Power-preserving reduction of laser linewidth via cavity quantum squeezing

We propose a protocol to reduce the linewidth of a weak laser field without power loss based on a quantum squeezing process. By taking advantage of the frequency-dependent noiseless amplification mechanism of the cavity squeezing process, the linewidth of the output field from the cavity can be evidently narrowed in comparison to that of the incident laser field. The reduction effect depends on the strength of the cavity squeezing process, and order-of-magnitude reduction can be made possible in the vicinity of the lasing threshold. Moreover, we find a simple and favorable scaling law for the output field from the cascade system consisting of $M$ identical nonlinear cavities at certain conditions. Our results may be beneficial for a variety of applications where narrow linewidth is crucial, such as quantum metrology and sensing.