The electroprotonic ground-state wave function of CH${}_3$OH is calculated beyond the Born-Oppenheimer (BO) approximation using multiconfiguration wave-function theory for a system composed of electrons and protons. A CH${}_3$OH molecule is treated as a quasidiatomic molecule in which orbitals for both electrons and protons are described in a laboratory fixed cylindrical coordinate system with C and O atoms being fixed on the $z$ axis. The probability density of the four protons shows that the C atom is surrounded by three protons and the O atom by one proton, and that the dihedral angle of the O-H bond axis with respect to one of the C-H bond axes becomes 180${}^{\circ }$, exhibiting appropriately the conformational correlation between the two functional groups. The optimized spatial configuration of the protons was found to be in good agreement with that obtained by the standard BO-based electronic structure calculation. The non-BO electroprotonic wave functions introduced here afford the basis for describing ultrafast hydrogen migration in hydrocarbon molecules in an intense laser field.

The geometric spin Hall effect describes spin-dependent transverse shifts in beam position observed in a tilted frame of reference. Here, we study the effects of orbital angular momentum on the shift. The results show that the orbital angular momentum causes a shift in addition to (and independent of) the shift caused by the spin.

In this paper, we show that the average three-tangle of the reduced tripartite density matrix for some quadripartite pure states can be increased by some potential measurements on the fourth subsystem, which means this type of quadripartite entanglement can be localized. In particular, we prove that the maximal increment with all potential measurements taken into account is a quadripartite entanglement monotone, so it quantifies this localized quadripartite entanglement. By analyzing quadripartite pure states based on the previous classification, we find that this quadripartite entanglement monotone not only present is in the standard Greenberger-Horne-Zeilinger state but also is absent in the standard $W$ states. In addition, based on the proposed entanglement measure, we construct a monogamy relation.

We demonstrate rotational excitation of molecular ions that are sympathetically cooled by laser-cooled atomic ions to a temperature as low as approximately 10 mK. The molecular hydrogen ions HD${}^{+}$ and the fundamental rotational transition $(v=0,N=0)\to (v^{\prime }=0,N^{\prime }=1)$ at 1.3 THz, the most fundamental dipole-allowed rotational transition of any molecule, are used as a test case. This transition has not been observed before. Rotational laser cooling was employed in order to increase the signal, and resonance-enhanced multiphoton dissociation was used as detection method. The black-body-radiation-induced rotational excitation is also observed. The extension of the method to other molecular species is briefly discussed.

In an effort to clarify the three-dimensional alignment dynamics of polyatomic molecules, we propose a single measure for the degree of angular confinement of such molecules. The measure proposed for three-dimensional orientation is the angle of the single rotation that takes the molecule to the desired target orientation. Further, taking into account the $D_2$ symmetry of a three-dimensionally aligned distribution, a symmetrized version of the measure is constructed that serves as a direct indicator of the degree of three-dimensional alignment of a distribution. The calculation of the rotational dynamics of iodobenzene under the influence of two cross-polarized laser pulses demonstrates the effectiveness of the proposed metric.

We present state-of-the-art ab initio–type computations of strong-field ionization (SFI) and the single-molecule response contribution to high-order-harmonic generation (HHG) in the polyatomic molecule N${}_2$O${}_4$. The numerical method uses a mixed orbital- and grid-based approach to model the multielectron bound states and single-electron continuum. The effects of ionic-core attraction and Coulomb-mediated interchannel coupling are rigorously included. We show that full-dimensionality time-dependent multielectron computations of SFI and HHG in polyatomic molecules are now feasible. The computational results indicate that (a) SFI yields in N${}_2$O${}_4$ are dominated by a single ionic state (the $A_g$ state), and are strongly modulated by the N-N stretch coordinate; and (b) the HHG radiating dipole as a function of the N${}_2$O${}_4$ N-N stretch is dominated by the same, single state. The molecular-beam coincidence measurements presented here support the computational results. Due to the differences in the estimated vibrational amplitude, however, the computations are not in full agreement with previous HHG data.

We investigate the dynamics of Mott-insulating regions of a trapped bosonic gas as the interaction strength is changed linearly with time. The bosonic gas considered is loaded into an optical lattice and confined to a parabolic trapping potential. Two situations are addressed: the formation of Mott domains in a superfluid gas as the interaction is increased and their melting as the interaction strength is lowered. In the first case, depending on the local filling, Mott-insulating barriers can develop and hinder the density and energy transport throughout the system. In the second case, the density and local energy adjust rapidly, whereas long-range correlations require a longer time to settle. For both cases, we consider the time evolution of various observables: the local density and energy and their respective currents, the local compressibility, the local excess energy, the heat, and single-particle correlators. The evolution of these observables is obtained using the time-dependent density-matrix renormalization-group technique and comparisons with time evolutions done within the Gutzwiller approximation are provided.

