- Home
- ▪
- About
- ▪
- News
- ▪
- Advanced Search
- ▪
- Mobile
- ▪
- Contact Us
- ▪
- Site Map
- ▪
- Help

1

Deterministically encoding quantum information using 100-photon Schrödinger cat states.

In contrast to a single quantum bit, an oscillator can store multiple excitations and coherences provided one has the ability to generate and manipulate complex multiphoton states. We demonstrate multiphoton control by using a superconducting transmon qubit coupled to a waveguide cavity resonator with a highly ideal off-resonant coupling. This dispersive interaction is much greater than decoherence rates and higher-order nonlinearities to allow simultaneous manipulation of hundreds of photons. With a tool set of conditional qubit-photon logic, we mapped an arbitrary qubit state to a superposition of coherent states, known as a "cat state." We created cat states as large as 111 photons and extended this protocol to create superpositions of up to four coherent states. This control creates a powerful interface between discrete and continuous variable quantum computation and could enable applications in metrology and quantum information processing. PMID:24072821

Vlastakis, Brian; Kirchmair, Gerhard; Leghtas, Zaki; Nigg, Simon E; Frunzio, Luigi; Girvin, S M; Mirrahimi, Mazyar; Devoret, M H; Schoelkopf, R J

2013-11-01

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

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.

4

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

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 system we propose a hybrid 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 storage of information, whose efficiency against the action of an ohmic bath show that this encoding can be readily implemented with present day technology. We extend the investigation to generate entanglement between several solid st...

Neto, O P de Sa

2011-01-01

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.

6

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

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.

Neto, O. P. de Sá; de Oliveira, M. C.

2012-09-01

7

Spatially Encoded Pseudo-Pure States for NMR Quantum Information Processing

Quantum information processing by liquid-state NMR spectroscopy uses pseudo-pure states to mimic the evolution and observations on true pure states. A new method of preparing pseudo-pure states is described, which involves the selection of the spatially labeled states of an ancilla spin with which the spin system of interest is correlated. This permits a general procedure to be given for the preparation of pseudo-pure states on any number of spins, subject to the limitations imposed by the loss of signal from the selected subensemble. The preparation of a single pseudo-pure state is demonstrated by carbon and proton NMR on 13C-labeled alanine. With a judicious choice of magnetic field gradients, the method further allows encoding of up to 2^N pseudo-pure states in independent spatial modes in an N+1 spin system. Fast encoding and decoding schemes are demonstrated for the preparation of four such spatially labeled pseudo-pure states.

Sharf, Y; Cory, D G; Sharf, Yehuda; Havel, Timothy F.; Cory, David G.

2000-01-01

8

Protecting Quantum Information Encoded in Decoherence Free States Against Exchange Errors

The exchange interaction between identical qubits in a quantum information processor gives rise to unitary two-qubit errors. It is shown here that decoherence free subspaces (DFSs) for collective decoherence undergo Pauli errors under exchange, which however do not take the decoherence free states outside of the DFS. In order to protect DFSs against these errors it is sufficient to employ a recently proposed concatenated DFS-quantum error correcting code scheme [D.A. Lidar, ...

Lidar, Daniel A.; Bacon, David; Kempe, Julia; Whaley, K. Birgitta

1999-01-01

9

Protecting Quantum Information Encoded in Decoherence Free States Against Exchange Errors

The exchange interaction between identical qubits in a quantum information processor gives rise to unitary two-qubit errors. It is shown here that decoherence free subspaces (DFSs) for collective decoherence undergo Pauli errors under exchange, which however do not take the decoherence free states outside of the DFS. In order to protect DFSs against these errors it is sufficient to employ a recently proposed concatenated DFS-quantum error correcting code scheme [D.A. Lidar, D. Bacon and K.B. Whaley, Phys. Rev. Lett. vol 82, 4556 (1999)

Lidar, D A; Lidar, Daniel A.

2000-01-01

10

Spatially Encoded Pseudo-Pure States for NMR Quantum Information Processing

Quantum information processing by liquid-state NMR spectroscopy uses pseudo-pure states to mimic the evolution and observations on true pure states. A new method of preparing pseudo-pure states is described, which involves the selection of the spatially labeled states of an ancilla spin with which the spin system of interest is correlated. This permits a general procedure to be given for the preparation of pseudo-pure states on any number of spins, subject to the limitations...

Sharf, Yehuda; Havel, Timothy F.; Cory, David G.

2000-01-01

11

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

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

Houshmand, Monireh; Wilde, Mark M

2011-01-01

12

Quantum logical operations on encoded qubits

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

13

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)

14

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

15

International Nuclear Information System (INIS)

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

16

Energy Technology Data Exchange (ETDEWEB)

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

Rodgers, P

1998-03-01

17

Quantum Computation and Quantum Information

Quantum computation and quantum information are of great current interest in computer science, mathematics, physical sciences and engineering. They will likely lead to a new wave of technological innovations in communication, computation and cryptography. As the theory of quantum physics is fundamentally stochastic, randomness and uncertainty are deeply rooted in quantum computation, quantum simulation and quantum information. Consequently quantum algorithms are random in na...

Wang, Yazhen

2012-01-01

18

Source Coding With Encoder Side Information

We introduce the idea of distortion side information, which does not directly depend on the source but instead affects the distortion measure. We show that such distortion side information is not only useful at the encoder, but that under certain conditions, knowing it at only the encoder is as good as knowing it at both encoder and decoder, and knowing it at only the decoder is useless. Thus distortion side information is a natural complement to the signal side information studied by Wyner and Ziv, which depends on the source but does not involve the distortion measure. Furthermore, when both types of side information are present, we characterize the penalty for deviating from the configuration of encoder-only distortion side information and decoder-only signal side information, which in many cases is as good as full side information knowledge.

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

2004-01-01

19

Controlling quantum information

Quantum information science explores ways in which quantum physical laws can be harnessed to control the acquisition, transmission, protection, and processing of information. This field has seen explosive growth in the past several years from progress on both theoretical and experimental fronts. Essential to this endeavor are methods for controlling quantum information. In this thesis, I present three new approaches for controlling quantum information. First, I present a new protocol for continuously protecting unknown quantum states from noise. This protocol combines and expands ideas from the theories of quantum error correction and quantum feedback control. The result can outperform either approach by itself. I generalize this protocol to all known quantum stabilizer codes, and study its application to the three-qubit repetition code in detail via Monte Carlo simulations. Next, I present several new protocols for controlling quantum information that are fault-tolerant. These protocols require only local quantum processing due to the topological properties of the quantum error correcting codes upon which they are built. I show that each protocol's fault-dependence behavior exhibits an order-disorder phase transition when mapped onto an associated statistical-mechanical model. I review the critical error rates of these protocols found by numerical study of the associated models, and I present new analytic bounds for them using a self-avoiding random walk argument. Moreover, I discuss fault-tolerant procedures for encoding, error-correction, computing, and decoding quantum information using these protocols, and calculate the accuracy threshold of fault-tolerant quantum memory for protocols using them. I end by presenting a new class of quantum algorithms that solve combinatorial optimization problems solely by measurement. I compute the running times of these algorithms by establishing an explicit dynamical model for the measurement process. This model, the digitized version of von Neumann's measurement model, is recognized as Kitaev's phase estimation algorithm. I show that the running times of these algorithms are closely related to the running times of adiabatic quantum algorithms. Finally, I present a two-measurement algorithm that achieves a quadratic speedup for Grover's unstructured search problem.

Landahl, Andrew John

20

Information encoding in homoclinic chaotic systems

In this work we describe a simple method of encoding information at real time in the inter-spike intervals of a homoclinic chaotic system. This has been experimentally tested by means of an instantaneous synchronization between the laser intensity of a CO2 laser with feedback in the regime of Sil'nikov chaos and an external pulsed signal of very low power. The information is previously encoded in the temporal intervals between consecutive pulses of the external signal. The value of the inter-pulse intervals is varied each time a new pulse is generated.

Marino, I P; Meucci, R; Boccaletti, S; Arecchi, F T

2001-01-01

21

Encoding and Retrieval of Information from Lecture.

Four different methods for attending to a lecture were studied: listening, listening with an outline, note-taking, and note-taking with an outline. Each method was designed to influence the learner's level of processing and, therefore, to effect the encoding and retrieval of information from a lecture. In addition, the effects of no review or…

Yu, Howard K.; Berliner, David C.

22

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

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...

Yan, Hui; Zhu, Shi-liang; Du, Shengwang

2010-01-01

23

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

24

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

25

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)

26

The science of quantum information has arisen over the last two decades centered on the manipulation of individual quanta of information, known as quantum bits or qubits. Quantum computers, quantum cryptography and quantum teleportation are among the most celebrated ideas that have emerged from this new field. It was realized later on that using continuous-variable quantum information carriers, instead of qubits, constitutes an extremely powerful alternative approach to quantum information processing. This review focuses on continuous-variable quantum information processes that rely on any combination of Gaussian states, Gaussian operations, and Gaussian measurements. Interestingly, such a restriction to the Gaussian realm comes with various benefits, since on the theoretical side, simple analytical tools are available and, on the experimental side, optical components effecting Gaussian processes are readily available in the laboratory. Yet, Gaussian quantum information processing opens the way to a wide vari...

Weedbrook, Christian; Garcia-Patron, Raul; Cerf, Nicolas J; Ralph, Timothy C; Shapiro, Jeffrey H; Lloyd, Seth

2011-01-01

27

Quantum Information Processing

Quantum processing and communication is emerging as a challenging technique at the beginning of the new millennium. This is an up-to-date insight into the current research of quantum superposition, entanglement, and the quantum measurement process - the key ingredients of quantum information processing. The authors further address quantum protocols and algorithms. Complementary to similar programmes in other countries and at the European level, the German Research Foundation (DFG) started a focused research program on quantum information in 1999. The contributions - written by leading experts - bring together the latest results in quantum information as well as addressing all the relevant questions

Leuchs, Gerd

2005-01-01

28

Quantum Information An Introduction

Recently, quantum information theory has been developing through a fusion of results from various research fields. This requires that understanding of basic results on diverse topics, and derived from different disciplinary perspectives, is required for appreciating the overall picture. Intended to merge key topics from both the information-theoretic and quantum- mechanical viewpoints, this graduate-level textbook provides a unified viewpoint of quantum information theory and lucid explanations of those basic results, so that the reader fundamentally grasps advances and challenges. For example, advanced topics in quantum communication such as quantum teleportation, superdense coding, quantum state transmission (quantum error-correction), and quantum encryption especially benefit from this unified approach. Unlike earlier treatments, the text requires knowledge of only linear algebra, probability theory, and quantum mechanics, while it treats the topics of quantum hypothesis testing and the discrimination of q...

Hayashi, Masahito

2006-01-01

29

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

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

30

Hiding Quantum Information in the Perfect Code

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

31

Quantum information and coherence

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

32

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

33

NMR Quantum Information Processing

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 comput...

Ramanathan, Chandrasekhar; Boulant, Nicolas; Chen, Zhiying; Cory, David G.; Chuang, Isaac; Steffen, Matthias

2004-01-01

34

Introduction to quantum information science

This book presents the basics of quantum information, e.g., foundation of quantum theory, quantum algorithms, quantum entanglement, quantum entropies, quantum coding, quantum error correction and quantum cryptography. The required knowledge is only elementary calculus and linear algebra. This way the book can be understood by undergraduate students. In order to study quantum information, one usually has to study the foundation of quantum theory. This book describes it from more an operational viewpoint which is suitable for quantum information while traditional textbooks of quantum theory lack this viewpoint. The current book bases on Shor's algorithm, Grover's algorithm, Deutsch-Jozsa's algorithm as basic algorithms. To treat several topics in quantum information, this book covers several kinds of information quantities in quantum systems including von Neumann entropy. The limits of several kinds of quantum information processing are given. As important quantum protocols,this book contains quantum teleport...

Hayashi, Masahito; Kawachi, Akinori; Kimura, Gen; Ogawa, Tomohiro

2015-01-01

35

Isotope - based Quantum Information

This paper is brief review of three aspects of the isotope - based quantum information: computation, teleportation and cryptography. Our results demonstrate not only that entanglement exists in elementary excitation of isotope - mixed solids but also it can be used for quantum information processing.

Plekhanov, Vladimir G.

2009-01-01

36

Hybrid quantum information processing

I will briefly explain the definition and advantage of hybrid quantum information processing, which is hybridization of qubit and continuous-variable technologies. The final goal would be realization of universal gate sets both for qubit and continuous-variable quantum information processing with the hybrid technologies. For that purpose, qubit teleportation with a continuousvariable teleporter is one of the most important ingredients.

Furusawa, Akira

2014-12-01

37

Source Coding With Distortion Side Information At The Encoder

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

38

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

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

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

2006-01-01

39

Robust Control of Quantum Information

Errors in the control of quantum systems may be classified as unitary, decoherent and incoherent. Unitary errors are systematic, and result in a density matrix that differs from the desired one by a unitary operation. Decoherent errors correspond to general completely positive superoperators, and can only be corrected using methods such as quantum error correction. Incoherent errors can also be described, on average, by completely positive superoperators, but can nevertheless be corrected by the application of a locally unitary operation that ``refocuses'' them. They are due to reproducible spatial or temporal variations in the system's Hamiltonian, so that information on the variations is encoded in the system's spatiotemporal state and can be used to correct them. In this paper liquid-state nuclear magnetic resonance (NMR) is used to demonstrate that such refocusing effects can be built directly into the control fields, where the incoherence arises from spatial inhomogeneities in the quantizing static magne...

Pravia, M A; Emerson, J; Farid, A; Fortunato, E M; Havel, T F; Cory, D G; Pravia, Marco A.; Boulant, Nicolas; Emerson, Joseph; Farid, Amro; Fortunato, Evan M.; Havel, Timothy F.; Cory, David G.

2003-01-01

40

Relativistic quantum information

Over the past few years, a new field of high research intensity has emerged that blends together concepts from gravitational physics and quantum computing. Known as relativistic quantum information, or RQI, the field aims to understand the relationship between special and general relativity and quantum information. Since the original discoveries of Hawking radiation and the Unruh effect, it has been known that incorporating the concepts of quantum theory into relativistic settings can produce new and surprising effects. However it is only in recent years that it has become appreciated that the basic concepts involved in quantum information science undergo significant revision in relativistic settings, and that new phenomena arise when quantum entanglement is combined with relativity. A number of examples illustrate that point. Quantum teleportation fidelity is affected between observers in uniform relative acceleration. Entanglement is an observer-dependent property that is degraded from the perspective of accelerated observers moving in flat spacetime. Entanglement can also be extracted from the vacuum of relativistic quantum field theories, and used to distinguish peculiar motion from cosmological expansion. The new quantum information-theoretic framework of quantum channels in terms of completely positive maps and operator algebras now provides powerful tools for studying matters of causality and information flow in quantum field theory in curved spacetimes. This focus issue provides a sample of the state of the art in research in RQI. Some of the articles in this issue review the subject while others provide interesting new results that will stimulate further research. What makes the subject all the more exciting is that it is beginning to enter the stage at which actual experiments can be contemplated, and some of the articles appearing in this issue discuss some of these exciting new developments. The subject of RQI pulls together concepts and ideas from special relativity, quantum optics, general relativity, quantum communication and quantum computation. The high level of current interest in these subjects is exemplified by the recent award of the 2012 Nobel Prize in Physics to Serge Haroche and David J Wineland for ground-breaking experimental methods that enable measuring and manipulation of individual quantum systems. It is our hope that this issue will encourage new researchers to enter this rapidly developing and exciting new field. R B Mann and T C RalphGuest Editors

Mann, R. B.; Ralph, T. C.

2012-11-01

41

Quantum information processing in spin chains via quantum Zeno dynamics

We show how the quantum Zeno effect can be exploited to control quantum information in a spin chain in a flexible way. In particular, we consider a one dimensional array of three level systems interacting via a swap operator, an interaction found in a generalized Heisenberg Hamiltonian. By encoding the qubit into two levels and using simple projective frequent measurements, the dynamics of the chain is guided to achieve basic quantum information manipulation tools, \\emph{i.e.}, quantum registers, single qubit operations and quantum state transfer on demand, while local addressability is not required. State transfer is perfect, robust against errors and delivers qubits at a constant rate, unconditional of the length of the transfer. Moreover, two dimensional lattices with tunable global interactions in different directions offer the possibility of performing two-qubit gates.

Monras, Alex

2008-01-01

42

Enhanced quantum state detection efficiency through quantum information processing

International Nuclear Information System (INIS)

We investigate theoretically and experimentally how quantum state-detection efficiency is improved by the use of quantum information processing (QIP). Experimentally, we encode the state of one 9Be+ ion qubit with one additional ancilla qubit. By measuring both qubits, we reduce the state-detection error in the presence of noise. The deviation from the theoretically allowed reduction is due to infidelities of the QIP operations. Applying this general scheme to more ancilla qubits suggests that error in the individual qubit measurements need not be a limit to scalable quantum computation

43

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)

44

Minimal memory requirements for pearl necklace encoders of quantum convolutional codes

One of the major goals in quantum computer science is to reduce the overhead associated with the implementation of quantum computers, and inevitably, routines for quantum error correction will account for most of this overhead. A particular technique for quantum error correction that may be useful in the outer layers of a concatenated scheme for fault tolerance is quantum convolutional coding. The encoder for a quantum convolutional code has a representation as a convolutional encoder or as a "pearl necklace" encoder. In the pearl necklace representation, it has not been particularly clear in the research literature how much quantum memory such an encoder would require for implementation. Here, we offer an algorithm that answers this question. The algorithm first constructs a weighted, directed acyclic graph where each vertex of the graph corresponds to a gate string in the pearl necklace encoder, and each path through the graph represents a non-commutative path through gates in the encoder. We show that the ...

Houshmand, Monireh; Wilde, Mark M

2010-01-01

45

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

46

Computational approach to quantum encoder design for purity optimization

International Nuclear Information System (INIS)

In this paper, we address the problem of designing a quantum encoder that maximizes the minimum output purity of a given decohering channel, where the minimum is taken over all possible pure inputs. This problem is cast as a max-min optimization problem with a rank constraint on an appropriately defined matrix variable. The problem is computationally very hard because it is nonconvex with respect to both the objective function (output purity) and the rank constraint. Despite this difficulty, we provide a tractable computational algorithm that produces the exact optimal solution for codespace of dimension 2. Moreover, this algorithm is easily extended to cover the general class of codespaces, in which case the solution is suboptimal in the sense that the suboptimized output purity serves as a lower bound of the exact optimal purity. The algorithm consists of a sequence of semidefinite programmings and can be performed easily. Two typical quantum error channels are investigated to illustrate the effectiveness of our method

47

Protecting Quantum Information with Entanglement and Noisy Optical Modes

We incorporate active and passive quantum error-correcting techniques to protect a set of optical information modes of a continuous-variable quantum information system. Our method uses ancilla modes, entangled modes, and gauge modes (modes in a mixed state) to help correct errors on a set of information modes. A linear-optical encoding circuit consisting of offline squeezers, passive optical devices, feedforward control, conditional modulation, and homodyne measurements performs the encoding. The result is that we extend the entanglement-assisted operator stabilizer formalism for discrete variables to continuous-variable quantum information processing.

Wilde, Mark M

2008-01-01

48

A Hybrid Quantum Encoding Algorithm of Vector Quantization for Image Compression

Many classical encoding algorithms of Vector Quantization (VQ) of image compression that can obtain global optimal solution have computational complexity O(N). A pure quantum VQ encoding algorithm with probability of success near 100% has been proposed, that performs operations 45sqrt(N) times approximately. In this paper, a hybrid quantum VQ encoding algorithm between classical method and quantum algorithm is presented. The number of its operations is less than sqrt(N) for ...

Pang, Chao-yang; Zhou, Zheng-wei; Guo, Guang-can

2006-01-01

49

Quantum information and computation

International Nuclear Information System (INIS)

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

50

International Nuclear Information System (INIS)

We propose efficient-phase-encoding protocols for continuous-variable quantum key distribution using coherent states and postselection. By these phase encodings, the probability of basis mismatch is reduced and total efficiency is increased. We also propose mixed-state protocols by omitting a part of classical communication steps in the efficient-phase-encoding protocols. The omission implies a reduction of information to an eavesdropper and possibly enhances the security of the protocols. We investigate the security of the protocols against individual beam splitting attack

51

Information-theoretic interpretation of quantum error-correcting codes

Quantum error-correcting codes are analyzed from an information-theoretic perspective centered on quantum conditional and mutual entropies. This approach parallels the classical description of coding in Shannon theory, while clarifying the differences between classical and quantum codes. More specifically, it is shown how quantum information theory accounts for the fact that redundant information can be distributed over quantum bits even though this does not violate the quantum non-cloning theorem. While the quantum bits that are altered appear statistically independent of the encoded logical word for any possible error, the quantum information stored in the entire codeword remains unaffected. This remarkable feature, which has no counterpart in classical coding, is related to the property that the ternary mutual entropy vanishes for a tripartite system in a pure state. These concepts are used to derive the quantum analogue of the Singleton bound on the number of logical bits that can be preserved by a code o...

Cerf, N J; Cerf, Nicolas J.; Cleve, Richard

1997-01-01

52

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

53

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.

54

Quantum information processing with Schrodinger cats

Quantum optics has proved a fertile field for experimental tests of quantum information science, from experimental verification of the violation of the Bell inequalities to quantum teleportation. However it was long believed that quantum optics would not provide a practical path to efficient and scaleable quantum computation, and most current efforts to achieve a scaleable quantum computer have focussed on solid state implementations. This orthodoxy was challenged recently when Knill et al. showed that given single photon sources and single photon detectors, linear optics alone would suffice to implement efficient quantum computation. While this result is surprising, the complexity of the optical networks required is daunting. In this talk we propose an efficient scheme which is elegant in its simplicity. We indicate how fundamental single and two qubit gates can be achieved. By encoding the quantum information in multi-photon coherent states, rather than single photon states, simple optical manipulations acquire unexpected power. As an application of this new information processing ability we investigate a class of high precision measurements. We show how superpositions of coherent states allow displacement measurements at the Heisenberg limit. Entangling many superpositions of coherent states offers a significant advantage over a single mode superposition states with the same mean photon number.

Nemoto, Kae; Gilchrist, Alexei; Munro, William J.; Ralph, Tim C.; Braunstein, Samuel L.; Milburn, Gerard J.

2003-05-01

55

Quantum Information and Relativity Theory

Quantum mechanics, information theory, and relativity theory are the basic foundations of theoretical physics. The acquisition of information from a quantum system is the interface of classical and quantum physics. Essential tools for its description are Kraus matrices and positive operator valued measures (POVMs). Special relativity imposes severe restrictions on the transfer of information between distant systems. Quantum entropy is not a Lorentz covariant concept. Lorentz...

Peres, Asher; Terno, Daniel R.

2002-01-01

56

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

57

Reducing pure dephasing of quantum bits by collective encoding in quantum dot arrays

International Nuclear Information System (INIS)

We show that phonon-induced pure dephasing of an excitonic (charge) quantum bit in a quantum dot (QD) may be reduced by collective encoding of logical qubits in QD arrays. We define the logical qubit on an array of 2, 4 and 8 QDs, connecting the logical 0) state with the presence of excitons in the appropriately chosen half of dots and the logical 1) state with the other half of the dots occupied. We give quantitative estimates of the resulting total error of a single qubit operation for an InAs/GaAs system

58

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

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

Houshmand, Monireh

2010-01-01

59

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

60

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

61

Tools for Multimode Quantum Information: Modulation, Detection, and Spatial Quantum Correlations

DEFF Research Database (Denmark)

We present here all the tools required for continuous variable parallel quantum information protocols based on spatial multi-mode quantum correlations and entanglement. We describe techniques for encoding and detecting this quantum information with high efficiency in the individual modes. We use the generation of spatial squeezing light in higher order transverse Hermite-Gauss modes as a demonstration of the quality of our scheme. The squeezing in selective modes is achieved by fine tuning of the phase matching condition of the nonlinear (2) material and the cavity resonance condition of the optical parametric amplifier. By combining these modes we can now build a practical multi-mode optical quantum information system.

Lassen, Mikael Østergaard; Delaubert, Vincent

2007-01-01

62

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

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

63

Quantum information and precision measurement

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

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

2000-01-01

64

Quantum Information Science and Nanotechnology

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

Vlasov, Alexander Yu

2009-01-01

65

Transduction and encoding sensory information by skin mechanoreceptors.

Physical contact with the external world occurs through specialized neural structures called mechanoreceptors. Cutaneous mechanoreceptors provide information to the central nervous system (CNS) about touch, pressure, vibration, and skin stretch. The physiological function of these mechanoreceptors is to convert physical forces into neuronal signals. Key questions concern the molecular identity of the mechanoelectric transducer channels and the mechanisms by which the physical parameters of the mechanical stimulus are encoded into patterns of action potentials (APs). Compelling data indicate that the biophysical traits of mechanosensitive channels combined with the collection of voltage-gated channels are essential to describe the nature of the stimulus. Recent research also points to a critical role of the auxiliary cell-nerve ending communication in encoding stimulus properties. This review describes the characteristics of ion channels responsible for translating mechanical stimuli into the neural codes that underlie touch perception and pain. PMID:25416542

Hao, Jizhe; Bonnet, Caroline; Amsalem, Muriel; Ruel, Jérôme; Delmas, Patrick

2015-01-01

66

Quantum information transfer using photons

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

67

We propose an effective realization of the universal set of elementary quantum gates in solid state quantum computer based on macroscopic (or mesoscopic) resonance systems - multi-atomic coherent ensembles, squids or quantum dots in quantum electrodynamic cavity. We exploit an encoding of logical qubits by the pairs of the macroscopic two- or three-level atoms that is working in a Hilbert subspace of all states inherent to these atomic systems. In this subspace, logical sing...

Ablayev, F. M.; Andrianov, S. N.; Moiseev, S. A.; Vasiliev, A. V.

2013-01-01

68

Proposals for physical systems to act as quantum computers are inevitably plagued by the unavoidable coupling with the environment (bath) that causes decoherence, and by technological difficulties connected with the controllability of quantum states. Several techniques exist for achieving reliable quantum computation by countering the effects of decoherence. At this time, however, not one, by itself, will serve as a panacea for error correction. In this paper, we introduce a method that combines system-bath decoupling operations with error avoidance or active error correction to address these major concerns. By using an empirical approach to error correction based on experimental data, and an efficient set of decoupling operations that will serve to protect encoded quantum information, we are able to propose a comprehensive method for reducing the adverse effects of decoherence, in particular in scalable solid state quantum computing devices. Our method has the added benefit of significantly reducing design c...

Byrd, M S; Byrd, Mark S.; Lidar, Daniel A.

