We show that bright squeezed vacuum light, combined with a single-shot quadrature measurement of the post-interaction light, enables the ultrafast generation of macroscopic quantum states in matter. Although in the weak-coupling regime multiphoton quantum light leaves the unconditional matter state as a classical mixture due to light--matter entanglement, quadrature-based heralding prepares the matter in a Gaussian-weighted quantum superposition of laser-driven matter states. For an ensemble of resonantly electric-dipole-coupled two-level systems, this heralding dynamics acts as a Gaussian filter with respect to the electric polarization, with brighter squeezed-vacuum light accelerating the preparation of the zero-eigenvalue Dicke state. Counter-rotating terms further drive a stroboscopic transition from this Dicke state to a cat-like state. Our results open a route to ultrafast engineering of macroscopic quantum matter with strong-field quantum light.
We show that bright squeezed vacuum light, combined with a single-shot quadrature measurement of the post-interaction light, enables the ultrafast generation of macroscopic quantum states in matter. Although in the weak-coupling regime multiphoton quantum light leaves the unconditional matter state as a classical mixture due to light--matter entanglement, quadrature-based heralding prepares the matter in a Gaussian-weighted quantum superposition of laser-driven matter states. For an ensemble of resonantly electric-dipole-coupled two-level systems, this heralding dynamics acts as a Gaussian filter with respect to the electric polarization, with brighter squeezed-vacuum light accelerating the preparation of the zero-eigenvalue Dicke state. Counter-rotating terms further drive a stroboscopic transition from this Dicke state to a cat-like state. Our results open a route to ultrafast engineering of macroscopic quantum matter with strong-field quantum light.
While the interface between strong-field physics and quantum optics offers a unique regime for combining extreme nonlinearity with quantum optical resources, its potential for generating non-classical states of light remains largely unexplored. Standard protocols for generating optical Schrödinger cat states, such as photon subtraction from squeezed light, are inherently limited in the achievable macroscopicity of the state and its scalability. In this work, we bridge this gap by demonstrating that above-threshold ionization driven by bright squeezed light provides a strong-field analogue of photon subtraction, where photoelectron detection acts as a high-intensity heralding mechanism, enabling the generation of large amplitude optical Schrödinger cat states. We characterize the resulting non-Gaussian features and show that they can be tuned via the detected photoelectron momentum, and study their robustness against the experimental imperfections arising from finite momentum resolution at the heralding step. Despite the noise, we show that the generated states can be manipulated to violate a Bell inequality, thereby highlighting their potential for foundational and practical applications. Our results establish strong-field processes as a scalable platform for macroscopic quantum state engineering, opening a route to quantum optics in previously inaccessible regimes.
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.
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.
High-harmonic generation (HHG) is a prototypical strong-field process in which intense light drives matter to emit radiation at integer multiples of the driving frequency. Extending HHG into the quantum-optical regime offers new opportunities to probe and control strongly nonlinear light-matter interactions using nonclassical states of light. Yet describing this regime requires a fully quantum treatment of the correlated electron-photon dynamics, which becomes computationally challenging for broadband, strongly squeezed fields. Here we solve the quantum-electrodynamical dynamics of a two-level system driven by bright squeezed vacuum in a converged multimode Hilbert space. Both the driving field and emitted harmonics are fully quantized, with the light-matter interaction treated nonperturbatively. This enables direct access to the multimode quantum state and its higher-order correlations beyond semiclassical sampling or perturbative descriptions. We show that squeezed-vacuum driving produces harmonic emission with qualitatively distinct second- and third-order photon correlations compared with coherent excitation. Moreover, back-action from the driven emitter strongly reshapes the incident squeezed field, generating pronounced Wigner-function negativities that evolve on attosecond timescales. Our results establish a fully quantum framework for broadband strong-field dynamics with squeezed light and provide a route to predicting and interpreting quantum-HHG experiments and their extension to more complex emitters.
Characterizing macroscopic quantum states of light is a frontier challenge at the interface of quantum optics and high-intensity photonics. Here, we demonstrate the first, to our knowledge, direct phase-space tomography of a bright, ultrafast quantum state. We adapt a single-shot f-2f interferometer to sample the Husimi Q-function of a 25 fs bright squeezed vacuum (BSV) pulse (mean photon number N ∼10 12 ) subject to Kerr nonlinearity. Our measurement reveals a clear transformation from a Gaussian distribution with pronounced quadrature antisqueezing to a characteristic "S"-shaped profile as the intensity-dependent nonlinear phase increases. Crucially, we show theoretically that despite optical loss, the state does not degrade into classically modulated light but is rigorously described as a statistical mixture of squeezed coherent states. While global Wigner negativity is masked by technical noise, our results show theoretically that the constituent states individually retain strong Wigner-negative features. This work bridges quantum optics and high-intensity photonics, establishing a platform for diagnosing bright quantum resources.
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].