Role reversal in a Bose-condensed optomechanical system

Supersensitive estimation of the coupling rate in cavity optomechanics with an impurity-doped Bose-Einstein condensate

We propose a scheme to implement a supersensitive estimation of the coupling strength in a hybrid optomechanical system which consists of a cavity-Bose-Einstein condensate system coupled to an impurity. This method can dramatically improve the estimation precision even when the involved photon number is small. The quantum Fisher information indicates that the Heisenberg scale sensitivity of the coupling rate could be obtained when the photon loss rate is smaller than the corresponding critical value in the input of either coherent state or squeezed state. The critical photon decay rate for the coherent state is larger than that of the squeezed state, and the coherent state input case is more robust against the photon loss than the squeezed state case. We also present the measurement scheme which can saturate the quantum Cramér-Rao bound.

Reconfigurable long-range phonon dynamics in optomechanical arrays

We investigate periodic optomechanical arrays as reconfigurable platforms for engineering the coupling between multiple mechanical and electromagnetic modes and for exploring many-body phonon dynamics. Exploiting structural resonances in the coupling between light fields and collective motional modes of the array, we show that tunable effective long-range interactions between mechanical modes can be achieved. This paves the way towards the implementation of controlled phononic walks and heat transfer on densely connected graphs as well as the coherent transfer of excitations between distant elements of optomechanical arrays.

Quantum-criticality-induced strong Kerr nonlinearities in optomechanical systems

We investigate a hybrid electro-optomechanical system that allows us to realize controllable strong Kerr nonlinearities even in the weak-coupling regime. We show that when the controllable electromechanical subsystem is close to its quantum critical point, strong photon-photon interactions can be generated by adjusting the intensity (or frequency) of the microwave driving field. Nonlinear optical phenomena, such as the appearance of the photon blockade and the generation of nonclassical states (e.g., Schrödinger cat states), are demonstrated in the weak-coupling regime, making the observation of strong Kerr nonlinearities feasible with currently available optomechanical technology.

Radiative transfer with partial coherence in optically thick plasmas

A quantum transport model for atomic line radiation in plasmas is developed and analyzed. It is found that the Wigner phase space formulation of QED provides a consistent way to address the wave-particle duality in radiative transfer problems. If the photons' thermal de Broglie length is much smaller than all of the spatial scales of the problem under consideration (large-spectral-band limit), the radiation is not coherent and radiative transfer can be addressed with the usual treatments. In the general case, the Heisenberg uncertainty relation yields ambiguities in the description of the radiation-matter interaction mechanisms. We examine this issue and show that an accurate description of radiative transfer should involve a model with nonlocal interactions and requires an appropriate coarse-graining procedure. Calculations of transmission factors and absorption spectra in ideal cases are performed and indicate that significant misinterpretations can be made in spectroscopic diagnostics if the radiation coherence is not well accounted for. Applications to laser physics are also discussed.