Efficient and broadband quantum frequency comb generation in a monolithic AlGaAs-on-insulator microresonator

TL;DR

The study tackles the challenge of scalable, on-chip quantum light sources suitable for frequency-encoded quantum information by exploiting SFWM in a monolithic AlGaAs-on-insulator microring with a $FSR ext{ of about }$ $200$ GHz. The device achieves 11 correlated photon-pair channels across a $35.2$ nm bandwidth, driven by a high effective nonlinearity of $oldsymbol{ extgamma} ext{ ≈ }550$ m$^{-1}$W$^{-1}$ and a net plasma of telecom compatibility, yielding a spectral brightness of $2.64$ GHz mW$^{-2}$nm$^{-1}$. Energy-time entanglement across all channel pairs is demonstrated via Franson interferometry with a net visibility of $V_{ ext{net}} ext{ ~}= 0.973$ and CHSH violations, highlighting robust quantum correlations in a multi-wavelength regime. The results underscore AlGaAsOI microrings as a promising platform for fully integrated, frequency-m multiplexed quantum photonic circuits with potential impact on large-scale quantum networks and frequency-domain quantum processing.

Abstract

The exploration of photonic systems for quantum information processing has generated widespread interest in multiple cutting-edge research fields. Photonic frequency encoding stands out as an especially viable approach, given its natural alignment with established optical communication technologies, including fiber networks and wavelength-division multiplexing systems. Substantial reductions in hardware resources and improvements in quantum performance can be expected by utilizing multiple frequency modes. The integration of nonlinear photonics with microresonators provides a compelling way for generating frequency-correlated photon pairs across discrete spectral modes. Here, by leveraging the high material nonlinearity and low nonlinear loss, we demonstrate an efficient chip-scale multi-wavelength quantum light source based on AlGaAs-on-insulator, featuring a free spectral range of approximately 200 GHz at telecom wavelengths. The optimized submicron waveguide geometry provides both high effective nonlinearity (~550 m$^{-1}$W$^{-1}$) and broad generation bandwidth, producing eleven distinct wavelength pairs across a 35.2 nm bandwidth with an average spectral brightness of 2.64 GHz mW$^{-2}$nm$^{-1}$. The generation of energy-time entanglement for each pair of frequency modes is verified through Franson interferometry, yielding an average net visibility of 93.1%. With its exceptional optical gain and lasing capabilities, the AlGaAs-on-insulator platform developed here shows outstanding potential for realizing fully integrated, ready-to-deploy quantum photonic systems on chip.

Figures (12)

• Figure 1: (a) Optical microscopy image of the AlGaAsOI microring resonator. (b) Measured transmission spectrum and loaded Q factors from 1527 to 1565 nm with an averaged free spectral range (FSR) of about 200 GHz and Q factor of 7.8 $\times$ 10$^4$. (c) Measured and Lorentz fitted resonance dip around 1546 nm (C39) where the pump locates with a loaded, intrinsic and external Q factors of 8.3 $\times$ 10$^4$, 2.6 $\times$ 10$^5$ and 1.2 $\times$ 10$^5$, respectively. (d) Integrated dispersion $D_{int}$ extracted from the transmission and calculated based on the resonator wavelengths, indicating the second-order GVD of -1.12 $\times$ 10$^{-24}$ s$^2$ m$^{-1}$.
• Figure 2: Experimental setups for characterizing the multi-wavelength quantum light source. (a) Multi-wavelength correlated photon-pair generation. (b) Correlation properties. (c) Energy-time entanglement with two-photon interference.
• Figure 3: Measured results of generated multi-wavelength correlated photon pairs. (a) Single count rates of idler (C43) photon with different on-chip power and fitting results. (b) Coincidence count rate and the calculated CAR of signal (C35) and idler (C43) photons with different on-chip power. (c) Spectra of the correlated photons and noise photons in the on-resonance and off-resonance cases from 1527 nm to 1565 nm. (d) CAR of multi-wavelength correlated photons. (e) Spectral brightness of multi-wavelength correlated photons.
• Figure 4: Two-photon interference and energy-time entanglement. (a) Coincidence counts (red dots) and accidental coincidence counts (grey dots) of signal (C35) and idler (C43) photons with different phase shifter’s voltages. (b) single count rate of signal (C35) and idler (C43) photons with different phase shifter’s voltages. The sinusoidal fit of shows a raw visibility of 0.9636(217) without background subtraction. (c) Two-photon correlation histograms of constructive (top) and destructive (bottom) two-photon interference.
• Figure 5: The process flow of AlGaAsOI device fabrication.