WorldWideScience
 
 
1

Secure quantum private information retrieval using phase-encoded queries  

International Nuclear Information System (INIS)

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.

2011-08-01

2

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

3

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

4

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

5

Quantum bit encoding and information processing with field superposition states in a circuit  

International Nuclear Information System (INIS)

Solid-state superconducting devices coupled to coplanar transmission lines offer an exquisite architecture for quantum optical phenomena probing as well as for quantum computation implementation, which is the object of intense theoretical and experimental investigation lately. Under appropriate conditions, the transmission line radiation modes can become strongly coupled to a superconducting device with only two levels - for that reason called an artificial atom or qubit. Employing this system, we propose a two-quantum bit gate encoding, involving quantum electromagnetic field qubit states prepared in a coplanar transmission line capacitively coupled to a single charge qubit. Since dissipative effects are more drastic in the solid-state qubit than in the field one, it can be employed for the storage of information, whose efficiency against the action of an ohmic bath shows that this encoding can be readily implemented with present-day technology. We extend the investigation to generate entanglement between several solid-state qubits and the field qubit through the action of external classical magnetic pulses.

2012-09-28

6

Strong connections between quantum encodings, nonlocality, and quantum cryptography  

Science.gov (United States)

Encoding information in quantum systems can offer surprising advantages but at the same time there are limitations that arise from the fact that measuring an observable may disturb the state of the quantum system. In our work, we provide an in-depth analysis of a simple question: What happens when we perform two measurements sequentially on the same quantum system? This question touches upon some fundamental properties of quantum mechanics, namely the uncertainty principle and the complementarity of quantum measurements. Our results have interesting consequences, for example, they can provide a simple proof of the optimal quantum strategy in the famous Clauser-Horne-Shimony-Holt game. Moreover, we show that the way information is encoded in quantum systems can provide a different perspective in understanding other fundamental aspects of quantum information, like nonlocality and quantum cryptography. We prove some strong equivalences between these notions and provide a number of applications in all areas.

Sikora, Jamie; Chailloux, André; Kerenidis, Iordanis

2014-02-01

7

Quantum information to the home  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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, spontane...

2011-01-01

8

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

9

Hybrid Qubit gates in circuit QED: A scheme for quantum bit encoding and information processing  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Solid state superconducting devices coupled to coplanar transmission lines offer an exquisite architecture for quantum optical phenomena probing as well as for quantum computation implementation, being the object of intense theoretical and experimental investigation lately. In appropriate conditions the transmission line radiation modes can get strongly coupled to a superconducting device with only two levels -for that reason called artificial atom or qubit. Employing this s...

Neto, O. P. Sa; Oliveira, M. C.

2011-01-01

10

New encoding schemes for quantum authentication  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study the potential of general quantum operations, Trace-Preserving Completely-Positive Maps (TPCPs), as encoding and decoding mechanisms in quantum authentication protocols. The study shows that these general operations do not offer significant advantage over unitary encodings. We also propose a practical authentication protocol based on the use of two successive unitary encodings.

Garcia-fernandez, Priscila; Fernandez-martinez, Enrique; Perez, Esther; Santos, David J.

2003-01-01

11

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 M

2009-01-01

12

Nonlocal quantum information in bipartite quantum error correction  

CERN Multimedia

We show how to convert an arbitrary stabilizer code into a bipartite quantum code. A bipartite quantum code is one that involves two senders and one receiver. The two senders exploit both nonlocal and local quantum resources to encode quantum information with local encoding circuits. They transmit their encoded quantum data to a single receiver who then decodes the transmitted quantum information. The nonlocal resources in a bipartite code are ebits and nonlocal information qubits and the local resources are ancillas and local information qubits. The technique of bipartite quantum error correction is useful in both the quantum communication scenario described above and in fault-tolerant quantum computation. It has application in fault-tolerant quantum computation because we can prepare nonlocal resources offline and exploit local encoding circuits. In particular, we derive an encoding circuit for a bipartite version of the Steane code that is local and additionally requires only nearest-neighbor interactions....

Wilde, Mark M

2009-01-01

13

Quantum logical operations on encoded qubits  

CERN Multimedia

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 one bit errors which either preexisted or occurred in course of operation. The logical operations we consider allow one to cary out the vast majority of the steps in the quantum factoring algorithm. Thus, our results help bring quantum factoring and other quantum computations closer to reality

Zurek, W H; Zurek, Wojciech Hubert; Laflamme, Raymond

1996-01-01

14

Encoding entanglement-assisted quantum stabilizer codes  

International Nuclear Information System (INIS)

We address the problem of encoding entanglement-assisted (EA) quantum error-correcting codes (QECCs) and of the corresponding complexity. We present an iterative algorithm from which a quantum circuit composed of CNOT, H, and S gates can be derived directly with complexity O(n2) to encode the qubits being sent. Moreover, we derive the number of each gate consumed in our algorithm according to which we can design EA QECCs with low encoding complexity. Another advantage brought by our algorithm is the easiness and efficiency of programming on classical computers. (general)

2012-02-01

15

Quantum Optics, Quantum Nanophysics, Quantum Information  

Science.gov (United States)

This site contains the research news and project descriptions of the work in quantum physics by the research group of Prof. Anton Zeilinger. This includes quantum methods of teleportation and cryptography, quantum information, and entangled states.

Zeilinger, Anton

2003-10-10

16

Quantum Key Distribution with Qubits Encoded in Qutrit  

CERN Document Server

We present a novel one-way quantum key distribution protocol based on 3-dimensional quantum state, a qutrit, that encodes two qubits in its 2-dimensional subspaces. The qubits hold the classical bit information that has to be shared between the legitimate users. Alice sends such a qutrit to Bob where he decodes one of the qubit and measures it along the random Pauli basis. This scheme has higher secure key rate at longer transmission distance than the standard BB84 protocol.

Kumar, R; Banaszek, K

2012-01-01

17

Linear optical quantum computation with parity encoding  

International Nuclear Information System (INIS)

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

2005-05-20

18

Quantum Optics, Quantum Information and Quantum Control Group  

... Quantum Optics, Quantum Information and Quantum Control Group institute,physics,iop,quantum,information,optics,control,groups Quantum Optics, Quantum Information and Quantum ...Education Activities Careers Policy Resources You are here Activities Groups All Groups Quantum Optics, Quantum Information and Quantum Control Group Groups All Groups ... Quantum Optics, Quantum Information and Quantum Control Group Committee Contact Group calendar Newsletter Quantum Optics, Quantum Information and Quantum Control Group Over ...so a vigorous new research community has emerged in the field of Quantum optics - Quantum information - Quantum control, QQQ. (...

19

Quantum cryptography with polarization, phase and time encoding  

CERN Document Server

We develop and present a quantum cryptography concept in which phase determinations are made from the time that a photon is detected, as opposed to where the photon is detected, and hence is a non-interferometric process. The phase-encoded quantum information is contained in temporal and polarization superpositions of single photon states, forming a complex qudit of Hilbert dimension D equal to or greater than 4. Based on this, we have developed a new quantum key distribution protocol that allows the generation of secret key in the presence of higher noise than is possible with other protocols.

Buttler, W T

2008-01-01

20

Information encoder/decoder using chaotic systems  

Science.gov (United States)

The present invention discloses a chaotic system-based information encoder and decoder that operates according to a relationship defining a chaotic system. Encoder input signals modify the dynamics of the chaotic system comprising the encoder. The modifications result in chaotic, encoder output signals that contain the encoder input signals encoded within them. The encoder output signals are then capable of secure transmissions using conventional transmission techniques. A decoder receives the encoder output signals (i.e., decoder input signals) and inverts the dynamics of the encoding system to directly reconstruct the original encoder input signals. 32 figs.

Miller, S.L.; Miller, W.M.; McWhorter, P.J.

1997-10-21

 
 
 
 
21

Stability of encoded macroscopic quantum superpositions  

CERN Multimedia

The multipartite Greenberger-Horne-Zeilinger (GHZ) state is a paradigmatic example of a highly entangled multipartite states with distinct quantum features. However, the GHZ state is very sensitive to generic decoherence processes, where its quantum features and in particular its entanglement diminish rapidly, thereby hindering possible practical applications e.g. in the context of quantum metrology. In this paper, we discuss GHZ-like quantum states with a block-local structure and show that they exhibit a drastically increased stability against noise for certain choices of block-encoding. We analyze in detail the decay of the interference terms, the entanglement in terms of distillable entanglement and Negativity as well as the notion of macroscopicity as measured by the so-called q-index, and provide general bounds on these quantities. We focus on an encoding where logical qubits are themselves encoded as GHZ states, which leads to so-called concatenated GHZ (C-GHZ) states. We compare the stability of C-GHZ...

Fröwis, Florian

2012-01-01

22

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

23

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

24

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.

2011-06-01

25

Encoding information into precipitation structures  

International Nuclear Information System (INIS)

Material design at submicron scales would be profoundly affected if the formation of precipitation patterns could be easily controlled. It would allow the direct building of bulk structures, in contrast to traditional techniques which consist of removing material in order to create patterns. Here, we discuss an extension of our recent proposal of using electrical currents to control precipitation bands which emerge in the wake of reaction fronts in A+ + B– ? C reaction–diffusion processes. Our main result, based on simulating the reaction–diffusion–precipitation equations, is that the dynamics of the charged agents can be guided by an appropriately designed time-dependent electric current so that, in addition to the control of the band spacing, the width of the precipitation bands can also be tuned. This makes straightforward the encoding of information into precipitation patterns and, as an amusing example, we demonstrate the feasibility by showing how to encode a musical rhythm

2008-12-01

26

Quantum Information An Overview  

CERN Multimedia

This book is a comprehensive yet concise overview of quantum information science, which is a rapidly developing area of interdisciplinary investigation that now plays a significant role in physics, information technology and engineering. It is a handy reference for practitioners and students covering quantum mechanics, quantum key distribution, quantum computation and quantum communication, as well as explicating foundational issues of these topics. Specific protocols for quantum coding, quantum teleportation, quantum key distribution, quantum data compression and entanglement purification are discussed, as are quantum algorithms, including the Deutsch-Jozsa, Shor and Grover algorithms. Appendices on the mathematics of quantum information science and postulates of quantum mechanics are included. The book contains more than 25 illustrations that encapsulate essential ideas and fundamental constructs of quantum information science. The bibliography contains more than 400 articles from the literature of quantum ...

Jaeger, Gregg

2007-01-01

27

Quantum error correction of photon loss with quantum encoding  

Science.gov (United States)

Long-distance quantum communication with high fidelity is the main obstacle to creating a quantum network. A scheme to recover the loss of one photon with a three-to-eight qubit encoding is presented. The qubit loss is first detected using a quantum nondemolition measurement and is then transformed into a standard qubit error by inserting a new photon. The state of qubits is reconstructed via a sequence of one projective measurement, two single-qubit gates, and seven controlled-NOT operations. No ancillary qubits are required. Finally, the cost of resources is analyzed.

Han, Chao

2013-03-01

28

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

29

Quantum information with Rydberg atoms  

CERN Document Server

Rydberg atoms with principal quantum number n >> 1 have exaggerated atomic properties including dipole-dipole interactions that scale as n^4 and radiative lifetimes that scale as n^3. It was proposed a decade ago to take advantage of these properties to implement quantum gates between neutral atom qubits. The availability of a strong, long-range interaction that can be coherently turned on and off is an enabling resource for a wide range of quantum information tasks stretching far beyond the original gate proposal. Rydberg enabled capabilities include long-range two-qubit gates, collective encoding of multi-qubit registers, implementation of robust light-atom quantum interfaces, and the potential for simulating quantum many body physics. We review the advances of the last decade, covering both theoretical and experimental aspects of Rydberg mediated quantum information processing.

Saffman, M; Mølmer, K

2009-01-01

30

Quantum information with Rydberg atoms  

Energy Technology Data Exchange (ETDEWEB)

Rydberg atoms with principal quantum number n>>1 have exaggerated atomic properties including dipole-dipole interactions that scale as n{sup 4} and radiative lifetimes that scale as n{sup 3}. It was proposed a decade ago to take advantage of these properties to implement quantum gates between neutral atom qubits. The availability of a strong long-range interaction that can be coherently turned on and off is an enabling resource for a wide range of quantum information tasks stretching far beyond the original gate proposal. Rydberg enabled capabilities include long-range two-qubit gates, collective encoding of multiqubit registers, implementation of robust light-atom quantum interfaces, and the potential for simulating quantum many-body physics. The advances of the last decade are reviewed, covering both theoretical and experimental aspects of Rydberg-mediated quantum information processing.

Saffman, M.; Walker, T. G.; Moelmer, K. [Department of Physics, University of Wisconsin, 1150 University Avenue, Madison, Wisconsin 53706 (United States); Lundbeck Foundation Theoretical Center for Quantum System Research, Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark)

2010-07-15

31

Institute for Quantum Information  

Science.gov (United States)

The Institute for Quantum Information sponsors programs which encourage the growth and development of quantum information science. This web site contains information on regular seminars and inter-disciplinary workshops, current research, and links to courses relevant to quantum information (including lecture notes, problems, and solutions).

Kimble, Jeff; Preskill, John; Kitaev, Alexei; Mabuchi, Hideo; Schulman, Leonard

2005-11-20

32

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

33

Quantum Particles From Quantum Information  

International Nuclear Information System (INIS)

Many problems in modern physics demonstrate that for a fundamental entity a more general conception than quantum particles or quantum fields are necessary. These concepts cannot explain the phenomena of dark energy or the mind-body-interaction. Instead of any kind of 'small elementary building bricks', the Protyposis, an abstract and absolute quantum information, free of special denotation and open for some purport, gives the solution in the search for a fundamental substance. However, as long as at least relativistic particles are not constructed from the Protyposis, such an idea would remain in the range of natural philosophy. Therefore, the construction of relativistic particles without and with rest mass from quantum information is shown.

2012-08-24

34

Photonic Quantum Information Processing  

International Nuclear Information System (INIS)

The advantage of the photon's mobility makes optical quantum system ideally suited for delegated quantum computation. I will present results for the realization for a measurement-based quantum network in a client-server environment, where quantum information is securely communicated and computed. Related to measurement-based quantum computing I will discuss a recent experiment showing that quantum discord can be used as resource for the remote state preparation, which might shine new light on the requirements for quantum-enhanced information processing. Finally, I will briefly review recent photonic quantum simulation experiments of four frustrated Heisenberg-interactions spins and present an outlook of feasible simulation experiments with more complex interactions or random walk structures. As outlook I will discuss the current status of new quantum technology for improving the scalability of photonic quantum systems by using superconducting single-photon detectors and tailored light-matter interactions. (author)

2012-01-01

35

Quantum information and coherence  

CERN Multimedia

This book offers an introduction to ten key topics in quantum information science and quantum coherent phenomena, aimed at graduate-student level. The chapters cover some of the most recent developments in this dynamic research field where theoretical and experimental physics, combined with computer science, provide a fascinating arena for groundbreaking new concepts in information processing. The book addresses both the theoretical and experimental aspects of the subject, and clearly demonstrates how progress in experimental techniques has stimulated a great deal of theoretical effort and vice versa. Experiments are shifting from simply preparing and measuring quantum states to controlling and manipulating them, and the book outlines how the first real applications, notably quantum key distribution for secure communication, are starting to emerge. The chapters cover quantum retrodiction, ultracold quantum gases in optical lattices, optomechanics, quantum algorithms, quantum key distribution, quantum cont...

Öhberg, Patrik

2014-01-01

36

Quantum information inequalities  

CERN Document Server

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. Key words and phrases: Quantum covariance, metric adjusted skew information, Robertson-type uncertainty principle, operator monotone function.

Cai, Liang

2008-01-01

37

Quantum Information Technology  

Science.gov (United States)

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

Spiller, Timothy.

2002-01-01

38

Hybrid architecture for encoded measurement-based quantum computation  

Science.gov (United States)

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

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

2014-01-01

39

Hybrid architecture for encoded measurement-based quantum computation.  

Science.gov (United States)

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

Zwerger, M; Briegel, H J; Dür, W

2014-01-01

40

Elements of quantum information  

Energy Technology Data Exchange (ETDEWEB)

Elements of Quantum Information introduces the reader to the fascinating field of quantum information processing, which lives on the interface between computer science, physics, mathematics, and engineering. This interdisciplinary branch of science thrives on the use of quantum mechanics as a resource for high potential modern applications. With its wide coverage of experiments, applications, and specialized topics - all written by renowned experts - Elements of Quantum Information provides and indispensable, up-to-date account of the state of the art of this rapidly advancing field and takes the reader straight up to the frontiers of current research. The articles have first appeared as a special issue of the journal 'Fortschritte der Physik / Progress of Physics'. Since then, they have been carefully updated. The book will be an inspiring source of information and insight for anyone researching and specializing in experiments and theory of quantum information. Topics addressed in Elements of Quantum Information include - Cavity Quantum Electrodynamics - Segmented Paul Traps - Cold Atoms and Bose-Einstein Condensates in Microtraps, Optical Lattices, and on Atom Chips - Rydberg Gases - Factorization of Numbers with Physical Systems - Entanglement of Continuous Variables - NMR and Solid State Quantum Computation - Quantum Algorithms and Quantum Machines - Complexity Theory - Quantum Crytography. (orig.)

Schleich, W.P. [Ulm Univ. (Germany). Abt. fuer Quantenphysik; Walther, H. (eds.) [MPI fuer Quantenoptik, Garching (Germany)

2007-07-01

 
 
 
 
41

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

42

Quantum Information Theory  

CERN Document Server

In this thesis I present a short review of ideas in quantum information theory. The first chapter contains introductory material, sketching the central ideas of probability and information theory. Quantum mechanics is presented at the level of advanced undergraduate knowledge, together with some useful tools for quantum mechanics of open systems. In the second chapter I outline how classical information is represented in quantum systems and what this means for agents trying to extract information from these systems. The final chapter presents a new resource: quantum information. This resource has some bewildering applications which have been discovered in the last ten years, and continually presents us with unexpected insights into quantum theory and the universe. The treatment is pedagogical and suitable for beginning graduates in the field.

Schumann, R H

2000-01-01

43

Quantum Information Science Workshop (Proceedings)  

Science.gov (United States)

... Information Science An Emerging Field of Interdisciplinary Research and Education in Science and ... QUANTUM INFORMATION SCIENCE WORKSHOP ATTENDEES PREFACE Quantum Information Science (QIS) is an ...

44

Concealed Quantum Information  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study the teleportation scheme performed by means of a partially entangled pure state. We found that the information belonging to the quantum channel can be distributed into both the system of the transmitter and the system of the receiver. Thus, in order to complete the teleportation process it is required to perform an "unambiguous non-orthogonal quantum states discrimination" and an "extraction of the quantum information" processes. This general scheme allows one to de...

Roa, Luis

2007-01-01

45

Lectures on quantum information  

International Nuclear Information System (INIS)

Quantum Information Processing is a young and rapidly growing field of research at the intersection of physics, mathematics, and computer science. Its ultimate goal is to harness quantum physics to conceive - and ultimately build - 'quantum' computers that would dramatically overtake the capabilities of today's 'classical' computers. One example of the power of a quantum computer is its ability to efficiently find the prime factors of a large integer, thus shaking the supposedly secure foundations of standard encryption schemes. This comprehensive textbook on the rapidly advancing field introduces readers to the fundamental concepts of information theory and quantum entanglement, taking into account the current state of research and development. It thus covers all current concepts in quantum computing, both theoretical and experimental, before moving on to the latest implementations of quantum computing and communication protocols. With its series of exercises, this is ideal reading for students and lecturers in physics and informatics, as well as experimental and theoretical physicists, and physicists in industry. (orig.)

2007-01-01

46

Hiding Quantum Information in the Perfect Code  

CERN Document Server

We present and analyze a protocol for quantum steganography where the sender (Alice) encodes her steganographic information into the error syndromes of the perfect (five-qubit) quantum error-correcting code, and sends it to the receiver (Bob) over a depolarizing channel. Alice and Bob share a classical secret key, and hide quantum information in such a way that to an eavesdropper (Eve) without access to the secret key, the quantum message looks like an innocent codeword with a typical sequence of quantum errors. We calculate the average rate of key consumption, and show how the protocol improves in performance as information is spread over multiple codeword blocks. Alice and Bob utilize different encodings to optimize the average number of steganographic bits that they can send to each other while matching the error statistics of the depolarizing channel.

Shaw, Bilal A

2010-01-01

47

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

48

Quantum Private Comparison Based on Phase Encoding of Single Photons  

Science.gov (United States)

In this paper, we propose a scheme for quantum private comparison using phase encoding. The analysis indicates that the scheme is secure, and can prevent some familiar attacks. With the use of error-correcting code (ECC), it achieves a limited fault tolerant quantum private comparison. The scheme is easy to be realized in current experiments.

Li, Yan-Bing; Ma, Ying-Jie; Xu, Sheng-Wei; Huang, Wei; Zhang, Yan-shuo

2014-04-01

49

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

International Nuclear Information System (INIS)

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. We show that when the technique is applied to the conventional single photon phase-encoding BB84 and differential phase shift (DPS) quantum key distribution schemes, the key generation efficiencies can be improved by factors 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 systems. (general)

2011-07-01

50

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

Science.gov (United States)

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. We show that when the technique is applied to the conventional single photon phase-encoding BB84 and differential phase shift (DPS) quantum key distribution schemes, the key generation efficiencies can be improved by factors 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 systems.

Yan, Hui; Zhu, Shi-Liang; Du, Sheng-Wang

2011-07-01

51

Secret key rates for an encoded quantum repeater  

Science.gov (United States)

We investigate secret key rates for the quantum repeater using encoding [L. Jiang et al., Phys. Rev. A 79, 032325 (2009), 10.1103/PhysRevA.79.032325] and compare them to the standard repeater scheme by Briegel, Dür, Cirac, and Zoller. The former scheme has the advantage of a minimal consumption of classical communication. We analyze the trade-off in the secret key rate between the communication time and the required resources. For this purpose we introduce an error model for the repeater using encoding which allows for input Bell states with a fidelity smaller than one, in contrast to the model given by L. Jiang et al. [Phys. Rev. A 79, 032325 (2009), 10.1103/PhysRevA.79.032325]. We show that one can correct additional errors in the encoded connection procedure of this repeater and develop a suitable decoding algorithm. Furthermore, we derive the rate of producing entangled pairs for the quantum repeater using encoding and give the minimal parameter values (gate quality and initial fidelity) for establishing a nonzero secret key. We find that the generic quantum repeater is optimal regarding the secret key rate per memory per second and show that the encoded quantum repeater using the simple three-qubit repetition code can even have an advantage with respect to the resources compared to other recent quantum repeater schemes with encoding.

Bratzik, Sylvia; Kampermann, Hermann; Bruß, Dagmar

2014-03-01

52

Entanglement, Quantum Entropy and Mutual Information  

CERN Document Server

The operational structure of quantum couplings and entanglements is studied and classified for semifinite von Neumann algebras. We show that the classical-quantum correspondences such as quantum encodings can be treated as diagonal semi-classical (d-) couplings, and the entanglements characterized by truly quantum (q-) couplings, can be regarded as truly quantum encodings. The relative entropy of the d-compound and entangled states leads to two different types of entropy for a given quantum state: the von Neumann entropy, which is achieved as the maximum of mutual information over all d-entanglements, and the dimensional entropy, which is achieved at the standard entanglement -- true quantum entanglement, coinciding with a d-entanglement only in the case of pure marginal states. The d- and q- information of a quantum noisy channel are respectively defined via the input d- and q- encodings, and the q-capacity of a quantum noiseless channel is found as the logarithm of the dimensionality of the input algebra. T...

Belavkin, V P

2002-01-01

53

Duality Quantum Information and Duality Quantum Communication  

International Nuclear Information System (INIS)

Quantum mechanical systems exhibit particle wave duality property. This duality property has been exploited for information processing. A duality quantum computer is a quantum computer on the move and passing through a multi-slits. It offers quantum wave divider and quantum wave combiner operations in addition to those allowed in an ordinary quantum computer. It has been shown that all linear bounded operators can be realized in a duality quantum computer, and a duality quantum computer with n qubits and d-slits can be realized in an ordinary quantum computer with n qubits and a qudit in the so-called duality quantum computing mode. The quantum particle-wave duality can be used in providing secure communication. In this paper, we will review duality quantum computing and duality quantum key distribution.

2011-03-28

54

NMR Quantum Information Processing  

CERN Document Server

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

55

Entanglement and non local correlations: quantum resources for information processing  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Quantum Information Theory (QIT) studies how information can be processed and transmitted when encoded on quantum states. Practically, it can be understood as the effort to generalize Classical Information Theory to the quantum world. Interestingly, the fact that very-small scale Physics differs considerably from that of macroscopic objects offers a richer structure to the new theory. Among other phenomena, entanglement is at the heart of many quantum information protocols. It is the most spe...

Prettico, Giuseppe

2013-01-01

56

Quantum Information Processing.  

Science.gov (United States)

This effort supported a Quantum Information Workshop at the University of California, Berkeley. After a cut in funding, the remaining unspent funding was used to support: (1) research related to the internet involving the interplay between mechanism desig...

U. Vazirani C. Papadimitriou A. Sinclair

2004-01-01

57

Fundamentals of Quantum Optics and Quantum Information  

CERN Multimedia

This book is an introduction to the two closely related subjects of quantum optics and quantum information. Essentially, the physical aspects of quantum information processing have now become an integral part of quantum optics. The book gives a simple, self-contained introduction to both subjects, while illustrating the physical principles of quantum information processing using quantum optical systems. It thus has an interdisciplinary character. For the benefit of a wider audience and to make the subject matter of the book accessible to those with backgrounds other than physics, the authors also include a brief review of quantum mechanics. Although much of the material used here can also be found in other books, discussed at various depths, the particular combination of the topics covered in this book is unique. Furthermore, some aspects of quantum information, for example those pertaining to recent experiments on cavity QED and quantum dots, are described here for the first time in book form.

Lambropoulos, Peter

2006-01-01

58

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

59

Novel image encryption/decryption based on quantum Fourier transform and double phase encoding  

Science.gov (United States)

A novel gray-level image encryption/decryption scheme is proposed, which is based on quantum Fourier transform and double random-phase encoding technique. The biggest contribution of our work lies in that it is the first time that the double random-phase encoding technique is generalized to quantum scenarios. As the encryption keys, two phase coding operations are applied in the quantum image spatial domain and the Fourier transform domain respectively. Only applying the correct keys, the original image can be retrieved successfully. Because all operations in quantum computation must be invertible, decryption is the inverse of the encryption process. A detailed theoretical analysis is given to clarify its robustness, computational complexity and advantages over its classical counterparts. It paves the way for introducing more optical information processing techniques into quantum scenarios.

Yang, Yu-Guang; Xia, Juan; Jia, Xin; Zhang, Hua

2013-11-01

60

Quantum information processing with trapped ions  

International Nuclear Information System (INIS)

Single Ca+ ions and crystals of Ca+ ions are confined in a linear Paul trap and are investigated for quantum information processing. Here we report on recent experimental advancements towards a quantum computer with such a system. Laser-cooled trapped ions are ideally suited systems for the investigation and implementation of quantum information processing as one can gain almost complete control over their internal and external degrees of freedom. The combination of a Paul type ion trap with laser cooling leads to unique properties of trapped cold ions, such as control of the motional state down to the zero-point of the trapping potential, a high degree of isolation from the environment and thus a very long time available for manipulations and interactions at the quantum level. The very same properties make single trapped atoms and ions well suited for storing quantum information in long lived internal states, e.g. by encoding a quantum bit (qubit) of information within the coherent superposition of the S1/2 ground state and the metastable D5/2 excited state of Ca+. Recently we have achieved the implementation of simple algorithms with up to 3 qubits on an ion-trap quantum computer. We will report on methods to implement single qubit rotations, the realization of a two-qubit universal quantum gate (Cirac-Zoller CNOT-gate), the deterministic generation of multi-particle entangled states (GHZ- and W-states), their full tomographic reconstruction, the realization of deterministic quantum teleportation, its quantum process tomography and the encoding of quantum information in decoherence-free subspaces with coherence times exceeding 20 seconds. (author)

2005-06-13

 
 
 
 
61

Utilizing encoding in scalable linear optics quantum computing  

International Nuclear Information System (INIS)

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

2004-12-01

62

Reference frames, superselection rules, and quantum information  

International Nuclear Information System (INIS)

Recently, there has been much interest in a new kind of 'unspeakable' quantum information that stands to regular quantum information in the same way that a direction in space or a moment in time stands to a classical bit string: the former can only be encoded using particular degrees of freedom while the latter are indifferent to the physical nature of the information carriers. The problem of correlating distant reference frames, of which aligning Cartesian axes and synchronizing clocks are important instances, is an example of a task that requires the exchange of unspeakable information and for which it is interesting to determine the fundamental quantum limit of efficiency. There have also been many investigations into the information theory that is appropriate for parties that lack reference frames or that lack correlation between their reference frames, restrictions that result in global and local superselection rules. In the presence of these, quantum unspeakable information becomes a new kind of resource that can be manipulated, depleted, quantified, etc. Methods have also been developed to contend with these restrictions using relational encodings, particularly in the context of computation, cryptography, communication, and the manipulation of entanglement. This paper reviews the role of reference frames and superselection rules in the theory of quantum-information processing

2007-04-01

63

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

64

Stabilizing Quantum Information  

CERN Document Server

The algebraic structure underlying all the schemes for quantum information stabilization is argued to be fully contained in the reducibility of the operator algebra describing the interaction with the environment of the coding quantum system. This property amounts to the existence of a non-trivial group of symmetries for the global dynamics. We provide a unified framework which allows us to build sistematically new classes of (non-additive) error correcting codes and noiseless subsystems. Moreover relations between noiseless subsystems (and codes) and decoupling strategies are clarified.

Zanardi, P

2001-01-01

65

Block synchronization for quantum information  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Locating the boundaries of consecutive blocks of quantum information is a fundamental building block for advanced quantum computation and quantum communication systems. We develop a coding theoretic method for properly locating boundaries of quantum information without relying on external synchronization when block synchronization is lost. The method also protects qubits from decoherence in a manner similar to conventional quantum error-correcting codes, seamlessly achieving...

Fujiwara, Yuichiro

2012-01-01

66

Informational power of quantum measurements  

International Nuclear Information System (INIS)

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.

2011-06-01

67

Sending classical information through relativistic quantum channels  

CERN Multimedia

We investigate how special relativity influences the transmission of classical information through quantum channels by evaluating the Holevo bound when the sender and the receiver are in (relativistic) relative motion. By using the spin degrees of freedom of spin-1/2 fermions to encode the classical information we show that, for some configurations, the accessible information in the receiver can be increased when the spin detector moves fast enough. This is possible by allowing the momentum wave packet of one of the particles to be wide enough while the momentum wave packets of other particles are kept relatively narrow. In this way, one can take advantage of the fact that boosts entangle the spin and momentum degrees of freedom of spin-1/2 fermions to increase the accessible information in the former. We close the paper with a discussion of how this relativistic quantum channel cannot in general be described by completely positive quantum maps.

Landulfo, Andre G S

2013-01-01

68

High-fidelity linear optical quantum computing with polarization encoding  

CERN Document Server

We show that the KLM scheme [Knill, Laflamme and Milburn, Nature {\\bf 409}, 46] can be implemented using polarization encoding with only a small overhead with respect to the original dual-rail encoding. The main advantage of this new implementation is that the probability of a gate introducing a non-detected error, when non-ideal detectors are considered, does not depend on the detector efficiency but rather on the detector dark-count rate. Since very low dark-count rate detectors are 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.

