By the photoassociation method, the trimer superfluid phase disappears in the one-dimensional state-dependent optical lattice if the ratio of the three-body interaction $W$ to the trimer tunneling $J$ is kept at $W/J=12$ [W. Z. Zhang et al., Phys. Rev. A 90, 033622 (2014)]. To search for a trimer superfluid and trimer supersolid, we load the cold atom into two-dimensional lattices, whose coordinate number $z$ and kinetic energy $-zJ$ are respectively larger and lower than those of a one-dimensional lattice. Herein, we study the Bose-Hubbard model, which has an additional trimer tunneling term, a three-body interaction, and a next-nearest repulsion. The on-site trimer and trimer superfluid exist if the on-site two-body repulsion and three-body repulsion are smaller than some thresholds. With atom-tunneling terms, the phase transitions from trimer superfluid phase to both atom superfluid and atom supersolid phases are first order. With $W/J=12$, in a one-dimensional lattice, the trimer superfluid phase does not exist at all. In contrast, the trimer superfluid phase exists in the lower density regions $0<\rho <2$ on the square lattice if $J$ is not very large. The trimer superfluid phase emerges in a wider range $0<\rho <3$ in the triangular lattice, or in the cubic lattice $\left(z=6\right)$. When the three-body interaction is turned on, a trimer supersolid phase emerges due to the classical degeneracy between the quasitrimer solid and the trimer solid being broken by the quantum fluctuation. The phase transitions from the trimer supersolid phase to the quasitrimer solid are first order and the phase transition from the trimer supersolid phase to trimer solid is continuous. Our results, obtained by mean-field and quantum Monte Carlo methods, will be helpful in realizing the trimer superfluid and supersolid by cold-atom experiments.

We study the transport properties of a Bose-Einstein condensate formed by an ultracold gas of bosonic atoms that is coupled from a magnetic trap into a one-dimensional waveguide. Our theoretical approach to tackling this problem is based on the truncated Wigner method for which we assume the system to consist of two semi-infinite noninteracting leads and a finite interacting scattering region with two constrictions modeling an atomic quantum dot. The transmission is computed in the steady-state regime and we find a good agreement between truncated Wigner and matrix-product state calculations. We also identify clear signatures of inelastic resonant scattering by analyzing the distribution of energy in the transmitted atomic-matter wave beam.

Long-lived light bullets fully localized in both space and time can be generated in novel photonic media such as multicore optical fiber or waveguide arrays. In this paper we present detailed theoretical analysis on the existence and stability of the discrete-continuous light bullets using a very generic model that occurs in a number of applications.

Lossy atomic photonic crystals can be suitably tailored so that the real and imaginary parts of the susceptibility are, respectively, an odd and an even function of position. Such a parity-time $\left(PT\right)$ space antisymmetry in the susceptibility requires neither optical gain nor negative refraction, but is rather attained by a combined control of the spatial modulation of both the atomic density and their dynamic level shift. These passive photonic crystals made of dressed atoms are characterized by a tunable unidirectional reflectionlessness accompanied by an appreciable degree of transmission. Interestingly, such peculiar properties are associated with non-Hermitian degeneracies of the crystal scattering matrix, which can then be directly observed through reflectivity measurements via a straightforward phase modulation of the atomic dynamic level shift and even off resonance.

We investigate the propagation of electron vortex beams in a magnetic field. It is pointed out that when electron vortex beams carrying orbital angular momentum propagate in a magnetic field, the Berry curvature associated with the scalar electron moving in a cyclic path around the vortex line is modified from that in free space. This alters the spin-orbit interaction, which affects the propagation of nonparaxial beams. The electron vortex beams with tilted vortices lead to a spin Hall effect in free space. In the presence of a magnetic field in time-space we have spin filtering such that either positive or negative spin states emerge in spin Hall currents with clustering of spin $\frac{1}{2}$ states.

The distinction between the charged particle and antiparticle differential cross sections of high-energy bremsstrahlung in the electric field of a heavy atom is investigated. The consideration is based on the quasiclassical approximation to the wave functions in the external field. The charge asymmetry (the ratio of the antisymmetric and symmetric parts of the differential cross section) arises due to the account for the first quasiclassical correction to the differential cross section. All evaluations are performed with the exact account of the atomic field. We consider in detail the charge asymmetry for electrons and muons. For electrons, the nuclear size effect is not important while for muons this effect should be taken into account. For the longitudinal polarization of the initial charged particle, the account for the first quasiclassical correction to the differential cross section leads to the asymmetry in the cross section with respect to the replacement $\phi \to -\phi$, where $\phi$ is the azimuth angle between the photon momentum and the momentum of the final charged particle.

