Photonic wires are the simplest extended low-dimensional systems. Photonic crystal confinement confers them a divergent density of states at zero-group-velocity points, which leads to enhancement of spontaneous emission rates [D. Kleppner, Phys. Rev. Lett. 47, 233 (1981)10.1103/Phys. Rev. Lett. 47.233]. We experimentally evidence, for the first time, the spectral signature of these Purcell factor singularities, using the out-of-plane emission of InAs quantum dots buried in GaAs/AlGaAs based photonic crystal based wire. Additionally, in-plane collection at the wire exit shows large enhancements of the signal at some of the density of states singularities.

We demonstrate that a single photoexcited InGaAs semiconductor quantum dot (QD) grown by organo-metallic chemical vapor deposition on prepatterned substrates emits one photon at a time, with no uncontrolled background photon emission, making it an excellent single photon emitter. Moreover, our fabrication technique offers complete site control and small inhomogeneous broadening of QD arrays, which is essential for the practical implementation of QDs in efficient solid-state single photon emitting devices.

We report on the spontaneous emission of a single-quantum dot embedded in a two-dimensional photonic crystal cavity. The resonant coupling between the dot and the strongly localized optical mode significantly shortens the spontaneous emission lifetime, so that the coherence time of the emitted photons is dominated by radiative effects: The emitted photons are indistinguishable, with a mean wave-packet overlap as high as 72%.

We report on a series of experiments on the second-order interference of two single photons emitted sequentially by a single quantum dot. The visibility of this interference probes the indistinguishability of the emitted photons; visibilities as high as 0.75 at 4 K have been achieved. At higher temperatures, dephasing of the quantum dot exciton degrades the indistinguishability of the emitted photons and the visibility of the interference. However, we demonstrate that engineering of the radiative lifetime of the quantum dot by the implementation of the Purcell effect in a microcavity, can restore indistinguishability and improve the visibility of second-order interference. At the same time, we demonstrate the resonant character of the Purcell effect.When two indistinguishable single photons enter separately, but simultaneously, into the two input ports of a beam splitter, they both emerge together, along the same output port of the beam splitter, as if they had "coalescedЉ into a two-photon Fock state. 1 This second-order interference phenomenon has been used to highlight many fundamental aspects of quantum optics, such as the nonlocality of quantum mechanics, 2 or the measurement of the photon transit time in superluminal photon tunneling. 3 Moreover, the interference of two single photons on a beam splitter plays a central role in recent proposals for the realization of two-qubit gates as key elements of photon-based quantum computing schemes. 4 The two-photon interference phenomenon was first observed using pairs of twin photons produced simultaneously by parametric down conversion. 1 More recently, it was demonstrated using two single photons originating from two distinct emitters: two independent but synchronized optical parametric oscillators, 5 two sequential emission events of a single atom, 6 and a single semiconductor quantum dot 7 excited by a pair of laser pulses.The situation in which two-photon interference occurs between truly independent photons presents an important difference from that of twin parametric photons. Each individual emitter may be subject to fluctuations independently of the other, thus "marking" each of the two photons differently and destroying their indistinguishability. For the case of a semiconductor quantum dot, for example, such fluctuations are due to the exciton-phonon interaction which causes the dephasing of the emitting exciton state, with a characteristic dephasing time T 2 * . In order to reduce the impact of dephasing on the emission process, and thus restore the indistinguishability of the emitted photons, the radiative lifetime of the emitter ͑denoted by T 1 ͒ must be shortened, so that it dominates over T 2 * in determining the overall coherence time of the photon wave train, T 2 , defined byThis can be achieved by embedding the quantum dot in a microcavity, 8 thus taking advantage of cavity quantum electrodynamics effects ͑Purcell effect 9 ͒. The spontaneous emis-sion rate of a dipole is given by Fermi's Golden Rule aswhere E vac ͑r͒ is the vacuum electric field a...

We report on photon correlation measurements on a single quantum dot formed at fluctuations of the interface of a GaAs/GaAlAs quantum well. We demonstrate that under pulsed nonresonant excitation, the quantum dot emits a single photon per pulse. This shows that after the photon emission, there is no refill of the quantum dot by the nearby two-dimensional reservoir of delocalized states. The possibility of delivering Fourier transform limited single photons makes this system a good candidate for exciton- and photon-based quantum information processing schemes.