiabatic passage that allows communication of a qubit, entanglement, and joint measurements using a 1-D array of quantum sites with a single sender (Alice) and multiple receivers (Bobs). Alice need not know which Bob is the receiver, and if several Bobs try to receive the signal, they obtain a superposition state which can be converted into a globally entangled state by the use of local entangling operations.

Greentree, A D; Greentree, Andrew D.; Hollenberg, Lloyd C. L.

2005-01-01

175

Complementarity of quantum discord and classically accessible information.  

Science.gov (United States)

The sum of the Holevo quantity (that bounds the capacity of quantum channels to transmit classical information about an observable) and the quantum discord (a measure of the quantumness of correlations of that observable) yields an observable-independent total given by the quantum mutual information. This split naturally delineates information about quantum systems accessible to observers - information that is redundantly transmitted by the environment - while showing that it is maximized for the quasi-classical pointer observable. Other observables are accessible only via correlations with the pointer observable. We also prove an anti-symmetry property relating accessible information and discord. It shows that information becomes objective - accessible to many observers - only as quantum information is relegated to correlations with the global environment, and, therefore, locally inaccessible. The resulting complementarity explains why, in a quantum Universe, we perceive objective classical reality while flagrantly quantum superpositions are out of reach. PMID:23686384

Zwolak, Michael; Zurek, Wojciech H

2013-01-01

176

Operator quantum Zeno effect: protecting quantum information with noisy two-qubit interactions.  

UK PubMed Central (United Kingdom)

The time evolution of some quantum states can be slowed down or even stopped under frequent measurements. This is the usual quantum Zeno effect. Here, we report an operator quantum Zeno effect, in which the evolution of some physical observables is slowed down through measurements even though the quantum state changes randomly with time. Based on the operator quantum Zeno effect, we show how we can protect quantum information from decoherence with two-qubit measurements, realizable with noisy two-qubit interactions.

Wang SC; Li Y; Wang XB; Kwek LC

2013-03-01

177

Scavenging quantum information: Multiple observations of quantum systems  

CERN Document Server

Given an unknown state of a qudit that has already been measured optimally, can one still extract any information about the original unknown state? Clearly, after a maximally informative measurement, the state of the system `collapses' into a post-measurement state from which the {\\em{same}} observer cannot obtain further information about the original state of the system. However, the system still encodes a significant amount of information about the original preparation for a second observer who is unaware of the actions of the first one. We study how a series of independent observers can obtain, or scavenge, information about the unknown state of a system (quantified by the fidelity) when they sequentially measure it. We give closed-form expressions for the estimation fidelity, when one or several qudits are available to carry information about the single-qudit state, and study the `classical' limit when an arbitrarily large number of observers can obtain (nearly) complete information on the system. In add...

Rapcan, Peter; Munoz-Tapia, Ramon; Bagan, Emilio; Buzek, Vladimir

2011-01-01

178

Entanglement, information, and the interpretation of quantum mechanics  

International Nuclear Information System (INIS)

This book explores the nature of quantum entanglement and quantum information and their role in the quantum world. Their relations to a number of key experiments and thought experiments in the history of quantum physics are considered, as is a range of interpretations of quantum mechanics that have been put forward as a means of understanding the fundamental nature of microphysics - the traditionally accepted domain of quantum mechanics - and in some cases, the universe as a whole. In this way, the book reveals the deep significance of entanglement and quantum information for our understanding of the physical world. (orig.)

2009-01-01

179

Entanglement, information, and the interpretation of quantum mechanics  

Energy Technology Data Exchange (ETDEWEB)

This book explores the nature of quantum entanglement and quantum information and their role in the quantum world. Their relations to a number of key experiments and thought experiments in the history of quantum physics are considered, as is a range of interpretations of quantum mechanics that have been put forward as a means of understanding the fundamental nature of microphysics - the traditionally accepted domain of quantum mechanics - and in some cases, the universe as a whole. In this way, the book reveals the deep significance of entanglement and quantum information for our understanding of the physical world. (orig.)

Jaeger, Gregg [Boston Univ., MA (United States). Quantum Imaging Lab.

2009-07-01

180

A flow cytometric assay technology based on quantum dots-encoded beads  

International Nuclear Information System (INIS)

[en] A flow cytometric detecting technology based on quantum dots (QDs)-encoded beads has been described. Using this technology, several QDs-encoded beads with different code were identified effectively, and the target molecule (DNA sequence) in solution was also detected accurately by coupling to its complementary sequence probed on QDs-encoded beads through DNA hybridization assay. The resolution of this technology for encoded beads is resulted from two longer wavelength fluorescence identification signals (yellow and red fluorescent signals of QDs), and the third shorter wavelength fluorescence signal (green reporting signal of fluorescein isothiocyanate (FITC)) for the determination of reaction between probe and target. In experiment, because of QDs' unique optical character, only one excitation light source was needed to excite the QDs and probe dye FITC synchronously comparing with other flow cytometric assay technology. The results show that this technology has present excellent repeatability and good accuracy. It will become a promising multiple assay platform in various application fields after further improvement

2006-10-27

 
 
 
 
181

A flow cytometric assay technology based on quantum dots-encoded beads  

Energy Technology Data Exchange (ETDEWEB)

A flow cytometric detecting technology based on quantum dots (QDs)-encoded beads has been described. Using this technology, several QDs-encoded beads with different code were identified effectively, and the target molecule (DNA sequence) in solution was also detected accurately by coupling to its complementary sequence probed on QDs-encoded beads through DNA hybridization assay. The resolution of this technology for encoded beads is resulted from two longer wavelength fluorescence identification signals (yellow and red fluorescent signals of QDs), and the third shorter wavelength fluorescence signal (green reporting signal of fluorescein isothiocyanate (FITC)) for the determination of reaction between probe and target. In experiment, because of QDs' unique optical character, only one excitation light source was needed to excite the QDs and probe dye FITC synchronously comparing with other flow cytometric assay technology. The results show that this technology has present excellent repeatability and good accuracy. It will become a promising multiple assay platform in various application fields after further improvement.

Wang Haiqiao [Key Laboratory of Biomedical Photonics of Ministry of Education-Hubei Bioinformatics and Molecular Imaging Key Laboratory, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Liu Tiancai [Key Laboratory of Biomedical Photonics of Ministry of Education-Hubei Bioinformatics and Molecular Imaging Key Laboratory, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Cao Yuancheng [Key Laboratory of Biomedical Photonics of Ministry of Education-Hubei Bioinformatics and Molecular Imaging Key Laboratory, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Huang Zhenli [Key Laboratory of Biomedical Photonics of Ministry of Education-Hubei Bioinformatics and Molecular Imaging Key Laboratory, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Wang Jianhao [Key Laboratory of Biomedical Photonics of Ministry of Education-Hubei Bioinformatics and Molecular Imaging Key Laboratory, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Li Xiuqing [Key Laboratory of Biomedical Photonics of Ministry of Education-Hubei Bioinformatics and Molecular Imaging Key Laboratory, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Zhao Yuandi [Key Laboratory of Biomedical Photonics of Ministry of Education-Hubei Bioinformatics and Molecular Imaging Key Laboratory, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China)]. E-mail: zydi@mail.hust.edu.cn

2006-10-27

182

Towards quantum information with trapped ions at NIST  

International Nuclear Information System (INIS)

We report experiments on coherent quantum-state synthesis and the control of trapped atomic ions. This work has the overall goal of performing large-scale quantum information processing; however, such techniques can also be applied to fundamental tests and demonstrations of quantum mechanical principles, as well as to the improvement of quantum-limited measurements.

2003-02-14

183

Precisely timing dissipative quantum information processing  

CERN Document Server

Dissipative engineering constitutes a framework within which quantum information processing protocols are powered by weak (Markovian) system-environment interaction rather than by unitary dynamics alone. This framework embraces noise as a resource, and consequently, offers a number of advantages compared to one based on unitary dynamics alone, e.g., that large classes of initial states are rapidly driven to desirable steady states. One apparent drawback of this scheme is that it does not seem to allow for precisely timed sequential operations, conditional measurements or error correction. In this work, we provide a solution to these challenges, by introducing some basic dissipative gadgets which allow us to precisely initiate, trigger and time dissipative operations, while keeping the system Liouvillian time independent. These gadgets open up novel perspectives for thinking of timed, protected dissipative quantum information processing. As an example, we sketch how universal computation can be performed with ...

Kastoryano, M J; Eisert, J

2012-01-01

184

Black holes, information, and Hilbert space for quantum gravity  

Science.gov (United States)

A coarse-grained description for the formation and evaporation of a black hole is given within the framework of a unitary theory of quantum gravity preserving locality, without dropping the information that manifests as macroscopic properties of the state at late times. The resulting picture depends strongly on the reference frame one chooses to describe the process. In one description based on a reference frame in which the reference point stays outside the black hole horizon for sufficiently long time, a late black hole state becomes a superposition of black holes in different locations and with different spins, even if the back hole is formed from collapsing matter that had a well-defined classical configuration with no angular momentum. The information about the initial state is partly encoded in relative coefficients—especially phases—of the terms representing macroscopically different geometries. In another description in which the reference point enters into the black hole horizon at late times, an S-matrix description in the asymptotically Minkowski spacetime is not applicable, but it still allows for an “S-matrix” description in the full quantum gravitational Hilbert space including singularity states. Relations between different descriptions are given by unitary transformations acting on the full Hilbert space, and they in general involve superpositions of “distant” and “infalling” descriptions. Despite the intrinsically quantum mechanical nature of the black hole state, measurements performed by a classical physical observer are consistent with those implied by general relativity. In particular, the recently-considered firewall phenomenon can occur only for an exponentially fine-tuned (and intrinsically quantum mechanical) initial state, analogous to an entropy decreasing process in a system with large degrees of freedom.

Nomura, Yasunori; Varela, Jaime; Weinberg, Sean J.

2013-04-01

185

Quantum Information from Graviton-Matter Gas  

Directory of Open Access Journals (Sweden)

Full Text Available We present basics of conceptually new-type way for explaining of the origin, evolution and current physical properties of our Universe from the graviton-matter gas viewpoint. Quantization method for the Friedmann-Lemaitre Universe based on the canonical Hamilton equations of motion is proposed and quantum information theory way to physics of the Universe is showed. The current contribution from the graviton-matter gas temperature in quintessence approximation is discussed.

Lukasz-Andrzej Glinka

2007-01-01

186

Existence of an information unit as a postulate of quantum theory.  

UK PubMed Central (United Kingdom)

Does information play a significant role in the foundations of physics? Information is the abstraction that allows us to refer to the states of systems when we choose to ignore the systems themselves. This is only possible in very particular frameworks, like in classical or quantum theory, or more generally, whenever there exists an information unit such that the state of any system can be reversibly encoded in a sufficient number of such units. In this work, we show how the abstract formalism of quantum theory can be deduced solely from the existence of an information unit with suitable properties, together with two further natural assumptions: the continuity and reversibility of dynamics, and the possibility of characterizing the state of a composite system by local measurements. This constitutes a set of postulates for quantum theory with a simple and direct physical meaning, like the ones of special relativity or thermodynamics, and it articulates a strong connection between physics and information.

Masanes L; Müller MP; Augusiak R; Pérez-García D

2013-09-01

187

Some Notes on Quantum Information Theory and Emerging Computing Technologies  

CERN Multimedia

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

Vlasov, Alexander Yu

2011-01-01

188

Information Nano-Technologies: Transition from Classical to Quantum  

CERN Multimedia

In this presentation are discussed some problems, relevant with application of information technologies in nano-scale systems and devices. Some methods already developed in quantum information technologies may be very useful here. Here are considered two illustrative models: representation of data by quantum bits and transfer of signals in quantum wires.

Vlasov, Alexander Yu

2009-01-01

189

Multiparty secret sharing of quantum information based on entanglement swapping  

Energy Technology Data Exchange (ETDEWEB)

A protocol of multiparty secret sharing of quantum information based on entanglement swapping is analyzed. In this protocol, Bell states are needed in order to realize the quantum information secret sharing and it is convenient to realize the quantum secret sharing among the members of any subset of users.

Li Yongmin; Zhang Kuanshou; Peng Kunchi

2004-04-26

190

Quantifying non-Gaussianity for quantum information  

CERN Multimedia

We address the quantification of non-Gaussianity of states and operations in continuous-variable systems and its use in quantum information. We start by illustrating in details the properties and the relationships of two recently proposed measures of non-Gaussianity based on the Hilbert-Schmidt (HS) distance and the quantum relative entropy (QRE) between the state under examination and a reference Gaussian state. We then evaluate the non-Gaussianities of several families of non-Gaussian quantum states and show that the two measures have the same basic properties and also share the same qualitative behaviour on most of the examples taken into account. However, we also show that they introduce a different relation of order, i.e. they are not strictly monotone each other. We exploit the non-Gaussianity measures for states in order to introduce a measure of non-Gaussianity for quantum operations, to assess Gaussification and de-Gaussification protocols, and to investigate in details the role played by non-Gaussia...

Genoni, Marco

2010-01-01

191

Information, computing technology, and quantum computing  

International Nuclear Information System (INIS)

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

2006-05-31

192

Locally inaccessible information as a fundamental ingredient to quantum information  

International Nuclear Information System (INIS)

[en] Quantum discord (QD) measures the fraction of the pairwise mutual information that is locally inaccessible in a multipartite system. Fundamental aspects related to two important measures in quantum information theory, namely the entanglement of formation (EOF) and the conditional entropy, can be understood in terms of the distribution of this form of local inaccessible information (LII). As such, the EOF for an arbitrarily mixed bipartite system AB can be related to the gain or loss of LII due to the extra knowledge that a purifying ancillary system E has on the pair AB. Similarly, a clear meaning of the negativity of the conditional entropy for AB is given. We employ these relations to elucidate important and yet not well-understood quantum features, such as the bipartite entanglement sudden death and the distinction between EOF and QD for quantifying quantum correlation. For that we introduce the concept of LII flow that quantifies the LII shared in a multipartite system when sequential local measurements are carried out. (paper)

2012-01-01

193

Nature computes: information processing in quantum dynamical systems.  

Science.gov (United States)

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

Wiesner, Karoline

2010-09-01

194

Nature computes: information processing in quantum dynamical systems.  

UK PubMed Central (United Kingdom)

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

Wiesner K

2010-09-01

195

Geometric information in eight dimensions vs. quantum information  

CERN Document Server

Complementary idempotent paravectors and their ordered compositions, are used to represent multivector basis elements of geometric Clifford algebra for 3D Euclidean space as the states of a geometric byte in a given frame of reference. Two layers of information, available in real numbers, are distinguished. The first layer is a continuous one. It is used to identify spatial orientations of similar geometric objects in the same computational basis. The second layer is a binary one. It is used to manipulate with 8D structure elements inside the computational basis itself. An oriented unit cube representation, rather than a matrix one, is used to visualize an inner structure of basis multivectors. Both layers of information are used to describe unitary operations -- reflections and rotations -- in Euclidian and Hilbert spaces. The results are compared with ones for quantum gates. Some consequences for quantum and classical information technologies are discussed.

Tarkhanov, Victor I

2008-01-01

196

Quantum: information theory: technological challenge; Computacion Cuantica: un reto tecnologico  

Energy Technology Data Exchange (ETDEWEB)

The new Quantum Information Theory augurs powerful machines that obey the entangled logic of the subatomic world. Parallelism, entanglement, teleportation, no-cloning and quantum cryptography are typical peculiarities of this novel way of understanding computation. (Author) 24 refs.

Calixto, M.

2001-07-01

197

Relativistic Quantum Information in Detectors-Field Interactions  

CERN Document Server

We explore the use of moving Unruh-DeWitt detectors and other models of detector-field interaction in probing some key issues in relativistic quantum information science, from entanglement dynamics to quantum teleportation.

Hu, B L; Louko, Jorma

2012-01-01

198

Controlling the flow of information in quantum cloners Asymmetric cloning  

CERN Multimedia

We show that the distribution of information at the output of the quantum cloner can be efficiently controlled via preparation of the quantum cloner. We present a universal cloning network with the help of which asymmetric cloning can be performed.

Buzek, V; Bednik, R

1998-01-01

199

Quantum theory with possible leakage of information  

Energy Technology Data Exchange (ETDEWEB)

A model of quantum theory is presented where the evolution of pure states into mixed states is possible, so that information on the system states is not conserved. The theory is based upon an evolution equation for the density operator, which is an extension of the Landau-von Neumann equation. The equation contains the system hamiltonian and a single parameter characterizing the deviation from the standard theory. The model does not break usual conservation laws. The general solution is represented as an average over the solutions of conventional theory; this is an effect of the uncertainty in time. Predictions of the model are discussed in brief. Spectrometry and scattering do not experience the modification, it manifests itself only in processes with an observable time dependence. Neutral kaon decays are considered. The model is proposed in view of Hawking's suggestion that quantum gravity may be a reason for an additional unpredictability in elementary particle physics.

Marinov, M.S.

1985-05-13

200

Quantum-like model of processing of information in the brain based on classical electromagnetic field.  

Science.gov (United States)

We propose a model of quantum-like (QL) processing of mental information. This model is based on quantum information theory. However, in contrast to models of "quantum physical brain" reducing mental activity (at least at the highest level) to quantum physical phenomena in the brain, our model matches well with the basic neuronal paradigm of the cognitive science. QL information processing is based (surprisingly) on classical electromagnetic signals induced by joint activity of neurons. This novel approach to quantum information is based on representation of quantum mechanics as a version of classical signal theory which was recently elaborated by the author. The brain uses the QL representation (QLR) for working with abstract concepts; concrete images are described by classical information theory. Two processes, classical and QL, are performed parallely. Moreover, information is actively transmitted from one representation to another. A QL concept given in our model by a density operator can generate a variety of concrete images given by temporal realizations of the corresponding (Gaussian) random signal. This signal has the covariance operator coinciding with the density operator encoding the abstract concept under consideration. The presence of various temporal scales in the brain plays the crucial role in creation of QLR in the brain. Moreover, in our model electromagnetic noise produced by neurons is a source of superstrong QL correlations between processes in different spatial domains in the brain; the binding problem is solved on the QL level, but with the aid of the classical background fluctuations. PMID:21683119

Khrennikov, Andrei

2011-06-12

 
 
 
 
201

Coordinating quantum agents' perspectives: convex operational theories, quantum information, and quantum foundations  

CERN Multimedia

In this paper, I propose a project of enlisting quantum information science as a source of task-oriented axioms for use in the investigation of operational theories in a general framework capable of encompassing quantum mechanics, classical theory, and more. Whatever else they may be, quantum states of systems are compendia of probabilities for the outcomes of possible operations we may perform on the systems: ``operational theories.'' I discuss appropriate general frameworks for such theories, in which convexity plays a key role. Such frameworks are appropriate for investigating what things look like from an ``inside view,'' i.e. for describing perspectival information that one subsystem of the world can have about another. Understanding how such views can combine, and whether an overall ``geometric'' picture (``outside view'') coordinating them all can be had, even if this picture is very different in nature from the structure of the perspectives within it, is the key to understanding whether we may be able...

Barnum, H

2006-01-01

202

Leftover Hashing Against Quantum Side Information  

CERN Multimedia

The Leftover Hash Lemma states that the output of a two-universal hash function applied to an input with sufficiently high entropy is almost uniformly random. In its standard formulation, the lemma refers to a notion of randomness that is (usually implicitly) defined with respect to classical side information. Here, we prove a (strictly) more general version of the Leftover Hash Lemma that is valid even if side information is represented by the state of a quantum system. Furthermore, our result applies to arbitrary delta-almost two-universal families of hash functions. The generalized Leftover Hash Lemma has applications in cryptography, e.g., for key agreement in the presence of an adversary who is not restricted to classical information processing.

Tomamichel, Marco; Smith, Adam; Renner, Renato

2010-01-01

203

Quantum Information from Graviton-Matter Gas  

CERN Multimedia

One of main experimental datum about our Universe is presence of the Cosmic Microwave Background radiation. We present basics of conceptually new-type way for explain of the origin, evolution and today physical properties of our Universe from the CMB anisotropies viewpoint. Quantization method for the Friedmann-Lemaitre Universe based on the canonical Hamilton equations of motion is proposed and quantum information theory way to physics of the Universe is showed. Today contribution from the Graviton-Matter gas temperature in Quintessence approximation is concluded.

Glinka, L A

2007-01-01

204

Quantum Computers: A New Paradigm in Information Technology  

Directory of Open Access Journals (Sweden)

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

Mahesh S. Raisinghani

2001-01-01

205

Storing quantum information in chemically engineered nanoscale magnets  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We review the implementation of quantum information processing using quantum spins and pulsed spin resonance techniques. Molecular magnets, nanoscale clusters of coupled transition metal ions, offer various potential advantages over other spin systems as the building blocks of a quantum computer. We...

Ardavan, Arzhang; Blundell, Stephen J.

206

Information criteria for efficient quantum state estimation  

International Nuclear Information System (INIS)

Recently several more efficient versions of quantum state tomography have been proposed, with the purpose of making tomography feasible even for many-qubit states. The number of state parameters to be estimated is reduced by tentatively introducing certain simplifying assumptions on the form of the quantum state, and subsequently using the data to rigorously verify these assumptions. The simplifying assumptions considered so far were (i) the state can be well approximated to be of low rank, or (ii) the state can be well approximated as a matrix product state, or (iii) only the permutationally invariant part of the density matrix is determined. We add one more method in that same spirit: We allow in principle any model for the state, using any (small) number of parameters (which can, e.g., be chosen to have a clear physical meaning), and the data are used to verify the model. The proof that this method is valid cannot be as strict as in the above-mentioned cases, but is based on well-established statistical methods that go under the name of ''information criteria.'' We exploit here, in particular, the Akaike information criterion. We illustrate the method by simulating experiments on (noisy) Dicke states.

2011-01-01

207

Operator quantum Zeno effect: protecting quantum information with noisy two-qubit interactions.  

Science.gov (United States)

The time evolution of some quantum states can be slowed down or even stopped under frequent measurements. This is the usual quantum Zeno effect. Here, we report an operator quantum Zeno effect, in which the evolution of some physical observables is slowed down through measurements even though the quantum state changes randomly with time. Based on the operator quantum Zeno effect, we show how we can protect quantum information from decoherence with two-qubit measurements, realizable with noisy two-qubit interactions. PMID:23521242

Wang, Shu-Chao; Li, Ying; Wang, Xiang-Bin; Kwek, Leong Chuan

2013-03-08

208

Separating the classical and quantum information via quantum cloning  

CERN Multimedia

An application of quantum cloning to optimally interface a quantum system with a classical observer is presented, in particular we describe a procedure to perform a minimal disturbance measurement on a single qubit by adopting a 1->2 cloning machine followed by a generalized measurement on a single clone and the anti-clone or on the two clones. Such scheme has been applied to enhance the transmission fidelity over a lossy quantum channel.

Ricci, M; De Martini, F; Filip, R; Fiurasek, J; Sciarrino, F

2005-01-01

209

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

CERN Multimedia

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

Chung, Hyeyoun

2008-01-01

210

Prospects for using integrated atom-photon junctions for quantum information processing  

CERN Multimedia

We investigate the use of integrated, microfabricated photonic-atomic junctions for quantum information processing applications. The coupling between atoms and light is enhanced by using microscopic optics without the need for cavity enhancement. Qubits that are collectively encoded in hyperfine states of small ensembles of optically trapped atoms, coupled via the Rydberg blockade mechanism, seem a particularly promising implementation. Fast and high-fidelity gate operations, efficient readout, long coherence times and large numbers of qubits are all possible.

Nyman, R A; Hinds, E A

2011-01-01

211

Quantum information processing architecture with endohedral fullerenes in a carbon nanotube  

CERN Multimedia

A potential quantum information processor is proposed using a fullerene peapod, i.e., an array of the endohedral fullerenes 15N@C60 or 31P@C60 contained in a single walled carbon nanotube (SWCNT). The qubits are encoded in the nuclear spins of the doped atoms, while the electronic spins are used for initialization and readout, as well as for two-qubit operations.

Yang, Wan Li; Wei, Hua; Feng, Mang; Suter, Dieter

2010-01-01

212

The black hole information problem beyond quantum theory  

CERN Document Server

The origin of black hole entropy and the black hole information problem provide important clues for trying to piece together a quantum theory of gravity. Thus far, discussions on this topic have mostly assumed that in a consistent theory of gravity and quantum mechanics, quantum theory will be unmodified. Here, we examine the black hole information problem in the context of generalisations of quantum theory. In particular, we examine black holes in the setting of generalised probabilistic theories, in which quantum theory and classical probability theory are special cases. We compute the time it takes information to escape a black hole, assuming that information is preserved. We find that under some very general assumptions, the arguments of Page (that information should escape the black hole after half the Hawking photons have been emitted), and the black-hole mirror result of Hayden and Preskill (that information can escape quickly) need to be modified. The modification is determined entirely by what we cal...

