We study vortex dynamics in trapped two-component Bose-Einstein condensates with a laser-induced spin-orbit coupling using the numerical analysis of the Gross-Pitaevskii equation. The spin-orbit coupling leads to three distinct ground-state phases, which depend on some experimentally controllable parameters. When a vortex is put in one or both of the two-component condensates, the vortex dynamics exhibits very different behaviors in each phase, which can be observed in experiments. These dynamical behaviors can be understood by clarifying the stable vortex structure realized in each phase.

We study the storage of coherences in atomic rubidium vapor with a three-level coupling scheme with two ground states and one electronically excited state driven by one optical (control) and one radio frequency field. We initially store an atomic ground state coherence in the system. When retrieving the atomic coherence with a subsequent optical pulse, a second (signal) optical beam is created whose difference frequency to the control field is found to be determined by the atomic ground state's Raman transition frequency.

For ${\mathrm{H}}_2{}^{+}$ at the critical internuclear distance where the charge-resonance-enhanced ionization is most prominent, the lateral photoelectron momentum distribution presents the Fraunhofer-like diffraction pattern: a central disk surrounded by one or more rings. We study this phenomenon by simulating the time-dependent Schrödinger equation and unveil the mechanism: the stretched molecule constructs an interatomic Coulomb potential, which works as a circular aperture and diffracts the electron when it travels between two nuclei. This distinct lateral photoelectron momentum distribution offers another perspective to look into molecular structures.

Two types of electro-optic effect that are linear in the applied electric field strength are theoretically predicted to exist in transparent dielectric crystals due to high-order spatial dispersion. The first effect, which is quadratic in the wave vector of light, is possible in noncentrosymmetric crystals. The second, which is cubic in the wave vector, is possible in all crystals. In the $\mathit{O}\left(432\right)$ and ${\mathit{O}}_{\mathit{h}}\left(m\overline{3}m\right)$ crystal classes, for which the primary and secondary linear electro-optic effects and linear electrogyration are simultaneously absent, these effects lead, respectively, to qualitatively new behavior and constitute the dominant bulk electro-optic effect in the limit of small fields. Thus, bulk linear electro-optic effects are predicted to exist in a wide range of materials—including many of considerable technological importance, such as silicon—where they were previously considered impossible.

We study the interaction between a probe and a trigger weak fields in a sample of cold rubidium atoms in the presence of a coupling and a dressing strong fields. Dipole Rydberg blockade may occur and can be set to depend on the probe and trigger polarizations giving rise to diverse regimes of electromagnetically induced transparency (EIT) with a concomitant small probe and trigger absorption and dispersion. This is shown to be relevant to the implementation of polarization conditional probe and trigger cross nonlinearities in cold Rydberg atoms.

We describe measurements of the motional sidebands produced by a mechanical oscillator (with effective mass 43 ng and resonant frequency 705 kHz) that is placed in an optical cavity and cooled close to its quantum ground state. The red and blue sidebands (corresponding to Stokes and anti-Stokes scattering) from a single laser beam are recorded simultaneously via a heterodyne measurement. The oscillator's mean phonon number $\overline{n}$ is inferred from the ratio of the sidebands, and reaches a minimum value of $0.84\pm 0.22$ (corresponding to a mode temperature $T=28\pm 7\mu \mathrm{K}$). We also infer $\overline{n}$ from the calibrated area of each of the two sidebands, and from the oscillator's total damping. The values of $\overline{n}$ inferred from these four methods are in close agreement. The behavior of the sidebands as a function of the oscillator's temperature agrees well with theory that includes the quantum fluctuations of both the cavity field and the mechanical oscillator.

