We propose a method to generate arbitrary symmetric states of $N$ qubits, which can be easily associated with their entanglement classes. It is particularly suited to quantum optics systems like trapped ions or superconducting circuits. We encode each qubit in two metastable levels of the system and use a bosonic quantum bus for creating the states. The method is deterministic and relies on a sequence of selective unitary gates upon the qubits within the system coherence time.

Based on the theoretical analysis of the radiative recombination of heavy hydrogen-like ions with unpolarized electrons, a scheme is proposed for observing atomic parity nonconservation (PNC). The scheme employs the sensitivity of the polarization properties of recombination photons on the PNC-induced mixing of opposite-parity ionic levels. For the electron capture into the $1s2p{}^3{P}_0$ state of helium-like ions, in particular, the PNC leads to a rotation of the photon linear polarization on the angle, directly proportional to the $1s2p{}^3{P}_0$–$1s2s{}^1{S}_0$ mixing parameter. Owing to the recent advances in the development of x-ray polarimeters, the observation of such a rotation angle and, hence, the corresponding parity mixing is likely to become feasible in the future.

Motivated by recent observations [Soltan-Panahi et al., Nat. Phys. 8, 71 (2012)], we study the stability of a Bose-Einstein condensate within a spin-dependent honeycomb lattice towards forming a “twisted superfluid” state. Our exhaustive numerical search fails to find this phase, pointing to possible non-mean-field physics.

Molecular nitrogen at 0.8 atm and 300 and 500 K and methane at 0.8 atm and 300 K were subjected to optical lattices formed by narrow-band 532-nm laser pulses with intensities on the optical axis near, but below, the gas ionization limit. A third pulse was introduced to experimentally probe the response, as a function of the lattice velocity, of the gas to the deep monochromatic potential wells formed by the lasers. Coherent Rayleigh-Brillouin scattering (CRBS) line shapes were recorded and compared to numerically predicted magnitudes of the density perturbations induced in the gas. Both experimental results and those from direct simulation Monte Carlo simulations show a deviation from previously published low-intensity CRBS line-shape models. The deviation indicates a trend, as a function of lattice velocity, similar to that relating to previously published energy and momentum transfer calculations for high-intensity lattices. Furthermore, the deviation indicates a maximum intensity at which current CRBS theory is valid.

We introduce the concept of parity symmetry in restricted spatial domains—local parity—and explore its impact on the stationary transport properties of generic, one-dimensional aperiodic potentials of compact support. It is shown that, in each domain of local parity symmetry of the potential, there exists an invariant quantity in the form of a nonlocal current, in addition to the globally invariant probability current. For symmetrically incoming states, both invariant currents vanish if weak commutation of the total local parity operator with the Hamiltonian is established, leading to local parity eigenstates. For asymmetrically incoming states which resonate within locally symmetric potential units, the complete local parity symmetry of the probability density is shown to be necessary and sufficient for the occurrence of perfect transmission. We connect the presence of local parity symmetries on different spatial scales to the occurrence of multiple perfectly transmitting resonances, and we propose a construction scheme for the design of resonant transparent aperiodic potentials. Our findings are illustrated through application to the analytically tractable case of piecewise constant potentials.

We evaluate the polarizabilities of the $5p_{1/2}$, $6s$, $6p_{1/2}$, and $6p_{3/2}$ states of In using two high-precision relativistic methods: the linearized coupled-cluster approach, where single, double, and partial triple excitations of the Dirac-Fock wave function are included to all orders of perturbation theory, and an approach that combines the configuration interaction and the coupled-cluster method. An extensive comparison of the accuracy of these methods is carried out. The uncertainties of all recommended values are evaluated. Our result for the $6s$-$5p_{1/2}$ Stark shift is in excellent agreement with a recent measurement [Ranjit et al., Phys. Rev. A 87, 032506 (2013)]. Combining our calculation with this precision measurement allows us to infer the values of the $6p_{1/2}$ and $6p_{3/2}$ lifetimes in In with 0.8$\%$ accuracy. Our predictions for the $6p_{3/2}$ scalar and tensor polarizabilities may be combined with the future measurement of the $6s$-$6p_{3/2}$ Stark shift to accurately determine the $5d_j$-$6p_{j^{\prime }}$ matrix elements.

