Integrated-optics heralded controlled-NOT gate for polarization-encoded qubits

TL;DR

This paper demonstrates the first integrated-optics heralded controlled-NOT gate for polarization-encoded qubits, showcasing its potential for scalable quantum networks and entanglement generation on a chip.

Contribution

It presents the first on-chip implementation of a heralded CNOT gate using femtosecond-laser-written waveguides for polarization qubits.

Findings

The gate can generate polarization entanglement.

Optimized transmission with thermally-expanded-core fibers.

High-fidelity gate operation demonstrated.

Abstract

Recent progress in integrated-optics technology has made photonics a promising platform for quantum networks and quantum computation protocols. Integrated optical circuits are characterized by small device footprints and unrivalled intrinsic interferometric stability. Here, we take advantage of femtosecond-laser-written waveguides' ability to process polarization-encoded qubits and present the first implementation of a heralded controlled-NOT gate on chip. We evaluate the gate performance in the computational basis and a superposition basis, showing that the gate can create polarization entanglement between two photons. Transmission through the integrated device is optimized using thermally-expanded-core fibers and adiabatically reduced mode-field diameters at the waveguide facets. This demonstration underlines the feasibility of integrated quantum gates for all-optical quantum networks and quantum repeaters.