Mueller, Markus P; Dahlsten, Oscar C O

2012-01-01

213

Information criteria for efficient quantum state estimation  

CERN Document Server

Recently several more efficient versions of quantum state tomography have been proposed, with the purpose of making tomography feasible even for many-qubit states. The number of state parameters to be estimated is reduced by tentatively introducing certain simplifying assumptions on the form of the quantum state, and subsequently using the data to rigorously verify these assumptions. The simplifying assumptions considered so far were (i) the state can be well approximated to be of low rank, or (ii) the state can be well approximated as a matrix product state. We add one more method in that same spirit: we allow in principle any model for the state, using any (small) number of parameters (which can, e.g., be chosen to have a clear physical meaning), and the data are used to verify the model. The proof that this method is valid cannot be as strict as in above-mentioned cases, but is based on well-established statistical methods that go under the name of "information criteria." We exploit here, in particular, th...

Yin, J O S

2011-01-01

214

Transmission of classical and quantum information through a quantum memory channel with damping  

CERN Multimedia

We consider the transfer of classical and quantum information through a memory amplitude damping channel. Such a quantum channel is modeled as a damped harmonic oscillator, the interaction between the information carriers - a train of qubits - and the oscillator being of the Jaynes-Cummings kind. We prove that this memory channel is forgetful, so that quantum coding theorems hold for its capacities. We analyze entropic quantities relative to two uses of this channel. We show that memory effects improve the channel aptitude to transmit both classical and quantum information, and we investigate the mechanism by which memory acts in changing the channel transmission properties.

D'Arrigo, A; Falci, G

2011-01-01

215

Quantum mutual information and the one-time pad  

International Nuclear Information System (INIS)

Alice and Bob share a correlated composite quantum system AB. If AB is used as the key for a one-time pad cryptographic system, we show that the maximum amount of information that Alice can send securely to Bob is the quantum mutual information of AB.

2006-01-01

216

Tamper-resistant encryption of quantum information  

CERN Document Server

We introduce the notion of \\emph{tamper resistance} of a quantum state encryption scheme (in dimension $d$): in addition to the requirement that an adversary cannot learn information about the state, here we demand that no controlled modification of the encrypted state can be effected. We show that such a scheme is equivalent to a \\emph{unitary 2-design} [Dankert \\emph{et al.}], as opposed to normal encryption which is unitary 1-design. Our other main results include a new proof of the lower bound of $(d^2-1)^2+1$ on the number of unitaries in a 2-design [Gross \\emph{et al.}], which lends itself to a generalization to approximate 2-design. Furthermore, while in each dimension there is a unitary 2-design with $\\leq d^5$ elements, we show that there are approximate 2-designs with $O(\\epsilon^{-2} d^4 \\log d)$ elements.

Ambainis, Andris; Winter, Andreas

2008-01-01

217

Distributed quantum information processing with mobile electrons  

CERN Multimedia

In distributed quantum information processing, small devices composed of a single or a few qubits are networked together through shared entanglement to achieve a scalable machine. Typically, photons are utilized to generate remote entanglement between optically active matter qubits. In this paper, we consider another possibility for achieving entanglement between nodes: using mobile electron spins as mediators of the interaction between static qubits at each node. A strong interaction between electrons makes it feasible to couple the flying electron with the static electron. However, since the electrons easily interact with the environment, error accumulation during the entanglement operation could be more severe than with the other strategy using photons as flying qubits. We introduce a new scheme especially designed to minimize such error accumulation by using several distillation protocols. The conclusion is that a high fidelity entanglement operation can be constructed even under the effect of typical imp...

Matsuzaki, Yuichiro

2011-01-01

218

On the Possibility of Quantum Informational Structural Realism  

CERN Document Server

In The Philosophy of Information (2011 book), Luciano Floridi presents an ontological theory of Being qua Being, which he calls "Informational Structural Realism", a theory which applies, he says, to every possible world. He identifies primordial information ("dedomena") as the foundation of any structure in any possible world. The present essay examines Floridi's defense of that theory, as well as his refutation of "Digital Ontology" (which some people might confuse with his own). Then, using Floridi's ontology as a starting point, the present essay adds quantum features to dedomena, yielding an ontological theory for our own universe, Quantum Informational Structural Realism, which provides a metaphysical interpretation of key quantum phenomena, and diminishes the "weirdness" or "spookiness" of quantum mechanics. Key Words: digital ontology, dedomena, structural realism, quantum information, primordial qubit

Bynum, Terrell Ward

2013-01-01

219

Quantum public-key algorithms to encrypt and authenticate quantum messages with information-theoretic security  

CERN Multimedia

Public-key cryptosystems for quantum messages are considered from two aspects: public-key encryption and public-key authentication. Firstly, we propose a general construction of quantum public-key encryption scheme, and then construct an information-theoretic secure instance. Then, we propose a quantum public-key authentication scheme, which can protect the integrity of quantum messages. This scheme can both encrypt and authenticate quantum messages. It is information-theoretic secure with regard to encryption, and the success probability of tampering decreases exponentially with the security parameter with regard to authentication. Compared with classical public-key cryptosystems, one private-key in our schemes corresponds to an exponential number of public-keys, and every quantum public-key used by the sender is an unknown quantum state to the sender.

Liang, Min

2012-01-01

220

An Investigation of Quantum Interference in Information Retrieval  

Science.gov (United States)

In the related literature and in particular in the recent book by van Rijsbergen, it was hypothesized that a more general framework used to formalize quantum mechanics, and then quantum probability, would be useful for going beyond the classical retrieval models. This paper first discusses a situation in which that framework, and then quantum probability, can be necessary in Information Retrieval and then describes the experiments designed to this end. The necessity of considering quantum probability stemmed from the experimental observation carried out in this paper that the best terms for query expansion have probability which does not admit classical probability and which instead can be defined within a quantum probability function.

Melucci, Massimo

 
 
 
 
221

Reading and Fast Encoding the Information from Multi-Element Detector  

CERN Document Server

We propose a method for reading and encoding the information from the Central Tracker of the Heavy Ion Dedicated Detector at LHC. This method will also be suitable for other detectors such as CMS, ATLAS and the like. It enables one to reduce the (number of cables coming out of the detector) x (information reading, encoding and selection time) factor by 12 times compared to what one has with the FASTPLEX system.

Laptev, V D; CERN. Geneva

1992-01-01

222

Encoding and updating spatial information presented in narratives.  

UK PubMed Central (United Kingdom)

Four experiments investigated whether directional spatial relations encoded by reading narratives are updated following described protagonist rotations. Participants memorized locations of objects described in short stories that placed them, as the protagonist, in remote settings. After reading a description that the protagonist rotated to the left or the right of the initial orientation, participants made judgements about object relations in the described environment (Experiment 1). Before making these judgements, participants were instructed to physically rotate to match (Experiment 2) or mismatch (Experiment 4) the protagonist's described rotation and in Experiments 3 and 4 to also visualize the changed relations following rotation. Participants' performance suggested that they relied on the initial representation they constructed during encoding rather than on the updated protagonist-to-object relations. Participants' physical movement to match the described rotation and additional visualization instructions did not facilitate updating through a sensorimotor process. In these respects, updating spatial relations in situation models constructed from narratives differs from updating in perceptually experienced environments.

Avraamides MN; Galati A; Pazzaglia F; Meneghetti C; Denis M

2013-01-01

223

Experimental Demonstration of Localization on a Quantum Information Processor  

CERN Document Server

Quantum computers will be a unique tool for understanding complex quantum systems. We report an experimental implementation of a sensitive, quantum coherence-dependent localization phenomenon on a prototype of a quantum computer, a quantum information processor (QIP). The localization effect is demonstrated by simulating the dynamics of the quantum sawtooth map on a three qubit liquid state nuclear magnetic resonance (NMR) device. The degree to which the system is delocalized by experimental noise and decoherence is well accounted for by a previously determined error model for NMR QIPs. We further show how the stability of the localization effect provides a benchmark of practical relevance for determining the overall degree of coherent quantum control and for identifying the relative significance of different noise mechanisms affecting the system.

Henry, M K; Emerson, J; Cory, David G.; Emerson, Joseph; Henry, Michael K.

2005-01-01

224

Information and fundamental elements of the structure of quantum theory  

CERN Multimedia

Niels Bohr wrote: "There is no quantum world. There is only an abstract quantum physical description. It is wrong to think that the task of physics is to find out how Nature is. Physics concerns what we can say about Nature." In an analogous way, von Weizsaecker suggested that the notion of the elementary alternative, the "Ur", should play a pivotal role when constructing physics. Both approaches suggest that the concept of information should play an essential role in the foundations of any scientific description of Nature. We show that if, in our description of Nature, we use one definite proposition per elementary constituent of Nature, some of the essential characteristics of quantum physics, such as the irreducible randomness of individual events, quantum complementary and quantum entanglement, arise in a natural way. Then quantum physics is an elementary theory of information.

Brukner, C; Brukner, Caslav; Zeilinger, Anton

2002-01-01

225

Immunizing quantum information against decoherence via decoherence-free environments  

Energy Technology Data Exchange (ETDEWEB)

We construct decoherence-free environments (DFEs) within the Hamiltonian formalism and derive an exact equation of motion for a quantum subsystem interacting with a DFE. We discuss the feasibility of DFEs as a means to protect the quantum information in subsystem degrees of freedom. By studying a number of examples we show how to avoid entanglement-induced decoherence as well as decoherence induced by incoherence dynamics in a quantum subsystem coupled to a DFE.

Cetinbas, Murat; Leach, Gary W, E-mail: cetinbas@sfu.ca [Laboratory for Advanced Spectroscopy and Imaging Research, 4D LABS and Department of Chemistry, Simon Fraser University, Burnaby, British Columbia, V5A 1S6 (Canada)

2011-04-01

226

Schroedinger cats and their power for quantum information processing  

Energy Technology Data Exchange (ETDEWEB)

We outline a toolbox comprised of passive optical elements, single photon detection and superpositions of coherent states (Schroedinger cat states). Such a toolbox is a powerful collection of primitives for quantum information processing tasks. We illustrate its use by outlining a proposal for universal quantum computation. We utilize this toolbox for quantum metrology applications, for instance weak force measurements and precise phase estimation. We show in both these cases that a sensitivity at the Heisenberg limit is achievable.

Gilchrist, A [Centre for Quantum Computer Technology, University of Queensland, QLD 4072 (Australia); Nemoto, Kae [National Institute of Informatics, 2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo 101-8430 (Japan); Munro, W J [Hewlett Packard Laboratories, Filton Road, Stoke Gifford, Bristol BS34 8QZ (United Kingdom); Ralph, T C [Centre for Quantum Computer Technology, University of Queensland, QLD 4072 (Australia); Glancy, S [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Braunstein, Samuel L [Computer Science, York University, York YO10 5DD (United Kingdom); Milburn, G J [Centre for Quantum Computer Technology, University of Queensland, QLD 4072 (Australia)

2004-08-01

227

Schroedinger cats and their power for quantum information processing  

International Nuclear Information System (INIS)

We outline a toolbox comprised of passive optical elements, single photon detection and superpositions of coherent states (Schroedinger cat states). Such a toolbox is a powerful collection of primitives for quantum information processing tasks. We illustrate its use by outlining a proposal for universal quantum computation. We utilize this toolbox for quantum metrology applications, for instance weak force measurements and precise phase estimation. We show in both these cases that a sensitivity at the Heisenberg limit is achievable

2004-08-01

228

Dipole blockade and quantum information processing in mesoscopic atomic ensembles.  

UK PubMed Central (United Kingdom)

We describe a technique for manipulating quantum information stored in collective states of mesoscopic ensembles. Quantum processing is accomplished by optical excitation into states with strong dipole-dipole interactions. The resulting "dipole blockade" can be used to inhibit transitions into all but singly excited collective states. This can be employed for a controlled generation of collective atomic spin states as well as nonclassical photonic states and for scalable quantum logic gates. An example involving a cold Rydberg gas is analyzed.

Lukin MD; Fleischhauer M; Cote R; Duan LM; Jaksch D; Cirac JI; Zoller P

2001-07-01

229

Dipole Blockade and Quantum Information Processing in Mesoscopic Atomic Ensembles  

CERN Multimedia

We describe a technique for manipulating quantum information stored in collective states of mesoscopic ensembles. Quantum processing is accomplished by optical excitation into states with strong dipole-dipole interactions. The resulting ``dipole blockade'' can be used to inhibit transitions into all but singly excited collective states. This can be employed for a controlled generation of collective atomic spin states as well as non-classical photonic states and for scalable quantum logic gates. An example involving a cold Rydberg gas is analyzed.

Lukin, M D; Côté, R; Duan, L M; Jaksch, D; Cirac, J I; Zoller, P

2000-01-01

230

Quantum Information Approach to the Ultimatum Game  

Science.gov (United States)

The paper is devoted to quantization of extensive games with the use of both the Marinatto-Weber and the Eisert-Wilkens-Lewenstein concept of quantum game. We revise the current conception of quantum ultimatum game and we show why the proposal is unacceptable. To support our approach, we present a new idea of the quantum ultimatum game. Our scheme also makes a point of departure for a general protocol for quantizing extensive games.

Fraçkiewicz, Piotr; S?adkowski, Jan

2013-05-01

231

Trevisan's extractor in the presence of quantum side information  

CERN Multimedia

Randomness extraction involves the processing of purely classical information and is therefore usually studied in the framework of classical probability theory. However, such a classical treatment is generally too restrictive for applications, where side information about the values taken by classical random variables may be represented by the state of a quantum system. This is particularly relevant in the context of cryptography, where an adversary may make use of quantum devices. Here, we build upon prior work by Ta-Shma and by De and Vidick to show that the well known construction paradigm for extractors proposed by Trevisan is sound in the presence of quantum side information.

De, Anindya; Vidick, Thomas; Renner, Renato

2009-01-01

232

Geometric Algebra Methods in Quantum Information Processing by NMR Spectroscopy  

UK PubMed Central (United Kingdom)

This paper is intended to introduce physicists and mathematicians to themain ideas behind quantum information processing by liquid-state NMRspectroscopy, using the language and techniques of geometric algebra. Thefirst section provides a brief overview of multiparticle geometric algebra,mainly to set the notation and terminology (more complete accounts maybe found in the above references). The next section gives a quick introductionto quantum information processing, again referring to the literature forInformation Processing by NMR Spectroscopy 3more complete accounts. This is followed by a detailed presentation of thebasics of liquid-state NMR spectroscopy, using the product operator formalism,and how NMR can be used to perform universal logical operationson quantum information. The paper concludes with the results of recentexperiments which show how geometric algebra can be used to "program"an NMR spectrometer to perform analog information processing, i.e. todirectly simulate general quantum systems.1.2 Multiparticle Geometric Algebra

Timothy F. Havel; David G. Cory; Shyamal S; Somaroo Ching-hua Tseng

233

Quantum information processing using strongly-dipolar coupled nuclear spins  

CERN Multimedia

Dipolar coupled homonuclear spins present challenging, yet useful systems for quantum information processing. In such systems, eigenbasis of the system Hamiltonian is the appropriate computational basis and coherent control can be achieved by specially designed strongly modulating pulses. In this letter we describe the first experimental implementation of the quantum algorithm for numerical gradient estimation on the eigenbasis of a four spin system.

Mahesh, T S; Suter, Dieter

2006-01-01

234

Controlling the flow of information in quantum cloners: asymmetric cloning  

International Nuclear Information System (INIS)

We show that the distribution of information at the output of the quantum cloner can be efficiently controlled via preparation of the quantum cloner. We present a universal cloning network with the help of which asymmetric cloning can be performed. (author)

1998-05-15

235

Multicolor quantum dot-encoded microspheres for the fluoroimmunoassays of chicken newcastle disease and goat pox virus.  

UK PubMed Central (United Kingdom)

Semiconductor nanocrystals (or quantum dots, QDs) have the potential to overcome some of the limitations encountered by traditional fluorophores in fluorescence labeling applications. The unique spectroscopic properties of QDs make them hold immense promise as versatile labels for biological applications. In this work, we employ the layer-by-layer (LbL) method for the construction of bio-functional multicolor QD-encoded microspheres. Polystyrene microspheres with diameter of 3 microm were used as templates for the deposition of different sized CdTe QDs/polyelectrolyte multilayers. Two different antigens, Chicken newcastle disease (CND) antigen and goat pox virus (GPV) antigen, were conjugated to two kinds of biofunctional multicolor microspheres with different optical encoding. The multicolor microspheres can capture corresponding antibodies labeled with QDs, QDs-CND antibody and QDs-GPV antibody in the fluoroimmunoassays. The microspheres can be distinguished from each other based on their optical encoding.

Yuan P; Ma Q; Meng R; Wang C; Dou W; Wang G; Su X

2009-05-01

236

Simple scheme for expanding photonic cluster states for quantum information  

International Nuclear Information System (INIS)

We show how an entangled cluster state encoded in the polarization of single photons can be straightforwardly expanded by deterministically entangling additional qubits encoded in the path degree of freedom of the constituent photons. This can be achieved using a polarization-path controlled-phase gate. We experimentally demonstrate a practical and stable realization of this approach by using a Sagnac interferometer to entangle a path qubit and polarization qubit on a single photon. We demonstrate precise control over phase of the path qubit to change the measurement basis and experimentally demonstrate properties of measurement-based quantum computing using a two-photon, three-qubit cluster state.

2010-01-01

237

Encoding of episodic information through fast task-irrelevant perceptual learning.  

UK PubMed Central (United Kingdom)

The mechanisms guiding our learning and memory processes are of key interest to human cognition. While much research shows that attention and reinforcement processes help guide the encoding process, there is still much to know regarding how our brains choose what to remember. Recent research of task-irrelevant perceptual learning (TIPL) has found that information presented coincident with important events is better encoded even if participants are not aware of its presence (see Seitz & Watanabe, 2009). However a limitation of existing studies of TIPL is that they provide little information regarding the depth of encoding supported by pairing a stimulus with a behaviorally relevant event. The objective of this research was to understand the depth of encoding of information that is learned through TIPL. To do so, we adopted a variant of the "remember/know" paradigm, recently reported by Ingram, Mickes, and Wixted (2012), in which multiple confidence levels of both familiar (know) and remember reports are reported (Experiment 1), and in which episodic information is tested (Experiment 2). TIPL was found in both experiments, with higher recognition performance for target-paired than for distractor-paired images. Furthermore, TIPL benefitted both "familiar" and "remember" reports. The results of Experiment 2 indicate that the most confident "remember" response was associated with episodic information, where participants were able to access the location of image presentation for these items. Together, these results indicate that TIPL results in a deep enhancement in the encoding of target-paired information.

Leclercq V; Le Dantec CC; Seitz AR

2013-09-01

238

An Entropic Uncertainty Relation With Quantum Side Information  

CERN Multimedia

Quantum mechanical uncertainty relations provide bounds on the minimum uncertainties about the outcomes of two alternative measurements applied to the same quantum state. In this paper, we prove an entropic uncertainty relation which, in contrast to known such relations, is valid in the context of quantum side information. It strengthens and extends the entropic uncertainty relation of Maassen and Uffink [Phys. Rev. Lett. 60, 1103 (1988)] and also implies an inequality recently conjectured by Boileau and Renes [Phys. Rev. Lett. 103, 020402 (2009)].The proof uses the formalism of smooth quantum entropies.

Berta, Mario; Colbeck, Roger; Renes, Joseph M; Renner, Renato

2009-01-01

239

The Propagation of Quantum Information Through a Spin System  

CERN Multimedia

It has been recently suggested that the dynamics of a quantum spin system may provide a natural mechanism for transporting quantum information. We show that one dimensional rings of qubits with fixed (time-independent) interactions, constant around the ring, allow high fidelity communication of quantum states. We show that the problem of maximising the fidelity of the quantum communication is related to a classical problem in fourier wave analysis. By making use of this observation we find that if both communicating parties have access to limited numbers of qubits in the ring (a fraction that vanishes in the limit of large rings) it is possible to make the communication arbitrarily good.

Osborne, T J; Osborne, Tobias J.; Linden, Noah

2003-01-01

240

Confabulation in healthy aging is related to poor encoding and retrieval of over-learned information.  

UK PubMed Central (United Kingdom)

Normal aging is characterized by deficits that cross multiple cognitive domains including episodic memory and attention. Compared to young adults (YA), older adults (OA) not only show reduction in true memories, but also an increase in false memories. In this study we aim to elucidate how the production of confabulation is influenced by encoding and retrieval processes. We hypothesized that in OA, compared to YA, over-learned information interferes with the recall of specific, unique past episodes and this interference should be more prominent when a concurrent task perturbs the encoding of the episodes to be recalled. We tested this hypothesis using an experimental paradigm in which a group of OA and a group of YA had to recall three different types of story: a previously unknown story, a well-known fairy tale (Snow White), and a modified well-known fairy tale (Little Red Riding Hood is not eaten by the wolf), in three different experimental conditions: (1) free encoding and free retrieval; (2) Divided attention (DA) at encoding and free retrieval; and (3) free encoding and DA at retrieval. Results showed that OA produced significantly more confabulations than YA, particularly, in the recall of the modified fairy tale. Moreover, DA at encoding markedly increased the number of confabulations, whereas DA at retrieval had no effect on confabulation. Our findings reveal the implications of two phenomena in the production of confabulation in normal aging: the effect of poor encoding and the interference of strongly represented, over-learned information in episodic memory recall.

Attali E; Dalla Barba G

2013-01-01

 
 
 
 
241

Linear optical setups for active and passive quantum error correction in polarization encoded qubits  

CERN Multimedia

In this work, we present active and passive linear optical setups for error correction in quantum communication systems that employ polarization of single-photon and mesoscopic coherent states. Applications in quantum communication systems are described.

Nascimento, J C; Ramos, R V; Mendonca, Fabio Alencar; Nascimento, Jose Claudio do; Ramos, Rubens Viana

2006-01-01

242

Probability, unitarity, and realism from generally covariant quantum information  

CERN Multimedia

The formalism of covariant quantum theory, introduced by Reisenberger and Rovelli, casts the description of quantum states and evolution into a framework compatable with the principles of general relativity. The leap to this fully covariant formalism, however, outstripped the standard interpretation used to connect quantum theory to experimental predictions, leaving the predictions of the theory ambiguous. Here we discuss in detail some implications of our recently proposed description of covariant quantum information, which addresses these problems. We show explicit agreement with standard quantum mechanics in the appropriate limit. In addition to compatability with general covariance, we show that this framework has other attractive and surprising features -- it is fully unitary, realist, and self-contained. The full unitarity of the formalism in the presence of measurements allows us to invoke time-reversal symmetry to obtain new predictions closely related to the quantum Zeno effect.

Olson, S Jay

2007-01-01

243

Quasi-probability representations of quantum theory with applications to quantum information science  

International Nuclear Information System (INIS)

[en] This paper comprises a review of both the quasi-probability representations of infinite-dimensional quantum theory (including the Wigner function) and the more recently defined quasi-probability representations of finite-dimensional quantum theory. We focus on both the characteristics and applications of these representations with an emphasis toward quantum information theory. We discuss the recently proposed unification of the set of possible quasi-probability representations via frame theory and then discuss the practical relevance of negativity in such representations as a criteria for quantumness.

2011-01-01

244

On the Role of Encoder Side-Information in Source Coding for Multiple Decoders  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We consider a lossy source coding problem where the description of a source is going to be used by two decoders, each having access to information correlated with the source. This side-information is also present at the encoder. We give inner and outer bounds to the set of achievable rate and disto...

Perron, Etienne; Diggavi, Suhas; Telatar, Emre

245

Designing robust gate implementations for quantum information processing  

CERN Document Server

Quantum information processing systems are often operated through time dependent controls; choosing these controls in a way that makes the resulting operation insensitive to variations in unknown or uncontrollable system parameters is an important prerequisite for obtaining high-fidelity gate operations. In this article we present a numerical method for constructing such robust control sequences for a quite general class of quantum information processing systems. As an application of the method we have designed a robust implementation of a phase-shift operation central to rare earth quantum computing, an ensemble quantum computing system proposed by Ohlsson et. al. [Opt. Comm. 201, 71 (2002)]. In this case the method has been used to obtain a high degree of insensitivity with respect to differences between ensemble members, but it is equally well suited for quantum computing with a single physical system.

Wesenberg, J H

2003-01-01

246

Toward an Information-based Interpretation of Quantum Mechanics and the Quantum-Classical Transition  

CERN Document Server

I will show how an objective definition of the concept of information and the consideration of recent results about information-processing in the human brain help clarify some fundamental and often counter-intuitive aspects of quantum mechanics. In particular, I will discuss entanglement, teleportation, non-interaction measurements and decoherence in the light of the fact that pragmatic information, the one our brain handles, can only be defined in the classical macroscopic domain; it does not operate in the quantum domain. This justifies viewing quantum mechanics as a discipline dealing with mathematical models and procedures aimed exclusively at predicting possible macroscopic changes and their likelihood that a given quantum system may cause when it interacts with its environment, including man-made devices such as measurement instruments. I will discuss the informational and neurobiological reasons of why counter-intuitive aspects arise whenever we attempt to construct mental images of the "inner workings...

