Nonreciprocal Amplification in Coupled‐Rotating Cavities Around Exceptional Points

Abstract

A nonreciprocal‐amplified scheme for signal transmission is proposed in a coupled rotation‐cavity system, where the two cavities rotate with opposite directions, and an optical parametric amplifier (OPA) is attached to one cavity. The coupling between cavities can effectively compensate and enhance the frequency shift of the Sagnac effect, and a perfect nonreciprocity can be achieved. Owing to the introduction of an OPA medium, eigenvalues of the dynamic matrix exhibit exceptional points (EPs), and the amplified‐nonreciprocal transmission can be obtained around EPs.

Parameter estimation with the steady states of non-Hermitian spin chains

“…On the one hand, it is known that the non-Hermitian Hamiltonians with parity-time (PT ) symmetry still possess real spectra [15]. The PT -symmetric systems are of great interest in nonreciprocal light transport [16][17][18][19], mode switching [20], and quantum sensing [21,22]. On the other hand, the complex eigenvalues of non-Hermitian Hamiltonians break the unitary time-evolution of the state of quantum systems.…”