The slight deformations observed upon transmission of a light pulse through a short length of a silica glass nanofilament offer the possibility of determining the momentum of light inside the filament. Using precise numerical calculations that take into account not only the electromagnetic momentum inside and outside the filament, but also the Lorentz force exerted by a light pulse in its entire path through the nanowaveguide, we conclude that the net effect of a short pulse exiting the nanofilament should be a pull force on the end face of the filament.

$\Lambda$-doublet spectra of light diatomic radicals have high sensitivity to the possible variations in the fine-structure constant $\alpha$ and electron-to-proton mass ratio $\beta$. For molecules OH and CH sensitivity is further enhanced because of the $J$-dependent decoupling of the electron spin from the molecular axis, where $J$ is total angular momentum of the molecule. When $\Lambda$-splitting has different signs in two limiting coupling cases $a$ and $b$, decoupling of the spin leads to the change in sign of the splitting and to the growth of the dimensionless sensitivity coefficients. For example, sensitivity coefficients for the $\Lambda$-doublet lines $J=\frac{9}{2}$ of the ${\Pi }_{1/2}$ state of OH molecule are on the order of ${10}^3$.

We present several protocols for reliable quantum state transfer through an XY spin chain. Among these is a simple two-spin encoding that achieves a remarkably high-fidelity transfer for an arbitrary quantum state. The fidelity of the transfer also decreases slowly with increasing chain length. Furthermore, the reliability can be increased by taking advantage of a local memory and/or confirming transfer using a second spin chain. The simplicity and high fidelity of the encoding makes this a candidate for near-future experiments including a test of the quantum speed limit.

Exploring an analytical expression for the convex roof of the pure state squared concurrence for rank 2 mixed states the entanglement of a system of three particles under decoherence is studied, using the monogamy inequality for mixed states and the residual entanglement obtained from it. The monogamy inequality is investigated both for the concurrence and the negativity in the case of local independent phase damping channel acting on generalized Greenberger-Horne-Zeilinger states of three particles and the local independent amplitude damping channel acting on generalized $\mid \mathrm{W}⟩=\mid 001⟩+\mid 010⟩+\mid 100⟩$ state of three particles. It is shown that the bipartite entanglement between one qubit and the rest has a qualitative similar behavior to the entanglement between individual qubits, and that the residual entanglement in terms of the negativity cannot be a good entanglement measure for mixed states, since it can increase under local decoherence.

A controlled full addition or subtraction can be realized by a unitary transformation on a register of four qubits. The fourth qubit is then used as a control qubit to enforce the addition or the subtraction of two binary digits and a carry or a borrow. The transformation can be decomposed into six elementary gates. The network differs from the adder network of four elementary gates by including two new controlled-NOT gates. The scheme is general and its implementation using vibrational computing has the advantage that the single global transformation that connects the inputs to the outputs can be driven in one step by a single laser shot. This decreases the time of operation and allows for a better use of the optical resources and for an improvement of the fidelity. The laser pulses are optimized by optimal control theory.

Fragmentation of ground-state ortho-positronium in collision with Li ion $\left({\text{Li}}^{+}\right)$ including the electron loss to the continuum is studied. The present model takes account of the two-center effect on the ejected electron which is crucial for a proper description of the projectile ionization involving an ionic target. Both the triply differential cross section and the doubly differential cross section (DDCS) (energy spectra) are investigated at intermediate and high incident energies for the target elastic case. A broad distinct electron-loss peak (ELP) centered around $v_e\approx v_p$ is noted in the electron energy spectrum in contrast to the sharp ELP for a heavy projectile. Two salient features are noted in the present study: (i) the shift of the $e$ DDCS peak (summed over $e^{+}$ angles) toward higher ejection energy with respect to half the residual energy of the system and (ii) comparison of the $e$ and $e^{+}$ energy spectra reflects a strong $e\text{−}{e}^{+}$ asymmetry with respect to the ratio $v_e\left(\text{velocity}\text{of}e\right)/v_p\left(\text{velocity}\text{of}{e}^{+}\right)=1$. Both these features could be attributed to the postcollisional two-center effect on the $e$ due to its parent nucleus $\left(e^{+}\right)$ and the screened target ion. Two different wave functions of the Li ion are chosen in order to test the sensitivity of the present results with respect to the choice of the wave function.