In a previous work, Pohl et al. [Phys. Rev. Lett. 84, 5090 (2000)] have proposed a simple scheme for the evaluation of photoelectron spectra of clusters subject to a laser field by collecting one-particle wave functions at a given measuring point close to absorbing boundaries. The scheme gives reliable results for low and moderate laser fields, but it shows failures for strong laser fields. The formulation relies on the assumption of free-electron propagation close to the boundaries. The laser field, however, can still be active when the first bunches of outgoing electrons reach the measuring point, and therefore the free-particle scenario may not hold anymore in case of high laser intensities. In this paper, hence, we generalize the method by using a model of “free” particles in the presence of an electromagnetic dipole field. Numerical tests show that this generalized scheme reduces to that of Pohl et al. for low and moderate laser intensities, whereas it considerably improves the results of the latter for high intensities, thus extending the applicability of the method.

We apply the correlation-function quantum Monte Carlo (CFQMC) method to the calculation of the energies of ground and excited states for helium in neutron-star magnetic fields. The method has been successfully applied by Jones, Ortiz, and Ceperley to the calculation of helium in white dwarf magnetic fields [Phys. Rev. E 55, 6202 (1997)]. We extend the accessible range of magnetic field strengths by introducing a fixed-phase variant of the CFQMC method. We find that with growing magnetic field strength the variances increase significantly and put a limit to the applicability of the method for atoms in strong magnetic fields. The behavior of the variances is traced back to the logarithmic divergence of the energy of the bosonic ground state with increasing magnetic field strength. We use basis sets, which account for the growing dominance of the cylindrical symmetry as the magnetic field is increased and incorporate them into the CFQMC algorithm. These basis sets are taken from Hartree-Fock calculations, performed using a $B$-Spline and Landau expansion beyond the adiabatic approximation.

We study the behavior of the bound-state energy of a system consisting of two identical heavy fermions of mass $M$ and a light particle of mass $m$. The heavy fermions interact with the light particle through a short-range two-body potential with positive $s$-wave scattering length $a_s$. We impose a short-range boundary condition on the logarithmic derivative of the hyperradial wave function and show that, in the regime where Efimov states are absent, a nonuniversal three-body state cuts through the universal three-body states previously described by Kartavtsev and Malykh [O. I. Kartavtsev and A. V. Malykh, J. Phys. B 40, 1429 (2007)]. The presence of the nonuniversal state alters the behavior of the universal states in certain regions of the parameter space. We show that the existence of the nonuniversal state is predicted accurately by a simple quantum defect theory model that utilizes hyperspherical coordinates. An empirical two-state model is employed to quantify the coupling of the nonuniversal state to the universal states.

We study two-photon excitation of Rydberg states of atoms under stimulated adiabatic passage with delayed laser pulses. We find that the combination of strong interaction between the atoms in Rydberg state and the spontaneous decay of the intermediate exited atomic state leads to the Rydberg excitation of precisely one atom within the atomic ensemble. The quantum Zeno effect offers a lucid interpretation of this result: the Rydberg blocked atoms repetitively scattering photons effectively monitor a randomly excited atom, which therefore remains in the Rydberg state. This system can be used for deterministic creation and, possibly, extraction of Rydberg atoms or ions one at a time. The sympathetic monitoring via decay of ancilla particles may find wider applications for state preparation and probing of interactions in dissipative many-body systems.

$S$-matrix theory of electron-atom scattering assisted by a few-cycle laser pulse is introduced. The result obtained in the first Born approximation corresponds to the direct or single scattering, while the result in the second Born approximation corresponds to the rescattering or double scattering contribution to the laser-assisted scattering process. The rescattered electrons may acquire high energies while moving in the laser pulse. The dependence of the energy spectrum on the value of the carrier-envelope phase and the duration of the laser pulse is investigated. The abrupt cutoffs of the plateau structures in the energy spectra of the process are explained by the classical analysis. It is shown that the height of both the single and double scattering plateaus can be increased by orders of magnitude by choosing the heavier atomic targets.

