We analyse the effect of exciton-phonon interactions on reversible quantum-dot cavity coupling with techniques that have been used to study the “spin boson” Hamiltonian. We investigate the conditions under which vacuum-Rabi splitting would be observed.
Semiconductor quantum dots (QDs) in photonic nanocavities provide monolithic, robust platforms for both quantum information processing and cavity quantum electrodynamics (QED). An inherent feature of such solid-state cavity QED systems is the presence of electron-phonon interactions, which distinguishes these systems from conventional atomic cavity QED. Understanding the effects of electron-phonon interactions on these systems is indispensable for controlling and exploiting the rich physics that they exhibit. Here we investigate the effects of electron-phonon interactions on a QD-based cavity QED system. When the QD and the cavity are off-resonance, we observe phonon-assisted cavity mode emission that strongly depends on the temperature and cavity-detuning. When they are on-resonance, we observe an asymmetric vacuum Rabi doublet, the splitting of which narrows with increasing temperature. These experimental observations can be well reproduced using a cavity QED model that includes electron-acoustic-phonon interactions. Our work provides significant insight into the important but hitherto poorly understood mechanism of non-resonant QD-cavity coupling and into the physics of various cavity QED systems utilizing emitters coupled to phonons, such as nitrogen-vacancy centres in diamond and colloidal nanocrystals.
We study experimentally the influence of temperature on the emission characteristics of quantum dot-micropillars in the strong coupling regime of cavity quantum electrodynamics (cQED). In particular, we investigate its impact on the vacuum Rabi splitting (VRS) and we address the important question of the temperature stability of the coherent coupling regime in a semiconductor system, which is relevant in view of both fundamental study and future applications. To study the temperature dependence we investigate an unprecedentedly large number of strong coupling cases (89) in a wide temperature range from 10 up to 50 K, which constitutes a good basis for statistical analysis. The experiment indicates a statistically significant increase of the VRS with temperature in contrast to an expected decrease of the VRS due to the dephasing induced by acoustic phonons. From the theoretical point of view, the phonon-induced renormalization of the VRS is calculated using a real-time path-integral approach for strongly confined quantum dots (QDs), which allows for a numerical exact treatment of the coupling between the QD and a continuum of longitudinal acoustic phonons. The absence of the expected decrease of the VRS with temperature in our experimental data can be attributed to a unique optical property of laterally extended In0.4Ga0.6As QDs used in this study. Their electronic structure facilitates an effective temperature-driven increase of the oscillator strength of the excitonic state by up to 40% in the given temperature range. This leads to enhanced light-matter interaction and overcompensates the phonon-related decrease of the VRS. The observed persistence of strong coupling in the presence of phonon-induced decoherence demonstrates the appealing possibility to counteract detrimental phonon effects in the cQED regime via engineering the electronic structure of QDs.
The excitonic dynamics in a single quantum dot within a microcavity is investigated theoretically in terms of the perturbation treatment based on a unitary transformation. The excitonic Rabi oscillations with a damping rate are obtained explicitly. It is shown that the damping rate depends on exciton-phonon coupling constant and the vacuum Rabi frequency. Even at absolute zero temperature and in the vacuum cavity, the exciton-phonon interaction and exciton-photon interaction still cause excitonic decoherence. We also predict that under strong control fields the collapse and revival of excitonic Rabi oscillation may be observed for the quantum dots with small exciton-phonon coupling in the $T\ensuremath{\rightarrow}0$ limit.
We present a numerically complete study of the combined dynamics of a quantum dot exciton coupled to a single quantized cavity mode and a continuum of acoustic phonons. We demonstrate that acoustic phonons have a pronounced impact on effects characteristic of the strong light-matter coupling regime, such as vacuum Rabi oscillations and collapse and revival scenarios. This impact is considerable already at zero temperature, where initially no phonons are present. Counterintuitively it is found that an increase of the light-matter coupling does not necessarily enhance the visibility of strong-coupling effects. In fact, for typical experimental situations, a stronger light-matter coupling will considerably reduce the visibility.