We report an electron-atom Compton scattering experiment on the ${\mathrm{H}}_2$ molecule. The momentum distribution of the H atom due to intramolecular motion was obtained by using a protocol developed for the data analysis. Furthermore, it is shown that the experimental result agrees well with associated calculations based on quantum chemistry theory. This indicates not only the validity of the protocol but also the feasibility of use of the experiment as an unconventional molecular spectroscopy, opening the door to direct and precise mapping of intramolecular motion of each atom with different masses.

We theoretically investigate the influence of a longitudinal laser polarization component from beam focusing on spin dynamics in Kapitza-Dirac scattering by solving the relativistic Dirac equation with time-dependent perturbation theory. The transverse spacial dependence of the longitudinal beam polarization component is accounted for by approximating a Gaussian beam with plane-wave components. We find that corrections from a longitudinal laser beam polarization component approximately scale with the second power of the diffraction angle $\epsilon$, from which we conclude that a related influence from beam focusing can be made negligibly small for sufficiently low beam foci.

Cooling a solid-state nanoparticle, as a significant prerequisite of the mesoscale quantum sensing, is experimentally challenging. Here we propose an efficient cooling scheme assisted by a strong magnetic-field gradient to cool a nanoparticle down to the ground state of the vibrational degrees of freedom. By combining the Zeeman effect with quantum interference effect, the scheme can accomplish the precooling of the nanoparticle from room temperature to the Doppler cooling limit in several seconds, and can then further cool the precooled nanoparticle to the vibrational ground state within milliseconds. We specify the scheme by exemplifying the nanocrystal of diamond nitrogen-vacancy center suspended in an electromagnetic potential, indicating that this cooling scheme can accomplish the ground-state cooling from room temperature within a few seconds under the condition of currently available techniques. Our work lays a foundation for further three-dimensional cooling of suspended nanoparticles and also for realizing quantum sensing using mesoscopic particles in the future.

High-order harmonic generation (HHG) in solid and gaseous targets has been proven to be a powerful avenue for the generation of attosecond pulses, whereas the influence of electron-phonon scattering on HHG is a critical outstanding problem. Here we first introduce a temperature-dependent lattice vibration model by characterizing the spacing fluctuation. Our results reveal that (i) structural disorder induced by lattice vibration does not lead to generation of even-order harmonics; (ii) dephasing of HHG occurs as the lattice temperature is growing; (iii) an open-trajectory picture predicts the maximal photon energy in the temperature-dependent HHG spectra. Moreover, a formula assessing dephasing time with lattice temperature is proposed to identify the timescale of electron-phonon scattering. This work paves the way to study the non-Born-Oppenheimer effect in solids driven by a strong field.

A detailed treatment of an electro-optical trap for polar molecules, realized by embedding an optical trap within a uniform electrostatic field, is presented and the trap's properties analyzed and discussed. The electro-optical trap offers significant advantages over an optical trap that include an increased trap depth and conversion of alignment of the trapped molecules to marked orientation. Tilting the polarization plane of the optical field with respect to the electrostatic field diminishes both the trap depth and orientation and lifts the degeneracy of the $\pm M$ states of the trapped molecules. These and other features of the electro-optical trap are examined in terms of the eigenproperties of the polar and polarizable molecules subject to the combined permanent and induced electric dipole interactions at play.

We present several toy models for predicting the character and strength of the roughness of ac Zeeman trapping potentials generated by imperfections in wire traces on an atom chip. An ac Zeeman trapping potential is generated by targeting a microwave or rf magnetic field at hyperfine or Zeeman ground-state transitions, respectively, while a dc Zeeman trap uses a static magnetic field to manipulate an atom via its magnetic moment. We find that an ac Zeeman trap suppresses potential roughness by several orders of magnitude with respect to a comparable dc Zeeman trap. This suppression stems from the inherent differences between an atom's response to dc and ac (namely rf and microwave) magnetic fields, in concert with how the ac skin effect smooths out a current distribution disturbed by a conductivity variation. For chip wires fabricated by evaporation, we find that an ac Zeeman trap for ${}^{87}\mathrm{Rb}$ atoms, located $100\mu \mathrm{m}$ from the chip and operating on a 6.8 GHz hyperfine transition, is expected to suppress potential roughness by a factor of $4\times {10}^5$ compared with a similar dc Zeeman trap. For a comparable ac Zeeman trap operating on a 10 MHz Zeeman transition, the suppression is $2\times {10}^4$. Conversely, the ac skin effect also slightly exacerbates potential roughness, in ac Zeeman traps, from defects in the sidewall of a wire trace.