Spedalieri, F M; Lee, H

2005-01-01

69

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

CERN Document Server

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

70

Quantum: information theory: technological challenge  

International Nuclear Information System (INIS)

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

71

Encoding and decoding phase information in high-n circular wave packets  

Science.gov (United States)

We demonstrate theoretically and experimentally the extraction of detailed information on the density matrix of very-high-n (>300) near-circular Rydberg wave packets through Fourier analysis of the quantum beat and quantum revival signals. The remarkably long coherence times associated with circular wave packets facilitate the preservation and read-out of phase information encoded in this matrix. We illustrate the power of the method by determining the angular localization of the components of a wave packet.

Yoshida, S.; Reinhold, C. O.; Burgdörfer, J.; Wyker, B.; Dunning, F. B.

2010-06-01

72

Encoding and Decoding Information in High-n Circular Wave Packets  

Energy Technology Data Exchange (ETDEWEB)

We demonstrate theoretically and experimentally the extraction of detailed information on the density matrix of very-high-n(> 300) near-circular Rydberg wave packets through Fourier analysis of the quantum beat and quantum revival signal. The remarkably long coherence times associated with circular wave packets facilitate the preservation and read-out of information encoded in this matrix. We illustrate the power of the method by determining the angular localization of the components of a wave packet.

Yoshida, S. [Vienna University of Technology, Austria; Reinhold, Carlos O [ORNL; Burgdorfer, J. [Vienna University of Technology, Austria; Wyker, B. [Rice University; Dunning, F. B. [Rice University

2010-01-01

73

Quantum information can be negative  

CERN Multimedia

Given an unknown quantum state distributed over two systems, we determine how much quantum communication is needed to transfer the full state to one system. This communication measures the "partial information" one system needs conditioned on it's prior information. It turns out to be given by an extremely simple formula, the conditional entropy. In the classical case, partial information must always be positive, but we find that in the quantum world this physical quantity can be negative. If the partial information is positive, its sender needs to communicate this number of quantum bits to the receiver; if it is negative, the sender and receiver instead gain the corresponding potential for future quantum communication. We introduce a primitive "quantum state merging" which optimally transfers partial information. We show how it enables a systematic understanding of quantum network theory, and discuss several important applications including distributed compression, multiple access channels and multipartite a...

Horodecki, M; Horodecki, Michal; Winter, Jonathan Oppenheim & Andreas

2005-01-01

74

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

75

Quantum information can be negative  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Given an unknown quantum state distributed over two systems, we determine how much quantum communication is needed to transfer the full state to one system. This communication measures the "partial information" one system needs conditioned on it's prior information. It turns out to be given by an extremely simple formula, the conditional entropy. In the classical case, partial information must always be positive, but we find that in the quantum world this physical quantity c...

Horodecki, Michal; Oppenheim, Jonathan; Winter, Andreas

2005-01-01

76

Entanglement, Quantum Entropy and Mutual Information  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The operational structure of quantum couplings and entanglements is studied and classified for semifinite von Neumann algebras. We show that the classical-quantum correspondences such as quantum encodings can be treated as diagonal semi-classical (d-) couplings, and the entanglements characterized by truly quantum (q-) couplings, can be regarded as truly quantum encodings. The relative entropy of the d-compound and entangled states leads to two different types of entropy for...

Belavkin, V. P.; Ohya, M.

2002-01-01

77

Experimental Implementation of Encoded Logical Qubit Operations in a Perfect Quantum Error Correcting Code  

Science.gov (United States)

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, Jingfu; Laflamme, Raymond; Suter, Dieter

2012-09-01

78

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

79

Quantum information theory and quantum statistics  

CERN Multimedia

Based on lectures given by the author, this book focuses on providing reliable introductory explanations of key concepts of quantum information theory and quantum statistics - rather than on results. The mathematically rigorous presentation is supported by numerous examples and exercises and by an appendix summarizing the relevant aspects of linear analysis. Assuming that the reader is familiar with the content of standard undergraduate courses in quantum mechanics, probability theory, linear algebra and functional analysis, the book addresses graduate students of mathematics and physics as well as theoretical and mathematical physicists. Conceived as a primer to bridge the gap between statistical physics and quantum information, a field to which the author has contributed significantly himself, it emphasizes concepts and thorough discussions of the fundamental notions to prepare the reader for deeper studies, not least through the selection of well chosen exercises.

Petz, Dénes

2008-01-01

80

Quantum information theory and quantum statistics  

Energy Technology Data Exchange (ETDEWEB)

Based on lectures given by the author, this book focuses on providing reliable introductory explanations of key concepts of quantum information theory and quantum statistics - rather than on results. The mathematically rigorous presentation is supported by numerous examples and exercises and by an appendix summarizing the relevant aspects of linear analysis. Assuming that the reader is familiar with the content of standard undergraduate courses in quantum mechanics, probability theory, linear algebra and functional analysis, the book addresses graduate students of mathematics and physics as well as theoretical and mathematical physicists. Conceived as a primer to bridge the gap between statistical physics and quantum information, a field to which the author has contributed significantly himself, it emphasizes concepts and thorough discussions of the fundamental notions to prepare the reader for deeper studies, not least through the selection of well chosen exercises. (orig.)

Petz, D. [Alfred Renyi Institute of Mathematics, Budapest (Hungary)

2008-07-01

 
 
 
 
81

Quantum information transfer using photons  

Science.gov (United States)

Optical communication channels have redefined the scope and applications of classical computing; similarly, photonic transfer of quantum information promises to open new horizons for quantum computing. The implementation of light-matter interfaces that preserve quantum information is technologically challenging, but key building blocks for such devices have recently been demonstrated by several research groups. Here, we outline the theoretical framework for information transfer between the nodes of a quantum network, review the current experimental state of the art and discuss the prospects for hybrid systems currently in development.

Northup, T. E.; Blatt, R.

2014-05-01

82

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

83

Quantum Information: Opportunities and Challenges  

Energy Technology Data Exchange (ETDEWEB)

Modern society is shaped by the ability to transmit, manipulate, and store large amounts of information. Although we tend to think of information as abstract, information is physical, and computing is a physical process. How then should we understand information in a quantum world, in which physical systems may exist in multiple states at once and are altered by the very act of observation? This question has evolved into an exciting new field of research called Quantum Information (QI). QI challenges many accepted rules and practices in computer science. For example, a quantum computer would turn certain hard problems into soft problems, and would render common computationally-secure encryption methods (such as RSA) insecure. At the same time, quantum communication would provide an unprecedented kind of intrinsic information security at the level of the smallest physical objects used to store or transmit the information. This talk provides a general introduction to the subject of quantum information and its relevance to cyber security. In the first part, two of the stranger aspects of quantum physics namely, superposition and uncertainty are explained, along with their relation to the concept of information. These ideas are illustrated with a few examples: quantum ID cards, quantum key distribution, and Grover s quantum search algorithm. The state-of-the-art in quantum computing and communication hardware is then discussed, along with the daunting technological challenges that must be overcome. Relevant experimental and theoretical efforts at ORNL are highlighted. The talk concludes with speculations on the short- and long-term impact of quantum information on cyber security.

Bennink, Ryan S [ORNL

2008-01-01

84

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

85

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

International Nuclear Information System (INIS)

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.

2011-11-01

86

A quantum computer in the scheme of an atomic quantum transistor with logical encoding of qubits  

Science.gov (United States)

A scheme of a multiqubit quantum computer on atomic ensembles using a quantum transistor implementing two qubit gates is proposed. We demonstrate how multiatomic ensembles permit one to work with a large number of qubits that are represented in a logical encoding in which each qubit is recorded on a superposition of single-particle states of two atomic ensembles. The access to qubits is implemented by appropriate phasing of quantum states of each of atomic ensembles. An atomic quantum transistor is proposed for use when executing two qubit operations. The quantum transistor effect appears when an excitation quantum is exchanged between two multiatomic ensembles located in two closely positioned QED cavities connected with each other by a gate atom. The dynamics of quantum transfer between atomic ensembles can be different depending on one of two states of the gate atom. Using the possibilities of control for of state of the gate atom, we show the possibility of quantum control for the state of atomic ensembles and, based on this, implementation of basic single and two qubit gates. Possible implementation schemes for a quantum computer on an atomic quantum transistor and their advantages in practical implementation are discussed.

Moiseev, S. A.; Andrianov, S. N.; Moiseev, E. S.

2013-09-01

87

Isotope-based quantum information  

Energy Technology Data Exchange (ETDEWEB)

The present book provides to the main ideas and techniques of the rapid progressing field of quantum information and quantum computation using isotope - mixed materials. It starts with an introduction to the isotope physics and then describes of the isotope - based quantum information and quantum computation. The ability to manipulate and control electron and/or nucleus spin in semiconductor devices provides a new route to expand the capabilities of inorganic semiconductor-based electronics and to design innovative devices with potential application in quantum computing. One of the major challenges towards these objectives is to develop semiconductor-based systems and architectures in which the spatial distribution of spins and their properties can be controlled. For instance, to eliminate electron spin decoherence resulting from hyperfine interaction due to nuclear spin background, isotopically controlled devices are needed (i.e., nuclear spin-depleted). In other emerging concepts, the control of the spatial distribution of isotopes with nuclear spins is a prerequisite to implement the quantum bits (or qbits). Therefore, stable semiconductor isotopes are important elements in the development of solid-state quantum information. There are not only different algorithms of quantum computation discussed but also the different models of quantum computers are presented. With numerous illustrations this small book is of great interest for undergraduate students taking courses in mesoscopic physics or nanoelectronics as well as quantum information, and academic and industrial researches working in this field.

Plekhanov, Vladimir G. [Computer Science College, Tallinn (Estonia). Mathematics and Physics Dept.

2012-07-01

88

Encoding an Arbitrary State in a [7,1,3] Quantum Error Correction Code  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We calculate the fidelity with which an arbitrary state can be encoded into a [7,1,3] CSS quantum error correction code in a non-equiprobable Pauli operator error environment with the goal of determining whether this encoding can be used for practical implementations of quantum computation. This determination is accomplished by applying ideal error correction to the encoded state which demonstrates the correctability of errors that occurred during the encoding process. We th...

Buchbinder, Sidney D.; Huang, Channing L.; Weinstein, Yaakov S.

2011-01-01

89

Quantum Correlations, Chaos and Information  

Science.gov (United States)

Quantum chaos is the study of quantum systems whose classical description is chaotic. How does chaos manifest itself in the quantum world? In this spirit, we study the dynamical generation of entanglement as a signature of chaos in a system of periodically kicked coupled-tops, where chaos and entanglement arise from the same physical mechanism. The long-time entanglement as a function of the position of an initially localized wave packet very closely correlates with the classical phase space surface of section - it is nearly uniform in the chaotic sea, and reproduces the detailed structure of the regular islands. The uniform value in the chaotic sea is explained by the random state conjecture. As classically chaotic dynamics take localized distributions in phase space to random distributions, quantized versions take localized coherent states to pseudo-random states in Hilbert space. Such random states are highly entangled, with an average value near that of the maximally entangled state. For a map with global chaos, we derive that value based on new analytic results for the entropy of random states. For a mixed phase space, we use the Percival conjecture to identify a "chaotic subspace" of the Hilbert space. The typical entanglement, averaged over the unitarily invariant Haar measure in this subspace, agrees with the long-time averaged entanglement for initial states in the chaotic sea. In all cases the dynamically generated entanglement is that of a random complex vector, even though the system is time-reversal invariant, and the Floquet operator is a member of the circular orthogonal ensemble. Continuing on our journey to find the footprints of chaos in the quantum world, we explore quantum signatures of classical chaos by studying the rate of information gain in quantum tomography. The measurement record is obtained as a sequence of expectation values of a Hermitian operator evolving under repeated application of the Floquet operator of the quantum kicked top on a large ensemble of identical systems. We find an increase in the rate of information gain and hence higher fidelities in the process when the Floquet maps employed increase in chaoticity. We make predictions for the information gain using random matrix theory in the fully chaotic regime and show a remarkable agreement between the two. Finally we discuss how this approach can be used in general as a benchmark for information gain in an experimental implementation based on nonlinear dynamics of atomic spins measured weakly by the Faraday rotation of a laser probe. The last part of this thesis is devoted to the study of the nature of quantum correlations themselves. Quantum correlations are at the heart of the weirdness of quantum mechanics and at the same time serve as a resource for the potential benefits quantum information processing might provide. For example, Einstein described quantum entanglement as "spooky action at a distance". However, even entanglement does not fully capture the complete quantum character of a system. Quantum discord aims to fill this gap and captures essentially all the quantum correlations in a quantum state. There is a considerable interest in the research community about quantum discord, since there is evidence showing this very quantity as responsible for the exponential speed up of a certain class of quantum algorithms over classical ones. Now, an important question arises: Is discord just a mathematical construct or does it have a definable physical role in information processing? This thesis provides a link between quantum discord and an actual physical task involving communication between two parties. We present an operational interpretation of quantum discord based on the quantum state merging protocol. Quantum discord is the markup in the cost of quantum communication in the process of quantum state merging, if one discards relevant prior information. We further derive a quantitative relation between the yield of the fully quantum Slepian-Wolf protocol in the presence of noise and the quantum discord of

Madhok, Vaibhav

90

Manipulating quantum information via quantum cloning  

Energy Technology Data Exchange (ETDEWEB)

An extensive characterization of the information flux underlying the 1 {yields}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 {yields}2 cloning to the 1 {yields}3 universal and covariant processes is reported with the first experimental optical realizations.

De Martini, F; Masullo, L; Ricci, M; Sciarrino, F; Secondi, V [Dipartimento di Fisica, Universita di Roma ' La Sapienza' , Istituto Nazionale per la Fisica della Materia, Rome 00185 (Italy)

2005-12-01

91

Source Coding With Distortion Side Information At The Encoder  

CERN Multimedia

We consider lossy source coding when side information affecting the distortion measure may be available at the encoder, decoder, both, or neither. For example, such distortion side information can model reliabilities for noisy measurements, sensor calibration information, or perceptual effects like masking and sensitivity to context. When the distortion side information is statistically independent of the source, we show that in many cases (e.g, for additive or multiplicative distortion side information) there is no penalty for knowing the side information only at the encoder, and there is no advantage to knowing it at the decoder. Furthermore, for quadratic distortion measures scaled by the distortion side information, we evaluate the penalty for lack of encoder knowledge and show that it can be arbitrarily large. In this scenario, we also sketch transform based quantizers constructions which efficiently exploit encoder side information in the high-resolution limit.

Martinian, E; Zamir, R; Martinian, Emin; Wornell, Gregory W.; Zamir, Ram

2004-01-01

92

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

CERN Multimedia

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. The system is based on the interference of phase encoded coherent states of light and our implementation utilises polarisation maintaining optical fibre and photon...

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

2013-01-01

93

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

Energy Technology Data Exchange (ETDEWEB)

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{sup -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.

Xavier, G B; Vilela de Faria, G; Temporao, G P; Von der Weid, J P [Centre for Telecommunication Studies, Pontifical Catholic University of Rio de Janeiro-R Marques de Sao Vicente 225 Gavea, Rio de Janeiro (Brazil); Walenta, N; Gisin, N; Zbinden, H [GAP-Optique, University of Geneva, rue de l' Ecole-de-Medecine 20, CH-1211 Geneva 4 (Switzerland)], E-mail: guix@opto.cetuc.puc-rio.br

2009-04-15

94

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

International Nuclear Information System (INIS)

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.

2009-04-01

95

Quantum information and computing  

CERN Document Server

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

Ohya, M; Watanabe, N

2006-01-01

96

Some Charicteristics and Applications for Quantum Information  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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.

2012-01-01

97

Quantum information and convex optimization  

Energy Technology Data Exchange (ETDEWEB)

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.)

Reimpell, Michael

2008-07-01

98

Encoding simplicial quantum geometry in group field theories  

International Nuclear Information System (INIS)

An extended group field theory formalism for quantum gravity, based on a field that is a function of both group variables, interpreted as discretized connection, and Lie algebra variables, interpreted as discretized triads, has been proposed recently as an attempt to define models with a clearer link with simplicial geometry. In the context of such a formalism, we introduce a new symmetry requirement on the field. This leads, in 3D, to Feynman amplitudes interpreted as simplicial path integrals based on the Regge action, to a proper relation between the discrete connection and the triad vectors appearing in the Regge action, and to a much more satisfactory and transparent encoding of simplicial geometry already at the level of the group field theory action.

2010-07-07

99

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

2012-10-01

100

Chaos and quantum Fisher information in the quantum kicked top  

International Nuclear Information System (INIS)

Quantum Fisher information is related to the problem of parameter estimation. Recently, a criterion has been proposed for entanglement in multipartite systems based on quantum Fisher information. This paper studies the behaviours of quantum Fisher information in the quantum kicked top model, whose classical correspondence can be chaotic. It finds that, first, detected by quantum Fisher information, the quantum kicked top is entangled whether the system is in chaotic or in regular case. Secondly, the quantum Fisher information is larger in chaotic case than that in regular case, which means, the system is more sensitive in the chaotic case. (general)

2011-05-01

 
 
 
 
101

Information dynamics in quantum theory  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Shannon entropy and Fisher information functionals are known to quantify certain information-theoretic properties of continuous probability distributions of various origins. We carry out a systematic study of these functionals, while assuming that the pertinent probability density has a quantum mechanical appearance $\\rho \\doteq |\\psi |^2$, with $\\psi \\in L^2(R)$. Their behavior in time, due to the quantum Schr\\"{o}dinger picture evolution-induced dynamics of $\\rho (x,t)$ is...

Garbaczewski, Piotr

2006-01-01

102

Quantum information. Teleporation - cryptography - quantum computer  

International Nuclear Information System (INIS)

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

2010-01-01

103

Tight informationally complete quantum measurements  

International Nuclear Information System (INIS)

We introduce a class of informationally complete positive-operator-valued measures which are, in analogy with a tight frame, 'as close as possible' to orthonormal bases for the space of quantum states. These measures are distinguished by an exceptionally simple state-reconstruction formula which allows 'painless' quantum state tomography. Complete sets of mutually unbiased bases and symmetric informationally complete positive-operator-valued measures are both members of this class, the latter being the unique minimal rank-one members. Recast as ensembles of pure quantum states, the rank-one members are in fact equivalent to weighted 2-designs in complex projective space. These measures are shown to be optimal for quantum cloning and linear quantum state tomography

2006-10-27

104

Quantum Tomograms and Their Application in Quantum Information Science  

International Nuclear Information System (INIS)

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.

2013-02-08

105

Quantum Optics and Quantum Information Laboratory  

Science.gov (United States)

This website contains information on a laboratory course at the Institute of Optics, University of Rochester, on quantum optics. It includes descriptions and manuals for four teaching experiments on single and entangled photons for undergraduates. It also includes a course syllabus and studentsâ assignments, reports and presentations. This work is supported by the NSF grants ECS-0420888 and DUE-0633621, the University of Rochester Kauffman Foundation Initiative, and the Spectra-Physics division of Newport Corporation.

Lukisova, Svetlana

2009-01-16

106

Quantum Information Processing with Graphs  

CERN Document Server

Graph states are an elegant and powerful quantum resource for measurement based quantum computation (MBQC). They are also used for many quantum protocols (error correction, secret sharing, etc.). The main focus of this paper is to provide a structural characterization of the graph states that can be used for quantum information processing. The existence of a gflow (generalized flow) is known to be a requirement for open graphs (graph, input set and output set) to perform uniformly and strongly deterministic computations. We weaken the gflow conditions to define two new more general types of MBQC: uniform equiprobability and constant probability. These classes can be useful from a cryptographic and information point of view because even though we can not do a deterministic computation in general we can preserve the information and transfer it perfectly from the inputs to the outputs. We derive simple graph characterizations for these classes and prove that the deterministic and uniform equiprobability classes ...

Mhalla, Mehdi; Perdrix, Simon; Someya, Masato; Turner, Peter S

2010-01-01

107

Quantum information. Teleportation - cryptography - quantum computer  

International Nuclear Information System (INIS)

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

2012-01-01

108

Quantum information processing in nanostructures  

International Nuclear Information System (INIS)

Since information has been regarded os a physical entity, the field of quantum information theory has blossomed. This brings novel applications, such as quantum computation. This field has attracted the attention of numerous researchers with backgrounds ranging from computer science, mathematics and engineering, to the physical sciences. Thus, we now have an interdisciplinary field where great efforts are being made in order to build devices that should allow for the processing of information at a quantum level, and also in the understanding of the complex structure of some physical processes at a more basic level. This thesis is devoted to the theoretical study of structures at the nanometer-scale, 'nanostructures', through physical processes that mainly involve the solid-state and quantum optics, in order to propose reliable schemes for the processing of quantum information. Initially, the main results of quantum information theory and quantum computation are briefly reviewed. Next, the state-of-the-art of quantum dots technology is described. In so doing, the theoretical background and the practicalities required for this thesis are introduced. A discussion of the current quantum hardware used for quantum information processing is given. In particular, the solid-state proposals to date are emphasised. A detailed prescription is given, using an optically-driven coupled quantum dot system, to reliably prepare and manipulate exciton maximally entangled Bell and Greenberger-Horne-Zeilinger (GHZ) states. Manipulation of the strength and duration of selective light-pulses needed for producing these highly entangled states provides us with crucial elements for the processing of solid-state based quantum information. The all-optical generation of states of the so-called Bell basis for a system of two quantum dots (QDs) is exploited for performing the quantum teleportation of the excitonic state of a dot in an array of three coupled QDs. Theoretical predictions suggest that several hundred single quantum bit rotations and controlled-NOT gates could be performed before decoherence of the excitonic states takes place. In addition, the exciton coherent dynamics of a coupled QD system confined within a semiconductor single mode microcavity is reported. It is shown that this system enables the control of exciton entanglement by varying the coupling strength between the optically-driven dot system and the microcavity. The exciton entanglement shows collapses and revivals for suitable amplitudes of the incident radiation field and dot-cavity coupling strengths. The results given here could offer a new approach for the control of decoherence mechanisms arising from entangled 'artificial molecules'. In addition to these ultrafast coherent optical control proposals, an approach for reliable implementation of quantum logic gates and long decoherence times in a QD system based on nuclear magnetic resonance (NMR) is given, where the nuclear resonance is controlled by the ground state 'magic number' transitions of few-electron QDs in an external magnetic field. The dynamical evolution of quantum registers of arbitrary length in the presence of environmentally-induced decoherence effects is studied in detail. The cases of quantum bits (qubits) coupling individually to different environments ('independent decoherence'), and qubits interacting collectively with the same reservoir ('collective decoherence') are analysed in order to find explicit decoherence functions for any number of qubits. The decay of the coherences of the register is shown to strongly depend on the input states: this sensitivity is a characteristic of both types of coupling (collective and independent) and not only of the collective coupling, as has been reported previously. A non-trivial behaviour--'recoherence'-- is found in the decay of the off-diagonal elements of the reduced density matrix in the specific situation of independent decoherence. The results lead to the identification of decoherence-free states in the collective decoherence limit. These states belong to s

2002-01-01

109

Quantum information and relativity theory  

International Nuclear Information System (INIS)

This article discusses the intimate relationship between quantum mechanics, information theory, and relativity theory. Taken together these are the foundations of present-day theoretical physics, and their interrelationship is an essential part of the theory. The acquisition of information from a quantum system by an observer occurs at the interface of classical and quantum physics. The authors review the essential tools needed to describe this interface, i.e., Kraus matrices and positive-operator-valued measures. They then discuss how special relativity imposes severe restrictions on the transfer of information between distant systems and the implications of the fact that quantum entropy is not a Lorentz-covariant concept. This leads to a discussion of how it comes about that Lorentz transformations of reduced density matrices for entangled systems may not be completely positive maps. Quantum field theory is, of course, necessary for a consistent description of interactions. Its structure implies a fundamental tradeoff between detector reliability and localizability. Moreover, general relativity produces new and counterintuitive effects, particularly when black holes (or, more generally, event horizons) are involved. In this more general context the authors discuss how most of the current concepts in quantum information theory may require a reassessment

2004-01-01

110

Symmetric Informationally Complete Quantum Measurements  

CERN Document Server

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

111

Geometrical and Topological Aspects of Quantum Information Systems  

CERN Document Server

In this Thesis we examine the interplay between the encoding of information in quantum systems and their geometrical and topological properties. We first study photonic qubit probes of space-time curvature, showing how gauge-independent trajectories of photons can help to perform quantum information tasks in space. Then we introduce the first example of topologically ordered systems constructed using interacting light modes on a two-dimensional lattice, which paves the way for feasible observations of topological order in bosonic systems. To conclude, motivated by a theory of quantum gravity we analyze the convergence of entropy in unitarily inequivalent quantization schemes.

Demarie, Tommaso F

2014-01-01

112

Entanglements and compound states in quantum information theory  

CERN Document Server

Quantum entanglements, describing truly quantum couplings, are stu died and classified from the point of view of quantum compound states. We show that c lassical-quantum correspondences such as quantum encodings can be treated as d-entanglements leading to a special class of the separable compound states. The mutual information of the d-compound and entangled states lead to two di fferent types of entropies for a given quantum state: the von Neumann entrop y, which is achieved as the supremum of the information over all d-entanglem ents, and the dimensional entropy, which is achieved at the standard entangl ement, the true quantum entanglement, coinciding with a d-entanglement only in the commutative case. The q-capacity of a quantum noiseless channel, defi ned as the supremum over all entanglements, is given as the logarithm of the dimensionality of the input von Neumann algebra. It can double the classical capacity, achieved as the supremum over all semi-quantum couplings (d-entang lements, or encodings), w...

Belavkin, V P; Belavkin, Viacheslav P; Ohya, Masanori

2000-01-01

113

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

Science.gov (United States)

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. PMID:23005271

Zhang, Jingfu; Laflamme, Raymond; Suter, Dieter

2012-09-01

114

Efficient optical quantum information processing  

Energy Technology Data Exchange (ETDEWEB)

Quantum information offers the promise of being able to perform certain communication and computation tasks that cannot be done with conventional information technology (IT). Optical quantum information processing (QIP) holds particular appeal, since it offers the prospect of communicating and computing with the same type of qubit. Linear optical techniques have been shown to be scalable, but the corresponding quantum computing circuits need many auxiliary resources. Here we present an alternative approach to optical QIP, based on the use of weak cross-Kerr nonlinearities and homodyne measurements. We show how this approach provides the fundamental building blocks for highly efficient non-absorbing single photon number resolving detectors, two qubit parity detectors, Bell state measurements and finally near deterministic control-not (CNOT) gates. These are essential QIP devices.

Munro, W J [Quantum Information Processing Group, Hewlett-Packard Laboratories, Filton Road, Stoke Gifford, Bristol BS34 8QZ (United Kingdom); Nemoto, Kae [Quantum Information Science Group, National Institute of Informatics, 2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo 101-8430 (Japan); Spiller, T P [Quantum Information Processing Group, Hewlett-Packard Laboratories, Filton Road, Stoke Gifford, Bristol BS34 8QZ (United Kingdom); Barrett, S D [Quantum Information Processing Group, Hewlett-Packard Laboratories, Filton Road, Stoke Gifford, Bristol BS34 8QZ (United Kingdom); Kok, Pieter [Quantum Information Processing Group, Hewlett-Packard Laboratories, Filton Road, Stoke Gifford, Bristol BS34 8QZ (United Kingdom); Beausoleil, R G [Hewlett-Packard Laboratories, 13837 175th Place NE, Redmond, WA 98052-2180 (United States)

2005-07-01

115

Efficient optical quantum information processing  

CERN Document Server

Quantum information offers the promise of being able to perform certain communication and computation tasks that cannot be done with conventional information technology (IT). Optical Quantum Information Processing (QIP) holds particular appeal, since it offers the prospect of communicating and computing with the same type of qubit. Linear optical techniques have been shown to be scalable, but the corresponding quantum computing circuits need many auxiliary resources. Here we present an alternative approach to optical QIP, based on the use of weak cross-Kerr nonlinearities and homodyne measurements. We show how this approach provides the fundamental building blocks for highly efficient non-absorbing single photon number resolving detectors, two qubit parity detectors, Bell state measurements and finally near deterministic control-not (CNOT) gates. These are essential QIP devices

Munro, W J; Spiller, T P; Barrett, S D; Kok, P; Beausoleil, R G; Nemoto, Kae; Kok, Pieter

2005-01-01

116

Endophysical information transfer in quantum processes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We give a mathematical criterion for the concept of information flow within closed quantum systems described by quantum registers. We define the concepts of separations and entanglements over quantum registers and use them with the quantum zip properties of inner products over quantum registers to establish the concept of partition change, which is fundamental to our criterion of endophysical information exchange within such quantum systems.

Eakins, Jon; Jaroszkiewicz, George

2004-01-01

117

No-partial erasure of quantum information  

Energy Technology Data Exchange (ETDEWEB)

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.

Pati, Arun K. [Institute of Physics, Sainik School Post, Bhubaneswar 751005, Orissa (India)]. E-mail: akpati@iopb.res.in; Sanders, Barry C. [Institute for Quantum Information Science, University of Calgary, Alberta T2N 1N4 (Canada) and Australian Centre of Excellence for Quantum Computer Technology, Macquarie University, Sydney, New South Wales 2109 (Australia)]. E-mail: bsanders@qis.ucalgary.ca

2006-11-06

118

Examples of minimal-memory, non-catastrophic quantum convolutional encoders  

CERN Document Server

One of the most important open questions in the theory of quantum convolutional coding is to determine a minimal-memory, non-catastrophic, polynomial-depth convolutional encoder for an arbitrary quantum convolutional code. Here, we present a technique that finds quantum convolutional encoders with such desirable properties for several example quantum convolutional codes (an exposition of our technique in full generality will appear elsewhere). We first show how to encode the well-studied Forney-Grassl-Guha (FGG) code with an encoder that exploits just one memory qubit (the former Grassl-Roetteler encoder requires 15 memory qubits). We then show how our technique can find an online decoder corresponding to this encoder, and we also detail the operation of our technique on a different example of a quantum convolutional code. Finally, the reduction in memory for the FGG encoder makes it feasible to simulate the performance of a quantum turbo code employing it, and we present the results of such simulations.

Wilde, Mark M; Hosseini-Khayat, Saied

2010-01-01

119

Representation of Quantum Field Theory by Elementary Quantum Information  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this paper is considered relativistic quantum field theory expressed by elementary units of quantum information as they are considered as fundamental entity of nature by Carl Friedrich von Weizsaecker. Through quantization of a Weyl spinor describing an elementary unit of quantum information and consisting of four real components one obtains four pairs of creation and annihilation operators acting in a tensor space of states containing many units of quantum information. T...