We analyze scattering of a heavy atom off a weakly bound molecule comprising an identical heavy and a light atom in the Born-Oppenheimer approximation. We focus on the situation where the heavy atoms are bosons, which was realized in several experiments. The elastic and inelastic cross sections for the atom-molecular scattering exhibit a series of resonances corresponding to three-body Efimov states. Resonances in elastic collisions are accessible experimentally through thermalization rates and thus constitute an alternative way of observing Efimov states.

Photoassociation of spin-polarized metastable helium to the three lowest rovibrational levels of the $J=1$, $0_u^{+}$ state asymptoting to $2s{{}^{3}S}_1+2p{{}^{3}P}_0$ is studied using a second-order perturbative treatment of the line shifts valid for low laser intensities, and two variants of a nonperturbative close-coupled treatment, one based upon dressed states of the matter plus laser system, and the other on a modified radiative coupling which vanishes asymptotically, thus simulating experimental conditions. These nonperturbative treatments are valid for arbitrary laser intensities and yield the complete photoassociation resonance profile. Both variants give nearly identical results for the line shifts and widths of the resonances and show that their dependence upon laser intensity is very close to linear and quadratic, respectively, for the two lowest levels. The resonance profiles are superimposed upon a significant background loss, a feature for this metastable helium system not present in studies of photoassociation in other systems, which is due to the very shallow nature of the excited state $0_u^{+}$ potential. The results for the line shifts from the close-coupled and perturbative calculations agree very closely at low laser intensities.

We are pursuing an experiment to measure the electric dipole moment of the electron using the molecule PbO. This measurement requires the ability to prepare quantum states with selectable orientation of the molecular axis and, simultaneously, alignment of the electron spin perpendicular to this axis. It also requires efficient detection of the evolution of the spin-alignment direction within such a state. We describe a series of experiments that have achieved these goals, and the features and limitations of the techniques. Our results include observation of and explanation for a small electric-field dependence of the magnetic $g$ factor in the oriented states. We also discuss possible approaches for improved efficiency in this and similar systems.

In this paper we propose a pumping scheme to concentrate nearly all the atoms of an alkali-metal vapor into one of the ground-state Zeeman sublevels. We report theory and experiment for the case of ${}^{87}\text{R}\text{b}$ in a cell with buffer gas but the technique easily applies to other alkali-metal atoms. The pumping scheme consists of a suitable sequence of laser and microwave pulses after which a large fraction of atoms is transferred into the desired level. The efficiency of this technique depends mainly on the laser power and on the relaxation effects taking place inside the cell; in principle, more than 95% of the atoms can be prepared in a well-defined quantum state. Diagnostic of the resulting population distribution is made observing the free-induction decay signal at the output of a microwave cavity. This multistep laser-microwave pumping technique is particularly suited for compact vapor-cell frequency standards working in pulsed regime or in experiments where it is necessary to maintain the cylindrical symmetry of the experimental arrangement.

We study the Bloch dynamics of a quasi-one-dimensional Bose-Einstein condensate of cold atoms in a tilted optical lattice modeled by a Hamiltonian of Bose-Hubbard type. The corresponding mean-field system described by a discrete nonlinear Schrödinger equation can exhibit dynamical (or modulation) instability due to chaotic dynamics and equipartition over the quasimomentum modes. It is shown that these phenomena are related to Bogoliubov’s depletion of the Bose-Einstein condensate and a decoherence of the condensate in the many-particle description. Three types of dynamics are distinguished: (i) decaying oscillations in the region of dynamical instability and (ii) persisting Bloch oscillations or (iii) periodic decay and revivals in the region of stability.

We investigate the dynamics of turbulent flow in a two-dimensional trapped Bose-Einstein condensate by solving the Gross-Pitaevskii equation numerically. The development of the quantum turbulence is activated by the disruption of an initially embedded vortex quadrupole. By calculating the incompressible kinetic-energy spectrum of the superflow, we conclude that this quantum turbulent state is characterized by the Kolmogorov-Saffman scaling law in the wave-number space. Our study predicts the coexistence of two subinertial ranges responsible for the energy cascade and enstrophy cascade in this prototype of two-dimensional quantum turbulence.

