Entangled Telecom Photon Generation using Twisted Van der Waals Crystals

TL;DR

This paper demonstrates a high-brightness, tunable entangled photon source at telecom wavelengths using twisted van der Waals crystals, advancing integrated quantum photonic systems.

Contribution

It introduces a novel twisted van der Waals crystal platform for generating high-fidelity, tunable entangled photons with superior brightness at telecom wavelengths.

Findings

Achieved entanglement fidelities over 95% for Bell states.

Obtained a coincidence-to-accidental ratio of ~335.

Brightness is about ten times higher than previous TMD-based sources.

Abstract

Nanoscale quantum light sources are essential building blocks for integrated quantum photonic systems. Here, we report a wavelength-scale entangled-photon source based on van der Waals-engineered NbOBr$_2$, and benchmark its performance for telecom-wavelength quantum light generation. By exploiting the material's second-order nonlinearity, we generate quantum-correlated photon pairs via spontaneous parametric down-conversion. We then use a 90$^{\circ}$ twisted stacking to induce quantum interference in photon-pair generation, yielding polarization-entangled photons. This approach enables tunability of the quantum optical state via control of the excitation laser polarization. We experimentally obtain entanglement fidelities exceeding 95% for Bell states, along with a high coincidence-to-accidental ratio of $\sim$335, and a brightness approximately one order of magnitude higher than recently reported telecom sources based on transition metal dichalcogenide (TMD) 2D materials. These results establish twisted van der Waals engineering as a powerful platform for highly tunable, high-brightness quantum light sources at telecom wavelengths.