Twist-Engineered Nonlinearity in Two-Dimensional Crystals for Tailored Quantum Light

TL;DR

This paper demonstrates how twist-angle engineering in van der Waals two-dimensional crystals enables continuous and precise control of nonlinear optical properties, significantly improving quantum light source performance.

Contribution

It introduces a novel twist-angle domain engineering method to tailor $$ nonlinearity profiles in vdW materials, surpassing traditional binary domain approaches.

Findings

Enhanced phase-matching function approximation

Higher single-photon purity in compact devices

Effective in mid-infrared wavelength regimes

Abstract

Van der Waals (vdW) materials enable nonlinear-optical engineering with unprecedented resolution: their strong second-order susceptibilities ($\chi^{(2)}$) and twist-tunable interlayer symmetry allow the effective nonlinearity to be shaped continuously, rather than through binary $\pm\chi^{(2)}$ domain inversion as in bulk ferroelectrics. Here, we show that twist-angle domain engineering exploits this continuous degree of freedom to reconstruct target longitudinal nonlinearity profiles with high fidelity. Using spontaneous parametric down-conversion (SPDC) as a benchmark, we demonstrate that twist-engineered vdW crystals yield significantly improved approximations of target phase-matching functions and correspondingly higher single-photon purities, particularly in compact devices where fabrication constraints limit conventional approaches. We further show that this framework remains effective in experimentally relevant vdW materials and demanding non-degenerate wavelength regimes involving mid-infrared photons. More broadly, the ability to continuously and locally program $\chi^{(2)}$ establishes a general framework for tailoring a wide range of SPDC properties, including absolute brightness, joint spectral amplitude structure, signal-idler frequency separation, and temporal wavepacket shape beyond what is accessible in conventional nonlinear crystals. These results position vdW heterostructures as a powerful platform for engineered quantum light sources and open new opportunities for nonlinear-optical devices shaped with monolayer thickness scale.