2002-01-01

69

BRICS and Quantum Information Processing

DEFF Research Database (Denmark)

BRICS is a research centre and international PhD school in theoretical computer science, based at the University of Aarhus, Denmark. The centre has recently become engaged in quantum information processing in cooperation with the Department of Physics, also University of Aarhus. This extended abstract surveys activities at BRICS with special emphasis on the activities in quantum information processing.

Schmidt, Erik Meineche

1998-01-01

70

Quantum information theory and quantum statistics

International Nuclear Information System (INIS)

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.)

71

Quantum information theory and quantum statistics

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

72

Information transfer via implicit encoding with delay time modulation in a time-delay system

International Nuclear Information System (INIS)

A new encoding scheme for information transfer with modulated delay time in a time-delay system is proposed. In the scheme, the message is implicitly encoded into the modulated delay time. The information transfer rate as a function of encoding redundancy in various noise scales is presented and it is analyzed that the implicit encoding scheme (IES) has stronger resistance against channel noise than the explicit encoding scheme (EES). In addition, its advantages in terms of secure communication and feasible applications are discussed. -- Highlights: ? We propose new encoding scheme with delay time modulation. ? The message is implicitly encoded with modulated delay time. ? The proposed scheme shows stronger resistance against channel noise.

73

International Nuclear Information System (INIS)

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

74

Physics as quantum information processing

The experience from Quantum Information has lead us to look at Quantum Theory (QT) and the whole Physics from a different angle. The information-theoretical paradigm---"It from Bit'---prophesied by John Archibald Wheeler is relentlessly advancing. Recently it has been shown that QT is derivable from pure informational principles. The possibility that there is only QT at the foundations of Physics has been then considered, with space-time, Relativity, quantization rules and Q...

D Ariano, Giacomo Mauro

2010-01-01

75

Hadamard-encoded high-resolution NMR spectroscopy via intermolecular single-quantum coherences

NMR spectroscopy plays an important role in metabolite studies because it can provide atomic level information critical for understanding biological systems. Nevertheless, NMR investigations on biological tissues are hampered by the magnetic field inhomogeneities originating from variations in macroscopic magnetic susceptibility, which lead to broad spectral lines and subsequently obscure metabolite signals. A new pulse sequence based on intermolecular single-quantum coherences was proposed to obtain one-dimensional high-resolution NMR spectra in inhomogeneous magnetic fields via Hadamard encoding. The new method can provide resolution-improved spectra directly through one-dimensional acquisition within a relatively short acquisition time. Theoretical derivation was performed and the conclusion was tested by solution samples in purposely de-shimmed magnetic fields and pig brain tissue sample. The experimental results show that this sequence can yield useful structural information, even when the field inhomogeneity is sufficiently severe to erase almost all spectral information with conventional one-dimensional single-quantum coherence techniques. Moreover, good solvent suppression efficiency can be achieved by this sequence. This sequence may provide a promising way for high-resolution NMR spectroscopy of biological tissue.

Ke, Hanping; Cai, Honghao; Cai, Shuhui; Chen, Hao; Lin, Yanqin; Chen, Zhong

2014-11-01

76

Studies in quantum information theory

Quantum information theory started as the backdrop for quantum computing and is often considered only in relation to this technology, which is still in its infancy. But quantum information theory is only partly about quantum computing. While much of the interest in this field is spurred by the possible use of quantum computers for code breaking using fast factoring algorithms, to a physicist interested in deeper issues, it presents an entirely new set of questions based on an entirely different way of looking at the quantum world. This thesis is an exploration of several topics in quantum information theory. But it is also more than this. This thesis explores the new paradigm brought about by quantum information theory---that of physics as the flow of information. The thesis consists of three main parts. The first part describes my work on continuous-variable cluster states, a new platform for quantum computation. This begins with background material discussing classical and quantum computation and emphasizing the physical underpinnings of each, followed by a discussion of two recent unorthodox models of quantum computation. These models are combined into an original proposal for quantum computation using continuous-variable cluster states, including a proposed optical implementation. These are followed by a mathematical result radically simplifying the optical construction. Subsequent work simplifies this connection even further and provides a constructive proposal for scalable generation of large-scale cluster states---necessary if there is to be any hope of using this method in practical quantum computation. Experimental implementation is currently underway by my collaborators at The University of Virginia. The second part describes my work related to the physics of trapped ions, starting with an overview of the basic theory of linear ion traps. Although ion traps are often discussed in terms of their potential use for quantum computation, my work looks at their potential for use as generic quantum systems over which the experimenter has exquisite control and which can be used to simulate other quantum systems and also study generic quantum phenomena. This is followed by a proposal for using a trapped ion as a time-dependent harmonic oscillator---a quantum system that is common in theoretical literature but of which few laboratory examples are known. A second project studies the way that quantum fluctuations in the vibrational state of a chain of ions influence correlations in optical measurements made on the ions. The final part looks at quantum information theory in a relativistic setting. An introduction discusses the interface between quantum information theory and relativity in general, including the nonclassical notion of entanglement and the peculiar features of curved-space quantum field theory. An original gedankenexperiment combines these ideas and examines whether entanglement---a quantum information-theoretic concept and physical resource---can be used to distinguish universes of different curvature in a situation where local measurements would show no difference. These three parts are followed by a personal (and possibly controversial) conclusion, which describes my fascination with---and ultimately my reason for pursuing---studies in quantum information theory.

Menicucci, Nicolas C.

77

Physics as Quantum Information Processing: Quantum Fields as Quantum Automata

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

D'Ariano, Giacomo Mauro

2011-01-01

78

Quantum heat engines and information

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 worki...

Yeo, Ye; Kwong, Chang Chi

2007-01-01

79

NMR quantum information processing

Quantum computing exploits fundamentally new models of computation based on quantum mechanical properties instead of classical physics, and it is believed that quantum computers are able to dramatically improve computational power for particular tasks. At present, nuclear magnetic resonance (NMR) has been one of the most successful platforms amongst all current implementations. It has demonstrated universal controls on the largest number of qubits, and many advanced techniqu...

Ramanathan, Chandrasekhar; Boulant, Nicolas; Chen, Zhiying; Cory, David G.; Chuang, Isaac; Steffen, Matthias

2015-01-01

80

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

81

Energy Technology Data Exchange (ETDEWEB)

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

Turner, Leaf [Los Alamos, New Mexico (United States)

2004-04-09

82

Geometrical and Topological Aspects of Quantum Information Systems

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

83

Quantum information science as an approach to complex quantum systems

What makes quantum information science a science? These notes explore the idea that quantum information science may offer a powerful approach to the study of complex quantum systems. We discuss how to quantify complexity in quantum systems, and argue that there are two qualitatively different types of complex quantum system. We also explore ways of understanding complex quantum dynamics by quantifying the strength of a quantum dynamical operation as a physical resource. This...

Nielsen, Michael A.

2002-01-01

84

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

Moiseev, S A

2010-01-01

85

International Nuclear Information System (INIS)

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

86

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

International Nuclear Information System (INIS)

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

87

Quantum States as Ordinary Information

Directory of Open Access Journals (Sweden)

Full Text Available Despite various parallels between quantum states and ordinary information, quantum no-go-theorems have convinced many that there is no realistic framework that might underly quantum theory, no reality that quantum states can represent knowledge about. This paper develops the case that there is a plausible underlying reality: one actual spacetime-based history, although with behavior that appears strange when analyzed dynamically (one time-slice at a time. By using a simple model with no dynamical laws, it becomes evident that this behavior is actually quite natural when analyzed “all-at-once” (as in classical action principles. From this perspective, traditional quantum states would represent incomplete information about possible spacetime histories, conditional on the future measurement geometry. Without dynamical laws imposing additional restrictions, those histories can have a classical probability distribution, where exactly one history can be said to represent an underlying reality.

Ken Wharton

2014-03-01

88

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

Lidar, D A

2003-01-01

89

International Nuclear Information System (INIS)

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

90

Using Patterns to Encode Color Information for Dichromats.

Color is one of the most common ways to convey information in visualization applications. Color vision deficiency (CVD) affects approximately 200 million individuals worldwide and considerably degrades their performance in understanding such contents by creating red-green or blue-yellow ambiguities. While several content-specific methods have been proposed to resolve these ambiguities, they cannot achieve this effectively in many situations for contents with a large variety of colors. More importantly, they cannot facilitate color identification. We propose a technique for using patterns to encode color information for individuals with CVD. We present the first content-independent method to overlay patterns on colored visualization contents that not only minimizes ambiguities but also allows color identification. We validated our method with two user studies. Our results show that overlaying patterns significantly improves the performance of dichromats in several color-based visualization tasks, making it almost similar to normal trichromats'. More interestingly, allow normal trichromats to perform with greater accuracy. Finally, using patterns enable the preliminary design of a passive device, like eyeglasses, that can overlay different patterns on the image perceived by a dichromat facilitating color information retrieval. We have built a simple low-cost prototype to demonstrate the feasibility of this design. PMID:22450823

Sajadi, Behzad; Majumder, Aditi; Oliveira, Manuel M; Schneider, Rosalia G; Raskar, Ramesh

2012-03-22

91

Encoding simplicial quantum geometry in group field theories

We show that a new symmetry requirement on the GFT field, in the context of an extended GFT formalism, involving both Lie algebra and group elements, leads, in 3d, to Feynman amplitudes with a simplicial path integral form based on the Regge action, to a proper relation between the discrete connection and the triad vectors appearing in it, and to a much more satisfactory and transparent encoding of simplicial geometry already at the level of the GFT action.

Oriti, Daniele

2009-01-01

92

Step-by-step magic state encoding for efficient fault-tolerant quantum computation

Quantum error correction allows one to make quantum computers fault-tolerant against unavoidable errors due to decoherence and imperfect physical gate operations. However, the fault-tolerant quantum computation requires impractically large computational resources for useful applications. This is a current major obstacle to the realization of a quantum computer. In particular, magic state distillation, which is a standard approach to universality, consumes the most resources in fault-tolerant quantum computation. For the resource problem, here we propose step-by-step magic state encoding for concatenated quantum codes, where magic states are encoded step by step from the physical level to the logical one. To manage errors during the encoding, we carefully use error detection. Since the sizes of intermediate codes are small, it is expected that the resource overheads will become lower than previous approaches based on the distillation at the logical level. Our simulation results suggest that the resource requirements for a logical magic state will become comparable to those for a single logical controlled-NOT gate. Thus, the present method opens a new possibility for efficient fault-tolerant quantum computation.

Goto, Hayato

2014-12-01

93

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

94

Black holes as mirrors: quantum information in random subsystems

International Nuclear Information System (INIS)

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

95

Encoding and storage of spatial information in the retrosplenial cortex.

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

96

Renormalization group and quantum information

International Nuclear Information System (INIS)

The renormalization group is a tool that allows one to obtain a reduced description of systems with many degrees of freedom while preserving the relevant features. In the case of quantum systems, in particular, one-dimensional systems defined on a chain, an optimal formulation is given by White's 'density matrix renormalization group'. This formulation can be shown to rely on concepts of the developing theory of quantum information. Furthermore, White's algorithm can be connected with a peculiar type of quantization, namely, angular quantization. This type of quantization arose in connection with quantum gravity problems, in particular, the Unruh effect in the problem of black-hole entropy and Hawking radiation. This connection highlights the importance of quantum system boundaries, regarding the concentration of quantum states on them, and helps us to understand the optimal nature of White's algorithm

97

Renormalization Group and Quantum Information

The renormalization group is a tool that allows one to obtain a reduced description of systems with many degrees of freedom while preserving the relevant features. In the case of quantum systems, in particular, one-dimensional systems defined on a chain, an optimal formulation is given by White's "density matrix renormalization group". This formulation can be shown to rely on concepts of the developing theory of quantum information. Furthermore, White's algorithm can be conn...

Gaite, Jose

2006-01-01

98

Quantum key distribution based on phase encoding in long-distance communication fiber.

A robust two-way quantum key distribution system based on phase encoding is demonstrated in 50 km and 100 km commercial communication fiber. The system can automatically compensate for birefringence effects and remain stable over 23 h. A low quantum bit error rate and high visibility are obtained. Furthermore, the storage fiber is unnecessary and train of pulses is only needed in the test with 100 km fiber. PMID:20410967

Sun, Shi-Hai; Ma, Hai-Qiang; Han, Jia-Jia; Liang, Lin-Mei; Li, Cheng-Zu

2010-04-15

99

Multiplexed SNP genotyping using the Qbead™ system: a quantum dot-encoded microsphere-based assay

We have developed a new method using the Qbead™ system for high-throughput genotyping of single nucleotide polymorphisms (SNPs). The Qbead system employs fluorescent Qdot™ semiconductor nanocrystals, also known as quantum dots, to encode microspheres that subsequently can be used as a platform for multiplexed assays. By combining mixtures of quantum dots with distinct emission wavelengths and intensities, unique spectral ‘barcodes’ are created that enable the high levels of multiplexi...

Xu, Hongxia; Sha, Michael Y.; Wong, Edith Y.; Uphoff, Janet; Xu, Yanzhang; Treadway, Joseph A.; Truong, Anh; O’brien, Eamonn; Asquith, Steven; Stubbins, Michael; Spurr, Nigel K.; Lai, Eric H.; Mahoney, Walt

2003-01-01

100

Efficient Computations of Encodings for Quantum Error Correction

We show how, given any set of generators of the stabilizer of a quantum code, an efficient gate array that computes the codewords can be constructed. For an n-qubit code whose stabilizer has d generators, the resulting gate array consists of O(n d) operations, and converts k-qubit data (where k = n - d) into n-qubit codewords.

Cleve, R; Cleve, Richard; Gottesman, Daniel

1997-01-01

101

Efficient Computations of Encodings for Quantum Error Correction

We show how, given any set of generators of the stabilizer of a quantum code, an efficient gate array that computes the codewords can be constructed. For an n-qubit code whose stabilizer has d generators, the resulting gate array consists of O(n d) operations, and converts k-qubit data (where k = n - d) into n-qubit codewords.

Cleve, Richard; Gottesman, Daniel

1996-01-01

102

Malus' law and quantum information

International Nuclear Information System (INIS)

The information content of the most elementary quantum system is represented by one single proposition. Therefore such an elementary system can only give a definite result in one specific experimental arrangement. A change of experimental parameters then necessarily implies probabilistic measurement results in the new experimental arrangement. Assumption of the invariance of the information content of a system upon change of the representation of our knowledge of the system together with homogeneity of the experimental parametric axis leads to the Malus' law in quantum mechanics, the familiar sinusoidal relation between the probabilities and the laboratory parameters. (Authors)

103

The operational meaning of quantum conditional information

With a statistical view towards information and noise, information theory derives ultimate limitations on information processing tasks. These limits are generally expressed in terms of entropic measures of information and correlations. Here we answer the quantum information-theoretic question: ``How correlated are two quantum systems from the perspective of a third?" by solving the following `quantum state redistribution' problem. Given an arbitrary quantum state of three sy...

Devetak, Igor; Yard, Jon

2006-01-01

104

Decoherence-Free Quantum Information Processing with Four-Photon Entangled States

Decoherence-free states protect quantum information from collective noise, the predominant cause of decoherence in current implementations of quantum communication and computation. Here we demonstrate that spontaneous parametric down-conversion can be used to generate four-photon states which enable the encoding of one qubit in a decoherence-free subspace. The immunity against noise is verified by quantum state tomography of the encoded qubit. We show that particular states of the encoded qubit can be distinguished by local measurements on the four photons only.

Bourennane, M; Gaertner, S; Kurtsiefer, C; Cabello, A; Weinfurter, H; Bourennane, Mohamed; Eibl, Manfred; Gaertner, Sascha; Kurtsiefer, Christian; Cabello, Adan; Weinfurter, Harald

2004-01-01

105

Quantum Theory and Classical Information

Transmission of classical information using quantum objects such as polarized photons is studied. The classical (Shannon) channel capacity and its relation to quantum (von Neumann) channel capacity is investigated for various receiver arrangements. A quantum channel with transmission impairment caused by attenuation and random polarization noise is considered. It is shown that the maximal (von Neumann) capacity of such a channel can be realized by a simple symbol by symbol detector followed by a classical error correcting decoder. For an intensity limited optical channel capacity is achieved by on-off keying (OOK). The capacity per unit cost is shown to be 1 nat/photon = 1.44 bit/photon, slightly larger than the 1 bit/photon obtained by orthogonal quantum signals.

Einarsson, G

2002-01-01

106

Generalized spin bases for quantum chemistry and quantum information

Symmetry adapted bases in quantum chemistry and bases adapted to quantum information share a common characteristics: both of them are constructed from subspaces of the representation space of the group SO(3) or its double group (i.e., spinor group) SU(2). We exploit this fact for generating spin bases of relevance for quantum systems with cyclic symmetry and equally well for quantum information and quantum computation. Our approach is based on the use of generalized Pauli ma...

Kibler, M.

2008-01-01

107

Fractal states in quantum information processing

The fractal character of some quantum properties has been shown for systems described by continuous variables. Here, a definition of quantum fractal states is given that suits the discrete systems used in quantum information processing, including quantum coding and quantum computing. Several important examples are provided.

Jaeger, Gregg

2007-01-01

108

Problems and solutions in quantum computing and quantum information

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

Steeb, Willi-Hans

2012-01-01

109

Quantum Key Distribution System with Six Polarization States Encoded by Phase Modulation

International Nuclear Information System (INIS)

An intrinsically stable quantum key distribution system (QKD) with six polarization states encoded by phase modulation is introduced. The encoder and decoder are in the same structures that consist of two polarizing Sagnac interferometers connected in tandem. The six polarization states are determined and distinguished by different sets of phase shifts induced by two respective electrically-driven integrated phase modulators. A mean visibility of interference fringes is kept stable at 97.58% for an hour's performance. Theoretical and experimental analyses show that the proposed QKD system features intrinsically stability immune from environment fluctuation. (general)

110

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

111

Quantum heat engines and information

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

112

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

113

Information Security and Quantum Mechanics: Security of Quantum Protocols

The problem of security of quantum key protocols is examined. In addition to the distribution of classical keys, the problem of encrypting quantum data and the structure of the operators which perform quantum encryption is studied. It is found that unitary bases are central to both encryption of quantum information, as well as the generation of states used in generalized quantum key distribution (which are called mutually unbiased bases). A one-to-one correspondence between ...

Boykin, P. Oscar

2002-01-01

114

Macroscopic quantum information processing using spin coherent states

Previously a new scheme of quantum information processing based on spin coherent states of two component Bose-Einstein condensates was proposed (Byrnes et al. Phys. Rev. A 85, 40306(R)). In this paper we give a more detailed exposition of the scheme, expanding on several aspects that were not discussed in full previously. The basic concept of the scheme is that spin coherent states are used instead of qubits to encode qubit information, and manipulated using collective spin operators. The scheme goes beyond the continuous variable regime such that the full space of the Bloch sphere is used. We construct a general framework for quantum algorithms to be executed using multiple spin coherent states, which are individually controlled. We illustrate the scheme by applications to quantum information protocols, and discuss possible experimental implementations. Decoherence effects are analyzed under both general conditions and for the experimental implementation proposed.

Byrnes, Tim; Rosseau, Daniel; Khosla, Megha; Pyrkov, Alexey; Thomasen, Andreas; Mukai, Tetsuya; Koyama, Shinsuke; Abdelrahman, Ahmed; Ilo-Okeke, Ebubechukwu

2015-02-01

115

Revealing quantum-control mechanisms through Hamiltonian encoding in different representations

International Nuclear Information System (INIS)

The Hamiltonian encoding is a means for revealing the mechanism of controlled quantum dynamics. In this context, the mechanism is defined by the dominant quantum pathways starting from the initial state and proceeding through a set of intermediate states to end at the final state. The nature and interpretation of the mechanism depends on the choice of the states to represent the dynamics. Alternative representations may provide distinct insights into the system mechanism, and representations producing fewer pathways are especially interesting. In addition, a suitable choice of representation may highlight the role of certain couplings in a system that would normally be masked by other, higher magnitude couplings. A simple three-level system is chosen for illustration, where different values for the Rabi frequencies lead to mechanistic analyses that are best described in terms of particular representations. As an examlple, the role of the nonadiabatic terms in stimulated Raman adiabatic passage dynamics is analyzed through the Hamiltonian encoding

116

Indexical Information, Encoding Difficulty, and Second Language Vocabulary Learning

Research has demonstrated that second language (L2) vocabulary learning improves when target words are presented in acoustically varied compared with acoustically consistent formats. The present study investigated the extent to which this benefit of acoustic variability is a consequence of difficult encoding demands (cognitive effort hypothesis)…

Sommers, Mitchell S.; Barcroft, Joe

2011-01-01

117

Anonymous Transmission of Quantum Information

We propose a protocol for anonymous distribution of quantum information which can be used in two modifications. In the first modification the receiver of the message is publicly known, but the sender remains unknown (even to receiver). In the second modification the sender is known, but the receiver is unknown (even to sender). Our protocol achieves this goal with unconditional security using classical anonymous message transfer proposed by Chaum as a subprotocol.

Bouda, J; Bouda, Jan; Sprojcar, Josef

2005-01-01

118

Sending Quantum Information with Gaussian States

Quantum information characteristics, such as quantum mutual information, loss, noise and coherent information are explicitly calculated for Bosonic attenuation/amplification channel with input Gaussian state. The coherent information is shown to be negative for the values of the attenuation coefficient $k<1/\\sqrt{2}$.

Holevo, Alexander S.

1998-01-01

119

For the past fifteen years, single semiconductor quantum dots, often referred to as solid-state artificial atoms, have been at the forefront of various research direction lines for experimental quantum information science, in particular in the development of practical sources of quantum states of light. Here we review the research to date, on the tailoring of the emission properties from single quantum dots producing single photons, indistinguishable single photons and entangled photon pairs. Finally, the progress and future prospects for applications of single dots in quantum information processing is considered.

Beveratos, Alexios; Abram, Izo; Gérard, Jean-Michel; Robert-Philip, Isabelle

2014-12-01

120

Reproducible electrochemically encoded quantum dot (QD) barcodes were prepared by using the reverse-micelle synthetic approach. The encoding elements, Zn2+, Cd2+, Pb2+ were confined within a single QD, which eliminates the cumbersome encapsulation process used by other common nanoparticle-based barcode preparation schemes. The distinct voltammetric stripping patterns of Zn2+, Cd2+, Pb2+ at distinguishable potentials with controllable current intensities offer excellent encoding capability for...

Xiang, Yun; Zhang, Yuyong; Chang, Yue; Chai, Yaqin; Wang, Joseph; Yuan, Ruo

2010-01-01

121

Reproducible electrochemically encoded quantum dot (QD) barcodes were prepared using the reverse-micelle synthetic approach. The encoding elements, Zn(2+), Cd(2+), and Pb(2+), were confined within a single QD, which eliminates the cumbersome encapsulation process used by other common nanoparticle-based barcode preparation schemes. The distinct voltammetric stripping patterns of Zn(2+), Cd(2+) and Pb(2+) at distinguishable potentials with controllable current intensities offer excellent encoding capability for the prepared electrochemical (EC) QDs. Additionally, the simultaneous modification of the QD barcode surface with organic ligands during the preparation process make them potentially useful in biomedical research. For proof of concept of their application in bioassays, the EC QD barcodes were further employed as tags for an immunoassay of a cancer marker, carcinoembryonic antigen (CEA). The voltammetric stripping response of the dissolved bardcode tags was proportional to log[CEA] in the range from 0.01 to 80 ng mL(-1), with a detection limit of 3.3 pg mL(-1). The synthesized EC QD barcodes hold considerable potential in biodetection, encrypted information, and product tracking. PMID:20067269

Xiang, Yun; Zhang, Yuyong; Chang, Yue; Chai, Yaqin; Wang, Joseph; Yuan, Ruo

2010-02-01

122

Modern Quantum Technologies of Information Security

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

123

Quantum information and physics: some future directions

I consider some promising future directions for quantum information theory that could influence the development of 21st century physics. Advances in the theory of the distinguishability of superoperators may lead to new strategies for improving the precision of quantum-limited measurements. A better grasp of the properties of multi-partite quantum entanglement may lead to deeper understanding of strongly-coupled dynamics in quantum many-body systems, quantum field theory, an...

Preskill, John

1999-01-01

124

Gaussian states in continuous variable quantum information

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

125

Phase Information in Quantum Oracle Computing

Computational devices may be supplied with external sources of information (oracles). Quantum oracles may transmit phase information which is available to a quantum computer but not a classical computer. One consequence of this observation is that there is an oracle which is of no assistance to a classical computer but which allows a quantum computer to solve undecidable problems. Thus useful relativized separations between quantum and classical complexity classes must exclu...

Machta, J.

1998-01-01

126

Encoding and updating spatial information presented in narratives.

Four experiments investigated whether directional spatial relations encoded by reading narratives are updated following described protagonist rotations. Participants memorized locations of objects described in short stories that placed them, as the protagonist, in remote settings. After reading a description that the protagonist rotated to the left or the right of the initial orientation, participants made judgements about object relations in the described environment (Experiment 1). Before making these judgements, participants were instructed to physically rotate to match (Experiment 2) or mismatch (Experiment 4) the protagonist's described rotation and in Experiments 3 and 4 to also visualize the changed relations following rotation. Participants' performance suggested that they relied on the initial representation they constructed during encoding rather than on the updated protagonist-to-object relations. Participants' physical movement to match the described rotation and additional visualization instructions did not facilitate updating through a sensorimotor process. In these respects, updating spatial relations in situation models constructed from narratives differs from updating in perceptually experienced environments. PMID:22943593

Avraamides, Marios N; Galati, Alexia; Pazzaglia, Francesca; Meneghetti, Chiara; Denis, Michel

2013-01-01

127

Representation of Quantum Field Theory by Elementary Quantum Information

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

128

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

129

Philosophy of quantum information and entanglement

Recent work in quantum information science has produced a revolution in our understanding of quantum entanglement. Scientists now view entanglement as a physical resource with many important applications. These range from quantum computers, which would be able to compute exponentially faster than classical computers, to quantum cryptographic techniques, which could provide unbreakable codes for the transfer of secret information over public channels. These important advances in the study of quantum entanglement and information touch on deep foundational issues in both physics and philosophy. This interdisciplinary volume brings together fourteen of the world's leading physicists and philosophers of physics to address the most important developments and debates in this exciting area of research. It offers a broad spectrum of approaches to resolving deep foundational challenges - philosophical, mathematical, and physical - raised by quantum information, quantum processing, and entanglement. This book is ideal f...

Jaeger, Gregg

2010-01-01

130

Controlled Hawking Process by Quantum Information

Without using any non-established physics of quantum gravity, we show that black holes remember quantum information of swallowed matter even after the shifted horizons are settled. By using saved information, a part of the absorbed energy can be retrieved from the horizon by quantum energy teleportation in quantum information theory. This process can be regarded as a controlled Hawking process by measurement information about field fluctuation, in which negative energy flux is generated outside the horizon, falls into the horizon, and decreases mass of the black hole.

