Non-Markovian phonon dephasing of a quantum dot in a photonic-crystal nanocavity

Single quantum dots (QDs) can be embedded in nanocavities in order to enhance the interaction with a single mode of the electromagnetic field, thereby making them candidates for applications in quantum information systems. In this work [1], we investigate the coupling between single QDs and localized modes in photonic crystal (PC) cavities. From measurements of the detuning-dependent decay rate of a QD embedded in an L3 PC cavity we find a surprisingly broadband enhancement of the decay rate, cf. Fig. 1, which cannot be explained using the standard approach of a dissipative Jaynes-Cummings (JC) model. Similar measurements on a single QD tuned through an Anderson localized (AL) mode [2] in a PC waveguide show that in this system the decay rates closely follow the JC model.
We introduce a novel microscopic model taking the interaction with longitudinal-acoustic (LA) phonons into account. Using this model, we are able to explain the broadband enhancement in an L3 cavity, and the quantitative difference compared to the AL-cavity arises from a larger background decay rate in the AL-cavity due to the presence of leaky radiation modes. The concept of the effective phonon density of states (DOS) is introduced, which determines the rate of phonon-assisted spontaneous emission. If, e.g., the QD is blue-detuned from the cavity mode, the QD can emit a photon into the cavity mode by emitting the residual energy as a phonon [3]. Our microscopic model allows us to extract the effective phonon DOS, that turns out to agree with a model for bulk phonons.