Quantum-photonic chips, which integrate quantum light sources alongside active and passive optical elements, as well as single-photon detectors, show great potential for photonic quantum information processing and quantum technology. Mature semiconductor nanofabrication processes allow for scaling such photonic integrated circuits to on-chip networks of increasing complexity. Second-order nonlinear materials are the method of choice for generating photonic quantum states in the overwhelming majority of linear optic experiments using bulk components, but integration with waveguide circuitry on a nanophotonic chip proved to be challenging. Here, we demonstrate such an on-chip parametric down-conversion source of photon pairs based on second-order nonlinearity in an aluminum-nitride microring resonator. We show the potential of our source for quantum information processing by measuring the high visibility anti-bunching of heralded single photons with nearly ideal state purity. Our down-conversion source yields measured coincidence rates of 80 Hz, which implies MHz generation rates of correlated photon pairs. Low noise performance is demonstrated by measuring high coincidence-to-accidental ratios. The generated photon pairs are spectrally far separated from the pump field, providing great potential for realizing sufficient on-chip filtering and monolithic integration of quantum light sources, waveguide circuits and single-photon detectors. A chip-based source of photon pairs for applications in quantum information processing has been built by a team of scientists in the US. Xiang Guo and co-workers from Yale University built the quantum light source from an aluminum nitride microring resonator. The strong second-order nonlinearity of the aluminum nitride yields efficient parametric down-conversion. This allows 775-nm-wavelength pump photons to be converted into a pair of entangled photons in the telecommunications window of 1550 nm. Tests indicated that the heralded photons generated by the microring source are anti-bunched and have high visibility and a high purity of state, indicating that they are highly suitable for use in quantum optics experiments. In principle, the on-chip source is compatible with megahertz generation rates and large-scale manufacture of integrated optical circuits.
Squeezed light is a fundamental resource for a broad spectrum of quantum technologies, including precision metrology, secure communication, and quantum simulation and computing. The integration of squeezed-light sources with photonic circuits presents a transformative approach—not only offering compactness, stability, and scalability, but also enabling seamless high-fidelity on-chip generation, manipulation, and processing of quantum states without being hampered by inter-component quantum decoherence arising from loss and noise. In this work, we report the experimental generation of a two-mode squeezed vacuum state on a thin-film silicon-nitride photonic integrated circuit with normal group velocity dispersion of 6.3×105 fs2/m. Quadrature squeezing of −2.1 dB±0.09 dB and anti-squeezing of 7.1 dB±0.04 dB are directly measured. To fully understand the dynamics of the quantum process, a comprehensive theoretical model is developed to capture the squeezing performance, showing excellent agreement with experimental results. Our findings highlight the potential of the thin-film silicon nitride platform that capitalizes on fully foundry-compatible fabrication technologies to advance robust, large-scale, and manufacturing-ready quantum information processing systems.
Heterogeneous integration of gain and strongly nonlinear materials with ultra-low-loss silicon nitride (SiN) photonics offers a route to scalable quantum circuits, but concurrent wafer-scale manufacturability, low interlayer loss, and high performance have been challenging to realize. Here we demonstrate a wafer-scale III-V-on-SiN quantum photonic platform that directly integrates III-V layers to foundry-fabricated SiN circuits. The SiN layer provides 200-300 nm thick waveguides with
<1 dB/m loss and a mature passive photonics ecosystem, while III-V materials provide large
χ(2) and
χ(3) nonlinearities for parametric gain, frequency conversion and quantum light generation. Adiabatic interlayer couplers yield
<25 mdB loss to InGaP waveguides and resonators with intrinsic quality factors exceeding
106, enabling
15× brighter entanglement sources and efficient nonlinear conversion on SiN. Integrated components--including low-loss beam splitters, waveguide crossers, and tunable interferometers--are complemented by III-V lasers and InP photodetectors with amplifiers achieving up to
99−12+1% quantum efficiency and
3 GHz bandwidth. This architecture unites ultra-efficient sources, nonlinear elements and detectors on a wafer-scale, low-loss platform, establishing a path toward large-scale, low-noise quantum photonic systems.
We demonstrate integrated photonic circuits for quantum devices using sputtered polycrystalline aluminum nitride (AlN) on insulator. On-chip AlN waveguide directional couplers, which are one of the most important components in quantum photonics, are fabricated and show the output power splitting ratios from 50:50 to 99:1. Polarization beam splitters with an extinction ratio of more than 10 dB are also realized from the AlN directional couplers. Using the fabricated AlN waveguide beam splitters, we observe Hong–Ou–Mandel interference with a visibility of 91.7 % ±5.66 % .
The field of photonic integrated circuits (PIC) has flourished in the past two decades, fueling numerous cutting-edge applications across sensing, networking, data interconnect, and quantum information processing. As a guiding material for PIC, Si
3N
4 has seen extensive use for its ultra-low loss, broad transparency, and diversity in implementation across both thin and thick films. Although the standard, traditional silicon dioxide (SiO
2) on silicon (Si) substrates that underpin the majority of Si
3N
4 photonics face drawbacks in the form of long-wavelength transparency limited by SiO
2, high-stress deposition for anomalous dispersion thick-film Si
3N
4, and leakage loss to the Si layer for low-confinement thin-film Si
3N
4. Featuring increased long-wavelength transparency into the mid-infrared, low-stress deposition of Si
3N
4, and a low index, this work investigates sapphire substrates as alternate hosts for Si
3N
4 photonics with greater spectral coverage and reduced fabrication complexity. This work presents a robust method of fabricating ultra-low loss photonic integrated circuits on a 500-nm-thick Si
3N
4-on-sapphire platform, exhibiting record-low losses below
0.1dB/cm. Implemented using this process are high-Q microrings with intrinsic quality factors in excess of
4.5×106 and coupled-ring photonic molecules to support nonlinear gain. Leveraging the achievable low loss and high-Q, this work further reports the first demonstration of Kerr-comb and soliton generation on the Si
3N
4-on-sapphire platform. These advances in loss, quality factor, and soliton generation on this versatile, broad-transparency platform pave the way for future work in spectroscopy and quantum-enhanced sensing across previously prohibited spectral regions for Si
3N
4 photonics with reduced fabrication complexity.
Optical integrated quantum computing protocols, in particular using the dual-rail encoding, require that waveguides cross each other to realize, e.g., SWAP or Toffoli gate operations. We demonstrate efficient adiabatic crossings. The working principle is explained using simulations, and several test circuits are fabricated in silicon nitride (SiN) to characterize the coupling performance and insertion loss. Well-working crossings are found by experimentally varying the coupler parameters. The adiabatic waveguide crossing (WgX) outperforms a normal directional coupler in terms of spectral working range and fabrication variance stability. The insertion loss is determined using two different methods: using the transmission and by incorporating crossings in microring resonators. We show that the latter method is very efficient for low-loss photonic components. The lowest insertion loss is 0.18 dB (4.06%) enabling high-fidelity NOT operations. The presented WgX represents a high-fidelity (96.2%) quantum NOT operation.