Cavity quantum electrodynamics, a central research field in optics and solid-state physics, addresses properties of atom-like emitters in cavities and can be divided into a weak and a strong coupling regime. For weak coupling, the spontaneous emission can be enhanced or reduced compared with its vacuum level by tuning discrete cavity modes in and out of resonance with the emitter. However, the most striking change of emission properties occurs when the conditions for strong coupling are fulfilled. In this case there is a change from the usual irreversible spontaneous emission to a reversible exchange of energy between the emitter and the cavity mode. This coherent coupling may provide a basis for future applications in quantum information processing or schemes for coherent control. Until now, strong coupling of individual two-level systems has been observed only for atoms in large cavities. Here we report the observation of strong coupling of a single two-level solid-state system with a photon, as realized by a single quantum dot in a semiconductor microcavity. The strong coupling is manifest in photoluminescence data that display anti-crossings between the quantum dot exciton and cavity-mode dispersion relations, characterized by a vacuum Rabi splitting of about 140 microeV.

We observe antibunching in the photons emitted from a strongly-coupled single quantum dot and pillar microcavity in resonance. When the quantum dot was spectrally detuned from the cavity mode, the cavity emission remained antibunched, and also anticorrelated from the quantum dot emission. Resonant pumping of the selected quantum dot via an excited state enabled these observations by eliminating the background emitters that are usually coupled to the cavity. This device demonstrates an on-demand single photon source operating in the strong coupling regime, with a Purcell factor of 61 ± 7 and quantum efficiency of 97%.PACS numbers: 78.67. Hc, 78.55.Cr, 78.90.+t Cavity quantum electrodynamics (CQED), addressing the interaction between a quantum emitter and a cavity, has been a central topic in atomic physics for decades [1,2,3,4] and has recently come to the forefront of semiconductor physics [5,6,7,8]. If the coupling between the single quantum emitter and cavity mode is strong compared to their decay rates, the emitter and cavity coherently exchange energy back and forth leading to Rabi oscillations. This strong coupling (SC) regime is of great interest for a variety of quantum information applications, especially with a solid-state implementation. A SC QD-microcavity system could lead to a nearly ideal single photon source (SPS) for quantum information processing, with extremely high efficiency and photon indistinguishability [9]. The same technology could be applied as an interface between a spin qubit and single photon qubit in a quantum network [10].SC between a single atom and a cavity was first achieved more than a decade ago [4]. An analogous system in the solid-state is the excitonic transition of a semiconductor quantum dot (QD) together with a semiconductor microcavity. Several groups have recently reported SC between a single (In,Ga)As QD and either micropillar [5], photonic crystal [6], or microdisk [7] resonators. SC can also occur between a single cavity mode and a collection of degenerate emitters, such as an ensemble of atoms or a quantum well [11]. However, in the latter case the behavior is classical: adding or removing one emitter or one photon from the system has little effect.In previous studies of QD-cavity SC [5,6,7] it was argued that the spectral density of QDs was sufficiently low that it is unlikely that several degenerate emitters contributed to the anticrossing. However, it was not verified that the system had one and only one emitter. There was a surprisingly large amount of emission from the cavity mode when the QD was far detuned. It was unclear whether this emission originated from the particular single QD or from many background emitters. An important step to establish SC in solid-state CQED is verification that the double-peaked spectrum originates from a single quantum emitter, not a collection of emitters, interacting with the cavity mode.In this Letter we present proof that the emission from a strongly-coupled QD-microcavity system is dominated by a single quantum emitter....

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We present measurements of first- and second-order coherence of quantum-dot micropillar lasers together with a semiconductor laser theory. Our results show a broad threshold region for the observed high-beta microcavities. The intensity jump is accompanied by both pronounced photon intensity fluctuations and strong coherence length changes. The investigations clearly visualize a smooth transition from spontaneous to predominantly stimulated emission which becomes harder to determine for high beta. In our theory, a microscopic approach is used to incorporate the semiconductor nature of quantum dots. The results are in agreement with the experimental intensity traces and the photon statistics measurements.

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The authors report on AlAs∕GaAs micropillar cavities with unprecedented quality factors based on high reflectivity distributed Bragg reflectors (DBRs). Due to an increased number of mirror pairs in the DBRs and an optimized etching process record quality (Q) factors up to 165.000 are observed for micropillars with diameters of 4μm. Optical studies reveal a very small ellipticity of 5×10−4 of the pillar cross section. Because of the high Q factors, strong coupling with a vacuum Rabi splitting of 23μeV is observed for micropillars with a diameter of 3μm.

In a homogeneous two-dimensional system at non-zero temperature there can be no ordering of infinite range 1,2 . However, for a Bose liquid under such conditions, a superfluid phase is predicted 3-5 . Bound vortex-antivortex pairs dominate the thermodynamics and phase coherence properties in this superfluid regime. It is believed that several systems share this behaviour when the parameter describing their ordered state has two degrees of freedom 6 . This theory has been tested for some of them 7-12 , but there has been no direct experimental observation of a quasi-condensate that includes a bound vortex-antivortex pair. Here we present an experimental technique that can identify a single vortex-antivortex pair in a two-dimensional exciton-polariton condensate. The pair is generated through the inhomogeneous spot profile of the pumping laser, and is revealed in the time-integrated phase maps acquired using Michelson interferometry. Numerical modelling based on the open-dissipative Gross-Pitaevskii equation suggests that the pair evolution is distinctly different in this non-equilibrium system compared with atomic condensates 13 .Microcavity exciton polaritons 14 behave as a system of strictly two-dimensional bosons when their density is below the exciton saturation density. As a result of their half-light half-matter nature, their effective mass is extremely small, so that quantum many-body effects are important at relatively high temperatures, even up to room temperature 15 . In particular, dynamic polariton condensation is observed [16][17][18] , and its signatures are similar to Bose-Einstein condensation, namely massive occupation of the ground state and phase coherence up to large distances. However, the short lifetime allows only the formation of a quasi-equilibrium steady state, in which polaritons escaping from the cavity are continuously replenished by the external pump through an intermediate reservoir state.Here, we show that single vortex-antivortex pairs can be observed in an exciton-polariton condensate. We have created a pumping spot that generates a minimum of the condensate density at the centre. A zero in density can be thought of as a superposition of a vortex and antivortex that can be separated by an external perturbation 19 . Thus, the centre of the condensate acts as a source of vortex-antivortex pairs. We have found that for a particular condensate size, there is on average one pair at any time. A Michelson interferometer is used to reconstruct the time-integrated phase map of the system. When the sample disorder potential is stronger than the blueshift induced by polaritonpolariton interactions, pinned pairs appear at certain locations. When the sample disorder potential is weak, on the other hand, they are mobile. They appear along a fixed axis, because of a small asymmetry in the pumping spot, and are created with a random polarization, namely the vortex can appear on the right side of the spot and the antivortex on the left, or vice versa. In the time-integrated measurement, two disti...

Detailed properties of resonance fluorescence from a single quantum dot in a micropillar cavity are investigated, with particular focus on emission coherence in the dependence on optical driving field power and detuning. A power-dependent series over a wide range reveals characteristic Mollow triplet spectra with large Rabi splittings of |Ω|≤15  GHz. In particular, the effect of dephasing in terms of systematic spectral broadening ∝Ω(2) of the Mollow sidebands is observed as a strong fingerprint of excitation-induced dephasing. Our results are in excellent agreement with predictions of a recently presented model on phonon-dressed quantum dot Mollow triplet emission in the cavity-QED regime.