Kober, Martin

2011-01-01

120

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

2012-09-01

 
 
 
 
121

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

122

Small-scale quantum information processing with linear optics  

International Nuclear Information System (INIS)

Full text: Photons are the ideal systems for carrying quantum information. Although performing large-scale quantum computation on optical systems is extremely demanding, non scalable linear-optics quantum information processing may prove essential as part of quantum communication networks. In addition efficient (scalable) linear-optical quantum computation proposal relies on the same optical elements. Here, by constructing multirail optical networks, we experimentally study two central problems in quantum information science, namely optimal discrimination between nonorthogonal quantum states, and controlling decoherence in quantum systems. Quantum mechanics forbids deterministic discrimination between nonorthogonal states. This is one of the central features of quantum cryptography, which leads to secure communications. Quantum state discrimination is an important primitive in quantum information processing, since it determines the limitations of a potential eavesdropper, and it has applications in quantum cloning and entanglement concentration. In this work, we experimentally implement generalized measurements in an optical system and demonstrate the first optimal unambiguous discrimination between three non-orthogonal states with a success rate of 55 %, to be compared with the 25 % maximum achievable using projective measurements. Furthermore, we present the first realization of unambiguous discrimination between a pure state and a nonorthogonal mixed state. In a separate experiment, we demonstrate how decoherence-free subspaces (DFSs) may be incorporated into a prototype optical quantum algorithm. Specifically, we present an optical realization of two-qubit Deutsch-Jozsa algorithm in presence of random noise. By introduction of localized turbulent airflow we produce a collective optical dephasing, leading to large error rates and demonstrate that using DFS encoding, the error rate in the presence of decoherence can be reduced from 35 % to essentially its pre-noise value 7 %. (author)

2005-05-20

123

Black holes as mirrors: quantum information in random subsystems  

CERN Multimedia

We study information retrieval from evaporating black holes, assuming that the internal dynamics of a black hole is unitary and rapidly mixing, and assuming that the retriever has unlimited control over the emitted Hawking radiation. If the evaporation of the black hole has already proceeded past the "half-way" point, where half of the initial entropy has been radiated away, then additional quantum information deposited in the black hole is revealed in the Hawking radiation very rapidly. Information deposited prior to the half-way point remains concealed until the half-way point, and then emerges quickly. These conclusions hold because typical local quantum circuits are efficient encoders for quantum error-correcting codes that nearly achieve the capacity of the quantum erasure channel. Our estimate of a black hole's information retention time, based on speculative dynamical assumptions, is just barely compatible with the black hole complementarity hypothesis.

Hayden, Patrick

2007-01-01

124

Channel simulation with quantum side information  

CERN Multimedia

We study and solve the problem of classical channel simulation with quantum side information at the receiver. This is a generalization of both the classical reverse Shannon theorem, and the classical-quantum Slepian-Wolf problem. The optimal noiseless communication rate is found to be reduced from the mutual information between the channel input and output by the Holevo information between the channel output and the quantum side information. Our main theorem has two important corollaries. The first is a quantum generalization of the Wyner-Ziv problem: rate-distortion theory with quantum side information. The second is an alternative proof of the trade-off between classical communication and common randomness distilled from a quantum state. The fully quantum generalization of the problem considered is quantum state redistribution. Here the sender and receiver share a mixed quantum state and the sender wants to transfer part of her state to the receiver using entanglement and quantum communication. We present o...

Luo, Z; Devetak, Igor; Luo, Zhicheng

2006-01-01

125

The role of quantum memory in quantum information processing  

Science.gov (United States)

Until recently, it was believed that long-lived quantum memories were necessary for long-distance quantum communication. However, by using error-correction codes in an efficient way—specifically, by correcting for photon loss—it is possible to transmit quantum information over long distances without quantum memories. For quantum computation, recent architectures for topological quantum computation indicate that the simplest large-scale structure could be memory-less. While a quantum memory may no longer be an essential resource for quantum networks, it could nonetheless be a key device in the development of quantum information technology. However, it is still not clear what benefits a functioning device could bring to quantum information systems, largely due to a lack of detailed models. Recently we have developed a detailed model for a quantum network based on a simple device designed to act as a building block for a full system architecture. The device is based on an optical cavity containing a negatively charged nitrogen-vacancy center in diamond. This model naturally integrates quantum communication with computation, and using this model we can assess quantitatively the costs and benefits of quantum memories. With or without quantum memories, it is necessary for us to preserve quantum information for a long period of time in either communication or computation.

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

2013-09-01

126

Progressing of Quantum Tomography for Quantum Information Acquisition  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper we review a number of recent developments in the study of quantum tomography which is one of the useful methods for quantum state estimation and quantum information acquisition, having sparked explosion of interest in recent years. The quantum process tomography is also analyzed. At the same time, some success experiments and applications of quantum tomography are introduced. Finally, a number of open problems and future directions in this field are proposed.

Chenbin Zhang

2010-06-01

127

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

128

Quantum Physics and Information; Quanta e Informacion  

Energy Technology Data Exchange (ETDEWEB)

Quantum physics allows information coding in classically unexpected and subtle nonlocal ways, as well as information processing with an efficiency largely surpassing that of the present and foreseeable classical computers. Some outstanding aspects of classical and quantum information theory will be addressed here. Quantum teleportation, dense coding, and quantum cryptography are discussed as a few samples of the impact of quanta in the transmission of information. (Author) 116 refs.

Galindo, A.

2000-07-01

129

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

2013-12-01

130

Processing quantum information in diamond  

International Nuclear Information System (INIS)

Quantum computing is an attractive and multidisciplinary field, which became a focus for experimental and theoretical research during the last decade. Among other systems, such as ions in traps and superconducting circuits, solid state based qubits are considered to be promising candidates for use in first experimental tests of quantum hardware. Here we report recent progress in quantum information processing with point defects in diamond. Qubits are defined as single spin states (electron or nuclear). This allows exploration of long coherence times (up to seconds for nuclear spins at cryogenic temperatures). In addition, the optical transition between ground and excited electronic states allows coupling of spin degrees of freedom to the state of the electromagnetic field. Such coupling gives access to spin state read-out via spin-selective scattering of photons. This also allows the use of spin states as robust memory for flying qubits (photons)

2006-05-31

131

Quantum systems, channels, information. A mathematical introduction  

Energy Technology Data Exchange (ETDEWEB)

The subject of this book is theory of quantum system presented from information science perspective. The central role is played by the concept of quantum channel and its entropic and information characteristics. Quantum information theory gives a key to understanding elusive phenomena of quantum world and provides a background for development of experimental techniques that enable measuring and manipulation of individual quantum systems. This is important for the new efficient applications such as quantum computing, communication and cryptography. Research in the field of quantum informatics, including quantum information theory, is in progress in leading scientific centers throughout the world. This book gives an accessible, albeit mathematically rigorous and self-contained introduction to quantum information theory, starting from primary structures and leading to fundamental results and to exiting open problems.

Holevo, Alexander S.

2012-07-01

132

No-compressing of quantum phase information  

CERN Document Server

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

133

Quantum heat engines and information  

CERN Document Server

Recently, Zhang {\\em et al.} [PRA, {\\bf 75}, 062102 (2007)] extended Kieu's interesting work on the quantum Otto engine [PRL, {\\bf 93}, 140403 (2004)] by considering as working substance a bipartite quantum system $AB$ composed of subsystems $A$ and $B$. In this paper, we express the net work done $W_{AB}$ by such an engine explicitly in terms of the macroscopic bath temperatures and information theoretic quantities associated with the microscopic quantum states of the working substance. This allows us to gain insights into the dependence of positive $W_{AB}$ on the quantum properties of the states. We illustrate with a two-qubit XY chain as the working substance. Inspired by the expression, we propose a plausible formula for the work derivable from the subsystems. We show that there is a critical entanglement beyond which it is impossible to draw positive work locally from the individual subsystems while $W_{AB}$ is positive. This could be another interesting manifestation of quantum nonlocality.

Yeo, Ye

2007-01-01

134

Simple fault-tolerant encoding over q-ary CSS quantum codes  

CERN Document Server

CSS codes are a subfamily of stabilizer codes especially appropriate for fault-tolerant quantum computations. A very simple method is proposed to encode a general qudit when a Calderbank-Shor-Steane quantum code, defined over a q-ary alphabet, is used.

Salas, Pedro J

2007-01-01

135

Relative entropy in quantum information theory  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We review the properties of the quantum relative entropy function and discuss its application to problems of classical and quantum information transfer and to quantum data compression. We then outline further uses of relative entropy to quantify quantum entanglement and analyze its manipulation.

Schumacher, Benjamin; Westmoreland, Michael D.

2000-01-01

136

Quantum Information in Space and Time  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Many important results in modern quantum information theory have been obtained for an idealized situation when the spacetime dependence of quantum phenomena is neglected. However the transmission and processing of (quantum) information is a physical process in spacetime. Therefore such basic notions in quantum information theory as the notions of composite systems, entangled states and the channel should be formulated in space and time. We emphasize the importance of the inv...

Volovich, Igor V.

2001-01-01

137

Basic concepts in quantum information theory  

International Nuclear Information System (INIS)

Full text: Quantum information theory provides a framework for the description of quantum systems and their applications in the context of quantum computation and quantum communication. Although several of the basic concepts on which such theory is built are reminiscent of those of (classical) Information Theory, the new rules provided by quantum mechanics introduce properties which have no classical counterpart and that are responsible for most of the applications. In particular, entangled states appear as one of the basic resources in this context. In this lecture I will introduce the basic concepts and applications in Quantum Information, particularly stressing the definition of entanglement, its quantification, and its applications. (author)

2005-05-20

138

Quantum State Merging and Negative Information  

Science.gov (United States)

We consider a quantum state shared between many distant locations, and define a quantum information processing primitive, state merging, that optimally merges the state into one location. As announced in [Horodecki, Oppenheim, Winter, Nature 436, 673 (2005)], the optimal entanglement cost of this task is the conditional entropy if classical communication is free. Since this quantity can be negative, and the state merging rate measures partial quantum information, we find that quantum information can be negative. The classical communication rate also has a minimum rate: a certain quantum mutual information. State merging enabled one to solve a number of open problems: distributed quantum data compression, quantum coding with side information at the decoder and sender, multi-party entanglement of assistance, and the capacity of the quantum multiple access channel. It also provides an operational proof of strong subadditivity. Here, we give precise definitions and prove these results rigorously.

Horodecki, Micha?; Oppenheim, Jonathan; Winter, Andreas

2007-01-01

139

Quantum Encoder and Decoder for Secret Key Distribution with Check Bits  

Directory of Open Access Journals (Sweden)

Full Text Available The focus of this study is to develop a novel method of encoding the qubits and use as secret key in public key cryptography. In BB 84 protocol, 50% of the random number (generated at source is used as secret key and the remaining bits are used as “check bits”. The check bits are used to detect the presence of eve as well as the nature of quantum channels. In this protocol, random qubits are encoded using different type of polarizations like horizontal, veritical and diagonal. In the proposed quantum encoder, basic quantum gates are used to encode the random secret key along with the check bits. Quantum key distribution, (a cryptographic mechanism relies on the inherent randomness of quantum mechanics and serves as an option to replace techniques made vulnerable by quantum computing. However, it is still subject to clever forms of eavesdropping and poses a significant challenge to implementation. To study the challenges, quantum circuits are first simulated using QCAD.

T. Godhavari

2013-12-01

140

Modern Quantum Technologies of Information Security  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this paper, the systematisation and classification of modern quantum technologies of information security against cyber-terrorist attack are carried out. The characteristic of the basic directions of quantum cryptography from the viewpoint of the quantum technologies used is given. A qualitative analysis of the advantages and disadvantages of concrete quantum protocols is made. The current status of the problem of practical quantum cryptography use in telecommunication ne...

Korchenko, Oleksandr; Vasiliu, Yevhen; Gnatyuk, Sergiy

2010-01-01

 
 
 
 
141

Information encoding and reconstruction from the phase of action potentials  

Directory of Open Access Journals (Sweden)

Full Text Available Fundamental questions in neural coding are how neurons encode, transfer, and reconstruct information from the pattern of action potentials exchanged between different brain structures. We propose a general model of neural coding where neurons encode information by the phase of their action potentials relative to their subthreshold membrane oscillations. We demonstrate by means of simulations that action potential phase retains the spatial and temporal content of the input under the assumption that the membrane potential oscillations are coherent across neurons and between structures and have a constant spatial phase gradient. The model explains many unresolved physiological observations and makes a number of concrete, testable predictions about the relationship between action potentials, LFP, and subthreshold membrane oscillations, and provides an estimate of the spatio-temporal precision of neuronal information processing.

ZoltanNadasdy

2009-07-01

142

Useless Qubits in "Relativistic Quantum Information"  

CERN Document Server

I draw attention to previous work that shows that the observables corresponding to relativistic quantum field modes commonly employed in papers on "relativistic quantum information" cannot be measured by ideal measurements.

Dowker, Fay

2011-01-01

143

Representation of Quantum Field Theory by Elementary Quantum Information  

CERN Multimedia

In this paper is considered relativistic quantum field theory expressed by elementary units of quantum information as they are considered as fundamental entity of nature by Carl Friedrich von Weizsaecker. Through quantization of a Weyl spinor describing an elementary unit of quantum information and consisting of four real components one obtains four pairs of creation and annihilation operators acting in a tensor space of states containing many units of quantum information. There can be constructed position and momentum operators from the creation and annihilation operators and based on these operators the Poincare group can be represented in this abstract tensor space of quantum information. A general state in the tensor space can be mapped to a state in Minkowski space-time by using the position representation of the eigenstates of the occupation number operators which correspond to the eigenstates of the harmonic oscillator. This yields a description of relativistic quantum mechanics. Quantization of the co...

Kober, Martin

2011-01-01

144

Gaussian states in continuous variable quantum information  

CERN Multimedia

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

145

Quantum Information Theoretical Analysis of Quantum Secret Sharing  

International Nuclear Information System (INIS)

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

2012-11-01

146

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

147

Non-deterministic quantum CNOT gate with double encoding  

Science.gov (United States)

We define an Asymmetric Partially Polarizing Beam Splitter (APPBS) to be a linear optical component having different reflectivity (transmittance) coefficients, on the upper and the lower arms, for horizontally and vertically Polarized incident photons. Our CNOT model is composed by two APPBSs, one Half Wave Plate (HWP), two Polarizing Beam Splitters (PBSs), a Beam Splitter (BS) and a -phase rotator for specific wavelength. Control qubit operates with dual rail encoding while target qubit is based on polarization encoding. To perform CNOT operation in 4/27 of the cases, input and target incoming photons are injected with different wavelengths.

Gueddana, Amor; Attia, Moez; Chatta, Rihab

2013-09-01

148

Information transmission through a noisy quantum channel  

CERN Multimedia

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

149

Quantum-like information processing using vector solitons  

Science.gov (United States)

The concept of simulating the quantum logic via collisions of vector solitons (Janutka 2006 J. Phys. A: Math. Gen. 39 12505, 2007 J. Phys. A: Math. Theor. 40 10813) is developed in the direction of designing a true quantum-information processor that is based on mesoscopic objects, solitons. In this concept, quantum-like information is encoded in the vector-soliton (polarization) parameters. An exponential increase of the logical-operating speed compared to that achievable in the earlier simulation schemes is found to be possible due to a coherent conversion of a 2n-component vector soliton that carries an n-cebit of information into an ensemble of 2n-1 two-component and 2n-2 four-component vector pulses. Two solid-state circuits (transmitting magnetic solitons or fluxons of long Josephson junctions) which enable such a pulse conversion are proposed.

Janutka, Andrzej

2008-09-01

150

Information Processing Structure of Quantum Gravity  

CERN Document Server

The theory of quantum gravity is aimed to fuse general relativity with quantum theory into a more fundamental framework. The space of quantum gravity provides both the non-fixed causality of general relativity and the quantum uncertainty of quantum mechanics. In a quantum gravity scenario, the causal structure is indefinite and the processes are causally non-separable. In this work, we provide a model for the information processing structure of quantum gravity. We show that the quantum gravity environment is an information resource-pool from which valuable information can be extracted. We analyze the structure of the quantum gravity space and the entanglement of the space-time geometry. We study the information transfer capabilities of quantum gravity space and define the quantum gravity channel. We reveal that the quantum gravity space acts as a background noise on the local environment states. We characterize the properties of the noise of the quantum gravity space and show that it allows the separate local...

Gyongyosi, Laszlo

2014-01-01

151

Encoding Gender and Individual Information in the Mouse Vomeronasal Organ  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The mammalian vomeronasal organ detects complex chemical signals that convey information about gender, strain, and the social and reproductive status of an individual. How these signals are encoded is poorly understood. We developed transgenic mice expressing the calcium indicator G-CaMP2 and analyzed population responses of vomeronasal neurons to urine from individual animals. A substantial portion of cells was activated by either male or female urine, but only a small population of cells re...

He, Jie; Ma, Limei; Kim, Sangseong; Nakai, Junichi; Yu, C. Ron

2008-01-01

152

Information, disturbance and Hamiltonian quantum feedback control  

CERN Document Server

We consider separating the problem of designing Hamiltonian quantum feedback control algorithms into a measurement (estimation) strategy and a feedback (control) strategy, and consider optimizing desirable properties of each under the minimal constraint that the available strength of both is limited. This motivates concepts of information extraction and disturbance which are distinct from those usually considered in quantum information theory. Using these concepts we identify an information trade-off in quantum feedback control.

Doherty, A C; Jungman, G; Doherty, Andrew C.; Jacobs, Kurt; Jungman, Gerard

2001-01-01

153

The Nature of Information in Quantum Mechanics  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A suitable unified statistical formulation of quantum and classical mechanics in a *-algebraic setting leads us to conclude that information itself is noncommutative in quantum mechanics. Specifically we refer here to an observer's information regarding a physical system. This is seen as the main difference from classical mechanics, where an observer's information regarding a physical system obeys classical probability theory. Quantum mechanics is then viewed purely as a mat...

Duvenhage, Rocco

2002-01-01

154

Manipulating quantum information on the controllable systems or subspaces  

CERN Document Server

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

155

Aspects of multistation quantum information broadcasting  

International Nuclear Information System (INIS)

We study quantum information transmission over multiparty quantum channel. In particular, we show an equivalence of different capacity notions and provide a multiletter characterization of a capacity region for a general quantum channel with k senders and m receivers. We point out natural generalizations to the case of two-way classical communication capacity.

2010-06-28

156

Matrix Techniques in Quantum Information Science  

Science.gov (United States)

Mathematical techniques in quantum information science will be discussed. The focus will be on two specific topics. The first one concerns the study of quantum operations (channels) using the theory of completely positive linear maps. The second one concerns the study of quantum error correction using the theory of generalized numerical ranges. The discussion includes material from some recent research papers.

Li, Chi-Kwong

2013-09-01

157

Transfer and teleportation of quantum states encoded in decoherence-free subspace  

Science.gov (United States)

Quantum state transfer and teleportation, with qubits encoded in internal states of atoms in cavities, among spatially separated nodes of a quantum network in a decoherence-free subspace are proposed, based on a cavity-assisted interaction with single-photon pulses. We show in detail the implementation of a logic-qubit Hadamard gate and a two-logic-qubit conditional gate, and discuss the experimental feasibility of our scheme.

Wei, Hua; Deng, Zhijiao; Zhang, Xiaolong; Feng, Mang

2007-11-01

158

Transfer and teleportation of quantum states encoded in decoherence-free subspace  

International Nuclear Information System (INIS)

Quantum state transfer and teleportation, with qubits encoded in internal states of atoms in cavities, among spatially separated nodes of a quantum network in a decoherence-free subspace are proposed, based on a cavity-assisted interaction with single-photon pulses. We show in detail the implementation of a logic-qubit Hadamard gate and a two-logic-qubit conditional gate, and discuss the experimental feasibility of our scheme

2007-11-01

159

Transfer and teleportation of quantum states encoded in decoherence-free subspace  

CERN Document Server

Quantum state transfer and teleportation, with qubits encoded in internal states of the atoms in cavities, among spatially separated nodes of a quantum network in decoherence-free subspace are proposed, based on a cavity-assisted interaction by single-photon pulses. We show in details the implementation of a logic-qubit Hadamard gate and a two-logic-qubit conditional gate, and discuss the experimental feasibility of our scheme.

Wei, Hua; Zhang, XiaoLong; Feng, Mang

2007-01-01

160

Modern Quantum Technologies of Information Security  

CERN Document Server

In the paper systematization and classification of modern quantum technologies of the information security against cyber-terrorist attack are carried out. The characteristic of the basic directions of quantum cryptography from the viewpoint of used quantum technologies is given. The qualitative analysis of advantages and disadvantages of concrete quantum protocols is made. The current status of a problem of practical quantum cryptography using in telecommunication networks is considered. In particular, the short review of existing commercial systems of quantum key distribution is given.

Korchenko, Oleksandr; Gnatyuk, Sergiy

2010-01-01

 
 
 
 
161

Information geometric foundations of quantum theory  

Digital Repository Infrastructure Vision for European Research (DRIVER)

ABSTRACT: This thesis is concerned with a new approach to the mathematical foundations of quantum theory. On the basis of noncommutative integration theory and quantum information geometry, a construction of nonlinear quantum kinematics and dynamics is proposed, defined in terms of geometric and algebraic objects that are completely independent of Hilbert spaces. The starting point is the definition of spaces of quantum states as sets of positive, finite, normal functionals on noncomm...

Kostecki, Ryszard Pawe?

2013-01-01

162

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

163

Quantum Bertrand duopoly of incomplete information  

International Nuclear Information System (INIS)

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

2005-05-13

164

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

2000-03-01

165

Quantum Information Protectorates in Coupled Quantum Dot Exchange Gates  

CERN Document Server

Using exact diagonalization we study the low energy Hilbert space of the two-electron, two-quantum dot artificial molecule under a perpendicular magnetic field. We show that electrons bind to vortices to induce several spin transitions among ground states. Furthermore, the lowest excited states of either even or odd vorticity mix, opening an anticrossing which protects the quantum information stored in the spin states of the strongly correlated quantum dot molecule.

Scarola, V W

2003-01-01

166

Quantum Information Transfer Based on Frequency Modes in Circuit QED  

International Nuclear Information System (INIS)

We propose a scheme for implementing quantum information transfer based on frequency modes of microwave photons in a superconducting circuit. In our proposal, quantum information can be encoded on frequency modes of microwave photons, which act as a qubit in the resonator. Operations for the qubit, which is a process involving parametric frequency conversion, can be implemented by adjusting biased-dc superconducting quantum interference (SQUID). The coupling between two resonators can be controlled by tuning the frequency of the LC circuit inserted by a dc SQUID with two Josephson-junctions (2JJ-SQUID). Compared with previous ones, our work can avoid dephasing and decoherence resulting from atom decay. In addition, the resonator which includes multiple photons in two frequency modes can play a role of an identical atomic ensemble, which could lead to photon blockade. (fundamental areas of phenomenology(including applications))

2012-08-01

167

Tradeoffs for reliable quantum information storage in 2D systems  

CERN Document Server

We ask whether there are fundamental limits on storing quantum information reliably in a bounded volume of space. To investigate this question, we study quantum error correcting codes specified by geometrically local commuting constraints on a 2D lattice of finite-dimensional quantum particles. For these 2D systems, we derive a tradeoff between the number of encoded qubits k, the distance of the code d, and the number of particles n. It is shown that kd^2=O(n) where the coefficient in O(n) depends only on the locality of the constraints and dimension of the Hilbert spaces describing individual particles. We show that the analogous tradeoff for the classical information storage is k\\sqrt{d} =O(n).

Bravyi, Sergey; Terhal, Barbara

2009-01-01

168

Thermal quantum Fisher information in quantum dot system  

Science.gov (United States)

Using the quantum Fisher information (QFI), we investigate the problem of the parameter estimation in quantum system dot (QDS) including the effects of different parameters. We find that the QFI is affected by the strength temperature and might be finite even for higher temperatures in the asymptotic limit. Furthermore, we show that there is an optimal value of temperature such that the precision of the parameter estimation is maximal and that revivals and retardation of information loss may occur by adjusting the initial conditions. Finally, we show that this quantity may be proposed to detect the amount of the total quantum information that a QDS state contains with respect to projective measurements.

Berrada, K.

2014-04-01

169

Quantum-information processing in bosonic lattices  

International Nuclear Information System (INIS)

We consider a class of models of self-interacting bosons hopping on a lattice. We show that properly tailored space-temporal coherent control of the single-body coupling parameters allows for the universal quantum computation in a given sector of the global Fock space. This general strategy for encoded universality in bosonic systems has, in principle, several candidates for physical implementation

2002-11-01

170

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

171

A quantum information approach to statistical mechanics  

International Nuclear Information System (INIS)

The field of quantum information and computation harnesses and exploits the properties of quantum mechanics to perform tasks more efficiently than their classical counterparts, or that may uniquely be possible in the quantum world. Its findings and techniques have been applied to a number of fields, such as the study of entanglement in strongly correlated systems, new simulation techniques for many-body physics or, generally, to quantum optics. This thesis aims at broadening the scope of quantum information theory by applying it to problems in statistical mechanics. We focus on classical spin models, which are toy models used in a variety of systems, ranging from magnetism, neural networks, to quantum gravity. We tackle these models using quantum information tools from three different angles. First, we show how the partition function of a class of widely different classical spin models (models in different dimensions, different types of many-body interactions, different symmetries, etc) can be mapped to the partition function of a single model. We prove this by first establishing a relation between partition functions and quantum states, and then transforming the corresponding quantum states to each other. Second, we give efficient quantum algorithms to estimate the partition function of various classical spin models, such as the Ising or the Potts model. The proof is based on a relation between partition functions and quantum circuits, which allows us to determine the quantum computational complexity of the partition function by studying the corresponding quantum circuit. Finally, we outline the possibility of applying quantum information concepts and tools to certain models of dis- crete quantum gravity. The latter provide a natural route to generalize our results, insofar as the central quantity has the form of a partition function, and as classical spin models are used as toy models of matter. (author)

2011-01-01

172

Quantum state merging and negative information  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We consider a quantum state shared between many distant locations, and define a quantum information processing primitive, state merging, that optimally merges the state into one location. As announced in [Horodecki, Oppenheim, Winter, Nature 436, 673 (2005)], the optimal entanglement cost of this task is the conditional entropy if classical communication is free. Since this quantity can be negative, and the state merging rate measures partial quantum information, we find tha...

Horodecki, Michal; Oppenheim, Jonathan; Winter, Andreas

2005-01-01

173

Quantum information processing and relativistic quantum fields  

Science.gov (United States)

It is shown that an ideal measurement of a one-particle wave packet state of a relativistic quantum field in Minkowski spacetime enables superluminal signalling. The result holds for a measurement that takes place over an intervention region in spacetime whose extent in time in some frame is longer than the light-crossing time of the packet in that frame. Moreover, these results are shown to apply not only to ideal measurements but also to unitary transformations that rotate two orthogonal one-particle states into each other. In light of these observations, possible restrictions on the allowed types of intervention are considered. A more physical approach to such questions is to construct explicit models of the interventions as interactions between the field and other quantum systems such as detectors. The prototypical Unruh-DeWitt detector couples to the field operator itself and so most likely respects relativistic causality. On the other hand, detector models which couple to a finite set of frequencies of field modes are shown to lead to superluminal signalling. Such detectors do, however, provide successful phenomenological models of atom-qubits interacting with quantum fields in a cavity but are valid only on time scales many orders of magnitude larger than the light-crossing time of the cavity.

Benincasa, Dionigi M. T.; Borsten, Leron; Buck, Michel; Dowker, Fay

2014-04-01

174

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

175

Distributed quantum information processing via quantum dot spins  

International Nuclear Information System (INIS)

We propose a scheme to engineer a non-local two-qubit phase gate between two remote quantum-dot spins. Along with one-qubit local operations, one can in principal perform various types of distributed quantum information processing. The scheme employs a photon with linearly polarisation interacting one after the other with two remote quantum-dot spins in cavities. Due to the optical spin selection rule, the photon obtains a Faraday rotation after the interaction process. By measuring the polarisation of the final output photon, a non-local two-qubit phase gate between the two remote quantum-dot spins is constituted. Our scheme may has very important applications in the distributed quantum information processing

2010-03-01

176

Cavity mode entanglement in relativistic quantum information  

CERN Document Server

A central aim of relativistic quantum information (RQI) is the investigation of quantum information tasks and resources taking into account the relativistic aspects of nature. More precisely, it is of fundamental interest to understand how the storage, manipulation, and transmission of information utilizing quantum systems are influenced by the fact that these processes take place in a relativistic spacetime. In particular, many studies in RQI have been focused on the effects of non-uniform motion on entanglement, the main resource of quantum information protocols. Early investigations in this direction were performed in highly idealized settings that prompted questions as to the practical accessibility of these results. To overcome these limitations it is necessary to consider quantum systems that are in principle accessible to localized observers. In this thesis we present such a model, the rigid relativistic cavity, and its extensions, focusing on the effects of motion on entanglement and applications such...

Friis, Nicolai

2013-01-01

177

Quantum Realism, Information, and Epistemological Modesty  

Science.gov (United States)

It is usually asserted that physical theories, in particular quantum mechanics, support a certain view of what the world really is. To such claims I oppose an attitude of epistemological modesty. Ontological statements on the nature of reality, when made on the basis of quantum mechanics, appear unwarranted. I suggest that an epistemic loop connects physical theory grounded in informational notions, and a theory of information developed through a theoretical account of the physical support of information.

Grinbaum, Alexei

2014-03-01

178

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

2013-06-01

179

Quantum information processing in semiconductor nanostructures  

CERN Multimedia

A major question for condensed matter physics is whether a solid-state quantum computer can ever be built. Here we discuss two different schemes for quantum information processing using semiconductor nanostructures. First, we show how optically driven coupled quantum dots can be used to prepare maximally entangled Bell and Greenberger-Horne-Zeilinger states by varying the strength and duration of selective light pulses. The setup allows us to perform an all-optical generation of the quantum teleportation of an excitonic state in an array of coupled quantum dots. Second, we give a proposal for reliable implementation of quantum logic gates and long decoherence times in a quantum dots system based on nuclear magnetic resonance (NMR), where the nuclear resonance is controlled by the ground state transitions of few-electron QDs in an external magnetic field. The dynamical evolution of these systems in the presence of environmentally-induced decoherence effects is also discussed.

Reina, J H; Johnson, N F

2000-01-01

180

Quantum information processing through nuclear magnetic resonance  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english We discuss the applications of Nuclear Magnetic Resonance (NMR) to quantum information processing, focusing on the use of quadrupole nuclei for quantum computing. Various examples of experimental implementation of logic gates are given and compared to calculated NMR spectra and their respective dens [...] ity matrices. The technique of Quantum State Tomography for quadrupole nuclei is briefly described, and examples of measured density matrices in a two-qubit I = 3/2 spin system are shown. Experimental results of density matrices representing pseudo-Bell states are given, and an analysis of the entropy of theses states is made. Considering an NMR experiment as a depolarization quantum channel we calculate the entanglement fidelity and discuss the criteria for entanglement in liquid state NMR quantum information. A brief discussion on the perspectives for NMR quantum computing is presented at the end.

