Nuclear-spin-dependent (NSD) parity-violating (PV) effects can be strongly enhanced in diatomic molecules containing heavy atoms. Future measurements are anticipated to provide nuclear anapole moments and strength constants for PV nuclear forces. In light molecules, the NSD electroweak electron-nucleus interaction may also be detected. Here we calculate NSD PV effects for molecular ions. Our calculations are motivated by rapid developments in trapping techniques for such systems at low temperatures.

We explore the properties of spin splitting for neutral particles possessing electric and magnetic dipole moments propagating in an electromagnetic field. Two notable features of the spin splitting and the associated Larmor precession are found, which are consequences of special relativity. First, we report the existence of an upper limit of spin splitting equal to twice the rest energy of the particle and a corresponding upper limit for the Larmor precession frequency. Second, we predict the noninvariance of the spin splitting and the corresponding Larmor frequency with respect to Lorentz boosts, which bears a resemblance to the classical Doppler effect.

By making use of the spatial shape of paired photons, parametric down-conversion allows the generation of two-photon entanglement in a multidimensional Hilbert space. How much entanglement can be generated in this way? In principle, the infinite-dimensional nature of the spatial degree of freedom renders unbounded the amount of entanglement available. However, in practice, the specific configuration used, namely, its geometry, the length of the nonlinear crystal, and the size of the pump beam, can severely limit the value that could be achieved. Here we show that the use of quasi-phase-matching engineering allows one to increase the amount of entanglement generated, reaching values of tens of ebits of entropy of entanglement under different conditions. Our work thus opens a way to fulfill the promise of generating massive spatial entanglement under a diverse variety of circumstances, some more favorable for its experimental implementation.

We present nonadiabatic, fully ab initio, systematic calculations of the 3$p$π $D$ ${}^1{\Pi }_u{}^{+}$ level energies, Λ doublings, and absorption line intensities and widths for H${}_2$ and D${}_2$ even for those levels that are strongly predissociated. The multichannel quantum defect theory calculations are based on the latest quantum-chemical clamped-nuclei data of Wolniewicz and collaborators [L. Wolniewicz and G. Staszewska, J. Mol. Spectrosc. 220, 45 (2003); G. Staszewska and L. Wolniewicz, J. Mol. Spectrosc. 212, 208 (2002)]. The theoretical values are compared with previously published data [G. D. Dickenson, T. I. Ivanov, M. Roudjane, N. de Oliveira, D. Joyeux, L. Nahon, W.-Ü. L. Tchang-Brillet, M. Glass-Maujean, I. Haar, A. Ehresmann, and W. Ubachs, J. Chem. Phys. 133, 144317 (2010); G. D. Dickenson, T. I. Ivanov, W. Ubachs, M. Roudjane, N. de Oliveira, D. Joyeux, L. Nahon, W.-Ü. L. Tchang-Brillet, M. Glass-Maujean, H. Schmoranzer, A. Knie, S. Kübler, and A. Ehresmann, Mol. Phys. 109, 2693 (2011)] and with absolute line intensity measurements. The overall agreement is very good. The enhanced precision of the calculations leads to additional assignments and to several corrections of previous literature data.

We study strongly correlated Hubbard systems extended to symmetric $N$-component fermions. We focus on the intermediate-temperature regime between magnetic superexchange and interaction energy, which is relevant to current ultracold fermionic atom experiments. The $N$-component fermions are represented by slave particles, and, by using a diagrammatic technique based on the atomic limit, spectral functions are analytically obtained as a function of temperature, filling factor, and the component number $N$. We also apply this analytical technique to the calculation of lattice modulation experiments. We compute the production rate of double occupancy induced by modulation of an optical lattice potential. Furthermore, we extend the analysis to take into account the trapping potential by use of the local density approximation. We find an excellent agreement with recent experiments on ${}^{173}$Yb atoms.

