Direct characterization of ultrafast energy-time entangled photon pairs

TL;DR

This paper introduces ultrafast photon counters based on nonlinear interactions to directly characterize energy-time entangled photon pairs with femtosecond resolution, enabling new insights into ultrafast quantum entanglement.

Contribution

It presents a novel technique using nonlinear interactions and femtosecond laser pulses to directly measure and analyze energy-time entanglement at ultrafast timescales.

Findings

Successful characterization of spectral and temporal correlations with femtosecond resolution

Witnessed energy-time entanglement using uncertainty relations

Observed nonlocal dispersion cancellation on ultrafast timescales

Abstract

Energy-time entangled photons are critical in many quantum optical phenomena and have emerged as important elements in quantum information protocols. Entanglement in this degree of freedom often manifests itself on ultrafast timescales making it very difficult to detect, whether one employs direct or interferometric techniques, as photon-counting detectors have insufficient time resolution. Here, we implement ultrafast photon counters based on nonlinear interactions and strong femtosecond laser pulses to probe energy-time entanglement in this important regime. Using this technique and single-photon spectrometers, we characterize all the spectral and temporal correlations of two entangled photons with femtosecond resolution. This enables the witnessing of energy-time entanglement using uncertainty relations and the direct observation of nonlocal dispersion cancellation on ultrafast timescales. These techniques are essential to understand and control the energy-time degree of freedom of light for ultrafast quantum optics.