Gigahertz-clocked Generation of Highly Indistinguishable Photons at C-band Wavelengths

Abstract

High-performance single-photon sources at telecom C-band wavelentghs are key building blocks for applications in long-distance quantum communication. Here, we report the generation of highly indistinguishable, single photons at a clock-rate of 2.5 GHz. This is achieved by coherently driving the biexciton transition ($T_1^\mathrm{XX}=64(1)\,$ps) of a semiconductor quantum dot embedded in a microcavity with strong asymmetric Purcell enhancement. Employing pulsed two-photon resonant excitation, strong multiphoton suppression with $g^{(2)}(0) < 4\%$ and high two-photon-interference visibility of $V_\mathrm{raw}> 85\%$ is observed. The observed photon indistinguishability is close to the theoretical limit expected for the photonically engineered radiative cascade and matches values obtained at lower repetition rates. Our results show a substantial advancement towards interference-based quantum information protocols at unprecedented data rates in the telecom C-Band.

Figures (2)

• Figure 1: (a) QD spectrum under 2.5 GHz clocked TPE. Neutral exciton (X), neutral biexciton (XX), as well as the excitation laser wavelength are indicated. The cavity mode is depicted in orange. The inset shows the power dependent photoluminescence (PL) signal of the XX state under 2.5 GHz clocked TPE revealing Rabi rotations. (b) Time resolved X and XX PL signal with decay times extracted from mono-exponential fits. (c) Theoretical time-dependent X emission $\rho_\mathrm{X}(t)$ based on convoluted XX and X decay. The dashed line indicates the time interval between the excitation pulses. (d) Second order autocorrelation function $g^{(2)}(\tau)$ of the XX state under 2.5 GHz (red) and 0.1 GHz (blue) clocked TPE, with integrated respective $g^{(2)}(0)$-values. The inset shows a zoom-in of the histogram around $\tau=0$ with indicated integration area for the GHz-clocked measurement indicated as black dashed lines.
• Figure 2: (a) Hong-Ou Mandel (HOM) autocorrelation measurement $g^{(2)}_\mathrm{HOM}(\tau)$ of the XX state under 2.5 GHz clocked TPE. The photon time delay corresponds to $1/f_\mathrm{rep}=400\,$ps. The maximally distinguishable cross-polarized measurement is shown in blue, the maximally indistinguishable co-polarized measurement in red. (b) 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 ($T_1^{\rm XX}$) and exciton ($T_1^{\rm X}$) lifetimes. The experimental corrected result (blue circle) shows excellent agreement with the theoretical limit, while the uncorrected result (red circle) shows a slight deviation from the theoretical maxiumum, due to the residual pulse overlap.