We study experimentally the equilibrium phase diagram of a spin-1 Bose-Einstein condensate with antiferromagnetic interactions, in a regime where spin and spatial degrees of freedom are decoupled. For a given total magnetization $m_z$, we observe for low magnetic fields an “antiferromagnetic” phase where atoms condense in the $m=\pm 1$ Zeeman states, and occupation of the $m=0$ state is suppressed. Conversely, for large enough magnetic fields, a phase transition to a “broken-axisymmetry” phase takes place: The $m=0$ component becomes populated and rises sharply above a critical field $B_c\left(m_z\right)$. This behavior results from the competition between antiferromagnetic spin-dependent interactions (dominant at low fields) and the quadratic Zeeman energy (dominant at large fields). We compare the measured $B_c$ as well as the global shape of the phase diagram with mean-field theory, and find good quantitative agreement.

We find an algebraic formula for the $N$-partite concurrence of $N$ qubits in an $X$ matrix. $X$ matrices are density matrices whose only nonzero elements are diagonal or antidiagonal when written in an orthonormal basis. We use our formula to study the dynamics of the $N$-partite entanglement of $N$ remote qubits in generalized $N$-party Greenberger-Horne-Zeilinger (GHZ) states. We study the case in which each qubit interacts with a local amplitude damping channel. It is shown that only one type of GHZ state loses its entanglement in finite time; for the rest, $N$-partite entanglement dies out asymptotically. Algebraic formulas for the entanglement dynamics are given in both cases. We directly confirm that the half-life of the entanglement is proportional to the inverse of $N$. When entanglement vanishes in finite time, the time at which entanglement vanishes can decrease or increase with $N$ depending on the initial state. In the macroscopic limit, this time is independent of the initial entanglement.

Photoionization of Kr${}^{+}$ ions was studied in the energy range from 23.3 to 39.0 eV at a photon energy resolution of 7.5 meV. Absolute measurements were performed by merging beams of Kr${}^{+}$ ions and of monochromatized synchrotron undulator radiation. Photoionization (PI) of this Br-like ion is characterized by multiple Rydberg series of autoionizing resonances superimposed on a direct PI continuum. Resonance features observed in the experimental spectra are spectroscopically assigned and their energies and quantum defects tabulated. The high-resolution cross-section measurements are benchmarked against state-of-the-art theoretical cross-section calculations from the Dirac-Coulomb $R$-matrix method [J. Phys. B 45, 085701 (2012)].

We explore the dissociative ionization of CO with carrier-envelope-phase (CEP) tagged few-cycle laser pulses. We observe the CEP dependence of the directional emission of C${}^{p+}$ and O${}^{q+}$ fragments from transient CO${}^{(p+q)+}$ ions, where $p+q\le 3$ and $q\le 1$. At $I_0=3.5\times {10}^{14}$ W/cm${}^2$, a ${180}^{\circ }$ phase difference between the C${}^{+}$ and O${}^{+}$ fragments from the ($p=1$, $q=0$) and ($p=0$, $q=1$) channels reflects the orientation dependence of the CO ionization. At $I_0=1.2\times {10}^{15}$ W/cm${}^2$, we find a $\sim$35${}^{\circ }$ phase shift between the C${}^{2+}$ fragments from the ($p=2$, $q=0$) and ($p=2,q=1$) channels, in contrast to the ${180}^{\circ }$ shift previously observed between the C${}^{2+}$ fragment channels at $I_0=6\times {10}^{14}$ W/cm${}^2$ [Phys. Rev. Lett. 106, 073004 (2011)].

We theoretically examine three-well interferometry in Bose-Einstein condensates (BECs) using adiabatic passage. Specifically, we demonstrate that a fractional coherent transport adiabatic passage protocol enables stable spatial splitting in the presence of nonlinear interactions. A reversal of this protocol produces a coherent recombination of the BEC with a phase-dependent population of the three wells. The effect of nonlinear interactions on the interferometric measurement is quantified and is found to lead to an enhancement in sensitivity for moderate interaction strengths.

The polarization state of a surface mode is a hybrid between linear and elliptical states, meaning that although one of its electric- and magnetic-field components is linearly polarized, the other rotates on the transverse-longitudinal plane, effectively in its elliptical polarization state. We show that the rotation of the electric-field component can induce transverse spin angular momentum of the surface mode. The rotation of the magnetic-field component, however, cannot generate the spin. We argue that this results from the fact that the rotation direction of the magnetic field is invariant under time reversal.

