Integrated photonic circuits are one of the most promising platforms for large-scale photonic quantum information systems due to their small physical size and stable interferometers with near-perfect lateral-mode overlaps. Since many quantum information protocols are based on qubits defined by the polarization of photons, we must develop integrated building blocks to generate, manipulate, and measure the polarization-encoded quantum state on a chip. The generation unit is particularly important. Here we show the first integrated polarization-entangled photon pair source on a chip. We have implemented the source as a simple and stable silicon-on-insulator photonic circuit that generates an entangled state with 91 \pm 2% fidelity. The source is equipped with versatile interfaces for silica-on-silicon or other types of waveguide platforms that accommodate the polarization manipulation and projection devices as well as pump light sources. Therefore, we are ready for the full-scale implementation of photonic quantum information systems on a chip.
@article{arxiv.1211.2885,
title = {A monolithically integrated polarization entangled photon pair source on a silicon chip},
author = {Nobuyuki Matsuda and Hanna Le Jeannic and Hiroshi Fukuda and Tai Tsuchizawa and William John Munro and Kaoru Shimizu and Koji Yamada and Yasuhiro Tokura and Hiroki Takesue},
journal= {arXiv preprint arXiv:1211.2885},
year = {2012}
}