Energy-loss measurements and theoretical calculations for Be and B ions in Zn are presented. The experimental ion energies range from 40 keV/u to 1 MeV/u, which includes the energy-loss maximum and covers a lack of experimental data for these systems from intermediate to high energies. The measurements were performed using the Rutherford backscattering technique. The ab initio calculations are based on the extended Friedel sum rule–transport cross-section method for the valence electrons and the Shellwise local plasma approximation for the bound electrons. A comparison of these calculations to the present experimental data for Be and B and previous values for H, He, and Li ions on the same target is included. This confirms the applicability of the employed theoretical framework also for ions of intermediate atomic number.

It has long been known that the inner walls of freshly manufactured glass cells filled with a few droplets of alkali metal undergo a “curing” process, where the properties of the cell wall change over a period of days to weeks. We report quantitative studies of “curing” in Pyrex cells filled with rubidium metal. Our experiment shows that at $94°\text{C}$, the surface of Pyrex glass adsorbs about $3\times {10}^{15}$ rubidium atoms per ${\text{cm}}^2$, which is equivalent to 6–7 monolayers of liquid rubidium.

We report on the experimental investigation of the response of a three-dimensional Bose-Einstein condensate (BEC) in the presence of a one-dimensional (1D) optical lattice. By means of Bragg spectroscopy we probe the band structure of the excitation spectrum in the presence of the periodic potential. We selectively induce elementary excitations of the BEC choosing the transferred momentum and we observe different resonances in the energy transfer, corresponding to the transitions to different bands. The frequency, the width, and the strength of these resonances are investigated as functions of the amplitude of the 1D optical lattice.

Ultracold clouds of dimeric molecules can dissociate into quantum mechanically correlated constituent atoms that are either both bosons or both fermions. We theoretically model the dissociation of two-dimensional anisotropic molecular condensates for which this difference manifests as complementary geometric structures of the dissociated atoms. Atomic bosons are preferentially emitted along the long axis of the molecular condensate, while atomic fermions are preferentially emitted along the short axis. This anisotropy potentially simplifies the measurement of correlations between the atoms through relative number squeezing.

The finite-temperature thermodynamics of a unitary Fermi gas is studied in detail. The chemical potential, energy density, and entropy are given analytically with the quasilinear approximation. The ground-state energy agrees with previous theoretical and experimental results. Recently, the generalized exclusion statistics is applied to the discussion of the finite-temperature unitary Fermi-gas thermodynamics. A concrete comparison between the two different approaches is performed. Emphasis is made on the behavior of the entropy per particle. In physics, the slope of entropy gives the information on the effective fermion mass $m^{\ast }/m$ in the low-temperature strongly degenerate region. Compared with $m^{\ast }/m\approx 0.70<1$ given in terms of the generalized exclusion statistics, our quasilinear approximation determines that $m^{\ast }/m\approx 1.11>1$.

We study the multiband superfluid (SF) and the SF to band-insulator transition of strongly interacting fermionic atoms in an optical lattice at a filling of two fermions per well. We present physical arguments to show that a consistent mean-field description of this problem is obtained by retaining only intraband pairing between the fermions. Using this approach we obtain a reasonable account of the experimentally observed critical lattice depth for the SF-BI transition and the modulated components of the condensate density and make predictions for the lattice depth dependence of the quasiparticle gap which can be tested in future experiments. We also highlight some interesting features unique to cold atom superfluids within this intraband pairing approximation; for instance, the pair field is forced to be uniform in space and the Hartree field vanishes identically. These arise as a result of the fact that while the pairing interaction is cut off at the scale of the Debye frequency in conventional superconductors or at the lattice scale in tight-binding model Hamiltonians, such a cutoff is absent for cold Fermi gases.

In this paper we undertake a theoretical study of the quantum properties of a dipole nanolaser proposed by Protsenko et al. [Phys. Rev. A 71, 063812 (2005)]. The dynamics of the system is studied in both density-matrix and quantum Langevin formulations, with attention directed to noise sources. The result of the analysis indicates that in the most directly accessible parameter regime, photons will be emitted in a broad spectral distribution and the time delay between consecutive emissions of single photons exceeds the coherence time. Another parameter regime exists within which the emitted light more closely resembles conventional laser light.

The transverse spatial attributes of an optical beam can be decomposed into the position, momentum, and orbital angular momentum observables. The position and momentum of a beam are directly related to the quadrature amplitudes, while the orbital angular momentum is related to the polarization (spin) variables. In this paper, we study the quantum properties of these spatial variables, using a representation in the Stokes-operator basis. We propose a spatial detection scheme to measure all three spatial variables and, consequently, propose a scheme for the generation of spatial Stokes-operator squeezing and entanglement.

We investigate theoretically the high-order harmonic generation in the argon gas cell driven with a 7-fs 800-nm intense laser pulse, by taking into account the phase-matching effect during the propagation process in the gas cell. We demonstrate a successful selection of single quantum path of the returning electrons and therefore the generation of an isolated xuv attosecond pulse in the plateau region of high-order harmonic spectrum, instead of the emission in the form of pulse trains if without optimizing the phase-matching process.

