Showing papers on "Quantum error correction published in 1989"
TL;DR: The theory of quantum computational networks is the quantum generalization of the theory of logic circuits used in classical computing machines, and a single type of gate, the universal quantum gate, together with quantum ‘unit wires' is adequate for constructing networks with any possible quantum computational property.
Abstract: The theory of quantum computational networks is the quantum generalization of the theory of logic circuits used in classical computing machines. Quantum gates are the generalization of classical logic gates. A single type of gate, the universal quantum gate, together with quantum ‘unit wires’, is adequate for constructing networks with any possible quantum computational property.
1,248 citations
TL;DR: A quantum optical model that obeys the nonlinear rotator dynamics and can generate superpositions of SU(2) coherent states of the two-mode electromagnetic field is presented.
Abstract: The quantum and classical dynamics of the nonlinear oscillator are contrasted by comparing the evolution of the quantum Q function with that of a similar classical probability distribution. The quantum nonlinear rotator is shown to generate a superposition of two distinct coherent states from a coherent-state input. Measurements of the angular-momentum components and the signature of a superposition state are discussed. The effects of a continual measurement of one angular-momentum component are introduced into the model, and its effects on quantum coherences are shown to degrade the quantum coherence effects. We present a quantum optical model that obeys the nonlinear rotator dynamics and can generate superpositions of SU(2) coherent states of the two-mode electromagnetic field.
156 citations
TL;DR: In this paper, the quantum behaviour of a periodically kicked nonlinear spin system is investigated and the evolution operator eigenvalue distribution is employed to prove coherent quantum tunneling occurs between the fixed points in the regular regions of phase space.
Abstract: We investigate the quantum dynamics of a periodically kicked nonlinear spin system which exhibits regular and chaotic dynamics in the classical regime. The quantum behaviour is characterised by the evolving eigenvalue distributions for the angular momentum components and the features, including recurrences in the quantum means and the presence of quantum tunneling, are discussed. We employ the evolution operator eigenvalue distribution to prove that coherent quantum tunneling occurs between the fixed points in the regular regions of phase space. Continual quantum measurement is included in the model: the classical dynamics are unchanged but a destruction of coherences occurs in the quantum system. Recurrences in the means are destroyed and quantum tunneling is suppressed by measurement, a manifestation of the quantum Zeno effect.
19 citations
17 citations
TL;DR: In this paper, the changes of entropy taking place in a quantum system during a measurement process are reviewed, with a view to clarifying the concepts of entropy, information and quantum measurement.
Abstract: The changes of entropy taking place in a quantum system during a measurement process are reviewed, with a view to clarifying the concepts of entropy, information and quantum measurement. It is shown that a non-negative amount of information is gained in spite of the loss of information (or entropy increase) caused by the reduction of the wavepacket.
13 citations
TL;DR: In this article, the origin of quantum noise emerging from the reversible or the irreversible part of the dynamics and compare it with the properties of purely classical fluctuations are discussed and illustrated by a number of physical examples such as the laser with loss or gain noise, nonlinear optical devices, and the phenomenon of quantum jumps.
Abstract: In quantum optics noise plays an important role, since many of the nonlinear optical systems are quite sensitive to the subtle influences of weak random perturbations, being either classical of quantum mechanical in nature. We discuss the origin of quantum noise emerging from the reversible or the irreversible part of the dynamics and compare it with the properties of purely classical fluctuations. These general features are illustrated by a number of physical examples, such as the laser with loss or gain noise, nonlinear optical devices, and the phenomenon of quantum jumps. These processes have been chosen mainly to illustrate the different aspects of noise, but also because, to a large extent, they can be described in analytical terms.
7 citations
TL;DR: In this paper, it was shown that classical Liouville dynamics can be recovered from quantum mechanically suppressed chaotic motion by introducing a measurement process into the pure dynamics, which is a quantum non-demolition measurement for information on the phase space probability distribution.
Abstract: It is shown that classical Liouville dynamics are recovered from quantum mechanically suppressed chaotic motion by introducing a measurement process into the pure dynamics. Such a process is a quantum non-demolition measurement for information on the phase space probability distribution. A fully quantum dynamical model of such a process, which is based on a von Neumann's (1932) lattice basis, is proposed. The quantum fluctuations of the measurement system releases the host system from a quantum suppression, thereby restoring an entire classical motion in the phase space.
6 citations