Two‐Photon Interference from an InAs Quantum Dot Emitting in the Telecom C‐Band

Two‐photon interference from an InAs/InAlGaAs quantum dot (QD) emitting in the telecom C‐band with a raw two‐photon interference visibility of VHOM=(71.9±0.2)${{V}_{{\mathrm{HOM}}}} = ( {71.9 \pm 0.2} )$ % 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 T1=(257.5±0.2)${{T}_1} = ( {257.5 \pm 0.2} )$ ps is found corresponding to a Purcell factor of Fp ≧ (4.7±0.5)$( {4.7 \pm 0.5} )$ . Pronounced anti‐bunching of the second‐order autocorrelation function at zero time delay g(2)(0)=(0.0307±0.0004)${{{\mathrm{g}}}^{( 2 )}}\ ( 0 ) = ( {0.0307 \pm 0.0004} )$ 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.