Entangling extreme ultraviolet photons through strong field pair generation

TL;DR

This paper introduces a novel method called strong field pair generation (SFPG) that enables the creation of entangled photon pairs at extreme ultraviolet frequencies using high harmonic generation, expanding quantum optics into new high-frequency regimes.

Contribution

The paper develops a general theory of photon pair emission from non-perturbatively driven systems and demonstrates their potential as high-frequency entangled photon sources.

Findings

Strongly driven noble gases can generate thousands of entangled pairs per shot.

The emitted pairs have distinctive angular and frequency properties.

The produced light exhibits attosecond Hong-Ou-Mandel correlations.

Abstract

Entangled photon pairs are a vital resource for quantum information, computation, and metrology. Although these states are routinely generated at optical frequencies, sources of quantum of light are notably lacking at extreme ultraviolet (XUV) and soft X-ray frequencies. Here, we show that strongly driven systems used for high harmonic generation (HHG) can become versatile sources of entangled photon pairs at these high frequencies. We present a general theory of photon pair emission from non-perturbatively driven systems, which we refer to as "strong field pair generation" (SFPG). We show that strongly driven noble gases can generate thousands of entangled pairs per shot over a large XUV bandwidth. The emitted pairs have distinctive properties in angle and frequency, which can be exploited to discriminate them from the background HHG signal. We connect SFPG theory to the three-step-model of HHG, showing that this pair emission originates from the impact of high frequency vacuum fluctuations on electron recombination. The light produced by SFPG exhibits attosecond Hong-Ou-Mandel correlations, and can be leveraged as a source of heralded single photon attosecond pulses. Our findings aid ongoing efforts to propel quantum optics into the XUV and beyond.