Hotta, Masahiro

2009-01-01

131

Quantum hierarchic models for information processing

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

Altaisky, Mikhail V

2011-01-01

132

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

133

Quantum Bertrand duopoly of incomplete information

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; Chen, Xi; Sun, Min; Du, Jiangfeng

2005-05-01

134

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

135

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.

136

Physics as Quantum Information Processing: Quantum Fields as Quantum Automata

Can we reduce Quantum Field Theory (QFT) to a quantum computation? Can physics be simulated by a quantum computer? Do we believe that a quantum field is ultimately made of a numerable set of quantum systems that are unitarily interacting? A positive answer to these questions corresponds to substituting QFT with a theory of quantum cellular automata (QCA), and the present work is examining this hypothesis. These investigations are part of a large research program on a "quantu...

D Ariano, Giacomo Mauro

2011-01-01

137

On-demand preparation of quantum dot-encoded microparticles using a droplet microfluidic system.

Optical barcoding technology based on quantum dot (QD)-encoded microparticles has attracted increasing attention in high-throughput multiplexed biological assays, which is realized by embedding different-sized QDs into polymeric matrixes at precisely controlled ratios. Considering the advantage of droplet-based microfluidics, producing monodisperse particles with precise control over the size, shape and composition, we present a proof-of-concept approach for on-demand preparation of QD-encoded microparticles based on this versatile new strategy. Combining a flow-focusing microchannel with a double T-junction in a microfluidic chip, biocompatible QD-doped microparticles were constructed by shearing sodium alginate solution into microdroplets and on-chip gelating these droplets into a hydrogel matrix to encapsulate CdSe/ZnS QDs. Size-controllable QD-doped hydrogel microparticles were produced under the optimum flow conditions, and their fluorescent properties were investigated. A novel multiplex optical encoding strategy was realized by loading different sized QDs into a single droplet (and thus a hydrogel microparticle) with different concentrations, which was triggered by tuning the flow rates of the sodium alginate solutions entrapped with different-colored QDs. A series of QD-encoded microparticles were controllably, and continuously, produced in a single step with the present approach. Their application in a model immunoassay demonstrated the potential practicability of QD-encoded hydrogel microparticles in multiplexed biomolecular detection. This simple and robust strategy should be further improved and practically used in making barcode microparticles with various polymer matrixes. PMID:21687836

Ji, Xing-Hu; Cheng, Wei; Guo, Feng; Liu, Wei; Guo, Shi-Shang; He, Zhi-Ke; Zhao, Xing-Zhong

2011-08-01

138

Rydberg atoms for quantum information

I examine interactions between ensembles of cold Rydberg atoms, and between Rydberg atoms and an intense, optical standing wave. Because of their strong electrostatic interactions, Rydberg atoms are prime candidates for quantum information and quantum computation. To this end, I study excitation dynamics in many-body Rydberg systems using a rotary echo technique similar to the echo sequences used in nuclear magnetic resonance schemes. In this method, a phase reversal of a narrow-band excitation field is applied at a variable time during the excitation pulse. The visibility of the resulting echo signal reveals the degree of coherence of the excitation process. Rotary echoes are measured for several nD5/2 Rydberg levels of rubidium with principal quantum numbers near n = 43, where the strength of electrostatic Rydberg-atom interactions is sharply modulated by a Forster resonance The Rydberg-atom interactions diminish the echo visibility, in agreement with theoretical work. The equivalence of echo signals with spectroscopic data is also examined. Applications of Rydberg atoms based on controlled interactions require a trapping device that holds the atoms at well-defined positions several microns apart. Rydberg atoms in ponderomotive optical lattices present a unique platform to meet this requirement, as well as to study properties and interactions of these highly excited atoms. Because the Rydberg electron is so loosely bound, the ponderomotive interaction for a Rydberg electron is very similar to a free electron. Ponderomotive lattices tailored to trap Rydberg atoms will allow new experiments in quantum information physics and high-precision spectroscopy. Microwave spectroscopy is used as a powerful technique to probe the motion and to verify trapping of Rydberg atoms in ponderomotive lattices. The potentials for non-degenerate, low angular momentum states, are used to obtain ensembles of Rydberg-atom trajectories in the lattice, and to simulate the spectra of microwave transitions of Rydberg atoms moving through the lattice. Additionally, adiabatic potentials are calculated for Rydberg atoms in one-dimensional ponderomotive lattices for a variety of atomic states and lattice parameters. The lattice induced mixing of nearly-degenerate, high-angular-momentum states is explained in terms of effective electric and magnetic fields.

Younge, Kelly Cooper

139

Modern Quantum Technologies of Information Security

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

140

Gaussian states in continuous variable quantum information

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 informat...

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

2005-01-01

141

Information capacity formula of quantum optical channels

The applications of the general formulae of channel capacity developed in the quantum information theory to evaluation of information transmission capacity of optical channel are interesting subjects. In this review paper, we will point out that the formulation based on only classical-quantum channel mapping model may be inadequate when one takes into account a power constraint for noisy channel. To define the power constraint well, we should explicitly consider how quantum ...

Sohma, Masaki; Hirota, Osamu

2001-01-01

142

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

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

143

Quantum Information Processing with Ferroelectrically Coupled Quantum Dots

I describe a proposal to construct a quantum information processor using ferroelectrically coupled Ge/Si quantum dots. The spin of single electrons form the fundamental qubits. Small (<10 nm diameter) Ge quantum dots are optically excited to create spin polarized electrons in Si. The static polarization of an epitaxial ferroelectric thin film confines electrons laterally in the semiconductor; spin interactions between nearest neighbor electrons are mediated by the nonlinear ...

Levy, Jeremy

2001-01-01

144

Information Causality in the Quantum and Post-Quantum Regime

Quantum correlations can be stronger than anything achieved by classical systems, yet they are not reaching the limit imposed by relativity. The principle of information causality offers a possible explanation for why the world is quantum and why there appear to be no even stronger correlations. Generalizing the no-signaling condition it suggests that the amount of accessible information must not be larger than the amount of transmitted information. Here we study this principle experimentally in the classical, quantum and post-quantum regimes. We simulate correlations that are stronger than allowed by quantum mechanics by exploiting the effect of polarization-dependent loss in a photonic Bell-test experiment. Our method also applies to other fundamental principles and our results highlight the special importance of anisotropic regions of the no-signalling polytope in the study of fundamental principles.

Ringbauer, Martin; Fedrizzi, Alessandro; Berry, Dominic W.; White, Andrew G.

2014-11-01

145

A Quantum Private Comparison Protocol with Splitting Information Carriers

Based on quantum information splitting and reconstruction, we present a quantum private comparison (QPC) protocol, enabling two distrustful parties (Alice and Bob) to compare the equality of their information without revealing the information content. In this protocol, the information carriers are split into two wave packets by a beam splitter (BS), which is owned by a semi-honest third party Trent, and then they are sent to Alice and Bob, respectively. Alice and Bob encodes their secret information on the received wave packets. Only the superimposition of the two wave packets in Trent's site can reveal the compared result. Compared with the QPC protocols using entangled states, the information carriers used in our protocol is single-photon pulse, which reduces the difficulty of realization in practical. In addition, our protocol is feasible with the present techniques since only linear optical components, BS, single-photon detector, phase shifter (PS) and switcher (SWT) are required. The security of the protocol is ensured by principles on the phenomenon of quantum interference. And through the security analysis it shows that the protocol is secure and resists against the well-known attacks.

Wang, Yu-kun; Zhang, Jie; Huang, Wei; Zhang, Jia-li; Sun, Ying

2014-07-01

146

Conventional quantum key distribution (QKD) typically uses binary encoding based on photon polarization or time-bin degrees of freedom and achieves a key capacity of at most one bit per photon. Under photon-starved conditions the rate of detection events is much lower than the photon generation rate, because of losses in long distance propagation and the relatively long recovery times of available single-photon detectors. Multi-bit encoding in the photon arrival times can be beneficial in such photon-starved situations. Recent security proofs indicate high-dimensional encoding in the photon arrival times is robust and can be implemented to yield high secure throughput. In this work we demonstrate entanglement-based QKD with high-dimensional encoding whose security against collective Gaussian attacks is provided by a high-visibility Franson interferometer. We achieve unprecedented key capacity and throughput for an entanglement-based QKD system because of four principal factors: Franson interferometry that does not degrade with loss; error correction coding that can tolerate high error rates; optimized time–energy entanglement generation; and highly efficient WSi superconducting nanowire single-photon detectors. The secure key capacity yields as much as 8.7 bits per coincidence. When optimized for throughput we observe a secure key rate of 2.7 Mbit s?1 after 20 km fiber transmission with a key capacity of 6.9 bits per photon coincidence. Our results demonstrate a viable approach to high-rate QKD using practical photonic entanglement and single-photon detection technologies.

Zhong, Tian; Zhou, Hongchao; Horansky, Robert D.; Lee, Catherine; Verma, Varun B.; Lita, Adriana E.; Restelli, Alessandro; Bienfang, Joshua C.; Mirin, Richard P.; Gerrits, Thomas; Nam, Sae Woo; Marsili, Francesco; Shaw, Matthew D.; Zhang, Zheshen; Wang, Ligong; Englund, Dirk; Wornell, Gregory W.; Shapiro, Jeffrey H.; Wong, Franco N. C.

2015-02-01

147

Quantum Causality, Stochastics, Trajectories and Information

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

148

Cavity mode entanglement in relativistic quantum information

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

149

Quantum Realism, Information, and Epistemological Modesty

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

150

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

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

151

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

152

Complementarity and Entanglement in Quantum Information Theory

The restrictions that nature places on the distribution of correlations in a multipartite quantum system play fundamental roles in the evolution of such systems, and yield vital insights into the design of protocols for the quantum control of ensembles with potential applications in the field of quantum computing. We show how this entanglement sharing behavior may be studied in increasingly complex systems of both theoretical and experimental significance and demonstrate that entanglement sharing, as well as other unique features of entanglement, e.g. the fact that maximal information about a multipartite quantum system does not necessarily entail maximal information about its component subsystems, may be understood as specific consequences of the phenomenon of complementarity extended to composite quantum systems. We also present a local hidden-variable model supplemented by an efficient amount of classical communication that reproduces the quantum-mechanical predictions for the entire class of Gottesman-Kni...

Tessier, T E

2004-01-01

153

Towards a quantum information technology industry

International Nuclear Information System (INIS)

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)

154

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)

155

Locally Inaccessible Information as a Fundamental Ingredient to Quantum Information

Quantum discord (QD) measures the fraction of the pairwise mutual information that is locally inaccessible, in a multipartite system. Fundamental aspects related to two important measures in quantum information theory the Entanglement of Formation (EOF) and the conditional entropy, can be understood in terms of the distribution of this form of Local Inaccessible Information (LII). As such, the EOF for an arbitrarily mixed bipartite system AB can be related to the gain or los...

Fanchini, F. F.; Castelano, L. K.; Cornelio, M. F.; Oliveira, M. C.

2011-01-01

156

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

157

Optical hybrid approaches to quantum information

This article reviews recent hybrid approaches to optical quantum information processing, in which both discrete and continuous degrees of freedom are exploited. There are well-known limitations to optical single-photon-based qubit and multi-photon-based qumode implementations of quantum communication and quantum computation, when the toolbox is restricted to the most practical set of linear operations and resources such as linear optics and Gaussian operations and states. Th...

Loock, Peter

2010-01-01

158

Relativistic quantum information and time machines

Relativistic quantum information combines the informational approach to understanding and using quantum mechanics systems - quantum information - with the relativistic view of the universe. In this introductory review we examine key results to emerge from this new field of research in physics and discuss future directions. A particularly active area recently has been the question of what happens when quantum systems interact with general relativistic closed timelike curves - effectively time machines. We discuss two different approaches that have been suggested for modelling such situations. It is argued that the approach based on matching the density operator of the quantum state between the future and past most consistently avoids the paradoxes usually associated with time travel.

Ralph, Timothy C.; Downes, Tony G.

2012-01-01

159

Relativistic quantum information and time machines

Relativistic quantum information combines the informational approach to understanding and using quantum mechanics systems - quantum information - with the relativistic view of the universe. In this introductory review we examine key results to emerge from this new field of research in physics and discuss future directions. A particularly active area recently has been the question of what happens when quantum systems interact with general relativistic closed timelike curves - effectively time machines. We discuss two different approaches that have been suggested for modelling such situations. It is argued that the approach based on matching the density operator of the quantum state between the future and past most consistently avoids the paradoxes usually associated with time travel.

Ralph, Timothy C

2011-01-01

160

Quantum Information Processing at the Attosecond Timescale

Coherent processing of quantum information and attosecond science had so far little in common. We here show that recent data in high harmonic emission reveal quantum information processing at the attosecond timescale. High harmonic generation in the strong-field regime is governed by tunneling ionization followed by the motion of the electron in the continuum and its re-collision in the atomic core. Before the actual photon detection the electron-photon state exhibits a high degree of quantum coherence and entanglement, that has so far remained elusive. By observing the interference pattern created by the spatiotemporal overlap of photons emitted by two interfering electron paths we generate a photon Hadamard gate and thus erase the electron-trajectory information. This allows the measurement of the relative phase in electron-trajectory quantum superpositions and establishes the era of electron-photon quantum coherence and entanglement at the attosecond timescale of high-field physics.

Kominis, I K; Charalambidis, D; Tzallas, P

2013-01-01

161

Quantum Information Processing and Relativistic Quantum Fields

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 ...

Benincasa, Dionigi M T; Buck, Michel; Dowker, Fay

2014-01-01

162

Neural Mechanisms of Encoding Social and Non-Social Context Information in Autism Spectrum Disorder

Individuals with autism spectrum disorder (ASD) often fail to attach context to their memories and are specifically impaired in processing social aspects of contextual information. The aim of the present study was to investigate the modulatory influence of social vs. non-social context on neural mechanisms during encoding in ASD. Using…

Greimel, Ellen; Nehrkorn, Barbara; Fink, Gereon R.; Kukolja, Juraj; Kohls, Gregor; Muller, Kristin; Piefke, Martina; Kamp-Becker, Inge; Remschmidt, Helmut; Herpertz-Dahlmann, Beate; Konrad, Kerstin; Schulte-Ruther, Martin

2012-01-01

163

Interference Phenomena in Quantum Information

One of the key features of quantum mechanics is the interference of probability amplitudes. The reason for the appearance of interference is mathematically very simple. It is the linear structure of the Hilbert space which is used for the description of quantum systems. In terms of physics we usually talk about the superposition principle valid for individual and composed quantum objects. So, while the source of interference is understandable it leads in fact to many counter...

Stefanak, Martin

2010-01-01

164

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 algebraf 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)

165

Quantum-information-processing architecture with endohedral fullerenes in a carbon nanotube

International Nuclear Information System (INIS)

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

166

Quantum metrology from a quantum information science perspective

We summarise important recent advances in quantum metrology, in connection to experiments in cold gases, trapped cold atoms and photons. First we review simple metrological setups, such as quantum metrology with spin squeezed states, with Greenberger-Horne-Zeilinger states, Dicke states and singlet states. We calculate the highest precision achievable in these schemes. Then, we present the fundamental notions of quantum metrology, such as shot-noise scaling, Heisenberg scaling, the quantum Fisher information and the Cramer-Rao bound. Using these, we demonstrate that entanglement is needed to surpass the shot-noise scaling in very general metrological tasks with a linear interferometer. We discuss some applications of the quantum Fisher information, such as how it can be used to obtain a criterion for a quantum state to be a macroscopic superposition. We show how it is related to the the speed of a quantum evolution, and how it appears in the theory of the quantum Zeno effect. Finally, we explain how uncorrela...

Toth, Geza

2015-01-01

167

Estimating locations of quantum-dot-encoded microparticles from ultra-high density 3-D microarrays.

We develop a maximum likelihood (ML)-based parametric image deconvolution technique to locate quantum-dot (q-dot) encoded microparticles from three-dimensional (3-D) images of an ultra-high density 3-D microarray. A potential application of the proposed microarray imaging is assay analysis of gene, protein, antigen, and antibody targets. This imaging is performed using a wide-field fluorescence microscope. We first describe our problem of interest and the pertinent measurement model by assuming additive Gaussian noise. We use a 3-D Gaussian point-spread-function (PSF) model to represent the blurring of the widefield microscope system. We employ parametric spheres to represent the light intensity profiles of the q-dot-encoded microparticles. We then develop the estimation algorithm for the single-sphere-object image assuming that the microscope PSF is totally unknown. The algorithm is tested numerically and compared with the analytical Cramér-Rao bounds (CRB). To apply our analysis to real data, we first segment a section of the blurred 3-D image of the multiple microparticles using a k-means clustering algorithm, obtaining 3-D images of single-sphere-objects. Then, we process each of these images using our proposed estimation technique. In the numerical examples, our method outperforms the blind deconvolution (BD) algorithms in high signal-to-noise ratio (SNR) images. For the case of real data, our method and the BD-based methods perform similarly for the well-separated microparticle images. PMID:19203872

Sarder, Pinaki; Nehorai, Arye

2008-12-01

168

Optimal generalized variance and quantum Fisher information

International Nuclear Information System (INIS)

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)].

169

Relative information encoded in the degree of entanglement to discriminate bipartite states

It has been recently shown (Bartlett et al. 2003) that information encoded into relative degrees of freedom enables communication without a common reference frame using entangled bipartite states. In this case the relative information stored in the two-qubit system is shared between the polarization degrees of freedom and the degree of entanglement. In the present article a specific state discrimination problem is envisioned where the degree of entanglement carries the only ...

Ve?rtesi, T.

2006-01-01

170

Information, disturbance and Hamiltonian quantum feedback control

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 identif...

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

2000-01-01

171

Quantum information processing with circuit quantum electrodynamics

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

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

2006-01-01

172

Ytterbium Ion Qubits for Quantum Information Processing

We present trapped ytterbium ions as quantum bits for quantum information processing. The viability of this atomic ion as a qubit is demonstrated through high-fidelity state initialization and detection of the first-order magnetic field-insensitive hyperfine ``clock'' states, with a measured coherence time of at least 2.5 seconds. The simple atomic structure, large fine and hyperfine splittings, and transition wavelengths that facilitate the use of optical fibers, may allow for the implementation of a variety of quantum information processing schemes. In addition, we present improved measurements of the ^2P1/2 excited state lifetime and branching ratio into ^2D3/2.

Olmschenk, Steven; Matsukevich, Dzmitry; Maunz, Peter; Moehring, David; Younge, Kelly; Monroe, Chris

2008-05-01

173

Principles of quantum computation and information

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

174

Quantum Information Processing in Disordered and Complex Quantum Systems

We investigate quantum information processing and manipulations in disordered systems of ultracold atoms and trapped ions. First, we demonstrate generation of entanglement and local realization of quantum gates in a quantum spin glass system. Entanglement in such systems attains significantly high values, after quenched averaging, and has a stable positive value for arbitrary times. Complex systems with long range interactions, such as ion chains or dipolar atomic gases, can be modeled by neural network Hamiltonians. In such systems, we find the characteristic time of persistence of quenched averaged entanglement, and also find the time of its revival.

De, A S; Ahufinger, V; Briegel, H J; Sanpera, A; Lewenstein, M; De, Aditi Sen; Sen, Ujjwal; Ahufinger, Veronica; Briegel, Hans J.; Sanpera, Anna; Lewenstein, Maciej

2005-01-01

175

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

176

Classical and Quantum Information Acquisition

This paper shows that classical and quantum measurement can be treated on the same foot provided that we make use of effects instead of projectors, of POVM instead ordinary projection measurement, and of amplitude operators instead of amplitudes.

Auletta Gennaro

2014-01-01

177

Environment-assisted quantum-information correction for continuous variables

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 reconst...

Sabuncu, Metin; Filip, R.; Leuchs, G.; Andersen, Ulrik Lund

2010-01-01

178

Mutual Entropy in Quantum Information and Information Genetics

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

Ohya, M

2004-01-01

179

Quantum information processing with graph states

International Nuclear Information System (INIS)

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

180

Quantum Computation and Information From Theory to Experiment

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

181

Trapped Atomic Ions and Quantum Information Processing

International Nuclear Information System (INIS)

The basic requirements for quantum computing and quantum simulation (single- and multi-qubit gates, long memory times, etc.) have been demonstrated in separate experiments on trapped ions. Construction of a large-scale information processor will require synthesis of these elements and implementation of high-fidelity operations on a very large number of qubits. This is still well in the future. NIST and other groups are addressing part of the scaling issue by trying to fabricate multi-zone arrays of traps that would allow highly-parallel and scalable processing. In the near term, some simple quantum processing protocols are being used to aid in quantum metrology, such as in atomic clocks. As the number of qubits increases, Schroedinger's cat paradox and the measurement problem in quantum mechanics become more apparent; with luck, trapped ion systems might be able to shed light on these fundamental issues

182

Trapped Atomic Ions and Quantum Information Processing

The basic requirements for quantum computing and quantum simulation (single- and multi-qubit gates, long memory times, etc.) have been demonstrated in separate experiments on trapped ions. Construction of a large-scale information processor will require synthesis of these elements and implementation of high-fidelity operations on a very large number of qubits. This is still well in the future. NIST and other groups are addressing part of the scaling issue by trying to fabricate multi-zone arrays of traps that would allow highly-parallel and scalable processing. In the near term, some simple quantum processing protocols are being used to aid in quantum metrology, such as in atomic clocks. As the number of qubits increases, Schrödinger's cat paradox and the measurement problem in quantum mechanics become more apparent; with luck, trapped ion systems might be able to shed light on these fundamental issues.

Wineland, D. J.; Leibfried, D.; Bergquist, J. C.; Blakestad, R. B.; Bollinger, J. J.; Britton, J.; Chiaverini, J.; Epstein, R. J.; Hume, D. B.; Itano, W. M.; Jost, J. D.; Knill, M.; Koelemeij, J. C. J.; Langer, C.; Ozeri, R.; Reichle, R.; Rosenband, T.; Schaetz, T.; Schmidt, P. O.; Seidelin, S.; Shiga, N.; Wesenberg, J. H.

2006-11-01

183

Hilbert's projective metric in quantum information theory

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

184

A New Approach to Encoding and Hiding Information in an Image

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

185

Theory of solid state quantum information processing

Recent theoretical work on solid-state proposals for the implementation of quantum computation and quantum information processing is reviewed. The differences and similarities between microscopic and macroscopic qubits are highlighted and exemplified by the spin qubit proposal on one side and the superconducting qubits on the other. Before explaining the spin and supercondcuting qubits in detail, some general concepts that are relevant for both types of solid-state qubits ar...

Burkard, Guido

2004-01-01

186

Quantum information reclaiming after amplitude damping

We investigate the quantum information reclaim from the environment after amplitude damping has occurred. In particular we address the question of optimal measurement on the environment to perform the best possible correction on two and three dimensional quantum systems. Depending on the dimension we show that the entanglement fidelity (the measure quantifying the correction performance) is or is not the same for all possible measurements and uncover the optimal measurement ...

Memarzadeh, Laleh; Cafaro, Carlo; Mancini, Stefano

2011-01-01

187

Fisher information, nonclassicality and quantum revivals

International Nuclear Information System (INIS)

Wave packet revivals and fractional revivals are studied by means of a measure of nonclassicality based on the Fisher information. In particular, we show that the spreading and the regeneration of initially Gaussian wave packets in a quantum bouncer and in the infinite square-well correspond, respectively, to high and low nonclassicality values. This result is in accordance with the physical expectations that at a quantum revival wave packets almost recover their initial shape and the classical motion revives temporarily afterward.

188

Quantum Entanglement and Conditional Information Transmission

We propose a new measure of quantum entanglement. Our measure is defined in terms of conditional information transmission for a Quantum Bayesian Net. We show that our measure is identically equal to the Entanglement of Formation in the case of a bipartite (two listener) system occupying a pure state. In the case of mixed states, the relationship between these two measures is not known yet. We discuss some properties of our measure. Our measure can be easily and naturally gen...

Tucci, Robert R.

1999-01-01

189

Fisher information, nonclassicality and quantum revivals

Energy Technology Data Exchange (ETDEWEB)

Wave packet revivals and fractional revivals are studied by means of a measure of nonclassicality based on the Fisher information. In particular, we show that the spreading and the regeneration of initially Gaussian wave packets in a quantum bouncer and in the infinite square-well correspond, respectively, to high and low nonclassicality values. This result is in accordance with the physical expectations that at a quantum revival wave packets almost recover their initial shape and the classical motion revives temporarily afterward.

Romera, Elvira [Instituto Carlos I de Física Teórica y Computacional, Universidad de Granada, Fuentenueva s/n, 18071 Granada (Spain); Departamento de Física Atómica, Molecular y Nuclear, Universidad de Granada, Fuentenueva s/n, 18071 Granada (Spain); Santos, Francisco de los, E-mail: dlsantos@onsager.ugr.es [Instituto Carlos I de Física Teórica y Computacional, Universidad de Granada, Fuentenueva s/n, 18071 Granada (Spain); Departamento de Electromagnetismo y Física de la Materia, Universidad de Granada, Fuentenueva s/n, 18071 Granada (Spain)

2013-11-08

190

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

191

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

192

Multiparty hierarchical quantum-information splitting

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

193

Complementarity of quantum discord and classically accessible information

The sum of the Holevo quantity (that bounds the capacity of quantum channels to transmit classical information about an observable) and the quantum discord (a measure of the quantumness of correlations of that observable) yields an observable-independent total given by the quantum mutual information. This split naturally delineates information about quantum systems accessible to observers -- information that is redundantly transmitted by the environment -- while showing that...

Michael Zwolak; Zurek, Wojciech H.

2013-01-01

194

Directory of Open Access Journals (Sweden)

Full Text Available Problem statement: Higher data transmission rate with Quality of Services (QoS guarantee is an important objective for wireless broadband communication systems. Unlike other communication system, real-time transmission requires high data rate and good error performance to ensure good quality of service. This study describes the design problem of real-time wireless data transmission which provides higher achievable data rate with Unequal Error Protection (UEP. Approach: Real-time data stream was divided equally into two streams, High Priority (HP and Low Priority (LP streams depending on their requirements. We considered these two bit streams as being encoded separately by two adaptive encoders. Feedback of Channel State Information (CSI was used in adaptive physical layer channel for efficient use of the current available bandwidth by controlling the encoders. High code rate were used in both encoders when the channel is good while low code rate is otherwise. The two coded data streams were superimposed together with two different adjustable levels of power to achieve the UEP at the receiver end. Results: In this proposed scheme, same design metrics, namely, time, bandwidth and power were used to increase the transmission efficiency. Conclusion/Recommendations: Results showed that our scheme provided higher error performance for HP stream compared with other schemes that transmit using one power level data stream. The finding can be modified for studying the effects of fading on this system in future research.

