Showing papers in "Physical Review A in 1999"
TL;DR: This work shows how GHZ states can be used to split quantum information into two parts so that both parts are necessary to reconstruct the original qubit.
Abstract: Secret sharing is a procedure for splitting a message into several parts so that no subset of parts is sufficient to read the message, but the entire set is. We show how this procedure can be implemented using Greenberger-Horne-Zeilinger (GHZ) states. In the quantum case the presence of an eavesdropper will introduce errors so that his presence can be detected. We also show how GHZ states can be used to split quantum information into two parts so that both parts are necessary to reconstruct the original qubit.
2,789 citations
TL;DR: In this article, it was shown that there is a trade-off between the entanglement between two qubits and the pair of qubits, and that for any values of the tangles satisfying the corresponding equality, one can find a quantum state consistent with those values.
Abstract: Consider three qubits A, B, and C which may be entangled with each other We show that there is a trade-off between A's entanglement with B and its entanglement with C This relation is expressed in terms of a measure of entanglement called the "tangle," which is related to the entanglement of formation Specifically, we show that the tangle between A and B, plus the tangle between A and C, cannot be greater than the tangle between A and the pair BC This inequality is as strong as it could be, in the sense that for any values of the tangles satisfying the corresponding equality, one can find a quantum state consistent with those values Further exploration of this result leads to a definition of the "three-way tangle" of the system, which is invariant under permutations of the qubits
1,913 citations
TL;DR: In this paper, it was shown that there is a finite gap between the mutual information obtainable by a joint measurement on these states and a measurement in which only local actions are permitted.
Abstract: We exhibit an orthogonal set of product states of two three-state particles that nevertheless cannot be reliably distinguished by a pair of separated observers ignorant of which of the states has been presented to them, even if the observers are allowed any sequence of local operations and classical communication between the separate observers. It is proved that there is a finite gap between the mutual information obtainable by a joint measurement on these states and a measurement in which only local actions are permitted. This result implies the existence of separable superoperators that cannot be implemented locally. A set of states are found involving three two-state particles that also appear to be nonmeasurable locally. These and other multipartite states are classified according to the entropy and entanglement costs of preparing and measuring them by local operations.
957 citations
TL;DR: In this article, a two-particle quantum entanglement protocol for secret sharing and splitting was proposed. But the secrecy sharing protocol must be carefully designed in order to detect eavesdropping or a dishonest participant.
Abstract: We show how a quantum secret sharing protocol, similar to that of Hillery, Buzek, and Berthiaume (Los Alamos e-print archive quant-ph/9806063), can be implemented using two-particle quantum entanglement, as available experimentally today. We also discuss in some detail how both two- and three-particle protocols must be carefully designed in order to detect eavesdropping or a dishonest participant. We also discuss the extension of a multiparticle entanglement secret sharing and splitting scheme toward a protocol so that m of n persons with $ml~n$ can retrieve the secret.
861 citations
TL;DR: In this article, the authors prove a direct relation between the optimal fidelity of teleportation and the maximal singlet fraction attainable by trace-preserving local quantum and classical communication (LQCC) action.
Abstract: We prove a theorem on direct relation between the optimal fidelity ${f}_{\mathrm{max}}$ of teleportation and the maximal singlet fraction ${F}_{\mathrm{max}}$ attainable by means of trace-preserving local quantum and classical communication (LQCC) action. For a given bipartite state acting on ${C}^{d}\ensuremath{\bigotimes}{C}^{d}$ we have ${f}_{\mathrm{max}}{=(F}_{\mathrm{max}}d+1)/(d+1)$. We assume completely general teleportation scheme (trace preserving LQCC action over the pair and the third particle in unknown state). The proof involves the isomorphism between quantum channels and a class of bipartite states. We also exploit the technique of $U\ensuremath{\bigotimes}{U}^{*}$ twirling states (random application of unitary transformation of the above form) and the introduced analogous twirling of channels. We illustrate the power of the theorem by showing that any bound entangled state does not provide better fidelity of teleportation than for the purely classical channel. Subsequently, we apply our tools to the problem of the so-called conclusive teleportation, then reduced to the question of optimal conclusive increasing of singlet fraction. We provide an example of state for which Alice and Bob have no chance to obtain perfect singlet by LQCC action, but still singlet fraction arbitrarily close to unity can be obtained with nonzero probability. We show that a slight modification of the state has a threshold for singlet fraction, which cannot be exceeded anymore.