Roederer, Juan G

2011-01-01

247

Smooth R\\'enyi Entropy of Ergodic Quantum Information Sources  

CERN Multimedia

We prove that the average smooth Renyi entropy rate will approach the entropy rate of a stationary, ergodic information source, which is equal to the Shannon entropy rate for a classical information source and the von Neumann entropy rate for a quantum information source.

Schoenmakers, Berry; Tuyls, Pim; Verbitskiy, Evgeny

2007-01-01

248

Classical information capacities for a class of quantum memory channels  

CERN Multimedia

The maximum rates for information transmission through noisy quantum channels has primarily been developed for memoryless channels, where the noise on each transmitted state is treated as independent. Many real world communication channels experience noise which is modelled better by errors that are correlated between separate channel uses. In this paper, the classical information capacities of a class of quantum memory channels are derived. The class of channels consists of fixed-point indecomposable quantum memory channels, a generalization of classical indecomposable finite-state channels.

Bowen, G; Mancini, S; Bowen, Garry; Devetak, Igor; Mancini, Stefano

2003-01-01

249

Complete methods set for scalable ion trap quantum information processing.  

UK PubMed Central (United Kingdom)

Large-scale quantum information processors must be able to transport and maintain quantum information and repeatedly perform logical operations. Here, we show a combination of all of the fundamental elements required to perform scalable quantum computing through the use of qubits stored in the internal states of trapped atomic ions. We quantified the repeatability of a multiple-qubit operation and observed no loss of performance despite qubit transport over macroscopic distances. Key to these results is the use of different pairs of 9Be+ hyperfine states for robust qubit storage, readout, and gates, and simultaneous trapping of 24Mg+ "re-cooling" ions along with the qubit ions.

Home JP; Hanneke D; Jost JD; Amini JM; Leibfried D; Wineland DJ

2009-09-01

250

Temporal encoding of spatial information during active visual fixation.  

UK PubMed Central (United Kingdom)

Humans and other species continually perform microscopic eye movements, even when attending to a single point. These movements, which include drifts and microsaccades, are under oculomotor control, elicit strong neural responses, and have been thought to serve important functions. The influence of these fixational eye movements on the acquisition and neural processing of visual information remains unclear. Here, we show that during viewing of natural scenes, microscopic eye movements carry out a crucial information-processing step: they remove predictable correlations in natural scenes by equalizing the spatial power of the retinal image within the frequency range of ganglion cells' peak sensitivity. This transformation, which had been attributed to center-surround receptive field organization, occurs prior to any neural processing and reveals a form of matching between the statistics of natural images and those of normal eye movements. We further show that the combined effect of microscopic eye movements and retinal receptive field organization is to convert spatial luminance discontinuities into synchronous firing events, beginning the process of edge detection. Thus, microscopic eye movements are fundamental to two goals of early visual processing: redundancy reduction and feature extraction.

Kuang X; Poletti M; Victor JD; Rucci M

2012-03-01

251

Initialization and Readout of Spin Chains for Quantum Information Transport  

CERN Multimedia

Linear chains of spins acting as quantum wires are a promising approach to achieve scalable quantum information processors. Nuclear spins in apatite crystals provide an ideal test-bed for the experimental study of quantum information transport, as they closely emulate a one-dimensional spin chain. Nuclear Magnetic Resonance techniques can be used to drive the spin chain dynamics and probe the accompanying transport mechanisms. Here we demonstrate initialization and readout capabilities in these spin chains, even in the absence of single-spin addressability. These control schemes enable preparing desired states for quantum information transport and probing their evolution under the transport Hamiltonian. We further optimize the control schemes by a detailed analysis of $^{19}$F NMR lineshape.

Kaur, Gurneet

2011-01-01

252

Quantum Kolmogorov Complexity and Information-Disturbance Theorem  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper, a representation of the information-disturbance theorem based on the quantum Kolmogorov complexity that was defined by P. Vit´anyi has been examined. In the quantum information theory, the information-disturbance relationship, which treats the trade-off relationship between information gain and its caused disturbance, is a fundamental result that is related to Heisenberg’s uncertainty principle. The problem was formulated in a cryptographic setting and the quantitative relationships between complexities have been derived.

Takayuki Miyadera

2011-01-01

253

QUBIT4MATLAB V3.0: A program package for quantum information science and quantum optics for MATLAB  

CERN Multimedia

A program package for MATLAB is introduced that helps calculations in quantum information science and quantum optics. It has commands for the following operations: (i) Reordering the qudits of a quantum register, computing the reduced state of a quantum register. (ii) Defining important quantum states easily. (iii) Formatted input and output for quantum states and operators. (iv) Constructing operators acting on given qudits of a quantum register and constructing spin chain Hamiltonians. (v) Partial transposition, matrix realignment and other commands related to the detection of quantum entanglement. (vi) Generating random state vectors, random density matrices and random unitaries.

Tóth, Géza

2007-01-01

254

Quantum secret sharing based on quantum error-correcting codes  

Science.gov (United States)

Quantum secret sharing(QSS) is a procedure of sharing classical information or quantum information by using quantum states. This paper presents how to use a [2k - 1, 1, k] quantum error-correcting code (QECC) to implement a quantum (k, 2k - 1) threshold scheme. It also takes advantage of classical enhancement of the [2k - 1, 1, k] QECC to establish a QSS scheme which can share classical information and quantum information simultaneously. Because information is encoded into QECC, these schemes can prevent intercept-resend attacks and be implemented on some noisy channels.

Zhang, Zu-Rong; Liu, Wei-Tao; Li, Cheng-Zu

2011-05-01

255

On the reversible extraction of classical information from a quantum source  

CERN Multimedia

Consider a source E of pure quantum states with von Neumann entropy S. By the quantum source coding theorem, arbitrarily long strings of signals may be encoded asymptotically into S qubits/signal (the Schumacher limit) in such a way that entire strings may be recovered with arbitrarily high fidelity. Suppose that classical storage is free while quantum storage is expensive and suppose that the states of E do not fall into two or more orthogonal subspaces. We show that if E can be compressed with arbitrarily high fidelity into A qubits/signal plus any amount of auxiliary classical storage then A must still be at least as large as the Schumacher limit S of E. Thus no part of the quantum information content of E can be faithfully replaced by classical information. If the states do fall into orthogonal subspaces then A may be less than S, but only by an amount not exceeding the amount of classical information specifying the subspace for a signal from the source.

Barnum, H N; Jozsa, R; Winter, A; Barnum, Howard; Hayden, Patrick; Jozsa, Richard; Winter, Andreas

2000-01-01

256

Neural encoding schemes of tactile information in afferent activity of the vibrissal system.  

UK PubMed Central (United Kingdom)

When rats acquire sensory information by actively moving their vibrissae, a neural code is manifested at different levels of the sensory system. Behavioral studies in tactile discrimination agree that rats can distinguish different roughness surfaces by whisking their vibrissae. The present study explores the existence of neural encoding in the afferent activity of one vibrissal nerve. Two neural encoding schemes based on "events" were proposed (cumulative event count and median inter-event time). The events were detected by using an event detection algorithm based on multiscale decomposition of the signal (Continuous Wavelet Transform). The encoding schemes were quantitatively evaluated through the maximum amount of information which was obtained by the Shannon's mutual information formula. Moreover, the effect of difference distances between rat snout and swept surfaces on the information values was also studied. We found that roughness information was encoded by events of 0.8 ms duration in the cumulative event count and event of 1.0 to 1.6 ms duration in the median inter-event count. It was also observed that an extreme decrease of the distance between rat snout and swept surfaces significantly reduces the information values and the capacity to discriminate among the sweep situations.

Farfán FD; Albarracín AL; Felice CJ

2013-02-01

257

Distribution of quantum information between an atom and two photons  

International Nuclear Information System (INIS)

[en] The construction of networks consisting of optically interconnected processing units is a promising way to scale up quantum information processing systems. To store quantum information, single trapped atoms are among the most proven candidates. By placing them in high finesse optical resonators, a bidirectional information exchange between the atoms and photons becomes possible with, in principle, unit efficiency. Such an interface between stationary and ying qubits constitutes a possible node of a future quantum network. The results presented in this thesis demonstrate the prospects of a quantum interface consisting of a single atom trapped within the mode of a high-finesse optical cavity. In a two-step process, we distribute entanglement between the stored atom and two subsequently emitted single photons. The long atom trapping times achieved in the system together with the high photon collection efficiency of the cavity make the applied protocol in principle deterministic, allowing for the creation of an entangled state at the push of a button. Running the protocol on this quasi-stationary quantum interface, the internal state of the atom is entangled with the polarization state of a single emitted photon. The entanglement is generated by driving a vacuum-stimulated Raman adiabatic passage between states of the coupled atom-cavity system. In a second process, the atomic part of the entangled state is mapped onto a second emitted photon using a similar technique and resulting in a polarization-entangled two-photon state. To verify and characterize the photon-photon entanglement, we measured a violation of a Bell inequality and performed a full quantum state tomography. The results prove the prior atom-photon entanglement and demonstrate a quantum information transfer between the atom and the two emitted photons. This reflects the advantages of a high-finesse cavity as a quantum interface in future quantum networks. (orig.)

2008-01-01

258

A four-level single-photon quantum cryptography system based on polarization, phase and time encoding  

CERN Multimedia

We describe a quantum cryptography protocol with up to twelve four-dimensional ($d = 4$) states generated by a polarization-, phase- and time-encoding transmitter. This protocol can be experimentally realized with existing technology, drawing from time-encoded and polarization-encoded systems. The protocol is error tolerant and has a quantum bit-rate of 2 per transmission, which when combined with state detection efficiency yields a qubit efficiency of up to 1 or double that of BB84-{\\it like} protocols. As a practical system, our result appears to contradict a fundamental theorem stating that there exists $d + 1$ maximally non-orthogonal bases for a $d$-dimensional space where $d$ is the power of a prime number. Evidently, this contradiction has its origin in the difference in the size of the vector spaces spanned by the basis states, semi-infinite in time and phase in our case, vs. a finite number of polarization states alone as previously considered.

Buttler, W T; Torgerson, J R

2010-01-01

259

Multiplexed CV quantum teleportation for high rates in quantum communication  

CERN Document Server

A major challenge of today's quantum communication systems lies in the transmission of quantum information with high rates over long distances in the presence of unavoidable losses. Thereby the achievable quantum communication rate is fundamentally limited by the amount of energy that can be transmitted per use of the channel. It is hence vital to develop quantum communication protocols which encode quantum information as energy efficiently as possible. To this aim we investigate continuous-variable quantum teleportation as a method of distributing quantum information. We explore the possibility to encode information on multiple optical modes and derive upper and lower bounds on the achievable quantum channel capacities. This analysis enables us to benchmark single-mode vs. multi-mode entanglement resources. Our research reveals that multiplexing does not only feature an enhanced energy efficiency, significantly increasing the achievable quantum communication rates in comparison to single-mode coding, but als...

Christ, Andreas; Silberhorn, Christine

2012-01-01

260

Three-dimensional information security combined fringe projection with double random phase encoding  

Science.gov (United States)

Three-dimensional (3D) information security with optical fringe projection encoding is proposed. The 3D information about an object, which is encoded into two-dimensional (2D) deformed and reference fringes by optical fringe projection, are encrypted by use of double random phase encoding (DRPE). Deformed and reference fringes, regarded as phase and amplitude respectively, are simultaneously modulated by random phase keys. The key-space is enlarged, because the keys for decryption are not only the random phase masks, but also the calibration parameters of the fringe projection system. The proposed method is robust to noise. Experiment is performed to obtain the reference and deformed fringes. Numerical simulations are employed to verify the validity of the proposed method.

Li, Sikun; Xiao, Yong-Liang; Wang, Xiangzhao

2013-06-01

 
 
 
 
261

Quantum Dots in H1 Photonic Crystal Microcavities for Quantum Information  

Science.gov (United States)

Coupling semiconductor quantum dots to optical microcavities is a promising technique for implementing quantum information processing protocols in the solid-state. By placing one or more emitters in a cavity, it is possible to create an efficient source of single photons or to explore collective interactions of few-emitter systems. Our devices consist of two layers of quantum dots, embedded in the cavity region of H1 photonic crystal microcavities. One of the quantum dot layers can be frequency-tuned deterministically, allowing two resonant quantum dots to be coupled to a single cavity mode. Because good mode-matching between the cavity mode and the input/output channel is necessary for many applications, we optimize the far-field profiles of our H1 cavities and demonstrate strong enhancement of the external mode matching properties. We will discuss our far-field optimization results as well as our ongoing work to study interactions of multiple emitters in a cavity.

Hagemeier, Jenna; Bonato, Cristian; Truong, Tuan-Anh; Kim, Hyochul; Bakker, Morten; Beirne, Gareth J.; van Exter, Martin P.; Petroff, Pierre; Bouwmeester, Dirk

2013-03-01

262

Quantum mechanics with applications to nanotechnology and information science  

CERN Document Server

Quantum mechanics transcends and supplants classical mechanics at the atomic and subatomic levels. It provides the underlying framework for many subfields of physics, chemistry and materials science, including condensed matter physics, atomic physics, molecular physics, quantum chemistry, particle physics, and nuclear physics. It is the only way we can understand the structure of materials, from the semiconductors in our computers to the metal in our automobiles. It is also the scaffolding supporting much of nanoscience and nanotechnology. The purpose of this book is to present the fundamentals of quantum theory within a modern perspective, with emphasis on applications to nanoscience and nanotechnology, and information-technology. As the frontiers of science have advanced, the sort of curriculum adequate for students in the sciences and engineering twenty years ago is no longer satisfactory today. Hence, the emphasis on new topics that are not included in older reference texts, such as quantum information th...

Band, Yehuda B

2013-01-01

263

EDITORIAL: Focus on Quantum Information and Many-Body Theory  

Science.gov (United States)

Quantum many-body models describing natural systems or materials and physical systems assembled piece by piece in the laboratory for the purpose of realizing quantum information processing share an important feature: intricate correlations that originate from the coherent interaction between a large number of constituents. In recent years it has become manifest that the cross-fertilization between research devoted to quantum information science and to quantum many-body physics leads to new ideas, methods, tools, and insights in both fields. Issues of criticality, quantum phase transitions, quantum order and magnetism that play a role in one field find relations to the classical simulation of quantum systems, to error correction and fault tolerance thresholds, to channel capacities and to topological quantum computation, to name but a few. The structural similarities of typical problems in both fields and the potential for pooling of ideas then become manifest. Notably, methods and ideas from quantum information have provided fresh approaches to long-standing problems in strongly correlated systems in the condensed matter context, including both numerical methods and conceptual insights. Focus on quantum information and many-body theory Contents TENSOR NETWORKS Homogeneous multiscale entanglement renormalization ansatz tensor networks for quantum critical systems M Rizzi, S Montangero, P Silvi, V Giovannetti and Rosario Fazio Concatenated tensor network states R Hübener, V Nebendahl and W Dür Entanglement renormalization in free bosonic systems: real-space versus momentum-space renormalization group transforms G Evenbly and G Vidal Finite-size geometric entanglement from tensor network algorithms Qian-Qian Shi, Román Orús, John Ove Fjærestad and Huan-Qiang Zhou Characterizing symmetries in a projected entangled pair state D Pérez-García, M Sanz, C E González-Guillén, M M Wolf and J I Cirac Matrix product operator representations B Pirvu, V Murg, J I Cirac and F Verstraete SIMULATION AND DYNAMICS A quantum differentiation of k-SAT instances B Tamir and G Ortiz Classical Ising model test for quantum circuits Joseph Geraci and Daniel A Lidar Exact matrix product solutions in the Heisenberg picture of an open quantum spin chain S R Clark, J Prior, M J Hartmann, D Jaksch and M B Plenio Exact solution of Markovian master equations for quadratic Fermi systems: thermal baths, open XY spin chains and non-equilibrium phase transition Tomaž Prosen and Bojan Žunkovi? Quantum kinetic Ising models R Augusiak, F M Cucchietti, F Haake and M Lewenstein ENTANGLEMENT AND SPECTRAL PROPERTIES Ground states of unfrustrated spin Hamiltonians satisfy an area law Niel de Beaudrap, Tobias J Osborne and Jens Eisert Correlation density matrices for one-dimensional quantum chains based on the density matrix renormalization group W Münder, A Weichselbaum, A Holzner, Jan von Delft and C L Henley The invariant-comb approach and its relation to the balancedness of multipartite entangled states Andreas Osterloh and Jens Siewert Entanglement scaling of fractional quantum Hall states through geometric deformations Andreas M Läuchli, Emil J Bergholtz and Masudul Haque Entanglement versus gap for one-dimensional spin systems Daniel Gottesman and M B Hastings Entanglement spectra of critical and near-critical systems in one dimension F Pollmann and J E Moore Macroscopic bound entanglement in thermal graph states D Cavalcanti, L Aolita, A Ferraro, A García-Saez and A Acín Entanglement at the quantum phase transition in a harmonic lattice Elisabeth Rieper, Janet Anders and Vlatko Vedral Multipartite entanglement and frustration P Facchi, G Florio, U Marzolino, G Parisi and S Pascazio Entropic uncertainty relations—a survey Stephanie Wehner and Andreas Winter Entanglement in a spin system with inverse square statistical interaction D Giuliano, A Sindona, G Falcone, F Plastina and L Amico APPLICATIONS Time-dependent currents of one-dimensional bosons in an optical lattice J Schachenmayer, G Pupillo and A J Daley Implementing quantum gates using t

Eisert, Jens; Plenio, Martin B.

2010-02-01

264

Dipole Blockade and Quantum Information Processing in Mesoscopic Atomic Ensembles  

Energy Technology Data Exchange (ETDEWEB)

We describe a technique for manipulating quantum information stored in collective states of mesoscopic ensembles. Quantum processing is accomplished by optical excitation into states with strong dipole-dipole interactions. The resulting ''dipole blockade'' can be used to inhibit transitions into all but singly excited collective states. This can be employed for a controlled generation of collective atomic spin states as well as nonclassical photonic states and for scalable quantum logic gates. An example involving a cold Rydberg gas is analyzed.

Lukin, M. D.; Fleischhauer, M.; Cote, R.; Duan, L. M.; Jaksch, D.; Cirac, J. I.; Zoller, P.

2001-07-16

265

Uncertainty principle with quantum Fisher information  

CERN Multimedia

In this paper we prove a nontrivial lower bound for the determinant of the covariance matrix of quantum mechanical observables, which was conjectured by Gibilisco and Isola. The lower bound is given in terms of the commutator of the state and the observables and their scalar product, which is generated by an arbitrary symmetric operator monotone function.

Andai, Attila

2007-01-01

266

Quantum Gloves  

CERN Multimedia

The slogan "information is physical" has been so successful that it led to some excess. Classical and quantum information can be thought of independently of any physical implementation. Pure information tasks can be realized using such abstract c- and qu-bits, but physical tasks require appropriate physical realizations of c- or qu-bits. As illustration we consider the problem of communicating chirality. We discuss in detail the physical resources this necessitates, and introduce the natural concept of "quantum gloves", i.e. rotationally invariant quantum states that encode as much as possible the concept of chirality and nothing more.

Collins, D; Gisin, Nicolas; Massar, S; Popescu, S

2004-01-01

267

Feasibility of two-way polarization encoded quantum communication in an optical fiber populated with telecom traffic  

CERN Multimedia

We experimentally show a two-way transmission of polarization encoded pseudo-single photons between two remote parties separated by a single 23 km optical fiber spool. Two optical classical channels are wavelength multiplexed in the same fiber and used as feedback to an active polarization drift compensation scheme. One of the classical channels contains a 10 Gb/s data stream simulating real telecom traffic. The feasibility of quantum communication is demonstrated in the fiber's two opposite directions of propagation over 6 hours of continuous operation, as well as a classical error rate in the data channel better than 1.0 x 10-9. The results are extended to show the estimated maximum transmission distance for the quantum signals based on the noise generated through Raman spontaneous scattering by up to 16 classical channels present in the fiber.

Xavier, G B; da Silva, T Ferreira; Temporao, G P; von der Weid, J P

2009-01-01

268

Quantum Private Information Retrieval with Sublinear Communication Complexity  

CERN Multimedia

This note presents a quantum protocol for private information retrieval, in the single-server case and with information-theoretical privacy, that has O(\\sqrt{n})-qubit communication complexity, where n denotes the size of the database. In comparison, it is known that any classical protocol must use \\Omega(n) bits of communication in this setting.

Gall, François Le

2011-01-01

269

Quantum-information processing using strongly dipolar coupled nuclear spins  

International Nuclear Information System (INIS)

Dipolar coupled homonuclear spins present challenging, yet useful systems for quantum-information processing. In such systems, the eigenbasis of the system Hamiltonian is the appropriate computational basis and coherent control can be achieved by specially designed strongly modulating pulses. In this paper we describe the first experimental implementation of the quantum algorithm for numerical gradient estimation by nuclear magnetic resonance, using the eigenbasis of a four spin system

2006-01-01

270

Fast, high fidelity information transmission through spin chain quantum wires  

CERN Document Server

Spin chains have been proposed as quantum wires for information transfer in solid state quantum architectures. We show that huge gains in both transfer speed and fidelity are possible using a minimalist control approach that relies only a single, local, on-off switch actuator. Effective switching time sequences can be determined using optimization techniques for both ideal and disordered chains. Simulations suggest that effective optimization is possible even in the absence of accurate models.

Schirmer, S G

2009-01-01

271

Dynamical suppression for decoherence of continuous variable quantum information  

Energy Technology Data Exchange (ETDEWEB)

A quantum master equation is derived in a rigorous way for a bosonic system coupled to a thermal reservoir when phase-modulation {pi}-pulses are applied to the relevant system. It is shown that decoherence of continuous variable quantum information can be suppressed if the pulse separation is shorter than the correlation time of the thermal reservoir. The time-evolutions of nonclassicality and entanglement are investigated.

Ban, Masashi [Graduate School of Humanities and Sciences, Ochanomizu University, 2-1-1 Ohtsuka, Bunkyo-ku, Tokyo 112-8610 (Japan); Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, 1-1-9 Yaesu, Chuo-ku, Tokyo 103-0028 (Japan)], E-mail: m.ban@phys.ocha.ac.jp; Kitajima, Sachiko [Graduate School of Humanities and Sciences, Ochanomizu University, 2-1-1 Ohtsuka, Bunkyo-ku, Tokyo 112-8610 (Japan)], E-mail: sachiko@phys.ocha.ac.jp; Shibata, Fumiaki [Graduate School of Humanities and Sciences, Ochanomizu University, 2-1-1 Ohtsuka, Bunkyo-ku, Tokyo 112-8610 (Japan)], E-mail: shibata@phys.ocha.ac.jp

2007-10-22

272

Quantum engineering of continuous variable quantum states  

Energy Technology Data Exchange (ETDEWEB)

Quantum information with continuous variables is a field attracting increasing attention recently. In continuous variable quantum information one makes use of the continuous information encoded into the quadrature of a quantized light field instead of binary quantities such as the polarization state of a single photon. This brand new research area is witnessing exciting theoretical and experimental achievements such as teleportation, quantum computation and quantum error correction. The rapid development of the field is mainly due higher optical data rates and the availability of simple and efficient manipulation tools in continuous-variable quantum information processing. We in this thesis extend the work in continuous variable quantum information processing and report on novel experiments on amplification, cloning, minimal disturbance and noise erasure protocols. The promising results we obtain in these pioneering experiments indicate that the future of continuous variable quantum information is bright and many advances can be foreseen. (orig.)

Sabuncu, Metin

2009-10-29

273

Quantum information approach to normal representation of extensive games  

CERN Document Server

We modify the concept of quantum strategic game to make it useful for extensive form games. We prove that our modification allows to consider the normal representation of any finite extensive game using the fundamental concepts of quantum information. The Selten's Horse game and the general form of two-stage extensive game with perfect information are studied to illustrate a potential application of our idea. In both examples we use Eisert-Wilkens-Lewenstein approach as well as Marinatto-Weber approach to quantization of games.

Fr\\kackiewicz, Piotr

2011-01-01

274

Information tracking and encoding in early L1: linguistic competence vs. cognitive limitations.  

UK PubMed Central (United Kingdom)

This study provides experimental evidence for preschool children's competence in basic information structure, with particular attention to the notions of topic and focus. It investigates their mastery of structural and definiteness distinctions to encode the information status of discourse referents, and seeks to distinguish linguistic competence from cognitive development as the source for children's 'errors'. Evidence comes from a story-telling experiment performed on 45 children acquiring French (between the ages of 2;6·22 and 5;6·15). The article demonstrates continuity between the child and adult systems of basic discourse representation. It further argues that children's definiteness errors are not due to a lack of knowledge of the adult rules of information encoding. Rather, such errors stem from cognitive limitations and from assuming a wider common ground than adults would.

