Beams of helium atoms in selected Rydberg-Stark states with principal quantum number $n=52$ and electric dipole moments as large as 9910 D have been guided and deflected in the electrostatic fields surrounding surface-based electrical transmission lines. The guided atoms were detected by pulsed-electric-field ionization. Information on their position at the time of ionization was obtained from the flight time of the resulting ions to a microchannel plate detector. Comparison of the experimentally recorded data with the results of numerical calculations of particle trajectories through the guide highlight the sensitivity of the guided signal to the interaction of the atoms with each other and the surrounding 300 K blackbody radiation field.

We study the nonequilibrium steady state of the one-dimensional Bose-Hubbard model coupled to Lindblad reservoirs, using the density-matrix renormalization group in operator space. We observe a transition from a flat particle density profile in the noninteracting limit to the linearly increasing profile with onset of the interparticle interaction. Analyzing the effect of coherent pumping on the nonequilibrium steady state, we find a subspace which remains unaffected by the pumping in the noninteracting limit with the protection gradually diminishing due to interparticle interaction. In the equilibrium situation with one or more symmetric reservoirs, we show analytically that the steady state of the system is a product state for any interaction strength. We also provide analytical results in the noninteracting limits, using the method of the third quantization in operator space.

We propose a two-photon subwavelength interference scheme for classical light in which multiple quantum-like entangled two-photon paths play an essential role. These entangled two-photon paths are introduced through a specially designed source composed of many point sources $j$ with $j$'s complex amplitude being a superposition of modes $e^{i{\varphi }_j}$ and $e^{i{\varphi }_j^{\left(1\right)}}$, where ${\varphi }_j$ and ${\varphi }_j^{\left(1\right)}$ are temporally random phases but satisfying ${\varphi }_j+{\varphi }_j^{\left(1\right)}={\varphi }_0$, with ${\varphi }_0$ being either a constant or a random phase in time. Interference between the entangled two-photon paths could lead to second-order subwavelength interference of an object put in front of the source plane. In a proof-of-principle experiment, by using a spatial light modulator to modulate the wave front of a coherent light, we have generated such a source and observed subwavelength interference of a double-slit mask via two-photon measurement.

We theoretically study spectrum reversal and spectral-temporal similarity-and-inversion phenomena in nondegenerate four-wave mixing of ultrashort optical pulses. The key ingredients leading to spectrum reversal between two waves are identified, showing that energy conservation alone is insufficient. Only under certain conditions can the shapes of the two waves in the time and frequency domains possess special relations. Specifically, the two waves can have nearly identical temporal shapes, whereas their spectral shapes are reversed. In addition, the temporal and spectral shapes are the same for one wave and reversed for the other. However, non-negligible parasitic effects in ultrafast dynamics can breakup these relationships under more general conditions. The physical mechanisms underlying these phenomena are explored analytically and confirmed by direct numerical computations of the governing equations.

It is known that the Heisenberg and Robertson-Schrödinger uncertainty relations can be replaced by sharper relations in which the “classical” (depending on the gradient of the phase of the wave function) and “quantum” (depending on the gradient of the envelope of the wave function) parts of the variances $\langle {\left(\Delta x\right)}^2\rangle$ and $\langle {\left(\Delta p\right)}^2\rangle$ are separated. In this paper, multidimensional generalization of these relations is discussed.

We characterize a model of universal quantum computation where the register (computational) qubits are controlled by ancillary qubits, using only a single fixed interaction between register and ancillary qubits. No additional access is required to the computational register and the dynamics of both the register and ancilla are unitary. This scheme is inspired by the measurement-based ancilla-driven quantum computation of Anders et al.  [Phys. Rev. A 82, 020301(R) (2010)], but does not require measurements of the ancillas, and in this respect is similar to the original gate-based model of quantum computation. We consider what possible forms this ancilla-register interaction can take, with a proof that the interaction is necessarily locally equivalent to swap combined with an entangling controlled gate. We further show which Hamiltonians can create such interactions and discuss two examples; the two-qubit XY Hamiltonian and a particular case of the XXZ Hamiltonian. We then give an example of a simple, finite, and fault-tolerant gate set for universal quantum computation in this model.

Time-dependent density-functional methods are used to compute excitation energies and, via the adiabatic-connection fluctuation-dissipation theorem, ground-state correlation energies of atoms, ions, and the H${}_2$ molecule at various bond lengths. Various exchange-correlation potentials $v_{xc}$ and exchange-correlation kernels $f_{xc}$ are tested. Accurate exchange-correlation potentials are found to be essential for getting accurate energies. Methods employing in the Kohn-Sham self-consistency process the exact local Kohn-Sham exchange potential while neglecting completely the correlation potential lead to better excitation and correlation energies than methods with exchange-correlation potentials within the local density approximation or the generalized gradient approximation. Taking into account the exact exchange-correlation potential and thus the exact Kohn-Sham potential further improves excitation and correlation energies.

