We investigate how quantum correlations in squeezed driving fields determine scaling laws in dissipative multiphoton quantum sensing. Independently squeezed fields yield \emph{factorized} scaling, with separate absorption and emission contributions and nonlinear thresholds that suppress exponential scaling in linear processes. In contrast, jointly squeezed fields generate \emph{collective} scaling governed by the total nonlinear photon order of the dissipative interaction. Remarkably, we show that normally ordered observables do not inherit the full nonlinear scaling of the underlying multiphoton fluctuations. Instead, they exhibit asymptotic behavior with an effective nonlinear order reduced by one. This arises because normally ordered observables probe only part of the underlying multiphoton fluctuation structure. These findings reveal how multiphoton fluctuations, quantum correlations, and measurement structure jointly determine the experimentally accessible sensitivity of nonlinear dissipative quantum sensors and establish design principles for quantum sensing protocols based on structured squeezed light.
We investigate how quantum correlations in squeezed driving fields determine scaling laws in dissipative multiphoton quantum sensing. Independently squeezed fields yield \emph{factorized} scaling, with separate absorption and emission contributions and nonlinear thresholds that suppress exponential scaling in linear processes. In contrast, jointly squeezed fields generate \emph{collective} scaling governed by the total nonlinear photon order of the dissipative interaction. Remarkably, we show that normally ordered observables do not inherit the full nonlinear scaling of the underlying multiphoton fluctuations. Instead, they exhibit asymptotic behavior with an effective nonlinear order reduced by one. This arises because normally ordered observables probe only part of the underlying multiphoton fluctuation structure. These findings reveal how multiphoton fluctuations, quantum correlations, and measurement structure jointly determine the experimentally accessible sensitivity of nonlinear dissipative quantum sensors and establish design principles for quantum sensing protocols based on structured squeezed light.
Quantum mechanics is fundamentally governed by the Schrödinger equation, which is linear in the wave function. Nevertheless, quantum systems can exhibit highly nonlinear behavior in their observable dynamics. Such nonlinearities can emerge from many-body interactions, nonlinear coupling mechanisms, or the interplay between coherent evolution and dissipation. In the collective limit, microscopic quantum interactions can give rise to qualitatively new macroscopic behavior. Open quantum systems provide a rich setting for such phenomena, as environmental coupling introduces dissipation and fluctuations that compete with coherent dynamics and can alter the steady states and dynamical phases of a system. Combined with nonlinear interactions, this competition can produce behavior with no direct counterpart in conventional linear light--matter systems. In this thesis, I investigate such collective phenomena through nonlinear two-photon light--matter interactions and engineered quantum reservoirs. I first investigate the driven--dissipative two-photon Dicke model and demonstrate the emergence of a dissipative superradiant phase transition. The quadratic light--matter interaction introduces distinct stability requirements in the presence of dissipation. In particular, two-photon loss stabilizes the superradiant phase, allowing its steady states and critical behavior to be characterized. I next investigate photon blockade and transient quadrature-squeezed radiation in the two-photon Tavis--Cummings model. I show that two-photon interactions collectively enhance photon blockade and squeezing, in contrast to the conventional one-photon model, where the effective nonlinearity diminishes in the collective limit. Finally, I consider collective behavior induced by reservoir engineering. Two spatially separated open quantum systems without direct coherent interaction can undergo a nonlocal quantum phase transition when coupled to correlated quantum reservoirs. Remarkably, the transition is hidden from local observables and emerges only through nonlocal correlations and collective observables. Together, these results demonstrate how nonlinear interactions and engineered dissipation can reshape collective behavior in open quantum systems.
Multiphoton absorption is of vital importance in many spectroscopic, microscopic, or lithographic applications. However, given that it is an inherently weak process, the detection of multiphoton absorption signals typically requires large field intensities, hindering its applicability in many practical situations. In this Letter, we show that placing a multiphoton absorbent inside an imbalanced nonlinear interferometer can enhance the precision of multiphoton cross section estimation with respect to strategies based on photon-number measurements using coherent or even squeezed light directly transmitted through the medium. In particular, the power scaling of the sensitivity with photon flux can be increased by 1 order compared with transmission measurements of the sample with coherent light, such that the measurement precision at any given intensity can be greatly enhanced. Furthermore, we show that this enhanced measurement precision is robust against experimental imperfections leading to photon losses, which usually tend to degrade the detection sensitivity. We trace the origin of this enhancement to an optimal degree of squeezing which has to be generated in a nonlinear SU(1,1) interferometer.