Yaseen H. Tahir

2009-01-01

195

Quantum state estimation with informationally overcomplete measurements

We study informationally overcomplete measurements for quantum state estimation so as to clarify their tomographic significance as compared with minimal informationally complete measurements. We show that informationally overcomplete measurements can improve the tomographic efficiency significantly over minimal measurements when the states of interest have high purities. Nevertheless, the efficiency is still too limited to be satisfactory with respect to figures of merit based on monotone Riemannian metrics, such as the Bures metric and quantum Chernoff metric. In this way, we also pinpoint the limitation of nonadaptive measurements and motivate the study of more sophisticated measurement schemes. In the course of our study, we introduce the best linear unbiased estimator and show that it is equally efficient as the maximum likelihood estimator in the large sample limit. This estimator may significantly outperform the canonical linear estimator for states with high purities. It is expected to play an important role in experimental designs and adaptive quantum state tomography besides its significance to the current study.

Zhu, Huangjun

2014-07-01

196

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.

197

No partial erasure of quantum information

We prove theorems that qubits and qudits cannot be partially erased, even by irreversible operations, where partial erasure refers to a reduction of the dimension for its parameter space. The no-flipping theorem, which rules out the existence of a universal NOT gate, emerges as a corollary to this theorem. The `no partial erasure' theorem is shown to apply to spin and bosonic coherent states, with the latter result showing that the `no partial erasure' theorem applies to continuous variable quantum information schemes as well. The no partial erasure theorem suggests an integrity principle that quantum information is indivisible.

Pati, A K; Pati, Arun K.; Sanders, Barry C.

2005-01-01

198

Quantum information and computation for chemistry

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

199

Information encoding in the temporal characteristics of auditory-evoked neuromagnetic fields

Imaging data, provided by functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) has allowed insights into spatial organization of human cortical brain function. In the auditory system, a spatially-organized 'tonotopic' representation of frequency has been proposed. To provide an additional dimension to the description of functional organization, this study investigates the temporal signature of neuronal responses to auditory stimuli, detected using magnetoencephalography (MEG), to identify and characterize temporal encoding of stimulus attributes such as pitch and timbre. Stimuli elicited neuromagnetic fields with distinct peaks approximately 100 ms post-stimulus (M100). For sinusoidal tones frequency-dependent variation of the M100 latency was observed. This was mimicked using triangle and square waveforms, although the magnitude of the latency shift was attenuated. Amplitude-modulated tones and speech sounds demonstrated M100 latencies dominated by the carrier frequency and formats, and secondarily influenced by modulation frequency and fundamental, respectively. Information is encoded in the time domain of neuronal responses to auditory stimulation. Both the fundamental frequency and the timbre of a stimulus influence the specific latency of neuronal coherence. High temporal resolution recording of electromagnetic activity induced by stimuli allows new insights into the brain's functional encoding of presented information.

Roberts, Timothy P. L.

1998-07-01

200

Two accounts explain why studying pictures reduces false memories within the Deese-Roediger-McDermott paradigm (J. Deese, 1959; H. L. Roediger & K. B. McDermott, 1995). The impoverished relational-encoding account suggests that studying pictures interferes with the encoding of relational information, which is the primary basis for false memories…

Hege, Amanda C. G.; Dodson, Chad S.

2004-01-01

201

Quantum Spread Spectrum Communication

Energy Technology Data Exchange (ETDEWEB)

We demonstrate that spectral teleportation can coherently dilate the spectral probability amplitude of a single photon. In preserving the encoded quantum information, this variant of teleportation subsequently enables a form of quantum spread spectrum communication.

Humble, Travis S [ORNL

2010-01-01

202

Color Information Encoding Based on Phase-Truncated Gyrator Transform Domain

Directory of Open Access Journals (Sweden)

Full Text Available A color information encryption method using phase-truncated gyrator transform domain is proposed. In this technique, the color image is decomposed into R, G and B channels. The decomposed three RBG channels evade the interference of crosstalks efficiently. Each channel is separately modulated to the first random phase mask and then gyrator transformed. The transformed image is phase-truncated to get first encoded image and amplitude-truncated to produce first asymmetric phase key. The obtained image is modulated to the second random phase mask and then again gyrator transformed. The resulted image is phase-truncated to obtain second encoded image and amplitude-truncated to generate second asymmetric phase key. The proposed system includes transformation angles of GT and asymmetric phase keys as decryption keys. The proposed system can be implemented digitally or optically. The optical setup is free from optical misalignment problem. The theoretical analysis and numerical simulation results both validate the proposed technique.

Muhammad Rafiq Abuturab

2014-04-01

203

Quantum gravity and the Information Loss Problem

Energy Technology Data Exchange (ETDEWEB)

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

Varadarajan, Madhavan [Raman Research Institute, Bangalore 560 080 (India)], E-mail: madhavan@rri.res.in

2008-11-01

204

Quantum gravity and the Information Loss Problem

International Nuclear Information System (INIS)

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

205

Nonlinear coherent states for optimizing quantum information

International Nuclear Information System (INIS)

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

206

Quantum information processing with trapped ion chains

Trapped atomic ion systems are currently the most advanced platform for quantum information processing. Their long coherence times, pristine state initialization and detection, and precisely controllable and versatile interactions make them excellent quantum systems for experiments in quantum computation and quantum simulation. One of the more promising schemes for quantum computing consists of performing single and multi-qubit quantum gates on qubits in a linear ion crystal. Some of the key challenges of scaling such a system are the individual addressing of arbitrary subsets of ions and controlling the growing complexity of motional mode interactions as the number of qubits increases or when the gates are performed faster. Traditional entangling quantum gates between ion qubits use laser pulses to couple the qubit states to the collective motion of the crystal, thereby generating a spin-spin interaction that can produce entanglement between selected qubits. The intrinsic limitations on the performance of gates using this method can be alleviated by applying optimally shaped pulses instead of pulses with constant amplitude. This thesis explains the theory behind this pulse shaping scheme and how it is implemented on a chain of Yb ions held in a linear radiofrequency 'Paul' trap. Several experiments demonstrate the technique in chains of two, three, and five ions using various types of pulse shapes. A tightly focused individual addressing beam allows us to apply the entangling gates to a target pair of ions, and technical issues related to such tight focusing are discussed. Other advantages to the pulse shaping scheme include a robustness against detuning errors and the possibility of suppressing undesirable coupling due to optical spillover on neighboring ions. Combined with ion shuttling, we harness these features to perform sequential gates to different qubit pairs in order to create genuine tripartite entangled states and demonstrate the programmable quantum information processing capability of our system.

Manning, Timothy Andrew

207

Information-theoretic interpretation of quantum error-correcting codes

Quantum error-correcting codes are analyzed from an information-theoretic perspective centered on quantum conditional and mutual entropies. This approach parallels the description of classical error correction in Shannon theory, while clarifying the differences between classical and quantum codes. More specifically, it is shown how quantum information theory accounts for the fact that "redundant" information can be distributed over quantum bits even though this does not viol...

Cerf, Nicolas J.; Cleve, Richard

1997-01-01

208

Photon engineering for quantum information processing

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

209

From Information Geometry to Quantum Theory

In this paper, we show how information geometry, a geometry of discrete probability distributions, can be used as a framework for a derivation of the quantum formalism. The derivation rests upon three elementary features of quantum phenomena, namely complementarity, global gauge invariance, and the simulability of measurements. When appropriately formulated within the information geometric framework and supplemented with a few additional plausible assumptions, these features lead to the finite-dimensional quantum formalism. The notion of complementarity is expressed by the assertion that the results of a measurement coarse-grain over the objectively-realized outcomes of the measurement. Using this idea, we obtain a formalism in which states are represented by unit vectors in a real Euclidean space, and physical transformations are represented by orthogonal transformations. A global gauge invariance condition allows this formalism to be rewritten in complex form, with physical transformations represented by un...

Goyal, Philip

2008-01-01

210

Quantum information cannot be split into complementary parts

International Nuclear Information System (INIS)

We prove a new impossibility for quantum information (the no-splitting theorem): an unknown quantum bit (qubit) cannot be split into two complementary qubits. This impossibility, together with the no-cloning theorem, demonstrates that an unknown qubit state is a single entity, which cannot be cloned or split. This sheds new light on quantum computation and quantum information

211

Quantum Symmetrically-Private Information Retrieval

Private information retrieval systems (PIRs) allow a user to extract an item from a database that is replicated over k>=1 servers, while satisfying various privacy constraints. We exhibit quantum k-server symmetrically-private information retrieval systems (QSPIRs) that use sublinear communication, do not use shared randomness among the servers, and preserve privacy against honest users and dishonest servers. Classically, SPIRs without shared randomness do not exist at all.

Kerenidis, Iordanis; Wolf, Ronald

2003-01-01

212

Quantum Information Processing with Nanomechanical Qubits

We introduce an approach to quantum information processing where the information is stored in the motional degrees of freedom of nanomechanical devices. The qubits of our approach are formed by the two lowest energy levels of mechanical resonators which are tuned to be strongly anharmonic by suitable electrostatic fields. Single qubit rotations are conducted by radio frequency voltage pulses that are applied to individual resonators. Two qubit entangling gates in turn are im...

Rips, Simon; Hartmann, Michael J.

2012-01-01

213

Quantum Information Science Workshop (Proceedings)

... while publishing services were provided by Kelly DuBose and the NSF Publishing and Information ... decision to make the report as generally accessible as possible, without the normal scholarly detail ...

214

Quantum Information through Angular momentum of Photon

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

215

Partially reversible quantum operations and their information-theoretical properties

Partial reversibility of quantum operations (or quantum channels) is considered from the information-theoretical point of view. The necessary and sufficient condition for quantum operations to be partially reversible is shown. The condition can be expressed in terms of information-theoretical quantities (von Neumann entropy and PSI-information). The quantum information-theoretical meanings of the condition are discussed. The results are compared with those obtained for completely reversible quantum operations. The PSI-information is calculated for the quantum depolarizing channel of a qubit and the linear dissipative channel of a single-mode bosonic system.

Ban, M

2003-01-01

216

Black Holes, Information, and Hilbert Space for Quantum Gravity

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

217

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

218

Quantum information, oscillations and the psyche

In this paper, taking the theory of quantum information as a model, we consider the human unconscious, pre-consciousness and consciousness as sets of quantum bits (qubits). We view how there can be communication between these various qubit sets. In doing this we are inspired by the theory of nuclear magnetic resonance. In this way we build a model of handling a mental qubit with the help of pulses of a mental field. Starting with an elementary interaction between two qubits we build two-qubit quantum logic gates that allow information to be transferred from one qubit to the other. In this manner we build a quantum process that permits consciousness to ``read{''} the unconscious and vice versa. The elementary interaction, e.g. between a pre-consciousness qubit and a consciousness one, allows us to predict the time evolution of the pre-consciousness + consciousness system in which pre-consciousness and consciousness are quantum entangled. This time evolution exhibits Rabi oscillations that we name mental Rabi o...

Martin, F; Carminati, G Galli

2010-01-01

219

Quantum control, quantum information processing, and quantum-limited metrology with trapped ions

We briefly discuss recent experiments on quantum information processing using trapped ions at NIST. A central theme of this work has been to increase our capabilities in terms of quantum computing protocols, but we have also applied the same concepts to improved metrology, particularly in the area of frequency standards and atomic clocks. Such work may eventually shed light on more fundamental issues, such as the quantum measurement problem.

Wineland, D J; Barrett, M D; Ben-Kish, A; Bergquist, J C; Blakestad, R B; Bollinger, J J; Britton, J L; Chiaverini, J; De Marco, B L; Hume, D; Itano, W M; Jensen, M; Jost, J D; Knill, E; Koelemeij, J C J; Langer, C; Oskay, W; Ozeri, R; Reichle, R; Rosenband, T; Schätz, T; Schmidt, P O; Seidelin, S

2005-01-01

220

Bounds on the Information Rate of Quantum Secret Sharing Schemes

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 $...

Sarvepalli, Pradeep

2010-01-01

221

Quantum information processing with optical vortices

International Nuclear Information System (INIS)

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)

222

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

223

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)

224

Energy Technology Data Exchange (ETDEWEB)

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

Breuer, Reinhard (comp.)

2010-07-01

225

Impossible and Possible Operations in Quantum Information

We prove a general limitation in quantum information that unifies the no-cloning and no-complementing principles. We show that one cannot design Hadamard and unitary gates for creating equal and unequal superpositions of the original and its complement state. We show that if an unknown qubit is chosen from polar great circle then it is possible to design above logic gates. But qubits chosen from equatorial great circle cannot be. We also discuss why one cannot design a controlled-NOT gate for unknown qubits. An important implication of these limitations is that ultimate quantum computers will be inherently personal.

Pati, A K

2001-01-01

226

A quantum password is a quantum mechanical analogue of the classical password. Our proposal is completely quantum mechanical in nature, i.e. at no point is information stored and manipulated classically. We show that, in contrast to quantum protocols that encode classical information, we are able to prevent the distribution of reusable passwords even when Alice actively cooperates with Eve. This allows us to confront and address security issues that are unavoidable in classi...

Gu, Mile; Weedbrook, Christian

2005-01-01

227

Quantum mechanics and quantum information a guide through the quantum world

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

228

Quantifying non-Gaussianity for quantum information

International Nuclear Information System (INIS)

We address the quantification of non-Gaussianity (nG) of states and operations in continuous-variable systems and its use in quantum information. We start by illustrating in detail the properties and the relationships of two recently proposed measures of nG based on the Hilbert-Schmidt 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 behavior in most of the examples taken into account. However, we also show that they introduce a different relation of order; that is, they are not strictly monotone to each other. We exploit the nG measures for states in order to introduce a measure of nG for quantum operations, to assess Gaussification and de-Gaussification protocols, and to investigate in detail the role played by nG in entanglement-distillation protocols. Besides, we exploit the QRE-based nG measure to provide different insight on the extremality of Gaussian states for some entropic quantities such as conditional entropy, mutual information, and the Holevo bound. We also deal with parameter estimation and present a theorem connecting the QRE nG to the quantum Fisher information. Finally, since evaluation of the QRE nG measure requires the knowledge of the full density matrix, we derive some experimentally friendly lowwe derive some experimentally friendly lower bounds to nG for some classes of states and by considering the possibility of performing on the states only certain efficient or inefficient measurements.

229

Synchronicity, Quantum Information and the Psyche

In this paper we describe synchronicity phenomena. As an explanation of these phenomena we propose quantum entanglement between the psychic realm known as the "unconscious" and also the classical illusion of the collapse of the wave-function. Then, taking the theory of quantum information as a model we consider the human unconscious, pre-consciousness and consciousness as sets of quantum bits (qu-bits). We analyze how there can be communication between these various qu-bit sets. In doing this we are inspired by the theory of nuclear magnetic resonance. In this manner we build quantum processes that permit consciousness to "read" the unconscious and vice-versa. The most elementary interaction, e.g. between a pre-consciousness qu-bit and a consciousness one, allows us to predict the time evolution of the pre-consciousness + consciousness system in which pre-consciousness and consciousness are quantum entangled. This time evolution exhibits Rabi oscillations that we name mental Rabi oscillations. This time evolu...

Martin, Francois; Galli Carminati, Giuliana

2009-01-01

230

Information geometry, dynamics and discrete quantum mechanics

We consider a system with a discrete configuration space. We show that the geometrical structures associated with such a system provide the tools necessary for a reconstruction of discrete quantum mechanics once dynamics is brought into the picture. We do this in three steps. Our starting point is information geometry, the natural geometry of the space of probability distributions. Dynamics requires additional structure. To evolve the Pk, we introduce coordinates Sk canonically conjugate to the Pk and a symplectic structure. We then seek to extend the metric structure of information geometry, to define a geometry over the full space of the Pk and Sk. Consistency between the metric tensor and the symplectic form forces us to introduce a Kähler geometry. The construction has notable features. A complex structure is obtained in a natural way. The canonical coordinates of the ?k = ?Pk eiSk Kähler space are precisely the wave functions of quantum mechanics. The full group of unitary transformations is obtained. Finally, one may associate a Hilbert space with the Kähler space, which leads to the standard version of quantum theory. We also show that the metric that we derive here using purely geometrical arguments is precisely the one that leads to Wootters' expression for the statistical distance for quantum systems.

Reginatto, Marcel; Hall, Michael J. W.

2013-08-01

231

Energy Technology Data Exchange (ETDEWEB)

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

Koenneker, Carsten (comp.)

2012-11-01

232

Precisely timing dissipative quantum information processing

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

Kastoryano, M J; Eisert, J

2012-01-01

233

Efficient error characterization in quantum information processing

International Nuclear Information System (INIS)

We describe how to use the fidelity decay as a tool to characterize the errors affecting a quantum information processor through a noise generator G?. For weak noise, the initial decay rate of the fidelity proves to be a simple way to measure the magnitude of the different terms in G?. When the generator has only terms associated with few-body couplings, our proposal is scalable. We present the explicit protocol for estimating the magnitude of the noise generators when the noise consists of only one- and two-body terms, and describe a method for measuring the parameters of more general noise models. The protocol focuses on obtaining the magnitude with which these terms affect the system during a time step of length ?; measurement of this information has critical implications for assessing the scalability of fault-tolerant quantum computation in any physical setup

234

General impossible operations in quantum information

We prove a general limitation in quantum information that unifies the impossibility principles such as no-cloning and no-anticloning. Further, we show that for an unknown qubit one cannot design a universal Hadamard gate for creating equal superposition of the original and its complement state. Surprisingly, we find that Hadamard transformations exist for an unknown qubit chosen either from the polar or equatorial great circles. Also, we show that for an unknown qubit one ca...

Pati, Arun K.

2001-01-01

235

PREFACE: International Conference on Quantum Optics and Quantum Information (icQoQi) 2013

Quantum Information can be understood as being naturally derived from a new understanding of information theory when quantum systems become information carriers and quantum effects become non negligible. Experiments and the realization of various interesting phenomena in quantum information within the established field of quantum optics have been reported, which has provided a very convenient framework for the former. Together, quantum optics and quantum information are among the most exciting areas of interdisciplinary research in modern day science which cover a broad spectrum of topics, from the foundations of quantum mechanics and quantum information science to the introduction of new types of quantum technologies and metrology. The International Conference on Quantum Optics and Quantum Information (icQoQi) 2013 was organized by the Faculty of Science, International Islamic University Malaysia with the objective of bringing together leading academic scientists, researchers and scholars in the domain of interest from around the world to share their experiences and research results about all aspects of quantum optics and quantum information. While the event was organized on a somewhat modest scale, it was in fact a rather fruitful meeting for established researchers and students as well, especially for the local scene where the field is relatively new. We would therefore, like to thank the organizing committee, our advisors and all parties for having made this event successful and last but not least would extend our sincerest gratitude to IOP for publishing these selected papers from icQoQi2013 in Journal of Physics: Conference Series.

2014-11-01

236

Quantum information can make us honest in commitment

One of the long-standing problems of cryptography is to establish unconditional security against cheating in bit commitment protocol. So far no such classical protocol has been found. It has been claimed that unconditionally secure quantum bit commitment is impossible. Succinctly, the claim states that if quantum state is used to encode/commit a bit value then cheating on commitment will remain undetectable primarily because quantum state cannot be verified due to quantum-computer-assisted-entanglement-attack. Although the claim has been widely accepted as no-go theorem but it missed the points why bit value need to be encoded only in quantum state and why quantum property, if used to commit a bit, cannot be verified. We present an alternative quantum bit commitment scheme where bit value is encoded in entanglement property of entangled states. It is pointed out that unconditional security can be ensured by the verification of entanglement without verifying the states. The probability of cheating can be made ...

Mitra, A

2005-01-01

237

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

238

Information Nano-Technologies: Transition from Classical to Quantum

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

Vlasov, Alexander Yu

2009-01-01

239

Storing Quantum Information via Atomic Dark Resonances

In this thesis, after a brief review of some concepts of Quantum Optics, we analyze a three-level atomic system in the conditions of electromagnetically induced transparency (EIT), and we investigate the propagation of a gaussian pulse along a cigar-shaped cloud of both cold and hot atoms in EIT regime. In particular, we show that it is possible to amplify a slow propagating pulse without population inversion. We also analyze the regime of anomalous light propagation showing that it is possible to observe superluminal energy propagation. In these conditions, it is possible to imprint reversibly ('write') the information carried by the photons onto the atoms, specifically as a coherent pattern of atomic spins, and later the information stored in the atomic spins can be transferred back ('read') to the light field, implementing in this way a quantum memory. Besides, we analyze the propagation of a quantum field in an EIT medium sustaining dark state polaritons (DSP) in a quasi-particle picture. Here, the decohe...

Caruso, Filippo

2010-01-01

240

Generalized mutual informations of quantum critical chains

We study the R\\'enyi mutual information $\\tilde{I}_n$ of the ground state of different critical quantum chains. The R\\'enyi mutual information definition that we use is based on the well established concept of the R\\'enyi divergence. We calculate this quantity numerically for several distinct quantum chains having either discrete $Z(Q)$ symmetries (Q-state Potts model with $Q=2,3,4$ and $Z(Q)$ parafermionic models with $Q=5,6,7,8$ and also Ashkin-Teller model with different anisotropies) or the $U(1)$ continuous symmetries(Klein-Gordon field theory, XXZ and spin-1 Fateev-Zamolodchikov quantum chains with different anisotropies). For the spin chains these calculations were done by expressing the ground-state wavefunctions in two special basis. Our results indicate some general behavior for particular ranges of values of the parameter $n$ that defines $\\tilde{I}_n$. For a system, with total size $L$ and subsystem sizes $\\ell$ and $L-\\ell$, the$\\tilde{I}_n$ has a logarithmic leading behavior given by $\\frac{\\til...

Alcaraz, F C

2015-01-01

241

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

Energy Technology Data Exchange (ETDEWEB)

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 | {+-} {alpha}), minimum average fidelity in our case is {>=}0.99 for |{alpha}| {>=} 1.6 (i.e. |{alpha}|{sup 2} {>=} 2.6), while previously proposed schemes referred above report the same for |{alpha}| {>=} 5 (i.e. |{alpha}|{sup 2} {>=} 25). Since it is very challenging to produce superposed coherent states of high coherent amplitude (|{alpha}|), our teleportation scheme is at the reach of modern technology.

Mishra, Manoj K; Prakash, Hari, E-mail: manoj.qit@gmail.co, E-mail: prakash_hari123@rediffmail.co [Department of physics, University of Allahabad, Allahabad (India)

2010-09-28

242

International Nuclear Information System (INIS)

Quantum-information theory predicts that when the transmission resource is doubled in quantum channels, the amount of information transmitted can be increased more than twice by quantum-channel coding technique, whereas the increase is at most twice in classical information theory. This remarkable feature, the superadditive quantum-coding gain, can be implemented by appropriate choices of code words and corresponding quantum decoding which requires a collective quantum measurement. Recently, an experimental demonstration was reported [M. Fujiwara et al., Phys. Rev. Lett. 90, 167906 (2003)]. The purpose of this paper is to describe our experiment in detail. Particularly, a design strategy of quantum-collective decoding in physical quantum circuits is emphasized. We also address the practical implication of the gain on communication performance by introducing the quantum-classical hybrid coding scheme. We show how the superadditive quantum-coding gain, even in a small code length, can boost the communication performance of conventional coding techniques

243

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

244

Quantum information storage using tunable flux qubits

International Nuclear Information System (INIS)

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 T2?2.5 ?s. However, energy lifetimes of the qubit are found to be short (?10 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)

245

Quantum information storage using tunable flux qubits.

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(2)? 2.5 µs. However, energy lifetimes of the qubit are found to be short (? 10 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. PMID:21386337

Steffen, Matthias; Brito, Frederico; DiVincenzo, David; Farinelli, Matthew; Keefe, George; Ketchen, Mark; Kumar, Shwetank; Milliken, Frank; Rothwell, Mary Beth; Rozen, Jim; Koch, Roger H

2010-02-10

246

Quantum transition and information properties of the Coulomb coupled trion (electron-electron-hole) in the double quantum dots under the influence of the time-dependent electric field have been studied. Tuning the Hubbard interaction strength amongst the states of electron-hole complexes and the parameters of the ac field, two strikingly different kinds of approximate qubit can be constructed within the eight trion states. The similarity and difference between the electron d...

Wen, Y. B.; Yan, W. -x

2008-01-01

247

NMR Quantum Information Processing with Para-Hydrogen

This thesis addresses the problems of initialization and separability in liquid state NMR based quantum information processors. We prepare pure quantum states lying above the entanglement threshold. Our pure state quantum computer derives its purity from the highly polarized nuclear spin states in the para-hydrogen molecule. The thesis begins with a critique of conventional NMR based quantum information processing outlining the major strengths and weaknesses of the technolog...

Anwar, M. S.

2005-01-01

248

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

249

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

250

Information measures and classicality in quantum mechanics

We study information measures in quantu mechanics, with particular emphasis on providing a quantification of the notions of classicality and predictability. Our primary tool is the Shannon - Wehrl entropy I. We give a precise criterion for phase space classicality and argue that in view of this a) I provides a measure of the degree of deviation from classicality for closed system b) I - S (S the von Neumann entropy) plays the same role in open systems We examine particular examples in non-relativistic quantum mechanics. Finally, (this being one of our main motivations) we comment on field classicalisation on early universe cosmology.

Anastopoulos, C

1999-01-01

251

Informational approach to the quantum symmetrization postulate

A remarkable feature of quantum theory is that particles with identical intrinsic properties must be treated as indistinguishable if the theory is to give valid predictions in all cases. In the quantum formalism, indistinguishability is expressed via the symmetrization postulate (Dirac P 1926 Proc. R. Soc. A 112 661, Heisenberg W 1926 Z. Phys. 38 411), which restricts a system of identical particles to the set of symmetric states (‘bosons’) or the set of antisymmetric states (‘fermions’). However, the physical basis and range of validity of the symmetrization postulate has not been established. A well-known topological derivation of the postulate implies that its validity depends on the dimensionality of the space in which the particles move (Laidlaw M and DeWitt C 1971 Phys. Rev. D 3 1375–8, Leinaas J M and Myrheim J 1977 Il Nuovo Cimento B 37 1–23). Here we show that the symmetrization postulate can be derived by strictly adhering to the informational requirement that particles which cannot be experimentally distinguished from one another are not labelled. Our key novel postulate is the operational indistinguishability postulate, which posits that the amplitude of a process involving several indistinguishable particles is determined by the amplitudes of all possible transitions of these particles when treated as distinguishable. The symmetrization postulate follows by requiring consistency with the rest of the quantum formalism. The derivation implies that the symmetrization postulate admits no natural variants. In particular, the possibility that identical particles generically exhibit anyonic behavior in two dimensions is excluded.

Goyal, Philip

2015-01-01

252

Quantum Information Paradox: Real or Fictitious?