De Cat C

2011-09-01

275

Entangled world. The fascination of quantum information and computation  

Energy Technology Data Exchange (ETDEWEB)

In the quantum world, a particle can behave like a wave and accordingly seems to be in two places at the same time. This of course is contradictory to our daily experiences with classical particles. How then should this be understood? What happens in the transitional area between the classical world and quantum mechanics? The present book answers exciting questions like these in a way that is easy to follow and to understand and it shows that the link between these two worlds will have concrete and applied effects on our daily life in the near future. It will, for example, improve and change the conventional methods of information processing. With the help of quantum cryptography, it will be possible to communicate tap-proof. Using quantum computers we will be able to solve highly complicated problems in a very short time. (orig.)

Audretsch, J. (ed.)

2006-07-01

276

Entangled world the fascination of quantum information and computation  

CERN Document Server

In the quantum world, a particle can behave like a wave and accordingly seems to be in two places at the same time. This of course is contradictory to our daily experiences with classical particles. How then should this be understood? What happens in the transitional area between the classical world and quantum mechanics? The present book answers exciting questions like these in a way that is easy to follow and to understand and is shows that the link between these two worlds will have concrete and applied effects on our daily life in the near future. It will, for example, improve and change the conventional methods of information processing. With the help of quantum cryptography, it will be possible to communicate tap-proof. Using quantum computers we will be able to solve highly complicated problems in a very short time

2006-01-01

277

Entangled world. The fascination of quantum information and computation  

International Nuclear Information System (INIS)

In the quantum world, a particle can behave like a wave and accordingly seems to be in two places at the same time. This of course is contradictory to our daily experiences with classical particles. How then should this be understood? What happens in the transitional area between the classical world and quantum mechanics? The present book answers exciting questions like these in a way that is easy to follow and to understand and it shows that the link between these two worlds will have concrete and applied effects on our daily life in the near future. It will, for example, improve and change the conventional methods of information processing. With the help of quantum cryptography, it will be possible to communicate tap-proof. Using quantum computers we will be able to solve highly complicated problems in a very short time. (orig.)

2006-01-01

278

On two misconceptions in current relativistic quantum information  

CERN Document Server

We describe two problems current relativistic quantum information suffers from. The first point is an explanation of an alleged ambiguity of entropic quantities detected in a number of publications and incorrectly resolved in [M. Montero and E. Mart{\\i}n-Mart{\\i}nez, Physical Review A 83, 062323 (2011)]. We found that the problem arises due to wrong algebraic manipulations with fermions and ignoring the superselection rule for bosons and fermions. This leads to a misinterpretation of certain entropic quantities when applied to fermion fields. The second discussed point is to alert to a conceptual misunderstanding of the role of entanglement (and quantum correlations in general) in some of the studied relativistic scenarios. Instead, we argue in favor of investigating capacities of quantum channels induced by the relevant physical processes as dictated by quantum Shannon theory.

Bradler, Kamil

2011-01-01

279

The Middle Way between Classical and Quantum Information Processing  

Science.gov (United States)

Classical information processing with shining achievements is approaching the quantum limit in its biannual two-fold way of miniaturization. Research on quantum information processing while developing splendidly is facing the hurdle on scaling the collection of quantum objects to an operating system of human scale. Is there a Middle way? The answer, some of us believe, is in the mesoscopic systems. The Middle Way is in the balancing act between the quantum and the classical. The aim is to search for answers to the questions of whether and how the ``quantum weirdness'' can have effects in the classical realm and provide innovation for devices. There may be a tradeoff between the frailty in a single particle as a qubit and the distinguishability between many-particle states. In miniaturization for high packing density of the memory bit, there may be two views of superparamagnetism: (i) as the blurring of two magnetization states for the bit to be stifled by the static shape anisotropy at the price of switching difficulty, (ii) as a density matrix of two states with dynamic stabilization turned on as needed and off during state control. I will discuss a possible approach starting from the quantum treatment and trying to connect with the classical behavior as the size of the system increases. For concreteness, the discussions will focus on a ferromagnet with 10^3 to 10^5 electron spins and a single semiconductor quantum dot of the same range of the number of nuclear spins. The objectives are the differences and connections between the semiclassical theories and the all-quantum theories and their consequences and prospects in finding new physics and applications in the Middle Way. I thank my many collaborators for the actual work described here and absolve them from my conjectures.

Sham, L. J.

2013-03-01

280

Decoding Reality The Universe as Quantum Information  

CERN Multimedia

For a physicist, all the world's information. The Universe and its workings are the ebb and flow of information. We are all transient patterns of information, passing on the recipe for our basic forms to future generations using a four-letter digital code called DNA. In this engaging and mind-stretching account, Vlatko Vedral considers some of the deepest questions about the Universe and considers the implications of interpreting it in terms of information. He explains the nature of information, the idea of entropy, and the roots of this thinking in thermodynamics. He describes the bizarre eff

Vedral, Vlatko

2010-01-01

 
 
 
 
281

Information gain versus coupling strength in quantum measurements  

CERN Multimedia

We investigate the relationship between the information gain and the interaction strength between the quantum system and the measuring device. A strategy is proposed to calculate the information gain of the measuring device as the coupling strength is a variable. For qubit systems, we prove that the information gain increases monotonically with the coupling strength. It is obtained that the information gain of the projective measurement along the x-direction reduces with the increasing of the measurement strength along the z-direction, and a complementarity of information gain in the measurements along those two directions is presented.

Zhu, Xuanmin; Liu, Quanhui; Wu, Shengjun

2012-01-01

282

H1 photonic crystal cavitites for hybrid quantum information protocols  

CERN Multimedia

Hybrid quantum information protocols are based on local qubits, such as trapped atoms, NV centers, and quantum dots, coupled to photons. The coupling is achieved through optical cavities. Here we demonstrate far-field optimized H1 photonic crystal membrane cavities combined with an additional back reflection mirror below the membrane that meet the optical requirements for implementing hybrid quantum information protocols. Using numerical optimization we find that 80% of the light can be radiated within an objective numerical aperture of 0.8, and the coupling to a single-mode fiber can be as high as 92%. We experimentally prove the unique external mode matching properties by resonant reflection spectroscopy with a cavity mode visibility above 50%.

Hagemeier, Jenna; Truong, Tuan-Anh; Kim, Hyochul; Beirne, Gareth J; Bakker, Morten; van Exter, Martin P; Luo, Yunqiu; Petroff, Pierre; Bouwmeester, Dirk

2012-01-01

283

H1 photonic crystal cavities for hybrid quantum information protocols.  

UK PubMed Central (United Kingdom)

Hybrid quantum information protocols are based on local qubits, such as trapped atoms, NV centers, and quantum dots, coupled to photons. The coupling is achieved through optical cavities. Here we demonstrate far-field optimized H1 photonic crystal membrane cavities combined with an additional back reflection mirror below the membrane that meet the optical requirements for implementing hybrid quantum information protocols. Using numerical optimization we find that 80% of the light can be radiated within an objective numerical aperture of 0.8, and the coupling to a single-mode fiber can be as high as 92%. We experimentally prove the unique external mode matching properties by resonant reflection spectroscopy with a cavity mode visibility above 50%.

Hagemeier J; Bonato C; Truong TA; Kim H; Beirne GJ; Bakker M; van Exter MP; Luo Y; Petroff P; Bouwmeester D

2012-10-01

284

H1 photonic crystal cavities for hybrid quantum information protocols.  

Science.gov (United States)

Hybrid quantum information protocols are based on local qubits, such as trapped atoms, NV centers, and quantum dots, coupled to photons. The coupling is achieved through optical cavities. Here we demonstrate far-field optimized H1 photonic crystal membrane cavities combined with an additional back reflection mirror below the membrane that meet the optical requirements for implementing hybrid quantum information protocols. Using numerical optimization we find that 80% of the light can be radiated within an objective numerical aperture of 0.8, and the coupling to a single-mode fiber can be as high as 92%. We experimentally prove the unique external mode matching properties by resonant reflection spectroscopy with a cavity mode visibility above 50%. PMID:23187235

Hagemeier, Jenna; Bonato, Cristian; Truong, Tuan-Anh; Kim, Hyochul; Beirne, Gareth J; Bakker, Morten; van Exter, Martin P; Luo, Yunqiu; Petroff, Pierre; Bouwmeester, Dirk

2012-10-22

285

Quantum metrology and information processing with entangled atoms  

International Nuclear Information System (INIS)

Full text: Our group at NIST is interested in the metrological and information-processing applications of state-engineered and entangled atoms, in particular, trapped atomic ions. One driver for the experimental work has been the prospect of realizing a quantum computer, but demonstrations of simple computing algorithms also elucidate fundamental aspects of entangled quantum systems. In addition, we are applying the elements of quantum information processing to such topics as increasing the signal-to-noise ratio in spectroscopy and atomic clocks. Future work is, in part, devoted to scaling to larger numbers of entangled ions. Work in collaboration with D. Leibfried, M. D. Barrett, J. C. Bergquist, R. B. Blakestad, J. Bollinger, J. Britton, J. Chiaverini, D. Hume, W. M. Itano, M. Jensen, J. D. Jost, E. Knill, J. Koelemeij, C. Langer, W. Oskay, R. Ozeri, R. Reichle, T. Rosenband, T. Schaetz, P. Schmidt, and S. Seidelin. (author)

2005-01-01

286

Decoherence, Control, and Symmetry in Quantum Computers  

CERN Multimedia

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

Bacon, D J

2003-01-01

287

Full polarization control for fiber optical quantum communication systems using polarization encoding  

CERN Multimedia

A real-time polarization control system employing two nonorthogonal reference signals multiplexed in either time or wavelength with the data signal is presented. It is shown, theoretically and experimentally, that complete control of multiple polarization states can be attained employing polarization controllers in closed-loop configuration. Experimental results show that negligible added penalties, corresponding to an average added optical Quantum Bit Error Rate of 0.044%, can be achieved with response times smaller than 10 ms, without significant introduction of noise counts in the quantum channel.

Xavier, G B; Temporao, G P; von der Weid, J P

2007-01-01

288

Encoding geometric and non-geometric information: a study with evolved agents.  

Science.gov (United States)

Vertebrate species use geometric information and non-geometric or featural cues to orient. Under some circumstances, when both geometric and non-geometric information are available, the geometric information overwhelms non-geometric cues (geometric primacy). In other cases, we observe the inverse tendency or the successful integration of both cues. In past years, modular explanations have been proposed for the geometric primacy: geometric and non-geometric information are processed separately, with the geometry module playing a dominant role. The modularity issue is related to the recent debate on the encoding of geometric information: is it innate or does it depend on environmental experience? In order to get insight into the mechanisms that cause the wide variety of behaviors observed in nature, we used Artificial Life experiments. We demonstrated that agents trained mainly with a single class of information oriented efficiently when they were exposed to one class of information (geometric or non-geometric). When they were tested in environments that contained both classes of information, they displayed a primacy for the information that they had experienced more during their training phase. Encoding and processing geometric and non-geometric information was run in a single cognitive neuro-representation. These findings represent a theoretical proof that the exposure frequency to different spatial information during a learning/adaptive history could produce agents with no modular neuro-cognitive systems that are able to process different types of spatial information and display various orientation behaviors (geometric primacy, non-geometric primacy, no primacy at all). PMID:19582489

Ponticorvo, Michela; Miglino, Orazio

2009-07-07

289

Encoding geometric and non-geometric information: a study with evolved agents.  

UK PubMed Central (United Kingdom)

Vertebrate species use geometric information and non-geometric or featural cues to orient. Under some circumstances, when both geometric and non-geometric information are available, the geometric information overwhelms non-geometric cues (geometric primacy). In other cases, we observe the inverse tendency or the successful integration of both cues. In past years, modular explanations have been proposed for the geometric primacy: geometric and non-geometric information are processed separately, with the geometry module playing a dominant role. The modularity issue is related to the recent debate on the encoding of geometric information: is it innate or does it depend on environmental experience? In order to get insight into the mechanisms that cause the wide variety of behaviors observed in nature, we used Artificial Life experiments. We demonstrated that agents trained mainly with a single class of information oriented efficiently when they were exposed to one class of information (geometric or non-geometric). When they were tested in environments that contained both classes of information, they displayed a primacy for the information that they had experienced more during their training phase. Encoding and processing geometric and non-geometric information was run in a single cognitive neuro-representation. These findings represent a theoretical proof that the exposure frequency to different spatial information during a learning/adaptive history could produce agents with no modular neuro-cognitive systems that are able to process different types of spatial information and display various orientation behaviors (geometric primacy, non-geometric primacy, no primacy at all).

Ponticorvo M; Miglino O

2010-01-01

290

Mathematical Modeling of Physical and Engineering Systems in Quantum Information  

CERN Document Server

Several concrete examples in quantum information are discussed to demonstrate the importance of proper modeling that relates the mathematical description to real-world applications. In particular, it is shown that some commonly accepted conclusions are not adequately supported by their purported justifications in the logical manner required.

Yuen, H P

2007-01-01

291

Quantum information processing, operational quantum logic, convexity, and the foundations of physics  

CERN Multimedia

Quantum information science is a source of task-related axioms whose consequences can be explored in general settings encompassing quantum mechanics, classical theory, and more. Quantum states are compendia of probabilities for the outcomes of possible operations we may perform a system: ``operational states.'' I discuss general frameworks for ``operational theories'' (sets of possible operational states of a system), in which convexity plays key role. The main technical content of the paper is in a theorem that any such theory naturally gives rise to a ``weak effect algebra'' when outcomes having the same probability in all states are identified, and in the introduction of a notion of ``operation algebra'' that also takes account of sequential and conditional operations. Such frameworks are appropriate for investigating what things look like from an ``inside view,'' i.e. for describing perspectival information that one subsystem of the world can have about another. Understanding how such views can combine, a...

Barnum, H

2003-01-01

292

Post-translational modification: nature's escape from genetic imprisonment and the basis for dynamic information encoding.  

UK PubMed Central (United Kingdom)

We discuss protein post-translational modification (PTM) from an information processing perspective. PTM at multiple sites on a protein creates a combinatorial explosion in the number of potential 'mod-forms', or global patterns of modification. Distinct mod-forms can elicit distinct downstream responses, so that the overall response depends partly on the effectiveness of a particular mod-form to elicit a response and partly on the stoichiometry of that mod-form in the molecular population. We introduce the 'mod-form distribution'-the relative stoichiometries of each mod-form-as the most informative measure of a protein's state. Distinct mod-form distributions may summarize information about distinct cellular and physiological conditions and allow downstream processes to interpret this information accordingly. Such information 'encoding' by PTMs may facilitate evolution by weakening the need to directly link upstream conditions to downstream responses. Mod-form distributions provide a quantitative framework in which to interpret ideas of 'PTM codes' that are emerging in several areas of biology, as we show by reviewing examples of ion channels, GPCRs, microtubules, and transcriptional co-regulators. We focus particularly on examples other than the well-known 'histone code', to emphasize the pervasive use of information encoding in molecular biology. Finally, we touch briefly on new methods for measuring mod-form distributions.

Prabakaran S; Lippens G; Steen H; Gunawardena J

2012-11-01

293

The classical capacity of a quantum dense coding system  

Energy Technology Data Exchange (ETDEWEB)

Quantum dense coding transmits classical information by sending a quantum system with the assistance of quantum entanglement. The classical information capacity of a quantum dense coding system is obtained, where a sender and receiver share a completely entangled state and a quantum system encoded by applying unitary operators is sent through an arbitrary quantum channel. The result is compared with that obtained in another setting. (letter to the editor)

Ban, Masashi [Advanced Research Laboratory, Hitachi, Ltd, 2520 Akanuma, Hatoyama, Saitama 350-0395 (Japan); Kitajima, Sachiko [Graduate School of Humanities and Sciences, Ochanomizu University, 2-1-1 Ohtsuka, Bunkyo-ku, Tokyo 112-8610 (Japan); Shibata, Fumiaki [Department of Physics, Faculty of Science, Ochanomizu University, 2-1-1 Ohtsuka, Bunkyo-ku, Tokyo 112-8610 (Japan)

2004-09-03

294

Hybrid ququart-encoded quantum cryptography protected by Kochen-Specker contextuality  

CERN Document Server

Quantum cryptographic protocols based on complementarity are nonsecure against attacks in which complementarity is imitated with classical resources. The Kochen-Specker (KS) theorem provides protection against these attacks, without requiring entanglement or spatially separated composite systems. We analyze the maximum tolerated noise to guarantee the security of a KS-protected cryptographic scheme against these attacks, and describe a photonic realization of this scheme using hybrid ququarts defined by the polarization and orbital angular momentum of single photons.

Cabello, Adan; Nagali, Eleonora; Sciarrino, Fabio; 10.1103/PhysRevA.84.030302

2011-01-01

295

Hybrid ququart-encoded quantum cryptography protected by Kochen-Specker contextuality  

Science.gov (United States)

Quantum cryptographic protocols based on complementarity are not secure against attacks in which complementarity is imitated with classical resources. The Kochen-Specker (KS) theorem provides protection against these attacks, without requiring entanglement or spatially separated composite systems. We analyze the maximum tolerated noise to guarantee the security of a KS-protected cryptographic scheme against these attacks and describe a photonic realization of this scheme using hybrid ququarts defined by the polarization and orbital angular momentum of single photons.

Cabello, Adán; D'Ambrosio, Vincenzo; Nagali, Eleonora; Sciarrino, Fabio

2011-09-01

296

Hybrid ququart-encoded quantum cryptography protected by Kochen-Specker contextuality  

International Nuclear Information System (INIS)

Quantum cryptographic protocols based on complementarity are not secure against attacks in which complementarity is imitated with classical resources. The Kochen-Specker (KS) theorem provides protection against these attacks, without requiring entanglement or spatially separated composite systems. We analyze the maximum tolerated noise to guarantee the security of a KS-protected cryptographic scheme against these attacks and describe a photonic realization of this scheme using hybrid ququarts defined by the polarization and orbital angular momentum of single photons.

2011-01-01

297

Hybrid ququart-encoded quantum cryptography protected by Kochen-Specker contextuality  

Energy Technology Data Exchange (ETDEWEB)

Quantum cryptographic protocols based on complementarity are not secure against attacks in which complementarity is imitated with classical resources. The Kochen-Specker (KS) theorem provides protection against these attacks, without requiring entanglement or spatially separated composite systems. We analyze the maximum tolerated noise to guarantee the security of a KS-protected cryptographic scheme against these attacks and describe a photonic realization of this scheme using hybrid ququarts defined by the polarization and orbital angular momentum of single photons.

Cabello, Adan [Departamento de Fisica Aplicada II, Universidad de Sevilla, E-41012 Sevilla (Spain); Department of Physics, Stockholm University, S-10691 Stockholm (Sweden); D' Ambrosio, Vincenzo; Nagali, Eleonora [Dipartimento di Fisica della ' ' Sapienza' ' Universita di Roma, I-00185 Roma (Italy); Sciarrino, Fabio [Dipartimento di Fisica della ' ' Sapienza' ' Universita di Roma, I-00185 Roma (Italy); Istituto Nazionale di Ottica, Consiglio Nazionale delle Ricerche (INO-CNR), I-50125 Florence (Italy)

2011-09-15

298

Efficient Quantum State Tomography for Quantum Information Processing using a two-dimensional Fourier Transform Technique  

CERN Multimedia

A new method of quantum state tomography for quantum information processing is described. The method based on two-dimensional Fourier transform technique involves detection of all the off-diagonal elements of the density matrix in a two-dimensional experiment. All the diagonal elements are detected in another one-dimensional experiment. The method is efficient and applicable to a wide range of spin systems. The proposed method is explained using a 2 qubit system and demonstrated by tomographing arbitrary complex density matrices of 2 and 4 qubit systems using simulations.

Das, R; Kumar, A; Das, Ranabir; Kumar, Anil

2002-01-01

299

Quantum Mechanical Model for Information Transfer from DNA to Protein  

CERN Multimedia

A model for the information transfer from DNA to protein using quantum information and computation techniques is presented. DNA is modeled as the sender and proteins are modeled as the receiver of this information. On the DNA side, a 64-dimensional Hilbert space is used to describe the information stored in DNA triplets (codons). A Hamiltonian matrix is constructed for this space, using the 64 possible codons as base states. The eigenvalues of this matrix are not degenerate. The genetic code is degenerate and proteins comprise only 20 different amino acids. Since information is conserved, the information on the protein side is also described by a 64-dimensional Hilbert space, but the eigenvalues of the corresponding Hamiltonian matrix are degenerate. Each amino acid is described by a Hilbert subspace. This change in Hilbert space structure reflects the nature of the processes involved in information transfer from DNA to protein.

Karafyllidis, Ioannis G

2008-01-01

300

High Efficiency Photon Number Detection for Quantum Information Processing  

CERN Multimedia

The Visible Light Photon Counter (VLPC) features high quantum efficiency and low pulse height dispersion. These properties make it ideal for efficient photon number state detection. The ability to perform efficient photon number state detection is important in many quantum information processing applications, including recent proposals for performing quantum computation with linear optical elements. In this paper we investigate the unique capabilities of the VLPC. The efficiency of the detector and cryogenic system is measured at 543nm wavelengths to be 85%. A picosecond pulsed laser is then used to excite the detector with pulses having average photon numbers ranging from 3-5. The output of the VLPC is used to discriminate photon numbers in a pulse. The error probability for number state discrimination is an increasing function of the number of photons, due to buildup of multiplication noise. This puts an ultimate limit on the ability of the VLPC to do number state detection. For many applications, it is suf...

Waks, E; Diamanti, E; Yamamoto, Y; Waks, Edo; Inoue, Kyo; Diamanti, Eleni; Yamamoto, Yoshihisa

2003-01-01

 
 
 
 
301

A Framework for Non-Asymptotic Quantum Information Theory  

CERN Multimedia

This thesis consolidates, improves and extends the smooth entropy framework for non-asymptotic information theory and cryptography. We investigate the conditional min- and max-entropy for quantum states, generalizations of classical R\\'enyi entropies. We introduce the purified distance, a novel metric for unnormalized quantum states and use it to define smooth entropies as optimizations of the min- and max-entropies over a ball of close states. We explore various properties of these entropies, including data-processing inequalities, chain rules and their classical limits. The most important property is an entropic formulation of the asymptotic equipartition property, which implies that the smooth entropies converge to the von Neumann entropy in the limit of many independent copies. The smooth entropies also satisfy duality and entropic uncertainty relations that provide limits on the power of two different observers to predict the outcome of a measurement on a quantum system. Finally, we discuss three example...

Tomamichel, Marco

2012-01-01

302

Encoding Subsystem Codes  

CERN Document Server

In this paper we investigate the encoding of operator quantum error correcting codes i.e. subsystem codes. We show that encoding of subsystem codes can be reduced to encoding of a related stabilizer code making it possible to use all the known results on encoding of stabilizer codes. Along the way we also show how Clifford codes can be encoded. We also show that gauge qubits can be exploited to reduce the encoding complexity.

Sarvepalli, Pradeep Kiran

2008-01-01

303

Rhythmic modulation of ? oscillations supports encoding of spatial and behavioral information in the rat hippocampus.  

Science.gov (United States)

Oscillatory patterns of activity in various frequency ranges are ubiquitously expressed in cortical circuits. While recent studies in humans emphasized rhythmic modulations of neuronal oscillations ("second-order" rhythms), their potential involvement in information coding remains an open question. Here, we show that a rhythmic (~0.7 Hz) modulation of hippocampal theta power, unraveled by second-order spectral analysis, supports encoding of spatial and behavioral information. The phase preference of neuronal discharge within this slow rhythm significantly increases the amount of information carried by action potentials in various motor/cognitive behaviors by (1) distinguishing between the spikes fired within versus outside the place field of hippocampal place cells, (2) disambiguating place firing of neurons having multiple place fields, and (3) predicting between alternative future spatial trajectories. This finding demonstrates the relevance of second-order spectral components of brain rhythms for decoding neuronal information. PMID:22958828

Molter, Colin; O'Neill, Joseph; Yamaguchi, Yoko; Hirase, Hajime; Leinekugel, Xavier

2012-09-01

304

Rhythmic modulation of ? oscillations supports encoding of spatial and behavioral information in the rat hippocampus.  

UK PubMed Central (United Kingdom)

Oscillatory patterns of activity in various frequency ranges are ubiquitously expressed in cortical circuits. While recent studies in humans emphasized rhythmic modulations of neuronal oscillations ("second-order" rhythms), their potential involvement in information coding remains an open question. Here, we show that a rhythmic (~0.7 Hz) modulation of hippocampal theta power, unraveled by second-order spectral analysis, supports encoding of spatial and behavioral information. The phase preference of neuronal discharge within this slow rhythm significantly increases the amount of information carried by action potentials in various motor/cognitive behaviors by (1) distinguishing between the spikes fired within versus outside the place field of hippocampal place cells, (2) disambiguating place firing of neurons having multiple place fields, and (3) predicting between alternative future spatial trajectories. This finding demonstrates the relevance of second-order spectral components of brain rhythms for decoding neuronal information.

