We study the mean-field dynamics of a Bose Josephson junction which is dispersively coupled to a single mode of a high-finesse optical cavity. An effective classical Hamiltonian for the Bose Josephson junction is derived, and its dynamics is studied from the perspective of a phase portrait. It is shown that the strong condensate-field interplay does alter the dynamics of the Bose Josephson junction drastically. The possibility of coherent manipulating and in situ observation of the dynamics of the Bose Josephson junction is discussed.

We present a study of the spectral properties of photon pairs generated through the process of spontaneous four-wave mixing (SFWM) in single mode fiber. Our analysis assumes narrowband pumps, which are allowed to be frequency degenerate or nondegenerate. Based on this analysis, we derive conditions on the pump frequencies and on the fiber dispersion parameters which guarantee the generation of ultrabroadband photon pairs. Such photon pairs are characterized by (i) a very large degree of entanglement, and (ii) a very high degree of temporal synchronization between the signal and idler photons. Through a numerical exercise, we find that the use of photonic crystal fiber (PCF) facilitates the fulfilment of the conditions for ultrabroadband photon pair generation; in particular, the spectral region in which emission occurs can be adjusted to particular needs through an appropriate choice of the PCF parameters. In addition, we present a quantum interference effect, resulting from indistinguishable pathways to the same outcome, which can occur when pumping a SFWM source with multiple spectral lines.

We theoretically study generation and conversion of optical vortices (OVs) in long-period helical core fibers (HCFs) produced by drawing from a perform with an eccentric core. Solving scalar waveguide equation in the helical coordinates we demonstrate that in such fibers topologically induced corrections to scalar propagation constants lead to convergence of spectral curves. At their intersection points a resonance coupling takes place between the fundamental and the vortex modes, as well as the coupling between OVs, whose topological charges differ by unity. This coupling leads to energy exchange between the coupled modes, which is manifested either in conversion of the input fundamental mode into an OV or transformation of an OV into the OV with higher by 1 (or lower, depending on core’s helicity) value of the topological charge. This effect can be used for creation of all-fiber generators of singular beams from regular input beams. We also study effect of ellipticity of the core’s form on transformation properties of HCFs and show that this leads to splitting of resonance fiber’s parameters, at which conversion of left and right circularly polarized input regular beams into OVs occurs. We prove that in long-period HCFs one can neglect this effect due to reduction of polarization mode dispersion in twisted fibers.

Precise potentials for the ground-state $X{}^1\Sigma _g^{+}$ and the minimum region of the excited state $2{}^1\Sigma _u^{+}$ of ${\mathrm{Sr}}_2$ are derived by high-resolution Fourier-transform spectroscopy of fluorescence progressions from single-frequency laser excitation of ${\mathrm{Sr}}_2$ produced in a heat pipe at $950°\mathrm{C}$. A change of the rotational assignment by four units compared to an earlier work [G. Gerber et al., J. Chem. Phys. 81, 1538 (1984)] is needed for a consistent description leading to a significant shift of the potentials toward longer interatomic distances. The huge amount of ground-state data derived for the three different isotopomers ${}^{88}\mathrm{Sr}_2$, ${}^{86}\mathrm{Sr}{}^{88}\mathrm{Sr}$, and ${}^{87}\mathrm{Sr}{}^{88}\mathrm{Sr}$ (almost 60% of all excisting bound rovibrational ground-state levels for the isotopomer ${}^{88}\mathrm{Sr}_2$) fixes this assignment beyond a doubt. The presented ground-state potential is derived from the observed transitions for the radial region from $4\text{to}11\mathrm{\AA }$ ($9{\mathrm{cm}}^{-1}$ below the asymptote) and is extended to the long-range region by the use of theoretical dispersion coefficients together with already available photoassociation data. New estimations of the scattering lengths for the complete set of isotopic combinations are derived by mass scaling with the derived potential. The data set for the excited state $2{}^1\Sigma _u^{+}$ was sufficient to derive a potential energy curve around the minimum.

Results from a joint experimental and theoretical investigation of electron-impact excitation of the $\left(5d^{10}6s\right){}^{2}S_{1∕2}\to \left(5d^{9}6s^2\right){}^{2}D_{5∕2,3∕2}$ transitions in gold atoms are presented. The relative experimental data are normalized to theoretical predictions obtained in a fully relativistic $B$-spline $R$-matrix (close-coupling) method. There is generally good agreement between the measured and predicted energy dependence of the integral cross section, although some discrepancies remain in the near-threshold maximum of the excitation function for the $\left(5d^{9}6s^2\right){}^{2}D_{3∕2}$ state.

