We have calculated collective-mode spectra for three-dimensional, rotating Bose-Einstein condensates in oblate harmonic traps using the microscopic Bogoliubov–de Gennes field theory. For condensates with $N_v$ vortices, $N_v$ Kelvin-Tkachenko-mode branches are obtained. The features of these modes are compared with those predicted by a classical point-vortex model. We have created movies to visualize the motion of the vortices corresponding to the Kelvin-Tkachenko waves.

We extend classical-field methods [Blakie et al., Adv. Phys. 57, 363 (2008)] to provide a description of atom-molecule systems. We use a model of Bose-Einstein condensation of atoms close to a Feshbach resonance, in which the tunable scattering length of the atoms is described using a system of coupled atom and molecule fields [Holland et al., Phys. Rev. Lett. 86, 1915 (2001)]. We formulate the basic theoretical methods for a coupled atom-molecule system, including the determination of the phenomenological parameters in our system, the Thomas-Fermi description of Bose-Einstein condensate, the Bogoliubov–de Gennes equations, and the Bogoliubov excitation spectrum for a homogenous condensed system. We apply this formalism to the special case of Bragg scattering from a uniform condensate and find that for moderate and large scattering lengths, there is a dramatic difference in the shift of the peak of the Bragg spectra, compared to that based on a structureless atom model. The result is compatible with the experimental results of Papp et al. [Phys. Rev. Lett 101, 135301 (2008)] for Bragg scattering from a nonuniform condensate.

We discuss a different scheme to achieve temporal cloaking in warm atomic vapors. Instead of creating a temporal-spatial window in a patched broadband short optical pulse using static differential dispersion of an optical fiber, we create a temporal-spatial window by directly controlling the propagation velocities of a pair of correlated narrow-band long optical pulses. This method eliminates the phase noise introduced by the broadband short-pulse swapping technique. When the event medium has a fast relaxation rate this leads to a temporal-cloaking scheme similar to that reported in fibers. When the event-medium relaxation cannot be neglected, we discuss a matched-mode scheme that can eliminate the phase change caused by the event field. The advantages of the dynamically and actively controlled atomic system over previously reported work are discussed.

We study quantum discord by using the geometric measure of quantum discord for a class of quantum states with bound entanglement. It is found that there exists a nondynamic sudden change in quantum discord accompanying transition from bound entanglement to free entanglement. The calculations presented here should be of interest to the continuing efforts to understand sudden transition of quantum correlations.

Characteristic radiation is used extensively in most high-accuracy x-ray experiments as a standard for calibration, both in laboratory physics and in astrophysics. $K\alpha$ and $K\beta$ radiations have complex asymmetric structure in their spectral profiles, especially for transition metals. Instrumental broadening in x-ray experiments shifts peak energies by small but significant amounts, especially for critical investigations. The spectral profiles must include an account of instrumental broadening so as to be able to transfer the calibration between experiments. We present a transferable characterization of the vanadium $K\beta$ spectral profile, using high-accuracy laboratory experiments. The peak energy of vanadium $K{\beta }_1$ is then found to be $5426.962\pm 0.015$ eV. This result decreases the uncertainty by a factor of 4.7 compared with Bearden and Burr [Rev. Mod. Phys. 39, 125 (1967)]. Characterization of the profile also permits an accurate and transferable standard and methodology. In the Supplemental Material we present the full profile with uncertainties for use in further analysis using the methodology presented.

We present an experimental study of laser-induced fluorescence spectra of Cs atoms embedded in superfluid and solid ${}^4$He, as well as in dense supercritical fluid He. The studied temperature range is increased with respect to earlier studies by the use of intense laser pulses for the transient local heating of the helium sample. The analysis of the experimental spectra is based on two different approaches: the atomic-bubble model and quasistatic line-broadening theory in the limit of high perturber density. Our results indicate that the temperature dependence of the experimentally observed spectra can be traced back to temperature-dependent correlations in the motion of He atoms in the sample.

A comprehensive set of coplanar symmetric ($e$,2$e$) ionization data are presented for the stable noble gas targets helium, neon, argon, krypton, and xenon. The incident electron energy ranged from 1.2 to 200 eV above the ionization potential of the target atoms, so as to span from near threshold to the high-energy regime. Data are presented with high precision, and cover a wide angular range from forward scattering where the electrons were detected at angles from 30° to the incident electron beam, through to the backscatter region where the deflection angle was up to 130°. The data are normalized to unity at each energy, and are compared to previously published theoretical calculations where available. The data show complex changes in the structure of the measured cross sections, depending upon both the energy and selected target. Similarities and differences in the cross sections were found between the different targets, which provide a challenge to future models of the ionization process.

