Abstract
Entangled-photon pairs are an essential resource for quantum information technologies. Chip-scale sources of entangled pairs have been integrated with various photonic platforms, including silicon, nitrides, indium phosphide, and lithium niobate, but each has fundamental limitations that restrict the photon-pair brightness and quality, including weak optical nonlinearity or high waveguide loss. Here, we demonstrate a novel, ultra-low-loss AlGaAs-on-insulator platform capable of generating time-energy entangled photons in a $Q$ $>1$ million microring resonator with nearly 1,000-fold improvement in brightness compared to existing sources. The waveguide-integrated source exhibits an internal generation rate greater than $20\times 10^9$ pairs sec$^{-1}$ mW$^{-2}$, emits near 1550 nm, produces heralded single photons with $>99\%$ purity, and violates Bell's inequality by more than 40 standard deviations with visibility $>97\%$. Combined with the high optical nonlinearity and optical gain of AlGaAs for active component integration, these are all essential features for a scalable quantum photonic platform.
Highlights
Entanglement is the cornerstone of quantum science and technologies
Silicon-based photonics is a versatile platform for quantum photonic integrated circuits (QPICs) owing to its relative low waveguide loss and existing foundry infrastructure developed for the telecommunications industry
We demonstrate that the combination of high Q, a small microring radius, a large χ (3) nonlinearity, and a tight modal-confinement factor of AlGaAsOI results in more than a 500-fold improvement in the time-energy entangledpair generation rate RPG = 20 × 109 pairs s−1 mW−2 over the state of the art, with 97.1 ± 0.6% visibility, a > 4300 coincidence-to-accidental ratio (CAR), and heralded single-photon antibunching gH(2)(0) < 0.004 ± 0.01
Summary
Entanglement is the cornerstone of quantum science and technologies. Compared to matter-based quantum systems, such as electronic spins [1], optomechanical resonators [2], superconducting circuits [3], and trapped atoms and ions [4], photons are unique in their ability to generate and distribute entangled quantum states across long distances in free space or fiber networks while retaining a high degree of coherence. State-of-the-art integrated quantum photonic circuits based on SOI are capable of implementing quantum gates between two qubits [16] and chip-to-chip teleportation [17], for example, but they have to rely on off-chip detectors that introduce significant loss, slow thermal-based active components for tuning and modulation, and off-chip high-power lasers to generate single and entangled photons due to the moderate optical nonlinearity of silicon. For fully etched submicron-scale AlGaAsOI waveguides, the loss is < 0.2 dB cm−1, resulting in microring-resonator quality factors of Q > 3 × 106, overperforming the SOI platform Such high-Q resonators have enabled record-low-threshold frequency-comb generations at 1550 nm [24,25] under a pump power at the level of tens of microwatts, which opens up an unprecedented highly nonlinear regime for integrated photonics.
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