An elementary experiment in optics consists of a light source and a detector. Yet, if the source generates nonclassical correlations such an experiment is capable of unambiguously demonstrating the quantum nature of light. We realized such an experiment with a defect center in diamond and a superconducting detector. Previous experiments relied on more complex setups, such as the Hanbury Brown and Twiss configuration, where a beam splitter directs light to two photodetectors, creating the false impression that the beam splitter is a fundamentally required element. As an additional benefit, our results provide a simplification of the widely used photon-correlation techniques.

We study the existence and stability of solitons in the quadratic nonlinear media with spatially localized parity-time- ($\mathcal{PT}$)-symmetric modulation of the linear refractive index. Families of stable one- and two-hump solitons are found. The properties of nonlinear modes bifurcating from a linear limit of small fundamental harmonic fields are investigated. It is shown that the fundamental branch, bifurcating from the linear mode of the fundamental harmonic is limited in power. The power maximum decreases with the strength of the imaginary part of the refractive index. The modes bifurcating from the linear mode of the second harmonic can exist even above the $\mathcal{PT}$-symmetry-breaking threshold. We found that the fundamental branch bifurcating from the linear limit can undergo a secondary bifurcation colliding with a branch of two-hump soliton solutions. The stability intervals for different values of the propagation constant and gain or loss gradient are obtained. The examples of dynamics and excitations of solitons obtained by numerical simulations are also given.

The spontaneous creation and persistence of ground-state coherence in an ensemble of intracavity Rb atoms has been observed as a quantum beat. Our system realizes a quantum eraser, where the detection of a first photon prepares a superposition of ground-state Zeeman sublevels, while detection of a second erases the stored information. Beats appear in the time-delayed photon-photon coincidence rate (intensity correlation function). We study the beats theoretically and experimentally as a function of system parameters, and find them remarkably robust against perturbations such as spontaneous emission. Although beats arise most simply through single-atom-mediated quantum interference, scattering pathways involving pairs of atoms interfere also in our intracavity experiment. We present a detailed model which identifies all sources of interference and accounts for experimental realities such as imperfect prepumping of the atomic beam, cavity birefringence, and the transit of atoms across the cavity mode.

A sufficient condition for a quantum state of a system of spin-1/2 particles to admit a local hidden variable description, i.e., to be classical, is the separability of the density matrix characterizing its state, but not all classical states are separable. This leads one to infer that separability and classicality are two different concepts. These concepts are examined here in the framework of a criterion for identifying the classicality of a system of spin-1/2 particles based on the concept of joint quasiprobability (JQP) for the eigenvalues of spin components [Puri, J. Phys. A 29, 5719 (1996)]. The said criterion identifies a state as classical if a suitably defined JQP of the eigenvalues of spin components in three suitably chosen orthogonal directions is non-negative. In agreement with other approaches, the JQP-based criterion also leads to the result that all nonfactorizable pure states of two spin-1/2 particles are nonclassical. In this paper it is shown that the application of the said criterion to mixed states suggests that the states it identifies as classical are also separable and that there exist states which, identified as classical by other methods, may not be identified as classical by the criterion as it stands. However, results in agreement with the known ones are obtained if the criterion is modified to identify as classical also those states for which the JQP of the eigenvalues of the spin components in two of the three prescribed orthogonal directions is non-negative. The validity of the modified criterion is confirmed by comparing its predictions with those arrived at by other methods when applied to several mixed states of two spin-1/2 particles and the Werner-like state of three spin-1/2 particles [Tòth and Acìn, Phys. Rev. A 74, 030306(R) (2006)]. The JQP-based approach, formulated as it is along the lines of the $P$-function approach for identifying classical states of the electromagnetic field, offers a unified approach for systems of an arbitrary number of spin-1/2 particles and the possibility of linking classicality with the nature of the measurement process.

We study the dynamics of a two-level quantum system interacting with an external environment that takes the form of an $\mathit{XY}$ spin chain in the presence of an external magnetic field. While the presence of the bath itself can enhance the transition probability from the lower level to the upper level of the system, we show that this noise-assisted phenomenon is sensitive to a change of the quantum phase of the environment. The derivative of the transition probability displays a maximum in correspondence with the critical value of the applied field in the case of both isotropic and anisotropic chains.

