We examine the attosecond electron recollision dissociation of $\mathrm{D}_2{}^{+}$ recently demonstrated experimentally [H. Niikura et al., Nature (London) 421, 826 (2003)] from a coherent control perspective. In this process, a strong laser field incident on ${\mathrm{D}}_2$ ionizes an electron, accelerates the electron in the laser field to eV energies, and then drives the electron to recollide with the parent ion, causing $\mathrm{D}_2{}^{+}$ dissociation. A number of results are demonstrated. First, a full dimensional strong field approximation model is constructed and shown to be in agreement with the original experiment. This is then used to rigorously demonstrate that the experiment is an example of coherent pump-dump control. Second, extensions to bichromatic coherent control are proposed by considering dissociative recollision of molecules prepared in a coherent superposition of vibrational states. Third, by comparing the results to similar scenarios involving field-free attosecond scattering of independently prepared $\mathrm{D}_2{}^{+}$ and electron wave packets, recollision dissociation is shown to provide an example of wave-packet coherent control of reactive scattering. Fourth, this analysis makes clear that it is the temporal correlations between the continuum electron and $\mathrm{D}_2{}^{+}$ wave packet, and not entanglement, that are crucial for the subfemtosecond probing resolution demonstrated in the experiment. This result clarifies some misconceptions regarding the importance of entanglement in the recollision probing of $\mathrm{D}_2{}^{+}$. Finally, signatures of entanglement between the recollision electron and the atomic fragments, detectable via coincidence measurements, are identified.

We present an analysis of the quantum state resulting from the dissociation of diatomic molecules prepared in a condensate vortex state. The many-body state preserves the rotational symmetry of the system in quantum correlated states by having two equally populated components with angular momentum adding to unity. A simple two-mode analysis and a full quantum field analysis are presented for the case of noninteracting atoms and weak depletion of the molecular condensate.

The two- and three-body correlation functions of the ground state of an optically trapped ultracold spin-$\frac{1}{2}$ Fermi gas (SFG) in a tight waveguide [one-dimensional (1D) regime] are calculated in the plane of even- and odd-wave coupling constants, assuming a 1D attractive zero-range odd-wave interaction induced by a 3D $p$-wave Feshbach resonance, as well as the usual repulsive zero-range even-wave interaction stemming from 3D $s$-wave scattering. The calculations are based on the exact mapping from the SFG to a “Lieb-Liniger-Heisenberg” model with delta-function repulsions depending on isotropic Heisenberg spin-spin interactions, and indicate that the SFG should be stable against three-body recombination in a large region of the coupling constant plane encompassing parts of both the ferromagnetic and antiferromagnetic phases. However, the limiting case of the fermionic Tonks-Girardeau gas, a spin-aligned 1D Fermi gas with infinitely attractive $p$-wave interactions, is unstable in this sense. Effects due to the dipolar interaction and a Zeeman term due to a resonance-generating magnetic field do not lead to shrinkage of the region of stability of the SFG.

We report the use of a preionized medium created by a capillary discharge to extend the cutoff photon energy in high-order harmonic generation. The observed enhancements result from a combination of reduced ionization energy loss and reduced ionization-induced defocusing of the driving laser. We observe harmonic emission from Xe up to a photon energy of $160\mathrm{eV}$, and we extend this technique to other noble gases, observing photons with energies up to $170\mathrm{eV}$ from Kr and $275\mathrm{eV}$ from Ar. The discharge plasma also provides a means to spectrally tune the harmonics by tailoring the initial level of ionization of the medium. Our results are interpreted using a hydrodynamic-atomic physics model of the discharge plasma. This work demonstrates that capillary discharges are a versatile and general method for generating harmonics, in particular from ions. Finally, this approach should be scalable to efficiently generate coherent light at much shorter wavelengths, in combination with phase-matching techniques.

Close to converged energies and expectation values for $e^{+}\mathrm{PsH}$ are computed using a ground-state wave function consisting of 1500 explicitly correlated Gaussians. The best estimate of the $e^{+}{\mathrm{PsH}}^{\infty }$ energy was $-0.810254\text{hartrees}$, which has a binding energy of $0.021057\text{hartrees}$ against dissociation into $e^{+}+\mathrm{PsH}$. The $2\gamma$ annihilation rate was $2.7508\times {10}^9{\mathrm{s}}^{-1}$. Binding energies and annihilation rates are also given for the different finite-mass variants of $e^{+}\mathrm{PsH}$. Comparisons between expectation values for $e^{+}\mathrm{PsH}$ and PsH provide compelling evidence that the $e^{+}\mathrm{PsH}$ ground state can be regarded as consisting of a weakly bound positron orbiting the PsH ground state.

We present a method to derive explicit forms of tight correlation-function Bell inequalities for three systems and dichotomic observables, which involve three settings for each observer. We also give sufficient and necessary conditions for quantum predictions to satisfy the new inequalities.

In this paper, we propose and study a hybrid mechanism for coherent transmission of photons in the coupled resonator optical waveguide (CROW) by incorporating the electromagnetically induced transparency (EIT) effect into the controllable band gap structure of the CROW. Here, the configuration setup of system consists of a CROW with homogeneous couplings and the artificial atoms with $\Lambda$-type three levels doped in each cavity. The roles of three levels are completely considered based on a mean field approach where the collection of three-level atoms collectively behave as two-mode spin waves. We show that the dynamics of low excitations of atomic ensemble can be effectively described by a coupling boson model. The exact solutions show that the light pulses can be stopped and stored coherently by adiabatically controlling the classical field.

