Polarization-entangled quantum frequency comb from a silicon nitride microring resonator

TL;DR

This paper reports the first broadband polarization-entangled quantum frequency comb generated using a silicon nitride micro-resonator combined with a Sagnac interferometer, enabling advanced quantum communication applications.

Contribution

First demonstration of a broadband polarization-entangled quantum frequency comb using integrated silicon nitride micro-resonator and Sagnac interferometer.

Findings

22 polarization entangled photon pairs generated covering telecom C-band

Entanglement fidelities for all pairs above 81%, with 17 above 90%

Broad spectral range with 99 GHz free spectral range and 190 MHz linewidth

Abstract

Integrated microresonator facilitates the realization of quantum frequency comb (QFC), which provides a large number of discrete frequency modes with broadband spectral range and narrow linewidth. However, all previous demonstrations have focused on the generation of energy-time or time-bin entangled photons from QFC. Realizing polarization-entangled quantum frequency comb, which is the important resource for fundamental study of quantum mechanics and quantum information applications, remains challenging. Here, we demonstrate, for the first time, a broadband polarization-entangled quantum frequency comb by combining an integrated silicon nitride micro-resonator with a Sagnac interferometer. With a free spectral range of about 99 GHz and a narrow linewidth of about 190 MHz, our source provides 22 polarization entangled photons pairs with frequency covering the whole telecom C-band. The entanglement fidelities for all 22 pairs are above 81%, including 17 pairs with fidelities higher than 90%. Our demonstration paves the way for employing the polarization-entangled quantum frequency comb in quantum network using CMOS technology as well as standard dense wavelength division multiplexing technology.