-bosons coupled to a system of interest through a cross-Kerr interaction is proposed and its effects on quantum superpositions are investigated. By means of analytical calculations we show that: (i) the reservoir induces a Gaussian decay of quantum coherences, and (ii) the inherent incommensurate character of the spectral distribution yields irreversibility. A state-independent decoherence time and a master equation are both derived analytically. These results, which have been extended for the thermodynamic limit, show that nondissipative decoherence can be suitably contemplated within the environment-induced decoherence (EID) approach. Finally, it is shown that the same mechanism yielding decoherence are also responsible for inducing dynamical disentanglement.

DOI: 10.1103/physreva.73.062107

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A phase damping reservoir composed by

N

A phase damping reservoir composed by

N

-bosons coupled to a system of interest through a cross-Kerr interaction is proposed and its effects on quantum superpo sitions are investigated. By means of analytical calculations we show that: i-) the reservoir induces a Gaussian decay of quantum coherences, and ii-) the inher ent incommensurate character of the spectral distribution yields irreversibility . A decoherence time and a master equation are both derived analytically. These results, which have been extended for the thermodynamic limit, show that non-dis sipative decoherence can be suitably contemplated within the EID approach. Final ly, it is shown that the same mechanism yielding decoherence are also responsibl e for inducing dynamical disentanglement.

We consider environment induced decoherence of quantum superpositions to mixtures in the limit in which that process is much faster than any competing one generated by the Hamiltonian

{H}_{\mathrm{sys}}

of the isolated system. This interaction-dominated decoherence limit is of importance for the emergence of classical behavior in the macroscopic domain, since it will always be the relevant regime for large enough separations between the superposed wave packets. The usual golden-rule treatment then does not apply, but we can employ a short-time expansion for the free motion while keeping the interaction

{H}_{\mathrm{int}}

in full. We thus reveal decoherence as a universal short-time phenomenon largely independent of the character of the system as well as the bath and of the basis the superimposed states are taken from. Simple analytical expressions for the decoherence time scales are obtained in the limit in which decoherence is even faster than any time scale emerging from the reservoir Hamiltonian

{H}_{\mathrm{res}}.

We develop and implement a method for modeling decoherence processes on an N-dimensional quantum system that requires only an

{N}^{2}

-dimensional quantum environment and random classical fields. This model offers the advantage that it may be implemented on small quantum-information processors in order to explore the intermediate regime between semiclassical and fully quantum models. We consider in particular ${\ensuremath{\sigma}}_{z}{\ensuremath{\sigma}}_{z}$ system-environment couplings which induce coherence (phase) damping, although the model is directly extendable to other coupling Hamiltonians. Effective, irreversible phase damping of the system is obtained by applying an additional stochastic Hamiltonian on the environment alone, periodically redressing it and thereby irreversibliy randomizing the system phase information that has leaked into the environment as a result of the coupling. This model is exactly solvable in the case of phase damping, and we use this solution to describe the model's behavior in some limiting cases. In the limit of small stochastic phase kicks the system's coherence decays exponentially at a rate that increases linearly with the kick frequency. In the case of strong kicks we observe an effective decoupling of the system from the environment. We present a detailed implementation of the method on a nuclear magnetic resonance quantum-information processor.