Biphoton state generation and engineering with bright hybrid III-V/Silicon photonic devices

TL;DR

This work addresses the need for bright, tunable biphoton sources on a scalable platform by integrating a III–V AlGaAs SPDC source with a silicon photonic chip. The authors demonstrate a heterogeneously integrated hybrid device employing a multimode evanescent taper to achieve high brightness and on-chip JSA engineering, quantified by a PGR above $10^{6}$ s$^{-1}$ mW$^{-1}$ and CAR up to $6\times10^{2}$, and validate a predictive model that links the coupling geometry to both amplitude and phase of the JSA. The model, grounded in device transmissions $T_u(\omega)$, $T_v(\omega)$ and phase shifts $\vartheta(\omega)$, is confirmed by HOM interferometry and used to explore advanced capabilities such as on-chip emulation of exchange statistics (including anyonic-like phases) and metrological enhancements via tailored JSA. Overall, the work establishes a compact, on-chip quantum photonic platform where amplitude and phase of biphoton states are engineered through inter-material coupling, paving the way for scalable quantum communication, computation, and precision sensing with hybrid materials. $PGR > $ $10^{6}$ s$^{-1}$ mW$^{-1}$ and CAR up to $6\times 10^{2}$ underscore the practical advantage of the approach, while the potential for inverse design and on-chip phase engineering signals broad applicability in future quantum technologies.

Abstract

Hybrid photonic circuits, harnessing the complementary strengths of multiple materials, represent a key resource to enable compact, scalable platforms for quantum technologies. In particular, the availability of bright sources of tunable biphoton states is eagerly awaited to meet the variety of applications currently under development. In this work we demonstrate a heterogeneously integrated device that merges biphoton generation and on-chip quantum state engineering, combining an AlGaAs photon-pair source with a CMOS-compatible silicon-on-insulator (SOI) circuit. Photon pairs are generated in the C telecom band via spontaneous parametric down-conversion and transferred to the SOI chip through a multimode evanescent coupling scheme. This design achieves a pair generation rate above 10$^{6}$ s$^{-1}$mW$^{-1}$ and a coincidence-to-accidental ratio up to 600. Crucially, the coupling design induces strong and predictable transformations of the biphoton joint spectral amplitude, enabling complex quantum state engineering entirely on-chip in a compact device compliant with electrical pumping.

Figures (4)

• Figure 1: (a) Schematic illustration (not to scale) of the hybrid device and its working principle. (b) Measured transmission efficiency spectra for TE and TM polarizations. Cavity oscillations, visible in the dotted lines, are averaged out in the solid lines. The green-shaded area marks the spectral region around the SPDC resonance (indicated by the vertical grey line) where the transmission efficiency exceeds 50%. (c) Internal PGR and CAR as functions of the coupled pump power, for the linearly shaped (LS, from Schuhmann24) and nonlinearly shaped (NLS, this work) tapers. Curve fittings are included to guide the eye and illustrate the expected trends; error bars are estimated assuming Poissonian statistics for the coincidence counts.
• Figure 2: Schematic of the experimental setup. After photon-pair generation and collection, the photons can be directed either to the PGR/CAR/Detection stage, or alternatively to the HOM stage -- optionally including spectral filtering -- followed by the Detection stage for Hong–Ou–Mandel (HOM) interferometry measurements. P: linear polarizer; MO: microscope objective; WG: waveguide; LPF: long-pass filter; PF: programmable filter
• Figure 3: (a) Simulated amplitude and phase of the JSA of the biphoton state generated by a 2 mm-long, 4 $\mu$m-wide AlGaAs waveguide (same parameters as the generation region of the hybrid device).(b) Corresponding simulation for the same AlGaAs waveguide coupled to a 560 nm-wide silicon waveguide via an 800 $\mu$m-long nonlinearly shaped taper. (c) Phase mismatch, $\Delta\vartheta=\vartheta(\omega_s)-\vartheta(\omega_i)$, for a straight AlGaAs waveguide (WG), a tapered AlGaAs WG, and the hybrid device. The grey-shaded region in (a) indicates the spectral range of interest in (b) and (c).
• Figure 4: (a) Simulated HOM interferograms (solid lines) and measured data points for hybrid devices with tapers 1, 2, and 3. (b) Top: Simulated HOM interferogram considering the JSA of the biphoton state generated in a 2 mm-long, 4 $\mu$m-wide AlGaAs waveguide. Center: Corresponding simulation for the hybrid device with taper 1, considering only the amplitude modification of the JSA introduced by the coupling region. Bottom: The same simulation including both amplitude and phase modifications. (c) Simulated HOM interferograms (solid lines) for the hybrid device with taper 1 when the JSA spectral width is modified using a rectangular band-pass filter. Experimental data (grey circles) are overlaid for the unfiltered case and for a 20 nm-wide filter. (d) Evolution of the HOM visibility -- assuming unchanged transmission spectra -- and simulated cross transmission ($T_{TE}(\omega_p/2)\times T_{TM}(\omega_p/2)$) as a function of the taper length for the hybrid device with taper 2. The dotted line marks the operating point of the device under study. (e) Simulated HOM interferogram for a phase profile $\vartheta(\omega_s)=\text{sign}(\omega_p-2\omega_s)i\pi/4$, corresponding to $\alpha=1/2$ anyonic particles. Experimental data for the hybrid device with taper 2 are superimposed for qualitative comparisons. The asymmetry score for both curves is reported. (f) Scaling of the Fisher information (FI) relative to the Quantum Fisher Information(QFI) as function of the HOM visibility for the hybrid device with taper 2. this is compared with the scaling obtained with the full state generated by a straight AlGaAs waveguide and with the best achievable scaling limit. Error bars, where present, are calculated assuming a Poissonian statistics for the coincidences counts.