Fluctuations and entanglement in open quantum systems

Jiří Pešek

Ohad Shpielberg

The macroscopic fluctuation theory provides a complete hydrodynamic description of nonequilibrium classical diffusive systems. As a first step towards a diffusive theory of open quantum systems, we propose a microscopic open quantum system model —the selective dephasing model. It exhibits genuine quantum diffusive scaling. Namely, the dynamics is diffusive and the density matrix remains entangled at large length scales and long time scales.

Diplomarbeit von Marc Busse

V. M. Akulin

Federico Carollo, Carlos Pérez-Espigares

Controlling dynamical fluctuations in open quantum systems is essential both for our comprehension of quantum nonequilibrium behavior and for its possible application in near-term quantum technologies. However, understanding these fluctuations is extremely challenging due, to a large extent, to a lack of efficient important sampling methods for quantum systems. Here, we devise a unified framework-based on population-dynamics methods-for the evaluation of the full probability distribution of generic time-integrated observables in Markovian quantum jump processes. These include quantities carrying information about genuine quantum features, such as quantum superposition or entanglement, not accessible with existing numerical techniques. The algorithm we propose provides dynamical free-energy and entropy functionals which, akin to their equilibrium counterpart, permit one to unveil intriguing phase-transition behavior in quantum trajectories. We discuss some applications and further disclose coexistence and hysteresis, between a highly entangled phase and a low entangled one, in large fluctuations of a strongly interacting few-body system.

Fabio Benatti