Experimental data obtained with a high-resolution transmission experiment are presented for the scattering of electrons in the energy range $20\mathrm{meV}–10\mathrm{eV}$ for $\mathrm{N}{\mathrm{H}}_3$, $25\mathrm{meV}–10\mathrm{eV}$ for ${\mathrm{H}}_2\mathrm{S}$, and $15\mathrm{meV}–2.5\mathrm{eV}$ for OCS. Data include cross sections for both integral scattering and scattering into the backward hemisphere, the latter up to $650\mathrm{meV}$ impact energy, with an electron energy resolution of between 1.6 and $3.5\mathrm{meV}$. The new data allow the first detailed comparison with theory for the energy regime dominated by rotationally inelastic and elastic scattering for these species. It is evident that theory still lacks quantitative predictive power at low energy, although qualitative agreement is consistently good for all three species. A discussion is given of the possible presence of a virtual state in OCS scattering as recently proposed on theoretical grounds.

We study electromagnetic response functions for metallic surfaces with diffusive carrier transport. The electric field noise at a distance $z_0$ from the surface is evaluated and compared with data from ion chips that show anomalous heating with a noise power decaying as $z_0^{-4}$. We find that a layer of surface charge with strong diffusion can account for the latter result.

Critical intensities at which the strong field photodissociation rates of a molecule are vanishing could play an important role in control scenarios to filter a given vibrational state. We have previously shown [O. Atabek, R. Lefebvre, and F. Gadéa, Phys. Rev. A 74, 063412 (2006)] that there is a multiplicity of such intensities when the diabatic curve crossing point is on the left of the minimum of the attractive potential in a photon dressed picture ($c^{-}$ case). A semiclassical explanation was given. We complete this study of the multiple occurrence of zero-width resonances (ZWRs) by addressing, both numerically and semiclassically, the more common $c^{+}$ case of a crossing point on the right of the potential minimum. Coincidences between modified diabatic and adiabatic levels are the fingerprints of such events. They occur several times because the adiabatic energies are moving upward more rapidly than the diabatic ones. Advantage can be taken of the frequency dependence of the critical intensities to produce the phenomenon even for weak fields, this circumstance leading to more favorable control issues. This is illustrated on the example of ${\mathrm{H}}_2^{+}$. The wave functions associated with the ZWRs reflect the fact that the adiabatic picture is the best zeroth order description in the limit of high fields.

As is now well known, when an atom or molecule is ionized by an intense linearly polarized multicycle laser pulse, an electron wave packet is launched into the continuum at each half optical cycle and returns to the ion core several times, forming a train of attosecond electron bunches. In this paper, the possibility of controlling the relative proportion between the different electron bunches in the train using a two-harmonic multicycle laser field is demonstrated. This offers a highly promising method for disentangling the contribution of the different electron bunches to the electron-ion-recollision dynamics and eventually for probing ultrafast atomic or molecular dynamics.

We study the influence of off-resonant two-photon transitions on high-precision measurements with atom interferometers based on stimulated Raman transitions. These resonances induce a two-photon light shift on the resonant Raman condition. The impact of this effect is investigated in two highly sensitive experiments using a gravimeter and a gyroscope-accelerometer. We show that it can lead to significant systematic phase shifts, which have to be taken into account in order to achieve the best performances in terms of accuracy and stability.

In this paper, various extensions of the design strategy for transformation media are proposed. We show that it is possible to assign different transformed spaces to the field strength tensor (electric field and magnetic induction) and to the excitation tensor (displacement field and magnetic field), respectively. In this way, several limitations of standard transformation media can be overcome. In particular, it is possible to provide a geometric interpretation of nonreciprocal as well as indefinite materials. We show that these transformations can be complemented by a continuous version of electric-magnetic duality and comment on the relation to the complementary approach of field-transforming metamaterials.