Molter C; O'Neill J; Yamaguchi Y; Hirase H; Leinekugel X

2012-09-01

305

Understanding Entanglement as a Resource for Quantum Information Processing  

Science.gov (United States)

Ever since Erwin Schrodinger shocked the physics world by killing (and not killing) his cat, entanglement has played a critical role in attempts to understand quantum mechanics. More recently, entanglement has been shown to be a valuable resource, of central importance for quantum computation and the processing of quantum information. In this talk, I will describe a new diagrammatic approach to understanding why entanglement is so valuable, the key idea being that entanglement between two systems ``creates'' multiple images of the state of a third. By way of example, I will show how to ``visualize'' teleportation of unknown quantum states, and how to use entanglement to determine the (unknown) state of a spatially distributed, multipartite quantum system. Illustrative examples of this entanglement-assisted local state discrimination are sets of orthogonal product states exhibiting what is known as ``non-locality without entanglement'', including unextendible product bases. These ideas have also proven useful in using entanglement to implement a unitary interaction between spatially separated (and therefore non-interacting!) systems.

Cohen, Scott M.

2009-03-01

306

Color information security system using Arnold transform and double structured phase encoding in gyrator transform domain  

Science.gov (United States)

A new method for encoding color information based on Arnold transform and double structured phase encoding in gyrator transform domain is introduced. The phase function of Fresnel zone plate is used as structured phase mask. Prior to the encryption, the decomposed red, green, and blue components of the color image are independently permutated by Arnold transform, transmitted through structured phase mask, and then performed gyrator transform. The system parameters of Arnold transform, structured phase mask, and gyrator transform in each component image provide as encryption keys of the scheme. The proposed system avoids problems arising from misalignment. The optical implementation has also been proposed. Numerical simulations' results are presented to verify the security, validity, and possibility of the proposed approach.

Abuturab, Muhammad Rafiq

2013-02-01

307

Characterizing the structure of preserved information in quantum processes.  

Science.gov (United States)

We introduce a general operational characterization of information-preserving structures-encompassing noiseless subsystems, decoherence-free subspaces, pointer bases, and error-correcting codes-by demonstrating that they are isometric to fixed points of unital quantum processes. Using this, we show that every information-preserving structure is a matrix algebra. We further establish a structure theorem for the fixed states and observables of an arbitrary process, which unifies the Schrödinger and Heisenberg pictures, places restrictions on physically allowed kinds of information, and provides an efficient algorithm for finding all noiseless and unitarily noiseless subsystems of the process. PMID:18232952

Blume-Kohout, Robin; Ng, Hui Khoon; Poulin, David; Viola, Lorenza

2008-01-22

308

Characterizing the structure of preserved information in quantum processes.  

UK PubMed Central (United Kingdom)

We introduce a general operational characterization of information-preserving structures-encompassing noiseless subsystems, decoherence-free subspaces, pointer bases, and error-correcting codes-by demonstrating that they are isometric to fixed points of unital quantum processes. Using this, we show that every information-preserving structure is a matrix algebra. We further establish a structure theorem for the fixed states and observables of an arbitrary process, which unifies the Schrödinger and Heisenberg pictures, places restrictions on physically allowed kinds of information, and provides an efficient algorithm for finding all noiseless and unitarily noiseless subsystems of the process.

Blume-Kohout R; Ng HK; Poulin D; Viola L

2008-01-01

309

Arbitrary waveform generator for quantum information processing with trapped ions.  

UK PubMed Central (United Kingdom)

Atomic ions confined in multi-electrode traps have been proposed as a basis for scalable quantum information processing. This scheme involves transporting ions between spatially distinct locations by use of time-varying electric potentials combined with laser or microwave pulses for quantum logic in specific locations. We report the development of a fast multi-channel arbitrary waveform generator for applying the time-varying electric potentials used for transport and for shaping quantum logic pulses. The generator is based on a field-programmable gate array controlled ensemble of 16-bit digital-to-analog converters with an update frequency of 50 MHz and an output range of ±10 V. The update rate of the waveform generator is much faster than relevant motional frequencies of the confined ions in our experiments, allowing diabatic control of the ion motion. Numerous pre-loaded sets of time-varying voltages can be selected with 40 ns latency conditioned on real-time signals. Here we describe the device and demonstrate some of its uses in ion-based quantum information experiments, including speed-up of ion transport and the shaping of laser and microwave pulses.

Bowler R; Warring U; Britton JW; Sawyer BC; Amini J

2013-03-01

310

Topics in quantum information--continuous quantum measurements and quantum walks  

Science.gov (United States)

The topics presented in this thesis have continuous quantum measurements and quantum walks at their core. The first topic being discussed centers around simulating a generalize measurement with a finite number of outcomes using a continuous measurement process with a continuous measurement history. We provide conditions under which it is possible to prove that such a process exists and that at long times it simulates faithfully the generalized measurement. We give the stochastic equations governing the feedback between the measurement history and the instantaneous weak measurements. The second topic examines a definition of "hitting time" for continuous-time quantum walks. A crucial component for such a definition is the use of weak measurements. Several methods using alternative but equivalent definitions of weak, continuous measurements are employed to derive a formula for the hitting time. The behavior of the thus defined hitting time is studied subsequently, in general and for specific graphs. The last topic explores continuous-time quantum walks on graphs with infinite tails. The equations for propagating and bound states are derived and the S-matrix is defined. Their properties, such as orthogonality of the propagating and bound states, unitarity of the S-matrix, are discussed. Formulas for the S-matrix under operations of cutting, adding or connecting tails are derived.

Varbanov, Martin

311

Algorithmic Information Theoretic Issues in Quantum Mechanics  

UK PubMed Central (United Kingdom)

ContentsI Preliminaries 20.1 Warning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30.2 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . 30.3 Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40.4 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10II Equivalent characterizations of classical algorithmicrandomness 161 Classical algorithmic randomness as classical algorithmic incompressibility1.1 The distinction between mathematical-classicality and physicalclassicality. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171.2 Uspensky's abstract denition of algorithmic information . . . . 251.3 Why prex algorithmic entropy is better than simple algorithmicentropy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331.4 Chaitin random strings and sequences of cbits . . . . . . . . . . . 391.5 Brudno random sequences of cbits . . . . . . . . . . . . . . . . .

Gavriel Segre Phd Thesis

312

Quantum walks of correlated photons.  

UK PubMed Central (United Kingdom)

Quantum walks of correlated particles offer the possibility of studying large-scale quantum interference; simulating biological, chemical, and physical systems; and providing a route to universal quantum computation. We have demonstrated quantum walks of two identical photons in an array of 21 continuously evanescently coupled waveguides in a SiO(x)N(y) chip. We observed quantum correlations, violating a classical limit by 76 standard deviations, and found that the correlations depended critically on the input state of the quantum walk. These results present a powerful approach to achieving quantum walks with correlated particles to encode information in an exponentially larger state space.

Peruzzo A; Lobino M; Matthews JC; Matsuda N; Politi A; Poulios K; Zhou XQ; Lahini Y; Ismail N; Wörhoff K; Bromberg Y; Silberberg Y; Thompson MG; OBrien JL

2010-09-01

313

Quantum walks of correlated particles  

CERN Multimedia

Quantum walks of correlated particles offer the possibility to study large-scale quantum interference, simulate biological, chemical and physical systems, and a route to universal quantum computation. Here we demonstrate quantum walks of two identical photons in an array of 21 continuously evanescently-coupled waveguides in a SiOxNy chip. We observe quantum correlations, violating a classical limit by 76 standard deviations, and find that they depend critically on the input state of the quantum walk. These results open the way to a powerful approach to quantum walks using correlated particles to encode information in an exponentially larger state space.

Peruzzo, Alberto; Matthews, Jonathan C F; Matsuda, Nobuyuki; Politi, Alberto; Poulios, Konstantinos; Zhou, Xiao-Qi; Lahini, Yoav; Ismail, Nur; Wörhoff, Kerstin; Bromberg, Yaron; Silberberg, Yaron; Thompson, Mark G; O'Brien, Jeremy L

2010-01-01

314

Parallel Information Transfer in a Multi-Node Quantum Information Processor  

CERN Multimedia

We describe a method for coupling disjoint quantum bits (qubits) in different local processing nodes of a distributed node quantum information processor. An effective channel for information transfer between nodes is obtained by moving the system into an interaction frame where all pairs of cross-node qubits are effectively coupled via an exchange interaction between actuator elements of each node. All control is achieved via actuator-only modulation, leading to fast implementations of a universal set of internode quantum gates. The method is expected to be nearly independent of actuator decoherence and may be made insensitive to experimental variations of system parameters by appropriate design of control sequences. We show, in particular, how the induced cross-node coupling channel may be used to swap the complete quantum states of the local processors in parallel.

Borneman, Troy W; Cory, David G

2011-01-01

315

Adaptive Controller Design for Faulty UAVs via Quantum Information Technology  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper, an adaptive controller is designed for a UAV flight control system against faults and parametric uncertainties based on quantum information technology and the Popov hyperstability theory. First, considering the bounded control input, the state feedback controller is designed to make the system stable. The model of adaptive control is introduced to eliminate the impact by the uncertainties of system parameters via quantum information technology. Then, according to the model reference adaptive principle, an adaptive control law based on the Popov hyperstability theory is designed. This law enable better robustness of the flight control system and tracking control performances. The closed?loop system’s stability is guaranteed by the Popov hyperstability theory. The simulation results demonstrate that a better dynamic performance of the UAV flight control system with faults and parametric uncertainties can be maintained with the proposed method.

Fuyang Chen; Rui Hou; Gang Tao

2012-01-01

316

Quantum Kolmogorov Complexity and Bounded Quantum Memory  

CERN Multimedia

In this study, the effect of bounded quantum memory in a primitive information protocol has been examined using the quantum Kolmogorov complexity as a measure of information. We employed a toy two-party protocol in which Bob by using a bounded quantum memory and an unbounded classical memory estimates a message that was encoded in qubits by Alice in one of the bases X or Z. Our theorem gave a nontrivial effect of the memory boundedness. In addition, a generalization of the uncertainty principle in the presence of quantum memory has been obtained.

Miyadera, Takayuki

2011-01-01

317

Quantum Rate-Distortion Coding  

CERN Document Server

I introduce rate-distortion theory for quantum coding, and derive a lower bound, involving the coherent information, on the rate at which qubits must be used to encode a quantum source with a given maximum level of distortion per source emission. The convexity of the "information rate-distortion function" which defines this bound is also derived.

Barnum, H N

1998-01-01

318

Optomechanical quantum information processing with photons and phonons  

CERN Multimedia

We describe how strong resonant interactions in multimode optomechanical systems can be used to induce controlled nonlinear couplings between single photons and phonons. Combined with linear mapping schemes between photons and phonons, these techniques provide a universal building block for various classical and quantum information processing applications. Our approach is especially suited for nano-optomechanical devices, where strong optomechanical coupling on a single photon level is within experimental reach.

Stannigel, K; Habraken, S J M; Bennett, S D; Lukin, M D; Zoller, P; Rabl, P

2012-01-01

319

The Quantum-Classical Transition as an Information Flow  

Directory of Open Access Journals (Sweden)

Full Text Available We investigate the classical limit of the semiclassical evolution with reference to a well-known model that represents the interaction between matter and a given field. This is done by recourse to a special statistical quantifier called the “symbolic transfer entropy”. We encounter that the quantum-classical transition gets thereby described as the sign-reversal of the dominating direction of the information flow between classical and quantal variables.

Andres M. Kowalski; Maria T. Martin; Luciano Zunino; Angelo Plastino; Montserrat Casas

2010-01-01

320

Visible light photon counters optimization for quantum information applications  

Energy Technology Data Exchange (ETDEWEB)

In this paper we describe the studies of the main parameters needed for optimal operation of Visible Light Photon Counters (VLPCs) when used in quantum information systems. The isolation of the single photon signal is analyzed through the definition of a contamination parameter. A compromise in the minimization of this parameter for temperature, bias voltage and dark count variation must be achieved and this depends on the experimental conditions.

Molina, J.; /Rio de Janeiro State U.; Estrada, J.; Bross, A.; /Fermilab; Ginther, G.; /Rochester U.; Buscher, V.; /Freiburg U.

2006-10-01

 
 
 
 
321

Private quantum decoupling and secure disposal of information  

Energy Technology Data Exchange (ETDEWEB)

Given a bipartite system, correlations between its subsystems can be understood as the information that each one carries about the other. In order to give a model-independent description of secure information disposal, we propose the paradigm of private quantum decoupling, corresponding to locally reducing correlations in a given bipartite quantum state without transferring them to the environment. In this framework, the concept of private local randomness naturally arises as a resource, and total correlations are divided into eliminable and ineliminable ones. We prove upper and lower bounds on the quantity of ineliminable correlations present in an arbitrary bipartite state, and show that, in tripartite pure states, ineliminable correlations satisfy a monogamy constraint, making apparent their quantum nature. A relation with entanglement theory is provided by showing that ineliminable correlations constitute an entanglement parameter. In the limit of infinitely many copies of the initial state provided, we compute the regularized ineliminable correlations to be measured by the coherent information, which is thus equipped with a new operational interpretation. In particular, our results imply that two subsystems can be privately decoupled if their joint state is separable.

Buscemi, Francesco [Institute for Advanced Research, Nagoya University (Japan)], E-mail: buscemi@iar.nagoya-u.ac.jp

2009-12-15

322

Private quantum decoupling and secure disposal of information  

International Nuclear Information System (INIS)

Given a bipartite system, correlations between its subsystems can be understood as the information that each one carries about the other. In order to give a model-independent description of secure information disposal, we propose the paradigm of private quantum decoupling, corresponding to locally reducing correlations in a given bipartite quantum state without transferring them to the environment. In this framework, the concept of private local randomness naturally arises as a resource, and total correlations are divided into eliminable and ineliminable ones. We prove upper and lower bounds on the quantity of ineliminable correlations present in an arbitrary bipartite state, and show that, in tripartite pure states, ineliminable correlations satisfy a monogamy constraint, making apparent their quantum nature. A relation with entanglement theory is provided by showing that ineliminable correlations constitute an entanglement parameter. In the limit of infinitely many copies of the initial state provided, we compute the regularized ineliminable correlations to be measured by the coherent information, which is thus equipped with a new operational interpretation. In particular, our results imply that two subsystems can be privately decoupled if their joint state is separable.

2009-01-01

323

Multi-photon entanglement and applications in quantum information  

International Nuclear Information System (INIS)

In this thesis, two new linear optics networks are introduced and their application for several quantum information tasks is presented. Spontaneous parametric down conversion, is used in different configurations to provide the input states for the networks. The first network is a new design of a controlled phase gate which is particularly interesting for applications in multi-photon experiments as it constitutes an improvement of former realizations with respect to stability and reliability. This is explicitly demonstrated by employing the gate in four-photon experiments. In this context, a teleportation and entanglement swapping protocol is performed in which all four Bell states are distinguished by means of the phase gate. A similar type of measurement applied to the subsystem parts of two copies of a quantum state, allows further the direct estimation of the state's entanglement in terms of its concurrence. Finally, starting from two Bell states, the controlled phase gate is applied for the observation of a four photon cluster state. The analysis of the results focuses on measurement based quantum computation, the main usage of cluster states. The second network, fed with the second order emission of non-collinear type ii spontaneous parametric down conversion, constitutes a tunable source of a whole family of states. Up to now the observation of one particular state required one individually tailored setup. With the network introduced here many different states can be obtained within the same arrangement by tuning a single, easily accessible experimental parameter. These states exhibit many useful properties and play a central role in several applications of quantum information. Here, they are used for the solution of a four-player quantum Minority game. It is shown that, by employing four-qubit entanglement, the quantum version of the game clearly outperforms its classical counterpart. Experimental data obtained with both networks are utilized to demonstrate a new method for the experimental discrimination of different multi-partite entangled states. The new tool presented here is based on operators which are formed by the correlations between local measurement settings that are typical for the respective quantum state. (orig.)

2008-01-01

324

Experimental continuous variable cloning of partial quantum information  

CERN Multimedia

The fidelity of a quantum transformation is strongly linked with the prior partial information of the state to be transformed. We illustrate this interesting point by proposing and demonstrating the superior cloning of coherent states with prior partial information. More specifically, we propose two simple transformations that under the Gaussian assumption optimally clone symmetric Gaussian distributions of coherent states as well as coherent states with known phases. Furthermore, we implement for the first time near-optimal state-dependent cloning schemes relying on simple linear optics and feedforward.

Sabuncu, Metin; Andersen, Ulrik L

2008-01-01

325

Information-disturbance tradeoff in sending direction information via antiparallel quantum spin  

International Nuclear Information System (INIS)

When sending unknown direction information, antiparallel spins contain more direction information than parallel spins (Gisin and Popescu 1999 Phys. Rev. Lett. 83 432). In this paper, the optimal information-disturbance tradeoff bound for antiparallel spins is derived. The quantum measurements which attain the optimal tradeoff bound are obtained. This result can be of practical relevance for posing some general limits on Eve's eavesdropping process. Finally, we also present a comparison between the bound for antiparallel spins and the bound for parallel spins.

2010-06-11

326

Fault-Tolerant Storage of Quantum Information by Large Block Codes  

Science.gov (United States)

An important issue in the implementation of a quantum computer is to protect quantum information from decoherence. Concatenated quantum codes and topological quantum codes are extensively studied for fault-tolerant quantum computation. However, there is not much research on large block codes in any fault-tolerant scheme. Here we propose a method for storage of quantum information by a large block code, which has a high code rate and high distance. To access or protect the quantum information stored in a large block code requires only the fault-tolerant implementation of the gates from the Clifford group. We derive the lifetime of the quantum information stored in a large block code by CSS code construction.

Lai, Ching-Yi; Brun, Todd

2013-03-01

327

Quantum stochastics and information statistics, filtering and control  

CERN Multimedia

Quantum stochastic calculus has become an indispensable tool in modern quantum physics, its effectiveness being illustrated by recent developments in quantum control which place the calculus at the heart of the theory. Quantum statistics is rapidly taking shape as an intrinsically quantum counterpart to classical statistics, motivated by advances in quantum engineering and the need for better statistical inference tools for quantum systems.This volume contains a selection of regular research articles and reviews by leading researchers in quantum control, quantum statistics, quantum probability

Belavkin, V P

2008-01-01

328

Two-Way Quantum Communication: `Secure Quantum Information Exchange'-II. Generalization to Arbitrary Number of Qubits  

CERN Multimedia

In this paper, we generalize the secure quantum information exchange (SQIE) protocol, originally proposed by the authors [J. Phys. B: At. Mol. Opt. Phys. 44 (2011) 115504] for secure exchange of one qubit information with each of Alice and Bob, to the case of secure exchange of quantum information of arbitrary qubits with Alice and Bob. We also discuss security of the original and generalized SQIE protocols with respect to the number of qubits with controller, Charlie.

Maurya, Ajay K; Prakash, Hari

2011-01-01

329

Information-theoretic approach to quantum error correction and reversible measurement  

CERN Document Server

Quantum operations provide a general description of the state changes allowed by quantum mechanics. The reversal of quantum operations is important for quantum error-correcting codes, teleportation, and reversing quantum measurements. We derive information-theoretic conditions and equivalent algebraic conditions that are necessary and sufficient for a general quantum operation to be reversible. We analyze the thermodynamic cost of error correction and show that error correction can be regarded as a kind of ``Maxwell demon,'' for which there is an entropy cost associated with information obtained from measurements performed during error correction. A prescription for thermodynamically efficient error correction is given.

Nielsen, M A; Schumacher, B; Barnum, H N; Caves, Carlton M.; Schumacher, Benjamin; Barnum, Howard

1997-01-01

330

Decoherence of quantum information in the non-Markovian qubit channel  

Energy Technology Data Exchange (ETDEWEB)

Decoherence of quantum information of qubits is investigated under the influence of the non-Markovian quantum channel, where the correlation time of reservoir variables takes a finite value. Degradation of purity, distinguishability and entanglement of qubit states are evaluated. It is found that the non-Markov effect makes the coherence time of quantum information longer than that obtained for the Markovian quantum channel. Furthermore, the quantum teleportation and quantum dense coding of qubits are considered under the influence of non-Markov channels. The fidelity between teleported and original states and the Holevo capacity are obtained.

Ban, Masashi [Advanced Research Laboratory, Hitachi Ltd, 2520 Akanuma, Hatoyama, Saitama 350-0395 (Japan); Kitajima, Sachiko [Department of Physics, Faculty of Science, Ochanomizu University, 2-1-1 Ohtsuka, Bunkyo-ku, Tokyo 112-8610 (Japan); Shibata, Fumiaki [Department of Physics, Faculty of Science, Ochanomizu University, 2-1-1 Ohtsuka, Bunkyo-ku, Tokyo 112-8610 (Japan)

2005-08-12

331

Quantum physics of nature. Theory, experiment and interpretation. in collaboration with 6th European QIPC workshop. General Information, program, abstracts  

International Nuclear Information System (INIS)

Quantum information processing and communication is one of the of the key research areas within the European community. Therefore these two events were dedicated to present the advances in this area. Papers dealing with topics such as atom-photon entanglement, matter waves and quantum gases, decoherence, photonic entanglement, solid state quantum physics, cooling and trapping of atoms and molecules, quantum communication, quantum computation, quantum information and quantum cryptography were addressed. (nevyjel)

2005-01-01

332

A versatile source of single photons for quantum information processing.  

UK PubMed Central (United Kingdom)

The generation of high-quality single-photon states with controllable narrow spectral bandwidths and central frequencies is key to facilitate efficient coupling of any atomic system to non-classical light fields. Such an interaction is essential in numerous experiments for fundamental science and applications in quantum communication and information processing, as well as in quantum metrology. Here we implement a fully tunable, narrow-band and efficient single-photon source based on a whispering gallery mode resonator. Our disk-shaped, monolithic and intrinsically stable resonator is made of lithium niobate and supports a cavity-assisted spontaneous parametric down-conversion process. The generated photon pairs are emitted into two highly tunable resonator modes. We verify wavelength tuning over 100 nm of both modes with controllable bandwidth between 7.2 and 13 MHz. Heralding of single photons yields anti-bunching with g(2)(0)<0.2.

Förtsch M; Fürst JU; Wittmann C; Strekalov D; Aiello A; Chekhova MV; Silberhorn C; Leuchs G; Marquardt C

2013-01-01

333

Quantum Information Processing by NMR using strongly coupled spins  

CERN Multimedia

The enormous theoretical potential of Quantum Information processing (QIP) is driving the pursuit for its practical realization by various physical techniques. Currently Nuclear Magnetic Resonance (NMR) has been the forerunner by demonstrating a majority of quantum algorithms. In NMR, spin systems consisting of coupled nuclear spins are utilized as qubits. In order to carry out QIP, a spin system has to meet two major requirements: (i) qubit addressability and (ii) mutual coupling among the qubits. It has been demonstrated that the magnitude of the mutual coupling among qubits can be increased by orienting the spin-systems in a liquid crystal matrix and utilizing the residual dipolar couplings. While utilizing residual dipolar coupling may be useful to increase the number of qubits, nuclei of same species might become strongly coupled. In strongly coupled spin-systems, spins loose their individual identity of being qubits. We propose that even such strongly coupled spin-systems can be used for QIP and the qub...

Mahesh, T S; Levitt, M H; Ramanathan, K V; Kumar, A; Sinha, Neeraj; Levitt, Malcolm H.; Kumar, Anil

2003-01-01

334

Microfabrication techniques for trapped ion quantum information processing  

CERN Document Server

Quantum-mechanical principles can be used to process information (QIP). In one approach, linear arrays of trapped, laser cooled ion qubits (two-level quantum systems) are confined in segmented multi-zone electrode structures. The ion trap approach to QIP requires trapping and control of numerous ions in electrode structures with many trapping zones. I investigated microfabrication of structures to trap, transport and couple large numbers of ions. Using 24Mg+ I demonstrated loading and transport between zones in microtraps made of boron doped silicon. This thesis describes the fundamentals of ion trapping, the characteristics of silicon-based traps amenable to QIP work and apparatus to trap ions and characterize traps. Microfabrication instructions appropriate for nonexperts are included. Ion motional heating was measured. Using MEMs techniques I built a Si micro-mechanical oscillator and demonstrated a method to reduce the kinetic energy of its lowest order mechanical mode via capacitive coupling to a driven...

Britton, Joe

2010-01-01

335

A versatile source of single photons for quantum information processing.  

