Nonreciprocal Relaxation Acceleration

In open quantum systems, accelerating the relaxation toward a nonequilibrium steady state (NESS) is significantly more complex than reaching thermal equilibrium. The authors investigate whether introducing a transient, engineered nonreciprocal dissipative channel can bypass the natural bottlenecks that slow down this convergence in continuous-variable bosonic systems.

The researchers model a two-mode bosonic system where each mode is coupled to an independent thermal reservoir. They engineer nonreciprocity by introducing a shared dissipative reservoir, which allows them to control the directionality of energy exchange between the modes. By applying a time-dependent pulse to this nonreciprocal channel, they analyze the system's evolution using both mean-field theory (for coherent states) and the covariance matrix formalism (for thermal states). They quantify the speedup using the trace distance between the transient state and the target NESS.

The study reveals that activating a nonreciprocal channel for a specific duration effectively suppresses the energy 'sloshing' that typically occurs between coupled modes. This suppression forces a rapid, unidirectional dump of excess energy into the environment, leading to a faster approach to the steady state. Surprisingly, the relaxation speedup is invariant under the reversal of the nonreciprocal direction, meaning the system accelerates regardless of whether the energy flow is directed from mode one to mode two or vice versa. Thermodynamic analysis of heat currents confirms that this pulse-assisted protocol stabilizes the system on a much shorter timescale than natural reciprocal decay.