One of the outstanding puzzles of theoretical physics is whether quantum information indeed gets lost in the case of Black Hole (BH) evaporation or accretion. Let us recall that Quantum Mechanics (QM) demands an upper limit on the acceleration of a test particle. On the other hand, it is pointed out here that, if a Schwarzschild BH would exist, the acceleration of the test particle would blow up at the event horizon in violation of QM. Thus the concept of an exact BH is in contradiction of QM and quantum gravity (QG). It is also reminded that the mass of a BH actually appears as an INTEGRATION CONSTANT of Einstein equations. And it has been shown that the value of this integration constant is actually zero. Thus even classically, there cannot be finite mass BHs though zero mass BH is allowed. It has been further shown that during continued gravitational collapse, radiation emanating from the contracting object gets trapped within it by the runaway gravitational field. As a consequence, the contracting body at...

Mitra, Abhas

2009-01-01

253

A New Approach to Encoding and Hiding Information in an Image

Directory of Open Access Journals (Sweden)

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

Fadhil Salman Abed

2011-09-01

254

Background and Purpose Nuclear magnetic resonance (NMR) spectroscopy has become an important technique for tissue studies. Since tissues are in semisolid-state, their high-resolution (HR) spectra cannot be obtained by conventional NMR spectroscopy. Because of this restriction, extraction and high-resolution magic angle spinning (HR MAS) are widely applied for HR NMR spectra of tissues. However, both of the methods are subject to limitations. In this study, the feasibility of HR 1H NMR spectroscopy based on intermolecular multiple-quantum coherence (iMQC) technique is explored using fish muscle, fish eggs, and a whole fish as examples. Materials and Methods Intact salmon muscle tissues, intact eggs from shishamo smelt and a whole fish (Siamese algae eater) are studied by using conventional 1D one-pulse sequence, Hadamard-encoded iMQC sequence, and HR MAS. Results When we use the conventional 1D one-pulse sequence, hardly any useful spectral information can be obtained due to the severe field inhomogeneity. By contrast, HR NMR spectra can be obtained in a short period of time by using the Hadamard-encoded iMQC method without shimming. Most signals from fatty acids and small metabolites can be observed. Compared to HR MAS, the iMQC method is non-invasive, but the resolution and the sensitivity of resulting spectra are not as high as those of HR MAS spectra. Conclusion Due to the immunity to field inhomogeneity, the iMQC technique can be a proper supplement to HR MAS, and it provides an alternative for the investigation in cases with field distortions and with samples unsuitable for spinning. The acquisition time of the proposed method is greatly reduced by introduction of the Hadamard-encoded technique, in comparison with that of conventional iMQC method. PMID:24466083

Cai, Honghao; Chen, Yushan; Cui, Xiaohong; Cai, Shuhui; Chen, Zhong

2014-01-01

255

The current study sought to examine the relative contributions of encoding and retrieval processes in accessing contextual information in the absence of item memory using an extralist cuing procedure in which the retrieval cues used to query memory for contextual information were related to the target item but never actually studied. In Experiments 1 and 2, participants studied 1 category member (e.g., onion) from a variety of different categories and at test were presented with an unstudied category label (e.g., vegetable) to probe memory for item and source information. In Experiments 3 and 4, 1 member of unidirectional (e.g., credit or card) or bidirectional (e.g., salt or pepper) associates was studied, whereas the other unstudied member served as a test probe. When recall failed, source information was accessible only when items were processed deeply during encoding (Experiments 1 and 2) and when there was strong forward associative strength between the retrieval cue and target (Experiments 3 and 4). These findings suggest that a retrieval probe diagnostic of semantically related item information reinstantiates information bound in memory during encoding that results in reactivation of associated contextual information, contingent upon sufficient learning of the item itself and the association between the item and its context information. PMID:24933700

Ball, B Hunter; DeWitt, Michael R; Knight, Justin B; Hicks, Jason L

2014-09-01

256

Quantum information processing using electron spins in quantum dots

International Nuclear Information System (INIS)

We review the theoretical proposal for quantum computing with electron spins of quantum confined structures and discuss the essential requirements for its implementation. The quantum bit is represented by the spin of the electron, as opposed to the charge (orbital) degrees of freedom. In this context, we analyze a number of physical realizations of the elementary building blocks for quantum computation: a universal set of quantum gates, state preparation and measurement. Finally, we discuss the production, transport, and detection of electronic Einstein-Podolski-Rosen pairs, Which are an important resource for quantum communication. (author)

257

A Comment on Fisher Information and Quantum Algorithms

We show that Grover's algorithm defines a geodesic in quantum Hilbert space with the Fubini-Study metric. From statistical point of view Grover's algorithm is characterized by constant Fisher's function. Quantum algorithms changing complexity class as Shor's factorization does not preserve constant Fisher's information. An adiabatic quantum factorization algorithm in non polynomial time is presented to exemplify the result.

Alvarez, J. J.; Gomez, C.

1999-01-01

258

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

259

We present a detailed study on the possibility of manipulating quantum information encoded in the "radial" modes of arrays of trapped ions (i.e., in the ions' oscillations orthogonal to the trap's main axis). In such systems, because of the tightness of transverse confinement, the radial modes pertaining to different ions can be addressed individually. In the first part of the paper we show that, if local control of the radial trapping frequencies is available, any linear optical and squeezing operation on the locally defined modes - on single as well as on many modes - can be reproduced by manipulating the frequencies. Then, we proceed to describe schemes apt to generate unprecedented degrees of bipartite and multipartite continuous variable entanglement under realistic noisy working conditions, and even restricting only to a global control of the trapping frequencies. Furthermore, we consider the transmission of the quantum information encoded in the radial modes along the array of ions, and show it to be p...

Serafini, A; Plenio, M B

2008-01-01

260

Entanglement, Information, and the Interpretation of Quantum Mechanics

This book explores the nature of quantum entanglement and quantum information and their role in the quantum world. Their relations to a number of key experiments and thought experiments in the history of quantum physics are considered, as is a range of interpretations of quantum mechanics that have been put forward as a means of understanding the fundamental nature of microphysics - the traditionally accepted domain of quantum mechanics - and in some cases, the universe as a whole. In this way, the book reveals the deep significance of entanglement and quantum information for our understanding of the physical world. This book is a major accomplishment and invaluable contribution -- Arkady Plotnitsky An encyclopedic treatment of conceptual quantum mechanics as seen from a very up-to-date point of view --Tom Toffoli A mine of ideas for physicists, philosophers, and all intellectuals interested in this scientific revolution -- Giacomo Mauro D'Ariano

Jaeger, Gregg

2009-01-01

261

A neural-network-like quantum information processing system

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, Mitja; Bischof, Horst

2003-01-01

262

An improved derivation of minimum information quantum gravity

Minimum information quantum gravity (MIQG) is a theory of quantum gravity which requires no explicite microscopic quantum structure. In this article, it is shown that the MIQG action can be derived using a more elegant and straight-forward method than in the first existence proof. The required assumptions are dramatically reduced. In particular, former assumptions regarding the existence of quantum boxes, the exact differential of the entropy variation and the role of the bo...

Mandrin, Pierre A.

2014-01-01

263

Quantum Information-Flow Security: Noninterference and Access Control

Quantum cryptography has been extensively studied in the last twenty years, but information-flow security of quantum computing and communication systems has been almost untouched in the previous research. Duo to the essential difference between classical and quantum systems, formal methods developed for classical systems, including probabilistic systems, cannot be directly applied to quantum systems. This paper defines an automata model in which we can rigorously reason abou...

Ying, Mingsheng; Feng, Yuang; Yu, Nengkun

2013-01-01

264

Dynamical Casimir effect in quantum-information processing

We demonstrate, in the regime of ultrastrong matter-field coupling, the strong connection between the dynamical Casimir effect (DCE) and the performance of quantum-information protocols. Our results are illustrated by means of a realistic quantum communication channel and show that the DCE is a fundamental limit for quantum computation and communication and that novel schemes are required to implement ultrafast and reliable quantum gates. Strategies to partially counteract the DCE are also discussed.

Benenti, Giuliano; D'Arrigo, Antonio; Siccardi, Stefano; Strini, Giuliano

2014-11-01

265

Episodic retrieval involves early and sustained effects of reactivating information from encoding.

Several fMRI studies have shown a correspondence between the brain regions activated during encoding and retrieval, consistent with the view that memory retrieval involves hippocampally-mediated reinstatement of cortical activity. With the limited temporal resolution of fMRI, the precise timing of such reactivation is unclear, calling into question the functional significance of these effects. Whereas reactivation influencing retrieval should emerge with neural correlates of retrieval success, that signifying post-retrieval monitoring would trail retrieval. The present study employed EEG to provide a temporal landmark of retrieval success from which we could investigate the sub-trial time course of reactivation. Pattern-classification analyses revealed that early-onsetting reactivation differentiated the outcome of recognition-memory judgments and was associated with individual differences in behavioral accuracy, while reactivation was also evident in a sustained form later in the trial. The EEG findings suggest that, whereas prior fMRI findings could be interpreted as reflecting the contribution of reinstatement to retrieval success, they could also indicate the maintenance of episodic information in service of post-retrieval evaluation. PMID:25463451

Johnson, Jeffrey D; Price, Mason H; Leiker, Emily K

2015-02-01

266

Quantum-Classical Hybrid for Information Processing

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

267

A real-time polarization control system employing two non-orthogonal reference signals multiplexed in either time or wavelength with the data signal is presented. It is shown, theoretically and experimentally, that complete control of multiple polarization states can be attained employing polarization controllers in closed-loop configuration. Experimental results on the wavelength multiplexing setup show that negligible added penalties, corresponding to an average added optical Quantum Bit Error Rate of 0.044%, can be achieved with response times smaller than 10 ms, without significant introduction of noise counts in the quantum channel. PMID:18542265

Xavier, G B; Vilela de Faria, G; Temporão, G P; von der Weid, J P

2008-02-01

268

How the dynamics of a continuous quantum field can be encoded by discrete ensembles

International Nuclear Information System (INIS)

Many spins can collectively couple to a continuous quantum field such that the ensemble approximate the state of the field well. Is this approximation also preserved during the time evolution? The answer largely depends on the state of the ensemble and is already challenging for quadratic Hamiltonians. The key is to use the appropriate collective quantities, the fluctuator operators (familiar from mean field theory) and the good limiting procedure. Important applications are light-matter interface experiments, which are used to implement a type of quantum memory.

269

Information Theory Density Matrix for a Simple Quantum System.

Derives the density matrix that best describes, according to information theory, a one-dimensional single particle quantum system when the only information available is the values for the linear and quadratic position-momentum moments. (Author/GA)

Titus, William J.

1979-01-01

270

Simple scheme for expanding photonic cluster states for quantum information

International Nuclear Information System (INIS)

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

271

The encoding of individual identity in dolphin signature whistles: how much information is needed?

Bottlenose dolphins (Tursiops truncatus) produce many vocalisations, including whistles that are unique to the individual producing them. Such "signature whistles" play a role in individual recognition and maintaining group integrity. Previous work has shown that humans can successfully group the spectrographic representations of signature whistles according to the individual dolphins that produced them. However, attempts at using mathematical algorithms to perform a similar task have been less successful. A greater understanding of the encoding of identity information in signature whistles is important for assessing similarity of whistles and thus social influences on the development of these learned calls. We re-examined 400 signature whistles from 20 individual dolphins used in a previous study, and tested the performance of new mathematical algorithms. We compared the measure used in the original study (correlation matrix of evenly sampled frequency measurements) to one used in several previous studies (similarity matrix of time-warped whistles), and to a new algorithm based on the Parsons code, used in music retrieval databases. The Parsons code records the direction of frequency change at each time step, and is effective at capturing human perception of music. We analysed similarity matrices from each of these three techniques, as well as a random control, by unsupervised clustering using three separate techniques: k-means clustering, hierarchical clustering, and an adaptive resonance theory neural network. For each of the three clustering techniques, a seven-level Parsons algorithm provided better clustering than the correlation and dynamic time warping algorithms, and was closer to the near-perfect visual categorisations of human judges. Thus, the Parsons code captures much of the individual identity information present in signature whistles, and may prove useful in studies requiring quantification of whistle similarity. PMID:24194893

Kershenbaum, Arik; Sayigh, Laela S; Janik, Vincent M

2013-01-01

272

Single-Photon Secure Quantum Dialogue Protocol Without Information Leakage

Combining the idea of ping-pong protocol with Controlled-NOT operation, we propose a secure quantum dialogue protocol based on single-photonss. Bob obtains the information of the encrypted quantum state by performing Controlled-NOT operation on the auxiliary particle and the encrypted single-photonss. Unlike the previous quantum dialogue protocols based on single-photonss, the proposed protocol not only overcomes information leakage but also possesses an acceptable efficiency.

Zhou, Nan-Run; Hua, Tian-Xiang; Wu, Gui-Tong; He, Chao-Sheng; Zhang, Ye

2014-11-01

273

Jerusalem Lectures on Black Holes and Quantum Information

In these lectures I give an introduction to the quantum physics of black holes, including recent developments based on quantum information theory such as the firewall paradox and its various cousins. I also give an introduction to holography and the AdS/CFT correspondence, focusing on those aspects which are relevant for the black hole information problem.

Harlow, Daniel

2014-01-01

274

Lamina 3D display: projection-type depth-fused display using polarization-encoded depth information.

In order to realize three-dimensional (3D) displays, various multiplexing methods have been proposed to add the depth dimension to two-dimensional scenes. However, most of these methods have faced challenges such as the degradation of viewing qualities, the requirement of complicated equipment, and large amounts of data. In this paper, we further developed our previous concept, polarization distributed depth map, to propose the Lamina 3D display as a method for encoding and reconstructing depth information using the polarization status. By adopting projection optics to the depth encoding system, reconstructed 3D images can be scaled like images of 2D projection displays. 3D reconstruction characteristics of the polarization-encoded images are analyzed with simulation and experiment. The experimental system is also demonstrated to show feasibility of the proposed method. PMID:25401648

Park, Soon-gi; Yoon, Sangcheol; Yeom, Jiwoon; Baek, Hogil; Min, Sung-Wook; Lee, Byoungho

2014-10-20

275

We develop a quantum process tomography method, which variationally reconstruct the map of a process, using noisy and incomplete information about the dynamics. The new method encompasses the most common quantum process tomography schemes. It is based on the variational quantum tomography method (VQT) proposed by Maciel et al. in arXiv:1001.1793[quant-ph].

Maciel, Thiago O.; Vianna, Reinaldo O.

2010-01-01

276

It has consistently been reported that "negative" subsequent memory effects--lower study activity for later remembered than later forgotten items--are attenuated in older individuals. The present functional magnetic resonance imaging study investigated whether these findings extend to subsequent memory effects associated with successful encoding of item-context information. Older (n = 25) and young (n = 17) subjects were scanned while making 1 of 2 encoding judgments on a series of pictures. Memory was assessed for the study item and, for items judged old, the item's encoding task. Both memory judgments were made using confidence ratings, permitting item and source memory strength to be unconfounded and source confidence to be equated across age groups. Replicating prior findings, negative item effects in regions of the default mode network in young subjects were reversed in older subjects. Negative source effects, however, were invariant with respect to age and, in both age groups, the magnitude of the effects correlated with source memory performance. It is concluded that negative item effects do not reflect processes necessary for the successful encoding of item-context associations in older subjects. Negative source effects, in contrast, appear to reflect the engagement of processes that are equally important for successful episodic encoding in older and younger individuals. PMID:23904464

Mattson, Julia T; Wang, Tracy H; de Chastelaine, Marianne; Rugg, Michael D

2014-12-01

277

Experimental Long-Distance Decoy-State Quantum Key Distribution Based On Polarization Encoding

We demonstrate the decoy-state quantum key distribution (QKD) with one-way quantum communication in polarization space over 75 km. So far, our experimental implementation is the only one that really offers the unconditionally secure final keys among all the implementations of long-distance QKD with weak coherent states. We use 3 different intensities of 0, 0.2 and 0.6 for the pulses of source in our experiment. In order to eliminate the influences of polarization mode dispersion in the long-distance single-mode optical fiber, an automatic polarization compensation system is utilized to implement the active compensation. Only one detector is used in our experiment. The secure distance can be raised to 120 km given 4 detectors.

Peng, C Z; Ma, H X; Pan, J W; Wang, X B; Yang, D; Yang, T; Yin, H; Zeng, H P; Zhang, J; Gao, Wei-Bo; Ma, Huai-Xin; Pan, Jian-Wei; Peng, Cheng-Zhi; Wang, Xiang-Bin; Yang, Dong; Yang, Tao; Yin, Hao; Zeng, He-Ping; Zhang, Jun

2006-01-01

278

Non-Markovianity as a Resource for Quantum Technologies

Quantum technologies rely on the ability to coherently manipulate, process and transfer information, encoded in quantum states, along quantum channels. Decoherence induced by the environment introduces errors, thus setting limits on the efficiency of any quantum-enhanced protocol or device. A fundamental bound on the ability of a noisy quantum channel to transmit quantum (classical) information is given by its quantum (classical) capacity. Generally, the longer is a quantum ...

Bylicka, Bogna; Chrus?cin?ski, Dariusz; Maniscalco, Sabrina

2013-01-01

279

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

280

The last century saw the advent of quantum mechanics, information processing and integrated optics.These fields lead to the integrated optics for quantum communication. One of the challenges is thedevelopment of single photon sources operating at fiber's telecommunication wavelength. In this workwe use quantum dots growth by MOVPE (MetalOrganic Vapour Phase Epitaxy). We demonstratethese emitters can generate some quantum state of light thanks to the antibunching experiment.Moreover the spectr...

Elvira Antunez, David

2012-01-01

281

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

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

D'Arrigo, A; Falci, G

2011-01-01

282

Information gain in tomography--a quantum signature of chaos.

We find quantum signatures of chaos in various metrics of information gain in quantum tomography. We employ a quantum state estimator based on weak collective measurements of an ensemble of identically prepared systems. The tomographic measurement record consists of a sequence of expectation values of a Hermitian operator that evolves under repeated application of the Floquet map of the quantum kicked top. We find an increase in information gain and, hence, higher fidelities in the reconstruction algorithm when the chaoticity parameter map increases. The results are well predicted by random matrix theory. PMID:24483900

Madhok, Vaibhav; Riofrío, Carlos A; Ghose, Shohini; Deutsch, Ivan H

2014-01-10

283

Towards Quantum Information Processing at the Attosecond Timescale

Coherent processing of quantum information and attosecond science had so far little in common. We here show that recent data in high harmonic emission reveal quantum information processing at the attosecond timescale. By observing the interference pattern created by the spatiotemporal overlap of photons emitted by two interfering electron paths we generate a photon Hadamard gate and thus erase the electron-trajectory information. This allows the measurement of the relative p...

Kominis, I. K.; Kolliopoulos, G.; Charalambidis, D.; Tzallas, P.

2013-01-01

284

Transfer of Gravitational Information through a Quantum Channel

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...

Zhang, Baocheng; Cai, Qing-yu; Zhan, Ming-sheng

2013-01-01

285

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

Liang, Min

2012-01-01

286

NMR Quantum Information Processing with Para-Hydrogen

This thesis addresses the problems of initialization and separability in liquid state NMR based quantum information processors. We prepare pure quantum states lying above the entanglement threshold. Our pure state quantum computer derives its purity from the highly polarized nuclear spin states in the para-hydrogen molecule. The thesis begins with a critique of conventional NMR based quantum information processing outlining the major strengths and weaknesses of the technology. We describe the enhanced magnetic ordering of the nuclear spin states in para-hydrogen and an initialization experiment exploiting this effect to achieve pure, entangled states. These states can indeed be used as initial states in implementing quantum algorithms: we describe mplementations of the Deutsch and the Grover quantum algorithms. The "twirl" operation converts a completely arbitrary input state to a Werner singlet. The NMR implementation of this operation is taken up. We also analyze the possibility of sharing the purity of som...

Anwar, M S

2005-01-01

287

The capacity of black holes to transmit quantum information

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

2014-01-01

288

Information and fundamental elements of the structure of quantum theory

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

Brukner, C; Brukner, Caslav; Zeilinger, Anton

2002-01-01

289

Physics Colloquium: The optical route to quantum information processing

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

290

Remembering in tool-use tasks in children and apes: the role of the information at encoding.

Providing adults with relevant information (knowledge that they will be tested at some future time) increases motivation to remember. Research has shown that it is more effective to have this information prior to, rather than after, an encoding phase. We investigated this effect in apes and children in the context of tool-use tasks. In Experiment 1 we presented chimpanzees, orangutans, and bonobos with two tool-use tasks and three different two-tool sets. We had two conditions: prospective (PP) and retrospective (RP). In the PP subjects were shown the task that they would have to solve before they were shown the tools with which they could solve it. In the RP this order was reversed. Apes remembered the location of the useful tool better in the PP than in the RP. In Experiment 2 we presented 3- and 4-year-olds with the same conditions. Both age groups remembered the location of the correct tool in the PP, but only the 4-year-olds did so in the RP. Thus providing apes and preschool children with relevant information prior to, rather than after, the encoding phase enhances memory. These results have important implications for the understanding of the evolution of memory in general, and encoding mechanisms in particular. PMID:23767928

Martin-Ordas, Gema; Atance, Cristina M; Call, Josep

2014-01-01

291

Schrodinger cats and their power for quantum information processing

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

Gilchrist, A; Munro, W J; Ralph, T C; Glancy, S; Braunstein, S L; Milburn, G J; Nemoto, Kae; Braunstein, Samuel. L.

2003-01-01

292

Meaning-focused and Quantum-inspired Information Retrieval

In recent years, quantum-based methods have promisingly integrated the traditional procedures in information retrieval (IR) and natural language processing (NLP). Inspired by our research on the identification and application of quantum structures in cognition, more specifically our work on the representation of concepts and their combinations, we put forward a 'quantum meaning based' framework for structured query retrieval in text corpora and standardized testing corpora. ...

Aerts, Diederik; Broekaert, Jan; Sozzo, Sandro; Veloz, Tomas

2013-01-01

293

Immunizing quantum information against decoherence via decoherence-free environments

International Nuclear Information System (INIS)

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

294

Towards quantum simulations of biological information flow.

Recent advances in the spectroscopy of biomolecules have highlighted the possibility of quantum coherence playing an active role in biological energy transport. The revelation that quantum coherence can survive in the hot and wet environment of biology has generated a lively debate across both the physics and biology communities. In particular, it remains unclear to what extent non-trivial quantum effects are used in biology and what advantage, if any, they afford. We propose an analogue quan...

Dorner, R.; Goold, J.; Vedral, V.

2012-01-01

295

Non-linear operations in quantum information theory

Quantum information theory is used to analize various non-linear operations on quantum states. The universal disentanglement machine is shown to be impossible, and partial (negative) results are obtained in the state-dependent case. The efficiency of the transformation of non-orthogonal states into orthogonal ones is discussed.

Terno, Daniel R.

1998-01-01

296

Quantum information processing using strongly-dipolar coupled nuclear spins

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

Mahesh, T S; Suter, Dieter

2006-01-01

297

Quantum Oblivious Transfer Based on a Quantum Symmetrically Private Information Retrieval Protocol

Private information retrieval implies oblivious transfer in classical cryptography. Following this clue, we present a novel quantum one-out-of-two OT protocol based on a practical quantum symmetrically private information retrieval protocol Jakobi et al. (Phys. Rev. A 83, 022301 2011), with changes only in the classical postprocessing of the key. While unconditionally secure oblivious transfer is known to be impossible, we argue that an interesting degree of security can be achieved by means of quantum physical principles instead of unproven security assumptions in order to protect both the sender and the receiver. The proposed OT protocol is loss tolerant, practical and robust against quantum memory attack.

Yang, Yu-Guang; Sun, Si-Jia; Wang, Yan

2014-08-01

298

Quantum secret sharing based on quantum error-correcting codes

International Nuclear Information System (INIS)

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

299

BOOK REVIEW: Time, Quantum and Information

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

300

Smooth Rényi entropy of ergodic quantum information sources

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, Lam; Tjoelker, J.; Tuyls, Pt; Verbitskiy, Ea

2007-01-01

301

How quantum theory is developing the field of Information Retrieval

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).

Song, D.; Lalmas, M.; Rijsbergen, C. J.; Frommholz, I.; Piwowarski, B.; Wang, J.; Zhang, P.; Zuccon, G.; Bruza, P. D.; Arafat, S.; Azzopardi, L.; Di Buccio, E.; Huertas-rosero, A.; Hou, Y.; Melucci, M.

2010-01-01

302

Multiplexed CV quantum teleportation for high rates in quantum communication

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

303

Quantum information transfer and models for black hole mechanics

General features of information transfer between quantum subsystems, via unitary evolution, are investigated, with applications to the problem of information transfer from a black hole to its surroundings. A particularly direct form of quantum information transfer is "subspace transfer," which can be characterized by saturation of a subadditivity inequality. We also describe more general unitary quantum information transfer, and categorize different models for black hole evolution. Evolution that only creates paired excitations inside/outside the black hole is shown not to extract information, but information-transferring models exist both in the "saturating" and "non-saturating" category. The former more closely capture thermodynamic behavior; the latter generically have enhanced energy flux, beyond that of Hawking.

Giddings, Steven B

2012-01-01

304

Quantum copying can increase the practically available information

While it is known that copying a quantum system does not increase the amount of information obtainable about the originals, it may increase the amount available in practice, when one is restricted to imperfect measurements. We present a detection scheme which using imperfect detectors, and possibly noisy quantum copying machines (that entangle the copies), allows one to extract more information from an incoming signal, than with the imperfect detectors alone. The case of sin...

Deuar, P.; Munro, W. J.

2000-01-01

305

Limitations on information-theoretically-secure quantum homomorphic encryption

Homomorphic encryption is a form of encryption which allows computation to be carried out on the encrypted data without the need for decryption. The success of quantum approaches to related tasks in a delegated computation setting has raised the question of whether quantum mechanics may be used to achieve information-theoretically-secure fully homomorphic encryption. Here we show, via an information localization argument, that deterministic fully homomorphic encryption necessarily incurs exponential overhead if perfect security is required.

Yu, Li; Pérez-Delgado, Carlos A.; Fitzsimons, Joseph F.

2014-11-01

306

Random states, quantum information theory and free probability

This thesis is at the intersection of random matrix theory, free probability and quantum information theory. In quantum information theory, there exist several models for random density matrices. Much in the spirit of random matrix theory, we analyze the asymptotic behavior of density matrices when the size of the systems converge to infinity. We also propose a new model of random density matrices that we compare to the existing models. A central problem studied in this thesis is Nielsen's co...

