Engineering integrated photonics for heralded quantum gates

TL;DR

This paper demonstrates the implementation of a heralded controlled-Z quantum gate using integrated photonics, highlighting the importance of fabrication tolerances and achieving high fidelity in device performance.

Contribution

It presents the first detailed analysis of integrated laser-written waveguide arrays for heralded quantum gates, emphasizing fabrication tolerances and fidelity metrics.

Findings

Device fidelity of 0.931 achieved

Process fidelity of 0.680 achieved

Performance more sensitive to coupler reflectivity deviations

Abstract

Scaling up linear-optics quantum computing will require multi-photon gates which are compact, phase-stable, exhibit excellent quantum interference, and have success heralded by the detection of ancillary photons. We investigate implementation of the optimal known gate design which meets these requirements: the Knill controlled-Z gate, implemented in integrated laser-written waveguide arrays. We show that device performance is more sensitive to the small deviations in the coupler reflectivity, arising due to the tolerance values of the fabrication method, than phase variations in the circuit. The mode fidelity was also shown to be less sensitive to reflectivity and phase errors than process fidelity. Our best device achieves a fidelity of 0.931+/-0.001 with the ideal 4x4 unitary circuit and a process fidelity of 0.680+/-0.005 with the ideal computational-basis process.