We study the proton-hydrogen collision in the energy range from 0 to 5 K where the hyperfine structure of the hydrogen atom becomes important. A proper multichannel treatment of the hyperfine structure is found to be crucial at cold temperatures compared to the elastic approximation traditionally used at higher temperatures. Both elastic and hyperfine-changing inelastic processes are investigated, using both the multichannel quantum-defect theory (MQDT) and the coupled-channel numerical method. Results from the two methods show excellent agreement with MQDT providing an efficient and basically analytic description of the proton-hydrogen interaction throughout this energy range. We also discuss the validity of the elastic approximation and its relation to other methods.

The nonequilibrium dynamics following a quench of strongly repulsive bosonic ensembles in one-dimensional finite lattices is investigated by employing interaction quenches and/or a ramp of the lattice potential. Both sudden and time-dependent quenches are analyzed in detail. For the case of interaction quenches we address the transition from the strong repulsive to the weakly interacting regime, suppressing in this manner the heating of the system. The excitation modes such as the cradle process and the local breathing mode are examined via local density observables. In particular, the cradle mode is inherently related to the initial delocalization and, following a negative interaction quench, can be excited only for incommensurate setups with filling larger than unity. Alternatively, a negative quench of the lattice depth which favors the spatial delocalization is used to access the cradle mode for setups with filling smaller than unity. Our results shed light on possible schemes to control the cradle and the breathing modes. Finally, employing the notion of fidelity we study the dynamical response of the system after a diabatic or adiabatic parameter modulation for short and long evolution times. The evolution of the system is obtained numerically using the ab initio multilayer multiconfiguration time-dependent Hartree method for bosons, which permits us to follow nonequilibrium dynamics including the corresponding investigation of higher-band effects.

Density correlations unambiguously reveal the quantum nature of matter. Here, we study correlations between measurements of density in cold-atom clouds at different times at one position, and also at two separated positions. We take into account the effects of finite-size and -duration measurements made by light beams passing through the atom cloud. We specialize to the case of Bose gases in harmonic traps above critical temperature, for weakly perturbative measurements. For overlapping measurement regions, shot-noise correlations revive after a trap oscillation period. For nonoverlapping regions, bosonic correlations dominate at long times, and propagate at finite speeds. Finally, we give a realistic measurement protocol for performing such experiments.

An implicit formula for the spectrum of the two-photon Rabi model was presented by Travěnec in Phys. Rev. A 85, 043805 (2012), in analogy to the method of Braak [Phys. Rev. Lett. 107, 100401 (2011)]. The spectrum is given by common zeros of four functions $G_c(z,E)$ taken with a fixed value of $z\in \mathbb{C}$. We point out that all the $G_c(z,E)$ functions defined by Travěnec are identically zero, thus the spectrum is not in fact given by their roots.

In the Comment, it is shown that functions used to find the spectrum of two-photon Rabi Hamiltonian vanish. This is true; nevertheless, our method evidently works. The trick is based on a substitution making the coefficients of following truncated Taylor series explicitly dependent on energies, and then the roots of the above-mentioned functions approach the eigenenergies. Thus it is the combination of entire exponential functions and truncated Taylor series that gives nontrivial results.

A scheme for the detection of photons generated by vacuum mixing processes is proposed to observe the quantum electrodynamic photon-photon interaction. The strategy consists in the utilization of a high numerical aperture parabolic mirror that tightly focuses two copropagating laser beams with different frequencies. This produces a very-high-intensity region in the vicinity of the focus, where the photon-photon nonlinear interaction can then induce new electromagnetic radiation by wave-mixing processes. These processes are investigated theoretically. The field at the focus is obtained from the Stratton-Chu vector diffraction theory, which can accommodate any configuration of an incoming laser beam. The number of photons generated is evaluated for an incident radially polarized beam. It is demonstrated that using this field configuration, vacuum mixing processes could be detected with envisaged laser technologies.

