Double resonance spectroscopy via the $EF{}^1\Sigma _g^{+},{\nu }_{EF}^{\prime }=6,J^{\prime }$ state has been used to probe the rovibrational structure of the ungerade double-well $B^{″}\overline{B}$ ${}^1\Sigma _u^{+}$ state of ${\mathrm{H}}_2$. Transitions to the $B^{″}\overline{B}{}^1\Sigma _u^{+},{\nu }_{\overline{B}}=17-35,J=0-4$ levels of the outer-well and to the ${\nu }_{B^{″}\overline{B}}=46-50,J=0-4$ levels of the combined inner and outer wells above the barrier have been recorded by detecting both molecular and atomic ion production as a function of energy by using a time of flight mass spectrometer. Theoretical energy calculations incorporating the most recent potential curves have been used to aid in the assignment of observed transitions. Over 70 new rovibrational term energies are reported. Where comparisons are possible, good agreement is observed between the experimental measurements reported here and those of previous measurements. While significant perturbations are observed in the energy region above the double-well barrier, assignments to states with dominant inner and outer-well characteristics can still be made. Distinct dynamical behaviors of the levels below, at, and above the barrier have also been observed.

We report precision measurements of the excited state lifetime of the $5p$ ${}^{2}P_{1∕2}$ and $5p$ ${}^{2}P_{3∕2}$ levels of a single trapped ${\mathrm{Cd}}^{+}$ ion. Combining ion trap and ultrafast laser technologies, the ion is excited with picosecond laser pulses from a mode-locked laser and the distribution of arrival times of spontaneously emitted photons is recorded. The resulting lifetimes are $3.148\pm 0.011\mathrm{ns}$ and $2.647\pm 0.010\mathrm{ns}$ for ${}^{2}P_{1∕2}$ and ${}^{2}P_{3∕2}$ respectively. With a total uncertainty of under 0.4%, these are among the most precise measurements of any atomic state lifetimes to date.

We report on coherent control of excitation processes of translationally ultracold rubidium dimers in a magneto-optical trap by using shaped femtosecond laser pulses. Evolution strategies are applied in a feedback loop in order to optimize the photoexcitation of the ${\mathrm{Rb}}_2$ molecules, which subsequently undergo ionization or fragmentation. A superior performance of the resulting pulses compared to unshaped pulses of the same pulse energy is obtained by distributing the energy among specific spectral components. The demonstration of coherent control to ultracold ensembles opens a path to actively influence fundamental photoinduced processes in molecular quantum gases.

We present an analytical model for a cold bosonic gas on an optical lattice (with densities of the order of 1 particle per site), targeting the critical regime of the Bose-Einstein-condensate superfluid–Mott-insulator transition. We focus on the computation of the one-body density matrix and its Fourier transform, the momentum distribution which is directly obtainable from “time-of-flight” measurements. The expected number of particles with zero momentum may be identified with the condensate population if it is close to the total number of particles. Our main result is an analytic expression for this observable, interpolating between the known results valid for the two regimes separately: the standard Bogoliubov approximation valid in the superfluid regime and the strong-coupling perturbation theory valid in the Mott regime.

We perform a theoretical investigation of the polarization dynamics in a vertical-cavity surface-emitting laser (VCSEL) subject to orthogonal optical injection, i.e., the injected field has a linear polarization (LP) orthogonal to that of the free-running VCSEL. In agreement with previous experiments [Z. G. Pan et al., Appl. Phys. Lett. 63, 2999 (1993)], an increase of the injection strength may lead to a polarization switching accompanied by an injection locking. We find that this route to polarization switching is typically accompanied by a cascade of bifurcations to wave-mixing dynamics and time-periodic and possibly chaotic regimes. A detailed mapping of the polarization dynamics in the plane of the injection parameters (detuning, injection strength) unveils a large richness of dynamical scenarios. Of particular interest is the existence of another injection-locked solution for which the two LP modes both lock to the master laser frequency, i.e., an elliptically polarized injection-locked (EPIL) steady state. Modern continuation techniques allow us to unveil an unfolding mechanism of the EPIL solution as the detuning varies and also to link the existence of the EPIL solution to a resonance condition between the master laser frequency and the free-running frequency of the normally depressed LP mode in the slave laser. We furthermore report an additional case of bistability, in which the EPIL solution may coexist with the second injection-locked solution (the one being locked to the master polarization). This case of bistability is a result of the interaction between optical injection and the two-polarization-mode characteristics of VCSEL devices.

Numerical simulations of the grazing-incidence pumped Ni-like Pd x-ray laser at $14.7\mathrm{nm}$ ($4d\to 4p$, $J=0\to 1$) is performed using a modified one-dimensional hydrodynamic code MEDUSA. The effective absorption of the main laser pulse in the gain region is greatly increased due to the lengthened propagation path. Results predict that a saturated output of the x-ray laser can be achieved with only subjoules driver energy on a $4\text{−}\mathrm{mm}$-long Pd target.