We study the quantum phases of mixtures of ultracold bosonic atoms held in an optical lattice that confines motion or hopping to one spatial dimension. The phases are found by using the Tomonaga-Luttinger liquid theory as well as the numerical method of time-evolving block decimation (TEBD). We consider a binary mixture of equal density with repulsive intraspecies interactions and either repulsive or attractive interspecies interaction. For a homogeneous system, we find paired and counterflow superfluid phases at different filling and hopping energies. We also predict parameter regions in which these types of superfluid order coexist with charge-density wave order. We show that the Tomonaga-Luttinger liquid theory and the TEBD qualitatively agree on the location of the phase boundary to superfluidity. We then describe how these phases are modified and can be detected when an additional harmonic trap is present. In particular, we show how experimentally measurable quantities, such as time-of-flight images and the structure factor, can be used to distinguish the quantum phases. Finally, we suggest applying a Feshbach ramp to detect the paired superfluid state and a $\pi /2$ pulse followed by Bragg spectroscopy to detect the counterflow superfluid phase.

For studying the spin evolution of a condensate of spin-1 atoms, the total magnetization $M$ relative to the $Z$ axis of quantization is prepared at a given value previously. During the evolution, $M$ would not be conserved if an inclined magnetic field is applied (i.e., the direction of the field deviates from the $Z$ axis). In this case, the inclined field can cause a strong spin evolution via the linear Zeeman term even the field is very weak (say, close to 0.01 mG). An approach beyond the mean-field theory is proposed to study the evolution of small ${}^{87}\text{R}\text{b}$ condensates under the weak inclined fields. The time-dependent populations of spin components are given in analytical forms. The evolution is found to be highly sensitive to the magnitude and direction of the field.

Tunneling times of electromagnetic planar wave propagating through a barrier made of split-ring resonators and long metallic wires embedded into a dielectric with saturable nonlinearity are analyzed. For such structure, analytical expressions for the tunneling times and relation between the group delay and the dwell time are obtained. The electric-field distribution inside the barrier is numerically evaluated and a detailed study of the influence of nonlinearity on the spectral structures of the tunneling times is performed. It is demonstrated that intensity variation in the incident field may change the wave propagation direction, the sign of the barrier’s refractive index, and group delay.

The recently demonstrated possibility of entangling opposite values of the orbital angular momentum (OAM) of a photon with its spin enables the realization of nontrivial one-photon spin-orbit four-dimensional states for quantum information purposes. Hitherto, however, an optical device that can able to perform arbitrary unitary transformations on such spin-orbit photon states has not been proposed yet. In this work we show how to realize such a “universal unitary gate” device, based only on the existing optical technology, and describe its operation. Besides the quantum information field, the proposed device may find applications wherever an efficient and convenient manipulation of the combined OAM and spin of light is required.

We present a general criterion which allows one to judge if an arbitrary multiparticle entanglement channel can be used to teleport faithfully an unknown quantum state of a given dimension. We also present a general multiparticle teleportation protocol which is applicable for all channel states satisfying this criterion.

In the framework of nuclear magnetic resonance, we consider the general problem of the coherent control of a spin coupled to a bath by means of composite or continuous pulses of duration ${\tau }_{\text{p}}$. We show explicitly that it is possible to design the pulse in order to achieve a decoupling of the spin from the bath up to the third order in ${\tau }_{\text{p}}$. The evolution of the system is separated in the evolution of the spin under the action of the pulse and of the bath times correction terms. We derive the correction terms for a general time dependent axis of rotation and for a general coupling between the spin and the environment. The resulting corrections can be made to vanish by an appropriate design of the pulse. For $\pi$ and $\pi /2$ pulses, we demonstrate explicitly that pulses exist which annihilate the first- and the second-order corrections even if the bath is fully quantum mechanical, i.e., it displays internal dynamics. Such pulses will also be useful for quantum information processing.

We propose a technique for design of quantum Fourier transforms, and ensuing quantum algorithms, in a single interaction step by engineered Hamiltonians of circulant symmetry. The method uses adiabatic evolution and is robust against fluctuations of the interaction parameters as long as the Hamiltonian retains a circulant symmetry.

We present a spectral method of configuration-interaction type for three-dimensional helium which combines the complex rotation method with an appropriate expansion of the atom wave function in a basis of products of Coulomb-Sturmian functions of the electron radial coordinates with independent dilation parameters for the two electrons and bipolar spherical harmonics of the angular coordinates. The matrix elements of the kinetic energy and of the electron-nucleus interaction term are calculated using Gauss-Laguerre integration techniques. A combination of Gauss-Laguerre integration techniques with the generalized Wigner-Eckart theorem and recurrence relations allows an efficient and stable calculation of the matrix elements of the electron-electron interaction. The freedom of the choice of the dilation parameters permits us to access highly excited states with rather small sizes of the basis. Highly doubly excited states up to the tenth ionization threshold of singlet and triplet $S$ states of helium are presented.