We consider the standard double-well setup extended with a laser beam in the center to create a “triple-well” potential. The beam in the center is much narrower than the barrier, and it creates a tunable depth well which can support a localized state in the middle. We show that the presence of the localized state in the central well changes the sign of tunneling between the left and the right wells and therefore controls the fixed-point dynamics of the bosonic Josephson junction.

There is a broad interest in enhancing the strength of light-atom interactions to the point where injecting a single photon induces a nonlinear material response. Here we show theoretically that sub-Doppler-cooled two-level atoms that are spatially organized by weak optical fields give rise to a nonlinear material response that is greatly enhanced beyond that attainable in a homogeneous gas. Specifically, in the regime where the intensity of the applied optical fields is much less than the off-resonance saturation intensity, we show that the third-order nonlinear susceptibility scales inversely with atomic temperature and, due to this scaling, can be two orders of magnitude larger than that of a homogeneous gas for typical experimental parameters. As a result, we predict that spatially bunched two-level atoms can exhibit single-photon nonlinearities. Our model is valid for all regimes of atomic bunching and simultaneously accounts for the backaction of the atoms on the optical fields. Our results agree with previous theoretical and experimental results for light-atom interactions that have considered only limited regimes of atomic bunching. For lattice beams tuned to the low-frequency side of the atomic transition, we find that the nonlinearity transitions from a self-focusing type to a self-defocusing type at a critical intensity. We also show that higher than third-order nonlinear optical susceptibilities are significant in the regime where the dipole potential energy is on the order of the atomic thermal energy. We therefore find that it is crucial to retain high-order nonlinearities to accurately predict interactions of laser fields with spatially organized ultracold atoms. The model presented here is a foundation for modeling low-light-level nonlinear optical processes for ultracold atoms in optical lattices.

We consider the Raman process developing in a disordered medium of alkali-metal atoms when the scattered modes are trapped on a closed transition. Our theoretical analysis, based on numerical simulations of the Bethe-Salpeter equation for the light correlation function, which includes all Zeeman states and light polarization, lets us track the stimulated amplification as well as the losses associated with the inverse anti-Stokes scattering channel. We discuss possible conditions when this process could approach the instability point and enter the regime of random lasing.

Ion chains are promising platforms for studying and simulating quantum reservoirs. One interesting feature is that their vibrational modes can mediate entanglement between two objects which are coupled through the vibrational modes of the chain. In this work we analyze entanglement between the transverse vibrations of two heavy impurity defects embedded in an ion chain, which is generated by the coupling with the chain vibrations. We verify general scaling properties of the defect dynamics and demonstrate that entanglement between the defects can be a stationary feature of these dynamics. We then analyze entanglement in chains composed of tens of ions and propose a measurement scheme which allows one to verify the existence of the predicted entangled state.

We investigate entanglement purification protocols based on hashing, where a large number of noisy entangled pairs are jointly processed to obtain a reduced number of perfect, noiseless copies. While hashing and breeding protocols are the only purification protocols that asymptotically obtain a nonzero yield, they are not applicable in a realistic scenario if local gates and measurements are imperfect. We show that such problems can be overcome by a compact measurement-based implementation, yielding entanglement purification schemes with nonzero yield that are applicable also in noisy scenarios, with tolerable noise per particle of several percent. We also generalize these findings to multiparty purification protocols for arbitrary graph states.

Based on the spectroscopic constants derived from highly accurate potential-energy surfaces, the SeD radical is identified as a spectroscopic probe for measuring spatial and temporal variation of fundamental physical constants such as the fine-structure constant (denoted as $\alpha =\frac{e^2}{\hslash c}$) and the proton-to-electron mass ratio (denoted as $\mu =\frac{m_p}{m_e}$). The ground state of SeD $\left(X^2\Pi \right)$, due to spin-orbit coupling, splits into two fine-structure multiplets ${}^2{\Pi }_{\frac{3}{2}}$ and ${}^2{\Pi }_{\frac{1}{2}}$. The potential-energy surfaces of these spin-orbit components are derived from a state of the art electronic structure method, MRCI + Q inclusive of scalar relativistic effects with the spin-orbit effects accounted for through the Breit-Pauli operator. The relevant spectroscopic data are evaluated using a Murrel-Sorbie fit to the potential-energy surfaces. The spin-orbit splitting ${\omega }_f$ between the two multiplets is similar in magnitude with the harmonic frequency ${\omega }_e$ of the diatomic molecule. The amplification factor $K$ derived from this theoretical method for this particular molecule can be as large as 350; on the lower side it can be about 34. The significantly large values of $K$ indicate that the SeD radical can be a plausible experimental candidate for measuring variation in $\alpha$ and $\mu$.

