Super-efficient optical frequency division referenced to μHz Schawlow-Townes-linewidth quantum-noise-limited lasers

Abstract

Optical frequency division (OFD) implements the conversion of ultra-stable optical frequencies into microwave frequencies through an optical frequency comb flywheel, generating microwave oscillators with record-low phase noise and time jitter. However, conventional OFD systems face significant trade-off between division complexity and noise suppression due to severe thermal noise and technical noise in the optical frequency references. Here, we address this challenge by generating common-cavity bi-color Brillouin lasers as the optical frequency references, which operate at the fundamental quantum noise limit with Schawlow-Townes linewidth on the 10 μHz level. Enabled by these ultra-coherent reference lasers, our OFD system uses a dramatically simplified comb divider with an unprecedented small division factor of 10, and generates 10 GHz microwave signal with exceptional phase noise of -65 dBc/Hz at 1Hz, -155 dBc/Hz at 10 kHz, and -172 dBc/Hz at 10 MHz offset. Moreover, to fully harness the spectral purity of the OFD technology, here we implement broadband frequency synthesis directly referenced to the OFD oscillator, covering 5 to 20 GHz with millisecond tuning time. Our work redefines the trade-off between noise suppression and division complexity in OFD, paving the way for compact, high-performance microwave synthesis for next-generation atomic clocks, quantum sensors, and low-noise radar systems.

We will make new work adjustments and key optimizations based on the existing manuscript. Due to the involvement of the disclosure of key parameters, we apply for the withdrawal of the current version of the manuscript