815 citations
TL;DR: In this paper, Horodecki et al. introduced a criterion of separability that relates the structures of the total density matrix and its reductions, and showed that any state violating the criterion can be distilled by a suitable generalization of the two-qubit protocol that distills any inseparable twoqubit state.
Abstract: We analyze the problem of distillation of entanglement of mixed states in higher-dimensional compound systems. Employing the positive maps method [M. Horodecki et al., Phys. Lett. A 223, 1 (1996)] we introduce and analyze a criterion of separability that relates the structures of the total density matrix and its reductions. We show that any state violating the criterion can be distilled by suitable generalization of the two-qubit protocol that distills any inseparable two-qubit state. In particular, this means that any state $\ensuremath{\varrho}$ of two N-level systems with $〈{\ensuremath{\psi}}_{+}|\ensuremath{\varrho}|{\ensuremath{\psi}}_{+}〉g1/N$ can be distilled $({\ensuremath{\psi}}_{+}$ is the singlet state generalized to higher dimension). The criterion also singles out all the states that can be distilled by a class of protocols. The proof involves construction of the family of states that are invariant under transformation $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\varrho}}U\ensuremath{\bigotimes}{U}^{*}\ensuremath{\varrho}{U}^{\ifmmode\dagger\else\textdagger\fi{}}\ensuremath{\bigotimes}{U}^{*\ifmmode\dagger\else\textdagger\fi{}},$ where U is a unitary transformation and the asterisk denotes complex conjugation. The states are related to the depolarizing channel generalized to the nonbinary case.
762 citations
TL;DR: In this paper, coherent atomic oscillations between two weakly coupled Bose-Einstein condensates are discussed, where the weak link is provided by a laser barrier in a (possibly asymmetric) double-well trap or by Raman coupling between two Condensates in different hyperfine levels.
Abstract: We discuss the coherent atomic oscillations between two weakly coupled Bose-Einstein condensates. The weak link is provided by a laser barrier in a (possibly asymmetric) double-well trap or by Raman coupling between two condensates in different hyperfine levels. The boson Josephson junction (BJJ) dynamics is described by the two-mode nonlinear Gross-Pitaevskii equation that is solved analytically in terms of elliptic functions. The BJJ, being a neutral, isolated system, allows the investigations of dynamical regimes for the phase difference across the junction and for the population imbalance that are not accessible with superconductor Josephson junctions (SJJ's). These include oscillations with either or both of the following properties: (i) the time-averaged value of the phase is equal to $\ensuremath{\pi} (\ensuremath{\pi}$-phase oscillations); (ii) the average population imbalance is nonzero, in states with macroscopic quantum self-trapping. The (nonsinusoidal) generalization of the SJJ ac and plasma oscillations and the Shapiro resonance can also be observed. We predict the collapse of experimental data (corresponding to different trap geometries and the total number of condensate atoms) onto a single universal curve for the inverse period of oscillations. Analogies with Josephson oscillations between two weakly coupled reservoirs of ${}^{3}\mathrm{He}\ensuremath{-}B$ and the internal Josephson effect in ${}^{3}\mathrm{He}\ensuremath{-}A$ are also discussed.
728 citations
TL;DR: A scheme is presented that allows entanglement purification over arbitrary long channels and tolerates errors on the percent level and requires a polynomial overhead in time, and an overhead in local resources that grows only logarithmically with the length of the channel.
Abstract: We study the use of entanglement purification for quantum communication over long distances. For distances much longer than the coherence length of a corresponding noisy quantum channel, the fidelity of transmission is usually so low that standard purification methods are not applicable. It is possible, however, to divide the channel into shorter segments that are purified separately and then connected by the method of entanglement swapping. This method can be much more efficient than schemes based on quantum error correction, as it makes explicit use of two-way classical communication. An important question is how the noise, introduced by imperfect local operations (that constitute the protocols of purification and the entanglement swapping), accumulates in such a compound channel, and how it can be kept below a certain noise level. To treat this problem, we first study the applicability and the efficiency of entanglement purification protocols in the situation of imperfect local operations. We then present a scheme that allows entanglement purification over arbitrary long channels and tolerates errors on the percent level. It requires a polynomial overhead in time, and an overhead in local resources that grows only logarithmically with the length of the channel.
660 citations
TL;DR: A quantum key distribution scheme in which small phase and amplitude modulations of cw light beams carry the key information and the presence of EPR-type correlations provides the quantum protection.
