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arXiv:2509.17746 · Optica

Single-shot pulse retrieval of femtosecond bright squeezed vacuum

Yuval Kern, Ido Nisim, Michael Birk, Andrei Rasputnyi, Doron Behar, Zhaopin Chen, Ido E. Kaminer, Pavel Sidorenko, Oren Cohen, Michael B. Kruger

Published Feb 10, 2026• 5 citations
arXivHTMLPDF

Abstract

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.

DOI
10.1364/optica.580767

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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.
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 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.
In the field of attosecond science, photoelectron spectroscopy and interferometry stand as a central topic not only for its ability to characterise attosecond pulses but also for its ability to make time resolved measurements of electron dynamics. This feature allows for its application across the many fields which depend on the behaviour of electrons. For these reasons, there is significant interest in improving these techniques. One such candidate is the implementation of quantum light states to replace the typical coherent light used for interferometry. In the past, this was not possible due to the weakness of quantum light sources. However, recent development has shown that high intensity bright squeezed vacuum sources are possible and can be made to have high enough intensities in order to drive nonlinear processes, which allows for possibilities within attosecond science. For this work, we will begin developing and characterising an intense bright squeezed vacuum source to be used for applications in photoelectron metrology.
The extreme light-matter interaction has brought unique tools for the subfemtosecond control of electron dynamics [1] and ultra-fast spectroscopy [2]. Until recently, the strong-field regime was accessible only with coherent states of light, which can be well described by classical electric fields when many photons are present (Fig. 1a). With the use of intense states of non-classical light, this situation has changed. New opportunities emerge with bright squeezed vacuum (BSV), which can be generated from optical parametric amplification of quantum vacuum fluctuations. Unlike classical light, BSV is a quantum superposition of coherent states with an amplitudes spanning a range from zero to very high values, up to ~1 TW/cm2[3]. BSV has a zero mean electric field and the variance of the electric field oscillates at the double carrier frequency (Fig. 1a). How such a non-classical electric field can affect the dynamics of photoemitted electrons was theoretically demonstrated recently [4]. Furthermore, the photon-number distribution of BSV has a very long tail in contrast to coherent light. These photon-number distributions can be imprinted onto the photon statistics of optical harmonics [3] and the statistics of electrons [5].
Nonlinear optical processes, mediated by multiphoton interactions rather than single-photon response, are routinely exploited to enable a range of light-based functionalities in devices and applications. Nonlinear effects are enhanced through higher intensity fields, which is a limiting strategy owing to potential radiation damage. An alternative strategy relies on the fluctuation redistribution typical of quantum light, but experimental demonstrations at the most fundamental level have been limited. Here we report experimental nonlinear tunnelling ionization of isolated atoms, a pivotal nonlinear process that drives high-harmonic generation and forms the basis of attosecond science, boosted by quantum light -- bright squeezed vacuum (BSV). A BSV light with an average pulse energy of 300 nJ achieves an effective intensity equivalent to that of a coherent light with 7.1 {\textmu}J, demonstrating a more than 20-fold quantum boost in nonlinear effect from BSV light. This boost is revealed by matching the peaks of the photoelectron momentum spectra produced by the BSV and coherent light using angular streaking. Furthermore, we demonstrate control of the effective intensity of the BSV by tuning the correlation function at fixed average pulse energy, establishing a robust method to tailor nonlinear processes via quantum statistics rather than classical intensity scaling. These findings may facilitate the development of quantum-controlled strong-field dynamics using tailored quantum light sources.