This work presents a theoretical analysis of the Autler-Townes splitting pattern in the four-wave mixing signal generated in a three-level cascade Doppler-broadened system. We employ the density matrix formalism to write the Bloch equations and solve them numerically. The solutions allow us to compare the response of the upper level population and the generated signal coherence for homogeneously and nonhomogeneously broadened systems. Our results reveal an AC Stark shift in the nonlinear signal when the frequency of the strong or weak laser beam is scanned, in contrast to what is observed in the fluorescence. Furthermore, we present experimental data for the four-wave mixing signal in a hot rubidium vapor for the copropagating configuration of the laser beams that drive the $5S\to 5P\to 5D$ transition. The behavior of the AC Stark displacement and signal amplitude as a function of laser power indicates a good agreement between the model and the experimental results.

We elucidate the itinerant ferromagnetism of a dipolar Fermi gas with a Raman-induced spin-orbit coupling by investigating the exotic phase diagrams. It is revealed that the dipolar interaction along with spin-orbit coupling can corroborate the formation of ferromagnetism and that the Raman coupling adversely eliminates the tendency to this ferromagnetism transition, which greatly transcends the general understanding of this subject with contact interaction only. We explore the ground states through the density and spin-flip distribution in momentum space. We calculate the transition temperatures well within the reach of an experimental system when altering the dipolar and spin-orbit-coupling strength, which paves a way to the further experimental realization.

We report on a simple method to reconstruct the band structure of a one-dimensional optical lattice using a thermal cloud with a momentum spread of about two photon recoils. We image the momentum distribution of a thermal cloud exposed to a standing-wave potential using time-of-flight absorption images and observe unique features. With the support of numerical calculations, we explain their appearance and show how they can be used to reconstruct the full band structure directly. While this can serve as a precise lattice depth calibration tool, we additionally propose a method to estimate the lattice depth in a single-shot manner.

The counterflow dynamics of two correlated impurities in a double well coupled to a one-dimensional bosonic medium is explored. We determine the ground-state phase diagram of the system according to the impurity-medium entanglement and the impurities' two-body correlations. Specifically, bound impurity structures reminiscent of bipolarons for strong attractive couplings as well as configurations with two clustered or separated impurities in the repulsive case are identified. The interval of existence of these phases depends strongly on the impurity-impurity interactions and external confinement of the medium. Accordingly the impurities' dynamical response, triggered by suddenly ramping down the central potential barrier, is affected by the medium's trapping geometry. In particular, for a box-confined medium, repulsive impurity-medium couplings lead, due to attractive induced interactions, to the localization of the impurities around the trap center. In contrast, for a harmonically trapped medium the impurities perform a periodic collision and expansion dynamics further interpreted in terms of a two-body effective model. Our findings elucidate the correlation aspects of the collisional physics of impurities which should be accessible in recent cold-atom experiments.

We analyze the emergence of unphysical superluminal group velocities in Su-Schrieffer-Heeger (SSH) parity-time ($\mathcal{PT}$) symmetric chains, and explore the origins of such a behavior. By comparing the band structure of an infinite loss-gain SSH chain with that of a continuous realization—a one-dimensional Bragg stack governed by the Helmholtz equation—we first exclude insufficient coupling consideration in the tight-binding description as the cause of group-velocity divergence. We then focus on material dispersion, and show that indeed, restoring causality in the description of both the lossy and the gain components resolves the problem and recovers finite group velocities, whose real part can only exceed the speed of light in vacuum when accompanied by a significant imaginary part. Our analysis introduces thus the required practical limits in the performance of common $\mathcal{PT}$-symmetric systems.

It was recently predicted [M. I. Bakunov, A. V. Maslov, and M. V. Tsarev, Phys. Rev. A 95, 063817 (2017)] that an ultrashort laser pulse producing multiphoton ionization in an electro-optic crystal can generate a quasistatic unipolar electromagnetic precursor propagating ahead of the laser pulse. Here we study the propagation dynamics of such a precursor outside the generating crystal. Our analysis is based on a specially developed semianalytical model that represents the precursor generation as radiation from sequentially switched discrete current-carrying ribbons distributed along the laser path. The model allows for calculating the precursor spatiotemporal structure at an arbitrarily long distance behind the crystal. The calculations reveal the complex propagation dynamics of the precursor. Starting as a unipolar pulse, it becomes quasiunipolar after some distance, which depends on the precursor transverse size, and then bipolar preserving a constant transverse size and maximum field strength. These findings are important for the experimental observation of the precursors and their practical use.

The elusive role of femtosecond pulsed excitation in enhancing the efficiency of optical trapping of nanoparticles over continuous-wave excitation is revisited. Using generalized Lorentz-Mie theory, optical trapping force on nanoparticles composed of materials having a wide range of linear refractive indices, including metamaterials having negative refractive indices, is investigated. It is shown how the incorporation of optical nonlinearity, fine-tuned by the laser parameters (for example, average power, pulse width, etc.), leads to the emergence of novel phenomena such as trap splitting facilitating trapping of multiple particles that were not captured in a previous study on nanoparticles with varying refractive indices using dipole approximation. Intriguingly, we show that the trap becomes highly stable due to negative optical scattering force, known as “Fano resonance.” Furthermore, we observe the disappearance and reappearance of trapping wells with increasing refractive index under both continuous-wave and pulsed excitations. These findings show promising applications in the field of photonics through nanoscale optical manipulation controlled by optical nonlinearity.

