Showing papers on "Quantum channel published in 1997"
TL;DR: In this article, the authors demonstrated the feasibility of quantum teleportation over arbitrary distances of the state of a quantum system by using a measurement such that the second photon of the entangled pair acquires the polarization of the initial photon.
Abstract: Quantum teleportation — the transmission and reconstruction over arbitrary distances of the state of a quantum system — is demonstrated experimentally. During teleportation, an initial photon which carries the polarization that is to be transferred and one of a pair of entangled photons are subjected to a measurement such that the second photon of the entangled pair acquires the polarization of the initial photon. This latter photon can be arbitrarily far away from the initial one. Quantum teleportation will be a critical ingredient for quantum computation networks.
4,232 citations
TL;DR: Previous results about the classical information capacity of a noiseless quantum-mechanical communication channel are extended to situations in which the final signal states are mixed states, that is, to channels with noise.
Abstract: This paper extends previous results about the classical information capacity of a noiseless quantum-mechanical communication channel to situations in which the final signal states are mixed states, that is, to channels with noise.
1,159 citations
TL;DR: An upper limit is given to the amount of quantum information that can be transmitted reliably down a noisy, decoherent quantum channel and a class of quantum error- correcting codes are presented that allow the information transmitted to attain this limit.
Abstract: An upper limit is given to the amount of quantum information that can be transmitted reliably down a noisy, decoherent quantum channel using the high-probability states of quantum sources. A class of quantum error-correcting codes is presented that allows the information transmitted to attain this limit. The result is a quantum analog of Shannon's bound and code for the noisy classical channel [C. E. Shannon and W. Weaver, The Mathematical Theory of Communication (University of Illinois Press, Chicago, 1948)].
802 citations
TL;DR: In this article, a scheme for protecting quantum states from both independent and cooperative decoherence is proposed by pairing each qubit (two-state quantum system) with an ancilla qubit and encoding the states of the qubits into corresponding coherence-preserving states of qubit pairs.
Abstract: A scheme for protecting quantum states from both independent and cooperative decoherence is proposed. The scheme operates by pairing each qubit (two-state quantum system) with an ancilla qubit and by encoding the states of the qubits into corresponding coherence-preserving states of qubit pairs. In this scheme, amplitude damping (loss of energy) as well as phase damping (dephasing) is prevented by a strategy called ``free-Hamiltonian elimination.'' We further extend the scheme to include quantum gate operations and show that loss and decoherence during such operations can also be prevented.
450 citations
Book•
31 Mar 1997
TL;DR: The aim of this book is to provide a Discussion of Information Thermodynamics and its Applications to Open Systems, as well as Specific Applications to Quantum Entropy and Quantum Channel.
Abstract: Preface. 1. Introduction. 2. Classical Entropy. 3. Quantum Entropy and Quantum Channel. 4. Information Dynamics. 5. Information Thermodynamics I. 6. Information Thermodynamics II. 7. Open Systems. 8. Fractals with Information. Appendix 1. Appendix 2. Bibliography. Index.
226 citations
TL;DR: In this paper, the dynamical equations of quantum mechanics are rewritten in the form of dynamical equation for the measurable, positive marginal distribution of the shifted, rotated, and squeezed quadrature introduced in the so-called "symplectic tomography" and a comparison with the well-known quasi-probabilities approach is given.
Abstract: The dynamical equations of quantum mechanics are rewritten in the form of dynamical equations for the measurable, positive marginal distribution of the shifted, rotated, and squeezed quadrature introduced in the so-called “symplectic tomography”. Then the possibility of a purely classical description of a quantum system as well as a reinterpretation of the quantum measurement theory is discussed and a comparison with the well-known quasi-probabilities approach is given. Furthermore, an analysis of the properties of this marginal distribution, which contains all the quantum information, is performed in the framework of classical probability theory. Finally, examples of the harmonic oscillator's states dynamics are treated.
218 citations
TL;DR: In this article, the authors considered the transmission of a quantum state between two distant atoms via photons and defined a noisy quantum channel which includes systematic errors as well as errors due to coupling to the environment, and presented a protocol that allows one to accomplish ideal transmission by repeating the transfer operation as many times as needed.
Abstract: We consider transmission of a quantum state between two distant atoms via photons. Based on a quantum-optical realistic model, we define a noisy quantum channel which includes systematic errors as well as errors due to coupling to the environment. We present a protocol that allows one to accomplish ideal transmission by repeating the transfer operation as many times as needed.
188 citations
TL;DR: Wavelength division multiplexing is used to add a secure quantum key distribution channel to a conventional 1.2 Gbit/s data channel operating over 28 km of installed fibre in BT's London and East Anglia multiservice network testbed (LEANET).
