Influence From Phonon Bath In A Quantum Dot Cavity QED System

Cavity quantum electrodynamics(cQED) is an important sub?eld in quantum optics. The newly developed solid state cQED system, i.e. the semiconductor quantum-dots(QDs)-microcavity system, has raised a lot of interest in recent years. The new QD-cavity system also shows its application in quantum information processing, ranging from the realization of a qubit to the single photon source(SPS). One important issue in the solid state system is the in?uence from the phonon bath and there are mainly three important e?ects: the coupling renormalization,o?-resonance feeding, and pure dephasing. In the present paper, the basic model(i.e. the Jaynes-Cummings model) and the in?uence mechanism from the phonon bath are reviewed.The in?uence from phonon bath comes from the electron-phonon(or hole-phonon) coupling,basically there are two kinds of coupling types: the piezoelectric coupling and the deformation potential coupling. By calculating the spectrum function of phonon bath from the electron(hole)wave function, it is shown that the in?uence caused by the piezoelectric coupling is at least one order lower than that of the deformation potential coupling. The result provides the direct support for the conclusion that the main contribution of the phonon bath comes from the LA phonons. Because of the manufacture technology, the outcome shape of a QD can be of di?erent types. This implies that the shape-dependence is an important issue in a real system. Starting from the wave function, the spectrum functions of three kinds QD, i.e. the spherical QD, the ellipsoidal QD, and the disk QD, are calculated and based on it, the caused in?uence are found.The obtained results show that the shape plays important role. It is seen that the disk QD has the strongest electron-phonon coupling strength which causes the widest spectral distribution,and hence the in?uence from the phonon bath in a disk-shape QD is the strongest in the QDs.One basic character of the in?uence from phonon bath is the temperature dependence. Due to the coupling renormalization, it is known that the cross-over from strong-coupling(SC) to weakcoupling(WC) regime will happen as temperature raises. Starting from the master equation of reduced density matrix, the condition for the cross-over can be obtained. In a QD cavity system, because of the in?uence from phonon bath, the decay rate of the QD two-state-system is temperature dependent, i.e. the decay rate shows a steep-raising when the temperature reaches40-50 K regime. It is shown that this temperature dependence will lead to abnormal cross-over behavior, i.e., as the temperature raises, the re-entrance happens: SC→WC→SC→WC, showing that the in?uence from the phonon bath can lead to some new observations di?erent from the atom-cavity system. The evolution of spectrum with the temperature is calculated and some related topics are discussed.