Measuring the quantum state of a photon pair entangled in frequency and time

TL;DR

This paper introduces a self-referencing spectral-shearing interferometry technique to fully characterize broadband entangled photon pairs in frequency and time, enabling new quantum state measurements.

Contribution

The authors develop a generalizable method for complete spectral-temporal wave function measurement of entangled photons, advancing quantum state characterization capabilities.

Findings

Successfully reconstructed the spectral-temporal wave function of entangled photon pairs.

Demonstrated controllable time-frequency entanglement in generated photon pairs.

Enabled measurement of previously unobservable quantum state features.

Abstract

We present a technique to completely characterise the spectral-temporal wave function of a broadband photon pair using spectral-shearing interferometry. Our method is fully self-referencing and is generalisable across a wide range of wavelengths. To demonstrate, we generate an entangled photon pair with controllable time-frequency entanglement and perform a full reconstruction. These results allow previously unobservable features of quantum states to be measured and utilised for the first time. We foresee this will unlock new opportunities in high-dimensional quantum technology, enabling the development of novel ways of generating and interacting with quantum systems.