Vortex lattices in rapidly rotating Bose-Einstein condensates are systems of topological excitations that arrange themselves into periodic patterns. Here we show how phase-imprinting techniques can be used to create a controllable number of defects in these lattices and examine the resulting dynamics. Even though we describe our system using the mean-field Gross-Pitaevskii theory, the full range of many-particle effects among the vortices can be studied. In particular we find the existence of localized vacancies that are quasistable over long periods of time and characterize the effects on the background lattice through the use of the orientational correlation function and Delaunay triangulation.

Families of soliton pairs, namely vector solitons, are found within the context of a coupled nonlocal nonlinear Schrödinger system of equations, as appropriate for modeling beam propagation in nematic liquid crystals. In the focusing case, bright soliton pairs have been found to exist provided their amplitudes satisfy a specific condition. In our analytical approach, focused on the defocusing regime, we rely on a multiscale expansion methods, which reveals the existence of dark-dark and antidark-antidark solitons, obeying an effective Korteweg-de Vries equation, as well as dark-bright solitons, obeying an effective Mel'nikov system. These pairs are discriminated by the sign of a constant that links all physical parameters of the system to the amplitude of the stable continuous wave solutions, and, much like the focusing case, the solitons' amplitudes are linked, leading to mutual guiding.

Temperature determines the relative probability of observing a physical system in an energy state when that system is energetically in equilibrium with its environment. In this paper we present a theory for engineering the temperature of a quantum system different from its ambient temperature. We define criteria for an engineered quantum bath that, when coupled to a quantum system with Hamiltonian $H$, drives the system to the equilibrium state $\frac{e^{-H/T}}{\mathrm{Tr}\left(e^{-H/T}\right)}$ with a tunable parameter $T$. This is basically an analog counterpart of the digital quantum metropolis algorithm. For a system of superconducting qubits, we propose a circuit-QED approximate realization of such an engineered thermal bath consisting of driven lossy resonators. Our proposal opens the path to simulate thermodynamical properties of many-body quantum systems of size not accessible to classical simulations. Also we discuss how an artificial thermal bath can serve as a temperature knob for a hybrid quantum-thermal annealer.

A way of constructing the unextendible maximally entangled basis (UMEB) from the maximally entangled basis (MEB) is proposed. Consequently, it is shown that if there is an $N$-member UMEB in ${\mathbb{C}}^d\otimes {\mathbb{C}}^d$, then there exists a ${\left(qd\right)}^2-q(d^2-N)$-member UMEB in ${\mathbb{C}}^{qd}\otimes {\mathbb{C}}^{qd}$ for any $q\in \mathbb{N}$. This improves the results in Wang et al. [Phys. Rev. A 90, 034301 (2014)], which shows that there exists a ${\left(qd\right)}^2-(d^2-N)$-member UMEB in ${\mathbb{C}}^{qd}\otimes {\mathbb{C}}^{qd}$ provided that an $N$-member UMEB exsits in ${\mathbb{C}}^d\otimes {\mathbb{C}}^d$. In addition, a very easy way of constructing UMEB in ${\mathbb{C}}^d\otimes {\mathbb{C}}^{d^{\prime }}$ with $d<d^{\prime }$ is presented, which promotes and covers all the previous related work.

We present a couple of protocols based on shortcut to adiabaticity techniques for rapid generation of robust entangled Bell states in a pair of two-state systems. Our protocol relies on the so-called transitionless quantum driving (TQD) algorithm and Lewis-Riesenfeld invariant (LRI) method. Both TQD and LRI methods result in high fidelity in population transfer. Our study shows that it is possible to prepare an entangled state in extremely short time without losing robustness and efficiency.

We use differential Ramsey interferometry of ultracold atoms to characterize the vector light shift (VLS) from a far-off-resonance optical dipole trap at $\lambda =1064$ nm. The VLS manifests as a “fictitious” magnetic field, which we perceive as a change in the Larmor frequency of two spinor condensates exposed to different intensities of elliptically polarized light. We use our measurement scheme to diagnose the light-induced magnetic field and suppress it to $2.1\left(8\right)\times {10}^{-4}$ of its maximum value by making the trapping light linearly polarized with a quarter-wave plate in each beam. Our sensitive measurement of the VLS-induced field demonstrates high-precision, in vacuo interferometric polarimetry of dipole-trapping light and can be adapted to measure vector shifts from other lasers, advancing the application of optically trapped atoms to precision metrology.

