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physica status solidi (b)

Highly indistinguishable photons from a quantum dot in a microcavity

Stefanie Weiler, Ata Ulhaq, Sven M. Ulrich, Stephan Reitzenstein, Andreas Löffler, A. Forchel, Peter Michler

Published Dec 22, 2010• 12 citations
Publisher

Abstract

Abstract We investigated the indistinguishability of photons emitted by single self‐assembled (In,Ga)As/GaAs quantum dots (QDs) coupled to the fundamental mode (FM) of a pillar microcavity. By systematic pre‐characterization, optimum conditions with respect to fast radiative decay (Purcell enhancement), long coherence time, and close to background‐free single‐photon emission have been derived. For different spectral detunings between QD and FM emission, Hong‐Ou‐Mandel‐type (HOM) two‐photon interference has been measured as a function of temporal photon wavepacket overlap. Detailed analysis of our data (under consideration of setup limitations) anticipates the generation of highly indistinguishable photons with up to VHOM = 0.82 visibility.

DOI
10.1002/pssb.201000781

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Abstract We investigated the indistinguishability of photons emitted by single self‐assembled (In,Ga)As/GaAs quantum dots (QDs) coupled to the fundamental mode (FM) of a pillar microcavity. By systematic pre‐characterization, optimum conditions with respect to fast radiative decay (Purcell enhancement), long coherence time, and close to background‐free single‐photon emission have been derived. For different spectral detunings between QD and FM emission, Hong‐Ou‐Mandel‐type (HOM) two‐photon interference has been measured as a function of temporal photon wavepacket overlap. Detailed analysis of our data (under consideration of setup limitations) anticipates the generation of highly indistinguishable photons with up to VHOM = 0.82 visibility.
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Applying continuous-wave pure resonant s-shell optical excitation of individual quantum dots in a high-quality micropillar cavity, we demonstrate the generation of post-selected indistinguishable photons in resonance fluorescence. Close to ideal visibility contrast of 90% is verified by polarization-dependent Hong-Ou-Mandel two-photon interference measurements. Furthermore, a strictly resonant continuous-wave excitation together with controlling the spontaneous emission lifetime of the single quantum dots via tunable emitter-mode coupling (Purcell) is proven as a versatile scheme to generate close to Fourier transform-limited (T2/(2T1)=0.91) single photons even at 80% of the emission saturation level.
Abstract Two‐photon interference from an InAs/InAlGaAs quantum dot (QD) emitting in the telecom C‐band with a raw two‐photon interference visibility of % is demonstrated. This is achieved by a two‐fold approach: an improvement of the molecular beam epitaxial growth for better QDs, and integration of the QDs into an optical circular Bragg grating resonator for a Purcell enhancement of the radiative decay rate. The quantum optical properties of the fabricated device are studied by means of time‐correlated single‐photon counting under quasi‐resonant excitation of the charged exciton line. A reduced lifetime of ps is found corresponding to a Purcell factor of F p ≧ . Pronounced anti‐bunching of the second‐order autocorrelation function at zero time delay confirms the single‐photon emission character. The two‐photon interference is demonstrated with an unbalanced Mach‐Zehnder interferometer in the Hong‐Ou‐Mandel configuration. Strategies are discussed on how to further improve the indistinguishability, and provide a survey of the state‐of‐the‐art.
Semiconductor pillar microcavities containing quantum dots have shown promise as efficient sources of single and correlated pairs of photons, which may find applications in quantum information processing. In this paper we discuss the use of these sources to generate single photons and the use of pillars with elliptical cross-section to enhance and select a particular photon state. Single-photon interference measurements are also performed and show coherence times of up to 180 ps for quasi-resonantly pumped dots. Hong–Ou–Mandel-type two-photon interference measurements using a fibre interferometer indicate that individually created photons display a large degree of indistinguishability.
We demonstrate the emission of highly indistinguishable photons from a quasi-resonantly pumped coupled quantum dot--microcavity system operating in the regime of cavity quantum electrodynamics. Changing the sample temperature allows us to vary the quantum dot--cavity detuning and, on spectral resonance, we observe a threefold improvement in the Hong-Ou-Mandel interference visibility, reaching values in excess of 80%. Our measurements off-resonance allow us to investigate varying Purcell enhancements, and to probe the dephasing environment at different temperatures and energy scales. By comparison with our microscopic model, we are able to identify pure dephasing and not time jitter as the dominating source of imperfections in our system.