We solve a time-optimal control problem in a linear chain of three coupled spins 1/2 with unequal couplings. We apply the Pontryagin maximum principle and show that the associated Hamiltonian system is the one of a three-dimensional rigid body. We express the optimal control fields in terms of the components of the classical angular momentum of the rigid body. The optimal trajectories and the minimum control time are given in terms of elliptic functions and elliptic integrals.

Single ionization of noble-gas atoms by linearly polarized synchrotron radiation has been studied by employing angle- and energy-resolved photoelectron spectroscopy. The measurements were carried out in the plane defined by the momentum and polarization vectors of the photon. Parameters describing the left-right asymmetry (LRA; relative to the photon propagation direction) of the photoelectron angular distribution were determined experimentally for the $s$ shells of He, Ne, Ar, Kr, and Xe atoms and $\mathrm{H}{}_2$ molecules and for the $p$ shells of Ne, Ar, Kr, and Xe atoms. The values of the left-right asymmetry differ significantly from zero for both subshells. The photon and photoelectron energy dependence of the LRA parameters is presented also. Possible experimental and instrumental sources that could generate asymmetry are discussed and excluded as well.

We study the interplay between rotation and openness for mode coupling in wavelength-scale microcavities. In cavities deformed from a circular disk, the decay rates of a quasidegenerate pair of resonances may cross or anticross with increasing rotation speed. The standing-wave resonances evolve to traveling-wave resonances at high rotation speed, however both the clockwise (CW) and counterclockwise (CCW) traveling-wave resonances can have a lower cavity decay rate, contrary to the intuitive expectation from the rotation-dependent effective index. With increasing rotation speed, a phase locking between the CW and CCW wave components in a resonance takes place. These phenomena result from the rotation-induced mode coupling, which is strongly influenced by the openness of the microcavity. The possibility of a nonmonotonic Sagnac effect is also discussed.

We address detection of quantum non-Gaussian states, i.e., nonclassical states that cannot be expressed as a convex mixture of Gaussian states, and present a method to derive a new family of criteria based on generic linear functionals. We then specialize this method to derive witnesses based on $s$-parametrized quasiprobability functions, generalizing previous criteria based on the Wigner function. In particular, we discuss in detail and analyze the properties of Husimi $Q$-function-based witnesses and prove that they are often more effective than previous criteria in detecting quantum non-Gaussianity of various kinds of non-Gaussian states evolving in a lossy channel.

A study is made of the nonlinear dynamics of bichromatically pumped microresonator Kerr frequency combs described by a driven and damped nonlinear Schrödinger equation, with an additional degree of freedom in the form of the modulation frequency. A truncated four-wave model is derived for the pump modes and the dominant sideband pair, which is found to be able to describe much of the essential dynamical behavior of the full equation. The stability of stationary states within the four-wave model is investigated, and numerical simulations are made to demonstrate that a large range of solutions, including cavity solitons, are possible beyond previously considered low-intensity patterns.

We introduce multiperiodicity in periodic metal-dielectric multilayers by stacking more than two types of metal and/or dielectric layers into the unit cell. A simple way to characterize arbitrary multiperiodic multilayers using permutation vectors is suggested and employed. Effects of multiperiodicity up to its fourth order are investigated. We demonstrate that various topologies of multiple-sheet isofrequency and dispersion surfaces exist for such plasmonic multilayers, including a photonic realization of nontrivial isolated Dirac cones.

The role of hollow states intermediately produced in electron-impact ionization of metastable He-like $N{}^{5+}\left(1s2s{}^3{S}_1\right)$ ions has been investigated in detail. A crossed-beam setup and suitable experimental techniques were employed for the measurement of accurate absolute cross sections and precise energy-scan data. Fine structures arising from $K$-shell excitations and associated resonances have been observed for this two-electron ion with less than $\pm$0.5 eV uncertainty on the energy scale. Fine details, such as interference of the reaction pathways of direct ionization and excitation with capture of the incident electron followed by double-Auger decay, could be revealed. Ab initio calculations based on the convergent close coupling (CCC) approach are in good agreement with the experiment.

