Quantum Nonreciprocal Interactions via Dissipative Gauge Symmetry

One-way nonreciprocal interactions between two quantum systems are typically described by a cascaded quantum master equation, and rely on an effective breaking of time-reversal symmetry (TRS) as well as the balancing of coherent and dissipative interactions. Here, we present a new approach for obtaining nonreciprocal quantum interactions that is completely distinct from cascaded quantum systems, and that does not in general require broken TRS. Our method relies on a local gauge symmetry present in any Markovian Lindblad master equation. This new kind of quantum nonreciprocity has many implications, including a new mechanism for performing dissipative steady-state unitary gate operations on a target quantum system. We also introduce a new, extremely general quantum-information-based metric for quantifying quantum nonreciprocity.