We propose a rapid ground-state optomechanical cooling scheme in a hybrid system, where a two-level quantum dot (QD) is placed in a single-mode cavity and a nanomechanical resonator (NMR) is also coupled to the cavity via radiation pressure. The cavity is driven by a weak laser field while the QD is driven by another weak laser field. Due to the quantum destructive interference arisen from different transition channels induced by simultaneously driving the QD-cavity system in terms of the two different lasers, two-photon absorption for the cavity field can be effectively eliminated by performing an optimal quantum interference condition. Furthermore, it is demonstrated that the QD-cavity system can be unbalancedly prepared in two single-polariton states with different eigenenergies. If the frequency of the NMR is tuned to be resonant with transition between two single-polariton states, it is found that a fast ground-state cooling for the NMR can also be achieved, even when the QD-cavity system is originally in the moderate-coupling regime. Thus the present ground-state cooling scheme for the NMR may be realized with currently available experimental technology.

We consider scattering of low-amplitude dispersive waves at an intense optical soliton which constitutes a nonlinear perturbation of the refractive index. Specifically, we consider a single-mode optical fiber and a group velocity matched pair: an optical soliton and a nearly perfectly reflected dispersive wave, a fiber-optical analog of the event horizon. By combining (i) an adiabatic approach that is used in soliton perturbation theory and (ii) scattering theory from quantum mechanics, we give a quantitative account of the evolution of all soliton parameters. In particular, we quantify the increase in the soliton peak power that may result in the spontaneous appearance of an extremely large, so-called champion soliton. The presented adiabatic theory agrees well with the numerical solutions of the pulse propagation equation. Moreover, we predict the full frequency band of the scattered dispersive waves and explain an emerging caustic structure in the space-time domain.

There exists an analogy between Maxwell equations in a rotating frame and the Schrödinger equation for a charged particle in the presence of a magnetic field. We exploit this analogy to point out that electromagnetic phenomena in the rotating frame, under appropriate conditions, can exhibit periodicity with respect to the angular velocity of rotation. In particular, in disordered ring cavities one finds the optical analog of the Al'tshuler-Aronov-Spivak effect well known in mesoscopic physics of disordered metals.

We study multipartite Bell nonlocality in a framework native of multipartite Einstein-Podolsky-Rosen (EPR) steering scenarios with a single trusted measurement device. We derive a closed-form necessary and sufficient criterion for systems composed of a qubit and $N-1$ untrusted black-box measurement devices to violate, under general dichotomic measurements on the qubit, a generic Bell inequality from a broad family of linear inequalities with arbitrarily many outputs for the $N-1$ untrusted devices and inputs for all $N$ parties. The optimal quantum measurements for maximal violation are also obtained. For two users and two inputs and two outputs per user, our criterion becomes necessary and sufficient for Bell nonlocality. Furthermore, in that setting, its form generalizes recently obtained steering inequalities, which allows us to provide useful feedback from nonlocality to the detection of steering. Our findings constitute a practical tool for the study of the interplay between EPR steering and Bell nonlocality, with potential applications in multipartite information processing.

The problem of longitudinal oscillations of an electric field and a charge polarization density in a quantum electrodynamics (QED) vacuum is considered. Within the framework of semiclassical analysis, we calculate time-periodic solutions of bosonized $\left(1+1\right)$-dimensional QED (massive Schwinger model). Applying the Bohr-Sommerfeld quantization condition, we determine the mass spectrum of charge-zero bound states (plasmons) which correspond in quantum theory to the found classical solutions. We show that the existence of such plasmons does not contradict any fundamental physical laws and study qualitatively their excitation in a $\left(3+1\right)$-dimensional real world.

We consider a measurement of the position of a spot painted on the surface of a trapped nano-optomechanical sphere. The measurement extracts information about the position of the spot and in doing so measures a combination of the orientation and position of the sphere. The quantum backaction of the measurement entangles and correlates these two degrees of freedom. Such a measurement is not available for atoms or ions and provides a mechanism to probe the quantum mechanical properties of trapped optomechanical spheres. In performing simulations of this measurement process we also test a numerical method introduced recently by Rouchon and collaborators [H. Amini, M. Mirrahimi, and P. Rouchon, in Proceedings of the 50th IEEE Conference on Decision and Control (CDC, 2011), pp. 6242–6247; P. Rouchon and J. F. Ralph, Phys. Rev. A 91, 012118 (2015)] for solving stochastic master equations. This method guarantees the positivity of the density matrix when the Lindblad operators for all simultaneous continuous measurements are mutually commuting. We show that it is both simpler and far more efficient than previous methods.