Absolute cross sections for charge-exchange, ionization, and excitation in ${\mathrm{Na}}^{+}$-Ne and ${\mathrm{Na}}^{+}$-Ar collisions were measured in the ion energy range $0.5–10$ keV using a refined version of a capacitor method and collision and optical spectroscopy methods simultaneously in the same experimental setup. Ionization cross sections for ${\mathrm{Ne}}^{+}$-Na and ${\mathrm{Ar}}^{+}$-Na collisions are measured at energies of $2–14$ keV using a crossed-beam spectroscopy method. The experimental data and the schematic correlation diagrams are used to analyze and determine the mechanisms for these processes. For the charge-exchange process in ${\mathrm{Na}}^{+}$-Ar collisions two nonadiabatic regions are revealed and mechanisms responsible for these regions are explained. Structural peculiarity on the excitation function for the resonance lines of argon atoms in ${\mathrm{Na}}^{+}$-Ar collisions are observed and the possible mechanisms of this phenomenon are explored. The measured ionization cross sections for ${\mathrm{Na}}^{+}$-Ne and ${\mathrm{Ne}}^{+}$-Na collisions in conjunction with the Landau-Zener formula are used to determine the coupling matrix element and transition probability in a region of pseudocrossing of the potential curves.

Attosecond-magnetic-field-pulse generation is simulated from numerical solutions of time-dependent Schrödinger equations for oriented ${{\mathrm{H}}_2}^{+}$. Two schemes with high frequency co- and counter-rotating bichromatic ${\omega }_2=2{\omega }_1$ circularly polarized UV laser pulses are investigated. Results show that comparing to single color processes, stronger induced localized magnetic fields $\mathbf{B}$ at the molecular center $O$ $\left(\mathbf{r}=0\right)$ are obtained with attosecond duration. This is attributed to frequent recollision and to interference effects of two pathways in photoionization. The induced magnetic fields are shown to be sensitive to (i) the helicity of the combined laser pulses due to different recollision laser-induced electron trajectories and currents, and (ii) also the carrier envelope phases of the combined attosecond laser pulses. The sensitivity of recollision to bichromatic pulses thus allows one to control the induced magnetic-field-pulse generation.

We predict that the maximal, steady-state ion capacity $N_s\left(\lambda \right)$ of radio-frequency (rf) traps, loaded at a rate of $\lambda$ particles per rf cycle, shows universal, nonlinear, nonmonotonic behavior as a function of loading rate $\lambda$. The shape of $N_s\left(\lambda \right)$, characterized by four dynamical regimes, is universal; i.e., it is predicted to manifest itself in all types of rf traps independent of the details of their construction and independent of particle species loaded. For $\lambda \ll$ 1 (region I), as expected, $N_s\left(\lambda \right)$ increases monotonically with $\lambda$. However, contrary to intuition, at intermediate $\lambda \sim 1$ (region II), $N_s\left(\lambda \right)$ reaches a maximum, followed by a local minimum of $N_s\left(\lambda \right)$ (region III). For $\lambda \gg 1$ (region IV), $N_s\left(\lambda \right)$ again rises monotonically. In region IV, numerical simulations, analytical calculations, and experiments show $N_s\left(\lambda \right)\sim {\lambda }^{2/3}$. We confirm our predictions both experimentally with magneto-optical-trap-loaded ${\mathrm{Na}}^{+}$ ions stored in a hybrid ion-neutral trap and numerically with the help of detailed ab initio molecular-dynamics simulations.

We study the dynamical depinning following a sudden turn off of an optical lattice for a gas of impenetrable bosons in a tight atomic waveguide. We use a Bose-Fermi mapping to infer the exact quantum dynamical evolution. At long times, in the thermodynamic limit, we observe the approach to a nonequilibrium steady state, characterized by the absence of quasi-long-range order and a reduced visibility in the momentum distribution. Similar features are found in a finite-size system at times corresponding to half the revival time, where we find that the system approaches a quasisteady state with a power-law behavior.

