The development and physical understanding of high-beta nanolasers operating in regime of cavity-quantum-electrodynamics (cQED) is a highly interdisciplinary field of research, involving important aspects of nanotechnology, quantum optics, and semiconductor physics. Of particular interest is the quantum limit of operation, in which a few or even a single emitter act as gain material.
The regime of strong light-matter coupling is typically associated with weak excitation. With current realizations of cQED systems, strong coupling may persevere even at elevated excitation levels sufficient to cross the threshold to lasing. In the presence of stimulated emission, the vacuum-Rabi doublet in the emission spectrum is modiﬁed and the established criterion for strong coupling no longer applies.
Based on an analytic approach, we provide a generalized criterion for strong coupling and the corresponding emission spectrum that includes the inﬂuence of higher Jaynes-Cummings states. The applicability is demonstrated in a theory-experiment comparison of a state-of-the-art few-emitter quantum-dot (QD)–micropillar laser as a particular realization of the driven dissipative Jaynes-Cummings model . Furthermore, we address the question if and for which parameters true single-emitter lasing can be achieved. By using a master-equation approach for up to 8 QDs coupled to the mode, we provide evidence for the coexistence of strong coupling and lasing in our system in the presence of background emitter contributions by identifying signatures in the mean-photon number, the photon-autocorrelation function, and the emission linewidth.
 C. Gies et al., accepted for publication in PRA, arxiv:1606.05591
The conditions for the appearance of a sharp laser transition are formulated in terms of a scaling limit, involving
vanishing cavity loss and light-matter coupling, k → 0, g → 0, such that g2/k stays finite. It is shown analytically
that in this asymptotic parameter domain, and for pump rates above the threshold value, the photon output
becomes large in a sense that is specified, and the photon statistics becomes strictly Poissonian. Numerical
examples for the case of a two-level and a three-level emitter are presented and discussed in relation to the
We study the optical properties of semiconductor quantum dots by means of a quantum-kinetic theory. The
excitation-induced dephasing and the corresponding line-shifts of the interband transitions due to carrier-carrier
Coulomb interaction and carrier-phonon interaction are determined and used in conjunction with the usual
ingredients of a gain calculation like Coulomb enhancement and State filling to set up a microscopic calculation
of the quantum dot gain. We find that for very high carrier densities in QD systems the maximum of the optical
gain can decrease with increasing carrier density due to a delicate balancing between state filling and dephasing.
The time evolution of optically excited carriers in semiconductor quantum wells and quantum dots is analyzed
for their interaction with LO-phonons. Both the full two-time Green's function formalism and the one-time
approximation provided by the generalized Kadanoff-Baym ansatz are considered, in order to compare their
description of relaxation processes. It is shown that the two-time quantum kinetics leads to thermalization in all
the examined cases, which is not the case for the one-time approach in the intermediate-coupling regime, even
though it provides convergence to a steady state. The thermalization criterion used is the Kubo-Martin-Schwinger