Transitions among the first three low-lying states in the highly charged $\mathrm{W}^{13+}, \mathrm{Ir}^{16+}$, and $\mathrm{Pt}^{17+}$ ions are found to be strongly forbidden with wavelengths in the optical regime. By determining their energy levels, lifetimes, and other spectroscopic properties that are decisive quantities for estimating dominant systematics due to stray electromagnetic interactions in an experiment, we demonstrate that it can be possible to measure frequencies of the lowest forbidden transitions below a ${10}^{-19}$ precision level in the above ions, and hence, they seem to be suitable for frequency standards. We employ a sophisticated relativistic coupled cluster method to carry out calculations of these properties of the above states involving $4f$- and $5s$-core orbitals. We also found, by estimating their relativistic sensitivity coefficients, that these clock transitions can be highly sensitive to the tiny drift in the fine-structure constant ${\alpha }_e$. Consequently, a clock based on one of these ions, particularly $\mathrm{Pt}^{17+}$, could be used for corroborating the hypothesis of temporal and spatial variation in ${\alpha }_e$.

The low-energy electron collisions with cyanamide molecule are investigated by using the UK molecular $R$-matrix codes for electron energies ranging from 0.01 eV to 10 eV. Three models including static-exchange, static-exchange plus polarization, and close-coupling (CC) approximations are employed to reveal the dynamic interaction. Elastic (integrated and differential), momentum-transfer, and excitation cross sections from the ground state to the three low-lying electron excited states have been presented. Two shape resonances, two core-excited resonances, and two Feshbach resonances are detected in the CC approximation. The role of active space in the target and scattering problem including the resonances is discussed. The precise resonance parameters are found to be sensitive to the treatment of polarization effects employed. These resonances may be responsible for the fragments observed in a recent experiment of the dissociative electron attachments to cyanamide. Since the cyanamide molecule has a large permanent dipole moment, a Born closure procedure is used to account for the contribution of partial waves higher than $l=4$ to obtain converged cross sections.

The transition from guiding to scattering in the transmission of $70-\mathrm{keV}\mathrm{N}{\mathrm{e}}^{7+}$ through mica nanocapillaries of rhombic cross section is studied. Transmitted ions and neutrals are separated and their angular distributions are measured for various tilt angles of the capillaries with respect to the beam direction. The ions and neutrals have different angular profiles and different transmission dependences on tilt angle. The profiles of the transmitted ions are of rectangular shape while bananalike shapes appear for the neutrals. The time evolution measurements during charging up show a shift of the center of the ion angular distribution while that of the neutrals remains fixed. Trajectory simulations are performed by taking the image force and the Coulomb repulsive force from the deposited charge, as well as scattering from capillary walls into account. These show good agreement with the data and how the deposited or image charge deflects and shapes the ionic portion of the beam differently from the neutral part. The experimental separation of the ions from neutrals and their very different behaviors together with simulations gives us further insight into the mechanisms of guiding and scattering in transmission through nanocapillaries.

The decay of copper clusters ${\mathrm{Cu}}_n^{-}$ with size $n=4-7$, produced in a metal ion sputter source, was studied in an electrostatic ion-beam trap. The neutral products after electron emission and fragmentation were monitored for ion storage times of up to a second. The observations indicated the presence of radiative cooling. The energy distributions of the remaining clusters were probed by laser irradiation up to several further seconds of storage time. This defined excitation lead to photoinduced decay signals which, again, showed signs of radiative cooling for ${\mathrm{Cu}}_{6,7}^{-}$, not, however, for ${\mathrm{Cu}}_{4,5}^{-}$.

We propose a numerical method using the discrete variable representation (DVR) for constructing real-valued Wannier functions localized in a unit cell for both symmetric and asymmetric periodic potentials. We apply these results to finding Wannier functions for ultracold atoms trapped in laser-generated optical lattices. Following S. Kivelson [Phys. Rev. B 26, 4269 (1982)], for a symmetric lattice with inversion symmetry, we construct Wannier functions as eigenstates of the position operators $\widehat{x}, \widehat{y}$, and $\widehat{z}$ restricted to single-particle Bloch functions belonging to one or more bands. To ensure that the Wannier functions are real-valued, we numerically obtain the band structure and real-valued eigenstates using a uniform Fourier grid DVR. We then show, by a comparison of tunneling energies, that the Wannier functions are accurate for both inversion-symmetric and asymmetric potentials to better than 10 significant digits when using double-precision arithmetic. The calculations are performed for an optical lattice with double-wells per unit cell with tunable asymmetry along the $x$ axis and a single sinusoidal potential along the perpendicular directions. Localized functions at the two potential minima within each unit cell are similarly constructed, but using a superposition of single-particle solutions from the two lowest bands. We finally use these localized basis functions to determine the two-body interaction energies in the Bose-Hubbard model and show the dependence of these energies on lattice asymmetry.

