# Two-photon Quantum Interference and Entanglement at 2 {\mu}m

## TL;DR

This paper demonstrates two-photon interference and entanglement at 2.09 micrometers using custom nonlinear crystals and detectors, opening new possibilities for quantum communication and sensing in the mid-infrared range.

## Contribution

It is the first to realize entangled photon sources and interference at 2 micrometers, expanding quantum optics into the mid-infrared spectrum.

## Key findings

- Successful generation of polarization-entangled photon pairs at 2090 nm
- Demonstration of two-photon interference at mid-infrared wavelengths
- Potential applications in quantum communication and sensing in the 2-2.5 μm range

## Abstract

Quantum-enhanced optical systems operating within the 2- to 2.5-$\mu$m spectral region have the potential to revolutionize emerging applications in communications, sensing, and metrology. However, to date, sources of entangled photons have been realized mainly in the near-infrared 700- to 1550-nm spectral window. Here, using custom-designed lithium niobate crystals for spontaneous parametric down-conversion and tailored superconducting nanowire single-photon detectors, we demonstrate two-photon interference and polarization-entangled photon pairs at 2090 nm. These results open the 2- to 2.5-$\mu$m mid-infrared window for the development of optical quantum technologies such as quantum key distribution in next-generation mid-infrared fiber communication systems and future Earth-to-satellite communications.

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Source: https://tomesphere.com/paper/1906.02082