Science.gov (United States)

The generation of high-quality single-photon states with controllable narrow spectral bandwidths and central frequencies is key to facilitate efficient coupling of any atomic system to non-classical light fields. Such an interaction is essential in numerous experiments for fundamental science and applications in quantum communication and information processing, as well as in quantum metrology. Here we implement a fully tunable, narrow-band and efficient single-photon source based on a whispering gallery mode resonator. Our disk-shaped, monolithic and intrinsically stable resonator is made of lithium niobate and supports a cavity-assisted spontaneous parametric down-conversion process. The generated photon pairs are emitted into two highly tunable resonator modes. We verify wavelength tuning over 100 nm of both modes with controllable bandwidth between 7.2 and 13 MHz. Heralding of single photons yields anti-bunching with g(2)(0)<0.2. PMID:23652006

Förtsch, Michael; Fürst, Josef U; Wittmann, Christoffer; Strekalov, Dmitry; Aiello, Andrea; Chekhova, Maria V; Silberhorn, Christine; Leuchs, Gerd; Marquardt, Christoph

2013-01-01

336

Accuracy of quantum-state estimation utilizing Akaike's information criterion  

International Nuclear Information System (INIS)

We report our theoretical and experimental investigations into errors in quantum-state estimation, putting a special emphasis on their asymptotic behavior. Tomographic measurements and maximum likelihood estimation are used for estimating several kinds of identically prepared quantum states (biphoton polarization states) produced via spontaneous parametric down-conversion. Excess errors in the estimation procedures are eliminated by introducing an estimation strategy utilizing Akaike's information criterion. We make a quantitative comparison between the errors of the experimentally estimated states and their asymptotic lower bounds, which are derived from the Cramer-Rao inequality. Our results reveal the influence of entanglement on the errors in the estimation. An alternative measurement strategy employing inseparable measurements is also discussed, and its performance is numerically explored.

2003-01-01

337

Information Geometry of Quantum Entangled Gaussian Wave-Packets  

CERN Document Server

Describing and understanding the essence of quantum entanglement and its connection to dynamical chaos is of great scientific interest. In this work, using information geometric (IG) techniques, we investigate the effects of micro-correlations on the evolution of maximal probability paths on statistical manifolds induced by systems whose microscopic degrees of freedom are Gaussian distributed. We use the statistical manifolds associated with correlated and non-correlated Gaussians to model the scattering induced quantum entanglement of two spinless, structureless, non-relativistic particles, the latter represented by minimum uncertainty Gaussian wave-packets. Knowing that the degree of entanglement is quantified by the purity P of the system, we express the purity for s-wave scattering in terms of the micro-correlation coefficient r - a quantity that parameterizes the correlated microscopic degrees of freedom of the system; thus establishing a connection between entanglement and micro-correlations. Moreover, ...

Kim, D -H; Cafaro, C; Mancini, S

2011-01-01

338

Channel kets, entangled states, and the location of quantum information  

CERN Document Server

The well-known duality relating entangled states and noisy quantum channels is expressed in terms of a channel ket, a pure state on a suitable tripartite system, which functions as a pre-probability allowing the calculation of statistical correlations between, for example, the entrance and exit of a channel, once a framework has been chosen so as to allow a consistent set of probabilities. In each framework the standard notions of ordinary (classical) information theory apply, and it makes sense to ask whether information of a particular sort about one system is or is not present in another system. Quantum effects arise when a single pre-probability is used to compute statistical correlations in different incompatible frameworks, and various constraints on the presence and absence of different kinds of information are expressed in a set of all-or-nothing theorems which generalize or give a precise meaning to the concept of ``no-cloning.'' These theorems are used to discuss: the location of information in quan...

Griffiths, R B

2004-01-01

339

Quantum fidelity in the thermodynamic limit.  

UK PubMed Central (United Kingdom)

We study quantum fidelity, the overlap between two ground states of a many-body system, focusing on the thermodynamic regime. We show how a drop in fidelity near a critical point encodes universal information about a quantum phase transition. Our general scaling results are illustrated in the quantum Ising chain for which a remarkably simple expression for fidelity is found.

Rams MM; Damski B

2011-02-01

340

Control of quantum information flow and quantum correlations in the two-atom Tavis-Cummings model  

Science.gov (United States)

We investigate the quantum information of the two non-interacting two-level atoms coupled to a single mode of the cavity field via selective measurements. It is found that the information of the two atoms can be protected by intensive measurements and can be enhanced by a single measurement which is demonstrated by the growth of the trace distance between two marginal states of the two atoms, as well as the positive information flow in the first instance. We also show that the single measurement is effective for enhancing the quantum information flow, which leads to the increase of quantum correlations including concurrence and quantum discord. Moreover, we explore the behaviour of total information measured by the trace distance when the total system is initially in its thermal equilibrium state and how the atom-cavity coupling and the temperature affect the total correlation for the thermal state of the entire system.

Hu, Zheng-Da; Xu, Jing-Bo

2013-04-01

 
 
 
 
341

A quantum information perspective of fermionic quantum many-body systems  

International Nuclear Information System (INIS)

In this Thesis fermionic quantum many-body system are theoretically investigated from a quantum information perspective. Quantum correlations in fermionic many-body systems, though central to many of the most fascinating effects of condensed matter physics, are poorly understood from a theoretical perspective. Even the notion of ''paired'' fermions which is widely used in the theory of superconductivity and has a clear physical meaning there, is not a concept of a systematic and mathematical theory so far. Applying concepts and tools from entanglement theory, we close this gap, developing a pairing theory allowing to unambiguously characterize paired states. We develop methods for the detection and quantification of pairing according to our definition which are applicable to current experimental setups. Pairing is shown to be a quantum correlation distinct from any notion of entanglement proposed for fermionic systems, giving further understanding of the structure of highly correlated quantum states. In addition, we show the resource character of paired states for precision metrology, proving that BCS-states allow phase measurements at the Heisenberg limit. Next, the power of fermionic systems is considered in the context of quantum simulations, where we study the possibility to simulate Hamiltonian time evolutions on a cubic lattice under the constraint of translational invariance. Given a set of translationally invariant local Hamiltonians and short range interactions we determine time evolutions which can and those which can not be simulated. Bosonic and finite-dimensional quantum systems (''spins'') are included in our investigations. Furthermore, we develop new techniques for the classical simulation of fermionic many-body systems. First, we introduce a new family of states, the fermionic Projected Entangled Pair States (fPEPS) on lattices in arbitrary spatial dimension. These are the natural generalization of the PEPS known for spin systems, and they approximate efficiently ground and thermal states of systems with short-range interaction. We give an explicit mapping between fPEPS and PEPS, allowing to extend previous simulation methods to fermions. In addition, we show that fPEPS naturally arise as exact ground states of certain fermionic Hamiltonians, and give an example that exhibits criticality while fulfilling the area law. Finally, we derive methods for the determination of ground and thermal states, as well as the time evolution, of interacting fermionic systems using generalized Hartree-Fock theory (gHFT). With the computational complexity scaling polynomially with the number of particles, this method can deal with large systems. As a benchmark we apply our methods to the translationally invariant Hubbard model with attractive interaction and find excellent agreement with known results. (orig.)

2009-01-01

342

Entanglement boosts quantum turbo codes  

CERN Multimedia

One of the unexpected breakdowns in the existing theory of quantum serial turbo coding is that a quantum convolutional encoder cannot simultaneously be recursive and non-catastrophic. These properties are essential for a quantum turbo code to have an unbounded minimum distance and for its iterative decoding algorithm to converge, respectively. Here, we show that the entanglement-assisted paradigm gives a theoretical and practical "turbo boost" to these codes, in the sense that an entanglement-assisted quantum (EAQ) convolutional encoder can possess both of the aforementioned desirable properties, and simulation results indicate that entanglement-assisted turbo codes can operate reliably in a noise regime 5.5 dB beyond that of standard quantum turbo codes. Entanglement is the resource that enables a convolutional encoder to satisfy both properties because an encoder acting on only information qubits, classical bits, gauge qubits, and ancilla qubits cannot simultaneously satisfy them. We give several examples o...

Wilde, Mark M

2010-01-01

343

Quantum computers.  

Science.gov (United States)

Over the past several decades, quantum information science has emerged to seek answers to the question: can we gain some advantage by storing, transmitting and processing information encoded in systems that exhibit unique quantum properties? Today it is understood that the answer is yes, and many research groups around the world are working towards the highly ambitious technological goal of building a quantum computer, which would dramatically improve computational power for particular tasks. A number of physical systems, spanning much of modern physics, are being developed for quantum computation. However, it remains unclear which technology, if any, will ultimately prove successful. Here we describe the latest developments for each of the leading approaches and explain the major challenges for the future. PMID:20203602

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

2010-03-01

344

Quantum computers.  

UK PubMed Central (United Kingdom)

Over the past several decades, quantum information science has emerged to seek answers to the question: can we gain some advantage by storing, transmitting and processing information encoded in systems that exhibit unique quantum properties? Today it is understood that the answer is yes, and many research groups around the world are working towards the highly ambitious technological goal of building a quantum computer, which would dramatically improve computational power for particular tasks. A number of physical systems, spanning much of modern physics, are being developed for quantum computation. However, it remains unclear which technology, if any, will ultimately prove successful. Here we describe the latest developments for each of the leading approaches and explain the major challenges for the future.

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

2010-03-01

345

Quantum Computing  

CERN Document Server

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

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

2010-01-01

346

Arbitrary Waveform Generator for Quantum Information Processing with Trapped Ions  

CERN Multimedia

Atomic ions confined in multi-electrode traps have been proposed as a basis for scalable quantum information processing. This scheme involves transporting ions between spatially distinct locations by use of time-varying electric potentials combined with laser or microwave pulses for quantum logic in specific locations. We report the development of a fast multi-channel arbitrary waveform generator for applying the time-varying electric potentials used for transport and for shaping quantum logic pulses. The generator is based on a field-programmable gate array controlled ensemble of 16-bit digital-to-analog converters with an update frequency of 50 MHz and an output range of $\\pm$10 V. The update rate of the waveform generator is much faster than relevant motional frequencies of the confined ions in our experiments, allowing diabatic control of the ion motion. Numerous pre-loaded sets of time-varying voltages can be selected with 40 ns latency conditioned on real-time signals. Here we describe the device and de...

Bowler, R; Britton, J W; Sawyer, B C; Amini, J

2013-01-01

347

Experimental Noiseless Filtering of Continuous-Variable Quantum Information  

CERN Multimedia

We propose and experimentally demonstrate the non destructive and noiseless removal (filtering) of vacuum noise from an arbitrary set of coherent states of continuous variable systems. Noise or errors in the quantum information are diagnosed through a weak measurement, and on that basis, probabilistically filtered out. We consider three different filters based on phase stabilized and phase randomized homodyne detection and on/off detection. We find that on/off detection, optimal in the ideal setting, is superior to the homodyne strategy in a practical setting.

Wittmann, C; Andersen, U L; Filip, R; Marek, P; Leuchs, G

2007-01-01

348

Information flow during the quantum-classical transition  

International Nuclear Information System (INIS)

We have exhaustively investigated the classical limit of the semi-classical evolution with reference to a well-known model that represents the interaction between matter and a given field. In this Letter we approach this issue by recourse to a new statistical quantifier called the 'symbolic transfer entropy' [T. Schreiber, Phys. Rev. Lett. 85 (2000) 461; M. Staniek, K. Lehnertz, Phys. Rev. Lett. 100 (2008) 158101]. We encounter that the quantum-classical transition gets thereby described as the sign reversal of the dominating direction of the information flow between classical and quantal variables. This can be considered as an evidence of the physical useful of this new statistical quantifier.

2010-04-12

349

Quantum-like model of processing of information in the brain based on classical electromagnetic field  

CERN Multimedia

We propose a model of quantum-like (QL) processing of mental information. This model is based on quantum information theory. However, in contrast to models of ``quantum physical brain'' reducing mental activity (at least at the highest level) to quantum physical phenomena in the brain, our model matches well with the basic neuronal paradigm of the cognitive science. QL information processing is based (surprisingly) on classical electromagnetic signals induced by joint activity of neurons. This novel approach to quantum information is based on representation of quantum mechanics as a version of classical signal theory which was recently elaborated by the author. The brain uses the QL representation (QLR) for working with abstract concepts; concrete images are described by classical information theory. Two processes, classical and QL, are performed parallely. Moreover, information is actively transmitted from one representation to another. A QL concept given in our model by a density operator can generate a var...

Khrennikov, Andrei

2010-01-01

350

State preparation for quantum information science and metrology  

International Nuclear Information System (INIS)

[en] The precise preparation of non-classical states of light is a basic requirement for performing quantum information tasks and quantum metrology. Depending on the assignment, the range of required states varies from preparing and modifying squeezed states to generating bipartite entanglement and establishing multimode entanglement networks. Every state needs special preparation techniques and hence it is important to develop the experimental expertise to generate all states with the desired degree of accuracy. In this thesis, the experimental preparation of different kinds of non-classical states of light is demonstrated. Starting with a multimode entangled state, the preparation of an unconditionally generated bound entangled state of light of unprecedented accuracy is shown. Its existence is of fundamental interest, since it certifies an intrinsic irreversibility of entanglement and suggests a connection with thermodynamics. The state is created in a network of linear optics, utilizing optical parametric amplifiers, operated below threshold, beam splitters and phase gates. The experimental platform developed here afforded the precise and stable control of all experimental parameters. Focusing on the aspect of quantum information networks, the generation of suitable bipartite entangled states of light is desirable. The optical connection between atomic transitions and light that can be transmitted via telecommunications fibers opens the possibility to employ quantum memories within fiber networks. For this purpose, a non-degenerate optical parametric oscillator is operated above threshold and the generation of bright bipartite entanglement between its twin beams at the wavelengths of 810 nm and 1550 nm is demonstrated. In the field of metrology, quantum states are used to enhance the measurement precision of interferometric gravitational wave (GW) detectors. Recently, the sensitivity of a GW detector operated at a wavelength of 1064 nm was increased using squeezed vacuum states. In order to enhance the sensitivity of future GW detectors operating at a wavelength of 532 nm, squeezed vacuum states at this wavelength are required. With this intention, a highly efficient up-conversion of coherent states from 1550 nm to 532 nm is demonstrated. The presented setup is suitable to convert squeezed states in frequency. The preparation of squeezed vacuum states at 1550 nm can be realized with a standard approach using parametric down-conversion, while the transition to 532 nm is achievable by the presented sum-frequency generation process. (orig.)

2012-01-01

351

Displacement encoder  

International Nuclear Information System (INIS)

In an optical encoder, light from an optical fibre input A is encoded by means of the encoding disc and is subsequently collected for transmission via optical fibre B. At some point in the optical path between the fibres A and B, the light is separated into component form by means of a filtering or dispersive system and each colour component is associated with a respective one of the coding channels of the disc. In this way, the significance of each bit of the coded information is represented by a respective colour thereby enabling the components to be re-combined for transmission by the fibre B without loss of information. (author)

1982-02-12

352

Problems in application of LDPC codes to information reconciliation in quantum key distribution protocols  

CERN Document Server

The information reconciliation in a quantum key distribution protocol can be studied separately from other steps in the protocol. The problem of information reconciliation can be reduced to that of distributed source coding. Its solution by LDPC codes is reviewed. We list some obstacles preventing the LDPC-based distributed source coding from becoming a more favorable alternative to the Cascade protocol for information reconciliation in quantum key distribution protocols. This exposition does not require knowledge of the quantum theory.

Matsumoto, Ryutaroh

2009-01-01

353

Precise evaluation of leaked information with universal2 privacy amplification in the presence of quantum attacker  

CERN Multimedia

We treat secret key extraction when the eavesdropper has correlated quantum states. We propose quantum privacy amplification theorems different from Renner's, which are based on quantum conditional Renyi entropy of order 1+s. Using those theorems, we derive an exponential decreasing rate for leaked information and the asymptotic equivocation rate.

Hayashi, Masahito

2012-01-01

354

Generating the Depth Map from the Motion Information of H.264-Encoded 2D Video Sequence  

Directory of Open Access Journals (Sweden)

Full Text Available An efficient method that estimates the depth map of a 3D-scene using the motion information of the H.264-encoded 2D-video is presented. The motion information of the video-frames captured via a single camera is either directly used or modified to approximate the displacement (disparity) that exists between the right and left images when the scene is captured by stereoscopic cameras. Then, depth is estimated based on its inverse relation with disparity. The low-complexity of this method and its compatibility with future broadcasting networks allow its real-time implementation at the receiver; thus 3D-signal is constructed at no additional burden to the network. Performance evaluations show that this method outperforms the other existing H.264-based technique by up to 1.98?dB PSNR, providing more realistic depth information of the scene. Moreover subjective comparisons of the results, obtained by viewers watching the generated stereo video sequences on a 3D-display system, confirm the superiority of our method.

Mahsa T. Pourazad; Panos Nasiopoulos; Rabab K. Ward

2010-01-01

355

Quantum Fisher information of the Greenberg-Horne-Zeilinger state in decoherence channels  

Science.gov (United States)

Quantum Fisher information of a parameter characterizes the sensitivity of the state with respect to changes of the parameter. In this article, we study the quantum Fisher information of a state with respect to SU(2) rotations under three decoherence channels: the amplitude-damping, phase-damping, and depolarizing channels. The initial state is chosen to be a Greenberg-Horne-Zeilinger state of which the phase sensitivity can achieve the Heisenberg limit. By using the Kraus operator representation, the quantum Fisher information is obtained analytically. We observe the decay and sudden change of the quantum Fisher information in all three channels.

Ma, Jian; Huang, Yi-Xiao; Wang, Xiaoguang; Sun, C. P.

2011-08-01

356

QIS-XML: An Extensible Markup Language for Quantum Information Science  

CERN Multimedia

This Master thesis examines issues of interoperability and integration between the Classic Information Science (CIS) and Quantum Information Science (QIS). It provides a short introduction to the Extensible Markup Language (XML) and proceeds to describe the development steps that have lead to a prototype XML specification for quantum computing (QIS-XML). QIS-XML is a proposed framework, based on the widely used standard (XML) to describe, visualize, exchange and process quantum gates and quantum circuits. It also provides a potential approach to a generic programming language for quantum computers through the concept of XML driven compilers. Examples are provided for the description of commonly used quantum gates and circuits, accompanied with tools to visualize them in standard web browsers. An algorithmic example is also presented, performing a simple addition operation with quantum circuits and running the program on a quantum computer simulator. Overall, this initial effort demonstrates how XML technologi...

Heus, Pascal

2011-01-01

357

Atomic quantum computer  

International Nuclear Information System (INIS)

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

1999-10-06

358

Fault-tolerant quantum secret sharing against collective noise  

Energy Technology Data Exchange (ETDEWEB)

We present two robust quantum secret sharing protocols against two kinds of collective noise with single logical qubits. Each logical qubit is encoded in two-qubit noiseless states and so it can function over a quantum channel subjected to a collective noise. The safety of transmission is ensured by nonorthogonality of the noiseless states traveling forward and backward on the quantum channel. Moreover, we construct efficient quantum circuits to implement channel encoding and information encoding by means of primitive operations in quantum computation.

Yang Yuguang; Teng Yiwei; Chai Haiping [College of Computer Science and Technology, Beijing University of Technology, Beijing 100124 (China); Wen Qiaoyan, E-mail: yangyang7357@bjut.edu.cn [State Key Laboratory of Networking and Switching Technology, Beijing University of Posts and Telecommunications, Beijing 100876 (China)

2011-02-15

359

Fault-tolerant quantum secret sharing against collective noise  

International Nuclear Information System (INIS)

We present two robust quantum secret sharing protocols against two kinds of collective noise with single logical qubits. Each logical qubit is encoded in two-qubit noiseless states and so it can function over a quantum channel subjected to a collective noise. The safety of transmission is ensured by nonorthogonality of the noiseless states traveling forward and backward on the quantum channel. Moreover, we construct efficient quantum circuits to implement channel encoding and information encoding by means of primitive operations in quantum computation.

2011-01-01

360

Fault-tolerant quantum secret sharing against collective noise  

Science.gov (United States)

We present two robust quantum secret sharing protocols against two kinds of collective noise with single logical qubits. Each logical qubit is encoded in two-qubit noiseless states and so it can function over a quantum channel subjected to a collective noise. The safety of transmission is ensured by nonorthogonality of the noiseless states traveling forward and backward on the quantum channel. Moreover, we construct efficient quantum circuits to implement channel encoding and information encoding by means of primitive operations in quantum computation.

Yang, Yu-Guang; Teng, Yi-Wei; Chai, Hai-Ping; Wen, Qiao-Yan

2011-02-01

 
 
 
 
361

Relativistic Quantum Communication  

CERN Multimedia

In this Ph.D. thesis, I investigate the communication abilities of non-inertial observers and the precision to which they can measure parametrized states. I introduce relativistic quantum field theory with field quantisation, and the definition and transformations of mode functions in Minkowski, Schwarzschild and Rindler spaces. I introduce information theory by discussing the nature of information, defining the entropic information measures, and highlighting the differences between classical and quantum information. I review the field of relativistic quantum information. We investigate the communication abilities of an inertial observer to a relativistic observer hovering above a Schwarzschild black hole, using the Rindler approximation. We compare both classical communication and quantum entanglement generation of the state merging protocol, for both the single and dual rail encodings. We find that while classical communication remains finite right up to the horizon, the quantum entanglement generation tend...

Hosler, Dominic

2013-01-01

362

Photonic quantum technologies  

CERN Multimedia

The first quantum technology, which harnesses uniquely quantum mechanical effects for its core operation, has arrived in the form of commercially available quantum key distribution systems that achieve enhanced security by encoding information in photons such that information gained by an eavesdropper can be detected. Anticipated future quantum technologies include large-scale secure networks, enhanced measurement and lithography, and quantum information processors, promising exponentially greater computation power for particular tasks. Photonics is destined for a central role in such technologies owing to the need for high-speed transmission and the outstanding low-noise properties of photons. These technologies may use single photons or quantum states of bright laser beams, or both, and will undoubtably apply and drive state-of-the-art developments in photonics.

O'Brien, Jeremy L; Vu?kovi?, Jelena; 10.1038/nphoton.2009.229

2010-01-01

363

Metallized DNA nanolithography for encoding and transferring spatial information for graphene patterning.  

Science.gov (United States)

The vision for graphene and other two-dimensional electronics is the direct production of nanoelectronic circuits and barrier materials from a single precursor sheet. DNA origami and single-stranded tiles are powerful methods to encode complex shapes within a DNA sequence, but their translation to patterning other nanomaterials has been limited. Here we develop a metallized DNA nanolithography that allows transfer of spatial information to pattern two-dimensional nanomaterials capable of plasma etching. Width, orientation and curvature can be programmed by specific sequence design and transferred, as we demonstrate for graphene. Spatial resolution is limited by distortion of the DNA template upon Au metallization and subsequent etching. The metallized DNA mask allows for plasmonic enhanced Raman spectroscopy of the underlying graphene, providing information on defects, doping and lattice symmetry. This DNA nanolithography enables wafer-scale patterning of two-dimensional electronic materials to create diverse circuit elements, including nanorings, three- and four-membered nanojunctions, and extended nanoribbons. PMID:23575667

Jin, Zhong; Sun, Wei; Ke, Yonggang; Shih, Chih-Jen; Paulus, Geraldine L C; Hua Wang, Qing; Mu, Bin; Yin, Peng; Strano, Michael S

2013-01-01

364

A New Approach to Encoding and Hiding Information in an Image  

Directory of Open Access Journals (Sweden)

Full Text Available The information age brings some unique challenges to society. New technology and new applications bring new threats and force us to invent new protection mechanisms. So every few years, computer security needs to reinvent itself. In this paper we propose a new image encoding system utilizing fractal theories; this approach exploits the main feature of fractals generated by IFS techniques. Two levels of encryption and decryption methods performed to enhance the security of the system, this is based on the fact that all fractal functions use real number to ensure satisfaction of contraction property. If the cryptosystem parameters are based on real numbers (a continuous infinite interval) then the search space is massive. Hence, many well known attacks fail to solve the nonlinear systems and find the imprecise secret key parameter from the given public one. Even if it is theoretically possible, it is computationally not feasible. The encrypted date represents the attractor generated by the IFS transformation, Collage theorem is used to find the IFS for decrypting data. The proposed method gives the possibility to hide maximum amount of data in an image that represent the attractor of the IFS without degrading its quality. Also to make the hidden data robust enough to withstand known cryptographic attacks and image processing techniques which do not change the appearance of image. The security level is high because the jointly coded images cannot be correctly reconstructed without all the required information.

Fadhil Salman Abed

2011-01-01

365

Remote Quantum-Information Concentration: Reversal of Ancilla-Free Phase-Covariant Telecloning  

Directory of Open Access Journals (Sweden)

Full Text Available Telecloning and its reverse process, referred to as remote quantum-information concentration (RQIC), have been attracting considerable interest because of their potential applications in quantum-information processing. The previous RQIC protocols were focused on the reverse process of the optimal universal telecloning. We here study the reverse process of ancilla-free phase-covariant telecloning (AFPCT). It is shown that the quantum information originally distributed into two spatially separated qubits from a single qubit via the optimal AFPCT procedure can be remotely concentrated back to a single qubit with a certain probability by using an asymmetric W state as the quantum channel.

