Nonlinear integrated quantum photonics with AlGaAs

TL;DR

This article reviews nonlinear integrated quantum photonics in AlGaAs, arguing that the material’s strong $χ^{(2)}$ and $χ^{(3)}$ nonlinearities, direct-bandgap and mature III–V processing, and compatibility with on-chip detectors position it as a versatile platform for source generation, circuit integration, and state engineering. It surveys device geometries (linear/spiral waveguides, Bragg-reflection waveguides, microrings) and phase-matching strategies that enable SPDC and SFWM at telecom wavelengths, including room-temperature operation and potential electrically pumped sources. The paper highlights demonstrations of polarization- and frequency-entangled photon pairs, on-chip Bell-state generation, and reconfigurable control of two-photon spectral properties, as well as even on-chip simulation of exotic particle statistics. It closes with perspectives on monolithic multi-source AlGaAs circuits, hybrid integrations with silicon, and the role of AlGaAs in advancing both discrete- and continuous-variable quantum information processing, while acknowledging remaining challenges in detector integration and large-scale manufacturing.

Abstract

Integrated photonics provides a powerful approach for developing compact, stable and scalable architectures for the generation, manipulation and detection of quantum states of light. To this end, several material platforms are being developed in parallel, each providing its specific assets, and hybridization techniques to combine their strengths are now possible. This review focuses on AlGaAs, a III-V semiconductor platform combining a mature fabrication technology, direct band-gap compliant with electrical injection, low-loss operation, large electro-optic effect, and compatibility with superconducting detectors for on-chip detection. We detail recent implementations of room-temperature sources of quantum light based on the high second- and third-order optical nonlinearities of the material, as well as photonic circuits embedding various functionalities ranging from polarizing beamsplitters to Mach-Zehnder interferometers, modulators and tunable filters. We then present several realizations of quantum state engineering enabled by these recent advances and discuss open perspectives and remaining challenges in the field of integrated quantum photonics with AlGaAs.

Figures (8)

• Figure 1: Examples of AlGaAs chips for quantum photonics. (a) AlGaAs Bragg reflection waveguide Autebert16. (b) AlGaAsOI microring resonator Chang2020. (c) Cross-section of an AlGaAsOI waveguide Chang2020. (d) GaAs chip combining quantum dot, beamsplitter and superconducting nanowire single photon detector Schwartz2018. (e) Fabrication of AlGaAsOI quantum photonic circuits on a 4" wafer Steiner2021.
• Figure 2: Comparison of the relevant metrics for quantum photonics for different nonlinear materials: silicon on insulator (SOI), silicon nitride (SiN), lithium niobate on insulator (LNOI), AlGaAs and AlGaAs on insulator (AlGaAsOI).
• Figure 3: AlGaAs-based prospective integrated quantum photonic circuit, including a variety of components needed for specific functionalities as classical and quantum light sources, single photon detectors, modulators, interferometers, filters and light-matter interfaces.
• Figure 4: (a) Tunable unbalanced Mach Zehnder Interferometer (MZI) exhibiting $>$ 40 dB ($>$23 dB) extinction for MZIs with directional coupler (MMI) 3-dB splitters. The top-right (bottom-left) panels show the transmission spectra for MZIs with MMIs (directional couplers). The bottom-right panel shows the coupling coefficients measured from 1450 nm to 1650 nm. (b) Waveguide crossers with $<$ 0.2 dB/crosser loss and $>$ 40 dB extinction between cross ports. (c) Inverse tapers for chip-to-fiber coupling with $<$ 3 dB loss. Data shown is modified with permission from CastroAlGaAsOI.
• Figure 5: (a) Sketch of an AlGaAs electrically pumped source of photon pairs Boitier14. (b) SEM image of an AlGaAs parametric source integrated with a 50/50 beamsplitter Belhassen18. (c) Quantum interference pattern of a two-photon state measured in an integrated GaAs-based Mach-Zehnder interferometer Wang14.