Abstract: We propose a quantum cryptographic scheme in which small phase and amplitude modulations of cw light beams carry the key information. The presence of Einstein-Podolsky-Rosen type correlations provides the quantum protection.
551 citations
TL;DR: It is shown that for any number of oracle lookups up to about {pi}/4thinsp{radical} (N) , Grover's quantum searching algorithm gives the maximal possible probability of finding the desired element.
Abstract: I show that for any number of oracle lookups up to about $\ensuremath{\pi}/4\sqrt{N},$ Grover's quantum searching algorithm gives the maximal possible probability of finding the desired element. I explain why this is also true for quantum algorithms which use measurements during the computation. I also show that unfortunately quantum searching cannot be parallelized better than by assigning different parts of the search space to independent quantum computers.
549 citations
TL;DR: In this article, the authors proposed a scheme to create distant entangled atomic states based on driving two or more atoms with a weak laser pulse, so that the probability that two atoms are excited is negligible.
Abstract: We propose a scheme to create distant entangled atomic states. It is based on driving two (or more) atoms with a weak laser pulse, so that the probability that two atoms are excited is negligible. If the subsequent spontaneous emission is detected, the entangled state is created. We have developed a model to analyze the fidelity of the resulting state as a function of the dimensions and location of the detector, and the motional properties of the atoms.
TL;DR: In this paper, robustness is defined as the minimal amount of mixing with locally prepared states which washes out all entanglement, and quantifies the endurance of entanglements against noise and jamming.
Abstract: In the quest to completely describe entanglement in the general case of a finite number of parties sharing a physical system of finite-dimensional Hilbert space an entanglement magnitude is introduced for its pure and mixed states: robustness. It corresponds to the minimal amount of mixing with locally prepared states which washes out all entanglement. It quantifies in a sense the endurance of entanglement against noise and jamming. Its properties are studied comprehensively. Analytical expressions for the robustness are given for pure states of two-party systems, and analytical bounds for mixed states of two-party systems. Specific results are obtained mainly for the qubit-qubit system (qubit denotes quantum bit). As by-products local pseudomixtures are generalized, a lower bound for the relative volume of separable states is deduced, and arguments for considering convexity a necessary condition of any entanglement measure are put forward.
TL;DR: In this paper, the authors proposed a method to solve the PDE problem in the context of the PhysRevA journal, which can be found at http://prola.aps.org/ Copyright American Physical Society DOI : 10.1103/PhysRevA.59.4249
Abstract: Original article can be found at: http://prola.aps.org/ Copyright American Physical Society DOI : 10.1103/PhysRevA.59.4249
TL;DR: In this article, a quantum telecloning process combining quantum teleportation and optimal quantum cloning from one input to M outputs is presented, which relies on the establishment of particular multiparticle entangled states, which function as multiuser quantum information channels.
Abstract: A quantum telecloning process combining quantum teleportation and optimal quantum cloning from one input to M outputs is presented. The scheme relies on the establishment of particular multiparticle entangled states, which function as multiuser quantum information channels. The entanglement structure of these states is analyzed and shown to be crucial for this type of information processing.
TL;DR: In this paper, the authors present a formulation of feedback in quantum systems in which the best estimates of the dynamical variables are obtained continuously from the measurement record, and fed back to control the system.
Abstract: We present a formulation of feedback in quantum systems in which the best estimates of the dynamical variables are obtained continuously from the measurement record, and fed back to control the system. We apply this method to the problem of cooling and confining a single quantum degree of freedom, and compare it to current schemes in which the measurement signal is fed back directly in the manner usually considered in existing treatments of quantum feedback. Direct feedback may be combined with feedback by estimation, and the resulting combination, performed on a linear system, is closely analogous to classical linear-quadratic-Gaussian control theory with residual feedback.
TL;DR: In this article, the authors investigated the possibility of making complete Bell measurements on a product Hilbert space of two two-level bosonic systems, and they restricted their tools to linear elements, such as beam splitters and phase shifters, delay lines and electronically switched linear elements.
Abstract: In this paper we investigate the possibility of making complete Bell measurements on a product Hilbert space of two two-level bosonic systems. We restrict our tools to linear elements, such as beam splitters and phase shifters, delay lines and electronically switched linear elements, photodetectors, and auxiliary bosons. As a result we show that with these tools a never failing Bell measurement is impossible.
