Quantum sensing with nonreciprocal couplings

Nonreciprocity can not only generate quantum resources but can also shield noise and reverse interference from driving signals. We investigate the advantages of nonreciprocal coupling in sensing a driving signal. In general, we find that nonreciprocal coupling performs better than the corresponding reciprocal coupling. And we show that homodyne measurement is the optimal measurement. A single nonreciprocal coupling can increase measurement precision by up to 2 times. With the use of $N$ nonreciprocal couplings in parallel, the measurement precision can be increased by ${N}^{2}$ times compared with the corresponding reciprocal coupling. In a nonzero-temperature dissipative environment, we demonstrate that nonreciprocal quantum sensing has greater robustness regarding thermal noise than reciprocal quantum sensing.