After formulating a no-go theorem for perfect quantum-classical hybrid systems, a consistency requirement based on standard statistical considerations is noted. It is shown that such requirement is not fulfilled by the mean-field approach or by the statistical ensemble in configuration space approach. Further unusual features of the latter scheme are pointed out.

The Berry phase acquired by an electromagnetic field undergoing an adiabatic and cyclic evolution in phase space is a purely quantum-mechanical effect of the field. However, this phase is usually accompanied by a dynamical contribution and cannot be manifested in any light-beam interference experiment because it is independent of the field state. We here show that such a phase can be produced using an atom coupled to a quantized field and driven by a slowly changing classical field, and it is manifested in atomic Ramsey interference oscillations. We also show how this effect may be applied to one-step implementation of multiqubit geometric phase gates, which is impossible by previous geometric methods. The effects of dissipation and fluctuations in the parameters of the pump field on the Berry phase and visibility of the Ramsey interference fringes are analyzed.

We illustrate a reverse Von Neumann measurement scheme in which a geometric phase induced on a quantum harmonic oscillator is measured using a microscopic qubit as a probe. We show how such a phase, generated by a cyclic evolution in the phase space of the harmonic oscillator, can be kicked back on the qubit, which plays the role of a quantum interferometer. We also extend our study to finite-temperature dissipative Markovian dynamics and discuss potential implementations in micro- and nanomechanical devices coupled to an effective two-level system.

The application of methods of time-dependent density-functional theory to systems of qubits provided the interesting possibility of simulating an assigned Hamiltonian evolution by means of an auxiliary Hamiltonian having different two-qubit interactions and hence a possibly simpler wave-function evolution. In this paper we extend these methods to some instances of Lindblad evolution of a spin chain.

Exploring the symmetries underlying a previously proposed encryption scheme that relies on single-qubit rotations, we derive an improved upper bound on the maximum information that an eavesdropper might extract from all the available copies of the public key. Subsequently, the robustness of the scheme is investigated in the context of attacks that address each public-key qubit independently. The attacks under consideration make use of projective measurements on single qubits and their efficiency is compared to attacks that address many qubits collectively and require complicated quantum operations.

We identify the key property that the exchange-correlation (XC) kernel of time-dependent density-functional theory must have in order to describe long-range charge-transfer excitations. We show that the discontinuity of the XC potential as a function of particle number induces a space- and frequency-dependent discontinuity of the XC kernel that diverges as $r\to \infty$. In a combined donor-acceptor system, the same discontinuity compensates for the vanishing overlap between the acceptor and donor orbitals, thereby yielding a finite correction to the Kohn-Sham eigenvalue differences. This mechanism is illustrated to first order in the Coulomb interaction.

The interaction of intense laser light with atomic nanoclusters is studied with a rigid sphere model and three-dimensional particle-in-cell simulations for ultrashort laser pulses of pulse durations $\tau$ down to one optical period $T$ and below. In this subcycle regime not all conventional pulse models are applicable and may lead to unphysical absorption of laser energy. For allowed pulse models, we show that for a given laser peak intensity, and cluster, the efficiency of laser absorption increases as $\tau$ shortens and reaches a maximum value in the subcycle regime. For deuterium clusters, where inner ionization quickly saturates, the absorbed energy and outer ionization reaches a peak at $\tau \approx 0.8T$. For argon clusters, however, such a peak disappears, and energy absorption continues even for $\tau <0.8T$ due to additional inner ionization.

In the tunneling regime we present a semiclassical model of above-threshold ionization with inclusion of the Stark shift of the initial state, the Coulomb potential, and a polarization induced dipole potential. The model is used for the investigation of the photoelectron momentum distributions in close to circularly polarized light, and it is validated by comparison with ab initio results and experiments. The momentum distributions are shown to be highly sensitive to the tunneling exit point, the Coulomb force, and the dipole potential from the induced dipole in the atomic core. This multielectron potential affects both the exit point and the dynamics, as illustrated by calculations on Ar and Mg. Analytical estimates for the position of the maximum in the photoelectron distribution are presented, and the model is compared with other semiclassical approaches.

