InAs(P)/InP QDs as sources of single indistinguishable photons at 1.55 µm

Epitaxial quantum dots (QDs) exhibit substantial promise as non-classical light sources in quantum technologies. In particular, the generation of single, indistinguishable photons on demand is pivotal for advanced quantum cryptographic key exchange algorithms. This study investigates the quantum optical characteristics of single photons emitted by InAs(P)/InP QDs heterogeneously integrated with silicon. The investigated QDs, grown via metalorganic vapor-phase epitaxy in the Stranski-Krastanow mode, showcase the emission at ~1.55 µm, indispensable for long-haul, low-loss optical transmission through standard silica fibers. The photon extraction efficiency is enhanced to ~10% by employing a metallic mirror beneath the QDs in combination with a top mesa structure [4]. Our study confirms the single-photon emission from the QDs through measurements of the second-order autocorrelation function, revealing (2) (0) = 0.005(4) for biexciton under two photon resonant excitation of the biexciton-exciton radiative cascade. To investigate the degree of indistinguishability of emitted photons, we conducted also HongOu-Mandel-type two-photon interference (TPI) experiment. The TPI visibility, quantifying the degree of indistinguishability of emitted photons, is crucial in examining the coherence of carriers within the QD. Exciton-phonon interactions and carrier-carrier scattering significantly contribute to the degradation of coherence within the QDs. Using direct integration of the raw experimental data or fitting to a model, we evaluated the raw (i.e., ‘as measured’) and the post-selected TPI visibility up to 35% and 73%, respectively [6], which represents a state-of-the-art achievement for InAs/InP QDs emitting at 1.55 µm. The significant progress in the generation of single indistinguishable photons in the telecom C-band offers crucial insights into their potential integration within quantum information technologies.