Showing papers on "Quantum error correction published in 1991"
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TL;DR: The only experiment in which the Zeno effect has yet been clearly demonstrated, though, allows no conclusion on the necessity or validity of the projection postulate, as shown by calculating the outcome of the experiment on the basis of the standard three-level Bloch equations.
Abstract: The change of dynamics in a quantum system under frequent or continuous observation, known as the quantum Zeno effect, is generally derived from the projection or reduction of the wave-packet hypothesis that is the central postulate in the theory of quantum measurements The only experiment in which the Zeno effect has yet been clearly demonstrated, though, allows no conclusion on the necessity or validity of the projection postulate This is shown by calculating, in detail, the outcome of the experiment on the basis of the standard three-level Bloch equations These equations follow from the quantum theory of irreversible processes with no additional assumptions necessary, such as which part of the system serves as measuring apparatus or how efficient the measurement would be
82 citations
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01 Jan 199150 citations
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TL;DR: This method allows the rigorous proof of recently adopted quantum stochastic approaches, including the presence of sources that form the active medium in the cavity, including quantum Langevin equations obtained in a coarse-graining approximation.
Abstract: Input-output relations in resonators are studied on the basis of a recently developed field-theoretical approach to the action of passive systems in quantum optics [Kn\"oll, Vogel, and Welsch, Phys. Rev. A 36, 3803 (1987)]. This method allows the rigorous proof of recently adopted quantum stochastic approaches, including the presence of sources that form the active medium in the cavity. Quantum Langevin equations are obtained in a coarse-graining approximation. Moreover, we derive all required commutation relations that have been postulated so far. Correlation functions of the field quantities measured outside the cavity are related to correlation functions of field operators of the intracavity field and the incoming field.
33 citations
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TL;DR: In this paper, it was shown that coherent states and associated phase-space methods can be generalized to this basis-independent representation, and coherent states of the radiation field can be defined without reference to a given basis of normal modes.
Abstract: States of the radiation field can be defined without reference to a given basis of normal modes. In this way optical systems for which there is no natural set of orthogonal modes can be handled quantum mechanically in a more rigorous manner. In particular, coherent states and associated phase‐space methods can easily be generalized to this basis‐independent representation.
21 citations
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TL;DR: In this article, a general approach is formulated for analyzing algebraic models of quantum composite systems with an internal symmetry described by group G. The case G = SU(2) is examined in detail as applied to the analysis of polarization invariance in quantum optics.
Abstract: A general approach is formulated for analyzing algebraic models of quantum composite systems with an internal symmetry described by group G. The case G = SU(2) is examined in detail as applied to the analysis of polarization invariance in quantum optics. A new class of fully depolarizable quantum states of light (scalar biphotons) is defined and investigated. Certain interactions of scalar biphoton light with material media are considered in the context of Dicke and Jaynes-Cummings models.
17 citations
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TL;DR: In this article, a novel description of quantum systems is employed for constructing a "time machine" capable of shifting in time the wave function of a quantum system using gravitational time dilations and a peculiar quantum interference effect due to preselection and postselection.
Abstract: A novel description of quantum systems is employed for constructing a “time machine” capable of shifting in time the wave function of a quantum system. This device uses gravitational time dilations and a peculiar quantum interference effect due to preselection and postselection. In most trials this time machine fails to operate but when it does succeed it accomplishes tasks which no other machine can.
10 citations
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01 Jan 1991TL;DR: In this paper, the error probabilities for a coherent state and a squeezed state for optical communication were derived from information theoretical points of view, and it was shown that a proper squeezed state provides a lower error probability, namely, better efficiency for optical communications.
Abstract: The optical communication theory has been developed in the fields of both mathematics and engineering, and it has become very important recently. In this paper we mathematically treat quantum control communication processes from information theoretical points of view, and we derive error probabilities for a concrete quantum channel in each digital modulation and detection. In paticular, several error probabilities for a coherent state and a squeezed state are rigorously calculated. It is shown that a proper squeezed state provides us a lower error probability, namely, better efficiency for optical communication.
5 citations
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TL;DR: In this article, it was shown that the predictions of the ground-state quantum fluctuations in the two frameworks disagree, and that the contributions to the fluctuations which arise from the matter in a system should not be neglected in a proper treatment of quantum noise and squeezing in dielectrics.
Abstract: In quantum optics dielectric materials may be dealt with in two ways. In a fundamental approach there are separate terms in the Lagrangian density for matter and radiation. Alternatively, the macroscopic Maxwell equations may be developed from a Lagrangian scheme. In the former method the electric field is conjugate to the vector potential, but in the latter the dielectric displacement is the conjugate momentum. There is therefore reason to question the compatibility of quantized versions of these theories. Using an exactly solvable model for the matter-radiation system, which is a scalar version of Hopfield's classical dielectric model, it is shown that the predictions of the ground-state quantum fluctuations in the two frameworks disagree. It is suggested that the contributions to the fluctuations which arise from the matter in a system should not be neglected in a proper treatment of quantum noise and squeezing in dielectrics.
2 citations
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TL;DR: In this paper, an optimal solution (optimal state, optical modulation, etc.) was obtained by controlling the energy associated with a quantum input state, giving the minimum value to the error probability in the attenuation optical communication process.
Abstract: Rigorous study of optical communication processes has become interesting since around 1970. Especially, quantum information theory has been developed in both mathematics and engineering. In this paper, by controlling the energy associated with a quantum input state, we obtain an optimal solution (optimal state, optical modulation, etc.) giving the minimum value to the error probability in the attenuation optical communication process. For instance, we find some relations between the energy constraint of the input state and the optimal error probabilities in each modulation.
1 citations
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01 Jan 1991TL;DR: In this article, the authors described the treatment of QND measurement from the view point of optical communication theory, and obtains the following results:==================¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯============The state vector and the wave function for QND measurements are obtained by using standard quantum theory.
Abstract: This paper describes the treatment of QND measurement from the view point of the optical communication theory, and obtains the following results:
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The state vector and the wave function for a QND measurement is obtained by using standard quantum theory.
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The QND measurement is modeled by a specific channel in communication theory.
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The effect of QND measurement to the signal light is completely specified by the amplitude gain and the variances of quantum noises of the signal and probe lights.
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01 Mar 1991
TL;DR: In this article, the quantum harmonic computer (QHC) is described as an idealized quantum harmonic computing system, which employs the well known energy characteristics of quantum mechanical oscillators; the associated creation and annihilation operators; and quantum mechanical axioms of state preparation and observability to perform computations.
Abstract: : Despite the obvious practical considerations (eg, stability, controllability), certain quantum mechanical systems seem to naturally lend themselves in a theoretical sense to the task of performing computations The purpose of this report is to describe one such idealized system-the quantum harmonic computer As its name might suggest, this theoretical device employs the well known energy characteristics of quantum mechanical oscillators; the associated creation and annihilation operators; and the quantum mechanical axioms of state preparation and observability to perform computations It is demonstrated that programs can be written for this device in terms of quantum mechanical observables and creation and annihilation operators which will algorithmically manipulate oscillator energy states to perform the desired calculations, the results of which are eigenvalues of a well defined system observable By definition, these programs are equivalent to Turing machines, so that anything that is Turing computable is also computable with this device