High-Harmonic Generation in a Crystal Driven by Quantum Light

TL;DR

This paper explores how quantum light influences high-harmonic generation in a crystal, revealing that thermal and squeezed vacuum states produce higher harmonic cutoffs than classical fields.

Contribution

It adapts a quantum optical framework to solid-state HHG, analyzing the effects of nonclassical driving fields on harmonic spectra and cutoff energies.

Findings

Thermal and bright-squeezed vacuum light yield higher harmonic cutoffs.

Quantum optical nature of the driving field affects harmonic intensity and fluctuations.

Analytical Floquet calculations explain differences between classical and nonclassical driving fields.

Abstract

We study intraband high-harmonic generation (HHG) in a crystal driven by quantum light. Previous theoretical studies have developed a framework based on coherent state expansions in terms of P distributions to consider nonclassical driving fields for HHG in atoms. Here, we adapt this framework to the context of solids and consider an intraband model of ZnO. We investigate the effect of the quantum optical nature of the driving field on the harmonic spectra including the cutoff and the intensity scaling of the harmonics with driving field intensity. Based on analytical calculations in the Floquet limit, we explain why driving with thermal light or bright-squeezed vacuum (BSV) produces a much higher cutoff than when driving with fields described by coherent or Fock states. Further, we derive an expression for the generated time-dependent electric field and its fluctuations and find that it inherits characteristics of the driving field. Finally, we discuss the limitations of an approximative positive P representation, which is introduced to be able to reduce the numerical complexity for Fock and BSV driving fields.