Photon number statistics uncover the fluctuations in non-equilibrium lattice dynamics
Martina Esposito, Kelvin Titimbo, Klaus D. Zimmermann, Francesca Giusti, Francesco Randi, D. Boschetto, F. Parmigiani, Roberto Floreanini B, Fabio Benatti, Daniele Fausti
Fluctuations of the atomic positions are at the core of a large class of unusual material properties ranging from quantum para-electricity to high temperature superconductivity. Their measurement in solids is the subject of an intense scientific debate focused on seeking a methodology capable of establishing a direct link between the variance of the atomic displacements and experimentally measurable observables. Here we address this issue by means of non-equilibrium optical experiments performed in shot-noise-limited regime. The variance of the time-dependent atomic positions and momenta is directly mapped into the quantum fluctuations of the photon number of the scattered probing light. A fully quantum description of the non-linear interaction between photonic and phononic fields is benchmarked by unveiling the squeezing of thermal phonons in α-quartz.
Fluctuations of the atomic positions are at the core of a large class of unusual material properties ranging from quantum para-electricity to high temperature superconductivity. Their measurement in solids is the subject of an intense scientific debate focused on seeking a methodology capable of establishing a direct link between the variance of the atomic displacements and experimentally measurable observables. Here we address this issue by means of non-equilibrium optical experiments performed in shot-noise-limited regime. The variance of the time-dependent atomic positions and momenta is directly mapped into the quantum fluctuations of the photon number of the scattered probing light. A fully quantum description of the non-linear interaction between photonic and phononic fields is benchmarked by unveiling the squeezing of thermal phonons in α-quartz.
The variance of the time dependent atomic positions and momenta is directly mapped into the quantum uctuations of the photon number of the scattered probing light. A fully quantum de-scription of the non-linear interactions between photonic and phononic fields unveils evidences of squeezing of thermal phonons. In here a pump-probe spectroscopy was proposed to observe phonon squeezing in solids. Numerical simulation showed pump-probe response due to coherent phonon and squeezed phonon in alpha-quartz.
Measuring fluctuations in matter's low-energy excitations is the key to unveiling the nature of the non-equilibrium response of materials. A promising outlook in this respect is offered by spectroscopic methods that address matter fluctuations by exploiting the statistical nature of light-matter interactions with weak few-photon probes. Here we report the first implementation of ultrafast phase randomized tomography, combining pump-probe experiments with quantum optical state tomography, to measure the ultrafast non-equilibrium dynamics in complex materials. Our approach utilizes a time-resolved multimode heterodyne detection scheme with phase-randomized coherent ultrashort laser pulses, overcoming the limitations of phase-stable configurations and enabling a robust reconstruction of the statistical distribution of phase-averaged optical observables. This methodology is validated by measuring the coherent phonon response in α-quartz. By tracking the dynamics of the shot-noise limited photon number distribution of few-photon probes with ultrafast resolution, our results set an upper limit to the non-classical features of phononic state in α-quartz and provide a pathway to access non-equilibrium quantum fluctuations in more complex quantum materials.
Different quantum states of atoms in optical lattices can be nondestructively monitored by off-resonant collective light scattering into a cavity. Angle resolved measurements of photon number and variance give information about atom-number fluctuations and pair correlations without single-site access. Observation at angles of diffraction minima provides information on quantum fluctuations insensitive to classical noise. For transverse probing, no photon is scattered into a cavity from a Mott insulator phase, while the photon number is proportional to the atom number for a superfluid.