Ultracold bosonic atoms in optical lattices self-organize into a variety of structural and quantum phases when placed into a single-mode cavity and pumped by a laser. Cavity optomechanical effects induce an atom density modulation at the cavity-mode wavelength that competes with the optical lattice arrangement. Simultaneously short-range interactions via particle hopping promote superfluid order such that a variety of structural and quantum coherent phases can occur. We analyze the emerging phase diagram in two dimensions by means of an extended Bose-Hubbard model using a local mean-field approach combined with a superfluid cluster analysis. For commensurate ratios of the cavity and external lattice wavelengths, the Mott insulator-superfluid transition is modified by the appearance of charge density wave and supersolid phases, at which the atomic density supports the buildup of a cavity field. For incommensurate ratios, the optomechanical forces induce the formation of Bose-glass and superglass phases, namely, nonsuperfluid and superfluid phases, respectively, displaying quasiperiodic density modulations, which in addition can exhibit structural and superfluid stripe formation. The onset of such structures is constrained by the on-site interaction and is favorable at fractional densities. Experimental observables are identified and discussed.

We explore the recently discovered solution of the driven Tavis-Cummings model (DTCM). It describes interaction of an arbitrary number of two-level systems with a bosonic mode that has linearly time-dependent frequency. We derive compact and tractable expressions for transition probabilities in terms of the well-known special functions. In this form, our formulas are suitable for fast numerical calculations and analytical approximations. As an application, we obtain the semiclassical limit of the exact solution and compare it to prior approximations. We also reveal connection between DTCM and $q$-deformed binomial statistics.

We analyze reactive collisions of a single ${\mathrm{Ba}}^{+}$ ion in contact with an ultracold gas of Rb atoms at low three-body collision energies of 2.2(9) $\mathrm{mK}\times k_{\mathrm{B}}$. Mapping out the ${\mathrm{Ba}}^{+}$ loss rate dependence on the Rb atom density we can discern two-body reactive collisions from three-body ones and determine both rate coefficients, which are $k_2=3.1\left(6\right)\left(6\right)\times {10}^{-13}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ and $k_3=1.04\left(4\right)\left(45\right)\times {10}^{-24}{\mathrm{cm}}^6{\mathrm{s}}^{-1}$, respectively (statistical and systematic errors in parentheses). Thus, the measured ternary recombination dominates over binary reactions even at moderate atom densities of $n\approx {10}^{12}{\mathrm{cm}}^{-3}$. The results for ${\mathrm{Ba}}^{+}$ and Rb are representative for a wide range of cold ion-atom systems and can serve as guidance for the future development of the field of hybrid atom-ion research.

During the last several decades the so-called Keldysh-Faisal-Reiss or strong-field approximation (SFA) has been highly useful for the analysis of atomic and molecular processes in intense laser fields. However, it is well known that SFA does not account for the final-state Coulomb interaction which is, however, unavoidable for the ubiquitous ionization process. In this Rapid Communication we solve this long-standing problem and give a complete strong-field $S$-matrix expansion that accounts for the final-state Coulomb interaction in all orders, explicitly.

In this work we develop two methods to construct Bell inequalities for multipartite systems. By considering non-Hermitian operators we study Bell inequalities for the cases of three settings, three outcomes, and three to six parties. The maximal value achieved in the framework of quantum theory is computed for subsystems with three levels each. The other technique, based on a mapping from pure entangled states to Bell operators, allows us to construct further multipartite Bell inequalities. As a consequence, we reproduce some known results in a different way and find some multipartite Bell inequalities for systems having three settings and three outcomes per party.

We simulate the process of continuous homodyne detection of the radiative emission from a quantum system, and we investigate how a Bayesian analysis can be employed to determine unknown parameters that govern the system evolution. Measurement backaction quenches the system dynamics at all times and we show that the ensuing transient evolution is more sensitive to system parameters than the steady state of the system. The parameter sensitivity can be quantified by the Fisher information, and we investigate numerically and analytically how the temporal noise correlations in the measurement signal contribute to the ultimate sensitivity limit of homodyne detection.

The exact exponential Foldy-Wouthuysen transformation operator applicable for a particle with an arbitrary spin is derived. It can be successfully utilized for verifying any Foldy-Wouthuysen transformation method based on the exponential operator. When a verified method is relativistic, the relativistic exponential operator should be expanded in the semirelativistic power series. The obtained exponential operator can be also used for a derivation of the Foldy-Wouthuysen Hamiltonian and its comparison with Hamiltonians found by other methods. This procedure makes it possible to check the validity of any other method of the Foldy-Wouthuysen transformation.

We conclusively show that the entanglement- and the mutual-information-based measures of quantum non-Markovianity are inequivalent. To this aim, we first analytically solve the optimization problem in the definition of the entanglement-based measure for a two-level system. We demonstrate that the optimal initial bipartite state of the open system and the ancillary is always given by one of the Bell states for any one-qubit dynamics. On top of this result, we present an explicit example dynamics where memory effects emerge according to the mutual-information-based measure, even though the time evolution remains memoryless with respect to the entanglement-based measure. Finally, we explain this disagreement between the two measures in terms of the information dynamics of the open system, exploring the accessible and inaccessible parts of information.