An elementary proof is given of the bound on “orthogonalization time” $t_0⩾\pi \hslash ∕2\Delta E$.

We propose a scheme to create an effective magnetic field for ultracold atoms in a planar geometry. The setup allows the experimental study of classical and quantum Hall effects in close analogy to solid-state systems including the possibility of finite currents. The present scheme is an extention of the proposal in Phys. Rev. Lett. 93, 033602 (2004), where the effective magnetic field is now induced for three-level $\Lambda$-type atoms by two counterpropagating laser beams with shifted spatial profiles. Under conditions of electromagnetically induced transparency the atom-light interaction has a space-dependent dark state, and the adiabatic center-of-mass motion of atoms in this state experiences effective vector and scalar potentials. The associated magnetic field is oriented perpendicular to the propagation direction of the laser beams. The field strength achievable is one flux quantum over an area given by the transverse beam separation and the laser wavelength. For a sufficiently dilute gas the field is strong enough to reach the lowest Landau level regime.

General Trojan-horse attacks on quantum-key-distribution systems, i.e., attacks on Alice or Bob’s system via the quantum channel, are analyzed. We illustrate the power of such attacks with today’s technology and conclude that all systems must implement active counter measures. In particular, all systems must include an auxiliary detector that monitors any incoming light. We show that such counter measures can be efficient, provided that enough additional privacy amplification is applied to the data. We present a practical way to reduce the maximal information gain that an adversary can gain using Trojan-horse attacks. This does reduce the security analysis of the two-way plug-and-play implementation to those of the standard one-way systems.

Entanglement concentration can be achieved in a deterministic fashion [Morikoshi, Phys. Rev. Lett. 84, 3189 (2000); Phys. Rev. A 64, 022316 (2001)]. We present a protocol for deterministic extraction of an Einstein-Podolsky-Rosen pair from two partially entangled pairs via local operations and classical communication. This protocol consists of a generalized measurement described by a positive operator-valued measure (POVM), one-way classical communication, and a corresponding unitary operation or a choice between the two pairs. Based on the theory of majorization, we explicitly construct the required POVM, which can be realized by performing a unitary operation in the extended space and a conventional Von Neuman orthogonal measurement. By decomposing the evolution process from the initial state to the final state, we construct the quantum circuits for realizing the unitary operation with quantum Toffoli gates, and thus provide a physical means to realize the deterministic entanglement concentration. Our method for constructing quantum circuits differs from the usual method based on decomposition of unitary matrices, and is convenient for a large class of quantum processes involving generalized measurements.

Given an ensemble of $n$ spins, at least some of which are partially polarized, we investigate the sharing of this polarization within a subspace of $k$ spins. We assume that the sharing results in a pseudopure state, characterized by a single purity parameter which we call the bias. As a concrete example we consider ensembles of spin-$1∕2$ nuclei in liquid-state nuclear magnetic resonance systems. The shared bias levels are compared with some current entanglement bounds to determine whether the reduced subspaces can give rise to entangled states.

The ionization rates of the electron-impact ionization and dissociative ionization of ethylene for two typical cases: thermal plasmas with an electron temperature in the range between 1000 and $24000\mathrm{K}$; and nonthermal plasmas with the reduced electric field in the range between 10 and $200\mathrm{Td}$ are presented. Electron-impact dissociative ionization rates were calculated for 11 fragment ions of ethylene in the case of low temperature thermal plasma, and in a case of nonthermal ionized mixture of argon and ethylene. Dissociative ionization cross sections were calculated using a semiempirical binary-encounter bethe (BEB) model [Y. K. Kim and M. E. Rudd, Phys. Rev. A 50, 3954 (1994)], with each of the four most dominant fragments, ${\mathrm{C}}_2\mathrm{H}_4{}^{+}$, ${\mathrm{C}}_2\mathrm{H}_3{}^{+}$, ${\mathrm{C}}_2\mathrm{H}_2{}^{+}$, and ${\mathrm{H}}^{+}$, being associated with a single molecular orbital. Calculated cross sections are used in this analysis due to the fact that the existing experimental data are the least accurate in the threshold region and the calculated results can improve the accuracy in that region. Also, the procedure may be extended to molecules for which experimental data are not available.

We study a model for a two-mode atomic-molecular Bose-Einstein condensate. Starting with a classical analysis we determine the phase space fixed points of the system. It is found that bifurcations of the fixed points naturally separate the coupling parameter space into four regions. The different regions give rise to qualitatively different dynamics. We then show that this classification holds true for the quantum dynamics.