A recurring structural pattern across several recent preprints in quantum optics and atomic physics is the use of photon statistics — intensity correlations, quadrature measurements, and spin-noise spectra — as primary diagnostic channels for the quantum state of matter rather than as end-products in themselves. This paper synthesizes five specific findings into a candidate reading of that pattern: (1) above-threshold ionization driven by bright squeezed vacuum provides a strong-field analogue of photon subtraction that heralds large-amplitude optical Schrödinger cat states [corpus:arxiv:2605.31160]; (2) bright squeezed vacuum combined with single-shot quadrature measurement enables ultrafast preparation of macroscopic quantum superpositions in matter, including Dicke states and cat-like states [corpus:arxiv:2605.30224]; (3) superradiant intensity-correlation measurements using N thermal light sources can reduce the Cramér–Rao bound on distance estimation by a factor of N relative to conventional LIDAR [corpus:arxiv:2605.28378]; (4) a nonlinear (quadratic) density dependence of spin-noise variance in warm rubidium vapor reveals atomic cross-correlations arising from resonant dipole–dipole interaction [corpus:arxiv:2605.31262]; and (5) a cryogenic confocal multimode optical cavity apparatus designed to exploit superradiant Raman excitation of phonons and charge-density waves in two-dimensional van der Waals materials demonstrates how optical mode geometry concentrates field enhancement for light–matter coupling [corpus:arxiv:2605.28815]. The unifying heuristic — explicitly flagged as such, not a formal derivation — is that photon statistics carry imprints of many-body correlations in matter, and conversely that engineering the photon mode structure (squeezed vacuum, supermode, superradiant emission) allows targeted preparation or sensing of those correlations. The primary falsification path for the central claim is the following: if spin-noise variance in the rubidium experiment were shown to scale linearly with density even after DDI quenching is removed, the correlation interpretation would be undermined. Abstract-only reading is acknowledged as a methodological limit throughout. --- Authorship: Saluca Agentic AI Research Team (Saluca LLC). AI-drafted from arXiv preprint corpus on the date in the filename. Cited arXiv preprints: 2605.28378, 2605.28695, 2605.28815, 2605.30047, 2605.30224, 2605.31160, 2605.31262, 2605.31442
A cluster of recent results across quantum optics, photonics, and atom-photon interaction suggests a unifying thesis: the **photon-number statistics of the driving or probe field** — whether thermal, coherent, squeezed, or manifestly non-Gaussian — function as an active control degree of freedom that determines the character of the quantum state produced, the fidelity of a light-matter interface, and the precision ceiling of a sensing protocol, rather than merely setting a noise floor to be minimized. We synthesize five specific findings to argue this point. First, bright squeezed vacuum (BSV) light enables photon-subtraction-like operations at high intensity via above-threshold ionization, generating large-amplitude optical Schrödinger cat states whose non-Gaussian character is tunable through the detected photoelectron momentum [corpus:arxiv:2605.31160]. Second, the same BSV resource, combined with single-shot quadrature measurement, heralds macroscopic quantum superpositions in matter on ultrafast timescales, with the squeezing amplitude directly controlling the preparation speed of zero-eigenvalue Dicke states [corpus:arxiv:2605.30224]. Third, chiral light-matter coupling in slow-light photonic-crystal waveguides is not fixed by geometry alone but can be electrically inverted through the quantum-confined Stark effect, demonstrating that the local optical chirality — a mode-structure property — acts as a tunable interface parameter [corpus:arxiv:2605.30047]. Fourth, superradiant intensity correlations of order *m* ≥ 2 from *N* thermal light sources provide a Cramér–Rao bound improvement scaling as 1/*N* relative to conventional LIDAR, showing that photon-bunching statistics encode metrological information inaccessible to first-order intensity measurements [corpus:arxiv:2605.28378]. Fifth, spin noise spectroscopy reveals a quadratic density dependence of spin noise variance in warm rubidium vapor that is attributable to resonant dipole-dipole interactions, and can be quenched by suppressing the residual optical excitation that mediates those correlations [corpus:arxiv:2605.31262]. Together these results support the hypothesis that photon statistics — Gaussian or non-Gaussian, first-order or higher-order, classical or quantum — constitute a primary design variable for quantum state engineering, chiral interfaces, and precision metrology. Falsification paths for each sub-claim are identified throughout. --- Authorship: Saluca Agentic AI Research Team (Saluca LLC). AI-drafted from arXiv preprint corpus on the date in the filename. Cited arXiv preprints: 2605.28378, 2605.30047, 2605.30224, 2605.31160, 2605.31262, 2605.31442
We study off-resonant collective light scattering from ultracold atoms trapped in an optical lattice. Scattering from different atomic quantum states creates different quantum states of the scattered light, which can be distinguished by measurements of the spatial intensity distribution, quadrature variances, photon statistics, or spectral measurements. In particular, angle-resolved intensity measurements reflect global statistics of atoms (total number of radiating atoms) as well as local statistical quantities (single-site statistics even without optical access to a single site) and pair correlations between different sites. As a striking example we consider scattering from transversally illuminated atoms into an optical cavity mode. For the Mott-insulator state, similar to classical diffraction, the number of photons scattered into a cavity is zero due to destructive interference, while for the superfluid state it is nonzero and proportional to the number of atoms. Moreover, we demonstrate that light scattering into a standing-wave cavity has a nontrivial angle dependence, including the appearance of narrow features at angles, where classical diffraction predicts zero. The measurement procedure corresponds to the quantum nondemolition measurement of various atomic variables by observing light.