Abstract: Wavelength division multiplexing (WDM) is used to add a secure quantum key distribution channel (/spl lambda/=1300 nm) to a conventional 1.2 Gbit/s data channel (/spl lambda//spl sim/1550 nm) operating over 28 km of installed fibre in BT's London and East Anglia multiservice network testbed (LEANET). Error-free operation of the data channel is demonstrated with no degradation of the quantum channel performance.
170 citations
TL;DR: The von Neumann capacity of quantum channels is proposed, which is a quantum-mechanical extension of the Shannon capacity and reverts to it in the classical limit, and an extended Hamming bound is derived that is consistent with that capacity.
Abstract: We discuss the capacity of quantum channels for information transmission and storage. Quantum channels have dual uses: they can be used to transmit known quantum states which code for classical information, and they can be used in a purely quantum manner, for transmitting or storing quantum entanglement. We propose here a definition of thevon Neumanncapacity of quantum channels, which is a quantum-mechanical extension of the Shannon capacity and reverts to it in the classical limit. As such, the von Neumann capacity assumes the role of a classical or quantum capacity depending on the usage of the channel. In analogy to the classical construction, this capacity is defined as the maximumvon Neumann mutual entropyprocessed by the channel, a measure which reduces to the capacity for classical information transmission through quantum channels ~the ‘‘Kholevo capacity’’ ! when known quantum states are sent. The quantum mutual entropy fulfills all basic requirements for a measure of information, and observes quantum data-processing inequalities. We also derive a quantum Fano inequality relating the quantum loss of the channel to the fidelity of the quantum code. The quantities introduced are calculated explicitly for the quantum depolarizing channel. The von Neumann capacity is interpreted within the context of superdense coding, and an extended Hamming bound is derived that is consistent with that capacity. @S1050-2947~97!04511-3#
167 citations
TL;DR: In this paper, the authors derive a relationship between two different notions of fidelity (entanglement fidelity and average fidelity) for a completely depolarizing quantum channel, which gives rise to a quantum analog of the MacWilliams identities in classical coding theory.
Abstract: We derive a relationship between two different notions of fidelity (entanglement fidelity and average fidelity) for a completely depolarizing quantum channel. This relationship gives rise to a quantum analog of the MacWilliams identities in classical coding theory. These identities relate the weight enumerator of a code to the one of its dual and, with linear programming techniques, provide a powerful tool to investigate the possible existence of codes. The same techniques can be adapted to the quantum case. We give examples of their power.
130 citations
Patent•
15 Aug 1997TL;DR: In this article, an interferometric system for quantum cryptography is described. But the system does not need alignment or balancing between the arms of the interferometers. And it does not support plug-and-play stations.
Abstract: System and method of communicating a key between two stations (1, 2) using an interferometric system for quantum cryptography. The method comprises the step of sending at least two light pulses over a quantum channel (3) and detecting the interference created by said pulses in one station (Bob). The interfering pulses run over the same arms of said interferometer, but in another sequence, so that they are delayed when they run over said quantum channel. The pulses are reflected by at least Faraday mirrors (14, 16, 22) at the ends of said quantum channel, so as to cancel polarization effects. Advantages: the system does not need alignment or balancing between the arms of the interferometers. Plug and play stations (1, 2).
Book•
01 Jan 1997
TL;DR: This volume brings together scientists working in the interdisciplinary fields of quantum communication science and technology on topics including quantum information theory, quantum computing, stochastic processes and filtering, and quantum measurement theory.
