Ultra-broadband Entangled Photons on a Nanophotonic Chip

TL;DR

This paper reports the creation of ultra-broadband entangled photons on a nanophotonic chip, enabling advanced quantum applications with high efficiency, purity, and spectral bandwidth.

Contribution

It demonstrates the first generation of ultra-broadband entangled photons with 100 THz bandwidth on a chip using dispersion-engineered lithium niobate waveguides.

Findings

Bandwidth of 100 THz achieved

High coincidence-to-accidental ratio (>10^5)

Two-photon interference visibility >98%

Abstract

Nanophotonic entangled-photon sources are a critical building block of chip-scale quantum photonic architecture and have seen significant development over the past two decades. These sources generate photon pairs that typically span over a narrow frequency bandwidth. Generating entanglement over a wide spectral region has proven to be useful in a wide variety of applications including quantum metrology, spectroscopy and sensing, and optical communication. However, generation of broadband photon pairs with temporal coherence approaching an optical cycle on a chip is yet to be seen. Here we demonstrate generation of ultra-broadband entangled photons using spontaneous parametric down-conversion in a periodically-poled lithium niobate nanophotonic waveguide. We employ dispersion engineering to achieve a bandwidth of 100 THz (1.2 - 2 $\mu$m), at a high efficiency of 13 GHz/mW. The photons show strong temporal correlations and purity with the coincidence-to-accidental ratio exceeding $10^5$ and $>$ 98\% two-photon interference visibility. These properties together with the piezo-electric and electro-optic control and reconfigurability, make thin-film lithium niobate an excellent platform for a controllable entanglement source for quantum communication and computing, and open a path towards femtosecond metrology and spectroscopy with non-classical light on a nanophotonic chip.