The fine-structure constant is usually regarded as a static fundamental parameter. Two recent independent experimental studies [4,5] have examined this notion from different perspectives. Building on this, we take a quantum sensing approach and treat a Rydberg EIT‑AT system as a nonlinear detector to probe possible high‑frequency statistical fluctuations of . We establish a theoretical framework that includes atom‑light nonlinear response and analyze how high‑order statistical features of squeezed light are converted into observable variance of frequency readings via the nonlinear response. Based on this framework, we propose a testable experimental prediction: there exists a squeezing parameter threshold such that, for and with the system operating in the regime, the frequency variance after subtracting shot noise under squeezed light exceeds that under coherent light. This prediction does not depend on the specific microscopic model of fluctuations, but assumes a macroscopic correlation length for (as a working hypothesis). It should be noted that the current estimate shows the required squeezing parameter lies beyond the present experimental capability (); thus the core positioning of this work is to propose a future detection direction and specify its technical requirements, rather than a near‑term realizable scheme. Notably, the recent experiment by Chao, You et al. [4] provides independent experimental evidence for the tunability of the key nonlinear parameter of this work. This paper aims to offer a possible theoretical reference framework for detecting high‑frequency fluctuations of fundamental constants. Keywords: fine‑structure constant; squeezed light; Rydberg atoms; non‑Gaussian fluctuations; quantum sensing; phenomenological model 摘要 精细结构常数 通常被视为一个静态的基本参数。近期两项独立的实验研究[4,5]从不同角度对这一观念提出了审视。本文在此基础上,从量子传感的角度出发,将里德堡 EIT‑AT 系统视为一个非线性探测器,用以探测 可能存在的高频统计涨落。我们建立了一个包含原子‑光场非线性响应的理论框架,分析了压缩态光的高阶统计特征如何通过非线性响应转换为频率读数的可观测方差。基于该框架,我们提出一个可检验的实验预言:存在某个压缩参数阈值 ,使得当 且系统工作于 的参数区域时,压缩态光下扣除散粒噪声后的频率方差大于相干光下扣除散粒噪声后的频率方差。这一预言不依赖于 涨落的具体微观模型,但要求 涨落具有宏观关联长度(作为工作假设)。需要明确的是,当前估算显示实现该预言所需的压缩参数 超出已有实验能力(),因此本文的核心定位是提出一个未来探测方向并明确其技术指标,而非近期可实现的实验方案。值得注意的是,近期 Chao、You 等人的实验[4]为本文关键非线性参数的可调控性提供了独立的实验侧佐证。本文旨在为基本常数的高频涨落探测提供一种可能的理论参考框架。 关键词: 精细结构常数;压缩态光;里德堡原子;非高斯涨落;量子传感;唯象模型
Bridging quantum optics and strong-field physics provides a pathway to explore how quantum light shapes extreme nonlinear light-matter interactions. However, direct characterization of non-classical light at damage-threshold intensities remains an open question. Here, we theoretically investigate the impact of photon-number fluctuations of squeezed light on strong-field photoelectron holography using a quantum-optical strong-field approximation. We identify a mechanism, ponderomotive dephasing, whereby the inherent quantum fluctuations of the driving field dictate the stability of the electron's semiclassical action. While amplitude-squeezed light stabilizes the action to enhance holographic contrast, phase-squeezed light amplifies photon-number noise, causing a rapid collapse of fringe visibility. This quantum-optical sensitivity follows a steep quartic wavelength scaling, rendering mid-infrared drivers uniquely sensitive to the field's underlying quantum nature. Crucially, we show that the collapse of holographic contrast is not a loss of information but a metrological gain. By evaluating the Classical Fisher Information, we identify a "dark-port" mechanism in the tunneling tail that enables the estimation of field quadrature noise beyond the Standard Quantum Limit. This fundamental trade-off between structural imaging fidelity and statistical sensitivity establishes the framework for Attosecond Quantum Tomography: an in-situ, reference-free protocol to reconstruct the Wigner distribution of intense quantum light. Our results identify strong-field ionization as a nonlinear quantum transducer, bridging attosecond electron dynamics with quantum information science.
Abstract The quantum theory of electromagnetic radiation predicts characteristic statistical fluctuations for light sources as diverse as sunlight, laser radiation, and molecule fluorescence. Indeed, these underlying statistical fluctuations of light are associated with the fundamental physical processes behind their generation. In this contribution, we experimentally demonstrate that the manipulation of the quantum electromagnetic fluctuations of two-mode squeezed vacuum states leads to a family of quantum-correlated multiphoton states with tunable mean photon numbers and degree of correlation. Our technique relies on the use of conditional measurements to engineer the excitation mode of the field through the simultaneous subtraction of photons from two-mode squeezed vacuum states. The experimental generation of nonclassical multiphoton states by means of photon subtraction unveils novel mechanisms to control fundamental properties of light. As a remarkable example, we demonstrate the engineering of a quantum state of light with up to ten photons, exhibiting nearly Poissonian photon statistics, that constitutes an important step towards the generation of entangled lasers. Our technique enables a robust protocol to prepare quantum states with multiple photons in high-dimensional spaces and, as such, it constitutes a novel platform for exploring quantum phenomena in mesoscopic systems.
We introduce a linear, canonical transformation of the fundamental single-mode field operators a and ${a}^{\ifmmode\dagger\else\textdagger\fi{}}$ that generalizes the linear Bogoliubov transformation familiar in the construction of the harmonic oscillator squeezed states. This generalization is obtained by adding a nonlinear function of any of the fundamental quadrature operators X1 and X2 to the linear transformation, thus making the original Bogoliubov transformation quadrature dependent. Remarkably, the conditions of canonicity do not impose any constraint on the form of the nonlinear function, and lead to a set of nontrivial algebraic relations between the c-number coefficients of the transformation. We examine in detail the structure and the properties of the quantum states defined as eigenvectors of the transformed annihilation operator b. These eigenvectors define a class of multiphoton squeezed states. The structure of the uncertainty products and of the quasiprobability distributions in phase space shows that besides coherence properties, these states exhibit a squeezing and a deformation (cooling) of the phase-space trajectories, both of which strongly depend on the form of the nonlinear function. The presence of the extra nonlinear term in the phase of the wave functions has also relevant consequences on photon statistics and correlation properties. The nonquadratic structure of the associated Hamiltonians suggests that these states be generated in connection with multiphoton processes in media with higher nonlinearities. We give a detailed description of the quadratic nonlinear transformation, which defines four-photon squeezed states. In particular, the behaviors of the second-order correlation function g(2)(0) and of the fourth-order correlation function g(4)(0) are studied. The former exhibits super-Poissonian statistics, while the latter indicates photon bunching in the four-photon emissions.