Coherent control and high purity single-photon emission from telecom quantum dots on metamorphic InGaAs

Abstract

Semiconductor quantum dots emitting in the telecommunication O- and C-bands are promising candidates as single-photon sources for fiber-based quantum communication. In this work, we show how coherent quasi-resonant and phonon-assisted excitation help reveal the intrinsic optical properties of InAs quantum dots embedded in relaxed InGaAs matrices on top of metamorphic InGaAs layers for achieving emission in the telecom bands. By systematically comparing excitation schemes, we separate excitation-induced effects from intrinsic emitter properties. This allows us to observe linewidths as narrow as 21 $μ$eV, the disappearance of slow decay channels, and single-photon purity reaching second-order autocorrelation values in the order of $10^{-2}$. Photoluminescence excitation reveals higher excited states, enabling coherent control of trion transitions and the observation of Rabi-like oscillations in both telecom bands. These results confirm the promising potential of these quantum dots for applications in quantum technologies.

This experimental study asks how excitation-induced carrier dynamics obscure the optical properties of InAs quantum dots embedded in relaxed InGaAs on metamorphic buffers, emitting in the telecom O- and C-bands. It compares above-bandgap, wetting-layer, quasi-resonant excited-state, and longitudinal-acoustic-phonon-assisted excitation using spectroscopy, photoluminescence excitation, time-resolved emission, and Hanbury Brown–Twiss measurements at 4 K. Across 17 dots per band, quasi-resonant excitation reduces median trion linewidths from $43$ to $31\,\mu\mathrm{eV}$ in the O-band and from $63$ to $41\,\mu\mathrm{eV}$ in the C-band. The narrowest measured linewidth is $21\pm1\,\mu\mathrm{eV}$, close to the spectrometer resolution. Excitation scans on 19 dots identify discrete excited-state resonances below the wetting-layer continuum. Driving these resonances produces damped Rabi-like oscillations observable up to approximately $3\pi$ pulse area. Time-resolved measurements show suppression of delayed population and slow decay channels, although a slow component persists under phonon-assisted excitation in the illustrated C-band dot. Representative intrinsic trion lifetimes are 0.95 and 1.62 ns; excited-state relaxation times of 28 and 25 ps are comparable to the excitation pulse durations. Phonon-assisted excitation improves measured $g^{(2)}(0)$ from $0.08\pm0.03$ to $0.02\pm0.01$ in the O-band and from $0.17\pm0.02$ to $0.04\pm0.02$ in the C-band. These measurements use sub-saturation excitation, with the C-band comparison taken at different saturation fractions. Fully resonant excitation, lifetime-limited linewidths, and near-unity indistinguishability remain development targets; the paper identifies resonant protocols and microcavity integration as next steps.