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arXiv:2610.30005

UNWRAP: Single-shot phase analysis of bright squeezed vacuum by Newton-ring interferometry

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

Published Oct 21, 2026• 0 citations
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Abstract

The mean field of pulsed bright squeezed vacuum (BSV) vanishes, but the variance can be large, and is strongly phase-dependent. We employ ultrafast Newton-ring wavefront retrieval and analysis of phase (UNWRAP) to extract the field amplitude and phase profile of each BSV pulse, by Fourier analysis of the interference rings between the BSV and a coherent reference with different phase-front curvature. The concentric ring interference fringes are robust against pointing mismatch and drift, thereby simplifying the analysis. The measured distribution has two phase peaks separated by π radians. The rings sweep the delay between the two pulses, so a single frame can capture the temporal field profile of the BSV, even when it is composed of several temporal modes.

DOI
10.48550/arxiv.2610.30005

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The mean field of pulsed bright squeezed vacuum (BSV) vanishes, but the variance can be large, and is strongly phase-dependent. We employ ultrafast Newton-ring wavefront retrieval and analysis of phase (UNWRAP) to extract the field amplitude and phase profile of each BSV pulse, by Fourier analysis of the interference rings between the BSV and a coherent reference with different phase-front curvature. The concentric ring interference fringes are robust against pointing mismatch and drift, thereby simplifying the analysis. The measured distribution has two phase peaks separated by π radians. The rings sweep the delay between the two pulses, so a single frame can capture the temporal field profile of the BSV, even when it is composed of several temporal modes.
Bright squeezed vacuum (BSV) is an intense quantum state of light with zero mean electric field and huge photon number fluctuations, sufficiently intense to drive extreme nonlinear processes and imprint nonclassical statistics. However, the temporal structure of single BSV shots has not been fully characterized. Here, we retrieve the spectral and temporal pulse characteristics of a set of single-peak BSV shots. It is obtained by realizing a femtosecond BSV source at 1040 nm with a single spatial mode and performing single-shot spectral interferometry with a fully characterized coherent-state reference pulse. Our approach reveals that the group delay is consistent between the various shots, resulting in an average pulse duration of 27.2 fs, much shorter than the pump pulse, and a variation of 5.5 fs (standard deviation). We also observe a characteristic nodal structure in the spectral interferograms, demonstrating the BSV’s random phase ambiguity of π rad. Our approach demonstrates that BSV is a viable source of femtosecond light pulses for attosecond sub-cycle metrology of ultrafast electron dynamics.
Bright squeezed vacuum (BSV) takes the phenomenon of squeezed vacuum to the extreme [1]. Extremely high photon numbers of up to 1013can be found inside a single BSV pulse due to the antisqueezed quadrature, with effective pulse durations down to tens of femtoseconds [2]. BSV is sufficiently intense to drive nonperturbative HHG from solids [2] and multiphoton electron emission from nanotips [3]. Intriguingly, BSV has the potential to explore sub-cycle light-matter interactions above the conventional damage threshold [2]. However, characterizing the full temporal properties (mean and distribution) of BSV pulses has remained elusive. Here we overcome this challenge by full temporal characterization (amplitude and phase) of single-shot BSV pulses, for the first time.
Non-Gaussian states of light are a critical resource for fault-tolerant quantum computing and enhanced metrology, but are typically faint and often obtained via post-selection. Here, we demonstrate the deterministic generation of a bright non-Gaussian state by introducing a Kerr nonlinearity to a macroscopic state of light called bright squeezed vacuum (BSV). To characterize the resulting state, we use a single-shot f-2f interferometer to sample its Husimi function. We observe a clear transformation from a 2D Gaussian distribution to an 'S'-shaped non-Gaussian profile, which is the direct statistical evidence of the intensity-dependent nonlinear phase. The negativity of the Wigner function, which is an intrinsic property of any pure non-Gaussian state, cannot be observed because BSV is a mixed state even under minute optical loss. However, we show that BSV can be considered as a mixture of pure squeezed coherent states, for some of which Kerr-induced Wigner-function negativity is quite tolerant to loss. This work bridges the gap between quantum optics and ultrafast nonlinear optics, opening a path to quantum applications that require high photon flux.
Abstract We theoretically investigate the nonlinear spectral broadening of bright squeezed vacuum (BSV) driven by Kerr nonlinearity in bulk sapphire and demonstrate a route toward generating ultrafast broadband BSV-based light. By analyzing the spectral evolution and frequency correlations during nonlinear propagation, we show that the intrinsic photon-number fluctuations sampled from the BSV input significantly enhance ensemble-averaged spectral broadening compared with coherent pulses of the same mean intensity. Quantum statistics enter through Husimi-Q sampling of the incident squeezed-vacuum state, whereas each realization is subsequently propagated as a semiclassical complex envelope. The generated broadband field exhibits strong photon-number and intensity correlations across a wide spectral range together with excellent temporal compressibility. After a common dispersion compensation, the source supports single-shot pulse durations ranging from approximately 7 fs to 70 fs. This work combines ultrafast temporal characteristics with quantum-originated input statistics in a single optical platform and may provide new opportunities for strong-field quantum optics, including high-harmonic generation and attosecond science.
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.