Transitions between stationary states during a self-organization process of open quantum systems

I. Vakulchyk, Mikhail Ivanchenko, Sergej Flach A +1 more

Thiago Ganascini, W. Silva, D. Valente

Finding principles of nonequilibrium self-organization in dissipative quantum systems is an open problem. One example is the notion of quantum dissipative adaptation (QDA), that relates the transition probability between the ground states of a quantum system to the nonequilibrium work absorbed during the transition. However, QDA was originally derived with three-level systems in lambda (Λ) configuration. Here, we consider a two-qubit model driven by single-photon pulses. We find that the absorbed work is generally related to the sum of Λ-type transition probabilities, instead of the direct transition probability between the two ground states. Although this is equivalent to standard QDA in most scenarios, we find an exception whereby optimal self-organization is not accompanied by maximum work consumption. We show how quantum coherence leaves this kind of imprint in the energetics of self-organization in the present model.

Dragomir Davidovic

Left alone, open quantum systems relax toward a Kubo--Martin--Schwinger (KMS) equilibrium state, yet the inner workings of this process remain opaque. It remains unclear why the intricate fourth-order time-convolutionless (TCL4) population generator reproduces the comparatively simple second-order stationary state corrections. Even more surprisingly, stationary-state corrections of such precision can be compressed into a simple virtual coherence pathway: an open quantum systems analogue of virtual transitions, in which populations communicate through coherences that are never occupied. Here we show that this simplification arises through a sequence of stationary-state-preserving transformations that progressively eliminate asymptotically redundant components while preserving the stationary state, ultimately yielding the virtual coherence pathway. This resolves the longstanding stationary-state problem of the Redfield equation and reveals that much of the apparent complexity of the TCL4 generator is asymptotically redundant.

Xiang‐Guo Meng, Ji‐Suo Wang, Bao‐Long Liang

Lorena Ballesteros Ferraz

B. C. S. Grandi, W. Figueiredo

We consider a two-dimensional antiferromagnet Ising system interacting with a heat bath at temperature T. The dynamics of the system is simulated by two competing stochastic processes: the two-spin-exchange Kawasaki kinetics at temperature T>0 and the one-spin-flip Glauber dynamics at T(G)-->0(-), which mimics the increase of the energy of the system. These two processes have probabilities 1-p and p, respectively. Monte Carlo simulations were employed to determine the phase diagram for the stationary states of the model and the corresponding critical exponents. Contrary to the ferromagnetic case, the phase diagram obtained does not exhibit the phenomenon of self-organization: for any nonzero value of the competing parameter p, and for any value of T, the only stationary phase which remains is the ferromagnetic one. At the phase transition between the antiferromagnetic and paramagnetic phases, at p=0, the values found for the critical exponents agree with those of the corresponding equilibrium Ising model.