In the present work we are reporting detailed quantum scattering calculations that describe the diffusion of a beam of low-energy positrons interacting with the pyrimidine target as a gas-phase partner. The calculations have employed an essentially ab initio model for the short-range correlation interaction and for the electrostatic interaction of an impinging positron and the electron+nuclear structure of the target molecule at its equilibrium geometry. The available experiments were also performed in the low-energy region below about 30 eV and have been reported by two different experimental groups cited in the main text. Those data include integral elastic plus rotationally and vibrationally summed cross sections, together with angular distributions over the same range of energies. The effects on the scattering observables which stem from the permanent dipole moment of the title molecule are carefully analyzed and computational corrections which ensure numerical convergence are introduced and discussed. The additional uncertainties introduced by the angular discrimination error present in the experiments are also discussed and analyzed, thereby providing a numerical procedure for correcting all available data. The final comparison between experimental angular distributions and the computed counterparts produced in the present work turns out to be very good. The same applies to the comparison in size and energy dependence of the integral cross sections, where we show that our calculated quantities and the corrected experiments are in very good agreement over the whole range of available energies.

We demonstrate theoretically the existence of one-way photonic band gaps, i.e., gaps which are experienced by electromagnetic waves impinging on a particular face of a finite photonic-crystal slab. These one-way photonic band gaps emerge in the absence of magnetic fields, as it is the case in magnetophotonic crystals, but they result from the low symmetry of the photonic crystal such as the monoclinic photonic crystal considered here, which possesses a single mirror plane. We report the existence of one-way frequency band gaps, which may span over extended regions of the Brillouin zone and can find application in photovoltaics by trapping light in properly designed multilayered structures.

The inherent connection between noise and disturbance is one of the most fundamental features of quantum measurements. In the two well-known extreme cases a measurement either makes no disturbance but then has to be totally noisy or is as accurate as possible but then has to disturb so much that all subsequent measurements become redundant. Most of the measurements are, however, somewhere between these two extremes. We derive a structural connection between certain order relations defined on observables and channels, and we explain how this connection properly explains the trade-off between noise and disturbance. A link to a quantitative noise-disturbance relation is demonstrated.

Based on the second-order perturbation theory, we investigate the two-photon decay of $K$-shell vacancies in heavy atoms. The many-electron transition amplitude that occurs in the theory is evaluated by means of the independent particle approximation (IPA). By using this approach, computations are performed for the decay of neutral gold and are directly compared with recent experimental data, not relying on any scaling assumptions. The obtained results confirm previously identified discrepancies between the IPA theory and the experiment for the $2s\to 1s$ transition, and an apparent “resonance” region of the $3s\to 1s$ transition, but they show a moderate agreement with the measured data for the $3d\to 1s$ and $4s+4d\to 1s$ cases. Moreover, with the help of the IPA we discuss the validity of the nonrelativistic scaling that was employed in the past to estimate the relative two-photon transition probabilities $P$ in heavy atoms based on calculations done for lighter elements and different decay geometries. We find, in particular, that the electric-dipole angular distribution of emitted photons holds rather well even in the high-$Z$ domain, while the assumption that the relative probability $P$ is independent of nuclear charge may result in 10–30% inaccuracy of theoretical predictions.

The momentum distribution of the electron in the reaction $p$ $+$ He $\to$ H $+$ He${}^{2+}$ $+$ $e$ is measured for projectile energies $E_p=300$ and 630 keV/u at very small scattering angles of the hydrogen. We present two-dimensional distributions parallel $\left(k_{\parallel }\right)$ and perpendicular $\left(k_{\perp }\right)$ to the projectile beam as well as distributions $k_{\parallel }$ for fixed $k_{\perp }$. Theoretical calculations were carried out within the plane wave first Born approximation, which includes both mechanisms of the electron emission, namely, the shake-off and the sequential capture and ionization. It is shown that electron correlations in the initial ground-state wave function of the target play the most important role in the explanation of the experimentally observed enhanced backward electron emission.

We report the generation of a squeezed vacuum state of light whose noise ellipse rotates as a function of the detection frequency. The squeezed state is generated via a four-wave mixing process in a vapor of ${}^{85}$Rb. We observe that rotation varies with experimental parameters such as pump power and laser detunings. We use a theoretical model based on the Heisenberg-Langevin formalism to describe this effect. Our model can be used to investigate the parameter space and potentially to tailor the ellipse rotation in order to obtain an optimum squeezing angle, for example, for coupling to an interferometer whose optimal noise quadrature varies with frequency.

We establish a universal complementarity relation between the capacity of classical information transmission by employing a multiparty quantum state as a multiport quantum channel, and the corresponding genuine multipartite entanglement. The classical information transfer is from a sender to several receivers by using the quantum dense coding protocol with the multiparty quantum state shared between the sender and several receivers. The relation is derived when the multiparty entanglement is the relative entropy of entanglement as well as when it is the generalized geometric measure. The relation holds for arbitrary pure or mixed quantum states of an arbitrary number of parties in arbitrary dimensions.

