Photon blockade induced by two-photon absorption in cavity quantum electrodynamics.

Photon blockade (PB) is an important quantum phenomenon in cavity quantum electrodynamics (QED). Here, we investigate the PB effect in the simplest cavity QED systems (one cavity containing first a single atom and then two atoms), where only the atoms are weakly driven. Via the analytical calculation and numerical simulation, we show that the strong PB can be generated even with the weak-coupling regime at the total resonance. This blockade is ascribed to the two-photon absorption, which is fundamentally different from the conventional and unconventional blockade mechanisms. Therefore, our study provides an alternative approach to produce the PB in the atom-driven cavity QED system.

Enhancing cross-Kerr coupling via mechanical parametric amplification.

We present a proposal to enhance the cross-Kerr coupling between the cavity and the mechanical oscillator significantly. Specifically, the periodic modulation of the mechanical spring constant induces strong mechanical parametric amplification, which leads to the cross-Kerr nonlinear enhancement. Also, we discuss its application in photon-phonon blockade and phonon-number measurement. We find that under the strong cross-Kerr coupling condition, not only the photon-phonon blockade effect is dramatically enhanced but also different phonon number is clearly distinguished. Our results offer an alternative approach to perform quantum manipulation between photon and phonon.

Enhancement of charge sensitivity by nonlinear optomechanics.

Quantum estimation of electrical charge is investigated by using nonlinear optomechanical interaction. Due to the light-matter decoupling at one mechanical period, we need to consider only the cavity state, meaning that no direct access to the oscillator state is required. It is shown that the charge sensitivity can be greatly improved by enhancing optomechanical coupling. Further, we find that our theoretical result can surpass the sensitivity obtained from electrical measurements.

Control of electromagnetically induced grating by surface plasmon and tunneling in a hybrid quantum dot-metal nanoparticle system.

We investigate the electromagnetically induced grating (EIG) in a quantum dot-metal nanoparticle (QD-MNP) hybrid system. The EIG can be controlled and improved by the surface plasmon effect and the interdot tunneling effect between quantum dots. By manipulating the tunneling effect and the QD-MNP distance, not only the first-order diffraction intensity of the grating can be efficiently enhanced, but also the EIG can be switched from the absorption grating to the gain grating. Almost two times the first-order diffraction efficiencies can be achieved in the gain gratings compared with the absorption gratings.

Strong mechanical squeezing in an electromechanical system.

The mechanical squeezing can be used to explore quantum behavior in macroscopic system and realize precision measurement. Here we present a potentially practical method for generating strong squeezing of the mechanical oscillator in an electromechanical system. Through the Coulomb interaction between a charged mechanical oscillator and two fixed charged bodies, we engineer a quadratic electromechanical Hamiltonian for the vibration mode of mechanical oscillator. We show that the strong position squeezing would be obtained on the currently available experimental technologies.

Entangling distant atoms by interference of polarized photons.

We propose a scheme to generate the entangled state of two Lambda-type three-level atoms trapped in distant cavities by using interference of polarized photons. Two possible spontaneous emission channels of each excited atom result in a coherent superposition of the states of two atoms. The subsequent detection of the different polarized photons reveals that both atoms are in different ground states, but an interference effect prevents us from distinguishing which atom is in which ground state; the atoms are thus entangled. In comparison with the original proposal of interference-induced entanglement [C. Cabrillo, J. Cirac, P. Garcia-Fernandez, and P. Zoller, Phys. Rev. A 59, 1025 (1999)]], in our scheme the weakly driven condition is not required, and the influence of atomic excitement and atomic recoil on the entanglement fidelity can be eliminated.