Hybrid III-V/Silicon Quantum Photonic Device Generating Broadband Entangled Photon Pairs

TL;DR

The paper presents a hybrid III-V/Si quantum photonic device that integrates a broadband SPDC photon-pair source with CMOS-compatible silicon circuitry. An AlGaAs Bragg-reflection waveguide generates photon pairs via SPDC and transfers them to a silicon-on-insulator circuit through adiabatic vertical coupling, achieving strong pump rejection and broadband telecom operation ($>40~\mathrm{nm}$) at room temperature with internal pair generation rates $>10^5$ s$^{-1}$. Both type-0 and type-2 SPDC produce energy-time entangled photons, demonstrated by high-visibility two-photon interference in a Franson setup (raw ~92%, up to ~99% with spectral filtering), validating on-chip quantum state generation and manipulation. The approach leverages the strengths of III-V nonlinear optics and silicon photonics, enabling scalable, electrically pumped, CMOS-compatible quantum photonic chips for real-world quantum information processing.

Abstract

The demand for integrated photonic chips combining the generation and manipulation of quantum states of light is steadily increasing, driven by the need for compact and scalable platforms for quantum information technologies. While photonic circuits with diverse functionalities are being developed in different single material platforms, it has become crucial to realize hybrid photonic circuits that harness the advantages of multiple materials while mitigating their respective weaknesses, resulting in enhanced capabilities. Here, we demonstrate a hybrid III-V/Silicon quantum photonic device combining the strong second-order nonlinearity and direct bandgap of the III-V semiconductor platform with the high maturity and CMOS compatibility of the silicon photonic platform. Our device embeds the spontaneous parametric down-conversion (SPDC) of photon pairs into an AlGaAs source and their vertical routing to an adhesively-bonded silicon-on-insulator circuitry, within an evanescent coupling scheme managing both polarization states. This enables the on-chip generation of broadband (> 40 nm) telecom photons by type 0 and type 2 SPDC from the hybrid device, at room temperature and with internal pair generation rates exceeding $10^5$ $s^{-1}$ for both types, while the pump beam is strongly rejected. Two-photon interference with 92% visibility (and up to 99% upon 5 nm spectral filtering) proves the high energy-time entanglement quality of the produced quantum state, thereby enabling a wide range of quantum information applications on-chip, within an hybrid architecture compliant with electrical pumping and merging the assets of two mature and highly complementary platforms in view of out-of-the-lab deployment of quantum technologies.

Figures (6)

• Figure 1: (a) Sketch of the hybrid III-V/Silicon structure (not in scale) with numerical simulations of the mode coupling profile (intensity) at different positions along the structure, for TM polarization at 1550 nm wavelength (similar results are obtained for TE polarization). (b) Transverse SEM image of the fabricated hybrid structure, in the coupling region.
• Figure 2: (a,b,c): Sketch of the experimental setup, showing (a) the generation and collection, (b) detection and counting, and (c) Franson interferometer parts of the experiment. Photons produced in (a) are directly sent to (b) for the PGR/CAR measurement (dotted grey connection); (c) is used for the quantum interference measurement (dotted yellow connections). [LP: linear polarizer; MO: microscope objective; HPF: high-pass filter; FC: fiber collimator; PC: polarization controller; T-BPF: tunable band-pass filter; (P)BS: (polarizing) beam splitter; FM: Faraday mirror; SNSPD: superconductive nanowire single-photon detector; TDC: time-to-digital converter.] (d) Measured type 0 and type 2 SHG efficiency in the hybrid device (normalized by the power injected in the silicon waveguide), as a function of the input laser wavelength. The rapid periodic structures are Fabry-Pérot oscillations due to the reflectivity of the facets. (e) Measured internal PGR (in blue) and CAR (in orange) as a function of the coupled optical power: circles for type 0, squares for type 2 phase-matching (PM) process. Curve fittings help visualizing the expected trends. Error bars are calculated assuming a Poissonian statistics of the coincidences counts.
• Figure 3: Calculated (plain lines) and measured (points) marginal JSI for (a) type 0 and (b) type 2 transmitted photon pairs; green vertical lines indicate the SPDC degeneracy wavelengths. (c) Recorded coincidence histograms and (d) detail on the central peak as a function of the phase shift for a Franson interferometry measurement. In panels a-b-d the error bars are calculated assuming a Poissonian statistics of the coincidences counts.
• Figure 4: Simulated TM mode transmission as a function of the coupling length and (a) the lateral displacement, (b) the BCB thickness and (c) the silicon waveguide width. Reference conditions are: no lateral shift, 40 nm of BCB thickness, 560 nm of silicon waveguide width.
• Figure 5: (a) Measured TM and TE transmission spectra of the hybrid device; cavity oscillations are averaged out in the superimposed curves (bold lines). (b) Numerically simulated transmission spectra.