The full-core-plus-correlation method (FCPC) is extended to calculate the energies and fine structures of 1$s^{2}nd$ and 1$s^{2}nf$ ($n\le 5$) states for the lithiumlike systems with high nuclear charge from $Z$ $=$ 41 to 50. In calculating energy, the higher-order relativistic contribution is estimated under a hydrogenic approximation. The nonrelativistic energies and wave functions are calculated by the Rayleigh-Ritz method. The mass polarization and the relativistic corrections including the kinetic energy correction, the Darwin term, the electron-electron contact term, and the orbit-orbit interaction are calculated perturbatively as the first-order correction. The quantum-electrodynamics contributions to the energy and to the fine-structure splitting are estimated by using the effective nuclear charge formula. The excited energies, the fine structures, and other relevant term energies are given and compared with the data available in the literature.

The dissociation of D${}_2$${}^{+}$ in the few-cycle UV and THz light pulses is studied by numerically simulating the time-dependent Schrödinger equation. With only the UV pulse, we find the dissociation probability does not increase monotonously with the increasing of the UV pulse intensity or duration. The UV-triggered dissociation is streaked by the time-delayed THz light pulse, i.e., the nuclear momentum oscillates with the half of the THz period when the UV-THz time delay or the carrier envelope phase of the THz pulse is scanned. The difference of the maximum and minimum nuclear momenta equals the THz laser vector potential. The classical calculation of the Newtonian equation for a mass point moving on the THz light-modified molecular potential curves reproduces the quantum simulation results and therefore intuitively explores the physical scenario: The nuclear wave packets propagate along the THz field-dressed molecular potential curves adiabatically but make a fully diabatic transition, while the THz electric field changes direction. This study offers a visual angle to understand the molecular dissociation in the strong laser field with very long wavelengths.

A simple theory for the tunneling of two cold atoms out of a trap in the presence of an attractive contact force is developed. Two competing decay channels, for single-atom and bound-pair tunneling, respectively, contribute independently to the decay law of the mean atom number in the trap. The single-atom tunneling rate is obtained through the quasiparticle wave function formalism. For pair tunneling an effective equation for the center-of-mass motion is derived, so the calculation of the corresponding tunneling rate is again reduced to a simpler one-body problem. The predicted dependence of tunneling rates on the interaction strength qualitatively agrees with a recent measurement of the two-atom decay time [G. Zürn, A. N. Wenz, S. Murmann, T. Lompe, and S. Jochim, arXiv:1307.5153].

We report the anomalous D'yakonov-Perel' spin relaxation in ultracold spin-orbit-coupled ${}^{40}$K gas when the coupling between $|9/2,9/2\rangle$ and $|9/2,7/2\rangle$ states, acting as an effective Zeeman magnetic field, is much stronger than the spin-orbit coupled field. Both the transverse and longitudinal spin relaxations are investigated with small and large spin polarizations. It is found that with small spin polarization, the transverse (longitudinal) spin relaxation is divided into four (two) regimes: the normal weak scattering regime, the anomalous D'yakonov-Perel'-like regime, the anomalous Elliott-Yafet-like regime, and the normal strong scattering regime (the anomalous Elliott-Yafet-like regime and the normal strong scattering regime). With large spin polarization, we find that the Hartree-Fock self-energy, which acts as an effective magnetic field, can markedly suppress the transverse spin relaxation in both weak and strong scattering limits. Moreover, by noting that as both the momentum relaxation time and the Hartree-Fock effective magnetic field vary with the scattering length in cold atoms, the anomalous D'yakonov-Perel'-like regime is suppressed and the transverse spin relaxation is hence divided into three regimes in the scattering length dependence: the normal weak scattering regime, the anomalous Elliott-Yafet-like regime, and the strong scattering regime. On the other hand, the longitudinal spin relaxation is again divided into the anomalous Elliott-Yafet-like and normal strong scattering regimes. Furthermore, it is found that the longitudinal spin relaxation can be either enhanced or suppressed by the Hartree-Fock effective magnetic field if the spin polarization is parallel or antiparallel to the effective Zeeman magnetic field.

We discuss an optical “cloaking” scheme using three-level active Raman gain media in tandem in the presence of a spatially distributed pump field. Using eikonal approximation we first derive analytically the deflection angle and show that the trajectory of light can be controlled dynamically using a spatially distributed pump. We further show an excellent agreement of analytical results with a full numerical calculation of the Maxwell equation for the probe field propagating across regions where an object is embedded. Our results show that the probe light travels around the object under detection, achieving the desired spatial cloaking of the object.

Recent progress in cooling and trapping of polarized clouds of chromium ${}^{52}\text{Cr}$, dysprosium ${}^{164}\text{Dy}$, and erbium ${}^{168}\text{Er}$ opens a roadmap to quantum systems where the shapes of interparticle interactions can be customized. The main purpose of this work is to get deeper insight into the role the overall shape of the interparticle interaction plays in the context of trapped ultracold bosons. We show that strong interparticle repulsion inevitably leads to multihump fragmentation of the ground state. The fragmentation phenomenon is universal—it takes place in traps of different dimensionalities and topologies and for very broad classes of repulsive interparticle potentials. The physics behind this is identified and explained.