# Photons with tunable spectral shapes: The transition from frequency anticorrelated to correlated photon pairs

## TL;DR

This paper demonstrates experimental control over the spectral correlations of entangled photon pairs, enabling continuous tuning from anticorrelation to correlation without altering wavelength or crystal, even with ultrafast laser pumping.

## Contribution

It introduces a method for full spectral correlation control of entangled photons without changing wavelength or nonlinear crystal.

## Key findings

- Achieved continuous tuning of photon spectral correlations from anticorrelation to correlation.
- Produced highly entangled frequency-anticorrelated photon pairs with ultrafast laser pump.
- Controlled spectral correlations without modifying wavelength or nonlinear crystal.

## Abstract

We present an experimental demonstration of the full control of the frequency correlations of entangled photon pairs. The joint spectrum of photon pairs is continuously varied from photons that exhibit anticorrelation in frequency to photons that exhibit correlation in frequency, passing through the case of uncorrelated photons. Highly entangled frequency-anticorrelated photon pairs were obtained even when an ultrafast laser was used as a pump. The different kinds of correlations are obtained without changing neither the wavelength, nor the nonlinear crystal.