Nechita, Ion

2009-01-01

307

Noiseless subsystems for collective rotation channels in quantum information theory

Collective rotation channels are a fundamental class of channels in quantum computing and quantum information theory. The commutant of the noise operators for such a channel is a C*-algebra which is equal to the set of fixed points for the channel. Finding the precise spatial structure of the commutant algebra for a set of noise operators associated with a channel is a core problem in quantum error prevention. We draw on methods of operator algebras, quantum mechanics and combinatorics to explicitly determine the structure of the commutant for the class of collective rotation channels.

Holbrook, J A; Laflamme, R; Poulin, D

2004-01-01

308

Quantum Information with Continuous Variable systems

This thesis deals with the study of quantum communication protocols with Continuous Variable (CV) systems. Continuous Variable systems are those described by canonical conjugated coordinates x and p endowed with infinite dimensional Hilbert spaces, thus involving a complex mathematical structure. A special class of CV states, are the so-called Gaussian states. With them, it has been possible to implement certain quantum tasks as quantum teleportation, quantum cryptography and quantum computation with fantastic experimental success. The importance of Gaussian states is two-fold; firstly, its structural mathematical description makes them much more amenable than any other CV system. Secondly, its production, manipulation and detection with current optical technology can be done with a very high degree of accuracy and control. Nevertheless, it is known that in spite of their exceptional role within the space of all Continuous Variable states, in fact, Gaussian states are not always the best candidates to perform...

Rodó, Carles

2010-01-01

309

Topological Protection and Quantum Noiseless Subsystems

Encoding and manipulation of quantum information by means of topological degrees of freedom provides a promising way to achieve natural fault-tolerance that is built-in at the physical level. We show that this topological approach to quantum information processing is a particular instance of the notion of computation in a noiseless quantum subsystem. The latter then provide the most general conceptual framework for stabilizing quantum information and for preserving quantum c...

Zanardi, Paolo; Lloyd, Seth

2002-01-01

310

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

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

2014-10-01

311

A Quantum Rosetta Stone for the Information Paradox

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

312

A quantum Rosetta Stone for the information paradox

The black hole information loss paradox epitomizes the contradictions between general relativity and quantum field theory. The AdS/conformal field theory (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.

Pando Zayas, Leopoldo A.

2014-11-01

313

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.

314

Quantum teleportation and entanglement. A hybrid approach to optical quantum information procesing

Energy Technology Data Exchange (ETDEWEB)

Unique in that it is jointly written by an experimentalist and a theorist, this monograph presents universal quantum computation based on quantum teleportation as an elementary subroutine and multi-party entanglement as a universal resource. Optical approaches to measurement-based quantum computation are also described, including schemes for quantum error correction, with most of the experiments carried out by the authors themselves. Ranging from the theoretical background to the details of the experimental realization, the book describes results and advances in the field, backed by numerous illustrations of the authors' experimental setups. Aimed at researchers, physicists, and graduate and PhD students in physics, theoretical quantum optics, quantum mechanics, and quantum information. (orig.)

Furusawa, Akira [Tokyo Univ. (Japan). Dept. of Applied Physics; Loock, Peter van [Erlangen-Nuernberg Univ. (Germany). Lehrstuhl fuer Optik

2011-07-01

315

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

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

316

Discusses how to increase user satisfaction by designing information retrieval systems that inform the user while the user is interacting online. Models the information processing operations of a user who has received an information message from the system and is stimulated into grasping at a higher understanding of the information need. (Contains…

Cole, Charles

2000-01-01

317

Quantum uncertainty of mixed states based on skew information

International Nuclear Information System (INIS)

The uncertainty of a mixed state has two quite different origins: classical mixing and quantum randomness. While the classical aspect (mixedness) is significantly quantified by the von Neumann entropy, it seems that we still do not have a well accepted measure of quantum uncertainty. In terms of the skew information introduced by Wigner and Yanase in 1963 in the context of quantum measurements, we will propose an intrinsic measure for synthesizing quantum uncertainty of a mixed state and investigate its fundamental properties. We illustrate how it arises naturally from a naive hidden-variable approach to entanglement and how it exhibits a simple relation to the notion of negativity, which is an entanglement monotone introduced quite recently. We further show that it has a dramatic nonextensive feature resembling the probability law relating operations of two events. This measure of quantum uncertainty provides an alternative quantity complementary to the von Neumann entropy for studying mixedness and quantum correlations

318

Toolbox for reconstructing quantum theory from rules on information acquisition

We develop a novel operational approach for reconstructing (qubit) quantum theory from elementary rules on information acquisition. The focus lies on an observer O interrogating a system S with binary questions and S's state is taken as O's `catalogue of knowledge' about S. The mathematical tools of the framework are simple and we attempt to highlight all underlying assumptions to provide a handle for future generalizations. Five principles are imposed, asserting (1) a limit on the amount of information available to O; (2) the mere existence of complementary information; (3) the possibility for O's information to be `in superposition'; (4) O's information to be preserved in between interrogations; and, (5) continuity of time evolution. This approach permits a constructive derivation of quantum theory, elucidating how the ensuing independence, complementarity and compatibility structure of O's questions matches that of projective measurements in quantum theory, how entanglement and monogamy of entanglement and...

Hoehn, Philipp A

2015-01-01

319

QIS-XML: A metadata specification for Quantum Information Science

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

320

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 compressrem 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)

321

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

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

322

A theoretical framework for the function of the medial temporal lobe system in memory defines differential contributions of the hippocampal subregions with regard to pattern recognition retrieval processes and encoding of new information. To investigate molecular programs of relevance, we designed a spatial learning protocol to engage a pattern separation function to encode new information. After background training, two groups of animals experienced the same new training in a novel environme...

Haberman, Rebecca P.; Lee, Hongjoo J.; Colantuoni, Carlo; Koh, Ming Teng; Gallagher, Michela

2008-01-01

323

Distribution of quantum information between an atom and two photons

Energy Technology Data Exchange (ETDEWEB)

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.)

Weber, Bernhard

2008-11-03

324

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.)

325

We discuss the architecture and design of parallel sampling front ends for analog to information (A2I) converters. As a way of example, we detail the design of a custom 0.5 µm CMOS implementation of a mixed signal parallel sampling encoder architecture. The system consists of configurable parallel analog processing channels, whose output is sampled by traditional analog-to-digital converters (ADCs). The analog front-end modulates the signal of interest with a high-speed digital chipping sequ...

Andreou, Andreas G.; Pouliquen, Philippe O.; Murray, Thomas S.

2013-01-01

326

Directory of Open Access Journals (Sweden)

Full Text Available We discuss the architecture and design of parallel sampling front ends for analog to information (A2I converters. As a way of example, we detail the design of a custom 0.5 µm CMOS implementation of a mixed signal parallel sampling encoder architecture. The system consists of configurable parallel analog processing channels, whose output is sampled by traditional analog-to-digital converters (ADCs. The analog front-end modulates the signal of interest with a high-speed digital chipping sequence and integrates the result prior to sampling at a low rate. An FPGA is employed to generate the chipping sequences and process the digitized samples.

Andreas G. Andreou

2013-03-01

327

Quantum Private Information Retrieval with Sublinear Communication Complexity

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

328

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

329

An improved derivation of minimum information quantum gravity

It is shown that, in minimum information quantum gravity (MIQG), the action can be derived using a more elegant and straight-forward method than has been used in the first existence proof. Assumptions regarding the quantum boxes, the exact differential of the entropy variation and the role of the boundary can be omitted, and the model structure requirements can be reduced. Moreover, the open problem of the quantum occupation number per box is solved. Thus, the arguments in favour of MIQG become even more stringent. The remaining assumptions are 1. the principle of optimization of the resulting per imposed degrees of freedom, 2. abstract quantum number conservation, 3. the validity of the laws of thermodynamics, 4. identification of a macroscopic parametrization with space-time and 6. unspecific interactions. Even though the assuptions are considerably reduced, all former results remain valid. In particular, no explicite microscopic quantum structure is required in order to recover all well established physics...

Mandrin, Pierre A

2014-01-01

330

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.)

331

Quantum mechanics with applications to nanotechnology and information science

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

Band, Yehuda B

2013-01-01

332

Distribution of quantum Fisher information in asymmetric cloning machines

An unknown quantum state cannot be copied on demand and broadcast freely due to the famous no-cloning theorem. Approximate cloning schemes have been proposed to achieve the optimal cloning characterized by the maximal fidelity between the original and its copies. Here, from the perspective of quantum Fisher information (QFI), we investigate the distribution of QFI in asymmetric cloning machines which produce two nonidentical copies. As one might expect, improving the QFI of ...

Xiao, Xing; Yao, Yao; Zhou, Lei-ming; Wang, Xiaoguang

2014-01-01

333

Information trade-offs for optical quantum communication

Recent work has precisely characterized the achievable trade-offs between three key information processing tasks---classical communication (generation or consumption), quantum communication (generation or consumption), and shared entanglement (distribution or consumption), measured in bits, qubits, and ebits per channel use, respectively. Slices and corner points of this three-dimensional region reduce to well-known protocols for quantum channels. A trade-off coding techniqu...

Wilde, Mark M.; Hayden, Patrick; Guha, Saikat

2012-01-01

334

Quantum information processing in the wall of microtubule

International Nuclear Information System (INIS)

Microtubule (MT) is described as an anisotropic two-dimensional pseudo-spin model on a triangular lattice, in which there are three different 'spin-spin' interactions. The mobile electron in each lattice site is described based on the pseudo-spin model. Then, the processing of quantum information in the MT wall is presented by virtue of the scheme of driving quantum computer in sequence of laser pulse developed by Lloyd. (authors)

335

Instrumental processes, entropies, information in quantum continual measurements

In this paper we will give a short presentation of the quantum Levy-Khinchin formula and of the formulation of quantum continual measurements based on stochastic differential equations, matters which we had the pleasure to work on in collaboration with Prof. Holevo. Then we will begin the study of various entropies and relative entropies, which seem to be promising quantities for measuring the information content of the continual measurement under consideration and for analysing its asymptotic behaviour.

Barchielli, A; Barchielli, Alberto; Lupieri, Giancarlo

2004-01-01

336

Unitary solution to a quantum gravity information paradox

International Nuclear Information System (INIS)

We consider a toy model of the interaction of a qubit with an exotic space-time containing a timelike curve. Consistency seems to require that the global evolution of the qubit be nonunitary. Given that quantum mechanics is globally unitary, this then is an example of a quantum gravity information paradox. However, we show that a careful analysis of the problem in the Heisenberg picture reveals an underlying unitarity, thus resolving the paradox

337

On positive maps in quantum information

Using the Grothendieck approach to the tensor product of locally convex spaces, we review a characterization of positive maps as well as Belavkin-Ohya characterization of PPT states. Moreover, within this scheme, a generalization of the idea of Choi matrices for genuine quantum systems will be presented.

Majewski, W. A.

2014-07-01

338

Quantum information processing with trapped electrons and superconducting electronics

International Nuclear Information System (INIS)

We describe a parametric frequency conversion scheme for trapped charged particles, which enables a coherent interface between atomic and solid-state quantum systems. The scheme uses geometric nonlinearities of the potential of coupling electrodes near a trapped particle, and can be implemented using standard charged-particle traps. Our scheme does not rely on actively driven solid-state devices, and is hence largely immune to noise in such devices. We present a toolbox which can be used to build electron-based quantum information processing platforms, as well as quantum hybrid platforms using trapped electrons and superconducting electronics. (paper)

339

EDITORIAL: Focus on Quantum Information and Many-Body Theory

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

Eisert, Jens; Plenio, Martin B.

2010-02-01

340

Quantum History cannot be Copied

We show that unitarity does not allow cloning of any two points in a ray. This has implication for cloning of the geometric phase information in a quantum state. In particular, the quantum history which is encoded in the geometric phase during cyclic evolution of a quantum system cannot be copied. We also prove that the generalized geometric phase information cannot be copied by a unitary operation. We argue that our result also holds in the consistent history formulation of quantum mechanics.

Pati, A K

2005-01-01

341

The faithful exchange of quantum information will soon become one of the challenges of the emerging quantum information technology. One of the possible solutions is to transfer a superposition through a chain of properly coupled spins. Such a system is called a quantum wire. We discuss the transfer in a quantum wire \\cite{christ,niko1,niko2}, when the process of thermalization of the state takes place together with the free evolution. We investigate which encoding scheme is ...

Wiesniak, Marcin

2007-01-01

342

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)

343

Information-disturbance tradeoff in quantum measurements

International Nuclear Information System (INIS)

We present a simple information-disturbance tradeoff relation valid for any general measurement apparatus: The disturbance between input and output states is lower bounded by the information the apparatus provides in distinguishing these two states

344

Information–theoretic implications of quantum causal structures

It is a relatively new insight of classical statistics that empirical data can contain information about causation rather than mere correlation. First algorithms have been proposed that are capable of testing whether a presumed causal relationship is compatible with an observed distribution. However, no systematic method is known for treating such problems in a way that generalizes to quantum systems. Here, we describe a general algorithm for computing information–theoretic constraints on the correlations that can arise from a given causal structure, where we allow for quantum systems as well as classical random variables. The general technique is applied to two relevant cases: first, we show that the principle of information causality appears naturally in our framework and go on to generalize and strengthen it. Second, we derive bounds on the correlations that can occur in a networked architecture, where a set of few-body quantum systems is distributed among some parties.

Chaves, Rafael; Majenz, Christian; Gross, David

2015-01-01

345

Information-theoretic implications of quantum causal structures.

It is a relatively new insight of classical statistics that empirical data can contain information about causation rather than mere correlation. First algorithms have been proposed that are capable of testing whether a presumed causal relationship is compatible with an observed distribution. However, no systematic method is known for treating such problems in a way that generalizes to quantum systems. Here, we describe a general algorithm for computing information-theoretic constraints on the correlations that can arise from a given causal structure, where we allow for quantum systems as well as classical random variables. The general technique is applied to two relevant cases: first, we show that the principle of information causality appears naturally in our framework and go on to generalize and strengthen it. Second, we derive bounds on the correlations that can occur in a networked architecture, where a set of few-body quantum systems is distributed among some parties. PMID:25562600

Chaves, Rafael; Majenz, Christian; Gross, David

2015-01-01

346

Information–theoretic implications of quantum causal structures

DEFF Research Database (Denmark)

It is a relatively new insight of classical statistics that empirical data can contain information about causation rather than mere correlation. First algorithms have been proposed that are capable of testing whether a presumed causal relationship is compatible with an observed distribution. However, no systematic method is known for treating such problems in a way that generalizes to quantum systems. Here, we describe a general algorithm for computing information–theoretic constraints on the correlations that can arise from a given causal structure, where we allow for quantum systems as well as classical random variables. The general technique is applied to two relevant cases: first, we show that the principle of information causality appears naturally in our framework and go on to generalize and strengthen it. Second, we derive bounds on the correlations that can occur in a networked architecture, where a set of few-body quantum systems is distributed among some parties.

Chaves, Rafael; Majenz, Christian

2014-01-01

347

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

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

348

Quantum information approach to normal representation of extensive games

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

Fr\\kackiewicz, Piotr

2011-01-01

349

Coherent control of diamond defects for quantum information science and quantum sensing

Quantum mechanics, arguably one of the greatest achievements of modern physics, has not only fundamentally changed our understanding of nature but is also taking an ever increasing role in engineering. Today, the control of quantum systems has already had a far-reaching impact on time and frequency metrology. By gaining further control over a large variety of different quantum systems, many potential applications are emerging. Those applications range from the development of quantum sensors and new quantum metrological approaches to the realization of quantum information processors and quantum networks. Unfortunately most quantum systems are very fragile objects that require tremendous experimental effort to avoid dephasing. Being able to control the interaction between a quantum system with its local environment embodies therefore an important aspect for application and hence is at the focus of this thesis. Nitrogen Vacancy (NV) color centers in diamond have recently attracted attention as a room temperature solid state spin system that expresses long coherence times. The electronic spin associated with NV centers can be efficiently manipulated, initialized and readout using microwave and optical techniques. Inspired by these extraordinary properties, much effort has been dedicated to use NV centers as a building block for scalable room temperature quantum information processing and quantum communication as well as a quantum sensing. In the first part of this thesis we demonstrate that by decoupling the spin from the local environment the coherence time of a NV quantum register can be extended by three order of magnitudes. Employing a novel dissipative mechanism in combination with dynamical decoupling, memory times exceeding one second are observed. The second part shows that, based on quantum control, NV centers in nano-diamonds provide a nanoscale temperature sensor with unprecedented accuracy enabling local temperature measurements in living biological cells. This opens the door for the engineering of nano-scaled chemical reactions to the study of temperature dependent biological processes. Finally, a novel technique is introduced that facilitates optical spin detection with nanoscale resolution based on an optical far-field technique; by combining this with a 'quantum Zeno' like effect coherent manipulation of nominally identical spins at a nanoscale is achieved.

Maurer, Peter

350

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

351

Continuous-Variable Quantum Computing in Optical Time-Frequency Modes Using Quantum Memories

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

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

2014-09-01

352

Entanglement and Quantum Information Transfer in Arrays of Interacting Quantum Systems

This thesis examines some of the more fundamental requirements of a successful quantum computation, namely the ability to transmit quantum information with maximum efficiency, and the creation of entanglement. I focus specifically on neutron entanglement, showing that the spins of two or more distinct neutrons can be measurably entangled by forward-scattering from an isotropic medium. The interpretation of `time' in scattering experiments is also discussed. I present a simple treatment based on the Heisenberg S-matrix, from which it emerges that in certain situations the quantum-mechanical time parameter appearing in the effective time-evolution operator for the spin system has an intuitive physical interpretation. The final part of the thesis deals with quantum information transfer in arrays of permanently coupled dipolar systems. It is shown that spin chains with dipolar couplings offer high fidelity long-distance state transmission, but transfer times in unmodulated chains are unfeasibly long. Possible opt...

Avellino, Martina

2009-01-01

353

Quantum nonlocality and applications in quantum-information processing of hybrid entangled states

International Nuclear Information System (INIS)

Hybrid entangled states generated, e.g., in a trapped-ion or atom-cavity system, have exactly one ebit of entanglement, but are not maximally entangled. We demonstrate this by showing that they violate, but, in general, not maximally, Bell's inequality due to Clauser, Horne, Shimony, and Holt [Phys. Rev. Lett. 23, 880 (1969)]. These states are interesting in that they exhibit the entanglement between two distinct degrees of freedom (one is discrete and another is continuous). We then demonstrate these entangled states as a valuable resource in quantum-information processing including quantum teleportation, entanglement swapping and quantum computation with 'parity qubits'. Our work establishes an interesting link between quantum-information protocols of discrete and continuous variables

354

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

355

There is considerable debate over whether the brain codes information using neural firing rate or the fine-grained structure of spike timing. We investigated this issue in spike discharge recorded from single units in the sensorimotor cortex, deep cerebellar nuclei, and dorsal root ganglia in macaque monkeys trained to perform a finger flexion task. The task required flexion to four different displacements against two opposing torques; the eight possible conditions were randomly interleaved. We used information theory to assess coding of task condition in spike rate, discharge irregularity, and spectral power in the 15- to 25-Hz band during the period of steady holding. All three measures coded task information in all areas tested. Information coding was most often independent between irregularity and 15-25 Hz power (60% of units), moderately redundant between spike rate and irregularity (56% of units redundant), and highly redundant between spike rate and power (93%). Most simultaneously recorded unit pairs coded using the same measure independently (86%). Knowledge of two measures often provided extra information about task, compared with knowledge of only one alone. We conclude that sensorimotor systems use both rate and temporal codes to represent information about a finger movement task. As well as offering insights into neural coding, this work suggests that incorporating spike irregularity into algorithms used for brain-machine interfaces could improve decoding accuracy. PMID:25298385

Witham, Claire L; Baker, Stuart N

2015-01-01

356

NMR Based Quantum Information Processing Achievements and Prospects

Nuclear magnetic resonance (NMR) provides an experimental setting to explore physical implementations of quantum information processing (QIP). Here we introduce the basic background for understanding applications of NMR to QIP and explain their current successes, limitations and potential. NMR spectroscopy is well known for its wealth of diverse coherent manipulations of spin dynamics. Ideas and instrumentation from liquid state NMR spectroscopy have been used to experiment with QIP. This approach has carried the field to a complexity of about 10 qubits, a small number for quantum computation but large enough for observing and better understanding the complexity of the quantum world. While liquid state NMR is the only present-day technology about to reach this number of qubits, further increases in complexity will require new methods. We sketch one direction leading towards a scalable quantum computer using spin 1/2 particles. The next step of which is a solid state NMR-based QIP capable of reaching 10-30 qub...

Cory, D G; Knill, E H; Viola, L; Havel, T F; Boulant, N; Boutis, G; Fortunato, E M; Lloyd, S; Martínez, R; Negrevergne, C; Pravia, M A; Sharf, Y; Teklemariam, G; Weinstein, Yu S; Zurek, W H

2000-01-01

357

Renyi generalizations of the conditional quantum mutual information

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

358

Geometric Approach to Digital Quantum Information

We present geometric methods for uniformly discretizing the N-qubit Hilbert space, producing the equivalent of the Platonic solids in 2^N- dimensional Hilbert space. The group of transformations leaving these uniform Hilbertian polytopes invariant - known as the Clifford group - provides a general language for describing discrete transformations on N qubits. Our geometric approach to discretization sheds light on the relationships between the discrete quantum states and the generalized $\\pi/2$ rotations belonging to the Clifford group. We describe in detail the uniform Hilbertian polytope $\\mathfrak{H}_{N}$ for one and two qubits.

Rigetti, C; Devoret, M H; Rigetti, Chad; Mosseri, Remy; Devoret, Michel

2003-01-01

359

Aiming the construction of quantum computers and quantum communication systems based on optical devices, in this work we present possible implementations of quantum and classical CNOTs gates, as well an optical setup for generation and distribution of bipartite entangled states, using linear optical devices and photon number quantum non-demolition measurement.

Silva, J B R; Ramos, Rubens Viana; Silva, Joao Batista Rosa

2006-01-01

360

International Nuclear Information System (INIS)

Aiming the construction of quantum computers and quantum communication systems based on optical devices, in this work we present possible implementations of quantum and classical CNOTs gates, as well an optical setup for generation and distribution of bipartite entangled states, using linear optical devices and photon number quantum non-demolition measurement

361

Energy Technology Data Exchange (ETDEWEB)

Aiming the construction of quantum computers and quantum communication systems based on optical devices, in this work we present possible implementations of quantum and classical CNOTs gates, as well an optical setup for generation and distribution of bipartite entangled states, using linear optical devices and photon number quantum non-demolition measurement.

Rosa Silva, Joao Batista [Department of Teleinformatic Engineering, Federal University of Ceara, Campus do Pici, 710, C.P. 6007, 60755-640 Fortaleza-Ceara (Brazil)]. E-mail: joaobrs@deti.ufc.br; Ramos, Rubens Viana [Department of Teleinformatic Engineering, Federal University of Ceara, Campus do Pici, 710, C.P. 6007, 60755-640 Fortaleza-Ceara (Brazil)]. E-mail: rubens@deti.ufc.br

2006-12-11

362

Avian egg odour encodes information on embryo sex, fertility and development.

Avian chemical communication is a rapidly emerging field, but has been hampered by a critical lack of information on volatile chemicals that communicate ecologically relevant information (semiochemicals). A possible, but as yet unexplored, function of olfaction and chemical communication in birds is in parent-embryo and embryo-embryo communication. Communication between parents and developing embryos may act to mediate parental behaviour, while communication between embryos can control the synchronicity of hatching. Embryonic vocalisations and vibrations have been implicated as a means of communication during the later stages of development but in the early stages, before embryos are capable of independent movement and vocalisation, this is not possible. Here we show that volatiles emitted from developing eggs of Japanese quail (Coturnix japonica) convey information on egg fertility, along with the sex and developmental status of the embryo. Specifically, egg volatiles changed over the course of incubation, differed between fertile and infertile eggs, and were predictive of embryo sex as early as day 1 of incubation. Egg odours therefore have the potential to facilitate parent-embryo and embryo-embryo interactions by allowing the assessment of key measures of embryonic development long before this is possible through other modalities. It also opens up the intriguing possibility that parents may be able to glean further relevant information from egg volatiles, such as the health, viability and heritage of embryos. By determining information conveyed by egg-derived volatiles, we hope to stimulate further investigation into the ecological role of egg odours. PMID:25629413

Webster, Ben; Hayes, William; Pike, Thomas W

2015-01-01

363

H1 photonic crystal cavitites for hybrid quantum information protocols

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

364

Information theory of quantum systems with some hydrogenic applications

The information-theoretic representation of quantum systems, which complements the familiar energy description of the density-functional and wave-function-based theories, is here discussed. According to it, the internal disorder of the quantum-mechanical non-relativistic systems can be quantified by various single (Fisher information, Shannon entropy) and composite (e.g. Cramer-Rao, LMC shape and Fisher-Shannon complexity) functionals of the Schr\\"odinger probability density. First, we examine these concepts and its application to quantum systems with central potentials. Then, we calculate these measures for hydrogenic systems, emphasizing their predictive power for various physical phenomena. Finally, some recent open problems are pointed out.

Dehesa, J S; Sánchez-Moreno, P S; Yáñez, R J

2010-01-01

365

Quantum metrology and information processing with entangled atoms

International Nuclear Information System (INIS)

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

366

Continuous variable quantum information: Gaussian states and beyond

The study of Gaussian states has arisen to a privileged position in continuous variable quantum information in recent years. This is due to vehemently pursued experimental realisations and a magnificently elegant mathematical framework. In this article, we provide a brief, and hopefully didactic, exposition of Gaussian state quantum information and its contemporary uses, including sometimes omitted crucial details. After introducing the subject material and outlining the essential toolbox of continuous variable systems, we define the basic notions needed to understand Gaussian states and Gaussian operations. In particular, emphasis is placed on the mathematical structure combining notions of algebra and symplectic geometry fundamental to a complete understanding of Gaussian informatics. Furthermore, we discuss the quantification of different forms of correlations (including entanglement and quantum discord) for Gaussian states, paying special attention to recently developed measures. The manuscript is conclud...

Adesso, Gerardo; Lee, Antony R

2014-01-01

367

Mutual information as an order parameter for quantum synchronization

Spontaneous synchronization is a fundamental phenomenon, important in many theoretical studies and applications. Recently, this effect has been analyzed and observed in a number of physical systems close to the quantum-mechanical regime. In this work we propose mutual information as a useful order parameter which can capture the emergence of synchronization in very different contexts, ranging from semiclassical to intrinsically quantum-mechanical systems. Specifically, we first study the synchronization of two coupled Van der Pol oscillators in both classical and quantum regimes and later we consider the synchronization of two qubits inside two coupled optical cavities. In all these contexts, we find that mutual information can be used as an appropriate figure of merit for determining the synchronization phases independently of the specific details of the system.

Ameri, V.; Eghbali-Arani, M.; Mari, A.; Farace, A.; Kheirandish, F.; Giovannetti, V.; Fazio, R.