Practical implementations of quantum computing are always done in the presence of decoherence. Geometric phase is useful in the context of quantum computing as a tool to achieve fault tolerance. Recent experimental progresses on coherent control of single electron have suggested that electron in quantum dot systems is a promising candidate of qubit in future quantum information processing devices. In this Brief Report, by considering a feasible quantum dot model, we calculate the geometric phase of the quantum dot system in nonunitary evolution and investigate the effect of environment parameters on the phase value.

Using a time operator, we define a tunneling time for a particle going through a barrier. This tunneling time is the average of the phase time introduced by other authors. In addition to the delay time caused by the resonances over the barrier, the present tunneling time is also affected by the branch point at the edge of the energy continuum. We find that when the particle energy is near the branch point, the tunneling time becomes strongly dependent on the width of the incoming wave packet, which implies that there is no intrinsic tunneling time. This effect is related to the quantum uncertainty in the particle’s momentum.

Recently a generalized master equation was derived that extends the Lindblad theory to highly non-Markovian quantum processes [H.-P. Breuer, Phys. Rev. A 75, 022103 (2007)]. We perform a stochastic unraveling of this master equation by considering $n$ random state vectors that satisfy the corresponding stochastic differential equation for a piecewise deterministic process. As an application we consider a two-state system randomly coupled to an environment consisting of two energy bands with finite number of levels. Our numerical results are compared to results obtained from the time-convolutionless projection operator method using correlated projection superoperators and the exact solution of the Schrödinger equation for this system.

We present a protocol for error characterization and its experimental implementation with four qubits in liquid state NMR. The method is designed to retrieve information about spatial correlations and scales as $O\left(n^w\right)$, where $w$ is the maximum number of qubits that have non-negligible interaction. We discuss the practical aspects regarding accuracy and implementation.

We introduce symmetric extensions of bipartite quantum states as a tool for analyzing protocols that distill secret key from quantum correlations. Whether the correlations are coming from a prepare-and-measure quantum key distribution scheme or from an entanglement-based scheme, the protocol has to produce effective states without a symmetric extension in order to succeed. By formulating the symmetric extension problem as a semidefinite program, we solve the problem for Bell-diagonal states. Applying this result to the six-state and Bennett-Brassard 1984 schemes, we show that for the entangled states that cannot be distilled by current key distillation procedures, the failure can be understood in terms of a failure to break a symmetric extension.

Simple constructions and protocols are demonstrated to allow the implementation of universal quantum computation on an arbitrarily large quantum system by controlling a fixed number of spins within a noiseless setting. Pulse sequences are derived for deterministic gate operation and system cooling, which only require pulse strengths that are comparable to the intrinsic Hamiltonian of the system. The analyticity of these protocols allows insights into, for example, scalability, which are not present in the numerical results derived from control theoretic solutions.

Vacuum-ultraviolet emissions following the dissociative excitation of ${\text{H}}_2\text{S}$ by electron impact at 100 eV incident energy have been measured. The absolute photoemission cross sections are presented over the wavelength range from 94 to 170 nm and the H, SI, or SII transitions producing the features identified. The measured cross section of the Lyman-$\alpha$ emission at 121.6 nm for an electron-impact energy of 100 eV is $\left(9.79\pm 0.67\right)\times {10}^{-18}{\text{cm}}^2$. Excitation functions of the dominant H and SI emission lines are shown for electron-impact energies from threshold to 300 eV. We study the near-threshold region of the excitation functions and use the measured threshold energies to identify the dominant fragmentation channels.

The time-dependent Dirac equation is solved numerically and compared to the corresponding prediction of the nonrelativistic Schrödinger equation for hydrogenlike systems exposed to intense laser pulses. It is found that for a correct description of effects beyond the dipole approximation, virtual electron-positron pairs can be very important. Relativistic effects in the ionization dynamics of highly charged systems are studied.

Using many-body results available from diagrammatic and ab initio Monte Carlo calculations we analyze the phase diagram $\mu =\left({\mu }_{\uparrow }+{\mu }_{\downarrow }\right)/2$ versus $h=\left({\mu }_{\uparrow }-{\mu }_{\downarrow }\right)/2$ of a unitary Fermi gas at zero temperature with population imbalance and unequal masses. We identify different regions where the gas is superfluid, partially polarized or fully polarized, and determine the corresponding coexistence conditions. The asymmetry in the phase diagram, caused by the mass imbalance, and its effect on the Chandrasekhar-Clogston limit for the critical polarization are explicitly discussed. The equation of state of the superfluid and normal phases is employed, within the local density approximation, to predict phase separated configurations in the presence of harmonic trapping potentials.

We measure experimentally the spatial intensity profiles and resonant frequencies of the transverse modes of nearly hemispherical microcavities for a range of cavity lengths and mirror curvatures. The experimental mode profiles are radially symmetric Gauss-Laguerre modes, but do not posses the radial frequency degeneracies typical of Gauss-Laguerre modes in large-scale optical cavities. We use a paraxial model of cavity propagation to interpret the experimental results. In particular, we show that the lifting of the radial frequency degeneracy may be due to the strength of spherical aberration in wavelength-scale microcavities.

The carrier-envelope phase (CEP)–dependent spectral effect of the reflected few-cycle ultrashort pulse from a dense medium is investigated. It is shown that when adding static electric field, a pronounced CEP dependence of the reflected spectrum can be obtained. Moreover, the period of the CEP-dependent signal becomes $2\pi$ because the inversion symmetry for laser-matter interaction is broken, which allows for extraction of the CEP information in both sign and amplitude.