Spectrally engineering photonic entanglement with a time lens

TL;DR

This paper demonstrates a novel single-photon time lens using dispersion and nonlinear sum-frequency generation to manipulate and analyze the spectral waveform of entangled photons, enabling advanced quantum state engineering.

Contribution

It introduces a new method for spectral shaping of entangled photons using a time lens based on dispersion and nonlinear optics, advancing quantum photonic manipulation techniques.

Findings

Spectral correlations change from negative to positive after the time lens.

The process achieves negative spectro-temporal magnification.

The technique enables new quantum state engineering applications.

Abstract

In the same manner that free-space propagation and curved glass lenses are used to shape the spatial properties of light, a combination of chromatic dispersion and devices known as time lenses may be used to reshape its temporal properties. These techniques have found extensive application in classical optical signal processing based on nonlinear optics. A new set of challenges presents itself when processing quantum signals, including noise suppression and high fidelity requirements. In this work, we construct a single-photon time lens based on dispersion and nonlinear sum-frequency generation to image the spectral waveform of half of an entangled photon pair. We find that the joint spectrum of the photon pair has strongly negative frequency correlations before the time lens and strongly positive correlations afterwards, verifying that the process has an overall negative spectro-temporal magnification. The temporal imaging of energy-time entangled systems opens up a host of new possible techniques for distinctly quantum tasks in the frequency domain, including state engineering, and our results demonstrate that the upconversion time lens is an essential part of the single-photon waveform manipulation toolkit.