Dual-driving parametric locking of GHz phonon sources to sub-hertz linewidth in optomechanical systems

In the exploration of collective dynamics and advanced information processing, synchronization and frequency locking of mechanical oscillations are cornerstone phenomena. Traditional synchronization techniques, which typically involve a single mechanical mode, are limited by their inability to distinguish between intrinsic mechanical oscillations and external signals after locking. Addressing this challenge, we introduce a parametric approach that enables simultaneous frequency locking of two gigahertz mechanical modes within an optomechanical crystal cavity. By modulating the pump light to match the sum and difference frequencies of the mechanical modes, we significantly narrow their linewidths from tens of kilohertz to below 1 Hz at room temperature and ambient pressure. This dual-locking scheme also drastically reduces the phase noise of the mechanical modes by 76.6 dBc/Hz at a 100 Hz offset, while allowing flexible tuning of the locked modes’ frequencies via input signal adjustments. Our method not only facilitates direct observation of mechanical oscillations under the locking regime but also enriches the understanding of coherent phonons in multimode regimes, opening new avenues for optomechanical applications in signal processing.