J. D., Bulnes; F. A., Bonk; R. S., Sarthour; E. R. de, Azevedo; J. C. C., Freitas; T. J., Bonagamba; I. S., Oliveira.

 
 
 
 
181

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

182

Quantum causality, stochastics, trajectories and information  

International Nuclear Information System (INIS)

A history of the discovery of 'new' quantum mechanics and the paradoxes of its probabilistic interpretation are briefly reviewed from the modern point of view of quantum probability and information. Modern quantum theory, which has been developed during the last 20 years for the treatment of quantum open systems including quantum noise, decoherence, quantum diffusions and spontaneous jumps occurring under continuous in time observation, is not yet a part of the standard curriculum of quantum physics. It is argued that the conventional formalism of quantum mechanics is insufficient for the description of quantum events, such as spontaneous decays say, and the new experimental phenomena related to individual quantum measurements, but they have all received an adequate mathematical treatment in quantum stochastics of open systems. Moreover, the only reasonable probabilistic interpretation of quantum mechanics put forward by Max Born was, in fact, in irreconcilable contradiction with traditional mechanical reality and causality. This led to numerous quantum paradoxes, some of them due to the great inventors of quantum theory such as Einstein and Schroedinger. They are reconsidered in this paper from the modern point of view of quantum stochastics and information. The development of quantum measurement theory, initiated by von Neumann, indicated a possibility for resolution of this interpretational crisis by divorcing the algebra of the dynamical generators and the algebra of the actual observables, or Bell's beables. It is shown that within this approach quantum causality can be rehabilitated in the form of a superselection rule for compatibility of the actual histories with the potential future. This rule, together with the self-compatibility of the measurements ensuring the consistency of the histories, is called the nondemolition, or causality principle in modern quantum theory. The application of this rule in the form of dynamical commutation relations leads to the derivation of the von Neumann projection postulate, and also to the more general reductions, instantaneous, spontaneous, and even continuous in time. This gives a dynamical solution, in the form of the quantum stochastic filtering equations, of the notorious measurement problem which was tackled unsuccessfully by many famous physicists starting with Schroedinger and Bohr. It has been recently proved that the quantum stochastic model for the continuous in time measurements is equivalent to a Dirac type boundary-value problem for the secondary quantized input 'offer waves from future' in one extra dimension, and to a reduction of the algebra of the consistent histories of past events to an Abelian subalgebra for the 'trajectories of the output particles'. This supports the corpuscular-wave duality in the form of the thesis that everything in the future are quantized waves, while everything in the past are trajectories of the recorded particles. (author)

2002-03-01

183

Towards a quantum information technology industry  

Energy Technology Data Exchange (ETDEWEB)

The research fields of quantum information processing and communication are now well established, although still growing and developing. It was realized early on that there is significant potential for new technologies and applications, leading to the vision of a whole new quantum information technology industry. The vision is not yet reality, and there are many open questions with regard to how it might become so. This article raises some of these questions, and gives a viewpoint on how we might proceed, from where we are today towards a quantum information technology industry in the future. (viewpoint)

Spiller, T P; Munro, W J [Hewlett-Packard Laboratories, Filton Road, Stoke Gifford, Bristol BS34 8QZ (United Kingdom)

2006-01-11

184

On the quantum information processing in nuclear magnetic resonance quantum computing experiments  

International Nuclear Information System (INIS)

Full text: Nuclear Magnetic Resonance appeared in the late nineties to be the most promising candidate to run quantum computing algorithms. An impressive number of experiments demonstrating the implementation of all logic gates and quantum algorithms in systems with a small number of qubits stimulated the general excitement about the technique, and greatly promoted the field. Particularly important were those experiments where entanglement of particles were aimed at. Entanglement is the most fundamental (and weird !) aspect of quantum systems, and is at the basis of quantum teleportation and quantum cryptography, yet impossible to prove in NMR experiments. The hardcore of NMR quantum computing are the so-called pseudo-pure states, upon which radiofrequency (RF) pulses act to implement quantum mechanical unitary transformations, promoting changes in both, Zeeman level populations and coherences in the density matrix. Whereas pseudo-pure states are special non-equilibrium diagonal states, coherences encode information about superposition states. Now, one could safely say that the whole business of quantum computing goes about controlling relative ket phases. In spite of the impossibility to univocally associating a given quantum state to a NMR spectrum, it is possible to demonstrate the phase action of RF pulses over relative ket phases, even if no population changes take place. In this talk these issues will be addressed, and we will show experimental results of our own where this is done in the two-qubit quadrupole nuclei 23Na in C10H21NaO4S liquid crystal. We demonstrate the reversibility of the Hadamard gate, and of a quantum circuit which generates pseudo-Bell states. The success of the operation reaches almost 100% in the case of the state |01+|10, 80% in the cases of |00> + |01> and |10> + |11>, and 65% for the cat-state |00> + |11>. (author)

2003-05-06

185

On the quantum information processing in nuclear magnetic resonance quantum computing experiments  

Energy Technology Data Exchange (ETDEWEB)

Full text: Nuclear Magnetic Resonance appeared in the late nineties to be the most promising candidate to run quantum computing algorithms. An impressive number of experiments demonstrating the implementation of all logic gates and quantum algorithms in systems with a small number of qubits stimulated the general excitement about the technique, and greatly promoted the field. Particularly important were those experiments where entanglement of particles were aimed at. Entanglement is the most fundamental (and weird !) aspect of quantum systems, and is at the basis of quantum teleportation and quantum cryptography, yet impossible to prove in NMR experiments. The hardcore of NMR quantum computing are the so-called pseudo-pure states, upon which radiofrequency (RF) pulses act to implement quantum mechanical unitary transformations, promoting changes in both, Zeeman level populations and coherences in the density matrix. Whereas pseudo-pure states are special non-equilibrium diagonal states, coherences encode information about superposition states. Now, one could safely say that the whole business of quantum computing goes about controlling relative ket phases. In spite of the impossibility to univocally associating a given quantum state to a NMR spectrum, it is possible to demonstrate the phase action of RF pulses over relative ket phases, even if no population changes take place. In this talk these issues will be addressed, and we will show experimental results of our own where this is done in the two-qubit quadrupole nuclei {sup 23}Na in C{sub 10}H{sub 21}NaO{sub 4}S liquid crystal. We demonstrate the reversibility of the Hadamard gate, and of a quantum circuit which generates pseudo-Bell states. The success of the operation reaches almost 100% in the case of the state |01+|10, 80% in the cases of |00> + |01> and |10> + |11>, and 65% for the cat-state |00> + |11>. (author)

Azevedo, E.R. de; Bonk, F.A.; Vidoto, E.L.G.; Bonagamba, T.J. [Universidade de Sao Paulo (IFSC/USP), Sao Carlos, SP (Brazil). Inst. de Fisica; Sarthour, R.S.; Guimaraes, A.P.; Oliveira, I.S. [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil); Freitas, J.C.C. [Universidade Federal do Espirito Santo (UFES), Vitoria, ES (Brazil). Dept. de Fisica

2003-07-01

186

Quantum correlations in information theory  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The project concerned the study of quantum correlations (QC) in compound systems, i.e. statistical correlations more general than entanglement which are predicted by quantum mechanics but not described in any classical scenario. I aimed to understand the technical and operational properties of the measures of QC, their interplay with entanglement quantifiers and the experimental accessibility.

2013-01-01

187

Quantum information processing : science & technology.  

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-09-01

188

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

189

Optimal generalized variance and quantum Fisher information  

Energy Technology Data Exchange (ETDEWEB)

We define the generalized variance based on requiring that (i) it equals the usual variance for pure states and (ii) it is concave. For a quantum system of any size, we show that the usual variance is the smallest generalized variance, which makes it optimal for using it in entanglement criteria based on uncertainty relations. Similarly, we define the generalized quantum Fisher information, replacing the requirement of concavity by convexity. For rank-2 density matrices, we show that the quantum Fisher information is the largest among generalized quantum Fisher informations. We relate our findings to the results of [D. Petz, J. Phys. A: Math. Gen. 35, 79 (2003); P. Gibilisco, F. Hiai and D. Petz, IEEE Trans. Inform. Theory 55, 439 (2009)].

Toth, Geza [IKERBASQUE, Basque Foundation for Science, E-48011 Bilbao (Spain); Research Institute for Solid State Physics and Optics, H-1525 Budapest (Hungary); Alfred Renyi Institute of Mathematics, Realtanoda utca 13-15, H-1051 Budapest (Hungary); Petz, Denes [Theoretical Physics, The University of the Basque Country, E-48080 Bilbao (Spain)

2012-07-01

190

Electron-Nuclear Quantum Information Processing.  

Science.gov (United States)

We devised a novel scheme for electron-nuclear quantum information processing that exploits the anisotropic hyperfine coupling. This scheme enables universal control over a 1-electron, N-nuclear spin system, addressing only a single electron spin transiti...

C. Ramanathan D. G. Cory

2008-01-01

191

Information and Errors in Quantum Teleportation  

CERN Document Server

This article considers the question of the teleportation protocol from an engineering perspective. The protocol ideally requires an authority that ensures that the two communicating parties have a perfectly entangled pair of particles available to them. But this cannot be unconditionally established to the satisfaction of the parties due to the fact that an unknown quantum state cannot be copied. This supports the view that quantum information cannot be treated on the same basis as classical information.

Nedurumalli, B

2006-01-01

192

Phase encoding schemes for measurement device independent quantum key distribution and basis-dependent flaw  

CERN Document Server

In this paper, we study the security of the so-called measurement device independent quantum key distribution (MDIQKD) with the basis-dependent flaw in the context of phase encoding schemes. We propose two schemes for the phase encoding, the first one employs a phase locking technique with the use of non-phase-randomized coherent pulses, and the second one uses conversion of standard BB84 phase encoding pulses into polarization modes. We prove the unconditional security of these schemes and we also simulate the key generation rate based on simple device models that accommodate imperfections. Our simulation results show the feasibility of these schemes with current technologies and highlights the importance of the state preparation with good fidelity between the density matrices in the two bases. Since the basis-dependent flaw is a problem not only for MDIQKD but also for standard QKD, our work highlights the importance of an accurate signal source in practical QKD systems.

Tamaki, Kiyoshi; Fung, Chi-Hang Fred; Qi, Bing

2011-01-01

193

On the distributed compression of quantum information  

CERN Multimedia

We consider the problem of distributed compression for correlated quantum sources. The classical version of this problem was solved by Slepian and Wolf, who showed that distributed compression could fully avail itself of redundancy in the local sources created by the presence of correlations. We show that, in general, this is not the case for quantum sources. In particular, we prove that for irreducible sources of product states, no advantage can be gained from correlations between the local sources. Nonetheless, strategies taking advantage of correlation do exist for some special classes of quantum sources. For example, Devetak and Winter demonstrated the existence of such a strategy when one of the sources is classical. Here we find optimal non-trivial strategies for a different extreme, sources of Bell states. In addition, we illustrate how distributed compression is connected to other problems in quantum information theory, including information-disturbance questions, entanglement distillation and quantum...

Ahn, C; Hayden, P; Winter, A; Ahn, Charlene; Doherty, Andrew; Hayden, Patrick; Winter, Andreas

2004-01-01

194

Principles of quantum computation and information  

CERN Document Server

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

Benenti, Giuliano; Strini, Giuliano

2004-01-01

195

Interface between path and OAM entanglement for high-dimensional photonic quantum information  

CERN Document Server

Photonics has become a mature field of quantum information science, where integrated optical circuits offer a way to scale the complexity of the setup as well as the dimensionality of the quantum state. On photonic chips, paths are the natural way to encode information. To distribute those high-dimensional quantum states over large distances, transverse spatial modes, like orbital angular momentum (OAM) possessing Laguerre Gauss modes, are favourable as flying information carriers. Here we demonstrate a quantum interface between these two vibrant photonic fields. We create three-dimensional path entanglement between two photons in a non-linear crystal and use a mode sorter as the quantum interface to transfer the entanglement to the OAM degree of freedom. Thus our results show a novel, flexible way to create high-dimensional spatial mode entanglement. Moreover, they pave the way to implement broad complex quantum networks where high-dimensionally entangled states could be distributed over distant photonic chi...

Fickler, Robert; Huber, Marcus; Lavery, Martin P J; Padgett, Miles J; Zeilinger, Anton

2014-01-01

196

Quantum information approach to the description of quantum phase transitions  

International Nuclear Information System (INIS)

The fidelity, linear entropy and entanglement entropy, concepts of information theory, are used to determine the localization of quantum phase transitions of the Lipkin–Meshkov–Glick (LMG) and the Dicke models for a finite number of particles. Another concept, the so-called fidelity susceptibility, gives us information of the scaling behavior of the quantum phase transitions of the models. In particular universal curves are presented for the specific susceptibility. It is shown that the control parameters of both models have a similar dependence in the number of particles when the systems approach to the thermodynamic limit.

2012-12-18

197

Quenching Dynamics and Quantum Information  

CERN Document Server

We review recent studies on the measures of zero temperature quantum correlations namely, the quantum entanglement (concurrence) and discord present in the final state of a transverse XY spin chain following a quench through quantum critical points; the aim of these studies is to explore the scaling of the above quantities as a function of the quench rate. A comparative study between the concurrence and the quantum discord shows that their behavior is qualitatively the same though there are quantitative differences. For the present model, the scaling of both the quantities are given by the scaling of the density of the defect present in the final state though one can not find a closed form expression for the discord. We also extend our study of quantum discord to a transverse Ising chain in the presence of a three spin interaction. Finally, we present a study of the dynamical evolution of quantum discord and concurrence when two central qubits, initially prepared in a Werner state, are coupled to the environm...

Nag, Tanay; Patra, Ayoti

2012-01-01

198

A mathematical foundation of quantum information and quantum computer on quantum mutual entropy and entanglement  

CERN Multimedia

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

Ohya, M

1998-01-01

199

Processing Information in Quantum Decision Theory  

Directory of Open Access Journals (Sweden)

Full Text Available A survey is given summarizing the state of the art of describing information processing in Quantum Decision Theory, which has been recently advanced as a novel variant of decision making, based on the mathematical theory of separable Hilbert spaces. This mathematical structure captures the effect of superposition of composite prospects, including many incorporated intended actions. The theory characterizes entangled decision making, non-commutativity of subsequent decisions, and intention interference. The self-consistent procedure of decision making, in the frame of the quantum decision theory, takes into account both the available objective information as well as subjective contextual effects. This quantum approach avoids any paradox typical of classical decision theory. Conditional maximization of entropy, equivalent to the minimization of an information functional, makes it possible to connect the quantum and classical decision theories, showing that the latter is the limit of the former under vanishing interference terms.

Vyacheslav I. Yukalov

2009-12-01

200

Encoding and storage of spatial information in the retrosplenial cortex.  

Science.gov (United States)

The retrosplenial cortex (RSC) is part of a network of interconnected cortical, hippocampal, and thalamic structures harboring spatially modulated neurons. The RSC contains head direction cells and connects to the parahippocampal region and anterior thalamus. Manipulations of the RSC can affect spatial and contextual tasks. A considerable amount of evidence implicates the role of the RSC in spatial navigation, but it is unclear whether this structure actually encodes or stores spatial information. We used a transgenic mouse in which the expression of green fluorescent protein was under the control of the immediate early gene c-fos promoter as well as time-lapse two-photon in vivo imaging to monitor neuronal activation triggered by spatial learning in the Morris water maze. We uncovered a repetitive pattern of cell activation in the RSC consistent with the hypothesis that during spatial learning an experience-dependent memory trace is formed in this structure. In support of this hypothesis, we also report three other observations. First, temporary RSC inactivation disrupts performance in a spatial learning task. Second, we show that overexpressing the transcription factor CREB in the RSC with a viral vector, a manipulation known to enhance memory consolidation in other circuits, results in spatial memory enhancements. Third, silencing the viral CREB-expressing neurons with the allatostatin system occludes the spatial memory enhancement. Taken together, these results indicate that the retrosplenial cortex engages in the formation and storage of memory traces for spatial information. PMID:24912150

Czajkowski, Rafa?; Jayaprakash, Balaji; Wiltgen, Brian; Rogerson, Thomas; Guzman-Karlsson, Mikael C; Barth, Alison L; Trachtenberg, Joshua T; Silva, Alcino J

2014-06-10

 
 
 
 
201

Unified meta-theory of information, consciousness, time and the classical-quantum universe  

CERN Document Server

As time advances in our perceived real world, existing information is preserved and new information is added to history. All the information that may ever be encoded in history must be about some fundamental, unique, atemporal and pre-physical structure: the bare world. Scientists invent model worlds to efficiently explain aspects of the real world. This paper explores the features of and relationships between the bare, real, and model worlds. Time -- past, present and future -- is naturally explained. Both quantum uncertainty and state reduction are needed for time to progress, since unpredictable new information must be added to history. Deterministic evolution preserves existing information. Finite, but steadily increasing, information about the bare world is jointly encoded in equally uncertain spacetime geometry and quantum matter. Because geometry holds no information independent of matter, there is no need to quantize gravity. At the origin of time, information goes to zero and geometry and matter fade...

Green, Martin A

2013-01-01

202

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

2013-10-11

203

Quantum Computation and Information From Theory to Experiment  

CERN Multimedia

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

Imai, Hiroshi

2006-01-01

204

Quantum Entropies Dynamics, Information and Complexity  

CERN Document Server

The leading theme of the book is complexity in quantum dynamics. This issue is addressed by comparison with the classical ergodic, information and algorithmic complexity theories. Of particular importance is the notion of Kolmogorov-Sinai dynamical entropy and of its inequivalent quantum extensions formulated by Connes, Narnhofer and Thirring on one hand and Alicki and Fannes on the other. Their connections with extensions to quantum systems of Kolmogorov-Chaitin-Solomonoff algorithmic complexity theory is also presented. The technical tools employed are those of the algebraic approach to quantum statistical mechanics which offers a unifying view of classical and quantum dynamical systems. Proofs and examples are provided in order to make the presentation self consistent.

Benatti, Fabio

2009-01-01

205

Hilbert's projective metric in quantum information theory  

CERN Document Server

We introduce and apply Hilbert's projective metric in the context of quantum information theory. The metric is induced by convex cones such as the sets of positive, separable or PPT operators. It provides bounds on measures for statistical distinguishability of quantum states and on the decrease of entanglement under LOCC protocols or other cone-preserving operations. The results are formulated in terms of general cones and base norms and lead to contractivity bounds for quantum channels, for instance improving Ruskai's trace-norm contraction inequality. A new duality between distinguishability measures and base norms is provided. For two given pairs of quantum states we show that the contraction of Hilbert's projective metric is necessary and sufficient for the existence of a probabilistic quantum operation that maps one pair onto the other. Inequalities between Hilbert's projective metric and the Chernoff bound, the fidelity and various norms are proven.

Reeb, David; Wolf, Michael M

2011-01-01

206

Quantum dot - nanocavity QED for quantum information processing  

Energy Technology Data Exchange (ETDEWEB)

Single quantum dots (QDs) in photonic crystal nanocavities are interesting both as a testbed for fundamental cavity quantum electrodynamics (QED) experiments, as well as a platform for quantum and classical information processing. In addition to providing a scalable, on-chip, platform, these systems also enable large dipole-field interaction strengths, as a result of the localization of the field to very small optical volumes. Such a platform could be employed to demonstrate a number of devices, including nonclassical light sources, electro-optic modulators and switches operating at the single photon level, and quantum gates. QD-cavity QED systems also exhibit interesting phonon-assisted off-resonant interaction between the QD and the cavity which can be employed for spectral filtering, as well as for coherent optical spectroscopy and quantum dot state readout, thereby overcoming issues coming from quantum dot inhomogeneous broadening. In order to make the platform compatible with fiber-optic telecommunication wavelengths, the intrinsic optical nonlinearity of the semiconductor employed to make a nanocavity can be employed for frequency conversion.

Vuckovic, Jelena [Ginzton Laboratory, Stanford University, Stanford, CA 94305-4088 (Germany)

2012-07-01

207

Quantum dot - nanocavity QED for quantum information processing  

International Nuclear Information System (INIS)

Single quantum dots (QDs) in photonic crystal nanocavities are interesting both as a testbed for fundamental cavity quantum electrodynamics (QED) experiments, as well as a platform for quantum and classical information processing. In addition to providing a scalable, on-chip, platform, these systems also enable large dipole-field interaction strengths, as a result of the localization of the field to very small optical volumes. Such a platform could be employed to demonstrate a number of devices, including nonclassical light sources, electro-optic modulators and switches operating at the single photon level, and quantum gates. QD-cavity QED systems also exhibit interesting phonon-assisted off-resonant interaction between the QD and the cavity which can be employed for spectral filtering, as well as for coherent optical spectroscopy and quantum dot state readout, thereby overcoming issues coming from quantum dot inhomogeneous broadening. In order to make the platform compatible with fiber-optic telecommunication wavelengths, the intrinsic optical nonlinearity of the semiconductor employed to make a nanocavity can be employed for frequency conversion.

2012-03-25

208

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

209

Quantum Mechanics as Quantum Information (and only a little more)  

CERN Document Server

In this paper, I try once again to cause some good-natured trouble. The issue remains, when will we ever stop burdening the taxpayer with conferences devoted to the quantum foundations? The suspicion is expressed that no end will be in sight until a means is found to reduce quantum theory to two or three statements of crisp physical (rather than abstract, axiomatic) significance. In this regard, no tool appears better calibrated for a direct assault than quantum information theory. Far from a strained application of the latest fad to a time-honored problem, this method holds promise precisely because a large part--but not all--of the structure of quantum theory has always concerned information. It is just that the physics community needs reminding. This paper, though taking quant-ph/0106166 as its core, corrects one mistake and offers several observations beyond the previous version. In particular, I identify one element of quantum mechanics that I would not label a subjective term in the theory--it is the in...

Fuchs, C

2002-01-01

210

Geometrical Identification of Quantum and Information Theories.  

Science.gov (United States)

The interrelation of quantum and information theories is investigated on the basis 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 ot...

E. R. Caianiello

1983-01-01

211

Encoding mutually unbiased bases in orbital angular momentum for quantum key distribution  

Science.gov (United States)

We encode mutually unbiased bases (MUBs) using the higher-dimensional orbital angular momentum (OAM) degree of freedom and illustrate how these states are encoded on a phase-only spatial light modulator (SLM). We perform (d - 1)- mutual unbiased measurements in both a classical prepare and measure scheme and on entangled photon pairs for dimensions ranging from d = 2 to 5. The calculated average error rate, mutual information and secret key rate show an increase in information capacity as well as higher generation rates as the dimension increases.

Dudley, A.; Mafu, M.; Goyal, S.; Giovannini, D.; McLaren, M.; Konrad, T.; Padgett, M. J.; Petruccione, F.; Lütkenhaus, N.; Forbes, A.

2014-02-01

212

Encoding visual information in retinal ganglion cells with prosthetic stimulation  

Science.gov (United States)

Retinal prostheses aim to restore functional vision to those blinded by outer retinal diseases using electric stimulation of surviving retinal neurons. The ability to replicate the spatiotemporal pattern of ganglion cell spike trains present under normal viewing conditions is presumably an important factor for restoring high-quality vision. In order to replicate such activity with a retinal prosthesis, it is important to consider both how visual information is encoded in ganglion cell spike trains, and how retinal neurons respond to electric stimulation. The goal of the current review is to bring together these two concepts in order to guide the development of more effective stimulation strategies. We review the experiments to date that have studied how retinal neurons respond to electric stimulation and discuss these findings in the context of known retinal signaling strategies. The results from such in vitro studies reveal the advantages and disadvantages of activating the ganglion cell directly with the electric stimulus (direct activation) as compared to activation of neurons that are presynaptic to the ganglion cell (indirect activation). While direct activation allows high temporal but low spatial resolution, indirect activation yields improved spatial resolution but poor temporal resolution. Finally, we use knowledge gained from in vitro experiments to infer the patterns of elicited activity in ongoing human trials, providing insights into some of the factors limiting the quality of prosthetic vision.

Freeman, Daniel K.; Rizzo, Joseph F., III; Fried, Shelley I.

2011-06-01

213

Controlling the dynamics of classical and quantum information in spin systems  

Science.gov (United States)

The precise, human control of quantum systems, by its definition, must combine models of the classical and the quantum world into a calculus that supports both. Open, irreversible quantum systems must interact with closed, reversible quantum systems to predict evolutions that are partially open and closed. Inevitably, the problems of quantum measurement, the assumptions of scattering, and the role of spacetime comes under scrutiny. Such considerations have extraordinary practical value: the precise control of a quantum information is the cornerstone of scalable quantum computing. Traditionally, quantum control theory as well as a formalism of redundancy and partial measurements, known as quantum error correction, attempt to remedy systematic quantum-noise and random quantum-noise respectively, but have had mixed success. This dissertation examines how the imprecision of control in quantum and classical spin systems affects the flow of select information to a receiver and how such systems may be optimized against the imprecise scattering of control fields and spins. To this end, this dissertation intertwines the physics of state evolution with the physics of information control in classical and quantum systems. First in classical systems, a method for encoding and decoding classical spin-processing information provides an example of information flow. Then an analytic calculation of a semi-conductor spin channel's information capacity is performed. The results limit the rate of information processing and inform the design of materials for optimal spintronic information-processing in semiconductors. Next, noisy quantum interactions are described, so that the complexities of correcting small, random phase errors using traditional control theory and quantum error correction may be explained. How these noisy processes affect the relevant information flow of a quantum algorithm (derivatives of the Quantum Fourier Transform and Grover Search) is considered, several novel methods of source-coding for these quantum channels are presented and their efficacy calculated. These methods include Unitary-Fault Tolerance, Clifford operations of locally-variant basis, and an entropic controller. Together they show classical systems in the steady state can be used to control scalable, high-precision quantum-computing machines, and ultimately may eliminate all temporal control from quantum operations.

Dalal, Parin B.

214

Trapped-ion quantum information processing  

International Nuclear Information System (INIS)

Full text: Trapped strings of cold ions provide an ideal system for quantum information processing. The quantum information can be stored in individual ions and these qubits can be individually prepared, the corresponding quantum states can be manipulated and measured with nearly 100 % detection efficiency. With a small ion-trap quantum computer based on two and three trapped Ca+ ions as qubits we have generated in a pre-programmed way genuine quantum states. These states are of particular interest for the implementation of an ion quantum register: we have demonstrated selective read-out of single qubits and manipulation of single qubits of the register conditioned on the read-out results. Moreover, entangled states of up to eight particles were generated using an algorithmic procedure and the resulting states were analyzed using state tomography proving genuine multi-partite entanglement. With a new cavity QED setup we create an ion-qubit to photon-qubit interface for interconnecting ion-trap based quantum computers. With this device a source of deterministically generated single photons can be built and atom-photon entanglement can be investigated

2006-09-18

215

Phase encoding schemes for measurement-device-independent quantum key distribution with basis-dependent flaw  

Science.gov (United States)

In this paper, we study the unconditional security of the so-called measurement-device-independent quantum key distribution (MDIQKD) with the basis-dependent flaw in the context of phase encoding schemes. We propose two schemes for the phase encoding: The first one employs a phase locking technique with the use of non-phase-randomized coherent pulses, and the second one uses conversion of standard Bennett-Brassard 1984 (BB84) phase encoding pulses into polarization modes. We prove the unconditional security of these schemes and we also simulate the key generation rate based on simple device models that accommodate imperfections. Our simulation results show the feasibility of these schemes with current technologies and highlight the importance of the state preparation with good fidelity between the density matrices in the two bases. Since the basis-dependent flaw is a problem not only for MDIQKD but also for standard quantum key distribution (QKD), our work highlights the importance of an accurate signal source in practical QKD systems.

Tamaki, Kiyoshi; Lo, Hoi-Kwong; Fung, Chi-Hang Fred; Qi, Bing

2012-04-01

216

Multiparty hierarchical quantum-information splitting  

CERN Document Server

We propose a scheme for multiparty hierarchical quantum-information splitting (QIS) with a multipartite entangled state, where a boss distributes a secret quantum state to two grades of agents asymmetrically. The agents who belong to different grades have different authorities for recovering boss's secret. Except for boss's Bell-state measurement, no nonlocal operation is involved. The presented scheme is also shown to be secure against eavesdropping. Such a hierarchical QIS is expected to find useful applications in the field of modern multipartite quantum cryptography.

Wang, Xin-Wen; Tang, Shi-Qing; Xie, Li-Jun

2011-01-01

217

Multiparty hierarchical quantum-information splitting  

Energy Technology Data Exchange (ETDEWEB)

We propose a scheme for multiparty hierarchical quantum-information splitting (QIS) with a multipartite entangled state, where a boss distributes a secret quantum state to two grades of agents asymmetrically. The agents who belong to different grades have different authorities for recovering the boss's secret. Except for the boss's Bell-state measurement, no nonlocal operation is involved. The presented scheme is also shown to be secure against eavesdropping. Such a hierarchical QIS is expected to find useful applications in the field of modern multipartite quantum cryptography.

Wang Xinwen; Zhang Dengyu; Tang Shiqing; Xie Lijun, E-mail: xwwang0826@yahoo.com.cn [Department of Physics and Electronic Information Science, Hengyang Normal University, Hengyang 421008 (China)

2011-02-14

218

Information Theoretic Resources in Quantum Theory  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Resource identification and quantification is an essential element of both classical and quantum information theory. Entanglement is one of these resources, arising when quantum communication and nonlocal operations are expensive to perform. In the first part of this thesis we quantify the effective entanglement when operations are additionally restricted to account for both fundamental restrictions on operations, such as those arising from superselection rules, as well as experimental err...

Meznaric, Sebastian; Jaksch, Dieter

2013-01-01

219

Quantum information-geometry of dissipative quantum phase transitions  

Science.gov (United States)

A general framework for analyzing the recently discovered phase transitions in the steady state of dissipation-driven open quantum systems is still lacking. To fill this gap, we extend the so-called fidelity approach to quantum phase transitions to open systems whose steady state is a Gaussian fermionic state. We endow the manifold of correlation matrices of steady states with a metric tensor g measuring the distinguishability distance between solutions corresponding to a different set of control parameters. The phase diagram can then be mapped out in terms of the scaling behavior of g and connections with the Liouvillean gap and the model correlation functions unveiled. We argue that the fidelity approach, thanks to its differential-geometric and information-theoretic nature, provides insights into dissipative quantum critical phenomena as well as a general and powerful strategy to explore them.

Banchi, Leonardo; Giorda, Paolo; Zanardi, Paolo

2014-02-01

220

Experimental Demonstration of Polarization Encoding Measurement-Device-Independent Quantum Key Distribution  

Science.gov (United States)

We demonstrate the first implementation of polarization encoding measurement-device-independent quantum key distribution (MDI-QKD), which is immune to all detector side-channel attacks. Active phase randomization of each individual pulse is implemented to protect against attacks on imperfect sources. By optimizing the parameters in the decoy state protocol, we show that it is feasible to implement polarization encoding MDI-QKD with commercial off-the-shelf devices. A rigorous finite key analysis is applied to estimate the secure key rate. Our work paves the way for the realization of a MDI-QKD network, in which the users only need compact and low-cost state-preparation devices and can share complicated and expensive detectors provided by an untrusted network server.

Tang, Zhiyuan; Liao, Zhongfa; Xu, Feihu; Qi, Bing; Qian, Li; Lo, Hoi-Kwong

2014-05-01

 
 
 
 
221

Quantum Fisher information as signature of superradiant quantum phase transition  

CERN Document Server

The single-mode Dicke model is well-known to undergo a quantum phase transition from the so-called normal phase to the supperradiant phase (hereinafter called the "superradiant quantum phase transition"). Normally, quantum phase transitions are closely related to the critical behavior of quantities such as entanglement, quantum fluctuations, and fidelity. In this paper, we study quantum Fisher information (QFI) of the field mode and that of the atoms in the ground state of the Dicke Hamiltonian. For finite and large enough number of atoms N, our numerical results show that near the critical atom-field coupling, the QFIs of the atomic and the field subsystems can surpass the classical limits, due to the appearance of nonclassical squeezed states. As the coupling increases far beyond the critical point, the two subsystems are in highly mixed states, which degrade the QFI and hence the ultimate phase sensitivity. In the thermodynamic limit, we present analytical results of the QFIs and their relationships with t...

