Parallel decoherence in composite quantum systems

Piotr Marecki

M. Dugić, J. Jeknić-Dugić

For the standard Quantum Brownian Motion (QBM) model, we point out the occurrence of simultaneous (parallel), mutually irreducible and autonomous decoherence processes. Besides the standard, one Brownian particle, we show there is at least another one system undergoing the dynamics described by the QBM effect. We do this by selecting the two mutually irreducible, global structures (decompositions into subsystems) of the composite system of the QBM model. A generalization of this observation is a new, challenging task in the foundations of the decoherence theory. We do not place our findings in any interpretational context.

Sergio Cano-Andrade, Gian Paolo Beretta, Michael R. von Spakovsky

The steepest-entropy-ascent quantum thermodynamic (SEAQT) framework is used to model the decoherence that occurs during the state evolution of two different microscopic composite systems. The test cases are a $\text{two}\ensuremath{-}\text{spin}\ensuremath{-}\frac{1}{2}\ensuremath{-}\text{particle}$ composite system and a particle-photon field composite system like that experimentally studied in cavity quantum electrodynamics. The first system is used to study the characteristics of the nonlinear equation of motion of the SEAQT framework when modeling the state evolution of a microscopic composite system with particular interest in the phenomenon of decoherence. The second system is used to compare the numerical predictions of the SEAQT framework with experimental cavity quantum electrodynamic data available in the literature. For the two different numerical cases presented, the time evolution of the density operator of the composite system as well as that of the reduced operators belonging to the two constituents is traced from an initial nonequilibrium state of the composite along its relaxation towards stable equilibrium. Results show for both cases how the initial entanglement and coherence is dissipated during the state relaxation towards a state of stable equilibrium.

Kalle‐Antti Suominen

M. Dugić

We develop a general algebraic method for investigating the diagonalizability of a composite-system observable in the, so-called, noncorrelated basis of the Hilbert state space of a composite ("two-body") quantum system. The method consists in rewriting a composite-system obsrvable in linear form, for which one directly and uniquely obtains an answer concerning the diagonalizability. The method has been applied to the analysis of the concept of separability of the interaction part of the Hamiltonian of the composite system, "quantum system plus environment (apparatus)". The application leads to a new (more precise) operational definition of separability, which represents a necessary condition concerning the occurrence of decoherence in the, so-called, orthodox approach to the theory of decoherence.