TL;DR: In this article, a pump-supercontinuum-probe (PSCP) spectroscopy with femtosecond time resolution was developed theoretically and experimentally, and it was shown that the supercontinuum can be described as a single chirped pulse.
Abstract: Pump--supercontinuum-probe (PSCP) spectroscopy with femtosecond time resolution is developed theoretically and experimentally. The connection to previous theoretical results on nonchirped probing is established. It is experimentally shown that the supercontinuum can be described as a single chirped pulse. A key problem of the technique---the precise time correction of transient spectra---is solved by monitoring the nonresonant electronic response from a pure solvent (liquids) or from a transparent substrate (solid films). This allows for an adequate characterization of the supercontinuum, in particular, for directly measuring the spectral dependence of the pump-probe cross correlation. For 50-fs pump pulses, a theoretical estimate gives an accuracy for the time correction of 10 fs, which is typically \ensuremath{\approx}1/30 of the supercontinuum pulse duration. Hence a time resolution of 10--20 fs can be experimentally realized. Contributions to the nonresonant transient signal from high-frequency Raman excitations and from low-frequency impulsive-stimulated Raman processes are discussed. The PSCP technique is illustrated by results from experiments with fused silica and several common solvents and with a chromophore in solution.
TL;DR: In this article, the authors proposed a method to solve the PDE problem in the context of physical physics, which is known as PRA-PRA-DEV (PhysRevA.59.2468).
Abstract: Original article can be found at: http://pra.aps.org/ Copyright American Physical Society DOI : 10.1103/PhysRevA.59.2468
TL;DR: In this article, the authors show how macroscopically distinct quantum superposition states (Schrodinger cat states) may be used as logical qubit encodings for the correction of spontaneous emission errors.
Abstract: We show how macroscopically distinct quantum superposition states (Schrodinger cat states) may be used as logical qubit encodings for the correction of spontaneous emission errors. Spontaneous emission causes a bit flip error, which is easily corrected by a standard error correction circuit. The method works arbitrarily well as the distance between the amplitudes of the superposed coherent states increases. [S1050-2947(99)06503-8].
TL;DR: In this paper, the shape of an ultrashort excitation pulse can be tailored to give a desired probability amplitude amplitude for two-photon and multiphoton transitions in atomic cesium.
Abstract: Multiphoton transitions can be reached by many routes through a continuum of virtual levels. We show that the transition probability of two-photon and multiphoton processes can be controlled by tailoring the shape of an ultrashort excitation pulse, so that the many paths leading to the final state interfere to give a desired probability amplitude. We analyze the effect of pulse shapes on N-photon absorption as well as on Raman transitions. We show theoretically that certain tailored dark pulses do not excite the system at all, while other shaped pulses induce transitions as effectively as transform limited pulses, even when their peak amplitudes are greatly reduced. These results are confirmed experimentally for two-photon transitions in atomic cesium. @S1050-2947~99!00808-2#
TL;DR: In this article, a universal technique for quantum-state estimation based on the maximum-likelihood method is presented, which provides a positive-definite estimate for the density matrix from a sequence of measurements performed on identically prepared copies of the system.
Abstract: We present a universal technique for quantum-state estimation based on the maximum-likelihood method. This approach provides a positive-definite estimate for the density matrix from a sequence of measurements performed on identically prepared copies of the system. The method is versatile and can be applied to multimode radiation fields as well as to spin systems. The incorporation of physical constraints, which is natural in the maximum-likelihood strategy, leads to a substantial reduction of statistical errors. Numerical implementation of the method is based on a particular form of the Gauss decomposition for positive-definite Hermitian matrices. PACS number~s!: 03.67.2a, 03.65.Bz In quantum mechanics, the achievable information on a physical system is encoded into the density matrix % ˆ , which allows one to evaluate all possible expectation values through the Born statistical rule ^O ˆ &5Tr(% ˆO ˆ). In order to obtain full information on a quantum system we need to estimate its density matrix. In principle, this can be accomplished by successive measurements on repeated identical preparations of the same system. With a proper choice of the measurements, and after collecting a suitably large number of data, we can arrive at a reliable knowledge of the quantum state of the system.
TL;DR: In this paper, the authors investigated the purification of entangled states by local actions using a variant of entanglement swapping and showed that there exists a measure of entenglement which is conserved in this type of purification procedure.