2015-01-01

368

Simplification of additivity conjecture in quantum information theory

We simplify some conjectures in quantum information theory; the additivity of minimal output entropy, the multiplicativity of maximal output p-norm and the superadditivity of convex closure of output entropy. We construct a unital channel for a given channel so that they share the above additivity properties; we can reduce the conjectures for all channels to those for unital channels.

Fukuda, Motohisa

2006-01-01

369

Quantum mechanical model for information transfer from DNA to protein.

A model for the information transfer from DNA to protein using quantum information and computation techniques is presented. DNA is modeled as the sender and proteins are modeled as the receiver of this information. On the DNA side, a 64-dimensional Hilbert space is used to describe the information stored in DNA triplets (codons). A Hamiltonian matrix is constructed for this space, using the 64 possible codons as base states. The eigenvalues of this matrix are not degenerate. The genetic code is degenerate and proteins comprise only 20 different amino acids. Since information is conserved, the information on the protein side is also described by a 64-dimensional Hilbert space, but the eigenvalues of the corresponding Hamiltonian matrix are degenerate. Each amino acid is described by a Hilbert subspace. This change in Hilbert space structure reflects the nature of the processes involved in information transfer from DNA to protein. PMID:18502029

Karafyllidis, Ioannis G

2008-09-01

370

Solution to Information Leakage in a Quantum Network System of QSS-QDC Using ?-Type Entangled States

Recently, Hong et al. (Chin. Phys. Lett. 29:050303, 2012) put forward two quantum secret sharing (QSS) protocols of quantum direct communication (QDC) by using ?-type entangled states. Later, some studies (Gao et al. in Chin. Phys. Lett. 29:110305, 2012; Chin. Phys. Lett. 30:079904, 2013; Liu et al. in Chin. Phys. Lett. 30:039901, 2013; Hong and Yang in Chin. Phys. Lett. 30:069901, 2013; Liu and Chen in Chin. Phys. Lett. 30:079903, 2013) made up for the drawbacks of Hong et al.'s two protocols to some extent. However, the information leakage weakness is still not thoroughly solved. In this Letter, the author analyzes the inner reason of information leakage weakness in detail at first. And then he suggests an effective encoding rule to avoid this weakness.

Ye, Tian-Yu

2014-05-01

371

Quantum Correlated Equilibria in Classical Complete Information Games

We study the scenario where the players of a classical complete information game initially share an entangled pure quantum state. Each player may perform arbitrary local operations on his own qubits, but no direct communication is allowed. In this framework, we define the concept of quantum correlated equilibrium (QCE) for both normal and extensive form games of complete information. We show that in a normal form game, any outcome distribution implementable by a QCE can also be implemented by a classical correlated equilibrium (CE). We prove that the converse is surprisingly false: we give an example of an outcome distribution of a normal form game which is implementably by a CE, yet we prove that in any attempted quantum protocol beginning with a partition of a pure quantum state, at least one of the players will have incentive to deviate. We extend our analysis to extensive form games, and find that the relation between classical and quantum correlated equilibria becomes less clear. We compare the outcome d...

Deckelbaum, Alan

2011-01-01

372

Entanglement versus mutual information in quantum spin chains

International Nuclear Information System (INIS)

The quantum entanglement E of a bipartite quantum Ising chain is compared with the mutual information I between the two parts after a local measurement of the classical spin configuration. As the model is conformally invariant, the entanglement measured in its ground state at the critical point is known to obey a certain scaling form. Surprisingly, the mutual information of classical spin configurations is found to obey the same scaling form, although with a different prefactor. Moreover, we find that mutual information and the entanglement obey the inequality I ? E in the ground state as well as in a dynamically evolving situation. This inequality holds for general bipartite systems in a pure state and can be proved using similar techniques as for Holevo’s bound. (paper)

373

The black-hole information paradox has fueled a fascinating effort to reconcile the predictions of general relativity and those of quantum mechanics. Gravitational considerations teach us that black holes must trap everything that falls into them. Quantum mechanically the mass of a black hole leaks away as featureless (Hawking) radiation, but if the black hole vanishes, where is the information about the matter that made it? We treat the states of the in-fallen matter quantum mechanically and show that the black-hole information paradox becomes more severe. Our formulation of the paradox rules out one of the most conservative resolutions: that the state of the in-falling matter might be hidden in correlations between semi-classical Hawking radiation and the internal states of the black hole. As a consequence, either unitarity or Hawking's semi-classical predictions must break down. Any resolution of the black-hole information crisis must elucidate one of these possibilities.

Braunstein, S L; Braunstein, Samuel L.; Pati, Arun K.

2006-01-01

374

Parallel Information Transfer in a Multi-Node Quantum Information Processor

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

Borneman, Troy W; Cory, David G

2011-01-01

375

Directory of Open Access Journals (Sweden)

Full Text Available Working memory (WM involves three cognitive events: information encoding, maintenance and retrieval; these are supported by brain activity in a network of frontal, parietal and temporal regions. Manipulation of WM load and duration of the maintenance period can modulate this activity. Although such modulations have been widely studied using the ERP technique, a precise description of the time course of brain activity during encoding and retrieval is still required. Here, we used this technique and principal component analysis to assess the time course of brain activity during encoding and retrieval in a delayed match to sample task. We also investigated the effects of memory load and duration of the maintenance period on ERP activity. Brain activity was similar during information encoding and retrieval and comprised six temporal factors, which closely matched the latency and scalp distribution of some ERP components: P1, N1, P2, N2, P300 and a slow wave. Changes in memory load modulated task performance and yielded variations in frontal lobe activation. Moreover, the P300 amplitude was smaller in the high than in the low load condition during encoding and retrieval. Conversely, the slow wave amplitude was higher in the high than in the low load condition during encoding, and the same was true for the N2 amplitude during retrieval. Thus, during encoding, memory load appears to modulate the processing resources for context updating and post-categorization processes, and during retrieval it modulates resources for stimulus classification and context updating. Besides, despite the lack of differences in task performance related to duration of the maintenance period, larger N2 amplitude and stronger activation of the left temporal lobe after long than after short maintenance periods were found during information retrieval. Thus, results regarding the duration of maintenance period were complex, and future work is required to test the time-based decay theory predictions.

Diego Pinal

2014-04-01

376

Entanglement boosts quantum turbo codes

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

Wilde, Mark M

2010-01-01

377

Experimental demonstration of a flexible time-domain quantum channel.

We present an experimental realization of a flexible quantum channel where the Hilbert space dimensionality can be controlled electronically. Using electro-optical modulators (EOM) and narrow-band optical filters, quantum information is encoded and decoded in the temporal degrees of freedom of photons from a long-coherence-time single-photon source. Our results demonstrate the feasibility of a generic scheme for encoding and transmitting multidimensional quantum information over the existing fiber-optical telecommunications infrastructure. PMID:25401545

Xing, Xingxing; Feizpour, Amir; Hayat, Alex; Steinberg, Aephraim M

2014-10-20

378

Experimental demonstration of a flexible time-domain quantum channel

We present the first experimental realization of a flexible multidimensional quantum channel where the Hilbert space dimensionality can be controlled electronically. Using electro-optical modulators (EOM) and narrow-band optical filters, quantum information is encoded and decoded in the temporal degrees of freedom of photons from a long-coherence-time single-photon source. Our results demonstrate the feasibility of a generic scheme for encoding and transmitting multidimensional quantum information over the existing fiber-optical telecommunications infrastructure.

Xing, Xingxing; Feizpour, Amir; Hayat, Alex; Steinberg, Aephraim M.

2014-10-01

379

An informationally-complete unification of quantum spacetime and matter

It was known long ago that quantum theory and general relativity, two pillars of modern physics, are in sharp conflict in their foundations. Their fundamental inconsistencies render a consistent theory of quantum gravity the most challenging problem in physics. Here we propose an informationally-complete quantum field theory (ICQFT), which describes elementary particles, their gauge fields and gravity as a trinity without the Hilbert-space inconsistency of Einstein's equation. We then argue that the ICQFT provide a coherent picture and conceptual framework of unifying matter and spacetime. The trinary field is characterized by dual entanglement and dual dynamics. Spacetime-matter entanglement allows us to give a natural explanation of the holographic principle, as well as two conjectures on black-hole states and on a possible candidate to dark matter/energy.

Chen, Zeng-Bing

2014-01-01

380

Distribution of quantum Fisher information in asymmetric cloning machines

An unknown quantum state cannot be copied and broadcast freely due to the no-cloning theorem. Approximate cloning schemes have been proposed to achieve the optimal cloning characterized by the maximal fidelity between the original and its copies. Here, from the perspective of quantum Fisher information (QFI), we investigate the distribution of QFI in asymmetric cloning machines which produce two nonidentical copies. As one might expect, improving the QFI of one copy results in decreasing the QFI of the other copy. It is perhaps also unsurprising that asymmetric phase-covariant cloning outperforms universal cloning in distributing QFI since a priori information of the input state has been utilized. However, interesting results appear when we compare the distributabilities of fidelity (which quantifies the full information of quantum states), and QFI (which only captures the information of relevant parameters) in asymmetric cloning machines. Unlike the results of fidelity, where the distributability of symmetric cloning is always optimal for any d-dimensional cloning, we find that any asymmetric cloning outperforms symmetric cloning on the distribution of QFI for d cloning strategies could be worse than symmetric ones when d > 18.

Xiao, Xing; Yao, Yao; Zhou, Lei-Ming; Wang, Xiaoguang

2014-12-01

381

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

International Nuclear Information System (INIS)

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

382

Quantum Kolmogorov complexity and bounded quantum memory

International Nuclear Information System (INIS)

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

383

Fault-tolerant quantum secret sharing against collective noise

International Nuclear Information System (INIS)

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

384

A quantum limit on the information retrievable from an image

We consider the physical limitations imposed on the information content of an image by the wave and quantum nature of light, when the image is obtained by illuminating a reflecting or transmitting planar object by natural---i.e., fully thermalized---light, or by observation of an object emitting incoherent (thermal) radiation. The discreteness of the degrees of freedom and the statistical properties of thermal radiation are taken into account. We derive the maximum amount of information that can be retrieved from the object. This amount is always finite and is proportional to the area of the object, the solid angle under which the entrance pupil of the receiver is seen from the object, and the time of observation. An explicit expression for the information in the case where the information recorded by the receiver obeys Planck's spectral distribution is obtained. The amount of information per photon of recorded radiation is a universal numerical constant, independent of the parameters of observation.

Levitin, Lev B

2014-01-01

385

Classical Enhancement of Quantum Error-Correcting Codes

We present a general formalism for quantum error-correcting codes that encode both classical and quantum information (the EACQ formalism). This formalism unifies the entanglement-assisted formalism and classical error correction, and includes encoding, error correction, and decoding steps such that the encoded quantum and classical information can be correctly recovered by the receiver. We formally define this kind of quantum code using both stabilizer and symplectic language, and derive the appropriate error-correcting conditions. We give several examples to demonstrate the construction of such codes.

Kremsky, Isaac; Brun, Todd A

2008-01-01

386

Quantum dots in photonic crystals are interesting both as a testbed for fundamental cavity quantum electrodynamics (QED) experiments, as well as a platform for quantum and classical information processing. Quantum dot-photonic crystal cavity QED has been probed both in photoluminescence and coherently, by resonant light scattering from such a system [1]. In the latter case, both intensity and photon statistics of the reflected beam have been analyzed as a function of wavelength, leading to observation of effects such as photon blockade and photon induced tunneling - for the first time in solid state [2]. The system has also been employed to achieve a controlled phase and amplitude modulation between two modes of light at the single photon level [3] - nonlinearity observed so far only in atomic physics systems. These demonstrations lie at the core of a number of proposals for quantum information processing, and could also be employed to build novel devices, such as optical switches controlled at a single photon level. [4pt] [1] Dirk Englund, Andrei Faraon, Ilya Fushman, Nick Stoltz, Pierre Petroff, and Jelena Vuckovic, ``Controlling cavity reflectivity with a single quantum dot," Nature ,ol. 450, No. 7171, pp. 857-861, December 2007[0pt] [2] Andrei Faraon, Ilya Fushman, Dirk Englund, Nick Stoltz, Pierre Petroff, and Jelena Vuckovic, ``Coherent generation of nonclassical light on a chip via photon-induced tunneling and blockade," Nature Physics ,ol. 4, pp. 859 - 863 (2008)[0pt] [3] Ilya Fushman, Dirk Englund, Andrei Faraon, Nick Stoltz, Pierre Petroff, and Jelena Vuckovic, ``Controlled phase shift with a single quantum dot," Science ,ol. 320, number 5877, pp. 769-772 ( 2008)

Vuckovic, Jelena

2009-05-01

387

Correlations in complex nonlinear systems and quantum information theory

International Nuclear Information System (INIS)

The dynamical evolution of classical complex systems such as coupled logistic maps or simple models of lattice gases and cellular automata can result in correlations between distant parts of the system. For the understanding of these systems, it is crucial to develop methods to characterize and quantify these multi-party correlations. On the other hand, the study of correlations between distant particles is also a central problem in the field of quantum information theory. There, correlations are often viewed as a resource and many tools have been developed for their characterization. In this talk, we explore the extent to which the tools from quantum information can be applied to study classical complex systems and whether they allow to study complex systems from a different perspective.

388

Tomita-Takesaki Modular Theory vs. Quantum Information Theory

Comment: 29 pages, LaTeX, this review article is not completed and to be continued. The first goal of writing this topic is just to understand the notion of cyclic and separating vector in von Neumann algebra. The second goal is to apply Tomita-Takesaki modular theory in Quantum Information Theory. All comments are welcome!. arXiv admin note: text overlap with arXiv:0906.3980, arXiv:1012.1417 by other authors

Zhang, Lin; Wu, Junde

2013-01-01

389

Does Considering Quantum Correlations Resolve the Information Paradox?

The absence of consideration of subtle correlations in radiation process is the reason why Hawking's semiclassical analysis is often criticized. There has been speculations that accounting for such quantum correlations would eventually invalidate Hawking's result that black hole evolution is non-unitary. However, it has been recently showed that considering small deviations from Hawking's analysis does not help significantly to bypass the information paradox-- the irreversib...

Roy, Avik; Rahat, Moinul Hossain; Alvi, Mishkat Al; Matin, Md Abdul

2013-01-01

390

Quantum emulation of query extension in information retrieval

An operationalistic scheme, called Melucci metaphor, is suggested representing Information Retrieval as physical measurements with beam of particles playing the role of the flow of retrieved documents. The possibilities of query expansion by extra term are studied from this perspective, when the particles-`docuscles' are assumed to be of classical or quantum nature. It is shown that in both cases the choice of an extra term based on Bayesian belief revision is still valid on...

Zapatrin, Roma?n

2014-01-01

391

One-way information reconciliation schemes of quantum key distribution

Information reconciliation(IR) is a basic step of quantum key distribution(QKD). Classical message interaction is necessary in a practical IR scheme, and large communication complexity has become a bottleneck of QKD. Here we propose a concatenated method of IR scheme which requires only one time one-way communication to achieve any given error rate level. In addition, a QKD scheme with the concatenated IR can work without a special step of the error rate estimation.

Yang, Li

2012-01-01

392

Discord as a quantum resource for bi-partite communication

Coherent interactions that generate negligible entanglement can still exhibit unique quantum behaviour. This observation has motivated a search beyond entanglement for a complete description of all quantum correlations. Quantum discord is a promising candidate. Here, we experimentally demonstrate that under certain measurement constraints, discord between bipartite systems can be consumed to encode information that can only be accessed by coherent quantum interactions. The inability to access this information by any other means allows us to use discord to directly quantify this `quantum advantage'.

Chrzanowski, Helen M.; Gu, Mile; Assad, Syed M.; Symul, Thomas; Modi, Kavan; Ralph, Timothy C.; Vedral, Vlatko; Lam, Ping Koy

2014-12-01

393

Quantum History cannot be Copied

We show that unitarity does not allow cloning of any two points in a ray. This has implication for cloning of the geometric phase information in a quantum state. In particular, the quantum history which is encoded in the geometric phase during cyclic evolution of a quantum system cannot be copied. We also prove that the generalized geometric phase information cannot be copied by a unitary operation. We argue that our result also holds in the consistent history formulation of...

Pati, Arun K.

2005-01-01

394

Quantum information and gravity cutoff in theories with species

International Nuclear Information System (INIS)

We show that lowering of the gravitational cutoff relative to the Planck mass, imposed by black hole physics in theories with N species, has an independent justification from quantum information theory. First, this scale marks the limiting capacity of any information processor. Secondly, by taking into the account the limitations of the quantum information storage in any system with species, the bound on the gravity cutoff becomes equivalent to the holographic bound, and this equivalence automatically implies the equality of entanglement and Bekenstein-Hawking entropies. Next, the same bound follows from quantum cloning theorem. Finally, we point out that by identifying the UV and IR threshold scales of the black hole quasi-classicality in four-dimensional field and high dimensional gravity theories, the bound translates as the correspondence between the two theories. In case when the high dimensional background is AdS, this reproduces the well-known AdS/CFT relation, but also suggests a generalization of the correspondence beyond AdS spaces. In particular, it reproduces a recently suggested duality between a four-dimensional CFT and a flat five-dimensional theory, in which gravity crosses over from four to five dimensional regime in far infrared.

395

We treat secret key extraction when the eavesdropper has correlated quantum states. We propose quantum privacy amplification theorems different from Renner's, which are based on quantum conditional Rényi entropy of order 1 + s. Using those theorems, we derive an exponential rate of decrease for leaked information and the asymptotic equivocation rate, which have not been derived hitherto in the quantum setting.

Hayashi, Masahito

2015-01-01

396

We treat secret key extraction when the eavesdropper has correlated quantum states. We propose quantum privacy amplification theorems different from Renner's, which are based on quantum conditional Rényi entropy of order 1 + s. Using those theorems, we derive an exponential rate of decrease for leaked information and the asymptotic equivocation rate, which have not been derived hitherto in the quantum setting.

Hayashi, Masahito

2014-11-01

397

Informação e teoria quântica / Information and quantum theory

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese Abstract in portuguese A pesquisa em informação quântica sugere uma íntima conexão entre o conceito de informação e a teoria quântica, mas essa conexão envolve nuances cuja análise é o objeto deste trabalho. A sabedoria comum nesse campo divide-se em duas grandes áreas, não excludentes entre si. Há os que são movidos pela [...] possibilidade de uso da teoria quântica em um novo campo, o da computação, independentemente do esclarecimento de seus fundamentos, aqui incluído o conceito de "informação". Alguns consideram que estamos diante de um grande problema conceitual sem resposta satisfatória no momento, enquanto que outros, dentre os que reconhecem a magnitude do problema, têm proposto formulações com a pretensão de solução do problema. Este artigo tem pretensões modestas. Não pretendemos aportar novas soluções ao problema, nem apoiar uma das soluções existentes. Temos a expectativa de através da análise histórico-conceitual do problema mapear as diversas possibilidades, apontando o que nos parecem ser aspectos fortes e fracos nessas possibilidades. Abstract in english Research in quantum information suggests a close connection between information and quantum theory. The aim of this article is to analyze nuances involved in this connection. Scientists in this field are divided into two overlapping camps. Some are motivated only by the use of quantum features to im [...] prove information processing, in spite of concerns about the foundations of the quantum theory, while others recognize deep conceptual problems of this theory, and attempt to solve them. This article has modest ambitions. It aims only to chart, by way of historical and conceptual analysis, the diverse possibilities available, indicating the strengths and weaknesses of each of them.

Olival, Freire Junior; Ileana Maria, Greca.

2013-03-01

398

Unbounded quantum Fisher information in two-path interferometry with finite photon number

International Nuclear Information System (INIS)

The minimum error of unbiased parameter estimation is quantified by the quantum Fisher information in accordance to the Cramér–Rao bound. We indicate that only superposed NOON states by simultaneous measurements can achieve the maximum quantum Fisher information with form 2> for a given photon number distribution by a POVM in linear two-path interferometer phase measurement. We present a series of specified superposed states with infinite quantum Fisher information but with finite average photon numbers. The advantage of this unbounded quantum Fisher information will be beneficial to many applications in quantum technology. (paper)

399

Multi-photon entanglement and applications in quantum information

Energy Technology Data Exchange (ETDEWEB)

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

Schmid, Christian I.T.

2008-05-30

400

Local hidden variable theoretic measure of quantumness of mutual information

Entanglement, a manifestation of quantumness of correlations between the observables of the subsystems of a composite system, and the quantumness of their mutual information are widely studied characteristics of a system of spin-1/2 particles. The concept of quantumness of correlations between the observables of a system is based on incommensurability of the correlations with the predictions of some local hidden variable (LHV) theory. However, the concept of quantumness of mutual information does not invoke the LHV theory explicitly. In this paper, the concept of quantumness of mutual information for a system of two spin-1/2 particles, named A and B, in the state described by the density matrix \\hat{\\rho }^{AB} is formulated by invoking explicitly the LHV theory. To that end, the classical mutual information I(a, b) of the spins is assumed to correspond to the joint probability p(\\epsilon ^A_a;\\epsilon ^B_b) (\\epsilon ^A_a, \\epsilon ^B_b=+/- 1) for the spin A to have the component \\epsilon ^A_a/2 in the direction a and the spin B to have the component \\epsilon ^B_b/2 in the direction b, constructed by invoking the LHV theory. The quantumness of mutual information is then defined as Q_LHV =I_Q(\\hat{\\rho }^AB)-I_LHV where I_Q(\\hat{\\rho }^AB) is the quantum theoretic information content in the state \\hat{\\rho }^AB and the LHV theoretic classical information ILHV is defined in terms of I(a, b) by choosing the directions a, b as follows. The choice of the directions a, b is made by finding the Bloch vectors \\langle \\hat{\\bf S}^A\\rangle and \\langle \\hat{\\bf S}^B\\rangle of the spins A and B where \\hat{\\bf S}^A (\\hat{\\bf S}^B) is the spin vector of spin A (spin B) and \\langle \\hat{P}\\rangle =Tr(\\hat{P}\\hat{\\rho }^{AB}). The directions a and b are taken to be along the Bloch vector of A and B respectively if those Bloch vectors are non-zero. In that case ILHV = I(a, b) and QLHV turns out to be identical with the measurement induced disturbance. If \\langle \\hat{\\bf S}^A\\rangle =\\langle \\hat{\\bf S}^B\\rangle =0, then ILHV is defined to be the maximum of I(a, b) over a and b. The said optimization in this case can be performed analytically exactly and QLHV is then found to be the same as the symmetric discord. If \\langle \\hat{\\bf S}^A\\rangle =0, \\langle \\hat{\\bf S}^B\\rangle \

Puri, R. R.

2014-03-01

401

Towards fast quantum key distribution with quantum frames

We propose and investigate a fibre-based quantum key distribution system, which employs polarization qubits encoded into faint laser pulses. As a novel feature, it allows sending of classical framing information via sequences of strong laser pulses that precede the quantum data. This allows synchronization, sender and receiver identification, and compensation of time-varying birefringence in the communication channel. Furthermore, this method also provides a platform to communicate implementation specific information such as encoding and protocol in view of future optical quantum networks. All optical components can be operated at Gbps rates, which is a first requirement for Mbps secret key rates.

Martinez, Itzel Lucio; Mo, Xiaofan; Hosier, Steve; Tittel, Wolfgang

2008-01-01

402

Integration of Advanced Optics for Trapped Ion Quantum Information Processing

Trapped ion systems are the leading candidate for quantum information processing because many of the critical components have already been demonstrated. Scaling trapped ion systems to large numbers of ions is currently believed possible, but much work remains to prove it. Microfabricated surface ion traps are increasing in popularity for their ease of mass production and their ability to manipulate individual ions and interact arbitrary pairs of ions. Even with the advent of scalable ion traps, detection of an individual ion trapped in a high vacuum poses a challenge. The internal state of the ion chosen for a quantum bit can be measured via exposure to a probe beam that causes one state to scatter light (a "bright" state), but not the other state (a "dark" state). In free space, a single ion acts like a point source that emits in all directions; a standard two inch lens system can only collect about 2% of the light emitted by the ion. Poor light collection results in a high error rate and slow determination of the internal state of the ion. Fast, high fidelity state detection is necessary for quantum error correction and loophole-free Bell experiments at short (less than 100microm) distances, and high efficiency collection is necessary to rapidly interconnect separate quantum computers. We demonstrate state detection fidelities of 99%, 99.856(8)% and 99.915(7) % which correspond to detection times of 10.5, 28.1 and 99.8 us, respectively.

Noek, Rachel M.

403

Entanglement and Quantum Information Transfer in Arrays of Interacting Quantum Systems

This thesis examines some of the more fundamental requirements of a successful quantum computation, namely the ability to transmit quantum information with maximum efficiency, and the creation of entanglement. I focus specifically on neutron entanglement, showing that the spins of two or more distinct neutrons can be measurably entangled by forward-scattering from an isotropic medium. The interpretation of `time' in scattering experiments is also discussed. I present a simple treatment based on the Heisenberg S-matrix, from which it emerges that in certain situations the quantum-mechanical time parameter appearing in the effective time-evolution operator for the spin system has an intuitive physical interpretation. The final part of the thesis deals with quantum information transfer in arrays of permanently coupled dipolar systems. It is shown that spin chains with dipolar couplings offer high fidelity long-distance state transmission, but transfer times in unmodulated chains are unfeasibly long. Possible optimization methods are discussed, concluding with a review of recent achievements in this field.

Avellino, Martina

2009-09-01

404

General quantum phase estimation and calibration of a timepiece in a quantum dot system

We present a physical scheme for implementing quantum phase estimation via weakly coupled double quantum-dot molecules embedded in a microcavity. During the same process of implementation, we can also realize the calibration of a timepiece based on the estimated phase. We use the electron-hole pair states in coupled double quantum-dot molecules to encode quantum information, where the requirement that two quantum dots are exactly identical is not necessary. Our idea can also...

Dong, Ping; Cao, Zhuo-liang

2007-01-01

405

Experimental demonstration of graph-state quantum secret sharing

Distributed quantum communication and quantum computing offer many new opportunities for quantum information processing. Here networks based on highly nonlocal quantum resources with complex entanglement structures have been proposed for distributing, sharing and processing quantum information. Graph states in particular have emerged as powerful resources for such tasks using measurement-based techniques. We report an experimental demonstration of graph-state quantum secret sharing, an important primitive for a quantum network. We use an all-optical setup to encode quantum information into photons representing a five-qubit graph state. We are able to reliably encode, distribute and share quantum information between four parties. In our experiment we demonstrate the integration of three distinct secret sharing protocols, which allow for security and protocol parameters not possible with any single protocol alone. Our results show that graph states are a promising approach for sophisticated multi-layered protoc...

