Dicke state, a coherent state of multiple particles, is fundamentally responsible for various intriguing collective behaviors many-body systems. Experimental access to states with scalable and deterministic number particles essential study how properties depend on the particle number. We report observation consisting two, three, four, five, six, seven atoms in an atomic vapor. Quantum coherences between ground multi-atom are created detected by using optical two-dimensional spectroscopy. The...

We use orthogonally polarized two-color (OTC) laser pulses to separate quantum paths in the multiphoton ionization of Ar atoms. Our OTC consist 400 and 800 nm light at a relative intensity ratio $10\ensuremath{\mathbin:}1$. find hitherto unobserved interference photoelectron momentum distribution, which exhibits strong dependence on phase pulse. Analysis model calculations reveals that is caused by pathways from nonadjacent quarter cycles.

Optical double-quantum two-dimensional coherent spectroscopy (2DCS) was implemented to probe interatomic dipole-dipole interactions in both potassium and rubidium atomic vapors. The interaction detected at densities of $4.81 \times 10^8$ cm$^{-3}$ $8.40 10^9$ for rubidium, respectively, corresponding a mean separation 15.8 $\mu$m or $3.0\times 10^5a_0$ 6.1 $1.2\times where $a_0$ is the Bohr radius. We report lowest density which are detected. experimental results confirm long range nature...

We study photoelectron angular distributions (PADs) near the ionization threshold with a newly developed Coulomb quantum-orbit strong-field approximation (CQSFA) theory. The CQSFA simulations present an excellent agreement result from time-dependent Schr\"odinger equation method. show that low-energy fan-shaped structure in PADs corresponds to subcycle time-resolved holographic and stems significant influence of potential on phase forward-scattering electron trajectories, which affects...

An improved self-imaging method for molecules that fixes the detected electron momentum while rotating internuclear axis of molecular target has advantage not requiring a priori knowledge atomic differential cross-section.

Quantum coherence of collective states plays a pivotal role in understanding many-body cooperative behaviors. Collective coherences between the ground state and excited potassium atoms were previously revealed; however, collectively has hitherto been overlooked, its observation remained challenging. Here we present joint experimental theoretical investigation effects K atomic vapor using two-dimensional coherent spectroscopy. By collecting zero-quantum, double-quantum,...

<title>Abstract</title> Two-dimensional coherent spectroscopy (2DCS) combined with dual-comb technology offers unprecedented resolution for probing many-body interactions and correlations in atomic vapors, yet its application to high-order multi-quantum transitions remains challenging due weaker nonlinear signals phase instability. Here, we demonstrate a triple-quantum 2DCS technique that achieves λ/110 stability through digital correction, enabling the observation of velocity-synchronized...

In this Letter, we propose a novel laser-induced inelastic diffraction (LIID) scheme based on the intense-field-driven atomic nonsequential double ionization (NSDI) process and demonstrate that, with LIID approach, doubly differential cross sections (DDCSs) of target ions, e.g., ${\mathrm{Ar}}^{+}$ ${\mathrm{Xe}}^{+}$, can be accurately extracted from two-dimensional photoelectron momentum distributions in NSDI corresponding atoms. The DDCSs exhibit strong dependence both laser intensity,...

We present theoretically obtained photoelectron momentum distributions (PMDs) for the strong field ionization of argon in an elliptically polarized laser at a central wavelength 400 nm. Three different theoretical approaches, namely, numerical solution time-dependent Schrödinger equation (TDSE), nonadiabatic model, and classical-trajectory Monte Carlo (CTMC) model are adopted our calculations. From TDSE calculations, it is found that attoclock offset angle (most probable electron emission...

Attoclock provides a powerful tool for probing the ultrafast electron dynamics in strong laser fields. However, this technique has remained restricted to single or sequential double ionized dynamics. Here, we propose novel attoclock scheme with polarization-gated few-cycle pulse and demonstrate its application timing correlated-electron emission field ionization of argon. Our experimental measurements reveal that occurs mainly through two channels time differences 234±22 as 1043±73 as,...

Quantum interference plays an important role in various intense-laser-driven atomic phenomena, e.g., above-threshold ionization and high-order-harmonic generation, provides a useful tool ultrafast imaging of molecular structure dynamics. However, it has eluded observation nonsequential double (NSDI), which serves as ideal prototype to study electron-electron correlation. Thus far, NSDI usually could be well understood from semiclassical perspective, where all quantum aspects have been...

Abstract In strong field atomic physics community, long-range Coulomb interaction has for a long time been overlooked and its significant role in intense laser-driven photoelectron dynamics eluded experimental observations. Here we report an investigation of the effect potential on near-zero-momentum photoelectrons produced photo-ionization process noble gas atoms midinfrared laser pulses. By exploring dependence distributions near zero momentum intensity wavelength, unambiguously...