Abstract: We investigate the purification of entangled states by local actions using a variant of entanglement swapping We show that there exists a measure of entanglement which is conserved in this type of purification procedure @S1050-2947~99!06807-9# PACS number~s!: 03672a The resource of entanglement @1# has many useful applications in quantum information processing, such as secret key distribution @2#, teleportation @3#, and dense coding @4# Polarization entangled photons have been used to demonstrate both dense coding @5# and teleportation @6# in the laboratory Teleportation has also been realized using pathentangled photons @7# and entangled electromagnetic field modes @8# Accompanying the practical applications of entanglement are some useful schemes for entanglement manipulation which may help in the distribution of entanglement between distant parties One such scheme is entanglement swapping @9,10#, which enables one to entangle two quantum systems that have never interacted directly with each other; we have discussed how this may be used in constructing a quantum telephone exchange @10# Recently, entanglement swapping has been demonstrated experimentally @11# There exists yet another useful manipulation of entanglement in which local actions and classical communication are used by two distant parties to distill a certain number of shared Bell states from a larger number of shared but less entangled states When the initial shared but less entangled states are pure, this manipulation is termed as entanglement concentration @12,13#, while for the more general case of the initial shared states being mixed, the process is termed as entanglement purification or distillation @14,15# The importance of such a scheme in the distribution of entanglement is obvious as Bell pairs are essential for the implementation of quantum communication schemes with perfect fidelity Curiously, such an important procedure remains to be realized in an experiment In this paper, we will show that a simple variant of the entanglement swapping scheme can be viewed as a type of entanglement concentration procedure and has a physical realization with polarization entangled photons Moreover, we show that there exists a certain measure of entanglement which remains conserved on average in this type of entanglement concentration Note that in this paper we will often use the terms ‘‘entanglement concentration’’ and ‘‘entanglement purification’’ in an interchangeble manner, though what we demonstrate is, in the strict sense, only the concentration of pure shared entanglement
TL;DR: All incoherent as well as 2- and 3-qubit coherent eavesdropping strategies on the 6 state protocol of quantum cryptography are classified and it is argued that by doing so, Eve gains only a negligibly small additional information.
Abstract: All incoherent as well as 2- and 3-qubit coherent eavesdropping strategies on the six-state protocol of quantum cryptography are classified. For a disturbance of $1/6$, the optimal incoherent eavesdropping strategy reduces to the universal quantum cloning machine. Coherent eavesdropping cannot increase Eve's Shannon information, neither on the entire string of bits, nor on the set of bits received undisturbed by Bob. However, coherent eavesdropping can increase as well Eve's Renyi information as her probability of guessing correctly all bits. The case that Eve delays the measurement of her probe until after the public discussion on error correction and privacy amplification is also considered. It is argued that by doing so, Eve gains only negligibly small additional information.
TL;DR: It turns out that a related argument can be used to give an even stronger bound on 2-locally distillable entanglement, and this bound is not additive in general.
Abstract: The best bound known on 2-locally distillable entanglement is that of Vedral and Plenio, involving a certain measure of entanglement based on relative entropy. It turns out that a related argument can be used to give an even stronger bound; we give this bound, and examine some of its properties. In particular, and in contrast to the earlier bounds, the new bound is not additive in general. We give an example of a state for which the bound fails to be additive, as well as a number of states for which the bound is additive.
TL;DR: In this paper, a large increase in atomic absorption due to coherent interaction with resonant radiation is predicted for a closed transition between two degenerate atomic levels verifying the total angular momentum of the ground and the excited levels, respectively.
Abstract: A large increase in atomic absorption due to coherent interaction with resonant radiation is predicted for a closed transition between two degenerate atomic levels verifying $0l{F}_{g}l{F}_{e}{(F}_{g}$ and ${F}_{e}$ are the total angular momentum of the ground and the excited levels, respectively). In good agreement with the theoretical prediction, a total absorption enhancement by a factor 1.7 was obtained on the ${D}_{2}$ line of ${}^{85}\mathrm{Rb}\mathrm{}$ in a vapor cell experiment.
TL;DR: In this article, a theoretical formulation for nonadiabatic quantum dynamics on coupled potential-energy surfaces is proposed, where the problem of a classical treatment of discrete quantum degrees of freedom (DoF) such as electronic states is bypassed by transforming the discrete quantum variables to continuous variables, and the mapping approach is composed of two steps: an exact quantum-mechanical transformation of discrete onto continuous DoF and a standard semiclassical treatment of the resulting dynamical problem.