A nonresonant microwave dressing field at $38.465\mathrm{GHz}$ was used to eliminate the static electric dipole moment difference between the $49s_{1/2}$ and $48s_{1/2}$ Rydberg states of ${}^{87}$Rb in dc fields of $\approx 1\mathrm{V}/\mathrm{cm}$. The reduced susceptibility to electric field fluctuations was measured using two-photon microwave spectroscopy. An anomalous spectral doublet is attributed to polarization ellipticity in the dressing field. The demonstrated ability to inhibit static dipole moment differences, while retaining sensitivity to high frequency fields, is applicable to sensors and/or quantum devices using Rydberg atoms.

We investigate the component separation in one-dimensional two-component fermion clouds in a spin-dependent external potential. The density distributions and the state diagram are studied by means of spin-dependent density-functional theory. The component separation between spin-up and spin-down atoms is induced by the interplay of the spin-dependent harmonic confinement and the strong repulsive interaction between the intercomponents. We find the existence of a threshold repulsive interaction strength above which the component separation evolves. Different state diagrams are mapped out numerically, from which two regions are distinguished, i.e., the phase-mixed region with both spin-up and spin-down mixtures in the center of the trap and the phase-separated region with only spin-up atoms remaining in the center.

We investigate the set of qutrit states in terms of symmetric states of two qubits that violate the minimal contextual inequality, namely the Klyachko-Can-Binicoglu-Shumovsky (KCBS) inequality. The physical system that provides a natural framework for this problem is a biphoton, which consists of two photons in the same spatiotemporal mode and whose effective polarization behaves as a three-level quantum system. The relationship between the KCBS contextual inequality and the Clauser-Horne-Shimony-Holt (CHSH) inequality is investigated. We find that every biphotonic state that is contextual with respect to KCBS is nonlocal as per the CHSH test when the two photons are apart, but the converse is not true.

We suggest an alternative definition of $N$-dimensional coined quantum walk by generalizing a recent proposal [Di Franco et al., Phys. Rev. Lett. 106, 080502 (2011)]. This $N$-dimensional alternate quantum walk, ${\mathrm{AQW}}_{\left(N\right)}$, in contrast with the standard definition of the $N$-dimensional quantum walk, ${\mathrm{QW}}_{\left(N\right)}$, requires only a coin qubit. We discuss the quantum diffusion properties of ${\mathrm{AQW}}_{\left(2\right)}$ and ${\mathrm{AQW}}_{\left(3\right)}$ by analyzing their dispersion relations that reveal, in particular, the existence of diabolical points. This allows us to highlight interesting similarities with other well-known physical phenomena. We also demonstrate that ${\mathrm{AQW}}_{\left(3\right)}$ generates considerable genuine multipartite entanglement. Finally, we discuss the implementability of ${\mathrm{AQW}}_{\left(N\right)}$.

The dynamics of two variants of quantum Fisher information under decoherence is investigated from a geometrical point of view. We first derive the explicit formulas of these two quantities for a single qubit in terms of the Bloch vector. Moreover, we obtain analytical results for them under three different decoherence channels, which are expressed as affine transformation matrices. Using the hierarchy equation method, we numerically study the dynamics of both sets of information in a dissipative model and compare the numerical results with the analytical ones obtained by applying the rotating-wave approximation. We further express the two information quantities in terms of the Bloch vector for a qudit by expanding the density matrix and Hermitian operators in a common set of generators of the Lie algebra $\text{su}\left(d\right)$. By calculating the dynamical quantum Fisher information, we find that the collisional dephasing significantly diminishes the precision of the phase parameter with the Ramsey interferometry.

We analyze fermionic modes as fundamental entities for quantum information processing. To this end we construct a density operator formalism on the underlying Fock space and demonstrate how it can be naturally and unambiguously equipped with a notion of subsystems in the absence of a global tensor product structure. We argue that any apparent similarities between fermionic modes and qubits are superficial and can only be applied in limited situations. In particular, we discuss the ambiguities that arise from different treatments of this subject. Our results are independent of the specific context of the fermionic fields as long as the canonical anticommutation relations are satisfied, e.g., in relativistic quantum fields or fermionic trapped ions.

In this paper we study experimentally the properties of three types of quantum -optical random-number generators and characterize them using the available National Institute for Standards and Technology statistical tests, as well as four alternate tests. The generators are characterized by a trade-off between, on one hand, the rate of generation of random bits and, on the other hand, the degree of randomness of the series which they deliver. We describe various techniques aimed at maximizing this rate without diminishing the quality (degree of randomness) of the series generated by it.