Wang, T L; Yang, W; Jin, G R; Lambert, N; Nori, F

2013-01-01

222

Scalable quantum information processing and the optical topological quantum computer  

Science.gov (United States)

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

Devitt, S.

2010-02-01

223

Protection of information in quantum databases  

CERN Document Server

The conventional protection of information by cryptographical keys makes no sense if a key can be quickly discovered by an unauthorized person. This way of penetration to the protected systems was made possible by a quantum computers in view of results of P.Shor and L.Grover. This work presents the method of protection of an information in a database from a spy even he knows all about its control system and has a quantum computer, whereas a database can not distinguish between operations of spy and legal user.

Ozhigov, Y I

1997-01-01

224

Achievable Qubit Rates for Quantum Information Wires  

CERN Document Server

Suppose Alice and Bob have access to two separated regions, respectively, of a system of electrons moving in the presence of a regular one-dimensional lattice of binding atoms. We consider the problem of communicating as much quantum information, as measured by the qubit rate, through this quantum information wire as possible. We describe a protocol whereby Alice and Bob can achieve a qubit rate for these systems which is proportional to N^-1/3 qubits per unit time, where N is the number of lattice sites. Our protocol also functions equally in the presence of interactions modelled via the t-J and Hubbard models.

Osborne, Tobias J

2011-01-01

225

Numerical algorithms for use in quantum information  

Science.gov (United States)

Quantum information theory is the new field of physics and electrical engineering that arose from the application of fundamental physics concepts in communications and computing. In this paper, aiming to calculate some properties of quantum communication systems and the quantum entanglement measure, for C 2?C 2 systems, based on relative entropy, two numerical algorithms are presented. The first one is based on the codification of the possible solution in a binary string and in the application, in that string, of an assembly algorithm, such as one used in DNA construction. The second one is the construction of a genetic algorithm where a string of density matrices and quantum gates in the reproduction stage are used. Both algorithms are used in situations where the best solution needs to be found. Numerical simulations are presented and the advantages and disadvantages of the algorithms are discussed.

Ramos, Rubens Viana

2003-11-01

226

On Grover's Search Algorithm from a Quantum Information Geometry Viewpoint  

CERN Multimedia

We present an information geometric characterization of Grover's quantum search algorithm. First, we quantify the notion of quantum distinguishability between parametric density operators by means of the Wigner-Yanase quantum information metric. We then show that the quantum searching problem can be recast in an information geometric framework where Grover's dynamics is characterized by a geodesic on the manifold of the parametric density operators of pure quantum states constructed from the continuous approximation of the parametric quantum output state in Grover's algorithm. We also discuss possible deviations from Grover's algorithm within this quantum information geometric setting.

Cafaro, Carlo

2011-01-01

227

Introduction to the theory of quantum information processing  

CERN Multimedia

Introduction to the Theory of Quantum Information Processing provides the material for a one-semester graduate level course on quantum information theory and quantum computing for students who have had a one-year graduate course in quantum mechanics. Many standard subjects are treated, such as density matrices, entanglement, quantum maps, quantum cryptography, and quantum codes. Also included are discussions of quantum machines and quantum walks. In addition, the book provides detailed treatments of several underlying fundamental principles of quantum theory, such as quantum measurements, the no-cloning and no-signaling theorems, and their consequences. Problems of various levels of difficulty supplement the text, with the most challenging problems bringing the reader to the forefront of active research. This book provides a compact introduction to the fascinating and rapidly evolving interdisciplinary field of quantum information theory, and it prepares the reader for doing active research in this area.

Bergou, János A

2013-01-01

228

On Grover's Search Algorithm from a Quantum Information Geometry Viewpoint  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present an information geometric characterization of Grover's quantum search algorithm. First, we quantify the notion of quantum distinguishability between parametric density operators by means of the Wigner-Yanase quantum information metric. We then show that the quantum searching problem can be recast in an information geometric framework where Grover's dynamics is characterized by a geodesic on the manifold of the parametric density operators of pure quantum states con...

Cafaro, Carlo; Mancini, Stefano

2011-01-01

229

Preparation of multipartite entangled states used for quantum information networks  

Science.gov (United States)

The preparation of multipartite entangled states is the prerequisite for exploring quantum information networks and quantum computation. In this paper, we review the experimental progress in the preparation of cluster states and multi-color entangled states with continuous variables. The preparation of lager scale multipartite entangled state provide valuable quantum resources to implement more complex quantum informational tasks.

Su, XiaoLong; Jia, XiaoJun; Xie, ChangDe; Peng, KunChi

2014-07-01

230

Noise, Errors and Information in Quantum Amplification  

Science.gov (United States)

We analyze and compare the characterization of a quantum device in terms of noise, transmitted bit-error-rate (BER) and mutual information, showing how the noise description is meaningful only for Gaussian channels. After reviewing the description of a quantum communication channel, we study the insertion of an amplifier. We focus attention on the case of direct detection, where the linear amplifier has a 3 decibels noise-figure, which is usually considered an unsurpassable limit, referred to as the standard quantum limit (SQL). Both noise and BER could be reduced using an ideal amplifier, which is feasible in principle. However, just a reduction of noise beyond the SQL does not generally correspond to an improvement of the BER or of the mutual information. This is the case of a laser amplifier, where saturation can greatly reduce the noise-figure, although there is no corresponding improvement of the BER. Such mechanism is illustrated on the basis of Monte Carlo simulations.

D'Ariano, G. M.; Macchiavello, C.; Maccone, L.

231

Noise, errors and information in quantum amplification  

CERN Document Server

We analyze and compare the characterization of a quantum device in terms of noise, transmitted bit-error-rate (BER) and mutual information, showing how the noise description is meaningful only for Gaussian channels. After reviewing the description of a quantum communication channel, we study the insertion of an amplifier. We focus attention on the case of direct detection, where the linear amplifier has a 3 decibels noise figure, which is usually considered an unsurpassable limit, referred to as the standard quantum limit (SQL). Both noise and BER could be reduced using an ideal amplifier, which is feasible in principle. However, just a reduction of noise beyond the SQL does not generally correspond to an improvement of the BER or of the mutual information. This is the case of a laser amplifier, where saturation can greatly reduce the noise figure, although there is no corresponding improvement of the BER. Such mechanism is illustrated on the basis of Monte Carlo simulations.

D'Ariano, G M; Maccone, L

1997-01-01

232

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

CERN Document Server

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

233

Quantum mechanics and quantum information a guide through the quantum world  

CERN Document Server

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

234

Fractals in Quantum Information Process  

International Nuclear Information System (INIS)

In the recent work of Kiss et al. [Phys. Rev. Lett. 107 (2011) 100501], the evolvement of two-qubit quantum states in a measurement-based purification process is studied. As they pointed out, the purification results manifest sensitivity to the applied initial states. The convergence regions to different stable circles are depicted on a complex plane. Because of the result patterns' likeness to typical fractals, we make further study on the interesting patterns' connection to fractals. Finally, through a numerical method we conclude that the boundaries of different islands of the patterns are fractals, which possess a non-integral fractal dimension. Also, we show that the fractal dimension would vary with the change of the portion of the noise added to the initial states

2013-01-01

235

Photon engineering for quantum information processing  

CERN Document Server

We study distinguishing information in the context of quantum interference involving more than one parametric downconversion (PDC) source and in the context of polarization-entangled photon pairs based on PDC. We arrive at specific design criteria for two-photon sources so that when used as part of complex optical systems, such as photon-based quantum information processing schemes, distinguishing information between the photons is eliminated guaranteeing high visibility interference. We propose practical techniques which lead to suitably engineered two-photon states that can be realistically implemented with available technology. Finally, we study an implementation of the nonlinear-sign shift (NS) logic gate with PDC sources and show the effect of distinguishing information on the performance of the gate.

Uren, A B; Walmsley, I A

2003-01-01

236

Quantum Information through Angular momentum of Photon  

CERN Document Server

The angular momentum of photons is the key source of quantum information. The transfer of angular momentum is possible as circularly polarized light is passed through wave plates. The passage of LCP through two consecutive half wave plates traces a closed curve on Poincare sphere. As a result the geometric phase is developed associated with gain of orbital angular momentum.

Banerjee, Dipti

2014-01-01

237

Quantum Fisher information in noninertial frames  

Science.gov (United States)

We investigate the performance of quantum Fisher information (QFI) under the Unruh-Hawking effect, where one of the observers (e.g., Rob) is uniformly accelerated with respect to other partners. In the context of relativistic quantum information theory, we demonstrate that quantum Fisher information, as an important measure of the information content of quantum states, has a rich and subtle physical structure compared with entanglement or Bell nonlocality. In this work, we mainly focus on the parametrized (and arbitrary) pure two-qubit states, where the weight parameter ? and phase parameter ? are naturally introduced. Intriguingly, we prove that QFI with respect to ? (F?) remains unchanged for both scalar and Dirac fields. Meanwhile, we observe that QFI with respect to ? (F?) decreases with the increase of acceleration r but remains finite in the limit of infinite acceleration. More importantly, our results show that the symmetry of F? (with respect to ? =?/4) has been broken by the influence of the Unruh effect for both cases.

Yao, Yao; Xiao, Xing; Ge, Li; Wang, Xiao-guang; Sun, Chang-pu

2014-04-01

238

International Journal of Quantum Information (IJQI)  

Science.gov (United States)

This is a refereed online journal for researchers to announce and disseminate their latest discoveries and results in the areas of quantum information, computation and communication theory. Included are research and review papers as well as short correspondences in both theoretical and experimental areas.

2003-10-10

239

Geometrical identification of quantum and information theories  

International Nuclear Information System (INIS)

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

240

Two-way quantum communication: 'secure quantum information exchange'  

International Nuclear Information System (INIS)

In this paper, we present a new idea of two-way quantum communication called 'secure quantum information exchange' (SQIE). If there are two arbitrary unknown quantum states |?)IA and |?)IB, initially with Alice and Bob, respectively, then SQIE protocol leads to the simultaneous exchange of these states between Alice and Bob with the aid of the special kind of six-qubit entangled (SSE) state and classical assistance of the third party, Charlie. The term 'secure' signifies the fact that SQIE protocol either faithfully exchanges the unknown quantum states proceeding in a prescribed way or, in case of any irregularity, the process generates no results. For experimental realization of the SQIE protocol, we have suggested an efficient scheme for generating SSE states using the interaction between highly detuned ?-type three-level atoms and the optical coherent field. By theoretical calculations, we found that SSE states of almost unit fidelity with perfect success rates for appreciable mean photon numbers (Fav ? 0.999 for |?|2 ? 1.5) can be generated by our scheme. Further, we have discussed possible experimental imperfections, such as atomic-radiative time, cavity damping time, atom-cavity interaction time, and the efficiency of discrimination between the coherent field and the vacuum state shows that our SQIE protocol is within the reach of technology presently available.

2011-06-14

 
 
 
 
241

Quantum information processing with optical vortices  

Energy Technology Data Exchange (ETDEWEB)

Full text: In this work we discuss several proposals for quantum information processing using the transverse structure of paraxial beams. Different techniques for production and manipulation of optical vortices have been employed and combined with polarization transformations in order to investigate fundamental properties of quantum entanglement as well as to propose new tools for quantum information processing. As an example, we have recently proposed and demonstrated a controlled NOT (CNOT) gate based on a Michelson interferometer in which the photon polarization is the control bit and the first order transverse mode is the target. The device is based on a single lens design for an astigmatic mode converter that transforms the transverse mode of paraxial optical beams. In analogy with Bell's inequality for two-qubit quantum states, we propose an inequality criterion for the non-separability of the spin-orbit degrees of freedom of a laser beam. A definition of separable and non-separable spin-orbit modes is used in consonance with the one presented in Phys. Rev. Lett. 99, 2007. As the usual Bell's inequality can be violated for entangled two-qubit quantum states, we show both theoretically and experimentally that the proposed spin-orbit inequality criterion can be violated for non-separable modes. The inequality is discussed both in the classical and quantum domains. We propose a polarization to orbital angular momentum teleportation scheme using entangled photon pairs generated by spontaneous parametric down conversion. By making a joint detection of the polarization and angular momentum parity of a single photon, we are able to detect all the Bell-states and perform, in principle, perfect teleportation from a discrete to a continuous system using minimal resources. The proposed protocol implementation demands experimental resources that are currently available in quantum optics laboratories. (author)

Khoury, Antonio Z. [Universidade Federal Fluminense (UFF), Niteroi, RJ (Brazil)

2012-07-01

242

A new type of complementarity between quantum and classical information  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Physical systems contain information which can be divided between classical and quantum information. Classical information is locally accessible and allows one to perform tasks such as physical work, while quantum information allows one to perform tasks such as teleportation. It is shown that these two kinds of information are complementarity in the sense that two parties can either gain access to the quantum information, or to the classical information but not both. This co...

Oppenheim, Jonathan; Horodecki, Karol; Horodecki, Michal Horodecki Pawel; Horodecki, Ryszard

2002-01-01

243

Quantum Dialogue Without Information Leakage Using a Single Quantum Entangled State  

Science.gov (United States)

At present, a lot of quantum dialogue protocols have the problem of information leakage, especially the ones merely using a single quantum state as the quantum resource. In this paper, the author successfully puts forward a novel kind of information leakage resistant quantum dialogue protocol merely using a single quantum entangled state. This kind of quantum dialogue protocol uses the measurement correlation property of a single quantum entangled state to prevent the information leakage problem. Its Bell state version is illustrated in detail at first in this paper, then it is generalized to the cases of three-particle, four-particle and five-particle quantum entangled states. Different from those previous information leakage resistant quantum dialogue protocols, the proposed protocol needs neither the auxiliary quantum state nor the entanglement swapping technology of quantum state.

Ye, Tian-Yu

2014-05-01

244

Scavenging quantum information: Multiple observations of quantum systems  

Energy Technology Data Exchange (ETDEWEB)

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 postmeasurement state from which the 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 can 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 we study the classical limit when an arbitrarily large number of observers can obtain (nearly) complete information on the system. In addition to the case where all observers perform most informative measurements, we study the scenario where a finite number of observers estimates the state with equal fidelity, regardless of their position in the measurement sequence and the scenario where all observers use identical measurement apparatuses (up to a mutually unknown orientation) chosen so that a particular observer's estimation fidelity is maximized.

Rapcan, P. [Research Center for Quantum Information, Institute of Physics, Slovak Academy of Sciences, Dubravska cesta 9, 845 11 Bratislava (Slovakia); Calsamiglia, J.; Munoz-Tapia, R. [Fisica Teorica: Informacio i Fenomens Quantics, Edifici Cn, Universitat Autonoma de Barcelona, E-08193 Bellaterra (Barcelona) (Spain); Bagan, E. [Fisica Teorica: Informacio i Fenomens Quantics, Edifici Cn, Universitat Autonoma de Barcelona, E-08193 Bellaterra (Barcelona) (Spain); Department of Physics, Hunter College of the City University of New York, 695 Park Avenue, New York, New York 10021 (United States); Physics Department, Brookhaven National Laboratory, Upton, New York 11973 (United States); Buzek, V. [Research Center for Quantum Information, Institute of Physics, Slovak Academy of Sciences, Dubravska cesta 9, 845 11 Bratislava (Slovakia); Faculty of Informatics, Masaryk University, Botanicka 68a, CZ-602 00 Brno (Czech Republic)

2011-09-15

245

Scavenging quantum information: Multiple observations of quantum systems  

International Nuclear Information System (INIS)

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 postmeasurement state from which the 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 can 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 we study the classical limit when an arbitrarily large number of observers can obtain (nearly) complete information on the system. In addition to the case where all observers perform most informative measurements, we study the scenario where a finite number of observers estimates the state with equal fidelity, regardless of their position in the measurement sequence and the scenario where all observers use identical measurement apparatuses (up to a mutually unknown orientation) chosen so that a particular observer's estimation fidelity is maximized.

2011-09-01

246

Optimal photons for quantum information processing  

CERN Multimedia

Photonic quantum information processing schemes, such as linear optics quantum computing, and other experiments relying on single-photon interference, inherently require complete photon indistinguishability to enable the desired photonic interactions to take place. Mode-mismatch is the dominant cause of photon distinguishability in optical circuits. Here we study the effects of photon wave-packet shape on tolerance against the effects of mode-mismatch in linear optical circuits, and show that Gaussian distributed photons with large bandwidth are optimal. The result is general and holds for arbitrary linear optical circuits, including ones which allow for post-selection and classical feed-forward.

Rohde, P P; Nielsen, M A; Rohde, Peter P.; Ralph, Timothy C.; Nielsen, Michael A.

2005-01-01

247

Quantum-information transport to multiple receivers  

International Nuclear Information System (INIS)

The importance of transporting quantum information and entanglement with high fidelity cannot be overemphasized. We present a scheme based on adiabatic passage that allows for transportation of a qubit, operator measurements, and entanglement, using a one-dimensional 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 that can be used to realize two-qubit operator measurements for the generation of maximally entangled states

2006-03-01

248

Quantum wells for optical information processing  

International Nuclear Information System (INIS)

Quantum wells, alternate thin layers of two different semiconductor materials, show an exceptional electric field dependence of the optical absorption, called the quantum-confined Stark effect (QCSE), for electric fields perpendicular to the layers. This enables electrically controlled optical modulators and optically controlled self-electro-optic-effect devices that can operate at high speed and low energy density. Recent developments in these QCSE devices are summarized, including new device materials and novel device structures. The variety of sophisticated devices now demonstrated is promising for applications to information processing

1989-01-01

249

Development of Microcomputer Based Software for Encoding and Retrieving Medical Information in Pathology  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The development of a microcomputer-based software package for the entry, encoding, storage and retrieval of medical information in anatomic pathology is described. Computer assisted encoding of diagnostic language was based on SNOMED nomenclature and was found to automatically encode 92% to 98% of the cases in routine surgical pathology. This application package was based on CP/M operating system so it functions on a variety of microcomputers and can integrate with other common microcomputer ...

Hause, L.; Rothwell, D.; Frey, C.

1983-01-01

250

Scavenging quantum information: Multiple observations of quantum systems  

CERN Multimedia

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

251

QUANTUM CRYPTOGRAPHY: A NEW GENERATION OF INFORMATION SECURITY SYSTEM  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Quantum Cryptography is an approach to securing communications by applying the phenomena of quantum physics. Unlike traditional classical cryptography, which uses mathematical techniques to restrict eavesdroppers, quantum cryptography is focused on the physics of information. The security of these transmissions is based on the inviolability of the laws of quantum mechanics. The quantum cryptography relies on two important elements of quantum mechanics-the Heisenberg Uncertainty principle a...

Ritesh Kumar Jain

2012-01-01

252

0-th quantization or quantum (information) theory in 42 minutes  

CERN Multimedia

We present a concise introduction of basic concepts in quantum information theory and quantum mechanics prepared as an introduction for a general audience. In our approach the rules of quantum mechanics are presented in a simple form of rules describing the method of constructing quantum objects corresponding to classical objects. As a byproduct of the introduced approach, we present some alternative rules and use them to describe basic ingredients of quantum information theory using different types of objects.

Miszczak, J A

2013-01-01

253

Quantum information processing based on cavity QED with mesoscopic systems  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Introduction: Recent developments in quantum communication and computing [1-3] stimulated an intensive search for physical systems that can be used for coherent processing of quantum information. It is generally believed that quantum entanglement of distinguishable quantum bits (qubits) is at the heart of quantum information processing. Significant efforts have been directed towards the design of elementary logic gates, which perform certain unitary processes on pairs of qubits. These gates m...

Lukin, Mikhail; Fleischhauer, Michael; Imamoglu, Atac

2000-01-01

254

Photon-to-electron quantum information transfer  

Science.gov (United States)

Spin is a fundamental property of electrons and plays an important role in information storage. For spin-based quantum information technology, preparation and read-out of the electron spin state must be spin coherent, but both the traditional preparation and read-out of the spin state are projective to up/down spin states, which do not have spin coherence. We have recently demonstrated that the polarization coherence of light can be coherently transferred to the spin coherence of electrons in a semiconductor. We have also developed a new scheme named tomographic Kerr rotation (TKR) by generalizing the traditional KR to directly readout the spin coherence of optically prepared electrons without the need for the spin dynamics, which allows the spin projection measurement in an arbitrary set of basis states. These demonstrations were performed using g-factor-controlled semiconductor quantum wells with precessing and nonprecessing electrons. The developed scheme offers a tool for performing basis-independent preparation and read-out of a spin quantum state in a solid. These results encourage us to make a quantum media converter between flying photon qubits and stationary electron spin qubits in semiconductors.

Kosaka, Hideo

2011-05-01

255

Towards Quantum Information Theory in Space and Time  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Modern quantum information theory deals with an idealized situation when the spacetime dependence of quantum phenomena is neglected. However the transmission and processing of (quantum) information is a physical process in spacetime. Therefore such basic notions in quantum information theory as qubit, channel, composite systems and entangled states should be formulated in space and time. In particlular we suggest that instead of a two level system (qubit) the basic notion in...

Volovich, Igor V.

2002-01-01

256

A Game Theoretic Approach to Quantum Information  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This work is an application of game theory to quantum information. In a state estimate, we are given observations distributed according to an unknown distribution $P_{\\theta}$ (associated with award $Q$), which Nature chooses at random from the set $\\{P_{\\theta}: \\theta \\in \\Theta \\}$ according to a known prior distribution $\\mu$ on $\\Theta$, we produce an estimate $M$ for the unknown distribution $P_{\\theta}$, and in the end, we will suffer a relative entropy cost $\\mathcal...

Dai, Xianhua; Belavkin, V. P.

2007-01-01

257

Information and measurement in covariant quantum theory  

CERN Document Server

Due to the absence of a pre-defined external time variable, the predictions of covariant quantum theory are ambiguous when repeated measurements are considered. Here, we introduce an information theoretic framework to the covariant formalism, and use it to interpret the measurement process. We find that the time ordering of measurements emerges as an entropy relationship in the state of the observer, giving unique and well-defined probabilities for repeated measurements.

Olson, S J; Dowling, Jonathan P.

2007-01-01

258

Processing Information in Quantum Decision Theory  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A survey is given summarizing the state of the art of describing information processing in Quantum Decision Theory, which has been recently advanced as a novel variant of decision making, based on the mathematical theory of separable Hilbert spaces. This mathematical structure captures the effect of superposition of composite prospects, including many incorporated intended actions. The theory characterizes entangled decision making, non-commutativity of subsequent decisions,...

Yukalov, V. I.; Sornette, D.

2008-01-01

259

PREFACE: Quantum Information, Communication, Computation and Cryptography  

Science.gov (United States)

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

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

2007-07-01

260

Byuons, Quantum Information Channel, Consciousness and Universe  

Directory of Open Access Journals (Sweden)

Full Text Available The physics of consciousness and universal mind is shown on the base of theory of byuons, the theory of “life’ of special unobservable discrete objects—byuons from which the surrounding space and the world of elementary particles are formed. An essential distinction of that theory from the modern models in the classical and quantum field theories is that the potentials of physical fields (gravitational, electromagnetic, asf. gain exactly fixable, measurable values. Basic axioms and some conclusions of this theory are discussed. The theory of byuons predicts the existence of a new force and a new quantum information channel in nature. All objects of the Universe are shown to be united into the unique information field due to the huge interval of uncertainty in the coordinate (?x = L = 1028 cm of objects 4b (object formed during four-contact byuon-byuon interaction ( mc24b = 33 eV forming the surrounding physical space. It is a new quantum information channel.

Y. A. Baurov

2011-08-01

 
 
 
 
261

Black Holes, Information, and Hilbert Space for Quantum Gravity  

CERN Document Server

A complete description for the formation and evaporation of a black hole is given within the framework of a unitary theory of quantum gravity preserving locality. 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 sill allows for an...

Nomura, Yasunori; Weinberg, Sean J

2012-01-01

262

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

263

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

264

Some Notes on Quantum Information Theory and Emerging Computing Technologies  

CERN Document Server

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

265

Multiparty secret sharing of quantum information based on entanglement swapping  

International Nuclear Information System (INIS)

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

2004-04-26

266

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

267

Quantum information processing beyond ten ion-qubits  

International Nuclear Information System (INIS)

Successful processing of quantum information is, to a large degree, based on two aspects: a) the implementation of high-fidelity quantum gates, as well as b) avoiding or suppressing decoherence processes that destroy quantum information. The presented work shows our progress in the field of experimental quantum information processing over the last years: the implementation and characterisation of several quantum operations, amongst others the first realisation of the quantum Toffoli gate in an ion-trap based quantum computer. The creation of entangled states with up to 14 qubits serves as basis for investigations of decoherence processes. Based on the realised quantum operations as well as the knowledge about dominant noise processes in the employed apparatus, entanglement swapping as well as quantum operations within a decoherence-free subspace are demonstrated. (author)

2011-01-01

268

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

269

A dynamical point of view of Quantum Information: Wigner measures  

CERN Multimedia

We analyze a known version of the discrete Wigner function and some connections with Quantum Iterated Funcion Systems. This paper is a follow up of "A dynamical point of view of Quantum Information: entropy and pressure" by the same authors.

Baraviera, A; Lopes, A O; Cunha, M Terra

2011-01-01

270

Entropy of quantum channel in the theory of quantum information  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Quantum channels, also called quantum operations, are linear, trace preserving and completely positive transformations in the space of quantum states. Such operations describe discrete time evolution of an open quantum system interacting with an environment. The thesis contains an analysis of properties of quantum channels and different entropies used to quantify the decoherence introduced into the system by a given operation. Part I of the thesis provides a general introduc...

Roga, Wojciech

2011-01-01

271

Quantum information storage using tunable flux qubits  

Energy Technology Data Exchange (ETDEWEB)

We present details and results for a superconducting quantum bit (qubit) design in which a tunable flux qubit is coupled strongly to a transmission line. Quantum information storage in the transmission line is demonstrated with a dephasing time of T{sub 2}approx2.5 mus. However, energy lifetimes of the qubit are found to be short (approx10 ns) and not consistent with predictions. Several design and material changes do not affect qubit coherence times. In order to determine the cause of these short coherence times, we fabricated standard flux qubits based on a design which was previously successfully used by others. Initial results show significantly improved coherence times, possibly implicating losses associated with the large size of our qubit. (topical review)

Steffen, Matthias; Brito, Frederico; DiVincenzo, David; Farinelli, Matthew; Keefe, George; Ketchen, Mark; Kumar, Shwetank; Milliken, Frank; Rothwell, Mary Beth; Rozen, Jim; Koch, Roger H, E-mail: msteffe@us.ibm.co [IBM Watson Research Center, Yorktown Heights, NY 10598 (United States)

2010-02-10

272

QUANTUM CRYPTOGRAPHY: A NEW GENERATION OF INFORMATION SECURITY SYSTEM  

Directory of Open Access Journals (Sweden)

Full Text Available Quantum Cryptography is an approach to securing communications by applying the phenomena of quantum physics. Unlike traditional classical cryptography, which uses mathematical techniques to restrict eavesdroppers, quantum cryptography is focused on the physics of information. The security of these transmissions is based on the inviolability of the laws of quantum mechanics. The quantum cryptography relies on two important elements of quantum mechanics-the Heisenberg Uncertainty principle and the principle of photon polarization. This paper summarizes the current state of quantum cryptography and the real–world application implementation of this technology.

Ritesh Kumar Jain

2012-12-01

273

Information theoretic approach to tactile encoding and discrimination  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The human sense of touch integrates feedback from a multitude of touch receptors, but how this information is represented in the neural responses such that it can be extracted quickly and reliably is still largely an open question. At the same time, dexterous robots equipped with touch sensors are becoming more common, necessitating better methods for representing sequentially updated information and new control strategies that aid in extracting relevant features for object man...

Saal, Hannes

2011-01-01

274

Correcting false information in memory: manipulating the strength of misinformation encoding and its retraction.  

Science.gov (United States)

Information that is presumed to be true at encoding but later on turns out to be false (i.e., misinformation) often continues to influence memory and reasoning. In the present study, we investigated how the strength of encoding and the strength of a later retraction of the misinformation affect this continued influence effect. Participants read an event report containing misinformation and a subsequent correction. Encoding strength of the misinformation and correction were orthogonally manipulated either via repetition (Experiment 1) or by imposing a cognitive load during reading (Experiment 2). Results suggest that stronger retractions are effective in reducing the continued influence effects associated with strong misinformation encoding, but that even strong retractions fail to eliminate continued influence effects associated with relatively weak encoding. We present a simple computational model based on random sampling that captures this effect pattern, and conclude that the continued influence effect seems to defy most attempts to eliminate it. PMID:21359617

Ecker, Ullrich K H; Lewandowsky, Stephan; Swire, Briony; Chang, Darren

2011-06-01

275

Study of localization in the quantum sawtooth map emulated on a quantum information processor  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Quantum computers will be unique tools for understanding complex quantum systems. We report an experimental implementation of a sensitive, quantum coherence-dependent localization phenomenon on a quantum information processor (QIP). The localization effect was studied by emulating the dynamics of the quantum sawtooth map in the perturbative regime on a three-qubit QIP. Our results show that the width of the probability distribution in momentum space remained essentially unch...

Henry, Michael K.; Emerson, Joseph; Martinez, Rudy; Cory, David G.

2005-01-01

276

Exploring molecular equilibria using quantum information measures  

International Nuclear Information System (INIS)

The quantum information-theoretic description of electron probabilities and currents in molecules is extended. The Harriman-Zumbach-Maschke framework of equidensity orbitals is reexamined and the nonclassical Fisher information contribution it generates is used to determine the system equilibrium states for the fixed (ground-state) electron density/energy. The lowest of such variational ''thermodynamic'' states can in general exhibit the space-dependent phase and hence also nonvanishing probability current. The phase/current feature of electronic states in Harriman's representation is emphasized throughout, the probability interpretation of its key constructs is given, and the phase shifts accompanying interactions between the equidensity orbitals are examined. The phase-''temperature'' concept is introduced as the information-theoretic descriptor of probability currents in molecules and their fragments. (copyright 2013 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

2013-03-01

277

Exploring molecular equilibria using quantum information measures  

Energy Technology Data Exchange (ETDEWEB)

The quantum information-theoretic description of electron probabilities and currents in molecules is extended. The Harriman-Zumbach-Maschke framework of equidensity orbitals is reexamined and the nonclassical Fisher information contribution it generates is used to determine the system equilibrium states for the fixed (ground-state) electron density/energy. The lowest of such variational ''thermodynamic'' states can in general exhibit the space-dependent phase and hence also nonvanishing probability current. The phase/current feature of electronic states in Harriman's representation is emphasized throughout, the probability interpretation of its key constructs is given, and the phase shifts accompanying interactions between the equidensity orbitals are examined. The phase-''temperature'' concept is introduced as the information-theoretic descriptor of probability currents in molecules and their fragments. (copyright 2013 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Nalewajski, Roman F. [Department of Theoretical Chemistry, Jagiellonian University (Poland)

2013-03-15

278

Protection of quantum information and optimal singlet conversion through higher dimensional quantum systems and environment monitoring  

CERN Document Server

We study how to protect quantum information in quantum systems subjected to local dissipation. We show that combining the use of three-level systems, environment monitoring, and local feedback can fully and deterministically protect any available quantum information, including entanglement initially shared by different parties. These results can represent a gain in resources and/or distances in quantum communication protocols such as quantum repeaters and teleportation as well as time for quantum memories. Finally, we show that monitoring local environments physically implements the optimum singlet conversion protocol, essential for classical entanglement percolation.

