We have studied a strongly coupled quantum dot-micropillar cavity system subject to an external magnetic field. The large diamagnetic response of elongated In_{0.3}Ga_{0.7}As quantum dots is exploited to demonstrate magneto-optical resonance tuning in the strong coupling regime. Furthermore, the magnetic field provides an additional degree of freedom to in situ manipulate the coupling constant. A transition from strong coupling towards the critical coupling regime is attributed to a reduction of the quantum dot oscillator strength when the magnetic confinement becomes significant with regards to the exciton confinement above 3 T.
We investigate the power-dependent photoluminescence spectra from a strongly coupled quantum dot-cavity system using a quantum master equation technique that accounts for incoherent pumping, pure dephasing, and fermion or boson statistics. Analytical spectra at the one-photon correlation level and the numerically exact multi-photon spectra for fermions are presented. We compare to recent experiments on a quantum dot-micropiller cavity system and show that an excellent fit to the data can be obtained by varying only the incoherent pump rates in direct correspondence with the experiments. Our theory and experiments together show a clear and systematic way of studying stimulated-emission induced broadening and anharmonic cavity-QED. Introduction.-Single quantum dot (QD) -cavity systems facilitate the realization of solid state qubits (quantum bits) and have applications for producing single photons [1,2,3] and entangled photons [4,5]. Rich in physics and potential applications, the coupled QDcavity has been inspiring theoretical and experimental groups to probe deeper into the underlying physics of both weak and strong coupling regimes of semiconductor cavity-QED (quantum electrodynamics). Key signatures of cavity-QED include the Purcell effect and vacuum Rabi oscillations. Although a well known phenomenon in atomic cavity optics [6], vacuum Rabi splitting in a semiconductor cavity was only realized a few years ago [7,8,9]. Inspired by the recent surge of related experiments, many researchers have been working hard to develop new theoretical tools to understand the semiconductor cavity-QED systems. For example, the persistent excitation of the cavity mode for large excitoncavity detunings was measured [10,11], and qualitatively explained by extended theoretical approaches that account for coupling between the leaky cavity mode and the exciton, and by showing that the main contribution to the emitted spectrum comes from the cavity-mode emission [12,13,14,15,16]. These formalisms assume an initially excited exciton or an initially excited leaky cavity mode, and they are valid for low pump powers. However, an interesting question that has been posed recently, e.g., see Refs. [17,18,19], is what is the role of an incoherent pump on the photoluminescence (PL) spectra, where the pump can excite the exciton or cavity mode? To experimentally investigate the pump-dependent spectra, two recent experiments have been respectively reported by Münch et al. [20] for a QD-micropillar system, and by Laucht et al.[21] for a QD-photonic crystal system; these measurements show the pump-induced crossover from strong to weak coupling.In this work, we present a master equation (ME) the-
A strongly coupled quantum dot-micropillar cavity system is studied under variation of the excitation power. The characteristic double peak spectral shape of the emission with a vacuum Rabi splitting of 85 microeV at low excitation transforms gradually into a single broad emission peak when the excitation power is increased. Modelling the experimental data by a recently published formalism [Laussy et al., Phys. Rev. Lett. 101, 083601 (2008)] yields a transition from strong coupling towards weak coupling which is mainly attributed to an excitation power driven decrease of the exciton-photon coupling constant.
Semiconductor microcavities play a key role in connecting exciton states and photons in advancing quantum information in solids. In this work we report on coherent interaction between high quality microcavity photon modes and spin states of a quantum dot in the strong coupling regime of cavity quantum electrodynamics. The coupling between the photon and exciton modes is studied by varying the temperature, where the spin states are resolved with a magnetic field applied in Faraday configuration. A detailed oscillator model is used to extract coupling parameters of the individual spin and cavity modes, which shows that the coupling depends on features of the mode symmetries. Our results demonstrate an effective coupling between photon modes that is mediated by the exciton spin states.Cavity quantum electrodynamics ͑cQED͒ of systems of quantum dots ͑QDs͒ coupled to semiconductor microcavities has attracted considerable attention, particularly after recent demonstrations of strong ͑coherent͒ coupling in them. 1,2 These systems extend long-standing work on atoms in cavities to the solid-state environment. They provide an interface between the atomic-like states of quantum dots and photon polarization states ͑flying qubits͒ in quantum information. Two-level quantum emitters, given by excitons or spins, coupled coherently to optical modes of microcavities are the essential building blocks in solid-state quantum information. 3,4 Optical manipulation of the quantum dot states coupled to cavity photons can provide two-qubit gates needed for logic operations 5 and also distributed architectures for quantum communications and computing. [6][7][8][9] Previous work on strong coupling in semiconductor microcavities has involved the interaction of spin degenerate excitons with the optical cavity modes. Strong coupling has been demonstrated using several microcavity structures, 1,2,10 and tuning of the modes with temperature and electric fields has been implemented. 11,12 Recently, we demonstrated tuning of the exciton-cavity interaction with a magnetic field through the diamagnetic shift and the exciton wave-function size. 13 In addition, cQED in the strong-coupling regime has been exploited as a tool for QD spectroscopy and to identify a cavity mediated mixing of bright and dark exciton states. 14 However, although spin-related light-matter interactions in cQED have been involved in a number of proposals, 5,15,16 they have not yet been demonstrated experimentally in the field of quantum optics of solid state.Here we study the interaction of the spin degree of freedom of excitons in InGaAs quantum dots with the photon cavity modes in pillar microcavities, and we address the question of how the polarization of the modes affects their coupling. The spin states are split with a Faraday magnetic field and their interactions with individual cavity modes are identified in magnetophotoluminescence experiments. The interactions between individual spin-resolved exciton states and cavity modes are obtained by comparison with a detailed co...
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