Noise immunity in quantum optical systems through non-Hermitian topology

Abstract

Multimode nonlinear optical systems are highly valued for their ability to withstand large amounts of optical power, transmit data with high bandwidth, perform physical computations, generate quantum correlations, and much more. For many of these applications, both classical and quantum noise place limitations on important performance metrics. Moreover, it is well known that nonlinear systems tend to develop noise due to their sensitivity to initial conditions, thus motivating the development of general principles which can be used to control and mitigate noise in such systems. In this work, we show that non-reciprocity can enable the unidirectional flow of noise from the non-equilibrium steady states of nonlinear driven-dissipative systems. We demonstrate that this unidirectional flow results from the non-Hermitian skin effect (NHSE) for quantum noise. This effect provides a robust mechanism for isolating parts of the system from degradation due to excess injected noise. Our findings may lead to novel design principles for multimode amplifiers or oscillators that support high power handling while mitigating the buildup of noise. Moreover, our approach provides a new means to connect non-Hermitian topology with nonlinear many-body systems, which is expected to lead to topological descriptions of interacting states of light.