Mascarenhas, E; Cavalcanti, D; Cunha, M Terra; Santos, M França

2010-01-01

279

Cavity quantum networks for quantum information processing in decoherence-free subspace  

Science.gov (United States)

We give a brief review on the quantum information processing in decoherence-free subspace (DFS). We show how to realize the initialization of the entangled quantum states, information transfer and teleportation of quantum states, two-qubit Grover search and how to construct the quantum network in DFS, within the cavity QED regime based on a cavity-assisted interaction by single-photon pulses.

Wei, Hua; Deng, Zhi-Jiao; Yang, Wan-Li; Zhou, Fei

2009-03-01

280

Information Hiding Method Based on Block DWT Sub-Band Feature Encoding  

Digital Repository Infrastructure Vision for European Research (DRIVER)

For realizing of long text information hiding and covert communication, a binary watermark sequence was obtained firstly from a text file and encoded by a redundant encoding method. Then, two neighboring blocks were selected at each time from the Hilbert scanning sequence of carrier image blocks, and transformed by 1-level discrete wavelet transformation (DWT). And then the double block based JNDs (just noticeable difference) were calculated with a visual model. According to the different cod...

Sun, Qiudong; Ma, Wenxin; Yan, Wenying; Dai, Hong

2009-01-01

 
 
 
 
281

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

Nyman, R. A.; Scheel, S.; Hinds, E. A.

2011-01-01

282

Hadamard NMR spectroscopy for two-dimensional quantum information processing and parallel search algorithms  

CERN Document Server

Hadamard spectroscopy has earlier been used to speed-up multi-dimensional NMR experiments. In this work we speed-up the two-dimensional quantum computing scheme, by using Hadamard spectroscopy in the indirect dimension, resulting in a scheme which is faster and requires the Fourier transformation only in the direct dimension. Two and three qubit quantum gates are implemented with an extra observer qubit. We also use one-dimensional Hadamard spectroscopy for binary information storage by spatial encoding and implementation of a parallel search algorithm.

Gopinath, T; Kumar, Anil

2006-01-01

283

Hadamard NMR spectroscopy for two-dimensional quantum information processing and parallel search algorithms.  

Science.gov (United States)

Hadamard spectroscopy has earlier been used to speed-up multi-dimensional NMR experiments. In this work, we speed-up the two-dimensional quantum computing scheme, by using Hadamard spectroscopy in the indirect dimension, resulting in a scheme which is faster and requires the Fourier transformation only in the direct dimension. Two and three qubit quantum gates are implemented with an extra observer qubit. We also use one-dimensional Hadamard spectroscopy for binary information storage by spatial encoding and implementation of a parallel search algorithm. PMID:17011221

Gopinath, T; Kumar, Anil

2006-12-01

284

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

285

Towards quantum information processing with impurity spins in silicon  

International Nuclear Information System (INIS)

The finding of algorithms for factoring and data base search that promise substantially increased computational power, as well as the expectation for efficient simulation of quantum systems have spawned an intense interest in the realization of quantum information processors [1]. Solid state implementations of quantum computers scaled to >1000 quantum bits ('qubits') promise to revolutionize information technology, but requirements with regard to sources of decoherence in solid state environments are sobering. Here, we briefly review basic approaches to impurity spin based qubits and present progress in our effort to form prototype qubit test structures. Since Kane's bold silicon based spin qubit proposal was first published in 1998 [2], several groups have taken up the challenge of fabricating elementary building blocks [3-5], and several exciting variations of single donor qubit schemes have emerged [6]. Single donor atoms, e. g. 31P, are 'natural quantum dots' in a silicon matrix, and the spins of electrons and nuclei of individual donor atoms are attractive two level systems for encoding of quantum information. The coupling to the solid state environment is weak, so that decoherence times are long (hours for nuclear spins, and ?60 ms for electron spins of isolated P atoms in silicon [7]), while control over individual spins for one qubit operations becomes possible when individual qubits are aligned to electrodes that allow shifting of electron spin resonances in global magnetic fields by application of control voltages. Two qubit operations require an interaction that couples, and entangles qubits. The exchange interaction, J, is a prime candidate for mediation of two qubit operations, since it can be turned on and off by variation of the wave function overlap between neighboring qubits, and coherent manipulation of quantum information with the exchange interaction alone has been shown to be universal [8]. However, detailed band structure calculations and theoretical analysis of J coupling between electrons bound to phosphorus atoms at low temperatures in silicon revealed strong oscillations of the coupling strength as a function of donor spacing on a sub-nm length scale [9]. These oscillations translate into scattering of interaction strength for ensembles of qubit spacings which in turn poses a serious obstacle to scalability [10]. Two alternatives to J coupling are dipolar coupling [11] and spin coherent shuttling of electrons between donor sites [12]. Readout of single electron spins poses another critical challenge [13, 14], and inferring spin orientations from charge measurements in spin dependent charge transfer reactions seems to be viable route to single shot single spin readout. This readout can be accomplished with single electron transistors, which are used as sensitive electrometers [15]. Impurity spin based qubit schemes in silicon have to overcome a significant nanofabrication challenge so that a test bed regime can be entered where fundamental properties and rudimentary operations can be investigated. In order to form such test devices, three key components have to be integrated: (1) an array of single dopant atoms has to be formed; (2) single dopant atoms are aligned to control gates; and (3) single dopant atoms are also aligned to a readout device

2004-03-01

286

Bounds on information and the security of quantum cryptography  

CERN Document Server

We present new physical bounds on quantum information, and use them to prove the security of quantum cryptography against a large class of collective attacks. Such attacks are directed against the final key, and security against them suggests that quantum cryptography is ultimately secure.

Biahm, E

1996-01-01

287

Fisher information in a quantum-critical environment  

International Nuclear Information System (INIS)

We consider a process of parameter estimation in a spin-j system surrounded by a quantum-critical spin chain. Quantum Fisher information lies at the heart of the estimation task. We employ Ising spin chain in a transverse field as the environment which exhibits a quantum phase transition. Fisher information decays with time almost monotonously when the environment reaches the critical point. By choosing a fixed time or taking the time average, one can see the quantum Fisher information presents a sudden drop at the critical point. Different initial states of the environment are considered. The phenomenon that the quantum Fisher information, namely, the precision of estimation, changes dramatically can be used to detect the quantum criticality of the environment. We also introduce a general method to obtain the maximal Fisher information for a given state.

2010-08-01

288

Bell Length as Mutual Information in Quantum Interference  

Directory of Open Access Journals (Sweden)

Full Text Available The necessity of a rigorously operative formulation of quantum mechanics, functional to the exigencies of quantum computing, has raised the interest again in the nature of probability and the inference in quantum mechanics. In this work, we show a relation among the probabilities of a quantum system in terms of information of non-local correlation by means of a new quantity, the Bell length.

Ignazio Licata

2014-04-01

289

Vacuum Fluctuations, Geometric Modular Action and Relativistic Quantum Information Theory  

CERN Multimedia

A summary of some lines of ideas leading to model-independent frameworks of relativistic quantum field theory is given. It is followed by a discussion of the Reeh-Schlieder theorem and geometric modular action of Tomita-Takesaki modular objects associated with the quantum field vacuum state and certain algebras of observables. The distillability concept, which is significant in specifying useful entanglement in quantum information theory, is discussed within the setting of general relativistic quantum field theory.

Verch, R

2005-01-01

290

Quantum information and statistical mechanics: an introduction to frontier  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This is a short review on an interdisciplinary field of quantum information science and statistical mechanics. We first give a pedagogical introduction to the stabilizer formalism, which is an efficient way to describe an important class of quantum states, the so-called stabilizer states, and quantum operations on them. Furthermore, graph states, which are a class of stabilizer states associated with graphs, and their applications for measurement-based quantum computation ar...

Fujii, Keisuke

2013-01-01

291

A neural-network-like quantum information processing system  

CERN Multimedia

The Hopfield neural networks and the holographic neural networks are models which were successfully simulated on conventional computers. Starting with these models, an analogous fundamental quantum information processing system is developed in this article. Neuro-quantum interaction can regulate the "collapse"-readout of quantum computation results. This paper is a comprehensive introduction into associative processing and memory-storage in quantum-physical framework.

Perus, M; Perus, Mitja; Bischof, Horst

2003-01-01

292

MURI Center for Photonic Quantum Information Systems.  

Science.gov (United States)

We have continued the development of several photonic quantum technologies: single-photon and entangled-photon sources from quantum dots and parametric down-conversion; solid-state quantum gates based on quantum dots in semiconductors and on NV centers in...

J. Vuckovic P. Kwiat

2009-01-01

293

Linking Classical and Quantum Key Agreement Is There "Bound Information"?  

CERN Multimedia

After carrying out a protocol for quantum key agreement over a noisy quantum channel, the parties Alice and Bob must process the raw key in order to end up with identical keys about which the adversary has virtually no information. In principle, both classical and quantum protocols can be used for this processing. It is a natural question which type of protocols is more powerful. We prove for general states but under the assumption of incoherent eavesdropping that Alice and Bob share some so-called intrinsic information in their classical random variables, resulting from optimal measurements, if and only if the parties' quantum systems are entangled. In addition, we provide evidence that the potentials of classical and of quantum protocols are equal in every situation. Consequently, many techniques and results from quantum information theory directly apply to problems in classical information theory, and vice versa. For instance, it was previously believed that two parties can carry out unconditionally secure...

Gisin, Nicolas

2000-01-01

294

Quantum-Classical Hybrid for Information Processing  

Science.gov (United States)

Based upon quantum-inspired entanglement in quantum-classical hybrids, a simple algorithm for instantaneous transmissions of non-intentional messages (chosen at random) to remote distances is proposed. The idea is to implement instantaneous transmission of conditional information on remote distances via a quantum-classical hybrid that preserves superposition of random solutions, while allowing one to measure its state variables using classical methods. Such a hybrid system reinforces the advantages, and minimizes the limitations, of both quantum and classical characteristics. Consider n observers, and assume that each of them gets a copy of the system and runs it separately. Although they run identical systems, the outcomes of even synchronized runs may be different because the solutions of these systems are random. However, the global constrain must be satisfied. Therefore, if the observer #1 (the sender) made a measurement of the acceleration v(sub 1) at t =T, then the receiver, by measuring the corresponding acceleration v(sub 1) at t =T, may get a wrong value because the accelerations are random, and only their ratios are deterministic. Obviously, the transmission of this knowledge is instantaneous as soon as the measurements have been performed. In addition to that, the distance between the observers is irrelevant because the x-coordinate does not enter the governing equations. However, the Shannon information transmitted is zero. None of the senders can control the outcomes of their measurements because they are random. The senders cannot transmit intentional messages. Nevertheless, based on the transmitted knowledge, they can coordinate their actions based on conditional information. If the observer #1 knows his own measurements, the measurements of the others can be fully determined. It is important to emphasize that the origin of entanglement of all the observers is the joint probability density that couples their actions. There is no centralized source, or a sender of the signal, because each receiver can become a sender as well. An observer receives a signal by performing certain measurements synchronized with the measurements of the others. This means that the signal is uniformly and simultaneously distributed over the observers in a decentralized way. The signals transmit no intentional information that would favor one agent over another. All the sequence of signals received by different observers are not only statistically equivalent, but are also point-by-point identical. It is important to assume that each agent knows that the other agent simultaneously receives the identical signals. The sequences of the signals are true random, so that no agent could predict the next step with the probability different from those described by the density. Under these quite general assumptions, the entangled observers-agents can perform non-trivial tasks that include transmission of conditional information from one agent to another, simple paradigm of cooperation, etc. The problem of behavior of intelligent agents correlated by identical random messages in a decentralized way has its own significance: it simulates evolutionary behavior of biological and social systems correlated only via simultaneous sensoring sequences of unexpected events.

Zak, Michail

2011-01-01

295

Quantum Theory, namely the pure and reversible theory of information  

CERN Document Server

After more than a century since its birth, Quantum Theory still eludes our understanding. If asked to describe it, we have to resort to abstract and ad hoc principles about complex Hilbert spaces. How is it possible that a fundamental physical theory cannot be described using the ordinary language of Physics? Here we offer a contribution to the problem from the angle of Quantum Information, providing a short non-technical presentation of a recent derivation of Quantum Theory from information-theoretic principles. The broad picture emerging from the principles is that Quantum Theory is the only standard theory of information compatible with the purity and reversibility of physical processes.

Chiribella, G; Perinotti, P

2012-01-01

296

Classical and quantum Fisher information in the geometrical formulation of quantum mechanics  

Energy Technology Data Exchange (ETDEWEB)

The tomographic picture of quantum mechanics has brought the description of quantum states closer to that of classical probability and statistics. On the other hand, the geometrical formulation of quantum mechanics introduces a metric tensor and a symplectic tensor (Hermitian tensor) on the space of pure states. By putting these two aspects together, we show that the Fisher information metric, both classical and quantum, can be described by means of the Hermitian tensor on the manifold of pure states.

Facchi, Paolo [Dipartimento di Matematica, Universita di Bari, I-70125 Bari (Italy); INFN, Sezione di Bari, I-70126 Bari (Italy); MECENAS, Universita Federico II di Napoli and Universita di Bari (Italy); Kulkarni, Ravi [Vivekananda Yoga Research Foundation, Bangalore 560 080 (India); Man' ko, V.I., E-mail: manko@na.infn.i [P.N. Lebedev Physical Institute, Leninskii Prospect 53, Moscow 119991 (Russian Federation); Marmo, Giuseppe [Dipartimento di Scienze Fisiche, Universita di Napoli ' Federico II' , I-80126 Napoli (Italy); INFN, Sezione di Napoli, I-80126 Napoli (Italy); MECENAS, Universita Federico II di Napoli and Universita di Bari (Italy); Sudarshan, E.C.G. [Department of Physics, University of Texas, Austin, TX 78712 (United States); Ventriglia, Franco [Dipartimento di Scienze Fisiche, Universita di Napoli ' Federico II' , I-80126 Napoli (Italy); INFN, Sezione di Napoli, I-80126 Napoli (Italy); MECENAS, Universita Federico II di Napoli and Universita di Bari (Italy)

2010-11-01

297

Quantum Theory, Namely the Pure and Reversible Theory of Information  

Digital Repository Infrastructure Vision for European Research (DRIVER)

After more than a century since its birth, Quantum Theory still eludes our understanding. If asked to describe it, we have to resort to abstract and ad hoc principles about complex Hilbert spaces. How is it possible that a fundamental physical theory cannot be described using the ordinary language of Physics? Here we offer a contribution to the problem from the angle of Quantum Information, providing a short non-technical presentation of a recent derivation of Quantum Theory from information-...

2012-01-01

298

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

2006-10-01

299

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

300

Quantum Kolmogorov Complexity and Information-Disturbance Theorem  

CERN Document Server

In this paper, a representation of the information-disturbance theorem based on the quantum Kolmogorov complexity that was defined by P. Vitanyi 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 quantitative relationships between complexities have been derived.

Miyadera, Takayuki

2011-01-01

 
 
 
 
301

Bounds on the Information Rate of Quantum Secret Sharing Schemes  

CERN Document Server

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. Further, not every scheme can be realized with rate one. In this paper we derive new 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 $O((\\log_2 n)/n)$. These results are the quantum analogues of the bounds for classical secret sharing schemes proved by Csirmaz.

Sarvepalli, Pradeep

2010-01-01

302

On the Possibility of Quantum Informational Structural Realism  

CERN Multimedia

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

303

Concepts of a quantum information theory of many letters  

CERN Document Server

A theoretical framework is presented allowing the treatment of quantum messages with components of variable length. To this aim a many-letter space is constructed which turns out to be a natural space for quantum messages of this type, generalizing the usual fixed-length quantum information theory which is fully contained within this framework. An observable is defined measuring the amount of quantum information carried by a particular message, with the "qbit" obtaining a second meaning as its unit. A general characterization of quantum codes is given where compression codes are defined by their property of decreasing the average information content of a given a priori message ensemble. A lossless quantum coding scheme - analog to the classical Huffman scheme but different from the Braunstein scheme - is implemented, which not only ensures perfect fidelity in retrieving the original messages but also provides optimal compression.

Boström, K J

2000-01-01

304

Quantum Cryptography for Information-Theoretic Security  

Science.gov (United States)

This article explains quantum computing and its potential for rendering current encrypted communication via public channels insecure. A review of quantum key distribution is given as a way to ensure secure public-channel communication regardless of the computational power of an adversary, that may possesses a quantum computer. Finally, state-of-the-art quantum key distribution is discussed with an insight into its future.

Sanders, Barry

305

Quantum information processing with atoms and cavities  

Science.gov (United States)

Cavity quantum electrodynamics (CQED) experiments realize the simplest matter-field system: a single atom coupled to a single field mode containing only a few photons. On the one hand, these experiments can be used to test fundamental features of the quantum world. On the other hand, they implement elementary quantum logic components: qubits and quantum gates. We present here a review of the CQED experiments performed at Ecole Normale Supérieure with circular Rydberg atoms and superconducting millimeter-wave cavities.

Raimond, J. M.

2002-12-01

306

PREFACE Quantum Groups, Quantum Foundations and Quantum Information: a Festschrift for Tony Sudbery  

Science.gov (United States)

On 29 July 2008, Professor Anthony Thomas Sudbery - known as Tony to his friends and colleagues - celebrated his 65th birthday. To mark this occasion and to honour Tony's scientific achievements, a 2-day Symposion was held at the University of York on 29-30 September 2008 under the sponsorship of the Institute of Physics and the London Mathematical Society. The breadth of Tony's research interests was reflected in the twelve invited lectures by A Beige, I Bengtsson, K Brown, N Cerf, E Corrigan, J Ladyman, A J Macfarlane, S Majid, C Manogue, S Popescu, J Ryan and R W Tucker. This Festschrift, also made possible by the generosity of the IOP and the LMS, reproduces the majority of these contributions together with other invited papers. Tony obtained his PhD from the University of Cambridge in 1970. His thesis, written under the guidance of Alan Macfarlane, is entitled Some aspects of chiral su(3) × su(3) symmetry in hadron dynamics. He arrived in York in 1971 with his wife Rodie, two young daughters, a lively mind and a very contemporary shock of hair. He was at that stage interested in mathematical physics and so was classed as an applied mathematician in the departmental division in place at that time. But luckily Tony did not fit into this category. His curiosity is combined with a good nose for problems and his capacity for knocking off conjectures impressed us all. Within a short time of his arrival he was writing papers on group theory, complex analysis and combinatorics, while continuing to work on quantum mechanics. His important paper on quaternionic analysis is an example of the imagination and elegance of his ideas. By developing a derivative, he replaced the relatively obscure analytical theory of quaternions by one informed by modern complex analysis. Other interests emerged, centred round the quantum: quantum mechanics and its foundations, quantum groups and quantum information. He didn't just dabble in these areas but mastered them, gaining a national and international reputation; for instance he joined Roger Penrose in a discussion on 'The Physics of Reality' in Melvyn Bragg's radio series 'In our time'. He was much in demand for contributions to the 'News and Views' section in Nature and has written numerous book reviews in scientific and semi-popular journals as well as newspaper commentaries on important scientific developments. Quantum foundations and quantum information have remained Tony's main professional preoccupations. As a contribution to the conceptual problems surrounding quantum measurement, he undertook a detailed analysis of the observation of decay, introducing the crucial distinction between continuous measurement and continual observation. A red thread through his work in quantum mechanics has been the critical scrutiny of different interpretations of quantum mechanics and the question of their experimental testability. As a result he has become an eloquent proponent of a version of what is commonly known as the 'many-worlds' interpretation in his most recent paper (arXiv:1009.3914), Tony explains why he considers the name 'Everett-Wheeler interpretation' as most appropriate and 'many worlds' unnecessary. Tony started directing his research effort to quantum information theory in the late 1990s. He quickly established himself in the quantum information community, putting York on the map in this field. He was among the first people to investigate entanglement properties of multipartite states, particularly the 3-qubit states. While studying the pure 4-qubit states he mysteriously came up with what could rightly be called the 'Sudbery state': equation (where ? is a primitive root of 1), which is the most entangled 4-qubit state in natural measures of entanglement. He continues to work in quantum information theory, particularly on quantum entanglement. Not least there is also Tony the philosopher who wrote articles with such intriguing titles as 'The necessity of not doing otherwise' or 'Why am I me? and why is my world so classical?'. Tony was a teacher of the old school. His lectures wer

Weigert, Stefan

2010-11-01

307

The capacity of a quantum channel for simultaneous transmission of classical and quantum information  

CERN Multimedia

An expression is derived characterizing the set of admissible rate pairs for simultaneous transmission of classical and quantum information over a given quantum channel, generalizing both the classical and quantum capacities of the channel. Although our formula involves regularization, i.e. taking a limit over many copies of the channel, it reduces to a single-letter expression in the case of generalized dephasing channels. Analogous formulae are conjectured for the simultaneous public-private capacity of a quantum channel and for the simultaneously 1-way distillable common randomness and entanglement of a bipartite quantum state.

Devetak, I

2003-01-01

308

Quantum Mechanics Emerges from Information Theory Applied to Causal Horizons  

Science.gov (United States)

It is suggested that quantum mechanics is not fundamental but emerges from classical information theory applied to causal horizons. The path integral quantization and quantum randomness can be derived by considering information loss of fields or particles crossing Rindler horizons for accelerating observers. This implies that information is one of the fundamental roots of all physical phenomena. The connection between this theory and Verlinde's entropic gravity theory is also investigated.

Lee, Jae-Weon

2011-04-01

309

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 ...

Toth, Geza

2007-01-01

310

The mother of all protocols: Restructuring quantum information's family tree  

CERN Multimedia

We give a simple, direct proof of the "mother" protocol of quantum information theory. In this new formulation, it is easy to see that the mother, or rather her generalization to the fully quantum Slepian-Wolf protocol, simultaneously accomplishes two goals: quantum communication-assisted entanglement distillation, and state transfer from the sender to the receiver. As a result, in addition to her other "children," the mother protocol generates the state merging primitive of Horodecki, Oppenheim and Winter, a fully quantum reverse Shannon theorem, and a new class of distributed compression protocols for correlated quantum sources which are optimal for sources described by separable density operators. Moreover, the mother protocol described here is easily transformed into the so-called "father" protocol whose children provide the quantum capacity and the entanglement-assisted capacity of a quantum channel, demonstrating that the division of single-sender/single-receiver protocols into two families was unnecess...

Abeyesinghe, A; Hayden, P; Winter, A; Abeyesinghe, Anura; Devetak, Igor; Hayden, Patrick; Winter, Andreas

2006-01-01

311

The capacity of black holes to transmit quantum information  

CERN Document Server

We study the properties of the quantum information transmission channel that emerges from the quantum dynamics of particles interacting with a black hole horizon. We calculate the quantum channel capacity in two limiting cases where a single-letter capacity is known to exist: the limit of perfectly reflecting and perfectly absorbing black holes. We find that the perfectly reflecting black hole channel is closely related to the Unruh channel and that its capacity is non-vanishing, allowing for the perfect reconstruction of quantum information. We also find that the complementary channel (transmitting entanglement behind the horizon) is entanglement-breaking in this case, with vanishing capacity. We calculate the quantum capacity of the black hole channel in the limit of a perfectly absorbing black hole and find that this capacity vanishes, while the capacity of the complementary channel is non-vanishing instead, implying that the quantum state itself survives unharmed beyond the horizon. These results together...

Bradler, Kamil

2013-01-01

312

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

CERN Document Server

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

313

Quantum Information Theoretical Analysis of Various Constructions for Quantum Secret Sharing  

CERN Document Server

Recently, an information theoretical model for Quantum Secret Sharing (QSS) schemes was introduced. By using this model, we prove that pure state Quantum Threshold Schemes (QTS) can be constructed from quantum MDS codes and vice versa. In particular, we consider stabilizer codes and give a constructive proof of their relation with QTS. Furthermore, we reformulate the Monotone Span Program (MSP) construction according to the information theoretical model and check the recoverability and secrecy requirement. Finally, we consider QSS schemes which are based on quantum teleportation.

Rietjens, K; Tuyls, P; Rietjens, Karin; Schoenmakers, Berry; Tuyls, Pim

2005-01-01

314

Simple scheme for expanding photonic cluster states for quantum information  

Energy Technology Data Exchange (ETDEWEB)

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.

Kalasuwan, P.; Laing, A.; Coggins, J.; Callaway, M.; O' Brien, J. L. [Centre for Quantum Photonics, H. H. Wills Physics Laboratory and Department of Electrical and Electronic Engineering, University of Bristol, Merchant Venturers Building, Woodland Road, Bristol, BS8 1UB (United Kingdom); Mendoza, G. [Centre for Quantum Photonics, H. H. Wills Physics Laboratory and Department of Electrical and Electronic Engineering, University of Bristol, Merchant Venturers Building, Woodland Road, Bristol, BS8 1UB (United Kingdom); California Institute of Technology, Pasadena, California 91125 (United States); Nagata, T.; Takeuchi, S. [Research Institute for Electronic Science, Hokkaido University, Sapporo 060-0812 (Japan); Institute of Scientific and Industrial Research, Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047 (Japan); Stefanov, A. [Federal Office of Metrology METAS, Laboratory Time and Frequency, Lindenweg 50, 3084 Wabern (Switzerland)

2010-06-15

315

Quantum information approach to the ultimatum game  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 comment, we present the new idea of the quantum ultimatum game. Our scheme also makes a point of departure for a protocol to quantize extensive games.

Frackiewicz, Piotr

2011-01-01

316

The Virtual Journal of Quantum Information  

Science.gov (United States)

This online journal is a multi-journal compilation of research in quantum computing, cryptography, and communication. This virtual journal prominently features review articles, news and announcements.

2005-11-21

317

Entanglement and optimal quantum information processing  

Energy Technology Data Exchange (ETDEWEB)

Today we are standing on the verge of new enigmatic era of quantum technologies. In spite of the significant progress that has been achieved over the last three decades in experimental generation and manipulation as well as in theoretical description of evolution of single quantum systems, there are many open problems in understanding the behavior and properties of complex multiparticle quantum systems. In this thesis, we investigate theoretically a number of problems related to the description of entanglement - the nonlocal feature of complex quantum systems - of multiparticle states of finite-dimensional quantum systems. We also consider the optimal ways of manipulation of such systems. The focus is made, especially, on such optimal quantum transformations that provide a desired operation independently on the initial state of the given system. The first part of this thesis, in particular, is devoted to the detailed analysis of evolution of entanglement of complex quantum systems subjected to general non-unitary dynamics. In the second part of the thesis we construct several optimal state independent transformations, analyze their properties and suggest their applications in quantum communication and quantum computing. (orig.)

Siomau, Michael

2011-07-06

318

Information Flow of quantum states interacting with closed timelike curves  

CERN Document Server

Recently, the quantum information processing power of closed timelike curves have been discussed. Because the most widely accepted model for quantum closed timelike curve interactions contains ambiguities, different authors have been able to reach radically different conclusions as to the power of such interactions. By tracing the information flow through such systems we are able to derive equivalent circuits with unique solutions, thus allowing an objective decision between the alternatives to be made. We conclude that closed timelike curves, if they exist and are well described by these simple models, would be a powerful resource for quantum information processing.

Ralph, T C

2010-01-01

319

Semiconductor sources of twin photons for quantum information  

Energy Technology Data Exchange (ETDEWEB)

A large number of scientific proposals made in the last few years are based on transport and manipulation of information using single quantum objects. Some of them make use of entanglement in pairs of particles such as twin photons. Although theoretical proposals have demonstrated highly interesting perspectives in the quantum information domain, experimental realizations and applications still suffer from the complexity of experimental set-ups and technological limitations. This paper presents various approaches aiming at efficient twin photon semiconductor sources. The emergence of these compact and integrated devices would be an important technological breakthrough in quantum information applications.

Ducci, S [Laboratoire Materiaux et Phenomenes Quantiques, UMR 7162, Universite Paris 7-Denis Diderot, 2, Place Jussieu, Case 7021, 75251 Paris (France); Lanco, L [Laboratoire Materiaux et Phenomenes Quantiques, UMR 7162, Universite Paris 7-Denis Diderot, 2, Place Jussieu, Case 7021, 75251 Paris (France); Seurin, Y [Laboratoire Materiaux et Phenomenes Quantiques, UMR 7162, Universite Paris 7-Denis Diderot, 2, Place Jussieu, Case 7021, 75251 Paris (France); Leo, G [Laboratoire Materiaux et Phenomenes Quantiques, UMR 7162, Universite Paris 7-Denis Diderot, 2, Place Jussieu, Case 7021, 75251 Paris (France); Berger, V [Laboratoire Materiaux et Phenomenes Quantiques, UMR 7162, Universite Paris 7-Denis Diderot, 2, Place Jussieu, Case 7021, 75251 Paris (France); Rossi, A De [Thales Research and Technology, Domaine de Corbeville, 91404 Orsay (France); Marcadet, X [Thales Research and Technology, Domaine de Corbeville, 91404 Orsay(France)

2005-07-01

320

Trevisan's extractor in the presence of quantum side information  

CERN Document Server

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

 
 
 
 
321

Quantum Key Distribution in Large Scale Quantum Network Assisted by Classical Routing Information  

Science.gov (United States)

Recently, small-scale Quantum Key Distribution (QKD) networks have been demonstrated and continuously operated in field environment. However, nodes of these QKD networks are less than 10 nodes. When the scale and structure of these networks becomes large and complex, such networks will subject to problem of intractable routing selection and limited transmission distance. We present a novel quantum network model and the corresponding protocol to solve these problems. The proposed quantum network model integrates classical communication network with quantum key distribution layer. Nodes in this quantum network model are divided into communication nodes for classical communication and quantum nodes for quantum key distribution. We use atomic ensembles to create entangled photons inside quantum nodes. Quantum repeaters are used to establish entanglement between remote quantum nodes so the maximum distribution distance of entangled photons can be extended. The main idea is to establish an appropriate key distribution path in the quantum key distribution layer based on the routing information obtained by the upper classical communication network. After the entanglement has been established between remote quantum nodes, these nodes will use the Ekert91 or BBM92 protocol to generate secret keys shared between each other. Then, these keys can be used to ensure the security of communication in the classical communication network.

Wu, Diance; Yu, Wanrong; Zhao, Baokang; Wu, Chunqing

2013-10-01

322

Physics Colloquium: The optical route to quantum information processing  

CERN Multimedia

Geneva University Physics Department 24, Quai Ernest Ansermet CH-1211 Geneva 4 Monday 11 April 2011 17h00 - Ecole de Physique, Auditoire Stückelberg The optical route to quantum information processing Prof. Terry Rudolph/Imperial College, London Photons are attractive as carriers of quantum information both because they travel, and can thus transmit information, but also because of their good coherence properties and ease in undergoing single-qubit manipulations. The main obstacle to their use in information processing is inducing an effective interaction between them in order to produce entanglement. The most promising approach in photon-based information processing architectures is so-called measurement-based quantum computing. This relies on creating upfront a multi-qubit highly entangled state (the cluster state) which has the remarkable property that, once prepared, it can be used to perform quantum computation by making only single qubit measurements. In this talk I will discuss generically the...

