Phase-sensitive symmetry breaking in microresonators with Kerr nonlinearity

Spontaneous symmetry breaking (SSB) is a fundamentally important concept known in many areas of physics: particle physics, condensed matter physics, and optics, to name a few. In photonics, there has been an increasing interest in studying symmetry breaking, chiral and nonreciprocal light propagation in optical macro- and microresonators with cubic nonlinearities. Here, we demonstrate theoretically and experimentally that linear coupling due to the backscattering between two counterpropagating modes in a microresonator with Kerr nonlinearity leads to extreme sensitivity of the intensity asymmetry of light states to the relative phase between the bidirectional pumps of equal power. In the absence of linear coupling, the relative pump phase does not affect counterpropagating intraresonator intensities, and two asymmetric states arise due to spontaneous symmetry breaking. Contrariwise, in the presence of weak linear intermode coupling, the asymmetry of the states is deterministically controlled via changes in phase (for all phases except 0 and $\pi$). Spontaneous symmetry breaking at zero phase is suppressed when the linear intermode coupling is increased, while for the $\pi$ phase it can be enhanced, so that the overall threshold for the spontaneous symmetry breaking can be significantly lower for nonzero linear coupling. These results are important for fundamental understanding of the processes in Kerr resonators and other systems with Kerr-like nonlinearities and linear intermode coupling and have high prospects for the development of photonic devices such as ultrasensitive sensors. Moreover, the study of such systems also allows one to obtain fundamental results that can be used outside of optics due to quantum-optical analogies (for example, for studying the well-known Bose-Hubbard dimer).
The work was supported by the Russian Science Foundation, grant No.20-72-10188-P.
E.A. Anashkina, A.V. Andrianov, “Phase-sensitive symmetry breaking in bidirectionally pumped Kerr microresonators,” arXiv preprint arXiv:2407.07594 (2024).