Enhancing the nonlinearity of optomechanical system via multiple mechanical modes.

We theoretically investigate the nonlinear dynamics of an optomechanical system, where the system consists of N identical mechanical oscillators individually coupled to a common cavity field. We find that the optomechanical nonlinearity can be enhanced N times through theoretical analysis and numerical simulation in such a system. This leads to the power thresholds to observe the nonlinear behaviors (bistable, period-doubling, and chaotic dynamics) being reduced to 1/N.

Mass sensing by quantum criticality.

Mass sensing connects mass variation to a frequency shift of a mechanical oscillator, whose limitation is determined by its mechanical frequency resolution. Here we propose a method to enlarge a minute mechanical frequency shift, which is smaller than the linewidth of the mechanical oscillator, into a huge frequency shift of the normal mode. Explicitly, a frequency shift of about 20 Hz of the mechanical oscillator would be magnified to be a 1 MHz frequency shift in the normal mode, which increases it by 5 orders of magnitude.

Enhanced photon-phonon cross-Kerr nonlinearity with two-photon driving.

We propose a scheme to significantly enhance the cross-Kerr (CK) nonlinearity between photons and phonons in a quadratically coupled optomechanical system (OMS) with two-photon driving. This CK nonlinear enhancement originates from the parametric-driving-induced squeezing and the underlying nonlinear optomechanical interaction. Moreover, the noise of the squeezed mode can be suppressed completely by introducing a squeezed vacuum reservoir.

Single-photon-induced two qubits excitation without breaking parity symmetry.

We investigate theoretically the model of two "qubits" system (one qubit having an auxiliary level) interacting with a single-mode resonator in the ultrastrong coupling regime. We show that a single photon could simultaneously excite two qubits without breaking the parity symmetry of system by properly encoding the excited states of qubits. The optimal parameter regime for achieving high probability approaching one is identified in the case of ignoring the system dissipation.