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Isaac Newton Institute for Mathematical Sciences

Parametric representation of open quantum systems and cross-over from quantum to classical environment

Presenter: Paola Verrucchi (Istituto dei Sistemi Complessi - CNR, Dipartimento di Fisica Universita' di Firenze, Istituto Nazionale di Fisica Nucleare sezione di Firenze, Italy)

Co-authors: Dario Calvani (Dipartimento di Fisica, Universita' di Firenze, Italy), Alessandro Cuccoli (Dipartimento di Fisica, Universita' di Firenze, Italy), Nikitas I. Gidopoulos (Univ Durham, Dept Phys, Durham DH1 3LE, England )


Open quantum systems and their dynamics are usually studied in terms of reduced density matrices. This approach allows a nonsymmetric description, which is useful when one of the two subsystems is to be considered an environment, at the expense of a loss of information, as tracing out the environmental degrees of freedom is an irreversible process. This has a series of consequences which can be severe.

In this work we present an alternative description, which is still nonsymmetric but yet exact: It is based on a parametric representation of composite systems, as obtained by introducing environmental coherent states, such that the principal system get to be described by a set of pure states parametrically dependent on environmental variables. The representation allows one to relate properties which typically arise in studying systems with parametrically dependent Hamiltonians, such as the emergence of geometrical phases, with features which specifically characterise open quantum systems, such as decoherence and entanglement generation.

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