We discuss the strong-field dynamics of HeH${}^{+}$, the simplest stable heteronuclear molecule, focusing on identifying a laser regime for which there is a sufficient dissociation signal for experimental measurement. We numerically solve the time-dependent Schrödinger equation to obtain total dissociation probabilities, kinetic-energy release spectra, and momentum distributions for wavelengths from 800 to 2400 nm. The suitability of this simple system as a prototype for understanding the strong-field nuclear dynamics of heteronuclear dissociation is discussed.

We study the decay of superflow of a one-dimensional (1D) superfluid in the presence of a periodic potential. In 1D, superflow at zero temperature can decay via quantum nucleation of phase slips even when the flow velocity is much smaller than the critical velocity predicted by mean-field theories. Applying the instanton method to the O(2) quantum rotor model, we calculate the nucleation rate of quantum phase slips $\Gamma$. When the flow momentum $p$ is small, we find that the nucleation rate per unit length increases algebraically with $p$ as $\Gamma /L\propto p^{2K-2}$, where $L$ is the system size and $K$ is the Tomonaga-Luttinger parameter. Based on the relation between the nucleation rate and the quantum superfluid-insulator transition, we present a unified explanation on the scaling formulas of the nucleation rate for periodic, disorder, and single-barrier potentials. Using the time-evolving block decimation method, we compute the exact quantum dynamics of the superflow decay in the 1D Bose-Hubbard model at unit filling. From the numerical analyses, we show that the scaling formula is valid for the case of the Bose-Hubbard model, which can quantitatively describe Bose gases in optical lattices.

The dynamical behavior of matter-wave solitons of two-component Bose-Einstein condensates (BEC) in combined linear and nonlinear optical lattices (OLs) is investigated. In particular, the dependence of the frequency of the oscillating dynamics resulting from initially slightly displaced components is investigated both analytically, by means of a variational effective potential approach for the reduced collective coordinate dynamics of the soliton, and numerically, by direct integrations of the mean field equations of the BEC mixture. We show that for small initial displacements binary solitons can be viewed as point masses connected by elastic springs of strengths related to the amplitude of the OL and to the intra- and interspecies interactions. Analytical expressions of symmetric and antisymmetric mode frequencies are derived and occurrence of beatings phenomena in the displaced dynamics is predicted. These expressions are shown to give a very good estimation of the oscillation frequencies for different values of the intraspecies interatomic scattering length, as confirmed by direct numerical integrations of the mean field Gross-Pitaevskii equations (GPE) of the mixture. The possibility to use displaced dynamics for indirect measurements of BEC mixture characteristics such as number of atoms and interatomic interactions is also suggested.

We report experimental demonstration of photonic band-edge lasing in three-dimensionally ordered self-assembled photonic crystals consisting of rhodamine-B dye doped nanospheres of diameter 295 nm. Our all-solid photonic crystal shows a well-resolved photonic stop gap in the visible region. Laser-induced emission experiments reveal more than 51$\%$ inhibition in spontaneous emission intensity of dye molecules within the stop gap and an enhancement near the blue side of the stop gap. With increase in incident pump energy, we achieve photonic-band-edge-induced lasing at room temperature with a lasing threshold of 0.7 mJ. We explain the origin of lasing as due to the enhancement of local density of states near the band edges and the light field distribution within the photonic crystal structure. Our results indicate that such all-solid, dye-activated self-assembled nanostructures are a promising candidate for realizing photonic devices.

We introduce a setting based on the one-dimensional nonlinear Schrödinger equation (NLSE) with the self-focusing cubic term modulated by a singular function of the coordinate ${\left|x\right|}^{-\alpha }$. It may be additionally combined with the uniform self-defocusing (SDF) nonlinear background, and with a similar singular repulsive linear potential. The setting, which can be implemented in optics and Bose-Einstein condensates, aims to extend the general analysis of the existence and stability of solitons in NLSEs. Results for fundamental solitons are obtained analytically and verified numerically. The solitons feature a quasicuspon shape, with the second derivative diverging at the center, and are stable in the entire existence range, which is $0\le \alpha <1$. Dipole (odd) solitons are also found. They are unstable in the infinite domain, but stable in the semi-infinite one. In the presence of the SDF background, there are two subfamilies of fundamental solitons, one stable and one unstable, which exist together above a threshold value of the norm (total power of the soliton). The system, which additionally includes the singular repulsive linear potential, emulates solitons in a uniform space of the fractional dimension, $0<D\le 1$. A two-dimensional extension of the system, based on the quadratic (${\chi }^{\left(2\right)}$) nonlinearity, is also formulated.