Abstract: Speeches of Organizers -- I. Quantum Communication and Information Theory -- Information Theoretic Interpretations of von Neumann Entropy -- Quantum Information Theory, the Entropy Bound, and Mathematical Rigor in Physics -- Classical and Quantum Information Transmission and Interactions -- Bounds of the Accessible Information under the Influence of Thermal Noise -- Techniques for Bounding Quantum Correlations -- Relation between Channel Capacity and Quantum Minimax Decision in Quantum Information Theory -- Optimum Binary Signal Detections for Error Probability and Mutual Information -- Entanglement-Enhanced Classical Communication on a Noisy Quantum Channel -- Security against Eavesdropping in Quantum Cryptography -- A Linear Programming Approach to Attainable Cramer-Rao Type Bounds -- Non-Commutative Extension of Information Geometry II -- Wavelets and Information-Preserving Transformations -- On the Realization of Received Quantum State Control by Unitary Transformation -- Properties of Quantum Cryptography Based on Orthogonal States: Goldenberg and Vaidman Scheme -- Computation of Mutual Entropy in Quantum Amplifier Processes -- II. Quantum Computing -- Quantum Computing and Decoherence in Quantum Optical Systems -- Unitary Dynamics for Quantum Codewords -- Quantum Error Correction with Imperfect Gates -- Eliminating the Effects of Spontaneous Emission in Quantum Computations with Cold Trapped Ions -- Integrability and Computability in Simulating Quantum Systems -- Slowing Down the Decoherence of Quantum Bits -- Quantum Capacity of Noisy Quantum Channel -- III. Quantum Measurement Theory and Statistical Physics -- On Covariant Instruments in Quantum Measurement Theory -- Quantum State Reduction and the Quantum Bayes Principle -- On the Quantum Theory of Direct Detection -- Homodyning as Universal Detection -- Resolutions of the Identity in Terms of Line Integrals of Coherent States and Their Use for Quantum State Engineering -- Unitary Control Process for Quantum Optimum Detection -- Quantum Zeno Effect and “Domination” of the Temporal Evolution of Quantum Systems -- Physical Interpretation of Optimum Quantum Detection Operators -- Generalised Uncertainties for Quantum Signal Processing -- Optimal Quantum Measurements for Phase Estimation in Interferometry -- Hypersensitivity to Perturbation: An Information-Theoretical Characterization of Classical and Quantum Chaos -- A Topological Approach to Phase of Quantum Chaos -- Subdynamics through Time Scales and Scattering Maps in Quantum Field Theory -- Time-Ordered Wick Exponential and Quantum Stochastic Differential Equations -- “Nonlocal” Interference Effects in Frequency Domain -- Quantum Stochastic Systems in Terms of Non-Equilibrium Thermo Field Dynamics -- Considerations in the Time-Energy Uncertainty Relation from the Viewpoint of Hypothesis Testing -- An Open System Approach to Quantum Computers -- IV. Quantum Optics -- Atom Lasers -- Measurement of Quantum Phase Distribution by Projection Synthesis -- Quantum Optical Phase -- Single-Shot Adaptive Measurements of the Phase of a Single Mode Field -- Amplitude Squeezing of the Fundamental Field by Means of Traveling-Wave Quasi-Phasematched Second-Harmonic Generation in a LiNbO3 Waveguide -- Quantum Noise Reduction of the Pump Field in an Optical Parametric Oscillator -- Optical Measurements of Weak Absorption beyond Shot-Noise Limit -- Decoherence and Relaxation of Two Strongly Coupled Spin 1/2 Atoms -- Spatial Correlation Effects in Multi—Transverse Mode Lasers -- Generation of Nonclassical Photons in a Josephson-Junction Cavity -- Polarization-Squeezed Light Generation in a Second Order Nonlinear Medium -- Reconstruction of External Forces in Quantum Noises of Parametric Measuring System with Dissipation -- Squeezed State Generation in the Process of Light Interaction with a System of Free Electrons -- Diode Structure for Generation of Sub-Poissonian Photon Fluxes by Stark-Effect Blockade of Emissions -- Control of Quantum States in Nonstationary Cavity QED Systems -- A Simulation of Pulsed Squeezing in Short Optical Fiber Loop Mirror -- Quantum Properties of the Traveling-Wave x(2) Process: Theory, Experiments, and Applications.
TL;DR: In this article, it was shown that the optimal classical information transmission rate can be achieved only by signaling alphabets consisting of nonorthogonal quantum states, which is not the case for noisy quantum channels.
Abstract: I demonstrate that, rather unexpectedly, there exist noisy quantum channels for which the optimal classical information transmission rate is achieved only by signaling alphabets consisting of nonorthogonal quantum states. {copyright} {ital 1997} {ital The American Physical Society}
TL;DR: It is shown that, for certain noisy quantum channels, such entangled transmissions increase the receiver’s probability of a correct inference, above what can be achieved by product state transmissions.
Abstract: We consider the problem of sending a single classical bit through a noisy quantum channel, when two uses of the channel are available as a resource. For a quantum channel, the possibility exists of entangling the channel inputs, which of course cannot be done with a classical channel. We show that, for certain noisy quantum channels, such entangled transmissions increase the receiver’s probability of a correct inference, above what can be achieved by product state transmissions.
TL;DR: In this paper, the necessary and sufficient conditions for an ideal quantum operation to be reversible by a unitary operation are derived, which generalize recent work on reversible measurements by Mabuchi and Zoller [Phys. Rev. Lett. 76, 3108].