We theoretically study counterflow instability and turbulence in a spin-1 spinor Bose-Einstein condensate by the Gross-Pitaevskii equation and the Bogoliubov-de Gennes equation. Our study considers (i) the dynamics induced by the counterflow of two components with different magnetic quantum numbers, which leads to turbulence with spin degrees of freedom, and (ii) the properties of the turbulence. For (i), the behavior of the condensate induced by the counterflow strongly depends on whether the spin-dependent interaction is ferromagnetic or antiferromagnetic, leading to different behaviors for the dispersion relation and the spin density vector, etc. For (ii), we numerically calculate the spectrum of the spin-dependent interaction energy, which also depends on the spin-dependent interaction. The spectrum of the spin-dependent interaction energy in the ferromagnetic case clearly exhibits a $-7/3$ power law, which can be explained by scaling analysis. The spectrum in the antiferromagnetic case seems to show some power law too, but the power exponent cannot be estimated as definitely as the ferromagnetic case.

Collisionless damping of a condensate of cold Fermi atoms, whose scattering is controlled by a Feshbach resonance, is explored throughout the BCS and Bose-Einstein condensate (BEC) regimes when small perturbations on its phase and amplitude modes are turned on to drive the system slightly out of equilibrium. Using a one-loop effective action, we first recreate the known result that for a broad resonance the amplitude of the condensate decays as $t^{-1/2}$ at late times in the BCS regime, whereas it decays as $t^{-3/2}$ in the BEC regime. We then examine the case of an idealized narrow resonance, and find that this collective mode decays as $t^{-3/2}$ throughout both the BCS and BEC regimes. Although this seems to contradict earlier results that damping is identical for both broad and narrow resonances, the breakdown of the narrow resonance limit restores this universal behavior. More measurably, the phase perturbation may give a shift on the saturated value to which the collective amplitude mode decays, which vanishes only in the deep BCS regime when the phase and amplitude modes are decoupled.

We show that, for fermionic atoms in a one-dimensional optical lattice, the fraction of atoms in doubly occupied sites is a highly nonmonotonic function of temperature. We demonstrate that this property persists even in the presence of realistic harmonic confinement, and that it leads to a suppression of entropy at intermediate temperatures that offers a route to adiabatic cooling. Our interpretation of the suppression is that such intermediate temperatures are simultaneously too high for quantum coherence and too low for significant thermal excitation of double occupancy thus offering a clear indicator of the onset of quantum fluctuations.

The steady-state cooling of a nanomechanical resonator interacting with three coupled quantum dots is studied. General conditions for the cooling to the ground state with single- and two-electron dark states are obtained. The results show that in the case of the interaction of the resonator with a single-electron dark state, no cooling of the resonator occurs unless the quantum dots are not identical. The steady-state cooling is possible only if the energy state of the quantum dot coupled to the drain electrode is detuned from the energy states of the dots coupled to the electron source electrode. The detuning has the effect of unequal shifting of the effective dressed states of the system in which the cooling and heating processes occur at different frequencies. For the case of two electrons injected to the quantum-dot system, the creation of a two-particle dark state is established to be possible with spin-antiparallel electrons. The results predict that with the two-particle dark state, an effective cooling can be achieved even with identical quantum dots subject to an asymmetry only in the charging potential energies coupling the injected electrons. It is found that, similar to the case of the single-electron dark state, the asymmetries result in the cooling and heating processes occurring at different frequencies. However, an important difference between the single- and two-particle dark-state cases is that the cooling process occurs at significantly different frequencies. This indicates that the frequency at which the resonator could be cooled to its ground state can be changed by switching from the one-electron to the two-electron Coulomb blockade process.

We consider a medium composed of three-level (cascade scheme) atoms prepared with coherence between the upper and the ground states (a yoked superfluorescence system). We obtain an analytical solution for propagation of seed pulses which are resonant with the upper and lower transitions for arbitrary level populations and pulse shapes. We find that if the initial coherence is large enough and the intermediate level is populated the system can have gain without population inversion. Coherence can also yield gain suppression in the inverted medium. We obtain conditions for the gain in terms of level populations and coherence.

We report the measurement of the linewidth and temporal coherence of a λ = 46.9 nm neon-like argon capillary discharge soft-x-ray laser and its variation with plasma column length. A wave-front-division interferometer was used to resolve the 3$p$${}^1$$S$${}_0$–3$s$${}^1{P}_1$ laser line, resulting in measured relative linewidths of Δλ/λ = (3–4)×10${}^{-5}$. The measurements do not observe saturation rebroadening when this clearly dominantly Doppler-broadened inhomogeneous line is amplified beyond the intensity corresponding to gain saturation. Model simulations indicate this is the result of a comparatively small collisional broadening that sufficiently homogenizes the line profile to practically eliminate inhomogeneous saturation rebroadening. Collisional redistribution is computed to play only a very minor role in homogenizing the line profile.

The dynamics of a state of interest coupled to a non-Markovian environment is studied by concatenating the non-Markovian quantum state diffusion equation and the Feshbach projection-operator partitioning technique. An exact one-dimensional stochastic master equation is derived as a general tool for controlling an arbitrary component of the system. We show that the exact one-dimensional stochastic master equation can be efficiently solved beyond the widely adapted second-order master equations. The generality and applicability of this hybrid approach is justified and exemplified by several coherence control problems concerning quantum state protection against leakage and decoherence.