The electron-impact collision cross sections are calculated for a ${\text{SiH}}_2$ molecule using the $R$-matrix approach in the low-energy range. The elastic and electron-excited inelastic cross sections are calculated in the correlated and uncorrelated approximations. All electronic states arising due to single-electron transitions from Hartree-Fock configurations up to threshold are considered in the target wave-function expansion. Partial waves up to $l=4$ are used to represent continuum electron orbitals. The Born corrected converged cross sections are obtained for the radical with a nonzero dipole moment by considering the contributions of higher partial waves $\left(l>4\right)$. The effect of a small dipole moment on cross sections is analyzed. Besides determining the cross sections, the role of active space in the target and scattering problem, including the resonances is discussed. This work reports elastic, inelastic, and differential cross sections and few-electron-collision energy-transfer parameters. In particular, we show the viscosity cross sections and rate coefficients for elastic and electron-excited processes.

Narrowband x- and $\gamma$-ray sources based on the inverse Compton scattering of laser pulses suffer from a limitation of the allowed laser intensity due to the onset of nonlinear effects that increase their bandwidth. It has been suggested that laser pulses with a suitable frequency modulation could compensate this ponderomotive broadening and reduce the bandwidth of the spectral lines, which would allow one to operate narrowband Compton sources in the high-intensity regime. In this paper we therefore present the theory of nonlinear Compton scattering in a frequency-modulated intense laser pulse. We systematically derive the optimal frequency modulation of the laser pulse from the scattering matrix element of nonlinear Compton scattering, taking into account the electron spin and recoil. We show that, for some particular scattering angle, an optimized frequency modulation completely cancels the ponderomotive broadening for all harmonics of the backscattered light. We also explore how sensitively this compensation depends on the electron-beam energy spread and emittance, as well as the laser focusing.

The photodetachment cross section of ${\mathrm{H}}^{-}$ was measured using the animated-crossed-beam technique in the 700- to 1064-nm range. The laser beam was repeatedly swept across the ion beam by tilting a fused silica plate in order to eliminate the need for beam profile measurements. After integration of the signal, the cross section was expressed in terms of easily measurable quantities, e.g., the laser power and the ion beam current. The present results are in excellent agreement with previous experiments and compelling theoretical works.

We investigate the superfluid–Mott-insulator transition of a two-dimensional photon gas in a dye-filled optical microcavity and in the presence of a periodic potential. We show that in the random-phase approximation the effects of the dye molecules, which generally lead to dissipation in the photonic system, can be captured by two dimensionless parameters that only depend on dye-specific properties. Within the mean-field approximation, we demonstrate that one of these parameters decreases the size of the Mott lobes in the phase diagram. By considering also Gaussian fluctuations, we show that the coupling with the dye molecules results in a finite lifetime of the quasiparticle and quasihole excitations in the Mott lobes. Moreover, we show that there are number fluctuations in the Mott lobes even at zero temperature and therefore that the true Mott-insulating state never exists if the interactions with the dye are included.

We study the zero-temperature grand potential of a three-dimensional superfluid made of ultracold fermionic alkali-metal atoms in the BCS-BEC crossover. In particular, we analyze the zero-point energy of both fermionic single-particle excitations and bosonic collective excitations. The bosonic elementary excitations, which are crucial to obtain a reliable equation of state in the Bose-Einstein condensate regime, are obtained with a low-momentum expansion up to the forth order of the quadratic (Gaussian) action of the fluctuating pairing field. By performing a cutoff regularization and renormalization of Gaussian fluctuations, we find that the scattering length $a_B$ of composite bosons, bound states of fermionic pairs, is given by $a_B=(2/3)a_F$, where $a_F$ is the scattering length of fermions.

Twisted light is light carrying orbital angular momentum. The profile of such a beam is a ringlike structure with a node at the beam axis, where a phase singularity exists. Due to the strong spatial inhomogeneity the mathematical description of twisted-light–matter interaction is nontrivial, in particular close to the phase singularity, where the commonly used dipole-moment approximation cannot be applied. In this paper we show that, if the handedness of circular polarization and the orbital angular momentum of the twisted-light beam have the same sign, a specific gauge—the twisted-light gauge—can be used where the Hamiltonian takes a form similar to the dipole-moment approximation. However, if the signs differ, no such gauge can be found. Here in general the magnetic parts of the light beam become of significant importance and an interaction Hamiltonian which only accounts for electric fields is inappropriate. We discuss the consequences of these findings for twisted-light excitation of a semiconductor nanostructure, e.g., a quantum dot, placed at the phase singularity.