Fluctuation-induced symmetry breaking in high harmonic generation for bicircular quantum light

TL;DR

This paper demonstrates that quantum fluctuations in bicircular quantum light can break classical symmetry rules in high harmonic generation, producing forbidden harmonics with distinctive quantum statistical signatures.

Contribution

It introduces a quantum optical framework showing how squeezing-induced fluctuations break classical selection rules in high harmonic generation.

Findings

Quantum fluctuations induce forbidden harmonic generation.

Enhanced squeezing in the driving field alters classical symmetry constraints.

New harmonics exhibit squeezing-like photon statistics.

Abstract

Symmetries are ubiquitous in physics and play a pivotal role in light-matter interactions, where they determine the selection rules governing allowed atomic transitions and define the associated conserved quantities. For the up-conversion process of high harmonic generation, the symmetries of the driving field determine the allowed frequencies and the polarization properties of the resulting harmonics. As a consequence, it is possible to establish classical selection rules when the process is driven by coherent radiation. In this work, we show that fluctuation-induced symmetry breaking in the driving field leads to the appearance of otherwise forbidden harmonics. This is achieved by considering bicircular quantum light, and demonstrate that the enhanced quantum fluctuations due to squeezing in the driving field break the classical selection rules. To this end, we develop a quantum optical description of the dynamical symmetries in the process of high harmonic generation, revealing corrections to the classical selection rules. Moreover, we show that the new harmonics show squeezing-like signatures in their photon statistics, allowing them to be clearly distinguished from classical thermal fluctuations.