We study modulation instability (MI) of flat states in two-component spin-orbit-coupled (SOC) Bose-Einstein condensates (BECs) in the framework of coupled Gross-Pitaevskii equations for two components of the pseudospinor wave function. The analysis is performed for equal densities of the components. Effects of the interaction parameters, Rabi coupling, and SOC on the MI are investigated. In particular, the results demonstrate that the SOC strongly alters the commonly known MI (immiscibility) condition, $g_{12}^2>g_1{g}_2$, for the binary superfluid with coefficients $g_{1,2}$ and $g_{12}$ of the intra- and interspecies repulsive interactions. In fact, the binary BEC is always subject to the MI under the action of the SOC, which implies that the ground state of the system is plausibly represented by a striped phase.

We measure photon occupancy in a thin-film superconducting lumped element resonator coupled to a transmon qubit at $20\mathrm{mK}$ and find a nonlinear dependence on the applied microwave power. The transmon-resonator system was operated in the strong dispersive regime, where the ac Stark shift $\left(2\chi \right)$ due to a single microwave photon present in the resonator was larger than the linewidth $\left(\mathrm{\Gamma }\right)$ of the qubit transition. When the resonator was coherently driven at 5.474 325 GHz, the transition spectrum of the transmon at 4.982 GHz revealed well-resolved peaks, each corresponding to an individual photon number-state of the resonator. From the relative peak heights we obtain the occupancy of the photon states and the average photon occupancy $\overline{n}$ of the resonator. We observe a nonlinear variation of $\overline{n}$ with the applied drive power $P_{\mathrm{rf}}$ for $\overline{n}<5$ and compare our results to numerical simulations of the system-bath master equation in the steady state, as well as to a semiclassical model for the resonator that includes the Jaynes-Cummings interaction between the transmon and the resonator. We find good quantitative agreement using both models and analysis reveals that the nonlinear behavior is principally due to shifts in the resonant frequency caused by a qubit-induced Jaynes-Cummings nonlinearity.

The interaction of intense ultrafast laser pulses with atomic ${\mathrm{F}}^{-}$ and with molecular $\mathrm{S}{{\mathrm{F}}_6}^{-}$ anions is directly compared. The double-detachment mechanism is investigated by a systematic variation of peak intensity, polarization ellipticity, and pulse shape. For both systems, the observed weak polarization ellipticity dependence is not consistent with a rescattering-based mechanism. A double-detachment saturation intensity of $22\pm 4\times {10}^{13}\mathrm{W}/\mathrm{c}{\mathrm{m}}^2$ is determined for the atomic anion, which is significantly higher than the $9\pm 2\times {10}^{13}\mathrm{W}/\mathrm{c}{\mathrm{m}}^2$ of the analogous molecular system. The different atomic and molecular responses to spectral chirp and third-order dispersion induced pulse shapes are discussed in the context of the double-detachment time scale.

We address the issue of reducing the resource required to compute information-theoretic quantum correlation measures such as quantum discord and quantum work deficit in two qubits and higher-dimensional systems. We show that determination of the quantum correlation measure is possible even if we utilize a restricted set of local measurements. We find that the determination allows us to obtain a closed form of quantum discord and quantum work deficit for several classes of states, with a low error. We show that the computational error caused by the constraint over the complete set of local measurements reduces fast with an increase in the size of the restricted set, implying usefulness of constrained optimization, especially with the increase of dimensions. We perform quantitative analysis to investigate how the error scales with the system size, taking into account a set of plausible constructions of the constrained set. Carrying out a comparative study, we show that the resource required to optimize quantum work deficit is usually higher than that required for quantum discord. We also demonstrate that minimization of quantum discord and quantum work deficit is easier in the case of two-qubit mixed states of fixed ranks and with positive partial transpose in comparison to the corresponding states having nonpositive partial transpose. Applying the methodology to quantum spin models, we show that the constrained optimization can be used with advantage in analyzing such systems in quantum information-theoretic language. For bound entangled states, we show that the error is significantly low when the measurements correspond to the spin observables along the three Cartesian coordinates, and thereby we obtain expressions of quantum discord and quantum work deficit for these bound entangled states.