Xinwen Wang; Shiqing Tang

2013-01-01

366

A gradient system on the quantum information space realizing the averaged learning equation of Hebb type  

CERN Document Server

The averaged learning equation (ALEH) applicable to the principal component analyzer is studied from both quantum information geometry and dynamical system viewpoints. On the quantum information space (QIS), the space of regular density matrices endowed with the quantum SLD-Fisher metric, a gradient system is given as an extension of the ALEH; on the submanifold, consisting of the diagonal matrices, of the QIS, the gradient flow coincides with the ALEH up to a local diffeomorphism.

Uwano, Yoshio

2009-01-01

367

Quantum information technology with Sagnac interferometer: Interaction-free measurement, quantum key distribution and quantum secret sharing  

CERN Multimedia

The interferometry of single-photon pulses has been used to implement quantum technology systems, like quantum key distribution, interaction-free measurement and some other quantum communication protocols. In most of these implementations, Mach-Zehnder, Michelson and Fabry-Perot interferometers are the most used. In this work we present optical setups for interaction-free measurement, quantum key distribution and quantum secret sharing using the Sagnac interferometer. The proposed setups are described as well the quantum protocols using them are explained.

de Brito, Wellington Alves

2007-01-01

368

On a Loss of Information in a Transition from Quantum to a Quasi-Classical Regime  

Directory of Open Access Journals (Sweden)

Full Text Available By defining information entropy in terms of the probability density |Ï?|2 (Ï? is a wave function in the coordinate representation) it is explicitly shown how a loss of quantum information occurs in a transition from a quantum to a quasi-classical regime.

Alex Granik

2004-01-01

369

Myoelectric Control of Artificial Limb by Quantum Information Processing  

CERN Document Server

Precise and elegant coordination of a prosthesis across many degrees of freedom is highly desired for rehabilitation of people with limb deficiency. Processing the electrical neural signals, collected from the surface of the remnant muscles of the stump, is a common way to activate certain function of the artificial limb. Based on the assumption that there are distinguishable and repeatable signal patterns among different types of muscular activation, the problem of the prosthesis control reduces to the pattern recognition. Widely accepted classical methods for pattern recognition, however, can not provide simultaneous and proportional control of the artificial limb. Here we show that quantum information processing of the neural signals allows us to overcome above difficulties suggesting a very simple scheme for myoelectric control of artificial limb with advanced functionalities.

Siomau, Michael

2013-01-01

370

Bounds on the information rate of quantum-secret-sharing schemes  

International Nuclear Information System (INIS)

An important metric of the performance of a quantum-secret-sharing scheme is its information rate. Beyond the fact that the information rate is upper-bounded by one, very little is known in terms of bounds on the information rate of quantum-secret-sharing schemes. Furthermore, not every scheme can be realized with rate one. In this paper we derive upper bounds for the information rates of quantum-secret-sharing schemes. We show that there exist quantum access structures on n players for which the information rate cannot be better than O((log2n)/n). These results are the quantum analogues of the bounds for classical-secret-sharing schemes proved by Csirmaz.

2011-01-01

371

Quantum microbiology.  

Science.gov (United States)

During his famous 1943 lecture series at Trinity College Dublin, the reknown physicist Erwin Schrodinger discussed the failure and challenges of interpreting life by classical physics alone and that a new approach, rooted in Quantum principles, must be involved. Quantum events are simply a level of organization below the molecular level. This includes the atomic and subatomic makeup of matter in microbial metabolism and structures, as well as the organic, genetic information code of DNA and RNA. Quantum events at this time do not elucidate, for example, how specific genetic instructions were first encoded in an organic genetic code in microbial cells capable of growth and division, and its subsequent evolution over 3.6 to 4 billion years. However, due to recent technological advances, biologists and physicists are starting to demonstrate linkages between various quantum principles like quantum tunneling, entanglement and coherence in biological processes illustrating that nature has exerted some level quantum control to optimize various processes in living organisms. In this article we explore the role of quantum events in microbial processes and endeavor to show that after nearly 67 years, Schrödinger was prophetic and visionary in his view of quantum theory and its connection with some of the fundamental mechanisms of life. PMID:21368338

Trevors, J T; Masson, L

2011-03-02

372

Quantum microbiology.  

UK PubMed Central (United Kingdom)

During his famous 1943 lecture series at Trinity College Dublin, the reknown physicist Erwin Schrodinger discussed the failure and challenges of interpreting life by classical physics alone and that a new approach, rooted in Quantum principles, must be involved. Quantum events are simply a level of organization below the molecular level. This includes the atomic and subatomic makeup of matter in microbial metabolism and structures, as well as the organic, genetic information code of DNA and RNA. Quantum events at this time do not elucidate, for example, how specific genetic instructions were first encoded in an organic genetic code in microbial cells capable of growth and division, and its subsequent evolution over 3.6 to 4 billion years. However, due to recent technological advances, biologists and physicists are starting to demonstrate linkages between various quantum principles like quantum tunneling, entanglement and coherence in biological processes illustrating that nature has exerted some level quantum control to optimize various processes in living organisms. In this article we explore the role of quantum events in microbial processes and endeavor to show that after nearly 67 years, Schrödinger was prophetic and visionary in his view of quantum theory and its connection with some of the fundamental mechanisms of life.

Trevors JT; Masson L

2011-01-01

373

Probing phase-space noncommutativity through quantum beating, missing information, and the thermodynamic limit  

Science.gov (United States)

In this work we examine the effect of phase-space noncommutativity on some typically quantum properties such as quantum beating, quantum information, and decoherence. To exemplify these issues we consider the two-dimensional noncommutative quantum harmonic oscillator whose component behavior we monitor in time. This procedure allows us to determine how the noncommutative parameters are related to the missing information quantified by the linear quantum entropy and by the mutual information between the relevant Hilbert space coordinates. Particular questions concerning the thermodynamic limit of some relevant properties are also discussed in order to evidence the effects of noncommutativity. Finally, through an analogy with the Zeeman effect, we identify how some aspects of the axial symmetry of the problem suggest the possibility of decoupling the noncommutative quantum perturbations from unperturbed commutative well-known solutions.

Bernardini, A. E.; Bertolami, O.

2013-07-01

374

Probing phase-space noncommutativity through quantum beating, missing information and the thermodynamic limit  

CERN Document Server

In this work we examine the effect of phase-space noncommutativity on some typically quantum properties such as quantum beating, quantum information, and decoherence. To exemplify these issues we consider the two-dimensional noncommutative quantum harmonic oscillator whose components behavior we monitor in time. This procedure allows to determine how the noncommutative parameters are related to the missing information quantified by the linear quantum entropy and by the mutual information between the relevant Hilbert space coordinates. Particular issues concerning the thermodynamic limit of some relevant properties are also discussed in order to evince the effects of noncommutativity. Finally, through an analogy with the Zeeman effect, we identify how some aspects of the axial symmetry of the problem suggest the possibility of decoupling the noncommutative quantum perturbations from unperturbed commutative well-known solutions.

Bernardini, Alex E

2013-01-01

375

A general quantum information model for the contextual dependent systems breaking the classical probability law  

CERN Multimedia

There exist several phenomena (systems) breaking the classical probability laws. Such systems are contextual dependent adaptive systems. In this paper, we present a new mathematical formula to compute the probability in those systems by using the concepts of the adaptive dynamics and quantum information theory -- quantum channels and the lifting. The basic examples of the contextual dependent phenomena can be found in quantum physics. And recently similar examples were found in biological and psychological sciences. Our novel approach is motivated by traditional quantum probability, but it is general enough to describe aforementioned phenomena outside of quantum physics.

Asano, Masanari; Khrennikov, Andrei; Ohya, Masanori; Yamato, Ichiro

2011-01-01

376

A simple scheme for quantum networks based on orbital angular momentum states of photons  

CERN Document Server

We propose a new quantum network scheme using orbital angular momentum states of photons to route the network and spin angular momentum states to encode the information. A four-user experimental scheme based on this efficient quantum network is analyzed in detail, which is particularly appealing for the free space quantum key distribution. Users can freely exchange quantum keys with each other.

Su, Zhi-Kun; Jin, Rui-Bo; Liang, Rui-Sheng; Liu, Song-Hao

2012-01-01

377

Can quantum information be cloned in Kerr black holes?  

Energy Technology Data Exchange (ETDEWEB)

The applications of the quantum non-cloning theorem to Kerr black holes are discussed. We find that whether the quantum non-cloning theorem is well established inside the inner horizon remains a question. Also the black hole complementarity principle and the quantum non-cloning theorem seem inconsistent inside the inner horizon.

Ge Xianhui [Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030 (China); Shen Yougen [Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030 (China)

2004-04-21

378

Information-theoretic outlook of the quantum dissipation problem  

International Nuclear Information System (INIS)

The interaction between two harmonic oscillators, a classical and a quantum one, coupled through a linear term, is analyzed by recourse to the generalized Ehrenfest theorem. The model is able to mimic dissipating behaviour for the quantum oscillator without violation of any quantum rule. (author). 13 refs, 5 figs

1992-01-01

379

Fault-tolerant quantum computation  

Energy Technology Data Exchange (ETDEWEB)

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

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

1996-12-31

380

Supercoherent Quantum Bits  

CERN Document Server

Real quantum systems couple to their environment and lose their intrinsic quantum nature through the process known as decoherence. Here we present a method for minimizing decoherence by making it energetically unfavorable. We present a Hamiltonian made up solely of two-body interactions between four two-level systems (qubits) which has a two-fold degenerate ground state. This degenerate ground state has the property that any decoherence process acting on an individual physical qubit must supply energy from the bath to the system. Quantum information can be encoded into the degeneracy of the ground state and such supercoherent qubits will then be robust to local decoherence at low bath temperatures. We show that this quantum information can be universally manipulated using nearest neighbor interactions without destroying the supercoherence. We demonstrate this approach with an analysis of supercoherence in the context of a quantum dot proposal for a quantum computer.

Bacon, D J; Whaley, K B

2001-01-01

 
 
 
 
381

Quantum-information transfer with nitrogen-vacancy centers coupled to a whispering-gallery microresonator  

International Nuclear Information System (INIS)

We propose an efficient scheme for the realization of quantum information transfer and entanglement with nitrogen-vacancy (N-V) centers coupled to a high-Q whispering-gallery mode (WGM) microresonator. We show that based on the effective dipole-dipole interaction between the N-V centers mediated by the WGM, quantum information can be transferred between the N-V centers through Raman transitions combined with laser fields. This protocol may open up promising possibilities for quantum communications with the solid-state quantum electrodynamic cavity system.

2011-01-01

382

Dynamics of the quantum Fisher information in a spin-boson model  

Science.gov (United States)

The quantum Fisher information characterizes the phase sensitivity of qubits in the spin-boson model with a finite bandwidth spectrum. In contrast with Markovian reservoirs, the quantum Fisher information flows from the environments to qubits after a number of times if the bath parameter s is larger than a critical value which is related to temperature. The sudden-change behavior will happen during the evolution of the quantum Fisher information of the maximal entanglement state in the non-Markovian environments. The sudden-change times can be varied with the change of the bath parameter s. For a very large number of entangled qubits, the sudden-change behavior of the maximal quantum Fisher information can be used to characterize the existence of the entanglement. The metrology strategy based on the quantum correlated state leads to a lower phase uncertainty when compared with the uncorrelated product state.

Hao, Xiang; Tong, Ning-Hua; Zhu, Shiqun

2013-09-01

383

A Geometrical Manifold of Entropy for Fisher Information and Quantum Potential  

CERN Document Server

It is here proposed a geometric approach for the problem of describing entropy in a quantum system. We make use of an extension of tensor calculus called morphogenetic calculus. By using such formalism we express the entropy of a quantum system as the superposition of Boltzmann entropies. In this way we also provide a reading of the relational interpretation of quantum mechanics. Moreover we show that the Bohm quantum potential emerges as a consequence of the classical equilibrium under the constraint of a minimum condition of Fisher information. In this way, Bohm quantum potential appears as a non-Euclidean deformation of the probabilistic space. Finally we investigate the possible quantum-relativistic extensions of the theory and the connections with the problem of quantum gravity.

Resconi, Germano; Fiscaletti, Davide

2011-01-01

384

Effects of Age on Negative Subsequent Memory Effects Associated with the Encoding of Item and Item-Context Information.  

UK PubMed Central (United Kingdom)

It has consistently been reported that "negative" subsequent memory effects-lower study activity for later remembered than later forgotten items-are attenuated in older individuals. The present functional magnetic resonance imaging study investigated whether these findings extend to subsequent memory effects associated with successful encoding of item-context information. Older (n = 25) and young (n = 17) subjects were scanned while making 1 of 2 encoding judgments on a series of pictures. Memory was assessed for the study item and, for items judged old, the item's encoding task. Both memory judgments were made using confidence ratings, permitting item and source memory strength to be unconfounded and source confidence to be equated across age groups. Replicating prior findings, negative item effects in regions of the default mode network in young subjects were reversed in older subjects. Negative source effects, however, were invariant with respect to age and, in both age groups, the magnitude of the effects correlated with source memory performance. It is concluded that negative item effects do not reflect processes necessary for the successful encoding of item-context associations in older subjects. Negative source effects, in contrast, appear to reflect the engagement of processes that are equally important for successful episodic encoding in older and younger individuals.

Mattson JT; Wang TH; de Chastelaine M; Rugg MD

2013-07-01

385

Experimental quantum coding against qubit loss error  

Science.gov (United States)

The fundamental unit for quantum computing is the qubit, an isolated, controllable two-level system. However, for many proposed quantum computer architectures, especially photonic systems, the qubits can be lost or can leak out of the desired two-level systems, posing a significant obstacle for practical quantum computation. Here, we experimentally demonstrate, both in the quantum circuit model and in the one-way quantum computer model, the smallest nontrivial quantum codes to tackle this problem. In the experiment, we encode single-qubit input states into highly entangled multiparticle code words, and we test their ability to protect encoded quantum information from detected 1-qubit loss error. Our results prove in-principle the feasibility of overcoming the qubit loss error by quantum codes.

Lu, Chao-Yang; Gao, Wei-Bo; Zhang, Jin; Zhou, Xiao-Qi; Yang, Tao; Pan, Jian-Wei

2008-01-01

386

Communicating through Probabilities: Does Quantum Theory Optimize the Transfer of Information?  

Directory of Open Access Journals (Sweden)

Full Text Available A quantum measurement can be regarded as a communication channel, in which the parameters of the state are expressed only in the probabilities of the outcomes of the measurement. We begin this paper by considering, in a non-quantum-mechanical setting, the problem of communicating through probabilities. For example, a sender, Alice, wants to convey to a receiver, Bob, the value of a continuous variable, ?, but her only means of conveying this value is by sending Bob a coin in which the value of ? is encoded in the probability of heads. We ask what the optimal encoding is when Bob will be allowed to flip the coin only a finite number of times. As the number of tosses goes to infinity, we find that the optimal encoding is the same as what nature would do if we lived in a world governed by real-vector-space quantum theory. We then ask whether the problem might be modified, so that the optimal communication strategy would be consistent with standard, complex-vector-space quantum theory.

William K. Wootters

2013-01-01

387

Fundamental properties of devices for quantum information technology  

DEFF Research Database (Denmark)

This thesis reports a theoretical investigation of the influence of the electronphonon interaction on semiconductor cavity quantum electrodynamical systems, specifically a quantum dot coupled to an optical microcavity. We develop a theoretical description of the decay dynamics of the quantum dot interacting with the cavity and the phonons. It is shown that the presence of the phonon interaction, fundamentally changes the spontaneous emission decay behavior of the quantum dot. Especially in the regime where the quantum dotcavity spectral detuning is significantly larger than any linewidth of the system, the effect of the phonon interaction is very pronounced. A simple approximate analytical expression for the quantum dot decay rate is derived, which predicts a strong asymmetry with respect to the quantum dot-cavity detuning at low temperatures, and allows for a clear interpretation of the physics. Furthermore, a study of the indistinguishability of single photons emitted from the coupled quantum dot-cavity system is performed, with special emphasis on non-Markovian decoherence due to the phonon interaction. We show that common theoretical approaches fail to predict the degree of indistinguishability, on both a qualitative and quantitative level, for experimentally relevant parameters regimes. The important role of non-Markovian effects in the shorttime regime, where virtual processes dominate the decoherence of the quantum dot-cavity system, is emphasized. Importantly, our investigations lead to a maximum achievable degree of indistinguishability, a prediction which eludes common approaches.

Nielsen, Per Kær

2012-01-01

388

Stabilization of Quantum Information A Unified Dynamical-Algebraic Approach  

CERN Multimedia

The notion of symmetry is shown to be at the heart of all error correction/avoidance strategies for preserving quantum coherence of an open quantum system S e.g., a quantum computer. The existence of a non-trivial group of symmetries of the dynamical algebra of S provides state-space sectors immune to decoherence. Such noiseless sectors, that can be viewed as a noncommutative version of the pointer basis, are shown to support universal quantum computation and to be robust against perturbations. When the required symmetry is not present one can generate it artificially resorting to active symmetrization procedures.

Zanardi, P

2002-01-01

389

Actionable Information, Repeatability, Quantum Jumps, and the Wavepacket Collapse  

CERN Document Server

Unknown quantum state cannot be discovered as the measured system is re-prepared -- it jumps into an eigenstate of the measured observable. This impossibility to find out a quantum state and other symptoms of the wavepacket collapse follow (as was recently demonstrated for pure states of measured systems) from unitarity (that doesn't, however, allow for a literal collapse) and from the repeatability of measurements. Here we extend this result to mixtures and decohering systems. This accounts for quantum jumps in a macroscopic and open (but ultimately quantum) apparatus.

Zurek, Wojciech H

2012-01-01

390

Processing quantum information in a hybrid topological qubit and superconducting flux qubit system  

Science.gov (United States)

A composite system of Majorana-hosted semiconductor nanowire and superconducting flux qubits, named top-flux-flux, is presented to process quantum information. We can electrically control the coupling between the Majorana-based topological qubit and the readout flux qubit, supplying a convenient method to implement a ?/8 phase gate of the topological qubit. In addition, we design a scheme to transfer quantum information back and forth between the topological qubit and the flux qubit by employing the Landau-Zener transition. With the demonstration of the entanglement of two topological qubits, it is very promising to use this hybrid system for quantum-information processing.

Zhang, Zhen-Tao; Yu, Yang

2013-03-01

391

Quantum information processing using nuclear and electron magnetic resonance: review and prospects  

CERN Document Server

This paper describes recent progress using nuclear magnetic resonance (NMR) as a platform for implementing quantum information processing (QIP) tasks. The basic ideas of NMR QIP are detailed, examining the successes and limitations of liquid and solid state experiments. Finally, a future direction for implementing quantum processors is suggested,utilizing both nuclear and electron spin degrees of freedom.

Baugh, J; Chandrasekhar, C M; Ditty, M; Hubbard, A; Laflamme, R; Laforest, M; Maslov, D; Moussa, O; Negrevergne, C; Silva, M; Simmons, S; Ryan, C A; Cory, D G; Hodges, J S; Ramanathan, C

2007-01-01

392

Quantum internet using code division multiple access.  

UK PubMed Central (United Kingdom)

A crucial open problem inS large-scale quantum networks is how to efficiently transmit quantum data among many pairs of users via a common data-transmission medium. We propose a solution by developing a quantum code division multiple access (q-CDMA) approach in which quantum information is chaotically encoded to spread its spectral content, and then decoded via chaos synchronization to separate different sender-receiver pairs. In comparison to other existing approaches, such as frequency division multiple access (FDMA), the proposed q-CDMA can greatly increase the information rates per channel used, especially for very noisy quantum channels.

Zhang J; Liu YX; Ozdemir SK; Wu RB; Gao F; Wang XB; Yang L; Nori F

2013-07-01

393

Quantum internet using code division multiple access  

Science.gov (United States)

A crucial open problem inS large-scale quantum networks is how to efficiently transmit quantum data among many pairs of users via a common data-transmission medium. We propose a solution by developing a quantum code division multiple access (q-CDMA) approach in which quantum information is chaotically encoded to spread its spectral content, and then decoded via chaos synchronization to separate different sender-receiver pairs. In comparison to other existing approaches, such as frequency division multiple access (FDMA), the proposed q-CDMA can greatly increase the information rates per channel used, especially for very noisy quantum channels.

Zhang, Jing; Liu, Yu-xi; Ozdemir, Sahin Kaya; Wu, Re-Bing; Gao, Feifei; Wang, Xiang-Bin; Yang, Lan; Nori, Franco

2013-01-01

394

Quantum internet using code division multiple access  

Science.gov (United States)

A crucial open problem inS large-scale quantum networks is how to efficiently transmit quantum data among many pairs of users via a common data-transmission medium. We propose a solution by developing a quantum code division multiple access (q-CDMA) approach in which quantum information is chaotically encoded to spread its spectral content, and then decoded via chaos synchronization to separate different sender-receiver pairs. In comparison to other existing approaches, such as frequency division multiple access (FDMA), the proposed q-CDMA can greatly increase the information rates per channel used, especially for very noisy quantum channels.

Zhang, Jing; Liu, Yu-Xi; Özdemir, ?ahin Kaya; Wu, Re-Bing; Gao, Feifei; Wang, Xiang-Bin; Yang, Lan; Nori, Franco

2013-07-01

395

A simple scheme for expanding photonic cluster states for quantum information  

CERN Multimedia

We show how an entangled cluster state encoded in the polarization of single photons can be straightforwardly expanded by deterministically entangling additional qubits encoded in the path degree of freedom of the constituent photons. This can be achieved using a polarization--path controlled-phase gate. We experimentally demonstrate a practical and stable realization of this approach by using a Sagnac interferometer to entangle a path qubit and polarization qubit on a single photon. We demonstrate precise control over phase of the path qubit to change the measurement basis and experimentally demonstrate properties of measurement-based quantum computing using a 2 photon, 3 qubit cluster state.

Kalasuwan, Pruet; Laing, Anthony; Nagata, Tomohisa; Coggins, Jack; Callaway, Mark; Takeuchi, Shigeki; Stefanov, Andre; O'Brien, Jeremy L

2010-01-01

396

Decoherence of quantum information of qubits by stochastic dephasing  

Energy Technology Data Exchange (ETDEWEB)

Decoherence of purity, distinguishability and entanglement of qubit states is investigated under the influence of stochastic dephasing which obeys the Gauss-Markov process and the two-state jump Markov process. The quantum teleportation and quantum dense coding under the influence of stochastic dephasing are also discussed.

Ban, Masashi [Advanced Research Laboratory, Hitachi, Ltd., Akanum 2520, Hatoyama, Saitama 350-0395 (Japan) and CREST, Japan Science and Technology Agency, 1-1-9 Yaesu, Chuo-ku, Tokyo 103-0028 (Japan)]. E-mail: masashi@activemail.jp; Kitajima, Sachiko [Department of Physics, Faculty of Science, Ochanomizu University, 2-1-1 Ohtsuka, Bunkyo-ku, Tokyo 112-8610 (Japan); Shibata, Fumiaki [Department of Physics, Faculty of Science, Ochanomizu University, 2-1-1 Ohtsuka, Bunkyo-ku, Tokyo 112-8610 (Japan)

2006-01-23

397

No Information Without Disturbance: Quantum Limitations of Measurement  

CERN Document Server

In this contribution I review rigorous formulations of a variety of limitations of measurability in quantum mechanics. To this end I begin with a brief presentation of the conceptual tools of modern measurement theory. I will make precise the notion that quantum measurements necessarily alter the system under investigation and elucidate its connection with the complementarity and uncertainty principles.

Busch, Paul

2007-01-01

398

Information carriers and (reading them through) information theory in quantum chemistry.  

UK PubMed Central (United Kingdom)

This Perspective discusses the reduction of the electronic wave function via the second-order reduced density matrix to the electron density ?(r), which is the key ingredient in density functional theory (DFT) as a basic carrier of information. Simplifying further, the 1-normalized density function turns out to contain essentially the same information as ?(r) and is even of preferred use as an information carrier when discussing the periodic properties along Mendeleev's table where essentially the valence electrons are at stake. The Kullback-Leibler information deficiency turns out to be the most interesting choice to obtain information on the differences in ?(r) or ?(r) between two systems. To put it otherwise: when looking for the construction of a functional F(AB) = F[?(A)(r),?(B)(r)] for extracting differences in information from an information carrier ?(r) (i.e. ?(r), ?(r)) for two systems A and B the Kullback-Leibler information measure ?S is a particularly adequate choice. Examples are given, varying from atoms, to molecules and molecular interactions. Quantum similarity of atoms indicates that the shape function based KL information deficiency is the most appropriate tool to retrieve periodicity in the Periodic Table. The dissimilarity of enantiomers for which different information measures are presented at global and local (i.e. molecular and atomic) level leads to an extension of Mezey's holographic density theorem and shows numerical evidence that in a chiral molecule the whole molecule is pervaded by chirality. Finally Kullback-Leibler information profiles are discussed for intra- and intermolecular proton transfer reactions and a simple S(N)2 reaction indicating that the theoretical information profile can be used as a companion to the energy based Hammond postulate to discuss the early or late transition state character of a reaction. All in all this Perspective's answer is positive to the question of whether an even simpler carrier of information than the electron density function ?(r) can be envisaged: the shape function, integrating to 1 by construction fulfils this role. On the other hand obtaining the information (or information difference) contained in one (or two) systems from ?(r) or ?(r) can be most efficiently done by using information theory, the Kulback-Leibler information deficiency being at the moment (one of) the most advisable functionals.

