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arXiv:2610.31811

Photoelectrons resolve the phase-dependent variance of bright squeezed vacuum

Haoran Ma, Yihe Wang, Chuan Cheng, Ian Gabalski, Aaron M. Ghrist, Eleanor Weckwerth, Mohammed Th. Hassan, Philip H. Bucksbaum

physics.atom-phphysics.opticsquant-phSubmitted Oct 22, 2026• Announced Oct 26, 2026• 0 citations
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Abstract

The variance of bright squeezed vacuum (BSV) is not only strong but also phase dependent, yet recent strong-field experiments with BSV have recorded only its magnitude. A coherent field of the same color provides the phase reference that resolves this phase-dependent noise. Strong-field ionization of xenon by this light shows that the photoelectron yield follows the BSV quadrature along the coherent field, and that the nonlinearity of ionization amplifies the quadrature noise many times over in the electron yield. The noise is moreover distributed unevenly over the photoelectron momentum distribution, differing by an order of magnitude between ionization channels. Strong-field ionization thus offers a phase-sensitive, channel-resolved detector of quantum light, while the quadrature noise of quantum light offers a probe of the intensity dependence of individual ionization pathways.

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6 pages, 3 figures

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The variance of bright squeezed vacuum (BSV) is not only strong but also phase dependent, yet recent strong-field experiments with BSV have recorded only its magnitude. A coherent field of the same color provides the phase reference that resolves this phase-dependent noise. Strong-field ionization of xenon by this light shows that the photoelectron yield follows the BSV quadrature along the coherent field, and that the nonlinearity of ionization amplifies the quadrature noise many times over in the electron yield. The noise is moreover distributed unevenly over the photoelectron momentum distribution, differing by an order of magnitude between ionization channels. Strong-field ionization thus offers a phase-sensitive, channel-resolved detector of quantum light, while the quadrature noise of quantum light offers a probe of the intensity dependence of individual ionization pathways.
Strong-field ionization provides a fundamental route for probing nonlinear electron dynamics on ultrafast timescales, but it has been explored almost exclusively with classical coherent driving fields. Intense quantum light sources, particularly bright squeezed vacuum (BSV), now make it possible to ask how macroscopic photon-number fluctuations affect nonperturbative electron emission. Here, we address this question by performing shot-resolved BSV-photoelectron coincidence measurements in strong-field ionization of xenon atoms, with simultaneous access to the single-shot driving pulse intensity and the energy- and momentum-resolved photoelectron response. By calibrating the intensity-dependent ionization probability with a pulse-integrated Ammosov-Delone-Krainov response, we reconstruct the single-pulse ionization-yield distribution and quantify its fluctuations in electron momentum space. We find that intensity-conditioned BSV-driven spectra recover coherent-field-like cutoff scaling, while the reconstructed yield fluctuations increase toward higher electron energies and momenta, showing that high-energy electrons preferentially sample rare high-intensity BSV shots. Beyond ensemble-averaged spectra or photoelectron-number statistics, this approach resolves the momentum- and energy-dependent transfer of quantum-light fluctuations into atomic ionization yields. These results establish yield fluctuations as observables for strong-field quantum optics and benchmarks for theories beyond the classical-field approximation.
Strong-field physics uses intense optical fields to probe and control electron motion on ultrafast timescales. Recent advances in bright squeezed vacuum have brought macroscopic quantum states of light into the ultrafast strong-field regime, opening prospects for high-harmonic generation and photoionization. Yet linking its phase-space structure to subcycle electron dynamics remains challenging. Here, we demonstrate strong-field tunneling ionization of xenon using a phase-referenced combination of coherent and squeezed fields, with the coherent field defining the ionization clock and quadrature fluctuations of the zero-mean squeezed field providing control. The squeezed field selectively modulates atomic tunneling barriers and electron wave packets, imprinting signatures on photoelectron momentum distributions, number statistics, and energy spectra. Using coincidence measurements of photon number and phase-sensitive photoelectron momentum distributions, we perform quantum state tomography of the driving field by reconstructing its Wigner function. These results establish a bidirectional interface between quantum optics and nonperturbative strong-field electron dynamics, in which the driving quantum field shapes subcycle electron motion while photoionization provides a phase-sensitive probe of the field's quantum state. This work opens new routes toward controlling electron dynamics with quantum light and phase-sensitive quantum state metrology through ultrafast strong-field electron dynamics.