We address the quantification of nonlinearity for quantum oscillators and introduce two measures based on the properties of the ground state rather than on the form of the potential itself. The first measure is a fidelity-based one and corresponds to the renormalized Bures distance between the ground state of the considered oscillator and the ground state of a reference harmonic oscillator. Then, in order to avoid the introduction of this auxiliary oscillator, we introduce a different measure based on the non-Gaussianity (nG) of the ground state. The two measures are evaluated for a sample of significant nonlinear potentials and their properties are discussed in some detail. We show that the two measures are monotone functions with respect to each other in most cases, and this suggests that the nG-based measure is a suitable choice to capture the anharmonic nature of a quantum oscillator, and to quantify its nonlinearity independently of the specific features of the potential. We also provide examples of potentials where the Bures measure cannot be defined, due to the lack of a proper reference harmonic potential, while the nG-based measure properly quantifies their nonlinear features. Our results may have implications in experimental applications where access to the effective potential is limited, e.g., in quantum control, and protocols rely on information about the ground or thermal state.

In this paper we propose a way to detect the Aharonov-Bohm effect for light in a moving medium. We use the position-dependent photon wave function to describe the propagation of the photon in order to evaluate the phase shift acquired by the photon while it passes around a rotating cylinder embedded in a viscous fluid. We show that this phase depends on the speed of the fluid as well as the electromagnetic properties of the cylinder.

This paper deals with the electronic structure of RbSr, a molecule possessing both a magnetic dipole moment and an electric dipole moment in its own frame, allowing its manipulation with external fields. Two complementary ab initio approaches are used for the ground and lowest excited states: first, an approach relying on optimized effective core potentials with core polarization potentials based on a full configuration interaction involving three valence electrons and second, an approach using a small-size effective core potential with 19 correlated electrons in the framework of coupled-cluster theory. We have found excellent agreement between these two approaches for the ground-state properties including the permanent dipole moment. We have focused on studies of excited states correlated to the two lowest asymptotes $\mathrm{Rb}(5p{}^{2}P)$$+\mathrm{Sr}(5s^2{}^{1}S)$ and $\mathrm{Rb}(5s{}^{2}S)$$+\mathrm{Sr}(5s5p{}^{3}P)$ relevant for ongoing experiments on ultracold quantum degenerate gases. We also present approximate potential curves including spin-orbit interaction based on atomic spin-orbit constants. These potential curves are an excellent starting point for experimental studies of molecular structure of RbSr using high-resolution spectroscopy.

The control of quantum dynamics is generally accomplished by seeking a tailored electromagnetic field to meet a posed objective. A particular shaped field can be thought of as specifying a point on a quantum control landscape, which is the objective as a functional of the controls. Optimizing the pulse shape corresponds to climbing the landscape, and previous work showed that the paths taken up the landscapes, guided by a gradient algorithm, are surprisingly straight when projected into the space of control fields. The direct nature of these control trajectories can be quantified by the metric $R\ge 1$, defined as the ratio of the length of the control trajectory to the Euclidean distance between its end points. The prior observation of often finding low values of $R$ implies that the landscapes are structurally simple. In this work, we investigate whether there is a relationship between the intricacy of the control mechanism and the complexity of the trajectory taken through the control space reflected in the value of $R$. We use the Hamiltonian encoding procedure to identify the mechanism, and we examine control of the state-to-state transition probability. No significant correlation is found between the landscape structure, reflected in the value of $R$, and the control mechanism. This result has algorithmic implications, opening up the prospect of seeking fields producing particular mechanisms at little penalty in the search effort due to encountering complex landscape structure.

We present a theoretical analysis of spin relaxation, for a polarized gas of spin 1/2 particles undergoing restricted adiabatic diffusive motion within a container of arbitrary shape, due to magnetic field inhomogeneities of arbitrary form.

A search for the variables that control a quantum system's dynamics occurs over a landscape, defined as the target objective as a function of the variables. Prior studies show that upon satisfaction of three specific assumptions, the topology of the landscape is free of suboptimal traps that could prematurely halt the search for an optimal control. One key assumption is free access to all necessary control variables; however, in practice, the controls are always limited in some fashion which may result in constraint-induced traps on the landscape. This paper aims to introduce the means to systematically explore the nature of constrained controls that yield suboptimal outcomes. The procedure utilizes kinematic controls, which comprise a simple set of time-independent variables, and then performs a landscape topology-preserving transformation into corresponding dynamic controls. The equivalent landscape topology of these two formulations permits the study of a family of dynamic controls that reflect constrained control landscape behavior. In particular, constrained dynamic controls are identified as isolated points on the landscape or as suboptimal level sets. The wide range of such dynamic controls indicates the richness and complexity of constraint-induced features on the landscape.