Abstract: Quantum operations provide a general description of the state changes allowed by quantum mechanics. Simple necessary and sufficient conditions for an ideal quantum operation to be reversible by a unitary operation are derived in this paper. These results generalize recent work on reversible measurements by Mabuchi and Zoller [Phys. Rev. Lett. 76, 3108 (1996)]. Quantum teleportation can be understood as a special case of the problem of reversing quantum operations. We characterize completely teleportation schemes of the type proposed by Bennett et al. [Phys. Rev. Lett. 70, 1895 (1993)].
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TL;DR: Bounds for the reliability function of a quantum pure state channel are given and an alternative proof of the coding theorem for quantum noiseless channel is suggested, which would make no use of the notion of typical subspace.
Abstract: The reliability function gives the rate of exponential convergence to zero of the error probability in a communication channel. In this paper bounds for the reliability function of a quantum pure state channel are given, reminiscent of the corresponding classical bounds. This in particular suggests an alternative proof of the coding theorem for quantum noiseless channel, which would make no use of the notion of typical subspace. Example of binary quantum channel is considered in some detail.
01 Jan 1997
TL;DR: The quantum capacity for purely quantum channels is studied and the supremum of the quantum mutual entropy over a certain set of states with a fixed quantum channel is the quantum capacity of the channel.
Abstract: In quantum communication theory, the quantum mutual entropy [4] is an important tool to analyse the efficiency of information transmission. It is the amount of information correctly transmitted from an input system to an output system through a quantum channel. The supremum of the quantum mutual entropy over a certain set of states with a fixed quantum channel is the quantum capacity of the channel. The capacity for quantum systems has been discussed in several papers, like [1,2,12]. In [8], we studied the quantum capacity for purely quantum channels.
TL;DR: In this paper, it was shown that superadditivity of the classical capacity of a quantum channel appears even for the third extension of a binary-pure-state-input channel.
TL;DR: In this article, it is shown that superadditivity appears even in the third extended coding of the simplest binary input channel, and a physical implementation of this channel is indicated based on cavity QED techniques.
Abstract: When classical information is sent through a quantum channel of nonorthogonal states, there is a possibility that transmittable classical information exceeds a channel capacity in a single use of the initial channel by extending it into multi-product channel. In this paper, it is shown that this remarkable feature of a quantum channel, so-called superadditivity, appears even in as low as the third extended coding of the simplest binary input channel. A physical implementation of this channel is indicated based on cavity QED techniques.
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TL;DR: The purpose of this work is to extend the result of previous papers to quantum channels with additive constraints onto the input signal, by showing that the capacity of such channel is equal to the supremum of the entropy bound with respect to all apriori distributions satisfying the constraint.
Abstract: The purpose of this work is to extend the result of previous papers quant-ph/9611023, quant-ph/9703013 to quantum channels with additive constraints onto the input signal, by showing that the capacity of such channel is equal to the supremum of the entropy bound with respect to all apriori distributions satisfying the constraint. We also make an extension to channels with continuous alphabet. As an application we prove the formula for the capacity of the quantum Gaussian channel with constrained energy of the signal, establishing the asymptotic equivalence of this channel to the semiclassical photon channel. We also study the lower bounds for the reliability function of the pure-state Gaussian channel.
15 Dec 1997-Philosophical transactions - Royal Society. Mathematical, physical and engineering sciences
TL;DR: In this article, it was shown explicitly how quantum teleportation utilizes this feature and how the randomness of the individual quantum event prohibits instantaneous communication, and how to use quantum teleportation for instantaneous communication.
Abstract: A two–state quantum system (a qubit) can carry one bit of classical information. If two bits are not encoded into two qubits separately, but only into their joint properties, entangled states result. It is shown explicitly how quantum teleportation utilizes this feature and how the randomness of the individual quantum event prohibits instantaneous communication.
TL;DR: In this paper, the authors generalized the notion of a quantum state to the case of a single pre-and post-selected quantum system, described by a two-state vector, and achieved the measurement by coupling the quantum system to a pre-selected protected device yielding a nonhermitian effective Hamiltonian.
Abstract: A recent result about measurability of a quantum state of a single quantum system is generalized to the case of a single pre- and post-selected quantum system, described by a two-state vector. The protection required for such measurement is achieved by coupling the quantum system to a pre- and post-selected protected device yielding a nonhermitian effective Hamiltonian.
TL;DR: In this article, an efficient coding circuit for the perfect quantum-error correction of a single quantum bit ~qubit! against arbitrary onequbit errors within a five-qubit code was given.