Quantum optimal control is a powerful tool for designing a pulse that executes a specified gate, i.e., a unitary transformation in quantum computation. If we consider qubits characterized by different spectroscopic properties, we may design a pulse that executes a specified gate on a specified qubit ($S$ qubit) with the inclusion of neighboring qubits ($B$ qubits) but does not explicitly include the other qubits. In this situation, first we introduce sets of reduced time-evolution operators associated with the $S$ and $B$ qubits. Then, we apply quantum optimal control to these sets to design optimal pulses that could selectively execute the specified gate on the $S$ qubit while actively removing the effects of the pulse on the $B$ qubits, which would lead to a scalable pulse-design procedure. The present pulse design is applied to the quantum computation proposed by DeMille with the aim of executing the Hadamard and controlled-not gates on the $S$ qubits while actively suppressing the pulse-induced population transitions of the $B$ qubit states. The numerical results illustrate high fidelity even after introducing the extra qubits that are not included in the pulse design.

We provide an analysis of a family of device-independent quantum key distribution (QKD) protocols that has the following features. (a) The bits used for the secret key do not come from the results of the measurements on an entangled state but from the choices of settings. (b) Instead of a single security parameter (a violation of some Bell inequality) a set of them is used to estimate the level of trust in the secrecy of the key. The main advantage of these protocols is a smaller vulnerability to imperfect random number generators made possible by feature (a). We prove the security and the robustness of such protocols. We show that using our method it is possible to construct a QKD protocol which retains its security even if the source of randomness used by communicating parties is strongly biased. As a proof of principle, an explicit example of a protocol based on the Hardy's paradox is presented. Moreover, in the noiseless case, the protocol is secure in a natural way against any type of memory attack, and thus allows one to reuse the device in subsequent rounds. We also analyze the robustness of the protocol using semidefinite programming methods. Finally, we present a postprocessing method, and observe a paradoxical property that rejecting some random part of the private data can increase the key rate of the protocol.

The ${\mathrm{Ca}}^{+}, {\mathrm{Sr}}^{+}, {\mathrm{Ba}}^{+}$, and ${\mathrm{Yb}}^{+}$ ions immersed in an ultracold gas of the Cr atoms are proposed as experimentally feasible heteronuclear systems in which ion-atom interactions at ultralow temperatures can be controlled with magnetically tunable Feshbach resonances without charge transfer and radiative losses. Ab initio techniques are applied to investigate electronic-ground-state properties of the (CaCr)${}^{+}$, (SrCr)${}^{+}$, (BaCr)${}^{+}$, and (YbCr)${}^{+}$ molecular ions. The potential energy curves, permanent electric dipole moments, and static electric dipole polarizabilities are computed. The spin-restricted open-shell coupled-cluster method restricted to single, double, and noniterative triple excitations and the multireference configuration-interaction method restricted to single and double excitations are employed. The scalar relativistic effects are included within the small-core energy-consistent pseudopotentials. The leading long-range induction and dispersion interaction coefficients are also reported. Finally, magnetic Feshbach resonances between the ${\mathrm{Ca}}^{+}, {\mathrm{Sr}}^{+}, {\mathrm{Ba}}^{+}$, and ${\mathrm{Yb}}^{+}$ ions interacting with the Cr atoms are analyzed. The present proposal opens the way towards robust quantum simulations and computations with ultracold ion-atom systems free of radiative charge-transfer losses.

Quasiresonant scattering of light in two dimensions can be described either as a scalar or as a vectorial electromagnetic wave. Performing a scaling analysis we observe in both cases long lived modes, yet only the scalar case exhibits Anderson localized modes together with extremely long mode lifetimes. We show that the localization length of these modes is influenced only by their position, and not their lifetime. Investigating the reasons for the absence of localization, it appears that both the coupling of several polarizations and the presence of near-field terms are able to prevent long lifetimes and Anderson localization.