Ultrastrong light-matter interaction in an optomechanical system can result in nonlinear optical effects such as photon blockade. The system-bath couplings in such systems play an essential role in observing these effects. Here we study the quantum coherence of an optomechanical system with a dressed-state master equation approach. Our master equation includes photon-number-dependent terms that induce dephasing in this system. Cavity dephasing, second-order photon correlation, and two-cavity entanglement are studied with the dressed-state master equation.
We investigated the current unsolved problem of short-term enhancement and long-term decay of the luminescence intensity of quantum dots (QDs)-based lightemitting diodes (LEDs) in applications for lighting and displays, and proved that the interface interaction between the QD surface and atmospheres plays a key role in the QD-LED operation process. It is suggested that the initial luminescence enhancement of QD-LEDs would be caused by the QD surface-adsorbed species, such as ligands and gas molecules, rather than QDs themselves, whereas the luminescence decay is correlated to the interface reactions between QDs and photo-generated reactive oxygen species, which leads to formations of sulfate, hydroxide, and oxide compounds after QDs are illuminated by 450 nm blue light in oxygen and water environments according to surface analysis and theoretic thermodynamic calculations. It was also found that involvement of water in the QD-LED operation can cause crystal merging of QDs possibly because of the surface sulfates in the presence of water.
Circuit cavity quantum electrodynamics (QED) is proving to be a powerful platform to implement quantum feedback control schemes due to the ability to control superconducting qubits and microwaves in a circuit.Here, we present a simple and promising quantum feedback control scheme for deterministic generation and stabilization of a three-qubit W state in the superconducting circuit QED system. The control scheme is based on continuous joint Zeno measurements of multiple qubits in a dispersive regime, which enables us not only to infer the state of the qubits for further information processing but also to create and stabilize the target W state through adaptive quantum feedback control. We simulate the dynamics of the proposed quantum feedback control scheme using the quantum trajectory approach with an effective stochastic maser equation obtained by a polaron-type transformation method and demonstrate that in the presence of moderate environmental decoherence, the average state fidelity higher than 0.9 can be achieved and maintained for a considerably long time (much longer than the single-qubit decoherence time). This control scheme is also shown to be robust against measurement inefficiency and individual qubit decay rate differences. Finally, the comparison of the polaron-type transformation method to the commonly used adiabatic elimination method to eliminate the cavity mode is presented.
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