Université de Genève

2011-01-01

323

Experimental quantum deletion in an NMR quantum information processor  

Science.gov (United States)

We report an NMR experimental realization of a rapid quantum deletion algorithm that deletes marked states in an unsorted database. Unlike classical deletion, where search and deletion are equivalent, quantum deletion can be implemented with only a single query, which achieves exponential speed-up compared to the optimal classical analog. In the experimental realization, the GRAPE algorithm was used to obtain an optimized NMR pulse sequence, and the efficient method of maximum-likelihood has been used to reconstruct the experimental output state.

Long, Yu; Feng, GuanRu; Pearson, Jasong; Long, GuiLu

2014-05-01

324

Experimental quantum deletion in an NMR quantum information processor  

Science.gov (United States)

We report an NMR experimental realization of a rapid quantum deletion algorithm that deletes marked states in an unsorted database. Unlike classical deletion, where search and deletion are equivalent, quantum deletion can be implemented with only a single query, which achieves exponential speed-up compared to the optimal classical analog. In the experimental realization, the GRAPE algorithm was used to obtain an optimized NMR pulse sequence, and the efficient method of maximum-likelihood has been used to reconstruct the experimental output state.

Long, Yu; Feng, GuanRu; Pearson, Jasong; Long, GuiLu

2014-07-01

325

Two quantum analogues of Fisher information from a large deviation viewpoint of quantum estimation  

CERN Multimedia

We discuss two quantum analogues of the Fisher information, the symmetric logarithmic derivative (SLD) Fisher information and Kubo-Mori-Bogoljubov (KMB) Fisher information from a large deviation viewpoint of quantum estimation and prove that the former gives the true bound and the latter gives the bound of superefficient estimators. It is shown that the difference between them is characterized by the change of the order of limits.

Hayashi, M

2002-01-01

326

Information flow and quantum cryptography using statistical fluctuations  

International Nuclear Information System (INIS)

A procedure is formulated, using the quantum teleportation arrangement, that communicates knowledge of an apparatus setting between the wings of the experiment, using statistical fluctuations in a sequence of measurement results. It requires an entangled state, and transmission of classical information totally unrelated to the apparatus setting actually communicated. Our procedure has conceptual interest, and has applications to quantum cryptography

2003-02-01

327

Quantum optical implementation of quantum information processing and classical simulation of many-body physics from quantum information perspective  

Science.gov (United States)

This thesis is composed of two parts. In the first part we summarize our study on implementation of quantum information processing (QIP) in optical cavity QED systems, while in the second part we present our numerical investigations on strongly interacting Fermi systems using a powerful numerical algorithm developed from the perspective of quantum information theory. We explore various possible applications of cavity QED in the strong coupling regime to quantum information processing tasks theoretically, including efficient preparation of Schrodinger-cat states for traveling photon pulses, robust implementation of conditional quantum gates on neutral atoms, as well as implementation of a hybrid controlled SWAP gate. We analyze the feasibility and performance of our schemes by solving corresponding physical models either numerically or analytically. We implement a novel numerical algorithm called Time Evolving Block Decimation (TEBD), which was proposed by Vidal from the perspective of quantum information science. With this algorithm, we numerically study the ground state properties of strongly interacting fermions in an anisotropic optical lattice across a wide Feshbach resonance. The interactions in this system can be described by a general Hubbard model with particle assisted tunneling. For systems with equal spin population, we find that the Luther-Emery phase, which has been known to exist only for attractive on-site interactions in the conventional Hubbard model, could also be found even in the case with repulsive on-site interactions in the general Hubbard model. Using the TEBD algorithm, we also study the effect of particle assisted tunneling in spin-polarized systems. Fermi systems with unequal spin population and attractive interaction could allow the existence of exotic superfluidity, such as the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. In the general Hubbard model, such exotic FFLO pairing of fermions could be suppressed by high particle assisted tunneling rates. However, at low particle assisted tunneling rates, the FFLO order could be enhanced. The effect of particle density inhomogeneity due to the presence of a harmonic trap potential is also discussed based on the local density approximation.

Wang, Bin

328

Exponential speed-up with a single bit of quantum information: Testing the quantum butterfly effect  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present an efficient quantum algorithm to measure the average fidelity decay of a quantum map under perturbation using a single bit of quantum information. Our algorithm scales only as the complexity of the map under investigation, so for those maps admitting an efficient gate decomposition, it provides an exponential speed up over known classical procedures. Fidelity decay is important in the study of complex dynamical systems, where it is conjectured to be a signature o...

Poulin, David; Blume-kohout, Robin; Laflamme, Raymond; Ollivier, Harold

2003-01-01

329

BOOK REVIEW: Time, Quantum and Information  

Science.gov (United States)

Time, Quantum and Information, a paean to Professor Carl Friedrich von Weizsäcker, commemorates his 90th birthday. The range of Professor Weizsäcker’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 Weizsäcker’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 Weizsäcker’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 Weizsäcker’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 Weizsäcker’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 Weizsäcker--Williams technique of calculating the bremsstrahlung of relativistic electrons. But how many of us know of Weizsäcker’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, Weizsäcker 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 Lüst indicates that in 1951 Bohr enjoyed a friendly visit with Heisenberg in Göttingen. This 1941 meeting of Heisenberg and Bohr is discussed further in an article by Götz 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 G\\"ottingen Declarations that were both influenced by Weizsäcker. Time, Quantum and Information contains much anecdotal material. Examples include a touching quotation in a letter from Edward Teller to Weizsäcker: `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 Weizsäcker had made numerous errors in his habilitation thesis and realizing that Weizsäcker had accepted an offer from Peter Debye at Berlin: `The measure of sloppiness in Weizsäcker’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 Weizsäcker. 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 mat

Turner, Leaf

2004-04-01

330

Quantum Stackelberg Duopoly with Continuous Distributed Incomplete Information  

International Nuclear Information System (INIS)

A general model of the quantum Stackelberg duopoly is constructed by introducing the 'minimal' quantum structure into the Stackelberg duopoly with continuous distributed incomplete information, where both players only know the continuous distribution of the competitor's unit cost. In this model, the cases with complete information, discrete distributed incomplete information, and continuous distributed asymmetric information are all involved. Because of different roles played by the total information uncertainty and the information asymmetry, the game exhibits some new interesting features, such as the total information uncertainty can counteract or improve the first-mover advantage according to the value of the quantum entanglement. What's more, this general model will be helpful for the government to reduce the abuses of oligopolistic competition and to improve the economic efficiency

2012-12-01

331

Quantum Stackelberg Duopoly with Continuous Distributed Incomplete Information  

Science.gov (United States)

A general model of the quantum Stackelberg duopoly is constructed by introducing the “minimal" quantum structure into the Stackelberg duopoly with continuous distributed incomplete information, where both players only know the continuous distribution of the competitor's unit cost. In this model, the cases with complete information, discrete distributed incomplete information, and continuous distributed asymmetric information are all involved. Because of different roles played by the total information uncertainty and the information asymmetry, the game exhibits some new interesting features, such as the total information uncertainty can counteract or improve the first-mover advantage according to the value of the quantum entanglement. What's more, this general model will be helpful for the government to reduce the abuses of oligopolistic competition and to improve the economic efficiency.

Wang, Xia; Hu, Cheng-Zheng

2012-12-01

332

Squeezing Quantum Information through a Classical Channel: Measuring the "Quantumness" of a Set of Quantum States  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this paper we propose a general method to quantify how "quantum" a set of quantum states is. The idea is to gauge the quantumness of the set by the worst-case difficulty of transmitting the states through a purely classical communication channel. Potential applications of this notion arise in quantum cryptography, where one might like to use an alphabet of states that promises to be the most sensitive to quantum eavesdropping, and in laboratory demonstrations of quantum t...

Fuchs, Christopher A.; Sasaki, Masahide

2003-01-01

333

Relativistic quantum information in detectors–field interactions  

International Nuclear Information System (INIS)

We review Unruh–DeWitt detectors and other models of detector–field interaction in a relativistic quantum field theory setting as a tool for extracting detector–detector, field–field and detector–field correlation functions of interest in quantum information science, from entanglement dynamics to quantum teleportation. In particular, we highlight the contrast between the results obtained from linear perturbation theory which can be justified provided switching effects are properly accounted for, and the nonperturbative effects from available analytic expressions which incorporate the backreaction effects of the quantum field on the detector behavior. (paper)

2012-11-21

334

A New Approach to Encoding and Hiding Information in an Image  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 ...

Fadhil Salman Abed

2011-01-01

335

Quantum Information Teleportation without Entanglement: Non-Zero Quantum Discord Suffices  

CERN Document Server

We present a method to teleport the quantum information contained in a single qubit via shared quantum correlations that are weaker than the usual requirement of strong entanglement. A two-qubit, quantum-correlated, mixed-state system between Alice and Bob is deployed as the quantum channel. When Bob makes a Bell measurement on Charlie's unknown input qubit (C) in an arbitrary state, together with Bob's channel qubit (B), the Alice's qubit of the channel (A) will collapse. When the correlation matrix of the two-qubit channel is a full-rank matrix, the information required to reconstruct the input qubit C can be acquired by Alice's measurement of her collapsed output state (A'), along with a classical communication from Bob to Alice. Here the information teleportation requires only non-zero quantum discord, regardless of if there is entanglement or not.

Wang, Lei; Dowling, Jonathan P; Zhu, Shi-Yao

2011-01-01

336

Information flow at the quantum-classical boundary  

CERN Document Server

We study the nature of the information preserved by a quantum channel via the observables which exist in its image (in the Heisenberg picture), and can therefore be simulated on the receiver's side. The sharp observables preserved by a channel form an operator algebra which can be characterized in terms of the channel's elements. The effect of the channel on these observables can be reversed by another physical transformation. These results generalize the theory of quantum error correction to codes characterized by arbitrary von Neumann algebras, which can represent hybrid quantum-classical information, continuous variable systems, or certain quantum field theories. The preserved unsharp observables (positive operator-valued measures) allow for a finer characterization of the information preserved by a channel. We show that the only type of information which can be duplicated arbitrarily many times consists of coarse-grainings of a single POVM. Based on these results, we propose a model of decoherence which c...

Bény, Cédric

2008-01-01

337

How quantum theory is developing the field of Information Retrieval  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This position paper provides an overview of work conducted and an outlook of future directions within the field of Information Retrieval (IR) that aims to develop novel models, methods and frameworks inspired by Quantum Theory (QT).

2010-01-01

338

The capacity of black holes to transmit quantum information  

Science.gov (United States)

We study the properties of the quantum information transmission channel that emerges from the quantum dynamics of particles interacting with a black hole horizon. We calculate the quantum channel capacity in two limiting cases where a single-letter capacity is known to exist: the limit of perfectly reflecting and perfectly absorbing black holes. We find that the perfectly reflecting black hole channel is closely related to the Unruh channel and that its capacity is non-vanishing, allowing for the perfect reconstruction of quantum information outside of the black hole horizon. We also find that the complementary channel (transmitting entanglement behind the horizon) is entanglement-breaking in this case, with vanishing capacity. We then calculate the quantum capacity of the black hole channel in the limit of a perfectly absorbing black hole and find that this capacity vanishes, while the capacity of the complementary channel is non-vanishing instead. Rather than inviting a new crisis for quantum physics, this finding instead is in accordance with the quantum no-cloning theorem, because it guarantees that there are no space-like surfaces that contain both the sender's quantum state and the receiver's reconstructed quantum state.

Brádler, Kamil; Adami, Christoph

2014-05-01

339

Control, optimisation and transport problems in quantum information  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present an investigation of optimal control techniques applied to computational and transport processes in the field of quantum information. We implement these processes using a range of different quantum systems: a harmonic oscillator, a pair of trapped Rydberg atoms, and a spin chain. In each case, we explore how application of analytic and numerical optimal control techniques (such as the Krotov method) can effect fast, efficient, and error-free unitary operations and information transf...

Murphy, Michael

2014-01-01

340

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

 
 
 
 
341

Optical Lattices, Ultracold Atoms and Quantum Information Processing  

CERN Document Server

We review novel methods to investigate, control and manipulate neutral atoms in optical lattices. These setups allow unprecedented quantum control over large numbers of atoms and thus are very promising for applications in quantum information processing. After introducing optical lattices we discuss the superfluid (SF) and Mott insulating (MI) states of neutral atoms trapped in such lattices and investigate the SF-MI transition as recently observed experimentally. In the second part of the paper we give an overview of proposals for quantum information processing and show different ways to entangle the trapped atoms, in particular the usage of cold collisions and Rydberg atoms. Finally, we also briefly discuss the implementation of quantum simulators, entanglement enhanced atom interferometers, and ideas for robust quantum memory in optical lattices.

Jaksch, D

2004-01-01

342

Correlation dynamics of quantum fields and black hole information paradox.  

Science.gov (United States)

In recent years a statistical mechanics description of particles, fields and spacetime based on the concept of quantum open systems and the influence functional formalism has been introduced. It reproduces in full the established theory of quantum fields in curved spacetime and contains also a microscopic description of their statistical properties, such as noise, fluctuations, decoherence, and dissipation. This new framework allows one to explore the quantum statistical properties of spacetime at the interface between the semiclassical and quantum gravity regimes, as well as important non-equilibrium processes in the early universe and black holes, such as particle creation, entropy generation, galaxy formation, Hawking radiation, gravitational collapse, backreaction and the black hole end-state and information lost issues. Here the author gives a summary of the theory of correlation dynamics of quantum fields and describe how this conceptual scheme coupled with scaling behavior near the infrared limit can shed light on the black hole information paradox.

Hu, B. L.

343

Quantum information transfer between topological and spin qubit systems  

CERN Multimedia

We propose a method to coherently transfer quantum information, and to create entanglement, between topological qubits and conventional spin qubits. Our suggestion uses gated control to transfer an electron (spin qubit) between a quantum dot and edge Majorana modes in adjacent topological superconductors. Because of the spin polarization of the Majorana modes, the electron transfer translates spin superposition states into superposition states of the Majorana system, and vice versa. Furthermore, we show how a topological superconductor can be used to facilitate long-distance quantum information transfer and entanglement between spatially separated spin qubits.

Leijnse, Martin

2011-01-01

344

Quantum information transfer between topological and spin qubit systems  

International Nuclear Information System (INIS)

In this talk I introduce a method to coherently transfer quantum information, and to create entanglement, between topological qubits and conventional spin qubits. The transfer method uses gated control to transfer an electron (spin qubit) between a quantum dot and edge Majorana modes in adjacent topological superconductors. Because of the spin polarization of the Majorana modes, the electron transfer translates spin superposition states into superposition states of the Majorana system, and vice versa. Furthermore, I discuss how a topological superconductor can be used to facilitate long-distance quantum information transfer and entanglement between spatially separated spin qubits.

2012-03-25

345

Complete methods set for scalable ion trap quantum information processing.  

Science.gov (United States)

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. PMID:19661380

Home, Jonathan P; Hanneke, David; Jost, John D; Amini, Jason M; Leibfried, Dietrich; Wineland, David J

2009-09-01

346

Quantum Fisher information for states in exponential form  

Science.gov (United States)

We derive explicit expressions for the quantum Fisher information and the symmetric logarithmic derivative (SLD) of a quantum state in the exponential form ? =exp(G); the SLD is expressed in terms of the generator G. Applications include quantum-metrology problems with Gaussian states and general thermal states. Specifically, we give the SLD for a Gaussian state in two forms, in terms of its generator and its moments; the Fisher information is also calculated for both forms. Special cases are discussed, including pure, degenerate, and very noisy Gaussian states.

Jiang, Zhang

2014-03-01

347

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

International Nuclear Information System (INIS)

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.

2011-11-01

348

Quantized Detector Networks: a Quantum Informational Approach to the Description and Interpretation of Quantum Physics  

CERN Multimedia

We discuss the QDN (quantized detector network) approach to the formulation and interpretation of quantum mechanics. This approach gives us a system-free approach to quantum physics. By this, we mean having a proper emphasis on those aspects of physics which are observable and an avoidance of metaphysical concepts, which by definition are incapable of verification and should play no role in science on that account. By focusing on only what experimentalists deal with, i.e., quantum information, we avoid the ambiguities and confusion generated by the undue objectification of what are complex quantum processes.

Jaroszkiewicz, G

2005-01-01

349

Routing quantum information in spin chains  

Science.gov (United States)

Two different models are presented that allow for efficiently performing routing of a quantum state. Both cases involve an XX spin chain working as a data bus and additional spins that play the role of sender and receivers, one of which is selected to be the target of the quantum state transmission protocol via a coherent quantum coupling mechanism making use of local and/or global magnetic fields. Quantum routing is achieved in the first of the models considered by weakly coupling the sender and the receiver to the data bus. On the other hand, in the second model, local magnetic fields acting on additional spins located between the sender and receiver and the data bus allow us to perform high-fidelity routing.

Paganelli, Simone; Lorenzo, Salvatore; Apollaro, Tony J. G.; Plastina, Francesco; Giorgi, Gian Luca

2013-06-01

350

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

CERN Multimedia

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

351

A Quantum Rosetta Stone for the Information Paradox  

CERN Document Server

The black hole information loss paradox epitomizes the contradictions between general relativity and quantum field theory. The AdS/CFT correspondence provides an implicit answer for the information loss paradox in black hole physics by equating a gravity theory with an explicitly unitary field theory. Gravitational collapse in asymptotically AdS spacetimes is generically turbulent. Given that the mechanism to read out the information about correlations functions in the field theory side is plagued by deterministic classical chaos, we argue that quantum chaos might provide the true Rosetta Stone for answering the information paradox in the context of the AdS/CFT correspondence.

Zayas, Leopoldo A Pando

2014-01-01

352

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

2011-03-01

353

Free-Space Quantum Key Distribution using Multilevel Encoding via Transverse Field Modulation: Preprint.  

Science.gov (United States)

Transverse modulation of the complex optical field defines sets of orthogonal states for multilevel quantum key distribution. Principles of holography are evaluated as a means of generating and sorting the single photon states.

M. T. Gruneisen

2009-01-01

354

Practical realization of a quantum cryptography protocol exploiting polarization encoding in qutrits  

International Nuclear Information System (INIS)

We propose and discuss a specific scheme allowing realization of a quantum cryptography qutrit protocol. This protocol exploits the polarization properties of single-frequency and single-spatial-mode biphotons

2003-08-01

355

QIS-XML: A metadata specification for Quantum Information Science  

CERN Document Server

While Quantum Information Science (QIS) is still in its infancy, the ability for quantum based hardware or computers to communicate and integrate with their classical counterparts will be a major requirement towards their success. Little attention however has been paid to this aspect of QIS. To manage and exchange information between systems, today's classic Information Technology (IT) commonly uses the eXtensible Markup Language (XML) and its related tools. XML is composed of numerous specifications related to various fields of expertise. No such global specification however has been defined for quantum computers. QIS-XML is a proposed XML metadata specification for the description of fundamental components of QIS (gates & circuits) and a platform for the development of a hardware independent low level pseudo-code for quantum algorithms. This paper lays out the general characteristics of the QIS-XML specification and outlines practical applications through prototype use cases.

Heus, Pascal

2007-01-01

356

Quantum Theory, Namely the Pure and Reversible Theory of Information  

Directory of Open Access Journals (Sweden)

Full Text Available After more than a century since its birth, Quantum Theory still eludes our understanding. If asked to describe it, we have to resort to abstract and ad hoc principles about complex Hilbert spaces. How is it possible that a fundamental physical theory cannot be described using the ordinary language of Physics? Here we offer a contribution to the problem from the angle of Quantum Information, providing a short non-technical presentation of a recent derivation of Quantum Theory from information-theoretic principles. The broad picture emerging from the principles is that Quantum Theory is the only standard theory of information that is compatible with the purity and reversibility of physical processes.

Paolo Perinotti

2012-10-01

357

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

358

The information-theoretic costs of simulating quantum measurements  

International Nuclear Information System (INIS)

Winter’s measurement compression theorem stands as one of the most penetrating insights of quantum information theory. In addition to making an original and profound statement about measurement in quantum theory, it also underlies several other general protocols used for entanglement distillation and local purity distillation. The theorem provides for an asymptotic decomposition of any quantum measurement into noise and information. This decomposition leads to an optimal protocol for having a sender simulate many independent instances of a quantum measurement and send the measurement outcomes to a receiver, using as little communication as possible. The protocol assumes that the parties have access to some amount of common randomness, which is a strictly weaker resource than classical communication. In this review, we provide a second look at Winter’s measurement compression theorem, detailing the information processing task, giving examples for understanding it, reviewing Winter’s achievability proof, and detailing a new approach to its single-letter converse theorem. We prove an extension of the theorem to the case in which the sender is not required to receive the outcomes of the simulated measurement. The total cost of common randomness and classical communication can be lower for such a ‘non-feedback’ simulation, and we prove a single-letter converse theorem demonstrating optimality. We then review the Devetak–Winter theorem on classical data compression with quantum side information, providing new proofs of its achievability and converse parts. From there, we outline a new protocol that we call ‘measurement compression with quantum side information,’ announced previously by two of us in our work on triple trade-offs in quantum Shannon theory. This protocol has several applications, including its part in the ‘classically-assisted state redistribution’ protocol, which is the most general protocol on the static side of the quantum information theory tree, and its role in reducing the classical communication cost in a task known as local purity distillation. We also outline a connection between measurement compression with quantum side information and recent work on entropic uncertainty relations in the presence of quantum memory. Finally, we prove a single-letter theorem characterizing measurement compression with quantum side information when the sender is not required to obtain the measurement outcome. (topical review)

2012-11-16

359

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

360

Distribution of quantum information between an atom and two photons  

International Nuclear Information System (INIS)

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

 
 
 
 
361

PREFACE: Nobel Symposium 141: Qubits for Future Quantum Information Nobel Symposium 141: Qubits for Future Quantum Information  

Science.gov (United States)

Quantum mechanics is the most ground-breaking and fascinating theoretical concept developed in physics during the past century. Much of our present understanding of the microscopic world and its extension into the macroscopic world, including modern technical applications, is based upon quantum mechanics. We have experienced a remarkable development of information and communication technology during the past two decades, to a large extent depending upon successful fabrication of smaller and smaller components and circuits. However, we are finally approaching the physical limits of component miniaturization as we enter a microscopic world ruled by quantum mechanics. Present technology is mainly based upon classical physics such as mechanics and electromagnetism. We now face a similar paradigm shift as was experienced two hundred years ago, at the time of the industrial revolution. Engineered construction of systems is currently increasingly based on quantum physics instead of classical physics, and quantum information is replacing much of classical communication. Quantum computing is one of the most exciting sub-fields of this revolution. Individual quantum systems can be used to store and process information. They are called quantum bits, or qubits for short. A quantum computer could eventually be constructed by combining a number of qubits that act coherently. Important computations can be performed much more quickly than by classical computers. However, while we control and measure a qubit, it must be sufficiently isolated from its environment to avoid noise that causes decoherence at the same time. Currently, low temperature is generally needed to obtain sufficiently long decoherence times. Single qubits of many different kinds can be built and manipulated; some research groups have managed to successfully couple qubits and perform rudimentary logic operations. However, the fundamental problems, such as decoherence, entanglement, quantum measurements and error correction, have yet to be solved. It has been predicted that quantum computers will be able to perform certain complicated computations or simulations in minutes or hours instead of years as with present computers. So far there exist very few useful quantum algorithms; however there is hope that the development of these will be stimulated once there is a breakthrough in hardware. Remarkable progress has been made in quantum engineering and quantum measurements, but a large scale quantum computer is still far off. Quantum communication and cryptography are much closer to the market than a quantum computer. The development of quantum information has meant a large push in the field of quantum physics, that previously could only be studied in the microscopic world. Artificial atoms, realized by circuit technology and mimicking the properties of 'natural' atoms, are one example of the new possibilities opened up by quantum engineering. Several different types of qubits have been suggested. Some are based upon microscopic entities, like atoms and ions in traps, or nuclear spins in molecules. They can have long coherence times (i.e. a long period allowing many operations, of the order of 10 000, to be performed before the state needs to be refreshed) but they are difficult to integrate into large systems. Other qubits are based upon solid state components that facilitate integration and coupling between qubits, but they suffer from interactions with the environment and their coherent states have a limited lifetime. Advanced experiments have been performed with superconducting Josephson junctions and many breakthroughs have been reported in the last few years. They have an advantage in the inherent coherence of superconducting Cooper pairs over macroscopic distances. We chose to focus the Nobel Symposium on Qubits for Future Quantum Information on superconducting qubits to allow for depth in discussions, but at the same time to allow comparison with other types of qubits that may prevail in the long run. The purpose of the symposium was to bring together leading resear

Claeson, Tord; Delsing, Per; Wendin, Göran

2009-12-01

362

Optomechanical transducers for quantum-information processing  

International Nuclear Information System (INIS)

We discuss the implementation of optical quantum networks where the interface between stationary and photonic qubits is realized by optomechanical transducers [K. Stannigel et al., Phys. Rev. Lett. 105, 220501 (2010)]. This approach does not rely on the optical properties of the qubit and thereby enables optical quantum communication applications for a wide range of solid-state spin- and charge-based systems. We present an effective description of such networks for many qubits and give a derivation of a state transfer protocol for long-distance quantum communication. We also describe how to mediate local on-chip interactions by means of the optomechanical transducers that can be used for entangling gates. We finally discuss experimental systems for the realization of our proposal.

2011-10-01

363

Optomechanical transducers for quantum-information processing  

Energy Technology Data Exchange (ETDEWEB)

We discuss the implementation of optical quantum networks where the interface between stationary and photonic qubits is realized by optomechanical transducers [K. Stannigel et al., Phys. Rev. Lett. 105, 220501 (2010)]. This approach does not rely on the optical properties of the qubit and thereby enables optical quantum communication applications for a wide range of solid-state spin- and charge-based systems. We present an effective description of such networks for many qubits and give a derivation of a state transfer protocol for long-distance quantum communication. We also describe how to mediate local on-chip interactions by means of the optomechanical transducers that can be used for entangling gates. We finally discuss experimental systems for the realization of our proposal.

Stannigel, K.; Zoller, P. [Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences, A-6020 Innsbruck (Austria); Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck (Austria); Rabl, P. [Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences, A-6020 Innsbruck (Austria); Soerensen, A. S. [QUANTOP, Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen O (Denmark); Lukin, M. D. [Physics Department, Harvard University, Cambridge, Massachusetts 02138 (United States)

2011-10-15

364

Thermodynamics of quantum informational systems - Hamiltonian description  

CERN Multimedia

It is often claimed, that from a quantum system of d levels, and entropy S and heat bath of temperature T one can draw kT(ln d -S) amount of work. However, the usual arguments based on Szilard engine are not fully rigorous. Here we prove the formula within Hamiltonian description of drawing work from a quantum system and a heat bath, at a cost of entropy of the system. We base on the derivation of thermodynamical laws and quantities in [R. Alicki, J. Phys. A, 12, L103 (1979)] within a weak coupling limit. Our result provides fully physical scenario for extracting thermodynamical work from quantum correlations [J. Oppenheim et al. Phys. Rev. Lett. 89, 180402 (2002)]. We also derive Landauer principle as a consquence of second law within the considered model.

Alicki, R; Horodecki, P; Horodecki, R; Alicki, Robert; Horodecki, Michal; Horodecki, Pawel; Horodecki, Ryszard

2004-01-01

365

Quantum fluctuations from a local-causal information dynamics  

Science.gov (United States)

We shall show that the abstract and formal rules which govern the quantum kinematic and dynamics can be derived from a law of change of the information content or the degree of uncertainty that the system has a certain configuration in a microscopic time scale, which is singled out uniquely, up to a free parameter, by imposing the condition of Macroscopic Classicality and the principle of Locality. Unlike standard quantum mechanics, however, the system always has a definite configuration all the time as in classical mechanics, following a continuous trajectory fluctuating randomly in time. Moreover, we shall show that the average of the relevant physical quantities over the distribution of the configuration is equal to the quantum mechanical average of the corresponding quantum mechanical Hermitian operators over a quantum state.

Budiyono, Agung

2014-04-01

366

Correlation dynamics of quantum fields and black hole information paradox  

CERN Document Server

In recent years a statistical mechanics description of particles, fields and spacetime based on the concept of quantum open systems and the influence functional formalism has been introduced. It reproduces in full the established theory of quantum fields in curved spacetime and contains also a microscopic description of their statistical properties, such as noise, fluctuations, decoherence, and dissipation. This new framework allows one to explore the quantum statistical properties of spacetime at the interface between the semiclassical and quantum gravity regimes, as well as important non-equilibrium processes in the early universe and black holes, such as particle creation, entropy generation, galaxy formation, Hawking radiation, gravitational collapse, backreaction and the black hole end-state and information lost issues. Here we give a summary of the theory of correlation dynamics of quantum fields and describe how this conceptual scheme coupled with scaling behavior near the infrared limit can shed light...

Hu, B L

1995-01-01

367

Virtual photonic couplings of quantum nanostructures for quantum information technology  

DEFF Research Database (Denmark)

The effectiveness of virtual photons (VPHs) that need neither to conserve energy nor to follow temporal sequences because of the time-energy uncertainty principle, in the electric interactions between detuned non-identical two level atoms having different size and shape is demonstrated in terms of a model of resonance dynamic multipolemultipole interaction (RDMMI), on the basis of microphotoluminescence (μ-PL) experiment of a single asymmetric pair of GaAs/AlGaAs quantum dots (QDs). The ranges of the mediating photons in various RDMMI are estimated, proving the significance of RDMMI in the nanometer regime. Furthermore, prospective device concepts based on the RDMMI assistedby the VPHs, having possibility of autonomic routing of signals like a fallingdominoes effect not only throughout spatial extent but also over temporal differences are deiscussed.

Matsueda, H.; Hvam, Jørn Märcher

2008-01-01

368

Quantum mechanics, common sense and the black hole information paradox  

CERN Document Server

The purpose of this paper is to analyse, in the light of information theory and with the arsenal of (elementary) quantum mechanics (EPR correlations, copying machines, teleportation, mixing produced in sub-systems owing to a trace operation, etc.) the scenarios available on the market to resolve the so-called black-hole information paradox. We shall conclude that the only plausible ones are those where either the unitary evolution of quantum mechanics is given up, in which information leaks continuously in the course of black-hole evaporation through non-local processes, or those in which the world is polluted by an infinite number of meta-stable remnants.

Danielsson, U H; Danielsson, Ulf H.; Schiffer, Marcelo

1993-01-01

369

Superconducting Qubit Measurement and Information Conversion from Quantum to Classical  

International Nuclear Information System (INIS)

The Josephson bifurcation amplifier (JBA) readout process of a superconducting qubit is analyzed quantum mechanically. We examined the dynamics of the density operator of a detector (a driven nonlinear oscillator) and a qubit coupled system during the measurement process. We have observed the qubit-detector (JBA) entangled state and it is divided into two separable states at the moment the JBA transition begins. Moreover, we discuss the process from the viewpoint of time variations in information quantities, such as mutual information between the qubit and detector. We show that the measurement process corresponds to an information conversion from quantum to classical one.

2011-07-20

370

Transfer of Gravitational Information through a Quantum Channel  

CERN Multimedia

Gravitational information is incorporated into an atomic state by correlation of the internal and external degrees of freedom of the atom, in the present study of the atomic interferometer. Thus it is difficult to transfer information by using a standard teleportation scheme. In this paper, we propose a novel scheme for the transfer of gravitational information through a quantum channel provided by the entangled atomic state. Significantly, the existence of a quantum channel suppresses phase noise, improving the sensitivity of the atomic interferometer. Thus our proposal provides novel readout mechanism for the interferometer with an improved signal-to-noise ratio.

