Two-photon interference from as-grown InAsP/InP quantum dots under detuned excitation

This study evaluates the quantum optical properties of InAsP/InP quantum dots (QDs) grown via molecular beam epitaxy. Specifically, the authors investigate whether these as-grown emitters—without the use of complex cavity integration or Purcell enhancement—can generate indistinguishable single photons in the third telecommunication window while using detuned quasi-resonant excitation to suppress scattered laser light.

The researchers utilized a quasi-resonant excitation scheme with a 32 meV detuning from the emission energy to minimize background noise. They characterized the QDs using photoluminescence excitation (PLE) spectroscopy, power-dependent measurements, and polarization-resolved studies. To assess the quantum nature of the light, they performed Hanbury Brown and Twiss (HBT) experiments to measure multiphoton emission probability and Hong-Ou-Mandel (HOM) interferometry to determine photon indistinguishability at two different pulse separations (13.1 ns and 5.3 ns).

The study confirms the single-photon nature of the emission with a raw second-order autocorrelation value of g(2)(0) = 0.076(6). The HOM measurements revealed low but non-zero visibility, with values of 0.094(4) and 0.106(5) for pulse separations of 13.1 ns and 5.3 ns, respectively. The increase in visibility at shorter pulse separations suggests that the system is affected by slow spectral diffusion, where charge fluctuations in the environment cause decoherence on a nanosecond timescale. The authors conclude that while these as-grown dots are promising for fiber-based quantum applications, further improvements in indistinguishability will require Purcell enhancement via optical cavities to shorten the radiative lifetime relative to the dephasing time.