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  • Open Access

Nonclassical cutoff fluctuations in squeezed-light-driven high-harmonic generation

Tsendsuren Khurelbaatar1,2,*, R. T. Sang1,2,3, and Igor V. Litvinyuk1,2

  • 1Queensland Quantum and Advanced Technologies Research Institute, Griffith University, Brisbane, Queensland 4111, Australia
  • 2School of Environment and Science, Griffith University, Brisbane, Queensland 4111, Australia
  • 3Office of the Pro Vice-Chancellor (Research, Development and Commercialisation), University of Southern Queensland, Springfield 4300, Australia

  • *Contact author: t.khurelbaatar@griffith.edu.au
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Phys. Rev. Research 8, 043107 – Published 30 October, 2026

DOI: https://doi.org/10.1103/ffdj-mz2y

Abstract

In the conventional description of strong-field high-harmonic generation (HHG), the atom is treated quantum mechanically while the driving laser is represented by a classical field. Quantum fluctuations of the driver can become relevant in nanoscale interaction geometries, where tight spatial confinement can raise the vacuum-field amplitude to ∼10−2 of the mean driving-field amplitude. In this regime, fluctuations of a squeezed driver can imprint its quadrature statistics on HHG observables. To model this interaction, we sample the positive Wigner function of the driving field and solve the time-dependent Schrödinger equation for each sampled field realization. Within a single-mode Gaussian framework, we show that amplitude squeezing suppresses the shot-to-shot variance of the HHG cutoff below the coherent-state standard quantum limit (SQL) at the same mean field. To leading order in the vacuum-to-driver field ratio, the normalized variance follows e−2r, where r is the squeezing parameter, independently of the absolute vacuum-field amplitude. At stronger squeezing, quadratic coupling of the antisqueezed quadrature to the field modulus competes with this suppression, yielding a variance minimum near ropt≈1.55 for the parameters studied. A sub-SQL cutoff variance thus indicates subvacuum noise in the quadrature probed by the cutoff, suggesting that shot-resolved HHG cutoff measurements could witness driving-field nonclassicality.

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Phys. Rev. Research 8, 043107– Published 30 October, 2026
  • Received 20 May 2026
  • Accepted 6 October 2026
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