Geerlings P; Borgoo A

2011-01-01

399

Unification of Quantum and Gravity by Non Classical Information Entropy Space  

Directory of Open Access Journals (Sweden)

Full Text Available A quantum entropy space is suggested as the fundamental arena describing the quantum effects. In the quantum regime the entropy is expressed as the superposition of many different Boltzmann entropies that span the space of the entropies before any measure. When a measure is performed the quantum entropy collapses to one component. A suggestive reading of the relational interpretation of quantum mechanics and of Bohm’s quantum potential in terms of the quantum entropy are provided. The space associated with the quantum entropy determines a distortion in the classical space of position, which appears as a Weyl-like gauge potential connected with Fisher information. This Weyl-like gauge potential produces a deformation of the moments which changes the classical action in such a way that Bohm’s quantum potential emerges as consequence of the non classical definition of entropy, in a non-Euclidean information space under the constraint of a minimum condition of Fisher information (Fisher Bohm- entropy). Finally, the possible quantum relativistic extensions of the theory and the connections with the problem of quantum gravity are investigated. The non classical thermodynamic approach to quantum phenomena changes the geometry of the particle phase space. In the light of the representation of gravity in ordinary phase space by torsion in the flat space (Teleparallel gravity), the change of geometry in the phase space introduces quantum phenomena in a natural way. This gives a new force to F. Shojai’s and A. Shojai’s theory where the geometry of space-time is highly coupled with a quantum potential whose origin is not the Schrödinger equation but the non classical entropy of a system of many particles that together change the geometry of the phase space of the positions (entanglement). In this way the non classical thermodynamic changes the classical geodetic as a consequence of the quantum phenomena and quantum and gravity are unified. Quantum affects geometry of multidimensional phase space and gravity changes in any point the torsion in the ordinary four-dimensional Lorenz space-time metric.

Germano Resconi; Ignazio Licata; Davide Fiscaletti

2013-01-01

400

Decoherence of continuous variable quantum information in non-Markovian channels  

Energy Technology Data Exchange (ETDEWEB)

Decoherence of quantum information carried by single-mode and two-mode Gaussian states is investigated under the influence of non-Markovian quantum channels, where correlation times of reservoir variables are assumed to take finite values. Degradation of purity, distinguishability and non-classicality of single-mode Gaussian states and relaxation of entanglement of two-mode Gaussian states are examined. The results show the importance of the non-Markovian effect of a thermal reservoir. Furthermore, continuous variable quantum teleportation is considered when a sender and a receiver share a two-mode Gaussian state through non-Markovian quantum channels.

Ban, Masashi [Advanced Research Laboratory, Hitachi, Ltd, 2520 Akanuma, Hatoyama, Saitama 350-0395 (Japan); CREST, Japan Science and Technology Agency, 1-1-9 Yaesu, Chuo-ku, Tokyo 103-0028 (Japan)

2006-02-24

 
 
 
 
401

Generalization of Quantum Error Correction via the Heisenberg Picture and Application to Information Flow  

CERN Multimedia

We show that the theory of operator quantum error correction can be naturally generalized by allowing constraints not only on states but also on observables. The resulting theory describes the correction of algebras of observables and may therefore suitably be called "operator algebra quantum error correction". It allows for the simultaneous correction of several subsystems and does not require the state to be entirely in one of the corresponding subspaces. We also show how this formulation offers a formal framework for the study of information flows in quantum interactions, with applications to decoherence and quantum measurements.

Beny, C; Kribs, D W; Beny, Cedric; Kempf, Achim; Kribs, David W.

2006-01-01

402

A Versatile Source of Single Photons for Quantum Information Processing  

CERN Document Server

The quantum state of a single photon stands amongst the most fundamental and intriguing manifestations of quantum physics. At the same time single photons and pairs of single photons are important building blocks in the fields of linear optical based quantum computation and quantum repeater infrastructure. These fields possess enormous potential and much scientific and technological progress has been made in developing individual components, like quantum memories and photon sources using various physical implementations. However, further progress suffers from the lack of compatibility between these different components. Ultimately, one aims for a versatile source of single photons and photon pairs in order to overcome this hurdle of incompatibility. Such a photon source should allow for tuning of the spectral properties (wide wavelength range and narrow bandwidth) to address different implementations while retaining high efficiency. In addition, it should be able to bridge different wavelength regimes to make...

Förtsch, Michael; Wittmann, Christoffer; Strekalov, Dmitry; Aiello, Andrea; Chekhova, Maria V; Silberhorn, Christine; Leuchs, Gerd; Marquardt, Christoph

2012-01-01

403

Continuous-variable quantum information processing with squeezed states of light  

CERN Document Server

We investigate experiments of continuous-variable quantum information processing based on the teleportation scheme. Quantum teleportation, which is realized by a two-mode squeezed vacuum state and measurement-and-feedforward, is considered as an elementary quantum circuit as well as quantum communication. By modifying ancilla states or measurement-and-feedforwards, we can realize various quantum circuits which suffice for universal quantum computation. In order to realize the teleportation-based computation we improve the level of squeezing, and fidelity of teleportation. With a high-fidelity teleporter we demonstrate some advanced teleportation experiments, i.e., teleportation of a squeezed state and sequential teleportation of a coherent state. Moreover, as an example of the teleportation-based computation, we build a QND interaction gate which is a continuous-variable analog of a CNOT gate. A QND interaction gate is constructed only with ancillary squeezed vacuum states and measurement-and-feedforwards. We...

Yonezawa, Hidehiro

2008-01-01

404

Polarized Single-Photons on Demand - A New Source for Quantum Information.  

Science.gov (United States)

The goal of this project is the development of an efficient source, operating at room temperature, of deterministically polarized single photons on demand for quantum information. Our main results are as follows: (1) first demonstration of emitter fluores...

C. R. Stroud R. W. Boyd S. G. Lukishova

2006-01-01

405

Quantum teleportation  

Energy Technology Data Exchange (ETDEWEB)

Given a single copy of an unknown quantum state, it is impossible in principle to identify it. The mostly inaccessible information carried by the state is termed quantum information. In contrast to classical information, it cannot be copied or cloned. This concept provides a theoretical underpinning for all aspects of quantum communication and quantum computation. Here we use it to consider quantum teleportation. (orig.)

Braunstein, S.L. [Bangor Univ. (United Kingdom). Informatics

2002-07-01

406

Lower bound on the number of Toffoli gates in a classical reversible circuit through quantum information concepts  

CERN Multimedia

The question of finding a lower bound on the number of Toffoli gates in a classical reversible circuit is addressed. A method based on quantum information concepts is proposed. The method involves solely concepts from quantum information - there is no need for an actual physical quantum computer. The method is illustrated on the example of classical Shannon data compression.

Popescu, S; Massar, S; Popescu, Sandu; Groisman, Berry; Massar, Serge

2004-01-01

407

Informational Capacity and Recall Quality in Sparsely Encoded Hopfield-like Neural Network: Analytical Approaches and Computer Simulation.  

UK PubMed Central (United Kingdom)

A sparsely encoded Hopfield-like attractor neural network is investigated analytically and by computer simulation. Informational capacity and recall quality are evaluated. Three analytical approaches are used: replica method (RM); method of statistical neurodynamics (SN); and single-step approximation (SS). Computer simulation confirmed the good accuracy of RM and SN for all levels of network activity. SS is accurate only for large sparseness. It is shown that informational capacity monotonically increases when sparseness increases, while recall quality changes nonmonotonically: initially it decreases and then increases. Computer simulation revealed the main features of network behaviour near the saturation which are not predicted by the used analytical approaches. Copyright 1997 Elsevier Science Ltd.

Muraviev IP; Husek D; Frolov AA

1997-07-01

408

Quantum Fisher Information of N Particles in the Superposition of W and GHZ States  

Science.gov (United States)

We investigate the quantum Fisher information of a multipartite entangled state of N particles in a superposition of W and GHZ states. We find that the mean quantum Fisher information per particle (RMQFI) decreases with respect to the number of the particles and the peak is observed between 0.6 and 0.8 values of the superposition coefficient of W state. We present the behavior of RMQFI for N from 2 to 10 and discuss some interesting results.

Ozaydin, Fatih; Altintas, Azmi Ali; Bugu, Sinan; Yesilyurt, Can

2013-09-01

409

Neuronal type information encoded in the basic-helix–loop–helix domain of?proneural?genes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The proneural genes encode basic-helix–loop–helix (bHLH) proteins and promote the formation of distinct types of sensory organs. In Drosophila, two sets of proneural genes, atonal (ato) and members of the achaete–scute complex (ASC), are required for the formation of chordotonal (ch) organs and...

Chien, Cheng-ting; Hsiao, Chwan-Deng; Jan, Lily?Y.; Jan, Yuh?Nung

410

A contribution to quantum cryptography in finite-dimensional systems including further results from the field of quantum information theory  

International Nuclear Information System (INIS)

This PhD thesis deals with quantum-cryptographic protocols which allow general finite-dimensional quantum systems (qudits) as carriers of information in contrast to the predominantly used two-dimensional quantum systems (qubits). The main focus of investigations is the maximum tolerable error rate of such protocols and its behaviour as a function of the dimension of the information carriers. For this purpose, several concepts are introduced which allow the treatment of this problem. In particular, protocols are presented which work up to a maximum tolerate error rate, and it is shown that a wide class of protocols cannot be used for higher error rates. Among other things, it turns out that the maximum tolerable error rate for two-basis protocols increases up to 50% for high dimensions. Apart from the above-mentioned main subjects of this thesis, some other results from the field of quantum information theory are given, which were achieved during this PhD project. (orig.)

2009-01-01

411

Information-theoretical aspects of quantum-mechanical entropy  

International Nuclear Information System (INIS)

Properties of the quantum ( = von Neumann) entropy S(?) -k Tr? ln?, ? being a compact operator, are proved first, and differences against the classical case, e.g. the Shannon entropy, are worked out. The main result is on the strong subadditivity of this quantum entropy. Then another entropy, a function not of the state but of the dynamics of the system, is considered as a quantum analogue of the classical Kolmogorov-Sinai-entropy. An attempt in defining such a quantity had only recently sucess in a paper of Connes, Narnhofer and Thirring. A definition of this entropy is given. 34 refs

1990-01-01

412

Exploiting the Paradigm of Quantum Information in Nanosystem Modeling  

International Nuclear Information System (INIS)

Recently, we have introduced a novel approach to modeling of electronic properties of nanosystems. It is based upon a special type of Hamiltonian dynamics associated with mixed states of composite quantum systems. These concepts have been applied to modeling of several types of systems, including quantum Hall systems in equilibrium. In this report, in turn, we discuss a model for non-equilibrium evolution of quantum Hall systems. Quite surprisingly, the model suggests that such systems may spontaneously settle in a time-periodic regime - a potentially important conclusion, which brings to light the relevance of the many physical effects known to result from time-periodic Hamiltonian dynamics.

2009-08-13

413

Some Applications of Isotope - Based technologies: Human Health and Quantum Information  

CERN Multimedia

Technology is the sum of the information, knowledge and agency. This takes energy and information as fundamental concepts. In this paper I'll try to describe very briefly in popular form of some applications of radioactive and stable isotopes in medicine and quantum information, respectively.

Plekhanov, Vladimir G

2010-01-01

414

Measuring Gaussian quantum information and correlations using the Renyi entropy of order 2.  

UK PubMed Central (United Kingdom)

We demonstrate that the Rényi-2 entropy provides a natural measure of information for any multimode Gaussian state of quantum harmonic systems, operationally linked to the phase-space Shannon sampling entropy of the Wigner distribution of the state. We prove that, in the Gaussian scenario, such an entropy satisfies the strong subadditivity inequality, a key requirement for quantum information theory. This allows us to define and analyze measures of Gaussian entanglement and more general quantum correlations based on such an entropy, which are shown to satisfy relevant properties such as monogamy.

Adesso G; Girolami D; Serafini A

2012-11-01

415

Quantum information transfer with nitrogen-vacancy centers coupled to a whispering-gallery microresonator  

CERN Multimedia

We propose an efficient scheme for the realization of quantum information transfer and entanglement with nitrogen-vacancy (NV) centers coupled to a high-Q microspherical resonator. We show that, based on the effective dipole-dipole interaction between the NV centers mediated by the whispering-gallery mode (WGM), quantum information can be transferred between the NV centers through Raman transitions combined with laser fields. This protocol may open up promising possibilities for quantum communications with the solid state cavity QED system.

Li, Pengbo

2010-01-01

416

A gradient system on the quantum information space that realizes the Karmarkar flow for linear programming  

CERN Multimedia

In the paper of Uwano [Czech. J. of Phys., vol.56, pp.1311-1316 (2006)], a gradient system is found on the space of density matrices endowed with the quantum SLD Fisher metric (to be referred to as the quantum information space) that realizes a generalization of a gradient system on the space of multinomial distributions studied by Nakamura [Japan J. Indust. Appl. Math., vol.10, pp.179-189 (1993)]. On motived by those papers, the present paper aims to construct a gradient system on the quantum information space that realizes the Karmarkar flow, the continuous limit of the Karmarkar projective scaling algorithm for linear programming.

Uwano, Yoshio

2008-01-01

417

Efficient Quantum Polar Coding  

CERN Document Server

Polar coding, introduced 2008 by Arikan, is the first efficiently encodable and decodable coding scheme that provably achieves the Shannon bound for the rate of information transmission over classical discrete memoryless channels (in the asymptotic limit of large block sizes). Here we study the use of polar codes for the transmission of quantum information. Focusing on the case of qubit channels we construct a coding scheme which, using some pre-shared entanglement, asymptotically achieves a net transmission rate equal to the coherent information using efficient encoding and decoding operations and code construction. Furthermore, for channels with sufficiently low noise level, no pre-shared entanglement is required.

Renes, Joseph M; Renner, Renato

2011-01-01

418

Testing integrability with a single bit of quantum information  

International Nuclear Information System (INIS)

[en] We show that deterministic quantum computing with a single bit can determine whether the classical limit of a quantum system is chaotic or integrable using O(N) physical resources, where N is the dimension of the Hilbert space of the system under study. This is a square-root improvement over all known classical procedures. Our study relies strictly on the random matrix conjecture. We also present numerical results for the nonlinear kicked top

2003-01-01

419

Quantum gates and decoherence  

CERN Document Server

In the lectures we will be concerned with some aspects of physical implementations of quantum gate operations which are necessary for quantum information processing. We will discuss two possible realizations. One of them is based on qubits being encoded in atomic degrees of freedom where the atoms are manipulated in optical lattices above atom chips. The other realization is based on photonic qubits and measurement-induced nonlinearities in linear optics. Both implementations have in common that their main decoherence mechanism is absorption in dielectric materials. The quantum theory of light in absorbing media and its implications to decoherence will form the last part of the lectures.

Scheel, S; Hinds, E A; Knight, P L; Scheel, Stefan; Pachos, Jiannis; Knight, Peter L.

2004-01-01

420

Quantum Bio-Informatics II From Quantum Information to Bio-Informatics  

Science.gov (United States)

The problem of quantum-like representation in economy cognitive science, and genetics / L. Accardi, A. Khrennikov and M. Ohya -- Chaotic behavior observed in linea dynamics / M. Asano, T. Yamamoto and Y. Togawa -- Complete m-level quantum teleportation based on Kossakowski-Ohya scheme / M. Asano, M. Ohya and Y. Tanaka -- Towards quantum cybernetics: optimal feedback control in quantum bio informatics / V. P. Belavkin -- Quantum entanglement and circulant states / D. Chru?ci?ski -- The compound Fock space and its application in brain models / K. -H. Fichtner and W. Freudenberg -- Characterisation of beam splitters / L. Fichtner and M. Gäbler -- Application of entropic chaos degree to a combined quantum baker's map / K. Inoue, M. Ohya and I. V. Volovich -- On quantum algorithm for multiple alignment of amino acid sequences / S. Iriyama and M. Ohya --Quantum-like models for decision making in psychology and cognitive science / A. Khrennikov -- On completely positive non-Markovian evolution of a d-level system / A. Kossakowski and R. Rebolledo -- Measures of entanglement - a Hilbert space approach / W. A. Majewski -- Some characterizations of PPT states and their relation / T. Matsuoka -- On the dynamics of entanglement and characterization ofentangling properties of quantum evolutions / M. Michalski -- Perspective from micro-macro duality - towards non-perturbative renormalization scheme / I. Ojima -- A simple symmetric algorithm using a likeness with Introns behavior in RNA sequences / M. Regoli -- Some aspects of quadratic generalized white noise functionals / Si Si and T. Hida -- Analysis of several social mobility data using measure of departure from symmetry / K. Tahata ... [et al.] -- Time in physics and life science / I. V. Volovich -- Note on entropies in quantum processes / N. Watanabe -- Basics of molecular simulation and its application to biomolecules / T. Ando and I. Yamato -- Theory of proton-induced superionic conduction in hydrogen-bonded systems / H. Kamimura -- Massive collection of full-length complementary DNA clones and microarray analyses: keys to rice transcriptome analysis / S. Kikuchi -- Changes of influenza A(H5) viruses by means of entropic chaos degree / K. Sato and M. Ohya -- Basics of genome sequence analysis in bioinformatics - its fundamental ideas and problems / T. Suzuki and S. Miyazaki -- A basic introduction to gene expression studies using microarray expression data analysis / D. Wanke and J. Kilian -- Integrating biological perspectives: a quantum leap for microarray expression analysis / D. Wanke ... [et al.].

Accardi, L.; Freudenberg, Wolfgang; Ohya, Masanori

2009-02-01

 
 
 
 
421

Recent advances in exciton-based quantum information processing in quantum dot nanostructures  

International Nuclear Information System (INIS)

Recent experimental developments in the field of semiconductor quantum dot (QD) spectroscopy are discussed. Firstly, we report about single QD exciton two-level systems and their coherent properties in terms of single-qubit manipulations. In the second part, we report on coherent quantum coupling in a prototype 'two-qubit' system consisting of a vertically stacked pair of QDs. The interaction can be tuned in such QD molecule devices using an applied voltage as external parameter.

2005-01-01

422

One-way quantum computing in the optical frequency comb.  

Science.gov (United States)

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

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

2008-09-22

423

A short course in quantum information theory. An approach from theoretical physics. 2. ed.  

Energy Technology Data Exchange (ETDEWEB)

This short and concise primer takes the vantage point of theoretical physics and the unity of physics. It sets out to strip the burgeoning field of quantum information science to its basics by linking it to universal concepts in physics. An extensive lecture rather than a comprehensive textbook, this volume is based on courses delivered over several years to advanced undergraduate and beginning graduate students, but essentially it addresses anyone with a working knowledge of basic quantum physics. Readers will find these lectures a most adequate entry point for theoretical studies in this field. For the second edition, the authors has succeeded in adding many new topics while sticking to the conciseness of the overall approach. A new chapter on qubit thermodynamics has been added, while new sections and subsections have been incorporated in various chapter to deal with weak and time-continuous measurements, period-finding quantum algorithms and quantum error corrections. From the reviews of the first edition: ''The best things about this book are its brevity and clarity. In around 100 pages it provides a tutorial introduction to quantum information theory, including problems and solutions.. it's worth a look if you want to quickly get up to speed with the language and central concepts of quantum information theory, including the background classical information theory.'' (Craig Savage, Australian Physics, Vol. 44 (2), 2007). (orig.)

Diosi, Lajos [KFKI Research Institute for Particle and Nuclear Physics (RMKI), Budapest (Hungary). MTA Budapest

2011-07-01

424

Demonstration of deterministic and high fidelity squeezing of quantum information  

DEFF Research Database (Denmark)

By employing a recent proposal [R. Filip, P. Marek, and U.L. Andersen, Phys. Rev. A 71, 042308 (2005)] we experimentally demonstrate a universal, deterministic, and high-fidelity squeezing transformation of an optical field. It relies only on linear optics, homodyne detection, feedforward, and an ancillary squeezed vacuum state, thus direct interaction between a strong pump and the quantum state is circumvented. We demonstrate three different squeezing levels for a coherent state input. This scheme is highly suitable for the fault-tolerant squeezing transformation in a continuous variable quantum computer.

Yoshikawa, J-I.; Hayashi, T-

2007-01-01

425

Demonstration of deterministic and high fidelity squeezing of quantum information  

Science.gov (United States)

By employing a recent proposal [R. Filip, P. Marek, and U.L. Andersen, Phys. Rev. A 71, 042308 (2005)] we experimentally demonstrate a universal, deterministic, and high-fidelity squeezing transformation of an optical field. It relies only on linear optics, homodyne detection, feedforward, and an ancillary squeezed vacuum state, thus direct interaction between a strong pump and the quantum state is circumvented. We demonstrate three different squeezing levels for a coherent state input. This scheme is highly suitable for the fault-tolerant squeezing transformation in a continuous variable quantum computer.

Yoshikawa, Jun-Ichi; Hayashi, Toshiki; Akiyama, Takayuki; Takei, Nobuyuki; Huck, Alexander; Andersen, Ulrik L.; Furusawa, Akira

2007-12-01

426

Quantum information processing with delocalized qubits under global control.  

UK PubMed Central (United Kingdom)

Conventional quantum computing schemes are incompatible with nanometer-scale "hardware," where the closely packed spins cannot be individually controlled. We report the first experimental demonstration of a global control paradigm: logical qubits delocalize along a spin chain and are addressed via the two terminal spins. Using NMR studies on a three-spin molecule, we implement a globally clocked quantum mirror that outperforms the equivalent swap network. We then extend the protocol to support dense qubit storage and demonstrate this experimentally via Deutsch and Deutsch-Jozsa algorithms.

Fitzsimons J; Xiao L; Benjamin SC; Jones JA

2007-07-01

427

Quantum walks on general graphs  

CERN Multimedia

A scheme for a discrete time quantum walk on a general graph of N vertices with undirected edges is given, and compared with the continuous time quantum walk on a general graph introduced by Farhi and Gutmann [PRA 58 915 (1998)]. Both walks are contrasted with the examples of quantum walks in the literature treating graphs of fixed, small (< log N) degree. This illustrates the way in which extra information about the graph allows more efficient algorithms to be designed. To obtain a quantum speed up over classical for comparable resources it is necessary to code the position space of the quantum walk into a qubit register (or equivalent). The role of the oracle is also discussed and an efficient gate sequence is presented for implementing a discrete quantum walk given one copy of a quantum state encoding the adjacency matrix of the graph.

Kendon, V

2003-01-01

428

Microtrap arrays on magnetic film atom chips for quantum information science  

CERN Document Server

We present two different strategies for developing a quantum information science platform, based on our experimental results with magnetic microtrap arrays on a magnetic-film atom chip. The first strategy aims for mesoscopic ensemble qubits in a lattice of ~5 {\\mu}m period, so that qubits can be individually addressed and interactions can be mediated by Rydberg excitations. The second strategy aims for direct quantum simulators using sub-optical lattices of ~100 nm period. These would allow the realization of condensed matter inspired quantum many-body systems, such as Hubbard models in new parameter regimes. The two approaches raise quite different issues, some of which are identified and discussed.

Leung, V Y F; van Druten, N J; Spreeuw, R J C

2011-01-01

429

Storing quantum information in XXZ spin rings with periodically time-controlled interactions  

Energy Technology Data Exchange (ETDEWEB)

We introduce a general scheme to realize massive quantum memories in simple systems of interacting qubits. Such systems are described by spin rings with XXZ intersite couplings of suitably time-periodically controlled amplitudes. We show that initially localized excitations undergo perfect periodic revivals, allowing for the simultaneous storage of arbitrary sets of different local states. This novel approach to the problem of storing quantum information hints at a new way to control and suppress the effect of decoherence on a quantum computer realized in a system with nonvanishing interactions between the constituent qubits.

Giampaolo, S M; Illuminati, F; Mazzarella, G [Dipartimento di Fisica ' E. R. Caianiello' , Universita di Salerno, INFM UdR di Salerno, INFN Sezione di Napoli, Gruppo Collegato di Salerno, Via S. Allende, 84081 Baronissi, SA (Italy)

2005-10-01