Enhancement of Optomechanical Squeezing of Light Using the Optical Coherent Feedback.

A coherent feedback scheme is used to enhance the degree of squeezing of the output field in a cavity optomechanical system. In the feedback loop, a beam splitter (BS) plays the roles of both a feedback controller and an input-output port. To realize effective enhancement, the output quadrature should take the same form as the input quadrature, and the system should operate at the deamplification situation in the meantime.

Coherence and Anticoherence Induced by Thermal Fields.

Interesting coherence and correlations appear between superpositions of two bosonic modes when the modes are parametrically coupled to a third intermediate mode and are also coupled to external modes which are in thermal states of unequal mean photon numbers. Under such conditions, it is found that one of linear superpositions of the modes, which is effectively decoupled from the other modes, can be perfectly coherent with the other orthogonal superposition of the modes and can simultaneously exhibit anticoherence with the intermediate mode, which can give rise to entanglement between the modes. It is shown that the coherence effects have a substantial effect on the population distribution between the modes, which may result in lowering the population of the intermediate mode.

Creating a switchable optical cavity with controllable quantum-state mapping between two modes.

We describe how an ensemble of four-level atoms in the diamond-type configuration can be applied to create a fully controllable effective coupling between two cavity modes. The diamond-type configuration allows one to use a bimodal cavity that supports modes of different frequencies or different circular polarisations, because each mode is coupled only to its own transition. This system can be used for mapping a quantum state of one cavity mode onto the other mode on demand.

Collective dynamics and entanglement of two distant atoms embedded into single-negative index material.

We study the dynamics of two two-level atoms embedded near to the interface of paired meta-material slabs, one of negative permeability and the other of negative permittivity. This combination generates a strong surface plasmon field at the interface between the meta-materials. It is found that the symmetric and antisymmetric modes of the two-atom system couple to the plasmonic field with different Rabi frequencies.