We implement an interferometric method using two angular slits to measure the orbital-angular-momentum (OAM) mode spectrum of a field with partial angular coherence. As the angular separation of the slits changes, an interference pattern for a particular OAM mode is obtained. The visibility of this interference pattern as a function of angular separation is equivalent to the angular correlation function of the field. By Fourier transforming the angular correlation function obtained from the double-angular-slit interference, we are able to calculate the OAM spectrum of the partially coherent field. This method has potential application for characterizing the OAM spectrum in high-dimensional quantum information protocols.

We report the experimental observation of fine interference patterns in a reflection profile of a focused laser beam when it undergoes total internal reflection from a dielectric interface near its critical angle. In addition, we show that similar interference structures routinely appear in the reflection profile when long-range optical surface waves are excited at the plane interface by the focused laser beam. In both cases these interference patterns do not appear at all if the incident beam may be reckoned as a plane wave, that is, when the waist of the focused beam is much larger than the Goos-Hänchen shift or the surface wave propagation length correspondingly. A modified formula for the Goos-Hänchen shift is presented, and it is shown that a maximum value of the shift may reach several tens of microns for wide beams.

Silicon-on-insulator microrings both self-pulsate and are excitable due to the presence of thermal and free-carrier-related nonlinearities. We show how a dimensionless mean-field model, in which the fast light dynamics are neglected and only the temperature and the amount of free carriers remain as variables, can explain this dynamic behavior. Apart from a scaled detuning of the input wavelength to the resonance wavelength and a scaled input power, this system contains only a limited number of dimensionless parameters dependent on both the geometry and material system of the cavity. Moreover, the onset of oscillation is still analytically tractable, while the excitability onset can be obtained using continuation algorithms. In agreement with previous experiments, excitability is predicted to appear mainly at the blue side of the resonance. Finally, the proposed method of analysis paves the way for an easy comparison of the dynamics in different material systems or cavity types.

Recent calculations by Bromley et al. [Phys. Rev. Lett. 109, 063201 (2012)] have indicated that the He(2$s^2{}^1{S}^e$) state will bind a positron. The $e^{+}$He(2$s^2{}^1{S}^e$) state has a binding energy of 0.447 eV with respect to the He(2$s^2{}^1{S}^e$) state. Binding of a positron to the He 2$s^2$ state has been predicted to give rise to two resonances in positron scattering from ground-state helium: $e^{+}$He(2$s^2{}^1{S}^e$) at 57.3716 eV and a ${}^2{P}^o$ shape resonance just above the He(2$s^2{}^1{S}^e$) threshold at 57.8485 eV. To investigate these predicted resonances, low-energy positron scattering experiments were performed to measure the total and positronium cross sections in the doubly excited region of helium in this energy region. No experimental evidence has been found for these resonances, but upper bounds on the resonance strength were determined for both predicted resonances.

Here we consider both balanced and imbalanced Fermi gases throughout the BCS-BEC evolution, and we study the effects of spin-orbit coupling (SOC) on the spontaneously induced countercirculating mass currents and the associated intrinsic angular momentum via the Bogoliubov–de Gennes (BdG) formalism. In particular, we find that even a small SOC destabilizes Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) type spatially modulated superfluid phases and phase-separated states against the polarized superfluid phase. We also show that the continuum of the quasiparticle and quasihole excitation spectrum can be connected by zero, one, or two discrete branches of interface modes, depending on the number of interfaces between a topologically trivial phase and a nontrivial phase.

We study cavity optomechanics of a mixture of ultracold atoms with tunable nonlinear collisions. We show that atomic collisions provide linear couplings between fictitious condensate oscillators, leading to possibilities of achieving a globally coupled quantum optomechanical network with an integrated atom chip. Potential applications range from simulating collective nonequilibrium dynamics in fields well past physics to probing unique properties of quantum mixtures.

We show that for fermion states, measurements of any two finite outcome particle quantum numbers (e.g., spin) are not constrained by a minimum total uncertainty. We begin by defining uncertainties in terms of the outputs of a measurement apparatus. This allows us to compare uncertainties between multiparticle states of distinguishable and indistinguishable particles. Entropic uncertainty relations are derived for both distinguishable and indistinguishable particles. We then derive upper bounds on the minimum total uncertainty for bosons and fermions. These upper bounds apply to any pair of particle quantum numbers and depend only on the number of particles $N$ and the number of outcomes $n$ for the quantum numbers. For general $N$, these upper bounds necessitate a minimum total uncertainty much lower than that for distinguishable particles. The fermion upper bound on the minimum total uncertainty for $N$ an integer multiple of $n$ is zero. Our results show that uncertainty limits derived for single particle observables are valid only for particles that can be effectively distinguished. Outside this range of validity, the apparent fundamental uncertainty limits can be overcome.

