Highly-Indistinguishable Single-Photons at 1550 nm from a Two-photon Resonantly Excited Purcell-enhanced Quantum Dot

TL;DR

The study tackles the challenge of generating on-demand, highly indistinguishable single photons at 1550 nm for quantum networks. It uses a cavity-enhanced InAs/In_{0.53}Al_{0.23}Ga_{0.24}As QD in a circular Bragg-grating cavity driven by resonant two-photon excitation (TPE), leveraging asymmetric Purcell enhancement to approach the two-photon interference limit via $V_{ m max,TPE}=\frac{1}{1+T_1^{XX}/T_1^{X}}$. Key results include $T_1^{XX}=67.4(2)$ ps, $T_1^{X}=544(2)$ ps (deconvolved to $64(1)$ ps), $g^{(2)}_{XX}(0)=0.007(1)$ and $g^{(2)}_X(0)=0.006(1)$, with $V^{XX}_{raw}=0.90(3)$ and $V^{X}_{raw}=0.61(4)$ under TPE, aligned with theory. Implementing stimTPE with a second pulse tuned to the XX-X transition increases X indistinguishability to $V^{X}_{raw,stim}=0.69(3)$ while preserving low multiphoton probability, illustrating a practical route to high-quality telecom photons and potentially polarization-entangled pairs for fiber networks.

Abstract

In this work we present a cavity-enhanced InAs/$\mathrm{In_{0.53}Al_{0.23}Ga_{0.24}As}$ quantum dot (QD) single-photon source in the telecom C-band with a record-low biexciton emitter decay time of \SI{67.4(2)}{ps} under resonant two-photon excitation (TPE). We observe strong multiphoton suppression associated with $g^{(2)}_\mathrm{X}(0) = 0.006(1)$ and $g^{(2)}_\mathrm{XX}(0) = 0.007(1)$ for the exciton (X) and biexciton (XX) emission, respectively. Due to a asymmetric Purcell enhancement of the XX-X cascade, the two-photon interference (TPI) visibility of XX photons under $π$-pulse excitation of $V_{\rm{TPI}} = 90(3)\%$ reaches the theoretical limit and clearly exceeds the $\sim60\%$ expected for standard XX-X cascades without photonic engineering. Furthermore, adding a second timed laser pulse coinciding with XX emission energy, we demonstrate stimulated TPE in the telecom C-Band. The result is an improved TPI visibility of the X photons of $V_{\rm{TPI}}=0.69(3)$ compared to TPE with $V_{\rm{TPI}}=0.61(4)$, with both being reduced compared to the theoretical values due to present dephasing effects. The advances presented in this work hold important promises for the implementation of advanced schemes of quantum communication using deterministic quantum light sources.

Figures (3)

• Figure 1: (a) Spectrum of the QD-device under continuous wave above-band excitation (top) and pulsed TPE (bottom). In addition to the X state at 1550.4nm (green) and the XX state at 1557.0nm (red), a third suspected charged XX* state at 1557.7nm (blue) is observed. The excitation laser wavelength is tuned to 1553.6nm, which corresponds to half of the XX-X transition energy. The cavity's reflection signal using a broadband source is shown in orange. (b) Rabi oscillations of the XX state (top) and the X state (bottom) showing the resonant excitation of the QD system. (c) and (d) second-order autocorrelation measurement of the XX and X photons (red and green respectively), showing the single-photon-nature of the presented source as integrated $g^{(2)}(0)$-values are shown.
• Figure 2: HOM-type TPI visibility measurement of XX (a) and X photons (b). We observe a record-high TPI visibility of the XX photons of $V_{XX} = 90(3)\%$. The X photon's visibility is impaired due to dephasing effects ($V_X = 61(4)\%$). (c) Dependence of TPI visibility on the radiative lifetime ratio. The solid black curve represents the theoretical maximum visibility $V_{\mathrm{max, TPE}}$ as a function of the ratio between biexciton ($T_1^{XX}$) and exciton ($T_1^X$) lifetimes. The experimental result (red circle) shows excellent agreement with the theoretical limit.
• Figure 3: (a) Spectrum of the presented source under TPE (top) and stimTPE (bottom). The stimulation laser is energetically tuned to the XX-X transition, which effectively doubles the PL signal in the stimulated polarization state. (b) Relative PL signal of the X photons as a function of delay between the excitation and the stimulation laser. The optimal stimulation window is observed at $\approx$ 3ps. The inset shows Rabi oscillations on the X state as a function of stimulation pulse power showing the coherent nature of the stimulation. (c) Second-order autocorrelation measurement of the X photons under stimTPE. The amount of multi-photon events is not increased in comparison to the TPE. (d) HOM-type TPI visibility measurement of the X photons under stimTPE. The TPI visibility is increased by $8(7)\%$ with respect to the TPE case.