The electron emission pattern of transfer ionization in collisions of $\mathrm{H}{\mathrm{e}}^{2+}$ with He was investigated for impact velocities between 0.53 a.u. and 0.77 a.u. (7 keV/u–15 keV/u) employing recoil-ion momentum spectroscopy. This process is known to be dominated by the promotion of the $2p\pi$ quasimolecular orbital into the continuum which results in banana-shaped areas of high electron momentum densities in the collision plane extending from the target to the projectile in velocity space. Asymmetries are explained by a coherent superposition of the $1s\sigma$ channel of quasimolecular promotion with the $2p\pi$ channel. Here we report on additional contributions from channels of higher angular momentum which emerge at the smaller impact velocities. They show up as highly structured electron emission patterns in the plane perpendicular to the direction of impact.

We analyze the experiment by Hultgren et al. [Phys. Rev. A 87, 031404 (2013)] on orbital alignment and quantum beats in coherently excited atomic fine-structure manifolds produced by short-pulse laser photodetachment of ${\text{C}}^{-},{\text{Si}}^{-}$, and ${\text{Ge}}^{-}$ negative ions, and derive a formula that describes the beats. Analysis of the experimental data enables us to extract the noncoherent background contribution for each species, and indicates the need for a full density-matrix treatment of the problem.

We study the energy spectrum of atoms trapped in a vertical one-dimensional optical lattice in close proximity to a reflective surface. We propose an effective model to describe the interaction between the atoms and the surface at any distance. Our model includes the long-range Casimir-Polder potential together with a short-range Lennard-Jones potential, which are considered nonperturbatively with respect to the optical lattice potential. We find an intricate energy spectrum which contains a pair of loosely bound states localized close to the surface in addition to a surface-modified Wannier-Stark ladder at long distances. Atomic interferometry involving those loosely bound atom-surface states is proposed to probe the adsorption dynamics of atoms on mirrors.

Frozen waves (FWs) are a class of diffraction- and attenuation-resistant beams whose intensity pattern along the direction of propagation can be chosen arbitrarily, thus making them relevant for engineering the spatial configuration of optical fields. To date, analyses of such beams have been done essentially for the scalar case, with the vectorial nature of the electromagnetic fields often neglected. Although it is expected that the field components keep the fundamental properties of the scalar FWs, a deeper understanding of their electromagnetic counterparts is mandatory in order to exploit their different possible polarization states. The purpose of this paper is to study the properties of electromagnetic FWs with radial, azimuthal, linear, circular, and elliptical polarizations under paraxial and nonparaxial regimes in nonabsorbing media. An intensity pattern is chosen for a scalar FW, and the vectorial solutions are built after it via the use of Maxwell's equations. The results show that the field components and the longitudinal component of the time-averaged Poynting vector closely follow the pattern chosen even under highly nonparaxial conditions, showing the robustness of the FW structure to parameters variations.

A two-level system interacting with an electromagnetic mode experiences inversion collapses and revivals. They are an indirect signature of the field quantization and also hold information about the mode. Thus, they may be harnessed for quantum-state reconstruction. In this work, we investigate the inversion via the characteristic function of the field mode photon-number distribution. The characteristic function is the spectral representation of the photon-number probability distribution. Exploiting the characteristic function periodicity, we find that the inversion can be understood as the result of interference between a set of structures akin to a free quantum-mechanical wave packet, with each structure corresponding to a snapshot of this packet for different degrees of dispersion. The Fourier representation of each packet Fourier determines the photon-number distribution. We also derive an integral equation whose solution yields the underlying packets. This approach allows the retrieval of the field photon-number distribution directly from the inversion under fairly general conditions and paves the way for a partial tomography technique.

By spectrally hole burning an inhomogeneously broadened ensemble of ions while applying a controlled perturbation, one can obtain spectral holes that are functionalized for maximum sensitivity to different perturbations. We propose to use such hole-burned structures for the dispersive optical interaction with rare-earth-ion dopants whose frequencies are sensitive to crystal strain due to the bending motion of a crystal cantilever. A quantitative analysis shows that good optical sensitivity to the bending motion is obtained if a magnetic-field gradient is applied across the crystal during hole burning and that the resulting optomechanical coupling strength is sufficient for observing quantum features such as zero-point vibrations.

We apply a recently developed method [V. A. Dzuba, Phys. Rev. A 90, 012517 (2014); J. S. M. Ginges and V. A. Dzuba, Phys. Rev. A 91, 042505 (2015)] to calculate energy levels of superheavy elements Uut $\left(Z=113\right)$, Fl $\left(Z=114\right)$, and ${\mathrm{Fl}}^{+}$. The method combines the linearized single-double coupled-cluster technique, the all-order correlation potential method, and configuration-interaction method. Breit and quantum electrodynamic corrections are included. The role of relativistic and correlation effects is discussed. Similar calculations for Tl, Pb, and ${\mathrm{Pb}}^{+}$ are used to gauge the accuracy of the calculations.

