Generation of circular polarized high-order harmonics from single color quantum light

TL;DR

This paper demonstrates that quantum-engineered drivers with squeezing and ellipticity can generate high-order harmonics with circular polarization, revealing quantum properties of the driving field through spectral analysis.

Contribution

It introduces a novel method using squeezed, elliptically polarized quantum light to generate high-order harmonics in regimes inaccessible to classical drivers, linking spectral features to quantum field properties.

Findings

Squeezed elliptically polarized drivers enable HHG at large ellipticity.

Harmonic spectra encode information about the quantum nature of the driving field.

Spectral intensity depends on driver ellipticity and squeezing orientation.

Abstract

The atomic response to an ultra-intense driving field produces a characteristic high-harmonic spectrum featuring a rapid drop in intensity for the lower harmonics, followed by a plateau and a sharp cutoff. This response vanishes for circularly polarized classical drivers -- a limitation that can be overcome by introducing quantum features into the driving field. In this work, we show that squeezed highly elliptically polarized drivers not only enable the high-harmonic generation (HHG) process in classically forbidden regimes of large ellipticity, but also yield highly elliptical harmonic radiation with pronounced super-Poissonian photon statistics. Moreover, we show that the HHG spectral features encode information about the quantum nature of the driving field, revealing the presence of its squeezed field fluctuations. By analyzing the HHG spectral intensity dependence as a function of the driver's ellipticity and squeezing orientation, we identify a means to probe the driving field's quantum properties that intrinsically lie in the high-photon number regime.