Zhang, Baocheng; Zhan, Ming-sheng

2013-01-01

371

Information as a resource in distributed quantum systems  

CERN Multimedia

We develop a paradigm for distributed quantum systems, where not only quantum communication, but also information is a valuable resource. We construct a scheme for manipulating information in analogy to entanglement theory. In this scheme, instead of maximally entangled states, Alice and Bob distill product states. We then show that the main tools of entanglement theory are general enough to work also in this opposite scheme. We obtain, up to a plausible assumption, that the amount of information that must be lost during a concentration protocol can be expressed as the relative entropy distance from some set of states.

Horodecki, M; Horodecki, P; Horodecki, R; Oppenheim, J; Sen, A; Sen, U; Horodecki, Michal; Horodecki, Karol; Horodecki, Pawel; Horodecki, Ryszard; Oppenheim, Jonathan; Sen, Aditi; Sen, Ujjwal

2003-01-01

372

Quantum mechanics, common sense, and the black hole information paradox  

Science.gov (United States)

The purpose of this paper is to analyze, in the light of information theory and with the arsenal of (elementary) quantum mechanics (EPR, correlations, copying machines, teleportation, mixing produced in subsystems owing to a trace operation, etc.) the scenarios available on the market to resolve the so-called black hole information paradox. We shall conclude that the only plausible ones are those where either the unitary evolution of quantum mechanics is given up, in which information leaks continuously in the course of black hole evaporation through nonlocal processes, or those in which the world is polluted by an infinite number of metastable remnants.

Danielsson, Ulf H.; Schiffer, Marcelo

1993-11-01

373

Classical information transmission capacity of quantum black holes  

Science.gov (United States)

The fate of classical information incident on a quantum black hole has been the subject of an ongoing controversy in theoretical physics, because a calculation within the framework of semi-classical curved-space quantum field theory appears to show that the incident information is irretrievably lost, in contradiction to time-honored principles such as time-reversibility and unitarity. Here, we show within this framework embedded in quantum communication theory that signaling from past to future null infinity in the presence of a Schwarzschild black hole can occur with arbitrary accuracy, and thus that classical information is not lost in black hole dynamics. The calculation relies on a treatment that is manifestly unitary from the outset, where probability conservation is guaranteed because black holes stimulate the emission of radiation in response to infalling matter. This stimulated radiation is non-thermal and contains all of the information about the infalling matter, while Hawking radiation contains none of it.

Adami, Christoph; Ver Steeg, Greg

2014-04-01

374

Reduced randomness in quantum cryptography with sequences of qubits encoded in the same basis  

International Nuclear Information System (INIS)

We consider the cloning of sequences of qubits prepared in the states used in the BB84 or six-state quantum cryptography protocol, and show that the single-qubit fidelity is unaffected even if entire sequences of qubits are prepared in the same basis. This result is only valid provided that the sequences are much shorter than the total key. It is of great importance for practical quantum cryptosystems because it reduces the need for high-speed random number generation without impairing on the security against finite-size cloning attacks

2006-03-01

375

Reduced randomness in quantum cryptography with sequences of qubits encoded in the same basis  

Science.gov (United States)

We consider the cloning of sequences of qubits prepared in the states used in the BB84 or six-state quantum cryptography protocol, and show that the single-qubit fidelity is unaffected even if entire sequences of qubits are prepared in the same basis. This result is only valid provided that the sequences are much shorter than the total key. It is of great importance for practical quantum cryptosystems because it reduces the need for high-speed random number generation without impairing on the security against finite-size cloning attacks.

Lamoureux, L.-P.; Bechmann-Pasquinucci, H.; Cerf, N. J.; Gisin, N.; Macchiavello, C.

2006-03-01

376

Theoretical foundations of quantum information processing and communication. Selected topics  

International Nuclear Information System (INIS)

Based on eight extensive lectures selected from those given at the renowned Chris Engelbrecht Summer School in Theoretical Physics in South Africa, this text on the theoretical foundations of quantum information processing and communication covers an array of topics, including quantum probabilities, open systems, and non-Markovian dynamics and decoherence. It also addresses quantum information and relativity as well as testing quantum mechanics in high energy physics. Because these self-contained lectures discuss topics not typically covered in advanced undergraduate courses, they are ideal for post-graduate students entering this field of research. Some of the lectures are written at a more introductory level while others are presented as tutorials that survey recent developments and results in various subfields. (orig.)

2010-01-01

377

Quantum Private Information Retrieval with Sublinear Communication Complexity  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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, Franc?ois Le

2011-01-01

378

Entanglement transfer experiment in NMR quantum information processing  

International Nuclear Information System (INIS)

We report the implementation of an entanglement transfer on a four-qubit liquid-state nuclear-magnetic resonance quantum information processor. This consists of creating an (pseudopure) entangled state among two directly coupled spins, and then transferring this two-spin state to another pair of spins whose direct interactions are negligible. Such transfers are expected to be an essential operation in scalable quantum computer architectures, and provide a useful benchmark for the coherent control available in specific implementations

2002-02-01

379

Smooth composite pulses for high-fidelity quantum information processing  

International Nuclear Information System (INIS)

We present a systematic SU(2) approach for construction of composite sequences of pulses with smooth temporal shapes that produce high-fidelity two-state excitation profiles. This makes possible the application of composite pulses to quantum control and quantum information processing with short and ultrashort laser pulses. We present an exact analytic formula for the composite phases for arbitrarily accurate broadband pulses and examples of narrowband, passband, and fractional-? pulses as well as composite pulses with detuning compensation.

2011-05-01

380

Elementary gates for quantum information with superposed coherent states  

International Nuclear Information System (INIS)

We propose an alternative way of implementing several elementary quantum gates for qubits in the coherent-state basis. The operations are probabilistic and employ single-photon subtractions as the driving force. Our schemes for single-qubit phase gate and two-qubit controlled phase gate are capable of achieving arbitrarily large phase shifts with currently available resources, which makes them suitable for the near-future tests of quantum-information processing with superposed coherent states.

2010-07-01

 
 
 
 
381

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

382

Quantum tagging: Authenticating location via quantum information and relativistic signaling constraints  

Energy Technology Data Exchange (ETDEWEB)

We define the task of quantum tagging, that is, authenticating the classical location of a classical tagging device by sending and receiving quantum signals from suitably located distant sites, in an environment controlled by an adversary whose quantum information processing and transmitting power is unbounded. We define simple security models for this task and briefly discuss alternatives. We illustrate the pitfalls of naive quantum cryptographic reasoning in this context by describing several protocols which at first sight appear unconditionally secure but which, as we show, can in fact be broken by teleportation-based attacks. We also describe some protocols which cannot be broken by these specific attacks, but do not prove they are unconditionally secure. We review the history of quantum tagging protocols, and show that protocols previously proposed by Malaney and Chandran et al. are provably insecure.

Kent, Adrian; Munro, William J.; Spiller, Timothy P. [Centre for Quantum Information and Foundations, DAMTP, University of Cambridge, Cambridge, United Kingdom and Perimeter Institute for Theoretical Physics, Waterloo, Ontario (Canada); NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi-shi, Kanagawa 243-0198 (Japan); Quantum Information Science, School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom)

2011-07-15

383

Quantum engineering of continuous variable quantum states  

International Nuclear Information System (INIS)

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.)

2009-01-01

384

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

385

Quantum-information processing with circuit quantum electrodynamics  

International Nuclear Information System (INIS)

We theoretically study single and two-qubit dynamics in the circuit QED architecture. We focus on the current experimental design [Wallraff et al., Nature (London) 431, 162 (2004); Schuster et al., ibid. 445, 515 (2007)] 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 multiqubit gates between non-nearest qubits and for the realization of gates in parallel, opening the possibility of fault-tolerant quantum computation with superconducting 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 of two-qubit gates are discussed, these include gates based on virtual photons, real excitation of the resonator, and a gate based on the geometric phase. We also point out the importance of selection rules when working at the charge degeneracy point

2007-03-01

386

Statistical properties of quantum entanglement and information entropy  

International Nuclear Information System (INIS)

Key words: entropy, entanglement, atom-field interaction, trapped ions, cold atoms, information entropy. Objects of research: Pure state entanglement, entropy squeezing mazer. The aim of the work: Study of the new entanglement features and new measures for both pure-state and mixed state of particle-field interaction. Also, the impact of the information entropy on the quantum information theory. Method of investigation: Methods of theoretical physics and applied mathematics (statistical physics, quantum optics) are used. Results obtained and their novelty are: All the results of the dissertation are new and many new features have been discovered. Particularly: the most general case of the pure state entanglement has been introduced. Although various special aspects of the quantum entropy have been investigated previously, the general features of the dynamics, when a multi-level system and a common environment are considered, have not been treated before and our work therefore, field a gap in the literature. Specifically: 1) A new entanglement measure due to quantum mutual entropy (mixed-state entanglement) we called it DEM, has been introduced, 2) A new treatment of the atomic information entropy in higher level systems has been presented. The problem has been completely solved in the case of three-level system, 3) A new solution of the interaction between the ultra cold atoms and cavity field has been discovered, 4) Some new models of the atom-field interaction have been adopted. Practical value: The subject carries out theoretic character. Application region: Results can be used in quantum computer developments. Also, the presented results can be used for further developments of the quantum information and quantum communications. (author)

2007-01-01

387

Quantum Bio-Informatics:From Quantum Information to Bio-Informatics  

CERN Multimedia

The purpose of this volume is examine bio-informatics and quantum information, which are growing rapidly at present, and to attempt to connect the two, with a view to enumerating and solving the many fundamental problems they entail. To this end, we look for interdisciplinary bridges in mathematics, physics, and information and life sciences. In particular, research into a new paradigm for information science and life science on the basis of quantum theory is emphasized. Sample Chapter(s). Markov Fields on Graphs (599 KB). Contents: Markov Fields on Graphs (L Accardi & H Ohno); Some Aspects of

Freudenberg, W; Ohya, M

2008-01-01

388

Byuons, Quantum Information Channel, Consciousness and Universe  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The physics of consciousness and universal mind is shown on the base of theory of byuons, the theory of “life’ of special unobservable discrete objects—byuons from which the surrounding space and the world of elementary particles are formed. An essential distinction of that theory from the modern models in the classical and quantum field theories is that the potentials of physical fields (gravitational, electromagnetic, asf.) gain exactly fixable, measurable values. Basic axioms and som...

Baurov, Y. A.

2011-01-01

389

Delocalization power of global unitary operations on quantum information  

Energy Technology Data Exchange (ETDEWEB)

We investigate how two pieces of localized quantum information represented by a tensor product of two unknown qudit states are delocalized by performing two-qudit global unitary operations. To characterize the delocalization power of global unitary operations on quantum information, we analyze the necessary and sufficient condition to deterministically relocalize one of the two pieces of quantum information to its original Hilbert space by using only local operation and classical communication (LOCC). We prove that this LOCC one-piece relocalization is possible if and only if the global unitary operation is local unitary equivalent to a controlled-unitary operation. The delocalization power and the entangling power characterize different non-local properties of global unitary operations.

Soeda, A; Murao, M, E-mail: soeda@eve.phys.s.u-tokyo.ac.j [Department of Physics, Graduate School of Science, University of Tokyo, Tokyo 113-0033 (Japan)

2010-09-15

390

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

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

2012-01-01

391

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

392

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

393

Coherent Interactions in Rare-Earth-Ion-Doped Crystals for Applications in Quantum Information Science  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This thesis describes investigations of the use of cryogenically cooled rare-earth-ion-doped crystals for quantum information processing and quantum optics. Several aspects of the coherent interaction between light and rare-earth ions in solids are addressed. Quantum information science has given physicists new views of quantum mechanics. The transmission of quantum states has already found practical use and full scale quantum computers may one day perform computations and simu...

Nilsson, Mattias

2005-01-01

394

Grating-dot two-dimensional barcode patterns with extra binary data for encoding secret information  

Science.gov (United States)

The usual two-dimensional (2D) barcode patterns do not encrypt secret information. However, secret information is sometimes needed to increase the security features of barcode patterns. Therefore, this paper proposes 2D barcode patterns created by two-beam writers to encrypt extra binary data for encoding secret information. The proposed 2D barcode patterns are composed of many grating dots and the fringes of the grating dots are classified into four types. The first type of fringe possesses a pitch of 1.1 ?m and an orientation of -45°, the second type of fringe possesses a pitch of 1.2 ?m and an orientation of -45°, the third type of fringe possesses a pitch of 1.1 ?m and an orientation of 45°and the fourth type of fringe possesses a pitch of 1.2 ?m and an orientation of 45°. All the fringes with a 1.1 ?m pitch can show a color and all the fringes with a 1.2 ?m pitch can show another color when a microscope is used to inspect them. Therefore, extra binary data for encoding secret information can be formed with the two pitches. On the other hand, all the fringes with a -45° orientation can become bright for a viewing direction and all the fringes with a 45° orientation can become bright for another viewing direction when one looks at them. Therefore, the grating dots with the -45° fringe orientation and the grating dots with the 45° fringe orientation can be used to show a positive barcode image and a negative barcode image, respectively. Both the positive and negative barcode images can be used to derive the barcode data. The experiment shows that the proposed barcode patterns can be used conveniently and correctly.

Lih Yeh, Sheng; Lin, Shyh Tsong

2013-02-01

395

Advances in chemical physics, quantum information and computation for chemistry  

CERN Document Server

Examines the intersection of quantum information and chemical physics The Advances in Chemical Physics series is dedicated to reviewing new and emerging topics as well as the latest developments in traditional areas of study in the field of chemical physics. Each volume features detailed comprehensive analyses coupled with individual points of view that integrate the many disciplines of science that are needed for a full understanding of chemical physics. This volume of the series explores the latest research findings, applications, and new research paths from the quantum information science

Kais, Sabre; Rice, Stuart A

2014-01-01

396

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

397

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

398

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

399

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

400

Principles of quantum computation and information volume II  

Energy Technology Data Exchange (ETDEWEB)

Any new textbook in quantum information has some pretty strong competition to contend with. Not only is there the classic text by Nielsen and Chuang from 2000, but also John Preskill's lecture notes, available for free online. Nevertheless, a proper textbook seems more enduring than online notes, and the field has progressed considerably in the seven years since Nielsen and Chuang was published. A new textbook is a great opportunity to give a snapshot of our current state of knowledge in quantum information. Therein also lies a problem: The field has expanded so much that it is impossible to cover everything at the undergraduate level. Quantum information theory is relevant to an extremely large portion of physics, from solid state and condensed matter physics to particle physics. Every discipline that has some relation to quantum mechanics is affected by our understanding of quantum information theory. Those who wish to write a book on quantum information therefore have to make some profound choices: Do you keep the ultimate aim of a quantum computer in mind, or do you focus on quantum communication and precision measurements as well? Do you describe how to build a quantum computer with all possible physical systems or do you present only the underlying principles? Do you include only the tried and tested ideas, or will you also explore more speculative directions? You don't have to take a black-or-white stance on these questions, but how you approach them will profoundly determine the character of your book. The authors of 'Principles of Quantum Computation and Information (Volume II: Basic Tools and Special Topics)' have chosen to focus on the construction of quantum computers, but restrict themselves mainly to general techniques. Only in the last chapter do they explicitly address the issues that arise in the different implementations. The book is the second volume in a series, and consists of four chapters (labelled 5 to 8) called 'Quantum Information Theory', 'Decoherence', 'Quantum Error Correction', and 'First Experimental Implementations'. The first volume covers the basics of classical computation, quantum mechanics, quantum computation, and quantum communication. Chapter five starts with the density matrix formalism, and proceeds with the development of the Kraus representation, POVMs, von Neuman entropy, quantum data compression, the Holevo bound, the partial transpose criterion, and it ends with a very nice section on the various entropies that play a role in modern physics. This includes not only the thermodynamical and statistical entropy, but also the dynamical Kolmogorov-Sinai entropy, which is used in quantum chaos in chapter 6. On the whole, I think that this is a really clear and well-presented chapter. A minor drawback is that the concept of CP maps is not explained as well as it could have been, for example by relating it to the partial transpose criterion. Chapter six continues with the high standard set in chapter five, and presents a very thorough exposition of decoherence in general. It introduces the different decoherence channels, and gives truly excellent explanations of the master equation (tied in with the Kraus representation), quantum jumps, and the quantum trajectory formalism. It also has an elegant explanation for the sensitivity of Schroedinger cats to decoherence. The chapter ends with two sections on quantum chaos. Since the authors are experts in this fascinating area, this is a welcome addition to the canon of topics typically covered in quantum information. Unfortunately, the section is quite hard to follow, and as a result it is a bit of a missed opportunity. There is a section on chaos in the first volume of this series, and this may provide the required background. Chapter seven on quantum error correction is disappointing, and I have the feeling that the authors went through the motions without a real passion for the subject matter. The chapter describes various error correction codes, including Hamming codes and CSS

Kok, P [Department of Physics and Astronomy, Hicks Building, Hounsfield Road, Sheffield S3 7RH (United Kingdom)

2007-10-05

 
 
 
 
401

Principles of quantum computation and information volume II  

International Nuclear Information System (INIS)

Any new textbook in quantum information has some pretty strong competition to contend with. Not only is there the classic text by Nielsen and Chuang from 2000, but also John Preskill's lecture notes, available for free online. Nevertheless, a proper textbook seems more enduring than online notes, and the field has progressed considerably in the seven years since Nielsen and Chuang was published. A new textbook is a great opportunity to give a snapshot of our current state of knowledge in quantum information. Therein also lies a problem: The field has expanded so much that it is impossible to cover everything at the undergraduate level. Quantum information theory is relevant to an extremely large portion of physics, from solid state and condensed matter physics to particle physics. Every discipline that has some relation to quantum mechanics is affected by our understanding of quantum information theory. Those who wish to write a book on quantum information therefore have to make some profound choices: Do you keep the ultimate aim of a quantum computer in mind, or do you focus on quantum communication and precision measurements as well? Do you describe how to build a quantum computer with all possible physical systems or do you present only the underlying principles? Do you include only the tried and tested ideas, or will you also explore more speculative directions? You don't have to take a black-or-white stance on these questions, but how you approach them will profoundly determine the character of your book. The authors of 'Principles of Quantum Computation and Information (Volume II: Basic Tools and Special Topics)' have chosen to focus on the construction of quantum computers, but restrict themselves mainly to general techniques. Only in the last chapter do they explicitly address the issues that arise in the different implementations. The book is the second volume in a series, and consists of four chapters (labelled 5 to 8) called 'Quantum Information Theory', 'Decoherence', 'Quantum Error Correction', and 'First Experimental Implementations'. The first volume covers the basics of classical computation, quantum mechanics, quantum computation, and quantum communication. Chapter five starts with the density matrix formalism, and proceeds with the development of the Kraus representation, POVMs, von Neuman entropy, quantum data compression, the Holevo bound, the partial transpose criterion, and it ends with a very nice section on the various entropies that play a role in modern physics. This includes not only the thermodynamical and statistical entropy, but also the dynamical Kolmogorov-Sinai entropy, which is used in quantum chaos in chapter 6. On the whole, I think that this is a really clear and well-presented chapter. A minor drawback is that the concept of CP maps is not explained as well as it could have been, for example by relating it to the partial transpose criterion. Chapter six continues with the high standard set in chapter five, and presents a very thorough exposition of decoherence in general. It introduces the different decoherence channels, and gives truly excellent explanations of the master equation (tied in with the Kraus representation), quantum jumps, and the quantum trajectory formalism. It also has an elegant explanation for the sensitivity of Schroedinger cats to decoherence. The chapter ends with two sections on quantum chaos. Since the authors are experts in this fascinating area, this is a welcome addition to the canon of topics typically covered in quantum information. Unfortunately, the section is quite hard to follow, and as a result it is a bit of a missed opportunity. There is a section on chaos in the first volume of this series, and this may provide the required background. Chapter seven on quantum error correction is disappointing, and I have the feeling that the authors went through the motions without a real passion for the subject matter. The chapter describes various error correction codes, including Hamming codes and CSS codes, but it is virtually silent on fault tolerance; it do

2007-10-05

402

Generating and sensing signals for quantum cryptography using phase encoding in compact silica-on-silicon Mach-Zehnder circuits with Bragg gratings  

Science.gov (United States)

We have realized phase encoding and sensing of signals for quantum cryptography in compact circuits made with standard silica-on-silicon technology. The circuits include Bragg grating filters allowing multichannel cryptography with dense channel spacing, and they are thermally balanced to avoid crosstalk.

Kristensen, M.; Balle, T.; Selchau, J.; Sigvardt, K. B.; Groothoff, N.

2012-01-01

403

Controlled interactions, quantum noise and entanglement in systems for quantum information processing  

Science.gov (United States)

In this work, we study the effect of environment on quantum systems relevant for quantum information processing. We begin with the analysis of noise-distorted evolution (decoherence) for a single qubit (two-state quantum system) subject to time-dependent control (quantum gates). We develop two unitarity-preserving approximation schemes for the reduced density matrix and quantify decoherence at shortto-intermediate times. It is demonstrated that the structure of a time-dependent external control can suppress as well as enhance decoherence, and therefore should be taken into consideration while constructing quantum-computing schemes. For more complex quantum-computing systems, it turns out that in certain cases some decoherence can be beneficial. We present an analytical treatment of quantum walks on cycles and hyper-cycles and investigate a realistic physical model based on semiconductor heterostructure with the graph represented by coupled quantum dots formed using a split-gate technique. The decoherence is induced by continuous monitoring of each quantum dot by a nearby quantum point contact. We derive expressions for the probability distribution and calculate bounds for the mixing time. We show that mixing time can be minimized for some rates of decoherence. Apart from coherence, a crucial property of a multi-quoit system affected by environment is its ability to develop and maintain entanglement. It is anticipated that quantum noise destroys fragile entanglement between qubits, making dynamics rather classical. It is also expected that common environment can quantum correlate qubits. The interplay of these two phenomena is analyzed on the example of two spin systems emersed in a bosonic bath. We identify the time scales for which the spins develop entanglement for various spatial separations. Estimates for the interaction and the level of quantum noise for localized impurity electron spins in Si-Ge are given. Properties of entanglement are further investigated for larger qubit systems. An idling multi-qubit system interacting with a common bosonic field experiences quantum phase transition as one alters the coupling to the bath. We derive an exact solution in the limit of a large number of qubits and analyze critical behavior of pairwise entanglement.

Solenov, Dmitry

404

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

405

H1 photonic crystal cavitites for hybrid quantum information protocols  

CERN Document Server

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

406

Additivity of Entangled Channel Capacity for Quantum Input States  

Digital Repository Infrastructure Vision for European Research (DRIVER)

An elementary introduction into algebraic approach to unified quantum information theory and operational approach to quantum entanglement as generalized encoding is given. After introducing compound quantum state and two types of informational divergences, namely, Araki-Umegaki (a-type) and of Belavkin-Staszewski (b-type) quantum relative entropic information, this paper treats two types of quantum mutual information via entanglement and defines two types of corresponding qu...

Belavkin, V. P.; Dai, X.

2007-01-01

407

Renyi generalizations of the conditional quantum mutual information  

CERN Document Server

The conditional quantum mutual information $I(A;B|C)$ of a tripartite state $\\rho_{ABC}$ is an information quantity which lies at the center of many problems in quantum information theory. Three of its main properties are that it is non-negative for any tripartite state, that it decreases under local operations applied to systems $A$ and $B$, and that it obeys the duality relation $I(A;B|C)=I(A;B|D)$ for a four-party pure state on systems $ABCD$. It has been an open question to find Renyi generalizations of the conditional mutual information, that would allow for a deeper understanding of the original quantity and find applications beyond the traditional memoryless setting of quantum information theory. The present paper addresses this question, by defining different $\\alpha$-Renyi generalizations $I_{\\alpha}(A;B|C)$ of the conditional mutual information that all converge to the conditional mutual information in the limit $\\alpha \\to 1$. Furthermore, we prove that many of these generalizations satisfy the afo...

Berta, Mario; Wilde, Mark M

2014-01-01

408

High efficiency transfer of quantum information and multiparticle entanglement generation in translation-invariant quantum chains  

International Nuclear Information System (INIS)

We demonstrate that a translation-invariant chain of interacting quantum systems can be used for high efficiency transfer of quantum entanglement and the generation of multiparticle entanglement over large distances and between arbitrary sites without the requirement of precise spatial or temporal control. The scheme is largely insensitive to disorder and random coupling strengths in the chain. We discuss harmonic oscillator systems both in the case of arbitrary Gaussian states and in situations when at most one excitation is in the system. The latter case, which we prove to be equivalent to an xy-spin chain, may be used to generate genuine multiparticle entanglement. Such a 'quantum data bus' may prove useful in future solid state architectures for quantum information processing

2005-02-01

409

Mathematical Foundations of Quantum Information and Computation and Its Applications to Nano- and Bio-systems  

CERN Document Server

This monograph provides a mathematical foundation  to  the theory of quantum information and computation, with applications to various open systems including nano and bio systems. It includes introductory material on algorithm, functional analysis, probability theory, information theory, quantum mechanics and quantum field theory. Apart from standard material on quantum information like quantum algorithm and teleportation, the authors discuss findings on the theory of entropy in C*-dynamical systems, space-time dependence of quantum entangled states, entangling operators, adaptive dynamics, relativistic quantum information, and a new paradigm for quantum computation beyond the usual quantum Turing machine. Also, some important applications of information theory to genetics and life sciences, as well as recent experimental and theoretical discoveries in quantum photosynthesis are described.

Ohya, Masanori

2011-01-01

410

Probabilistic and information-theoretic interpretation of quantum evolutions  

International Nuclear Information System (INIS)

In quantum mechanics, outcomes of measurements on a state have a probabilistic interpretation while the evolution of the state is treated deterministically. Here we show that one can also treat the evolution as being probabilistic in nature and one can measure which unitary acted. In further analogy to states, one can also choose which basis of unitaries to measure. Likewise, one can give an information-theoretic interpretation to evolutions by defining the entropy of a completely positive map. This entropy gives the rate at which the informational content of the evolution can be compressed. One cannot compress this information and still have the evolution act on an unknown state, but we demonstrate a general scheme to do so probabilistically. This allows one to generalize super-dense coding to the sending of quantum information. One can also define the 'interaction-entanglement' of a unitary, and concentrate this entanglement

2004-08-01

411

DMRG and periodic boundary conditions: a quantum information perspective  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We introduce a picture to analyze the density matrix renormalization group (DMRG) numerical method from a quantum information perspective. This leads us to introduce some modifications for problems with periodic boundary conditions in which the results are dramatically improved. The picture also explains some features of the method in terms of entanglement and teleportation.

Verstraete, F.; Porras, D.; Cirac, J. I.

2004-01-01

412

Quantum information analysis of electronic states at different molecular structures  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have studied transition metal clusters from a quantum information theory perspective using the density-matrix renormalization group (DMRG) method. We demonstrate the competition between entanglement and interaction localization. We also discuss the application of the configuration interaction based dynamically extended active space procedure which significantly reduces the effective system size and accelerates the speed of convergence for complicated molecular electronic ...

Barcza, G.; Legeza, O?; Marti, K. H.; Reiher, M.

2010-01-01

413

Wavelet quantum search algorithm with partial information  

International Nuclear Information System (INIS)

It is questionable that Grover algorithm may be more efficient than classical one, when partial information is given in an unstructured database. In this letter, we propose to use the Haar wavelet transformation in the Grover algorithm, to consider partial information. Given a partial information L to an unstructured database of size N, we show the improved speedup, O(N/L). The speedup originates in the preparation of the initial state W-bar vertical bar k>, which provides a superposition of N/L states and L determines which state has to be chosen as vertical bar k>

2007-05-01

414

The FEYNMAN tools for quantum information processing: Design and implementation  

Science.gov (United States)

The FEYNMAN tools have been re-designed with the goal to establish and implement a high-level (computer) language that is capable to deal with the physics of finite, n-qubit systems, from frequently required computations to mathematically advanced tasks in quantum information processing. In particular, emphasis has been placed to introduce a small but powerful set of keystring-driven commands in order to support both, symbolic and numerical computations. Though the current design is implemented again within the framework of MAPLE, it is general and flexible enough to be utilized and combined with other languages and computational environments. The present implementation facilitates a large number of computational tasks, including the definition, manipulation and parametrization of quantum states, the evaluation of quantum measures and quantum operations, the evolution of quantum noise in discrete models, quantum measurements and state estimation, and several others. The design is based on a few high-level commands, with a syntax close to the mathematical notation and its use in the literature, and which can be generalized quite readily in order to solve computational tasks at even higher degree of complexity. In this work, I present and discuss the (re-design of the) FEYNMAN tools and make major parts of the code available for public use. Moreover, a few selected examples are shown and demonstrate possible application of this toolbox. The FEYNMAN tools are provided as MAPLE library and can hence be used on all platforms on which this computer-algebra system is accessible.

Fritzsche, S.

2014-06-01

415

A probabilistic and information theoretic interpretation of quantum evolutions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In quantum mechanics, outcomes of measurements on a state have a probabilistic interpretation while the evolution of the state is treated deterministically. Here we show that one can also treat the evolution as being probabilistic in nature and one can measure `which unitary' happened. Likewise, one can give an information-theoretic interpretation to evolutions by defining the entropy of a completely positive map. This entropy gives the rate at which the informational conten...

Oppenheim, J.; Reznik, B.

2003-01-01

416

Controllable quantum information network with a superconducting system  

Science.gov (United States)

We propose a controllable and scalable architecture for quantum information processing using a superconducting system network, which is composed of current-biased Josephson junctions (CBJJs) as tunable couplers between the two superconducting transmission line resonators (TLRs), each coupling to multiple superconducting qubits (SQs). We explicitly demonstrate that the entangled state, the phase gate, and the information transfer between any two selected SQs can be implemented, respectively. Lastly, numerical simulation shows that our scheme is robust against the decoherence of the system.

Zhang, Feng-yang; Liu, Bao; Chen, Zi-hong; Wu, Song-lin; Song, He-shan

2014-07-01

417

Quantum black-hole information missing in the semiclassical treatment  

CERN Document Server

In the semiclassical treatment of gravity, an external observer can measure only the mean (not the exact) mass of the black hole (BH). By contrast, in fully quantum gravity the exact (not only mean) BH mass is measurable by the external observer. This additional information (missing in the semiclassical treatment) available to the external observer significantly helps to understand how information leaks out during the BH evaporation.

Nikolic, H

2008-01-01

418

Teleportation of a two-mode entangled coherent state encoded with two-qubit information  

International Nuclear Information System (INIS)

We propose a scheme to teleport a two-mode entangled coherent state encoded with two-qubit information, which is better than the two schemes recently proposed by Liao and Kuang (2007 J. Phys. B: At. Mol. Opt. Phys. 40 1183) and by Phien and Nguyen (2008 Phys. Lett. A 372 2825) in that our scheme gives higher value of minimum assured fidelity and minimum average fidelity without using any nonlinear interactions. For involved coherent states | ± ?), minimum average fidelity in our case is ?0.99 for |?| ? 1.6 (i.e. |?|2 ? 2.6), while previously proposed schemes referred above report the same for |?| ? 5 (i.e. |?|2 ? 25). Since it is very challenging to produce superposed coherent states of high coherent amplitude (|?|), our teleportation scheme is at the reach of modern technology.

2010-09-28

419