We study universal bosonic few-body systems within the framework of effective field theory at leading order (LO). We calculate binding energies of systems of up to six particles and the atom-dimer scattering length. Convergence to the limit of zero-range two- and three-body interactions is shown, indicating that no additional few-body interactions need to be introduced at LO. Generalizations of the Tjon line are constructed, showing correlations between few-body binding energies and the binding energy of the trimer, for a given dimer energy. As a specific example, we implement our theory for ${}^4\mathrm{He}$ atomic systems and show that the results are in surprisingly good agreement with those of sophisticated ${}^4\mathrm{He}\text{−}{}^4\mathrm{He}$ potentials. Potential implications for the convergence of the EFT expansion are discussed.

Ionization of a hydrogen atom exposed to an attosecond pulse train and a few-cycle middle infrared (MIR) pulse is calculated with the strong field approximation. The ionization events initiated by two attosecond pulses in the train are streaked in the presence of a weak MIR pulse, making the two ionization events overlap or separate in momentum representation. By changing the weak MIR pulse intensity, the interference structure in the photoelectron momentum distribution can be precisely tailored. When the MIR field is strong enough to produce substantial ionization, the overlapped attosecond pulse train and MIR field trigger the XUV-phase-dependent photoelectron angular distribution. Either the interference pattern or the angular distribution can be used to extract the carrier envelope phase of attosecond pulses, which makes it possible to visualize the sub-XUV-cycle dynamics.

Most of the work done in the field of Bose-Einstein condensates with balanced gain and loss has been performed in the mean-field approximation using the $\mathcal{P}T$-symmetric Gross-Pitaevskii equation. In this work we study the many-particle dynamics of a two-mode condensate with balanced gain and loss described by a master equation in Lindblad form whose purity periodically drops to small values but then is nearly completely restored. This effect cannot be covered by the mean-field approximation, in which a completely pure condensate is assumed. We present analytic solutions for the dynamics in the noninteracting limit and use the Bogoliubov backreaction method to discuss the influence of the on-site interaction. Our main result is that the strength of the purity revivals is almost exclusively determined by the strength of the gain and loss and is independent of the amount of particles in the system and the interaction strength. For larger particle numbers, however, strong revivals are shifted towards longer times, but by increasing the interaction strength these strong revivals again occur earlier.

Violations of Bell inequalities are better preserved by turbulent atmospheric channels than by comparable optical fibers in the scenario of copropagating entangled photons [A. A. Semenov and W. Vogel, Phys. Rev. A 81, 023835 (2010)]. Here we reexamine this result for the case of counterpropagation also considering the fact that each receiver registers so-called double-click events, which are caused by dark counts, stray light, and multiphoton entangled pairs. We show that advantages of the atmospheric links are feasible only for the copropagation scenario in the case of strong fluctuations of losses. For counterpropagation, the violations of Bell inequalities can be improved with an additional postselection procedure testing the channel transmittance.

In contrast to a Hermitian system, in which zero modes are usually a degenerate and localized edge state in the thermodynamic limit, the zero mode of a finite non-Hermitian system can be a single nontrivial long-range entangled state at the exceptional point. In this work, we demonstrate this feature with a concrete example based on exact solutions. Numerical simulations show that the entangled state can be generated through the dynamic process with a high fidelity.

We express the positive-partial-transpose (PPT) separability criterion for symmetric states of multiqubit systems in terms of matrix inequalities based on the recently introduced tensor representation for spin states. We construct a matrix from the tensor representation of the state and show that it is similar to the partial transpose of the density matrix written in the computational basis. Furthermore, the positivity of this matrix is equivalent to the positivity of a correlation matrix constructed from tensor products of Pauli operators. This allows for a more transparent experimental interpretation of the PPT criteria for an arbitrary spin-$j$ state. The unitary matrices connecting our matrix to the partial transpose of the state generalize the so-called magic basis that plays a central role in Wootters' explicit formula for the concurrence of a two-qubit system and the Bell bases used for the teleportation of a one- or two-qubit state.

The energy spectrum of the electrons ejected in forward direction from Ar atoms with simultaneous bound-state capture of two electrons has been measured by impact of 30 keV/amu ${\mathrm{He}}^{2+}$ ions with the aim to clarify the discrepancy between the results of two previous experiments concerning the existence of the cusp-shaped peak for electrons with velocity close to the ion velocity. A peak structure has been observed which is dominated by a broad cusp attributed to the zero-energy electron emission in the projectile-centered reference system at the $2{}^{3}S$ excitation threshold of ${\mathrm{He}}^0$. Further narrower peaks have been identified as results of the decay of autodetachment resonant states of ${\mathrm{He}}^{-}$ populated during the collision by three-electron bound-state capture.