One of the major challenges in quantum computation has been to preserve the coherence of a quantum system against dephasing effects of the environment. The information stored in photon polarization, for example, is quickly lost due to such dephasing, and it is crucial to preserve the input states when one tries to transmit quantum information encoded in the photons through a communication channel. We propose a dynamical decoupling sequence, to protect photonic qubits from dephasing, by integrating wave plates into optical fiber at prescribed locations. We simulate random birefringent noise along realistic lengths of optical fiber and study preservation of polarization qubits through such fibers enhanced with Carr-Purcell-Meiboom-Gill (CPMG) dynamical decoupling. This technique can maintain photonic qubit coherence at high fidelity, making a step toward achieving scalable and useful quantum communication with photonic qubits.

Molecules consisting of actinide elements (Th, U) and hydrogen were detected as diatomic trications using low-energy accelerator mass spectrometry (AMS). In many AMS setups the molecules are destroyed by sending a negative ion beam through a foil or a gas medium (the so-called stripper) and by selecting ions in charge state 3+ or higher afterwards. During measurements of samples containing the abundant isotopes ${}^{232}$Th, ${}^{235}$U, and ${}^{238}$U, a stripper thickness dependent counting rate on the next higher mass, i.e., 233, 236, and 239, was observed when selecting the 3+ charge state. The dependence of the signal intensity on the thickness of the stripper gas indicates a partial survival of triply charged molecules of mass 233, 236, and 239, respectively. In a dedicated experiment, the existence of the molecule ${}^{232}$ThH${}^{3+}$ could be verified by directly detecting the breakup fragment ${}^{232}$Th${}^{3+}$. Quantum chemical ab initio calculations at the scalar-relativistic complete active space self-consistent field (CASSCF) and multireference configuration interaction (MRCI) level confirm the existence of both ThH${}^{3+}$ and UH${}^{3+}$ by revealing local minima on the potential curves.

An analysis of superradiant scattering of light by ultracold atoms is presented in which the pump and scattered light consist of hollow counterrotating Laguerre-Gaussian beams possessing orbital angular momentum. It is shown that the interaction between the Laguerre-Gaussian beams and the atoms can give rise to a superradiant instability in which orbital angular momentum is transferred to the atoms and the probe field is amplified. In the case where the atoms constitute a dilute Bose-Einstein condensate (BEC) that is trapped in a one-dimensional ring geometry, the transfer of orbital angular momentum to the BEC during the instability means that the BEC spontaneously develops rotation in the ring.

We report on observations of the thermal motion of a single, Doppler-cooled ion along the axis of a linear radio-frequency quadrupole trap. We show that for a harmonic potential the thermal occupation of energy levels leads to a Gaussian distribution of the ion's axial position. The dependence of the spatial thermal spread on the trap potential is used for precise calibration of our imaging system's point spread function and sub-millikelvin thermometry. We employ this technique to investigate the laser detuning dependence of the Doppler temperature.

We analyze the paraxial beam transformation upon reflection and refraction at a plane boundary. In contrast to the usual approach dealing with the beam angular spectrum, we apply the continuity conditions to explicit spatial representations of the electric and magnetic fields on both sides of the boundary. It is shown that the polarization-dependent distortions of the beam trajectory (in particular, the “longitudinal” Goos-Hänchen shift and the “lateral” Imbert-Fedorov shift of the beam center of gravity) are directly connected to the incident beam longitudinal component and appear due to its transformation at the boundary.

The existence, spatial properties, and stability of localized modes in nonlinear quadratic materials with periodically modulated linear refractive index and quadratic nonlinearity (the latter having the zero mean value along the structure) are investigated. The branches of stationary solutions existing in the semi-infinite and three higher gaps are computed. It is shown that modes may possess different symmetries of the fundamental field (i.e., profiles described either by even or odd functions of the transverse coordinate), while requiring the second harmonic to be symmetric. We found that only small-amplitude gap solitons can be stable. The respective modes can bifurcate only from an edge of a total gap when it coincides with the band edge of the linear spectrum of the fundamental field. Moreover, in this case stable modes can be excited with their centers belonging to a slab with either higher or lower refractive index. This simultaneous existence of different stable localized modes can be viewed as a bistability of gap solitons. Examples of the dynamics and excitations of gap solitons are also given.