Near-unity quantum interference of transverse spatial modes in an ultra-compact inverse-designed photonic device

TL;DR

This paper demonstrates ultra-compact, highly reproducible quantum interference of transverse spatial modes in integrated photonic devices, advancing scalable quantum photonics by using inverse-designed beamsplitters with near-unity visibility.

Contribution

It introduces the smallest transverse mode beamsplitters for 1550 nm photons, achieving high-visibility quantum interference on-chip with high reproducibility.

Findings

Achieved up to 99.56% Hong-Ou-Mandel visibility.

Demonstrated reproducibility across three devices.

Validated inverse-designed components for quantum interference.

Abstract

The transverse spatial mode of photons is an untapped resource for scaling up integrated photonic quantum computing. To be practically useful for improving scalability, reliable and high-visibility quantum interference between transverse spatial modes on-chip needs to be demonstrated. We show repeatable quantum interference using inverse-designed transverse mode beamsplitters that have an ultra-compact footprint of 3 $\mu m$ $\times$ 3 $\mu m$ -- the smallest transverse mode beamsplitters for 1550 nm photons to date. We measure a Hong-Ou-Mandel visibility of up to 99.56$\pm$0.64 % from a single device, with an average visibility across three identical devices of 99.38$\pm$0.41 %, indicating a high degree of reproducibility. Our work demonstrates that inverse-designed components are suitable for engineering quantum interference on-chip of multimode devices, paving the way for future compact integrated quantum photonic devices that exploit the transverse spatial mode of photons for high-dimensional quantum information.