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

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 $${\mathcal F} \mathrm{=0.973}\pm 0.003$$F= 0.973±0.003 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.Quantum Information: the realization of integrated entangled photons sourcesIn the context of quantum technology, integrated photonic devices demonstrated great potential to perform quantum tasks stably with ease. Despite the great development of integrated circuits, the generation of quantum states of light remains challenging in an integrated geometry. In particular, one of the most adopted source in quantum information processes, the one firstly proposed by Kwiat et al. (PRL 75, 4337 1995) which provides polarization entangled photons at the same wavelength, was still not available on an integrated platform. Christine Silberhorn and co-workers from the University of Paderborn (Germany), overcome the previous technological issues and realized such a quantum source. With this achievement the Authors provide a device that performs better than the corresponding bulk schemes and is an optimal candidate to be exploited with integrated linear circuit for a full generation and manipulation of polarization encoded qubits in integrated platforms.