Abstract: An efficient coding circuit is given for the perfect quantum-error correction of a single quantum bit ~qubit! against arbitrary one-qubit errors within a five-qubit code. The circuit presented employs a double ‘‘classical’’ code, i.e., one for bit flips and one for phase shifts. An implementation of this coding circuit on an ion-trap quantum computer is described that requires 26 laser pulses. Another circuit is presented requiring only 24 laser pulses, making it an efficient protection scheme against arbitrary one-qubit errors. In addition, the performances of two error-correction schemes, one based on the quantum Zeno effect and the other using standard methods, are compared. The quantum Zeno error correction scheme is found to fail completely for a model of noise based on phase diffusion. @S1050-2947~97!03902-4#
TL;DR: In this paper, a condition of integrability on the quantum current operators of Ug( §>l(2)), which is a deformation of the corresponding condition for §/(2), was given.
Abstract: For the current realization of the affine quantum groups, a simple comultiplication for the quantum current operators was given by Drinfeld. With this comultiplication, we study the zeros and poles of the quantum current operators and present a condition of integrability on the quantum current operators of Ug(§>l(2)), which is a deformation of the corresponding condition for §/(2). We also present the results about the zeros and poles of the quantum current operators of Uq(%l(n)).
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TL;DR: In this article, it was shown that the analytic structure of these C*-algebraic quantum groups can be pulled down to the algebraic quantum group and that such groups give rise to C* -algebraIC quantum groups in the sense of Masuda, Nakagami & Woronowicz.
Abstract: A. Van Daele introduced and investigated so-called algebraic quantum groups. We proved that such algebraic quantum groups give rise to C*-algebraic quantum groups in the sense of Masuda, Nakagami & Woronowicz. We prove in this paper that the analytic structure of these C*-algebraic quantum groups can be pulled down to the algebraic quantum group.
TL;DR: In this article, the entanglement fidelity and the fidelity of quantum information transmitted in noisy channels is investigated. But the fidelity is not a generalization of the entangling fidelity.
Abstract: The fidelity and the entanglement fidelity are two important quantities in describing the transmission of quantum information through (possibly noisy) quantum channels. In this paper these two quantities are calculated for different kinds of state which are transmitted in noisy channels. A general equation is obtained for these fidelities. Some examples are given to illustrate the general result and possible applications of these results to quantum cryptography and teleportation via noisy channels are discussed.
01 Jan 1997
TL;DR: In this article, the authors present a quantum information theory that allows for the consistent description of quantum entanglement, which is based entirely on density matrices, rather than probability distributions, for describing quantum ensembles.
Abstract: We present a quantum information theory that allows for the consistent description of quantum entanglement. It parallels classical (Shannon) information theory but is based entirely on density matrices, rather than probability distributions, for the description of quantum ensembles. We find that, unlike in Shannon theory, conditional entropies can be negative when considering quantum entangled systems such as an Einstein-Podolsky-Rosen pair, which leads to a violation of well-known bounds of classical information theory. Negative quantum entropy can be traced back to “conditional” density matrices which admit eigenvalues larger than unity. A straightforward definition of mutual quantum entropy, or “mutual entanglement,” can also be constructed using a “mutual” density matrix. Such a unified information-theoretic description of classical correlation and quantum entanglement clarifies the link between them: the latter can be viewed as “super-correlation” which can induce classical correlation when considering a ternary or larger system.
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TL;DR: In this article, it was shown that the conductance quantization of a quantum point contact is quantized in units of $2e^2/h$ and this quantization is destroyed by a non-adiabatic scatterer in the point contact, due to backscattering.
Abstract: It is known that the conductance of a quantum point contact is quantized in units of $2e^2/h$ and this quantization is destroyed by a non-adiabatic scatterer in the point contact, due to backscattering. Recently, it was shown [Phys. Rev. Lett. 71, 137 (1993)] that taking many non-adiabatic scatterers periodically in a quantum channel, the quantization can be recovered. We study this conductance quantization of a periodic system in the presence of a strong defect. A periodic arrangement of double-stubs give remarkable quantization of conductance. A periodic arrangement of double-constrictions also gives a very good quantization only when the separation between the constrictions is small. We conclude that conductance quantization of a periodically modulated channel is robust.
IBM1
TL;DR: In this paper, the authors survey known upper and lower bounds on the capacity of quantum channels, alone or assisted by one- or two-way classical communication, to transmit intact quantum states, and relation of this capacity on the one hand to classical capacity and on the other to the quantitative theory of entanglement of pure and mixed states.
Abstract: Quantum information theory has recently been enlarged to include the use of quantum channels for the transmission not only of classical information but also of intact quantum states. We survey known upper and lower bounds on the capacity of quantum channels, alone or assisted by one- or two-way classical communication, to transmit intact quantum states, and relation of this capacity on the one hand to classical capacity and on the other to the quantitative theory of entanglement of pure and mixed states.