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.
@article{arxiv.1708.06778,
title = {Integrated-optics heralded controlled-NOT gate for polarization-encoded qubits},
author = {Jonas Zeuner and Aditya N. Sharma and Max Tillmann and René Heilmann and Markus Gräfe and Amir Moqanaki and Alexander Szameit and Philip Walther},
journal= {arXiv preprint arXiv:1708.06778},
year = {2018}
}