Strong-field ionization is the cornerstone of attosecond physics, which has been extensively studied under coherent-state driving. Recently, the interface between attosecond physics and quantum optics has emerged as a new frontier. Yet, owing to experimental limitations, the role of the quantum nature of light in atomic strong-field ionization has remained unexplored. Here, we demonstrate strong-field ionization of xenon atoms driven by bright squeezed vacuum (BSV) with average pulse energy up to 10 \textmu J. We show that, as a nonclassical state with zero mean field and strong intensity fluctuations, BSV selectively enhances the spider-like holographic structures in the photoelectron momentum distributions. Using a quantum-light-corrected quantum-trajectory Monte Carlo (q-QTMC) model, we attribute this effect to the intrinsic coherence of trajectory pairs emitted within the same subcycle field fluctuation. These dynamically correlated paths exhibit enhanced phase stability and remain robust against dephasing, whereas asynchronous paths are filtered out by field noise. Our results reveal a quantum-fluctuation-induced mechanism for coherence protection in strong-field processes, positioning BSV as an effective coherence filter and establishing a new regime of quantum-enabled noise-resilient ultrafast dynamics.
We demonstrate that quantum light statistics can be used to control strong-field ionization at the tunneling step. Using a bichromatic linearly polarized field composed of a strong coherent driver and a weak bright squeezed vacuum (BSV), we show through simulation that photoelectron momentum distributions (PMDs) exhibit asymmetries that exceed those obtained with classical fields of comparable intensity by orders of magnitude. This enhancement is uniquely linked to the nonclassical statistics of the BSV field. A semiclassical analysis based on the strong-field approximation (SFA) reveals that the effect originates from fluctuations in the instantaneous field amplitude, which strongly modify the tunneling ionization probability while leaving the electron's continuum dynamics essentially unchanged. This selective control enables reconstruction of ionization pathways and provides a robust route to extract sub-cycle dynamics from strong-field observables.
Abstract Bright squeezed vacuum (BSV) has emerged as a macroscopic nonclassical light source capable of driving strong-field processes. Yet its broad, long-tailed photon-number distribution bears little resemblance to the narrow poissonian distribution of a coherent field, obscuring how the corresponding strong-field responses are connected. We show that field-quadrature space supplies the missing continuous description: coherent, squeezed coherent, and BSV states are Gaussian wave packets distinguished only by their centers and widths. This representation provides a unified framework for tracing the coherent-to-BSV transition at fixed mean photon number and for analyzing both ionization yields and photoelectron spectra. Crucially, BSV is a symmetry-protected endpoint in quadrature space. Near the BSV limit, we identify a simple scaling law of the ionization response associated with a residual coherent component. We show that this scaling arises from parity-induced stationarity with respect to the Gaussian center, together with the accompanying width variation near the BSV limit. The result provides a symmetry-based criterion for approaching the BSV regime and a potential probe of a mode-matched coherent displacement through the strong-field response itself.
Bright squeezed light has entered strong-field atomic physics, creating an immediate need to characterize the quantum field delivered to the target on subcycle timescales. Here we show that attosecond streaking maps the coherent displacement and phase-sensitive covariance of a displaced squeezed field onto distinct harmonics: the mean photoelectron momentum follows an ωωω-periodic shift of the spectral center, whereas the momentum variance exhibits a 2ω2ω2ω-periodic breathing. A Feynman--Vernon formulation represents Gaussian quantum light by stochastic vector-potential trajectories, enabling Coulomb-resolved TDSE simulations with a finite XUV gate and without explicit photon-state propagation. A coherent-state reference calibrates the streaking phase and variance background, enabling retrieval of the coherent amplitude and phase together with the squeezed-noise amplitude and squeezing phase. This establishes attosecond streaking as an in situ, gas-phase diagnostic of bright squeezed light.