We have performed high-precision experimental measurements of spin precession using a dressed ${}^3$He atomic beam. Spin dressing uses an oscillating magnetic field that is both detuned to high frequency and orthogonal to a static magnetic field to effectively change the gyromagnetic ratio of a spin. We verify the validity of the spin-dressing Hamiltonian in regions beyond the limiting solution in which the Larmor frequency is much smaller than the frequency of the dressing field. We also evaluate the effect of magnetic field misalignment, i.e. if the oscillating magnetic field is not orthogonal to the static magnetic field. Modulation of the dressing-field parameters is also discussed, with a focus on whether such a modulation can be approximated merely as a time-dependent, dressed gyromagnetic ratio. Furthermore, we discuss implications for a proposed search for the neutron electric dipole moment, which would employ spin dressing to make the effective ${}^3$He and neutron magnetic moments equal.

The previously developed technique for evaluation of charge transfer and electron-excitation processes in low-energy heavy-ion collisions [Tupitsyn et al., Phys. Rev. A 82, 042701 (2010)] is extended to collisions of ions with neutral atoms. The method employs the active-electron approximation, in which only the active-electron participates in the charge transfer and excitation processes while the passive electrons provide the screening density-functional theory (DFT) potential. The time-dependent Dirac wave function of the active electron is represented as a linear combination of atomic-like Dirac-Fock-Sturm orbitals, localized at the ions (atoms). The screening DFT potential is calculated using the overlapping densities of each ion (atom), derived from the atomic orbitals of the passive electrons. The atomic orbitals are generated by solving numerically the one-center Dirac-Fock and Dirac-Fock-Sturm equations by means of a finite-difference approach with the potential taken as the sum of the exact reference ion (atom) Dirac-Fock potential and of the Coulomb potential from the other ion within the monopole approximation. The method developed is used to calculate the $K$-$K$ charge transfer and $K$-vacancy production probabilties for the Ne$\left(1s^{2}2s^{2}2p^6\right)$-F${}^{8+}\left(1s\right)$ collisions at the F${}^{8+}\left(1s\right)$ projectile energies 130 and 230 keV/u. The obtained results are compared with experimental data and other theoretical calculations. The $K$-$K$ charge transfer and $K$-vacancy production probabilities are also calculated for the Xe-Xe${}^{53+}\left(1s\right)$ collision.

We consider multiple collisions of quantum wave packets in one dimension. The system under investigation consists of an impenetrable wall and two hard-core particles with very different masses. The lighter particle bounces between the heavier one and the wall. Both particles are initially represented by narrow Gaussian wave packets. A complete analytical solution of this problem is presented. The idea of the method used is to decompose the two-particle wave function into a continuous superposition of terms (channels), such that the multiple collisions within each channel do not lead to subsequent entanglement between the two particles. For each channel, the time evolution of the two-particle wave function is completely determined by the motion of the corresponding classical pointlike particles; therefore the whole quantum problem is reduced to a classical calculation. The calculation based on the above method reveals the following unexpected result: The entanglement between the two particles first increases with time due to the collisions, but then it begins to decrease, disappearing completely when the light particle becomes too slow to catch up with the heavy one.

The surface quadrupole mode of an harmonically trapped dipolar Fermi gas is studied in both the hydrodynamic and collisionless regimes. The anisotropy and long-range effects of the dipolar force as well as the role of the trapping geometry are explicitly investigated. In the hydrodynamic regime the frequency is always slightly smaller than the $\sqrt{2}{\omega }_{\perp }$ value holding for gases interacting with contact interactions. In the collisionless regime the frequency can be either pretty smaller or larger than the noninteracting value $2{\omega }_{\perp }$, depending on the cloud aspect ratio. Our results suggest that the frequency of the surface quadrupole oscillation can provide a useful test for studying, at very low temperatures, the transition between the normal and the superfluid phase and, in the normal phase at higher temperatures, the crossover between the collisional and collisionless regimes. The consequences of the anisotropy of the dipolar force on the virial theorem are also discussed.

Three-dimensional Weyl fermions are found to emerge from simple-cubic lattices with staggered fluxes. The mechanism is a gapping of the quadratic-band touching by time-reversal-symmetry-breaking hoppings. The system exhibits a rich phase diagram where the number of Weyl fermions and their topological charges are tunable via plaquette fluxes. The Weyl semimetal state is shown to be the intermediate phase between a nontopological semimetal and a quantum anomalous Hall insulator. The transitions between those phases can be understood through the evolution of the Weyl points as Berry-flux insertion processes. As the Weyl points move and split (or merge) through tuning of the plaquette fluxes, the Fermi arcs and surface states undergo significant manipulation. We also propose a possible scheme to realize the model in ultracold fermions in optical lattices with artificial gauge fields.