Dissipative Kerr solitons arising from parametric gain in ring microresonators are usually described within a classical mean-field framework. Here, we develop a quantum-mechanical model of dissipative Kerr solitons in terms of the Lindblad master equation and study the model via the truncated Wigner method, which accounts for quantum effects to leading order. We show that, within this open quantum system framework, the soliton experiences a finite coherence time due to quantum fluctuations originating from losses. Reading the results in terms of the theory of open quantum systems allows us to estimate the Liouvillian spectrum of the system. It is characterized by a set of eigenvalues with a finite imaginary part and a vanishing real part in the limit of vanishing quantum fluctuations. This feature shows that dissipative Kerr solitons are a specific class of dissipative time crystals.

We study the photon and phonon statistics of a qubit-plasmon-phonon hybrid system in the ultrastrong-coupling regime. The introduced qubit coupling causes parity-conserving and -nonconserving situations. We employ an analytic approximation approach for the parity-conserving case to reveal the statistical behaviors of photons and phonons. It indicates that both photons and phonons show strong antibunching at the same frequency. Even though the bunching properties of photons and phonons occupy the dominant regions of the considered frequencies, phonons tend to weak antibunching within the photonic strong-bunching area. In contrast, one can find that the configurations of correlation functions for both photons and phonons in the parity-conserving case are squeezed towards the central frequency by parity breaking, which directly triggers the reverse statistical behaviors of the different parties in the low-frequency regions and the strong-bunching properties in other frequency regions. The photon-phonon cross-correlation function also demonstrates similar parity-induced differences, indicating that the nonconserving parity induces the photon-phonon bunching behavior. We finally analyze the delayed second-order correlation function with different driving frequencies, which illustrates striking oscillations revealing the occurrence of simultaneous multiple excitations.

An electron electric dipole moment (eEDM) search using laser-coolable triatomics such as YbOH is one of the most sensitive probes for physics beyond the standard model. The eEDM-induced energy shift is proportional to the polarization ($P$) of the molecule. Similarly to diatomics with an $\mathrm{\Omega }$-doubling structure, it was assumed that for triatomics with an $l$-doubling structure, related to the vibrational angular momentum, $P$ can be easily saturated to almost 100% with a moderate external electric field. We developed a method for the calculation of the properties of triatomic molecules and applied it to a calculation of $P$ of ${}^{174}\mathrm{YbOH}$ in the first excited $v=1$ bending mode. Calculations showed that most of the levels reach less than 50% efficiency. We showed that this fact is related to the Hund's case $b$ coupling scheme of YbOH. As the coupling scheme (for $\mathrm{\Omega }=1/2$ molecules) approaches the $a$ (or $c$) case, polarization increases up to 100%. The results of our calculations should be used for the correct extracting of the eEDM value from YbOH experiments and similar calculations are required for other molecules.

We establish and analytically derive the cutoff law for high harmonics generated with two interfering electron wave packets in the continuum. The phenomenon occurs for laser intensities high enough to spark substantial ionization, yet low enough that depletion of the ground state remains moderate to ensure a large interference yield. The continuum-continuum (CC) cutoff emerges from the maximal action difference of the dominant classical trajectories in the phase of the time-dependent dipole response. This action difference translates into an interference of a maximally time-delayed, so called stranded continuum trajectory with the trajectory of a high energy continuum electron. The time delay renders the CC harmonics more sensitive to electron wave-packet dispersion than standard high harmonics. Hence, CC harmonics should be most prominent in dimensionally reduced systems.

We study the spin-mixing dynamics of a one-dimensional strongly repulsive Fermi gas under harmonic confinement. By employing a mapping onto an inhomogeneous isotropic Heisenberg model and the symmetries under particle exchange, we follow the dynamics until very long times. Starting from an initial spin-separated state, we observe superdiffusion, spin-dipolar large amplitude oscillations, and thermalization. We report a universal scaling of the oscillations with particle number $N^{1/4}$. Our Letter puts forward one-dimensional correlated fermions as a different system to observe the emergence of nonequilibrium universal features.

In this work we explore the critical behaviors of fidelity susceptibility and trace distance susceptibility associated with the steady states of dissipative systems at continuous phase transitions. We investigate two typical models: One is the dissipative spin-1/2 $XYZ$ model on a two-dimensional square lattice and the other is a driven-dissipative Kerr oscillator. We find that the susceptibilities of fidelity and trace distance exhibit singular behaviors near the critical points of phase transitions in both models. The critical points in the thermodynamic limit, extracted from the scalings of the critical controlling parameters to the system size or nonlinearity, agree well with the existing results.