Hybridized Frequency Combs in Multimode Cavity Electromechanical System

TL;DR

This paper demonstrates hybridized microwave frequency combs in a multimode cavity electromechanical system, showing how mechanical mode competition enables switchable comb tooth spacing and potential for multi-nonlinearity devices.

Contribution

It introduces the first observation of hybrid frequency combs mediated by indirect coupling between mechanical modes in a superconducting cavity system.

Findings

Independent combs with spacing equal to mechanical mode frequencies

Hybridization of combs at mode instability overlap boundaries

Switchable comb tooth spacing controlled by mode competition

Abstract

The cavity electromechanical devices with radiation-pressure-interaction induced Kerr-like nonlinearity are promising candidates to generate microwave frequency combs. We construct a silicon-nitride-membrane-based superconducting cavity electromechanical device and study two mechanical modes mediated synergistic frequency combs. Around the threshold of intracavity field instability, we firstly show independent frequency combs with tooth spacing equalling to each mechanical mode frequency. At the overlap boundaries of these two individual mechanical mode mediated instability thresholds, we observe hybridization of frequency combs based on the cavity field mediated indirect coupling between these two mechanical modes. The spectrum lines turn to be unequally spaced but can be recognized into combinations of the coexisting frequency combs. Beyond the boundary, the comb reverts to the single-mode case, and which mechanical mode frequency will the tooth spacing depend on the mode competition. Our work demonstrates mechanical mode competition enabled switchability of frequency comb tooth spacing and can be extended to other devices with multiple nonlinearities.