Recent adaptive feedback control experiments demonstrated control of transient (i.e. nonimpulsive) Stokes emission from two closely spaced Raman-active modes in liquid methanol [e.g., B. J. Pearson et al., Phys. Rev. A 63, 063412 (2001)]. Optimally shaped pulses were found that selectively excited one of the two Stokes lines alone, optimized emission from both modes together, or completely suppressed all Stokes emission. Here, two general control mechanisms capable of affecting the ratio of intensities of the Stokes lines are identified. The first is operational when the duration of the pump pulse $\left(t_p\right)$ is on the order of the collisional dephasing time $\left(t_d\right)$. The ratio of the peak heights of the two Stokes lines can then be controlled by simply varying the duration and/or intensity of the pump pulse. The second operates when $1∕t_p$ is on the order of the energy separation of the two Raman modes, and hence when the two Raman modes are coupled due to overlapping nonlinear polarizations that drive the stimulated Raman scattering. In this regime, asymmetry in the spectral amplitudes within the pump pulse can control the asymmetry in the peak heights of the Stokes emission. Both these mechanisms have the same clear physical interpretation: shaping the pump pulse controls the nonlinear optical response of the medium, which in turn controls the stimulated Stokes emission, itself a ${\chi }^{\left(3\right)}$ nonlinear effect. In neither mechanism does the ratio of peak heights in the Stokes spectrum reflect directly the ratio of excited-state populations associated with the two Raman modes, as was assumed in the experiments, nor does the control involve coherent quantum interference effects.

Experimental results on adaptive feedback control of transient (i.e., nonimpulsive) Stokes emission in liquid methanol [Pearson and Bucksbaum, Phys. Rev. Lett. 92, 243003 (2004)] are analyzed. In the experiment, a pump pulse comprising two frequency-shifted Gaussian pulses was used to control the ratio of two Stokes emission lines by varying the relative phase ${\varphi }_L$ between the pulses. Extending the theory of stimulated Raman scattering to accommodate two coupled levels, we show that control of this type is possible, in the strongly driven regime, using Raman coupling alone. Control via variation of ${\varphi }_L$ is shown to also result from self- and cross-phase-modulation of the pump and Stokes pulses as well as via the focused-beam geometry of the pump pulse. In all cases, the general control mechanism is nonlinear optical modulation between the pump and the Stokes pulse; no coherent quantum interference effects are involved. Finally, although the vibrational populations are affected by the same control mechanisms that affect the Stokes spectra, the ratio of the Stokes spectra peak heights does not directly reflect the ratio of the level populations, as was assumed in the experiment.

The mean excitation energy (the Bethe logarithm) is calculated for the lowest rotational (up to $L=4$) and vibrational (up to $v=4$) states of the hydrogen molecular ion ${{\mathrm{H}}_2}^{+}$. The calculations are based on a method of the direct integration over photon momenta. The estimated accuracy of obtained values is about ${10}^{-6}$. The Araki-Sacher $Q$ term is computed as well, which allows us to evaluate the leading order ${\alpha }^3$ radiative correction to the rovibrational energies of the hydrogen molecular ion.

We consider atomic mixtures of bosons and two-component fermions in an optical lattice potential. We show that if the bosons are in a Mott-insulator state with precisely one atom per lattice, the photoassociation of bosonic and fermionic atoms into heteronuclear fermionic molecules is described by the Anderson lattice model. We determine the ground-state properties of an inhomogeneous version of that model in the strong atom-molecule coupling regime, including an additional harmonic trap potential. Various spatial structures arise from the interplay between the atom-molecule correlations and the confining potential. Perturbation theory with respect to the tunneling coupling between fermionic atoms shows that antiferromagnetic correlations develop around a spin-singlet core of fermionic atoms and molecules.

We analyze reduced fringe visibilities and decoherence effects in two-center interference experiments involving photon scattering and trapped-ion and atom interferometry. We introduce an impulse approximation to analyze the resulting photon-atom momentum entanglement. We find that the simple decoherence due to photon scattering of double-humped center-of-mass states of a single trapped ion strongly resembles that observed in atom interferometry.

We study the phenomenon of wave-packet revivals of Bloch electrons and explore how to control them by a magnetic field for quantum-information transfer. It is shown that the single electron system can be modulated into a linear dispersion regime by the “quantized” flux and then an electronic wave packet with the components localized in this regime can be transferred without spreading. This feature can be utilized to perform the high-fidelity transfer of quantum information encoded in the polarization of the spin. Beyond the linear approximation, the relocalization and self-interference occur as the interesting phenomena of quantum coherence.

We propose a mechanism to interface a transmission line resonator (TLR) with a nanomechanical resonator (NAMR) by commonly coupling them to a charge qubit, a Cooper-pair box with a controllable gate voltage. Integrated in this quantum transducer or simple quantum network, the charge qubit plays the role of a controllable quantum node coherently exchanging quantum information between the TLR and NAMR. With such an interface, a quasiclassical state of the NAMR can be created by controlling a single-mode classical current in the TLR. Alternatively, a “Cooper pair” coherent output through the transmission line can be driven by a single-mode classical oscillation of the NAMR.