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Optics Letters

Mid-infrared entanglement in 220 nm silicon

Sebastian G. Currie, Samuel W. A. Gears, Jeremy C. Adcock, Dominic A. Sulway, Joshua W. Silverstone

Published Jan 29, 2026• 1 citation
Publisher

Abstract

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%.

DOI
10.1364/ol.572784

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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%.
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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.
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