We examine photonic crystals (PhC) made of periodic stacks of anisotropic dielectric layers with a split band edge (SBE) on the band diagram. Just below the band edge frequency, the dispersion relation $\omega \left(k\right)$ of SBE PhCs can be approximated as a linear combination of a quadratic term and a quartic term. This is in contrast to regular (conventional) band edge PhCs, which produce a quadratic dispersion relation, and to degenerate band edge (DBE) PhCs, which produce a quartic dispersion relation. Finite-size DBE PhCs and SBE PhCs are of interest because they both can support slow-wave Fabry-Perot resonances with very good transmittance. One of the most significant differences between DBE and SBE is that the transmittance of the former depends on the incident wave polarization whereas in the latter it does not. In this work, we investigate the transmittance behavior of SBE PhCs and perform a sensitivity analysis of their responses against geometrical and/or material perturbations. Dielectric losses, thickness perturbations, and misalignment angle perturbations are considered. The analysis uses a full-wave numerical technique for transient Maxwell’s equations in inhomogeneous anisotropic media based on a complex-envelope alternating-direction-implicit finite-difference time-domain. A comparison is also made between the sensitivity of the SBE PhCs response versus that of DBE PhCs.

The quantum Zeno effect for exponentially decaying systems predicted by Koshino Shimizu [Phys. Rev. Lett. 92, 030401 (2004)] is reexamined. A formula for the instantaneous decay rate reduced by the quantum Zeno effect is derived in the case of an exponentially decaying system. The present approach is based on the standard approaches in quantum optics: a master equation and a quantum Langevin equation. This approach provides a phenomenological interpretation of the Koshino-Shimizu model.

The effective Heisenberg interaction is generated by weakly interacting qubits with two strongly coupled chains. The system of two coupled chains can be regarded as a quantum bus. Universal quantum computation is enabled by restricting the bus to its ground state. The effective interaction is primarily determined by the energy spectrum of the bus. The interactions alternate between antiferromagnetic and ferromagnetic ones. The long-range interaction can also be attained in coupled chains with infinite size. The quantum gate operations with high precision can be realized when the quantum fluctuations are taken into account.

The Dirac hydrogen atom with spin symmetry is shown and has a SO(4) symmetry. The generators are derived, and the corresponding Casimir operator leads to the energy spectrum naturally. This type of hydrogen atom is connected to a four-dimensional Dirac system with equal scalar and vector harmonic oscillator potential by the Kustaanheimo-Stiefel transformation with a constraint.

Recent success in manipulating ultracold atomic systems allows one to probe different strongly correlated regimes in one dimension. Regimes such as the (spin-coherent) Luttinger liquid and the spin-incoherent Luttinger liquid can be realized by tuning the interatomic interaction strength and trap parameters. We identify the noise correlations of density fluctuations as a robust observable (uniquely suitable in the context of trapped atomic gases) to discriminate between these two regimes. Finally, we address the prospects of realizing and probing these phenomena experimentally using optical lattices.

In this paper we address the issue of universal or robust communication over quantum channels. Specifically, we consider a memoryless communication scenario with channel uncertainty which is an analog of the compound channel in classical information theory. We determine the quantum capacity of finite compound channels and arbitrary compound channels with an informed decoder. Our approach in the finite case is based on the observation that perfect channel knowledge at the decoder does not increase the capacity of finite quantum compound channels. As a consequence, we obtain a coding theorem for finite quantum averaged channels, the simplest class of channels with long-term memory. The extension of these results to quantum compound channels with uninformed encoder and decoder and infinitely many constituents remains an open problem.

Random quantum circuits take an input quantum state and randomize it. This is a task with a growing number of identified uses in quantum-information processing. We suggest a scheme to implement random circuits in a weighted graph state. The input state is entangled with the weighted graph state and a random circuit is implemented when the experimenter performs local measurements in one fixed basis only. The scheme uses no classical random numbers and is a new and natural application of weighted graph states.

Quantum-key-distribution (QKD) systems can send quantum signals over more than $100\mathrm{km}$ standard optical fiber and are widely believed to be secure. Here, we show experimentally a technologically feasible attack—namely, the time-shift attack—against a commercial QKD system. Our result shows that, contrary to popular belief, an eavesdropper, Eve, has a non-negligible probability $(\sim 4\%)$ to break the security of the system. Eve’s success is due to the well-known detection efficiency loophole in the experimental testing of Bell’s inequalities. Therefore, the detection efficiency loophole plays a key role not only in fundamental physics, but also in technological applications such as QKD systems.

We show how a quantum walk can be implemented in a quantum quincunx created via superconducting circuit quantum electrodynamics (QED) and how interpolation from a quantum to a random walk is implemented by controllable decoherence using a two-resonator system. Direct control over the coin qubit is difficult to achieve in either cavity or circuit QED, but we show that a Hadamard coin flip can be effected via direct driving of the cavity, with the result that the walker jumps between circles in phase space, but still exhibits quantum walk behavior over 15 steps.