Abstract: A theoretical formulation is outlined that allows us to extend the semiclassical Van Vleck--Gutzwiller formulation to the description of nonadiabatic quantum dynamics on coupled potential-energy surfaces. In this formulation the problem of a classical treatment of discrete quantum degrees of freedom (DoF) such as electronic states is bypassed by transforming the discrete quantum variables to continuous variables. The mapping approach thus consists of two steps: an exact quantum-mechanical transformation of discrete onto continuous DoF (the ``mapping'') and a standard semiclassical treatment of the resulting dynamical problem. Extending previous work [G. Stock and M. Thoss, Phys. Rev. Lett. 78, 578 (1997)], various possibilities for obtaining a mapping from discrete to continuous DoF are investigated, in particular the Holstein-Primakoff transformation, Schwinger's theory of angular momentum [in Quantum Theory of Angular Momentum, edited by L. C. Biedenharn and H. V. Dam (Academic, New York, 1965)], and the spin-coherent-state representation. Although all these representations are exact on the quantum-mechanical level, the accuracy of their semiclassical evaluation is shown to differ considerably. In particular, it is shown that a generalization of Schwinger's theory appears to be the only transformation that provides an exact description of a general N-level system within a standard semiclassical evaluation. Exploiting the connection between spin-coherent states and Schwinger's representation for a two-level system, furthermore, a semiclassical initial-value representation of the corresponding spin-coherent-state propagator is derived. Although this propagator represents an approximation, its appealing numerical features make it a promising candidate for the semiclassical description of large molecular systems with many DoF. Adopting various spin-boson-type models (i.e., a two-level system coupled to a single or many DoF), computational studies are presented for Schwinger's and the spin-coherent-state representation, respectively. The performance of the semiclassical approximation in the case of regular and chaotic classical dynamics as well as for multimode electronic relaxation dynamics is discussed in some detail.
TL;DR: In this article, the authors predict the possibility of sharp, high contrast resonances in the optical response of a broad class of systems, wherein interference effects are generated by coherent perturbation or interaction of dark states.
Abstract: We predict the possibility of sharp, high-contrast resonances in the optical response of a broad class of systems, wherein interference effects are generated by coherent perturbation or interaction of dark states. The properties of these resonances can be manipulated to design a desired atomic response.
TL;DR: In this article, it is shown how it is possible for a specific model to explicitly determine the loops generating any desired logical gate, thus producing a universal set of unitary transformations.
Abstract: In the holonomic approach to quantum computation, information is encoded in a degenerate eigenspace of a parametric family of Hamiltonians and manipulated by the associated holonomic gates. These are realized in terms of the non-Abelian Berry connection and are obtained by driving the control parameters along adiabatic loops. We show how it is possible for a specific model to explicitly determine the loops generating any desired logical gate, thus producing a universal set of unitary transformations. In a multipartite system unitary transformations can be implemented efficiently by sequences of local holonomic gates. Moreover, a conceptual scheme for obtaining the required Hamiltonian family, based on frequently repeated pulses, is discussed, together with a possible process whereby the initial state can be prepared and the final one can be measured.
TL;DR: In this article, a quantum optical version of Schr\"odinger's famous gedanken experiment is proposed, in which the state of a microscopic system (a cavity field) becomes entangled with and disentangled from the state (a movable mirror).
Abstract: We propose a quantum optical version of Schr\"odinger's famous gedanken experiment in which the state of a microscopic system (a cavity field) becomes entangled with and disentangled from the state of a massive object (a movable mirror). Despite the fact that a mixture of Schr\"odinger cat states is produced during the evolution (due to the fact that the macroscopic mirror starts off in a thermal state), this setup allows us to systematically probe the rules by which a superposition of spatially separated states of a macroscopic object decoheres. The parameter regime required to test environment-induced decoherence models is found to be close to those currently realizable, while that required to detect gravitationally induced collapse is well beyond current technology.
TL;DR: The aim of this paper is to give explicit calculation of the classical capacity of quantum Gaussian channels, in particular, involving squeezed states, based on a general formula for the entropy of a quantumGaussian state and on the recently proved coding theorem for quantum communication channels.
Abstract: The aim of this paper is to give explicit calculation of the classical capacity of quantum Gaussian channels, in particular, involving squeezed states. The calculation is based on a general formula for the entropy of a quantum Gaussian state, which is of independent interest, and on the recently proved coding theorem for quantum communication channels.