Direct Generation and Detection of Correlated Photons with 3.2 um Wavelength Spacing

TL;DR

This paper reports the first direct generation and detection of highly non-degenerate photon pairs separated by four optical octaves, enabling new quantum applications across diverse wavelengths including mid-infrared.

Contribution

The work demonstrates room-temperature generation and detection of photon pairs four octaves apart using specially designed lithium niobate waveguides, bridging visible and mid-IR quantum technologies.

Findings

Photon pairs generated at 780 nm and 3950 nm with high purity.

Achieved 34% internal conversion efficiency in upconversion detection.

High coincidence-to-accidental ratio of 54 indicating strong quantum correlation.

Abstract

Quantum correlated, highly non-degenerate photons can be used to synthesize disparate quantum nodes and link quantum processing over incompatible wavelengths, thereby constructing heterogeneous quantum systems for otherwise unattainable superior performance. Existing techniques for correlated photons have been concentrated in the visible and near-IR domains, with the photon pairs residing within one octave. Here, we demonstrate direct generation and detection of high-purity photon pairs at room temperature that are four octaves apart, one at 780 nm to match the rubidium D2 line, and the other at 3950 nm that falls in a transparent, low-scattering optical window for free space applications. The pairs are created via spontaneous parametric downconversion in a lithium niobate waveguide with specially designed geometry and periodic poling. The 780 nm photons are measured with a silicon avalanche photodiode, and the 3950 nm photons are measured with an upconversion photon detector using a similar waveguide, which attains 34% internal conversion efficiency. Quantum correlation measurement yields a high coincidence-to-accidental ratio of 54, which indicates the strong correlation with the extremely non-degenerate photon pairs. Our system bridges existing quantum technology to the challenging mid-IR regime, where unprecedented applications are expected in metrology, sensing, communications, medical diagnostics, and so on.