In this paper, we show that bipartite states of an electronic qubit and ionic qudit, produced in a laboratory in as simple an experiment as photoionization in electric dipole approximation, can be separable or can possess either free or bound entanglement. The dimension of the Hilbert space of the qudit depends upon the electronic state $|1^{+}\rangle$ of the residual photoion $A^{1+}$: In the absence of spin-orbit interaction (SOI), when Russell-Saunders coupling is applicable, it is equal to the spin multiplicity of $|1^{+}\rangle$, but becomes (2$J$+1) in $j-j$ coupling, where $J$ is the total angular momentum of $|1^{+}\rangle$ when SOI is taken into account. In the case of $L-S$ coupling, all the properties (relevant to a study in quantum information) of a qubit-qudit state can readily be predicted merely with a knowledge of the spins of the atomic target and of the residual photoion which can experimentally be verified by measuring them using an entanglement witness, or any other such protocols, or by doing a full quantum-state tomography.

Guiding of highly charged ions through tilted capillaries promises to develop into a tool to efficiently collimate and focus low-energy ion beams to sub-micrometer spot size. One control parameter to optimize guiding is the residual electrical conductivity of the insulating material. Its strong, nearly exponential temperature dependence is the key to transmission control and can be used to suppress transmission instabilities arising from flux fluctuations of incident ions which otherwise would lead to Coulomb blocking of the capillary. We demonstrate the strong dependence of transmission of Ar${}^{7+}$ ions through a single macroscopic glass capillary on temperature and ion flux. Results in the regime of dynamical equilibrium can be described by balance equations in the linear-response regime.

We have measured the transmission of 230-keV (10-keV/$q$) Xe${}^{23+}$ ions through insulating tapered glass capillaries of microscopic dimensions. The dynamics of charging and discharging processes have been investigated, evidencing an unexpected slow alignment of the beam along the capillary axis. Oscillations of the exiting beam position have been observed during the charging process associated to the formation of charge patches on the capillary inner walls. The emerging ions are guided with a characteristic guiding angle falling on a universal curve proposed for PET polymer nanocapillaries. This result, very similar to the channeling process, is somewhat surprising in view of the significant differences between the straight nanocapillary polymer foils and the tapered microscopic single glass capillary used here. The transmitted ions show no evidence of energy loss or charge changing except for the production of a small neutral fraction that was determined to be due to ions that had become neutralized to form atoms rather than due to photon emission. These results thus test and confirm the validity of transmission and guiding and provide insight into the dynamics of higher-energy ions than have been previously studied in this regard, allowing a determination of the maximum energy for which the guiding process might occur.

We theoretically study the sequential double ionization of He by two-color attosecond pulses. We show that, for short time delays between the two pulses, the ionization spectra cannot be explained by an independent model based on the time-dependent perturbation theory. By varying the time delay, one can probe the role of the electron correlation played in the double ionization, which is mostly obvious by examining the differential double-ionization yield. In the present scheme, we also identify a kind of “catch-up” interaction between the two ionized electrons.

In this paper we study a fast adiabatic-like expansion of a one-dimensional Bose-Einstein condensate (BEC) in the Thomas-Fermi regime confined in a harmonic potential, using the theory of time-optimal control. We find that under reasonable assumptions suggested by the experimental setup, the minimum-time expansion occurs when the frequency of the potential changes in a bang-bang form between the permitted values. We calculate the necessary expansion time and compare it with that obtained using the state-of-the-art inverse engineering method under the same constraints. We also show that this minimum time scales logarithmically with the expansion factor for large values of the latter. This work is expected to find applications in areas where efficient manipulation of a BEC is of utmost importance, for example, in atom interferometry with a BEC.

We investigate strong pairing fluctuations and effects of a harmonic trap in the superfluid phase of an ultracold Fermi gas. Including amplitude and phase fluctuations of the inhomogeneous superfluid order parameter $\Delta \left(r\right)$ in a trap within a combined $T$-matrix theory with the local density approximation, we examine local properties of single-particle excitations and a thermodynamic quantity in the BCS-BEC crossover region. Below the superfluid phase transition temperature $T_{\mathrm{c}}$, we show that inhomogeneous pairing fluctuations lead to a shell structure of the gas cloud in which the spatial region where the ordinary BCS-type superfluid density of states appears surrounded by the region where the pseudogap associated with strong pairing fluctuations dominates single-particle excitations. The former spatial region enlarges to eventually cover the whole gas cloud far below $T_{\mathrm{c}}$. We also examine how this shell structure affects the photoemission spectrum, as well as the local pressure. Since a cold Fermi gas is always trapped in a harmonic potential, our results would be useful for the study of strong-coupling superfluid physics, including this realistic situation.