We theoretically investigate the electron momentum distributions in orthogonally polarized two-color pulses with Coulomb-Volkov distorted-wave approximation (CVA) theory and focus on role of Coulomb potential by comparing CVA results strong-field (SFA) simulations. Our show that comparison SFA simulations, are better agreement experimental observations time-dependent Schr\"odinger equation calculations. By analyzing phase dipole moment, we find change can be ascribed to different corrections...

We theoretically investigate the atomic polarization effect on photoelectron angular distributions (PADs) in above-threshold ionization of noble gases with elliptically polarized laser fields at wavelength 800 nm, ellipticity 0.25, and intensity $1.5\ifmmode\times\else\texttimes\fi{}{10}^{14}\phantom{\rule{4pt}{0ex}}\text{W}/{\text{cm}}^{2}$. Simulations based a semiclassical model that includes both ionic Coulomb potential show surprisingly little difference between PADs for Ar, Kr, Xe,...

Using a semiclassical approach, we theoretically study the above-threshold ionization of magnesium by intense, mid-infrared laser pulses. The formation low-energy structures in photoelectron spectrum is found to be enhanced comparing with calculation based on single-active electron approximation. By performing trajectory and recollision-time distribution analysis, demonstrate that this phenomenon due laser-induced ionic core polarization effects recolliding electrons. We also show should...

We conceive an improved procedure to determine the laser intensity with momentum distributions from nonadiabatic tunneling ionization of atoms in close-to-circularly polarized fields. The measurements for several noble gas are accordance semiclassical calculations, where effect and influence Coulomb potential included. Furthermore, high-order above-threshold spectrum linearly fields Ar is measured compared numerical calculation time-dependent Schrödinger equation single-active-electron...

We report on an experimental and theoretical study of the ionization-fragmentation dynamics argon dimers in intense few-cycle laser pulses with a tagged carrier-envelope phase. find that field-driven electron transfer process from one atom across system boundary to other triggers sub-cycle electron-electron interaction neighboring atom. This attosecond electron-transfer between distant entities its implications manifest themselves as distinct phase-shift measured asymmetry emission curves...

We theoretically investigate the photoelectron momentum distributions of a diatomic molecule in linearly polarized two-color laser field by solving time-dependent Schr\"odinger equation. An upward curvature interference pattern is found two-dimensional spectra. Resorting to simple semiclassical analysis and strong-field approximation theory, we show that corresponds holographic from second-return backscattering electron orbits and, furthermore, underlying physics distinct observation such...

We report a novel, to the best of our knowledge, double-quantum-zero-quantum two-dimensional coherent spectroscopy (2DCS) that allows direct detection quantum coherence between multiparticle collective states. Through correlating double-quantum and zero-quantum coherence, signatures for states can be well isolated as side peaks readily identified in 2D spectrum. The experiment is implemented vapor rubidium atoms collinear 2DCS setup. Good agreement with theoretical simulation using density...

We investigate high harmonic generation (HHG) of an atom in the presence squeezed vacuum a single mode. Based on fully quantum time-dependent Schrödinger equation, we derive analytical formula for amplitude. Our simulations HHG spectrum with this show that amplitude corresponding mode can undergo significant changes different parameters vacuum. Using time-frequency analysis method, physics underlying effects fluctuation (VQF) is revealed, which found to be consistent explanation Fermi's...

We theoretically demonstrate the feasibility of separation various intracycle interferences in photoelectron momentum distributions (PMDs) with a polarization-gated (PG) pulse constructed by left-circularly polarized and time-delayed right-circularly few-cycle laser pulse. By numerically solving time-dependent Schr\"odinger equation, our simulations show that intercycle interference pattern is suppressed clear rightward curved stripes emerges PMDs appropriate parameters. This can be well...

We study the photoionization of molecule ${\mathrm{H}}_{2}^{+}$ in an XUV pulse by numerically solving time-dependent Schr\"odinger equation simulation and focus on a zeptosecond birth time delay photoelectron from different cores. propose simple robust method to extract accurately with double-slit interference minima. Based this extraction method, our results show that is strongly affected initial bound-electron wave function due deviation electron emission position central core....

We experimentally investigate the double ionization of molecular hydrogen subjected to ultrashort intense laser pulses. The total kinetic energy release two coincident H+ ions, which provides a diagnosis different processes H2, is measured for pulse durations, i.e., 25 and 5 fs, various intensities. It found that, long duration (i.e., fs), occurs mainly via processes, charge resonance enhanced recollision-induced ionization. Moreover, contributions from these can be significantly modulated...