Bell, B A; Herrera-Martí, D A; Marin, A; Wadsworth, W J; Rarity, J G; Tame, M S

2014-01-01

406

International Nuclear Information System (INIS)

We have combined the idea of renormalization group and quantum-information theory. We have shown how the entanglement or concurrence evolve as the size of the system becomes large, i.e., the finite size scaling is obtained. Moreover, we introduce how the renormalization-group approach can be implemented to obtain the quantum-information properties of a many-body system. We have obtained the concurrence as a measure of entanglement, its derivatives and their scaling behavior versus the size of system for the one-dimensional Ising model in transverse field. We have found that the derivative of concurrence between two blocks each containing half of the system size diverges at the critical point with the exponent, which is directly associated with the divergence of the correlation length

407

Hardware-Efficient Autonomous Quantum Memory Protection

We propose to encode a quantum bit of information in a superposition of coherent states of an oscillator, with four different phases. Our encoding in a single cavity mode, together with a protection protocol, significantly reduces the error rate due to photon loss. This protection is ensured by an efficient quantum error correction scheme employing the nonlinearity provided by a single physical qubit coupled to the cavity. We describe in detail how to implement these operations in a circuit quantum electrodynamics system. This proposal directly addresses the task of building a hardware-efficient quantum memory and can lead to important shortcuts in quantum computing architectures.

Leghtas, Zaki; Kirchmair, Gerhard; Vlastakis, Brian; Schoelkopf, Robert J.; Devoret, Michel H.; Mirrahimi, Mazyar

2013-09-01

408

Energy Technology Data Exchange (ETDEWEB)

We consider the problem of encoding classical information into unknown qudit states belonging to any basis, of a maximal set of mutually unbiased bases, by one party and then decoding by another party who has perfect knowledge of the basis. Working with qudits of prime dimensions, we point out a no-go theorem that forbids 'shift' operations on arbitrary unknown states. We then provide the necessary conditions for reliable encoding/decoding.

Shaari, J.S. [Faculty of Science, International Islamic University of Malaysia (IIUM), Jalan Gombak, 53100 Kuala Lumpur (Malaysia); Wahiddin, M.R.B. [Faculty of Science, International Islamic University of Malaysia (IIUM), Jalan Gombak, 53100 Kuala Lumpur (Malaysia); Cyberspace Security Laboratory, MIMOS Berhad, Technology Park Malaysia, 57000 Kuala Lumpur (Malaysia); Mancini, S. [Dipartimento di Fisica, Universita di Camerino, 62032 Camerino (Italy)], E-mail: stefano.mancini@unicam.it

2008-03-17

409

We consider the problem of encoding classical information into unknown qudit states belonging to any basis, of a maximal set of mutually unbiased bases, by one party and then decoding by another party who has perfect knowledge of the basis. Working with qudits of prime dimensions, we point out a no-go theorem that forbids shift operations on arbitrary unknown states. We then provide the necessary conditions for reliable encoding/decoding.

Shaari, J S; Mancini, S

2008-01-01

410

We consider the problem of encoding classical information into unknown qudit states belonging to any basis, of a maximal set of mutually unbiased bases, by one party and then decoding by another party who has perfect knowledge of the basis. Working with qudits of prime dimensions, we point out a no-go theorem that forbids ‘shift’ operations on arbitrary unknown states. We then provide the necessary conditions for reliable encoding/decoding.

Shaari, J. S.; Wahiddin, M. R. B.; Mancini, S.

2008-03-01

411

International Nuclear Information System (INIS)

We consider the problem of encoding classical information into unknown qudit states belonging to any basis, of a maximal set of mutually unbiased bases, by one party and then decoding by another party who has perfect knowledge of the basis. Working with qudits of prime dimensions, we point out a no-go theorem that forbids 'shift' operations on arbitrary unknown states. We then provide the necessary conditions for reliable encoding/decoding

412

Few-Qubit Magnetic Resonance Quantum Information Processors: Simulating Chemistry and Physics

We review recent progress made in quantum information processing (QIP) which can be applied in the simulation of quantum systems and chemical phenomena. The review is focused on quantum algorithms which are useful for quantum simulation of chemistry and advances in nuclear magnetic resonance (NMR) and electron spin resonance (ESR) QIP. Discussions also include a number of recent experiments demonstrating the current capabilities of the NMR QIP for quantum simulation and prospects for spin-based implementations of QIP.

Criger, Ben; Baugh, Jonathan

2012-01-01

413

A quantum theory with possible leakage of information

International Nuclear Information System (INIS)

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

414

Towards scaling up trapped ion quantum information processing

International Nuclear Information System (INIS)

Recent theoretical advances have identified several computational algorithms that can be implemented utilizing quantum information processing (QIP), which gives an exponential speedup over the corresponding (known) algorithms on conventional computers. QIP makes use of the counter-intuitive properties of quantum mechanics, such as entanglement and the superposition principle. Unfortunately it has so far been impossible to build a practical QIP system that outperforms conventional computers. Atomic ions confined in an array of interconnected traps represent a potentially scalable approach to QIP. All basic requirements have been experimentally demonstrated in one and two qubit experiments. The remaining task is to scale the system to many qubits while minimizing and correcting errors in the system. While this requires extremely challenging technological improvements, no fundamental roadblocks are currently foreseen.

415

Quantum Information Processing by NMR using strongly coupled spins

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

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

2003-01-01

416

Microfabrication techniques for trapped ion quantum information processing

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

Britton, Joe

2010-01-01

417

Quadrature Uncertainty and Information Entropy of Quantum Elliptical Vortex States

We study the quadrature uncertainty of the quantum elliptical vortex state using the associated Wigner function. Deviations from the minimum uncertainty states were observed due to the absence of the Gaussian nature. In our study of the entropy, we noticed that with increasing vorticity, entropy increases for both the modes. We further observed that, there exists an optimum value of ellipticity which gives rise to maximum entanglement of the two modes of the quantum elliptical vortex states. A further increase in ellipticity reduces the entropy thereby resulting in a loss of information carrying capacity. We check the validity of the entropic inequality relations, namely the subaddivity and the Araki-Lieb inequality. The later was satisfied only for a very small range of the ellipticity of the vortex while the former seemed to be valid at all values.

Banerji, Anindya; Singh, Ravindra Pratap; Chowdhury, Saurav; Bandyopadhyay, Abir

2013-01-01

418

Quadrature uncertainty and information entropy of quantum elliptical vortex states

International Nuclear Information System (INIS)

We study the quadrature uncertainty of the quantum elliptical vortex state using the associated Wigner function. Deviations from the minimum uncertainty states were observed due to the absence of Gaussianity. We further observed that there exists an optimum value of ellipticity which gives rise to the maximum entanglement of the two modes of the quantum elliptical vortex states. In our study of entropy, we noticed that with increasing vorticity, entropy increases for both the modes. A further increase in ellipticity reduces the entropy thereby resulting in a loss of information carrying capacity. We check the validity of the entropic inequality relations, namely the subaddivity and the Araki–Lieb inequality. The latter was satisfied only for a very small range of the ellipticity of the vortex, while the former seemed to be valid at all values. (paper)

419

Quantum mutual information of an entangled state propagating through a fast-light medium

Although it is widely accepted that classical information cannot travel faster than the speed of light in vacuum, the behavior of quantum correlations and quantum information propagating through actively-pumped fast-light media has not been studied in detail. To investigate this behavior, we send one half of an entangled state of light through a gain-assisted fast-light medium and detect the remaining quantum correlations. We show that the quantum correlations can be advance...

Clark, Jeremy B.; Glasser, Ryan T.; Glorieux, Quentin; Vogl, Ulrich; Li, Tian; Jones, Kevin M.; Lett, Paul D.

2014-01-01

420

Quantum limits to the flow of information and entropy

International Nuclear Information System (INIS)

The quantum limits to information flow are explored developing the central concept of a medium comprising several channels through which the information flows. In each channel there is an inequality between information flow (dI/dt) and energy flow (dE/dt) such that (dI/dt)222) a relationship which, though speculated on before or derived for only a restricted class of systems, is proven here for a wide range of systems. Applications are made to the energy cost of computing and to the maximum rate of cooling, (dQ/dt), which in any one channel is (dQ/dt)2sub(B)T2/(3h/2?). (author)

421

Information dynamics and open systems classical and quantum approach

This book aims to present an information-theoretical approach to thermodynamics and its generalisations On the one hand, it generalises the concept of `information thermodynamics' to that of `information dynamics' in order to stress applications outside thermal phenomena On the other hand, it is a synthesis of the dynamics of state change and the theory of complexity, which provide a common framework to treat both physical and nonphysical systems together Both classical and quantum systems are discussed, and two appendices are included to explain principal definitions and some important aspects of the theory of Hilbert spaces and operator algebras The concept of higher-order temperatures is explained and applied to biological and linguistic systems The theory of open systems is presented in a new, much more general form Audience This volume is intended mainly for theoretical and mathematical physicists, but also for mathematicians, experimental physicists, physical chemists, theoretical biologists, communicat...

Ingarden, R S; Ohya, M

1997-01-01

422

Does Considering Quantum Correlations Resolve the Information Paradox?

The absence of consideration of subtle correlations in radiation process is the reason why Hawking's semiclassical analysis is often criticized. There has been speculations that accounting for such quantum correlations would eventually invalidate Hawking's result that black hole evolution is non-unitary. However, it has been recently showed that considering small deviations from Hawking's analysis does not help significantly to bypass the information paradox-- the irreversible loss of information in the evolution of a black hole. This paper generalizes the above result by parametrization of the amount of deviation from Hawking's analysis that is required to resolve the paradox. With a more rigorous and non-trivial bound than that appeared in literature before, it is confirmed that information retrieval indeed requires `not-so-small' deviation from the Hawking state. In connection to this result, a previously proposed toy model of black hole evaporation is generalized in this paper, and it is showed that allow...

Roy, Avik; Alvi, Mishkat Al; Matin, Md Abdul

2013-01-01

423

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

Maurya, Ajay K.; Mishra, Manoj K.; Prakash, Hari

2011-01-01

424

Quantum Information Science with Single Atoms and Photons

Cavity quantum electrodynamics (QED) offers powerful possibilities for the deterministic control of atom-photon interactions quantum by quantum [1]. Indeed, modern experiments in cavity QED have achieved the exceptional circumstance of strong coupling, for which single quanta can profoundly impact the dynamics of the atom-cavity system. The diverse accomplishments of this field set the stage for advances into yet broader frontiers in quantum information science for which cavity QED offers unique advantages, including the creation of quantum networks [2]. The primary technical challenge on the road toward such scientific goals is the need to trap and localize atoms within a cavity in a setting suitable for strong coupling. Two separate experiments in our group have achieved significant milestones in this quest, namely the real-time trapping and tracking of single atoms in cavity QED [3-5]. In one experiment, an atom is trapped by an auxiliary field that functions as a far-detuned dipole-force trap (FORT) [3,4], with trap lifetime 3s, which should be compared to the nanosecond time scale for internal dynamics of the atom-cavity system. In a second experiment, we rely upon light forces at the single-photon level to trap a single atom within the cavity mode [5]. As illustrated by the movies available at http://www.its.caltech.edu/ qoptics/atomorbits/, these reconstructions reveal single atoms bound in orbit by the mechanical forces associated with single photons, and realize a new form of microscopy. Over the duration of the observation, the sensitivity is near the standard quantum limit for sensing the motion of a Cesium atom. This work is supported by the NSF, by the Caltech MURI for Quantum Networks administered by the ARO, and by the ONR. 1. For a review, see contributions in the Special Issue of Physica Scripta T76 (1998). 2. J. I. Cirac, S. J. van Enk, P. Zoller, H. J. Kimble, and H. Mabuchi, Physica Scripta T76, 223 (1998). 3. J. Ye, D. W. Vernooy, and H. J. Kimble, Phys. Rev. Lett. 83, 4987 (1999). 4. J. McKeever, J.R. Buck, A.D. Boozer, A. Kuzmich, H.-C.Nagerl, D.M. Stamper-Kurn, H.J. Kimble, quant-ph/0211013. 5. C. J. Hood, T. W. Lynn, A. C. Doherty, A.S. Parkins, and H. J. Kimble, Science 287, 1447 (2000).

Kimble, H. J.

2003-03-01

425

Accessible information and optimal strategies for real symmetrical quantum sources

We study the problem of optimizing the Shannon mutual information for sources of real quantum states i.e. sources for which there is a basis in which all the states have only real components. We consider in detail the sources ${\\cal E}_M$ of $M$ equiprobable qubit states lying symmetrically around the great circle of real states on the Bloch sphere and give a variety of explicit optimal strategies. We also consider general real group-covariant sources for which the group act...

Sasaki, Masahide; Barnett, Stephen M.; Jozsa, Richard; Osaki, Masao; Hirota, Osamu

1998-01-01

426

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

Khrennikov, Andrei

2010-01-01

427

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

Energy Technology Data Exchange (ETDEWEB)

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 |{xi}){sup I}{sub A} and |{eta}){sup I}{sub B}, 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 {Lambda}-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 (F{sub av} {>=} 0.999 for |{alpha}|{sup 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.

Mishra, Manoj K; Maurya, Ajay K; Prakash, Hari, E-mail: manoj.qit@gmail.com, E-mail: ajaymaurya.2010@gmail.com, E-mail: prakash_hari123@rediffmail.com [Physics Department, University of Allahabad, Allahabad (India)

2011-06-14

428

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

International Nuclear Information System (INIS)

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

429

Measurement-device-independent quantum key distribution (MDI-QKD) with weak coherent sources has been widely and meticulously analyzed. However, the analysis for MDI-QKD with spontaneous-parametric-down-conversion sources (SPDCS) is incomplete. In this paper, we propose two passive decoy protocols suitable for parameter estimation in MDI-QKD using SPDCS. By accounting for practical parameters of SPDCS with thermal distribution, we present an investigation on the performances of MDI-QKD under the active three-intensity decoy protocol, the passive two-intensity decoy protocol, and the modified passive three-intensity protocol, respectively. Phase randomization, inherently a prerequisite for decoy protocol, is taken into consideration for evaluating the overall quantum bit gain and quantum bit error rate. The numerical simulations show that the MDI-QKD using SPDCS with practical decoy protocols can be demonstrated to be comparable to the asymptotical case and has apparent superiority both in transmission distance and key generation rate compared to the one using weak coherent sources. Our results also indicate that the modified passive three-intensity decoy protocol can perform better than the active three-intensity decoy protocol in MDI-QKD using practical SPDCS.

Zhou, Chun; Bao, Wan-Su; Chen, Wei; Li, Hong-Wei; Yin, Zhen-Qiang; Wang, Yang; Han, Zheng-Fu

2013-11-01

430

Quantum Measurements and Information-Theoretical Restrictions in Observable Algebras Formalism

Information-Theoretical restrictions on the information transfer are applied to Quantum Measurements. For the measurement of quantum object S by information system O this restrictions are calculated in Algebraic QM formalism as the inference map to the (sub)algebra of O observables.

Mayburov, S.

2005-01-01

431

Optimization problems associated with the interaction of linked particles are at the heart of polymer science, protein folding and other important problems in the physical sciences. In this review we explain how to recast these problems as constraint satisfaction problems such as linear programming, maximum satisfiability, and pseudo-boolean optimization. By encoding problems this way, one can leverage substantial insight and powerful solvers from the computer science community which studies constraint programming for diverse applications such as logistics, scheduling, artificial intelligence, and circuit design. We demonstrate how to constrain and embed lattice heteropolymer problems using several strategies. Each strikes a unique balance between number of constraints, complexity of constraints, and number of variables. In addition, each strategy has distinct advantages and disadvantages depending on problem size and available resources. Finally, we show how to reduce the locality of couplings in these energ...

Babbush, Ryan; O'Gorman, Bryan; Macready, William; Aspuru-Guzik, Alán

2012-01-01

432

A novel microfluidic approach is developed to prepare multicolor QDs-encoded core-shell microparticles with precise and various barcode and enhanced stability performance. With the protection of the hydrogel shell, the leakage of QDs is avoided and the fluorescent stability is enhanced greatly. By embedding different QDs into different cores, no interaction between different QDs existed and the fluorescence spectrum of each kind of QDs can be recorded, respectively. Compared with QDs mixtures in a single particle, it is unnecessary to separate the emissions of QDs in different colors, and deconvolution algorithms are not needed. Therefore, it still maintains precise coding even if QDs with approximate emission wavelengths are used. PMID:24956221

Chen, Yang; Dong, Peng-Fei; Xu, Jian-Hong; Luo, Guang-Sheng

2014-07-22

433

Arbitrary Waveform Generator for Quantum Information Processing with Trapped Ions

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

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

2013-01-01

434

Encoding, symbolic dynamics, cryptography and C++ implementations

International Nuclear Information System (INIS)

We investigate three techniques which can be used to encode information using certain types of chaotic maps and provide implementations in C++. One of the three, the variable bit length encoding technique, is a new technique for encoding information using transient chaos. We describe all three techniques, including variable bit length encoding, in detail. Finally we investigate the use of the variable bit length encoding technique as a cryptographic scheme

435

Stronger no-cloning, no-signalling and conservation of quantum information

It is known that the stronger no-cloning theorem and the no-deleting theorem taken together provide the permanence property of quantum information. Also, it is known that the violation of the no-deletion theorem would imply signalling. Here, we show that the violation of the stronger no-cloning theorem could lead to signalling. Furthermore, we prove the stronger no-cloning theorem from the conservation of quantum information. These observations imply that the permanence property of quantum information is connected to the no-signalling and the conservation of quantum information.

Chakrabarty, I; Adhikari, S K; Chakrabarty, Indranil; Adhikari, Satyabrata

2006-01-01

436

Information geometric modeling of scattering induced quantum entanglement

Energy Technology Data Exchange (ETDEWEB)

We present an information geometric analysis of entanglement generated by an s-wave scattering between two Gaussian wave packets. We conjecture that the pre- and post-collisional quantum dynamical scenarios related to an elastic head-on collision are macroscopic manifestations emerging from microscopic statistical structures. We then describe them by uncorrelated and correlated Gaussian statistical models, respectively. This allows us to express the entanglement strength in terms of scattering potential and incident particle energies. Furthermore, we show how the entanglement duration can be related to the scattering potential and incident particle energies. Finally, we discuss the connection between entanglement and complexity of motion. -- Highlights: ? Information geometric characterization of scattering induced entanglement. ? Connection between purity, scattering potential and incident particle energies. ? Connection between complexity of motion and entanglement.

Kim, D.-H. [Institute for the Early Universe, Ewha Womans University, Seoul 120-750 (Korea, Republic of); International Institute for Theoretical Physics and Mathematics Einstein-Galilei, via Santa Gonda 14, 59100 Prato (Italy); Ali, S.A. [International Institute for Theoretical Physics and Mathematics Einstein-Galilei, via Santa Gonda 14, 59100 Prato (Italy); Department of Physics, State University of New York at Albany, 1400 Washington Avenue, Albany, NY 12222 (United States); Department of Arts and Sciences, Albany College of Pharmacy and Health Sciences, 106 New Scotland Avenue, Albany, NY 12208 (United States); Cafaro, C., E-mail: carlo.cafaro@unicam.it [School of Science and Technology, Physics Division, University of Camerino, I-62032 Camerino (Italy); Mancini, S. [School of Science and Technology, Physics Division, University of Camerino, I-62032 Camerino (Italy)

2011-07-18

437

On convex optimization problems in quantum information theory

Convex optimization problems arise naturally in quantum information theory, often in terms of minimizing a convex function over a convex subset of the space of hermitian matrices. In most cases, finding exact solutions to these problems is usually impossible. As inspired by earlier investigations into the relative entropy of entanglement (REE) (Miranowicz and Ishizaka 2008 Phys. Rev. A 78 032310), we introduce a general method to solve the converse problem rather than find explicit solutions. That is, given a matrix in a convex set, we determine a family of convex functions that are minimized at this point. This method allows us find explicit formulae for the REE and the Rains bound, two well-known upper bounds on the distillable entanglement, and yields interesting information about these quantities, such as the fact that they coincide in the case where at least one subsystem of a multipartite state is a qubit.

Girard, Mark W.; Gour, Gilad; Friedland, Shmuel

2014-12-01

438

We introduce quantum information engines that extract work from quantum states and a single thermal reservoir. They may operate under three general conditions—(1) unitarily steered evolution (US), driven by a restricted set of available Hamiltonians; (2) irreversible thermalization (IT), and (3) isothermal relaxation (IR)—and hence are called USITIR machines. They include novel engines without traditional feedback control mechanisms, as well as versions which also include them. Explicit constructions of USITIR engines are presented for one- and two-qubit states and their maximum extractable work is computed, which is optimal. Optimality is achieved when the notions of controllable thermalizability and density matrix controllability are fulfilled. Then many-body extensions of USITIR engines are also analyzed and conditions for optimal work extraction are identified. When they are not met, we measure their lack of optimality by means of newly defined uncontrollable entropies, which are explicitly computed for some selected examples. This includes cases of distinguishable and indistinguishable particles.

Diaz de la Cruz, J. M.; Martin-Delgado, M. A.

2014-03-01

439

Storing quantum information for 30 seconds in a nanoelectronic device.

The spin of an electron or a nucleus in a semiconductor naturally implements the unit of quantum information-the qubit. In addition, because semiconductors are currently used in the electronics industry, developing qubits in semiconductors would be a promising route to realize scalable quantum information devices. The solid-state environment, however, may provide deleterious interactions between the qubit and the nuclear spins of surrounding atoms, or charge and spin fluctuations arising from defects in oxides and interfaces. For materials such as silicon, enrichment of the spin-zero (28)Si isotope drastically reduces spin-bath decoherence. Experiments on bulk spin ensembles in (28)Si crystals have indeed demonstrated extraordinary coherence times. However, it remained unclear whether these would persist at the single-spin level, in gated nanostructures near amorphous interfaces. Here, we present the coherent operation of individual (31)P electron and nuclear spin qubits in a top-gated nanostructure, fabricated on an isotopically engineered (28)Si substrate. The (31)P nuclear spin sets the new benchmark coherence time (>30?s with Carr-Purcell-Meiboom-Gill (CPMG) sequence) of any single qubit in the solid state and reaches >99.99% control fidelity. The electron spin CPMG coherence time exceeds 0.5?s, and detailed noise spectroscopy indicates that-contrary to widespread belief-it is not limited by the proximity to an interface. Instead, decoherence is probably dominated by thermal and magnetic noise external to the device, and is thus amenable to further improvement. PMID:25305745

Muhonen, Juha T; Dehollain, Juan P; Laucht, Arne; Hudson, Fay E; Kalra, Rachpon; Sekiguchi, Takeharu; Itoh, Kohei M; Jamieson, David N; McCallum, Jeffrey C; Dzurak, Andrew S; Morello, Andrea

2014-12-01

440

Storing quantum information for 30 seconds in a nanoelectronic device

The spin of an electron or a nucleus in a semiconductor naturally implements the unit of quantum information—the qubit. In addition, because semiconductors are currently used in the electronics industry, developing qubits in semiconductors would be a promising route to realize scalable quantum information devices. The solid-state environment, however, may provide deleterious interactions between the qubit and the nuclear spins of surrounding atoms, or charge and spin fluctuations arising from defects in oxides and interfaces. For materials such as silicon, enrichment of the spin-zero 28Si isotope drastically reduces spin-bath decoherence. Experiments on bulk spin ensembles in 28Si crystals have indeed demonstrated extraordinary coherence times. However, it remained unclear whether these would persist at the single-spin level, in gated nanostructures near amorphous interfaces. Here, we present the coherent operation of individual 31P electron and nuclear spin qubits in a top-gated nanostructure, fabricated on an isotopically engineered 28Si substrate. The 31P nuclear spin sets the new benchmark coherence time (>30?s with Carr–Purcell–Meiboom–Gill (CPMG) sequence) of any single qubit in the solid state and reaches >99.99% control fidelity. The electron spin CPMG coherence time exceeds 0.5?s, and detailed noise spectroscopy indicates that—contrary to widespread belief—it is not limited by the proximity to an interface. Instead, decoherence is probably dominated by thermal and magnetic noise external to the device, and is thus amenable to further improvement.

Muhonen, Juha T.; Dehollain, Juan P.; Laucht, Arne; Hudson, Fay E.; Kalra, Rachpon; Sekiguchi, Takeharu; Itoh, Kohei M.; Jamieson, David N.; McCallum, Jeffrey C.; Dzurak, Andrew S.; Morello, Andrea

2014-12-01

441

A quantum information perspective of fermionic quantum many-body systems

Energy Technology Data Exchange (ETDEWEB)

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

Kraus, Christina V.

2009-11-02

442

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

Hayashi, Masahito

2012-01-01

443

We report the implementation of a 3-qubit quantum error correction code (QECC) on a quantum information processor realized by the magnetic resonance of Carbon nuclei in a single crystal of Malonic Acid. The code corrects for phase errors induced on the qubits due to imperfect decoupling of the magnetic environment represented by nearby spins, as well as unwanted evolution under the internal Hamiltonian. We also experimentally demonstrate sufficiently high fidelity control to implement two rounds of quantum error correction. This is a demonstration of state-of-the-art control in solid state nuclear magnetic resonance, a leading test-bed for the implementation of quantum algorithms.

Moussa, Osama; Ryan, Colm A; Laflamme, Raymond

2011-01-01

444

Fidelity enhancement by logical qubit encoding.

We demonstrate coherent control of two logical qubits encoded in a decoherence free subspace (DFS) of four dipolar-coupled protons in an NMR quantum information processor. A pseudopure fiducial state is created in the DFS, and a unitary logical qubit entangling operator evolves the system to a logical Bell state. The four-spin molecule is partially aligned by a liquid crystal solvent, which introduces strong dipolar couplings among the spins. Although the system Hamiltonian is never fully specified, we demonstrate high fidelity control over the logical degrees of freedom. In fact, the DFS encoding leads to higher fidelity control than is available in the full four-spin Hilbert space. PMID:18233272

Henry, Michael K; Ramanathan, Chandrasekhar; Hodges, Jonathan S; Ryan, Colm A; Ditty, Michael J; Laflamme, Raymond; Cory, David G

2007-11-30

445

Fidelity enhancement by logical qubit encoding

We demonstrate coherent control of two logical qubits encoded in a decoherence free subspace (DFS) of four dipolar-coupled protons in an NMR quantum information processor. A pseudo-pure fiducial state is created in the DFS, and a unitary logical qubit entangling operator evolves the system to a logical Bell state. The four-spin molecule is partially aligned by a liquid crystal solvent, which introduces strong dipolar couplings among the spins. Although the system Hamiltonian is never fully specified, we demonstrate high fidelity control over the logical degrees of freedom. In fact, the DFS encoding leads to higher fidelity control than is available in the full four-spin Hilbert space.

Henry, Michael K; Hodges, Jonathan S; Ryan, Colm A; Ditty, Michael J; Laflamme, Raymond; Cory, David G