Inline Quantum Measurements with SNSPDs Coupled to Photonic Bound States

TL;DR

This paper demonstrates inline quantum measurements using waveguide-integrated SNSPDs coupled via photonic BICs, achieving high efficiency and fast response, enabling advanced quantum photonic functionalities in compact devices.

Contribution

It introduces a novel BIC platform for integrating SNSPDs with waveguides, enabling efficient, low-jitter inline quantum measurements compatible with photonic circuits.

Findings

On-chip efficiency exceeds 80%

Recovery time less than 2 ns

Intrinsic jitter under 70 ps

Abstract

We report the realization of inline quantum measurements with waveguide-integrated superconducting nanowire single-photon detectors (SNSPDs). To suppress parasitic scattering at detector terminations, while ensuring compatibility with standard photonic substrates and cryogenic operation, we developed a photonic bound states in the continuum (BIC) platform based on etchless polymer waveguides. We show BIC-coupled inline detectors with on-chip efficiency exceeding 80%, recovery time of less than 2 ns, and intrinsic jitter of less than 70 ps. As a proof of principle, we implement Hanbury Brown and Twiss interferometry and photon number resolution with two collinear detectors within a footprint of $60 \cdot 6$ $\mu m^2$. The concept of inline quantum measurements could be further developed to support more complex circuit functionalities, such as higher-order correlation measurements, quantum state tomography, and multi-photon subtraction, within a compact architecture.