We develop and test a silicon photonics platform at 2.9 µdesigned for optimal coupling to selenium donors in the 500 nm device layer, and present progress toward high (> 10) cooperativity devices.
Photon-pair sources are essential for complex and scalable quantum photonics circuits. Silicon photonics offers a scalable and low cost platform with a mature fabrication technology for realising this [1] . Recent demonstrations of photon-pair generation and quantum interference in the 2.1 µm band have paved the way towards mid-infrared integrated photon sources [2] , where many gases can be sensed with unique ‘fingerprint’ absorption lines. Producing long wavelength photons with large spectral detunings from the pump, utilising anomalous group-velocity dispersion and type-0 phase matching, is hard due to the highly dispersive nature of nanoscale silicon waveguides.
Silicon photonics in the mid-infrared is a promising platform for quantum technologies. Previous demonstrations of silicon mid-infrared quantum optics have used a 340 nm silicon layer height. In this work, we use industry-standard 220 nm silicon to implement a novel, to the best of our knowledge, photon-pair source with a peak coincidence-to-accidental ratio (CAR) of 20.9±2.9 at a net measured rate of 0.63±0.02 Hz and an inferred source efficiency of 2.85±0.04 MHz W −2 . Finally, we report the first integrated mid-infrared entanglement, generating a Bell state with a fidelity of F =94±2%.
Applied quantum optics stands to revolutionise many aspects of information technology, provided performance can be maintained when scaled up. Silicon quantum photonics satisfies the scaling requirements of miniaturisation and manufacturability, but at 1.55 µm it suffers from problematic linear and nonlinear loss. Here we show that, by translating silicon quantum photonics to the mid-infrared, a new quantum optics platform is created which can simultaneously maximise manufacturability and miniaturisation, while reducing loss. We demonstrate the necessary platform components: photon-pair generation, single-photon detection, and high-visibility quantum interference, all at wavelengths beyond 2 µm. Across various regimes, we observe a maximum net coincidence rate of 448 ± 12 Hz, a coincidence-to-accidental ratio of 25.7 ± 1.1, and, a net two-photon quantum interference visibility of 0.993 ± 0.017. Mid-infrared silicon quantum photonics will bring new quantum applications within reach.