Subthreshold phonon generation in an optomechanical system with an exceptional point

A phonon laser based on an optomechanical system consisting of two optical modes interacting with each other via a phononic mode is considered. An external wave exciting one of the optical modes plays a role of the pumping. It is shown that at some amplitude of the external wave an exceptional point exists. When the external wave amplitude is less than one corresponding to the exceptional point, the splitting of the eigenfrequencies takes place. It is demonstrated that in this case, the periodic modulation of the external wave amplitude can result in simultaneous generation of photons and phonons even below the threshold of optomechanical instability

Spontaneous symmetry emergence as a source of new class of phase transitions

Spontaneous symmetry breaking in systems with symmetry is core-stone phenomenon accompanying second-order phase transitions. Here, we predict an opposite phenomenon, namely, spontaneous symmetry emergence in a system without symmetry. On the example of two coupled oscillators interacting non-symmetrically with a set of oscillators whose frequencies uniformly fill a finite frequency range, we demonstrate that the system state can acquire symmetry, which is not inherent to the system Hamiltonian. The symmetry emergence manifests in the change of the system dynamics, which can be interpreted as a new class of phase transitions