We show how the configuration-space form of the Bogoliubov ground-state wave function of a bosonic condensate with a single vortex in a harmonic trap can be described in terms of bosonic Jastrow correlations. We then generalize this result to study the effects of such correlations on a mean-field vortex lattice state and show that the included correlations lower the energy below that of the mean-field state. Although the reduction is relatively small, it is a precursor of the more general expected effect of correlations in describing the melting of the vortex lattice at a high angular momentum per particle.

We prove that the two-fluid Landau hydrodynamic equations, when applied to a gas interacting with infinite scattering length (unitary gas) in the presence of harmonic trapping, admit exact scaling solutions of mixed compressional and surface nature. These solutions are characterized by a linear dependence of the velocity field on the spatial coordinates and a temperature-independent frequency which is calculated in terms of the parameters of the trap. Our results are derived in the regime of small amplitude oscillations and hold both below and above the superfluid phase transition. They apply to isotropic as well as to deformed configurations, thereby providing a generalization of Castin's theorem [Castin, C. R. Phys. 5, 407 (2004)] holding for isotropic trapping. Our predictions agree with the experimental findings in resonantly interacting atomic Fermi gases. The breathing scaling solution, in the presence of isotropic trapping, is also used to prove the vanishing of two bulk viscosity coefficients in the superfluid phase.

We present a canonical quantization of macroscopic electrodynamics. The results apply to inhomogeneous media with a broad class of linear magnetoelectric responses, which are consistent with the Kramers-Kronig and Onsager relations. Through its ability to accommodate strong dispersion and loss, our theory provides a rigorous foundation for the study of quantum optical processes in structures incorporating metamaterials, provided these may be modeled as magnetoelectric media. Previous canonical treatments of dielectric and magnetodielectric media have expressed the electromagnetic field operators in either a Green's function or mode expansion representation. Here we present our results in the mode expansion picture with a view to applications in guided wave and cavity quantum optics.

In this Brief Report, we present a scheme to control the (2+1) resonance-enhanced multiphoton-ionization (REMPI) photoelectron spectrum in cesium (Cs) atom by shaping the femtosecond laser pulse with a rectangular amplitude modulation. We show that the amplitude-shaped laser pulse can induce a hole in the (2+1) REMPI photoelectron spectrum, and the position and width of the hole depend on the amplitude step position and amplitude modulation width. We also show that a high-resolution REMPI photoelectron spectrum and the fine energy-level structure of the excited states can be obtained by observing the holes in the (2+1) REMPI photoelectron spectrum. We believe that these theoretical results can provide a feasible method to study the excited-state or Rydberg-state structure and the laser-induced photoionization dynamics.

We show that the variance is its own concave roof. For rank-2 density matrices and operators with zero diagonal elements in the eigenbasis of the density matrix, we prove analytically that the quantum Fisher information is four times the convex roof of the variance. Strong numerical evidence suggests that this statement is true even for operators with nonzero diagonal elements or density matrices with a rank larger than $2.$ We also find that within the different types of generalized quantum Fisher information considered in Petz [J. Phys. A 35, 929 (2002)] and Gibilisco, Hiai, and Petz [IEEE Trans. Inf. Theory 55, 439 (2009)], after appropriate normalization, the quantum Fisher information is the largest. Hence, we conjecture that the quantum Fisher information is four times the convex roof of the variance even for the general case.

We perform atomic-structure calculations for the neutral Ne, Mg, and Ar atoms on the basis of the recently proposed correction method (scaling method) for the pair-density (PD) -functional theory [Phys. Rev. A 84, 044502 (2011)]. The formal features of the scaling method are that the search region of PDs is substantially extended and that the resultant variationally best PD, which can be obtained without the heavy calculation tasks, satisfies the virial theorem rigorously. To enjoy the benefit of these features, we also develop the approximate form of the kinetic energy functional. It is shown by the atomic-structure calculations that the scaling method can improve well not only various energy functionals but also the spatial profiles of the electron density and exchange-correlation hole. Especially it is found that the scaling method makes preferential modifications to the energetically effective regions of the electron density and exchange-correlation hole. These results suggest that the scaling method efficiently puts the PD close to the correct ground-state PD.