Electron collisions with O${}_2$ at scattering energies below 1 eV are studied in the fixed-nuclei approximation for a range of internuclear separations using the ab initio molecular R-matrix method. The ${}^2{\Pi }_{\mathrm{g}}$ scattering eigenphases and quantum defects are calculated. The parameters of the resonance and the energy of the bound negative ion are then extracted. Different models of the target that employ molecular orbitals calculated for the neutral target are compared with models based on anionic orbitals. A model using a basis of anionic molecular orbitals yields physically correct results in good agreement with experiment. An alternative method of calculation of the R matrix is tested, where instead of performing a single complete diagonalization of the Hamiltonian matrix in the inner region, the system of linear equations is solved individually for every scattering energy. This approach is designed to handle problems where diagonalization of an extremely large Hamiltonian is numerically too demanding.

The electron–polarized-photon coincidence method is used to determine linear and circular polarization correlations in vacuum ultraviolet (VUV) for the differential electron-impact excitation of neon and argon resonance transitions at impact energies of 25 and 30 eV at small scattering angles up to 40°. The circular polarization correlation is found to be positive in the case of Ne at 25 eV and supports the prediction of the present $B$-spline $R$-matrix theory concerning the violation of a long-established propensity rule regarding angular momentum transfer in electron-impact excitation of $S\to P$ transitions. Comparisons with the results from the present relativistic distorted-wave approximation and an earlier semirelativistic distorted-wave Born model are also made. For the case of Ar, at 25 and 30 eV, the circular polarization measurements remain in agreement with theory, but provide limited evidence as to whether or not the circular polarization at small scattering angles is also positive. For the linear polarizations, much better agreement with theory is obtained than in earlier measurements carried out by S. H. Zheng and K. Becker [Z. Phys. D 23, 137 (1992); J. Phys. B 26, 517 (1993)].

The signature of trapped antihydrogen ($\overline{\mathrm{H}}$) atoms is the annihilation signal detected when the magnetic trap that confines the atoms is suddenly switched off. This signal would be difficult to distinguish from the annihilation signal of any trapped $\overline{p}$ that is released when the magnetic trap is switched off. This work deduces the large cyclotron energy ($>$137 eV) required for magnetic trapping of $\overline{p}$, considers the possibility that such $\overline{p}$ are produced, and explores the effectiveness of an electric field applied to clear charged particles from the trapping volume before $\overline{\mathrm{H}}$ detection. No mechanisms are found that can give a $\overline{p}$ such a large cyclotron energy and allow it to mimic an $\overline{\mathrm{H}}$ annihilation. The method used to release $\overline{\mathrm{H}}$ atoms from their magnetic trap without removing the magnetic field gradient that could possibly confine $\overline{p}$ with a high cyclotron energy is also discussed.

We theoretically investigate the localization properties of a spin-orbit-coupled spin-1/2 particle moving in a one-dimensional quasiperiodic potential, which can be experimentally implemented using cold atoms trapped in a quasiperiodic optical lattice potential and external laser fields. We present the phase diagram in the parameter space of the disorder strength and those related to the spin-orbit coupling. The phase diagram is verified via multifractal analysis of the atomic wave functions and the numerical simulation of diffusion dynamics. We found that spin-orbit coupling can lead to spectra mixing (coexistence of extended and localized states) and the appearance of mobility edges.

We find analytic continuous-wave (cw) solutions for spinor Bose-Einstein condensates in a magnetic field that are more general than other published solutions. For particles with spin $F=1$ in a homogeneous one-dimensional trap, there exist cw states in which the chemical potential and wave vectors of the different spin components are different from each other. We include linear and quadratic Zeeman splitting. Linear Zeeman splitting, if the magnetic field is constant and uniform, can be mathematically eliminated by a gauge transformation, but quadratic Zeeman effects modify the cw solutions in a way similar to nonzero differences in the wave numbers between the different spin states. The solutions are stable fixed points within the continuous-wave framework, and the coherent spin mixing frequencies are obtained.

We consider the behavior of an ultracold Fermi gas across a narrow Feshbach resonance, where the occupation of the closed channel may not be negligible. While the corrections to the single-channel formulas associated with the nonzero chemical potential and with particle conservation have been considered in the existing literature, there is a further effect, namely, the “interchannel Pauli exclusion principle,” associated with the fact that a single hyperfine species may be common to the two channels. We focus on this effect and show that, as intuitively expected, the resulting corrections are of the order of $E_F/\eta$, where $E_F$ is the Fermi energy of the gas in the absence of interactions and $\eta$ is the Zeeman energy difference between the two channels. We also consider the related corrections to the fermionic excitation spectrum, and briefly discuss the collective modes of the system.