Quantum sensing with nonreciprocal couplings

Nonreciprocity can not only generate quantum resources, but also shield noise\nand reverse interference from driving signals. We investigate the advantages of\nnonreciprocal coupling in sensing a driving signal. In general, we find that\nthe nonreciprocal coupling performs better than the corresponding reciprocal\ncoupling. And we show that homodyne measurement is the optimal measurement. A\nsingle non-reciprocal coupling can increase measurement precision up to 2\ntimes. Using $N$ non-reciprocal couplings in parallel, the measurement\nprecision can be improved by $N^2$ times compared with the corresponding\nreciprocal coupling. In a non-zero temperature dissipative environment, we\ndemonstrate that the nonreciprocal quantum sensing has better robustness to\nthermal noise than the reciprocal quantum sensing.\n