For potential barriers with scalar and vector coupling, we show that a Dirac particle could experience nearly full transmission within a wide sub-barrier energy band in the Klein energy zone. Moreover, for certain potential configurations, including pseudospin symmetry where the scalar potential is the negative of the vector, full transmission occurs for arbitrarily small momentum.

We present full quantum statistical energetics of some electron–light-nuclei systems. This is accomplished with the path-integral Monte Carlo method. The effects on energetics arising from the change in the nuclear mass are studied. The obtained results may serve as reference data for the multicomponent density functional theory calculations of light-nuclei systems. In addition, the results reported here will enable better fitting of today's electron-nuclear energy functionals, for which the description of light nuclei is most challenging in particular.

We study numerically the long-time dynamics of a one-dimensional Bose-Einstein condensate expanding in a speckle or impurity disorder potential. Using the mean-field Gross-Pitaevskii equation, we demonstrate subdiffusive spreading of the condensate for long times. We find that interaction-assisted hopping between normal modes leads to this subdiffusion. A possible (partial) reason why the root-mean-square (rms) width saturates in the experiment [Nature (London) 453, 891 (2008)] is provided. We suggest that observing both the participation length and the rms width of a condensate, rather than only the rms width, could provide a more complete description of the long-time behavior of ultracold atoms in disorder potentials. Our study confirms subdiffusive spreading in spatially continuous disordered interacting models and highlights new features which spatially discrete models do not possess.

With use of the nonlinear Schrödinger (or Gross-Pitaevskii) equation with strong repulsive cubic nonlinearity, dynamics of multicomponent Bose-Einstein condensates (BECs) with a harmonic trap in two dimensions is investigated beyond the Thomas-Fermi regime. In the case when each component has a single vortex, we obtain an effective nonlinear dynamics for vortex cores (particles). The particles here acquire the inertia, in marked contrast to the standard theory of point vortices widely known in the usual hydrodynamics. The effective dynamics is equivalent to that of charged particles under a strong spring force and in the presence of Lorentz force with the uniform magnetic field. The interparticle (vortex-vortex) interaction is singularly repulsive and short ranged with its magnitude decreasing with increasing distance of the center of mass from the trapping center. “Chaos in the three-body problem” in the three-vortice system can be seen, which is not expected in the corresponding point vortices without inertia in two dimensions.

We investigate the effect of a surface-plasmon resonance on Goos-Hänchen and Imbert-Fedorov spatial and angular shifts in the reflection of a light beam by considering a three-layer system made of glass, gold, and air. We calculate these spatial and angular shifts as functions of the incidence angle showing that they are strongly enhanced in correspondence with the resonant angle. In particular, we find giant spatial and angular Goos-Hänchen shifts for the $p$-wave light close to the plasmon resonance. We also predict a similar but less pronounced resonant effect on spatial and angular Imbert-Fedorov shifts for both $s$-wave and $p$-wave light.

The angular momentum density and flux of light in a dispersive, rotationally symmetric medium are derived from Noether's theorem. Optical angular momentum in a dispersive medium has no simple relation to optical linear momentum, even if the medium is homogeneous. A circularly polarized monochromatic beam in a homogeneous, dispersive medium carries a spin angular momentum of $\pm \hslash$ per energy $\hslash \omega$, as in vacuum. This result demonstrates the nontrivial interplay of dispersive contributions to optical angular momentum and energy.

We report an optical one-way quantum computing experiment with stationary quantum memory involved. First we create a hybrid four-qubit cluster state with two qubits propagating as photons and the other two stationary and stored in a laser-cooled atomic-ensemble quantum memory, and characterize it with entanglement witnesses and quantum state tomography. Then, by making use of this cluster state and fast operations of electro-optic modulators, we realize memory-assisted feedforward operations and demonstrate deterministic single-qubit rotation as an example.

A quantum state contains the maximal amount of information available for a given quantum system. In this paper we use weak-value expressions to reconstruct quantum states of continuous-variable systems in the quantum optical domain. The role played by postselecting measured data will be particularly emphasized in the proposed setup, which is based on an interferometer just using simple homodyne detection.