SciPost Phys. 10, 045 (2021) ·
published 22 February 2021
We describe an efficient numerical method for simulating the dynamics and
steady states of collective spin systems in the presence of dephasing and
decay. The method is based on the Schwinger boson representation of spin
operators and uses an extension of the truncated Wigner approximation to map
the exact open system dynamics onto stochastic differential equations for the
corresponding phase space distribution. This approach is most effective in the
limit of very large spin quantum numbers, where exact numerical simulations and
other approximation methods are no longer applicable. We benchmark this
numerical technique for known superradiant decay and spin-squeezing processes
and illustrate its application for the simulation of non-equilibrium phase
transitions in dissipative spin lattice models.
Julian Huber, Peter Kirton, Stefan Rotter, Peter Rabl
SciPost Phys. 9, 052 (2020) ·
published 19 October 2020
The effect of PT-symmetry breaking in coupled systems with balanced gain and
loss has recently attracted considerable attention and has been demonstrated in
various photonic, electrical and mechanical systems in the classical regime.
Here we generalize the definition of PT symmetry to finite-dimensional open
quantum systems, which are described by a Markovian master equation.
Specifically, we show that the invariance of this master equation under a
certain symmetry transformation implies the existence of stationary states with
preserved and broken parity symmetry. As the dimension of the Hilbert space
grows, the transition between these two limiting phases becomes increasingly
sharp and the classically expected PT-symmetry breaking transition is
recovered. This quantum-to-classical correspondence allows us to establish a
common theoretical framework to identify and accurately describe PT-symmetry
breaking effects in a large variety of physical systems, operated both in the
classical and quantum regimes.