# Idealised EPR states from non-phase matched parametric down conversion

## TL;DR

This paper demonstrates that reducing the size of nonlinear materials in SPDC can significantly increase the transverse wavevector entanglement of photon pairs, enhancing quantum information capacity and imaging resolution.

## Contribution

It introduces a method to relax phase matching constraints by miniaturizing the nonlinear medium, achieving record entanglement levels in transverse modes.

## Key findings

- Over 1200 entangled angular modes estimated from micro-sized lithium niobate layer.
- High entanglement measured through correlation and stimulated emission tomography.
- Potential to boost quantum communication and imaging techniques.

## Abstract

Entanglement of high dimensional states is becoming increasingly important for quantum communication and computing. The most common source of entangled photons is spontaneous parametric down conversion (SPDC), where the degree of frequency and momentum entanglement is determined by the non-linear interaction volume. Here we show that by reducing the length of a highly non-linear material to the micrometer scale it is possible to relax the longitudinal phase matching condition and reach record levels of transverse wavevector entanglement. From a micro-sized layer of lithium niobate we estimate the number of entangled angular modes to be over 1200. The entanglement is measured both directly using correlation measurements and indirectly using stimulated emission tomography. The high entanglement of the state generated can be used to massively increase the quantum information capacity of photons, but it also opens up the possibility to improve the resolution of many quantum imaging techniques.