A two-channel, spectrally degenerate polarization entangled source on chip

TL;DR

This paper presents a fully integrated lithium niobate chip that generates high-fidelity, spectrally indistinguishable polarization entangled photon pairs in two spatial modes, advancing quantum information processing capabilities.

Contribution

The authors engineered a novel integrated waveguide source with polarization splitter to produce spectrally degenerate polarization entangled photons in two modes on a chip.

Findings

Fidelity of entangled states is 0.973(3).

Bell's inequality is violated by more than 14 standard deviations.

Operates in both pulsed and continuous wave regimes.

Abstract

Integrated optics provides the platform for the experimental implementation of highly complex and compact circuits for quantum information applications. In this context integrated waveguide sources represent a powerful resource for the generation of quantum states of light due to their high brightness and stability. However, the confinement of the light in a single spatial mode limits the realization of multi-channel sources. Due to this challenge one of the most adopted sources in quantum information processes, i.e. a source which generates spectrally indistinguishable polarization entangled photons in two different spatial modes, has not yet been realized in a fully integrated platform. Here we overcome this limitation by suitably engineering two periodically poled waveguides and an integrated polarization splitter in lithium niobate. This source produces polarization entangled states with fidelity of F = 0.973(3) and a test of Bell's inequality results in a violation larger than 14 standard deviations. It can work both in pulsed and continuous wave regime. This device represents a new step toward the implementation of fully integrated circuits for quantum information applications.