We report on the generation of broadband pulsed quadrature entanglement by combining two squeezed vacua, which are generated from two degenerate optical parametric amplifiers (OPAs), on a beam splitter. With a single pass through OPA, in which a periodically poled lithium niobate waveguide is used as a nonlinear material, the noise reduction of $3.4\pm 0.2$ dB below the shot noise limit is observed with a bandwidth of more than 200 MHz. The entanglement correlation or EPR correlation is confirmed with a sufficient criterion $⟨{\Delta }^2(X_a+X_b)⟩+⟨{\Delta }^2(Y_a-Y_b)⟩=1.28<2$.

We investigated the elastic scattering problem with deformed Heisenberg algebra leading to the existence of a minimal length. The continuity equations for the moving particle in deformed space were constructed. We obtained the Green’s function for a free particle, the scattering amplitude, and the cross section in deformed space. We also calculated the scattering amplitudes and differential cross sections for the Yukawa and the Coulomb potentials in the Born approximation.

Several theoretical models are used to explain the origin of the recently observed (unexpected) spectral progression in the Coulomb explosion spectra of the hydrogen molecule photoionized by an intense ultrashort laser pulse. In the first ionization step the molecule loses its first electron and then the $\mathrm{H}_2{}^{+}$ molecular ion dissociates. Next, at the intermediate stage of the dissociation process, a localized electron state is created from which the second ionization occurs at each laser half-cycle. It is shown that interference between a net-two-photon and a one-photon transition introduces a dynamic structure into the nuclear wave packet corresponding to this localized electron state which leads to the regular spectral progressions seen in the experiment. We confirm these spectral progressions using numerical simulations based on a time-dependent Schrödinger equation describing the exact three-body dynamics of $\mathrm{H}_2{}^{+}$ in one dimension.

We develop a semiclassical field method for the study of the weakly interacting Bose gas at finite temperature which, contrary to the usual classical field model, does not suffer from an ultraviolet cutoff dependence. We apply the method to the study of thermal vortices in spatially homogeneous, two-dimensional systems. We present numerical results for the vortex density and the vortex pair distribution function. Insight in the physics of the system is obtained by comparing the numerical results with the predictions of simple analytical models. In particular, we calculate the activation energy required to form a vortex pair at low temperature.

Coherent Stark nonlinear spectroscopy (CSNS) is a spectroscopic tool based on the cancellation of the phase sensitivity at frequency $5\omega$ in the ultrafast four-wave mixing (FWM) of two-color pulses with frequencies $\omega$ and $3\omega$. We develop a theory for CSNS in three-level V-type systems, and reveal that the mechanism for the phase sensitivity at $5\omega$ is the quantum interference between the two primary paths in the FWM of the $\omega$ and $3\omega$ fields. We find that the cancellation phenomenon occurs when the probability amplitude of one of these two primary pathways becomes equal to zero due to the competition effect between the two allowed transitions in the V-type system. The analytical expressions that describe the phase-sensitivity phenomenon and the conditions for its cancellation have been derived on the basis of perturbation theory, and are confirmed by numerical integration of the density matrix and Maxwell equations. We argue that CSNS can be utilized, in particular, for the investigation of optically dense media.

To beat photon-number splitting attack, decoy state quantum key distribution (QKD) based on the coherent state has been studied widely. We present a decoy state QKD protocol with a modified coherent state (MCS). By destructive quantum interference, a MCS with fewer multiphoton events can be obtained, which may improve the key bit rate and security distance of QKD. Through numerical simulation, we show about a 2-dB increment on the security distance for Bennett-Brassard (1984) protocol.

The Schrödinger-Robertson inequality generally provides a stronger bound on the product of uncertainties for two noncommuting observables than the Heisenberg uncertainty relation, and as such it can yield a stricter separability condition in conjunction with partial transposition. In this paper, using the Schrödinger-Robertson uncertainty relation, the separability condition previously derived from the su(2) and su(1,1) algebra is made stricter and refined to a form invariant with respect to local phase shifts. Furthermore, a linear optical scheme is proposed to test this invariant separability condition.

We investigate the Bose-Einstein condensation of fermionic pairs in a two-dimensional uniform two-component Fermi superfluid obtaining an explicit formula for the condensate density as a function of the chemical potential and the energy gap. By using the mean-field extended Bardeen-Cooper-Schrieffer theory, we analyze, as a function of the bound-state energy, the off-diagonal long-range order in the crossover from the Bardeen-Cooper-Schrieffer state of weakly bound Cooper pairs to the Bose-Einstein condensate of strongly-bound molecular dimers.

In their recent paper [Phys. Rev. A 71, 033622 (2005)], Seaman et al. studied Bloch states of the condensate wave function in a Kronig-Penney potential and calculated the band structure. They argued that the effective mass is always positive when a swallowtail energy loop is present in the band structure. In this Comment, we reexamine their argument by actually calculating the effective mass. It is found that there exists a region where the effective mass is negative even when a swallowtail is present. Based on this fact, we discuss the interpretation of swallowtails in terms of superfluidity.

In response to Danshita and Tsuchiya’s comment on our work on nonlinear band theory, we show that the size of the region of the swallowtail with a negative effective mass is inversely proportional to the interaction strength, i.e., for large interaction strengths, the region becomes negligibly small. We explain why the appearance of swallowtails is not related to superfluidity, but instead to a more universal nonlinear feature valid for both signs of the underlying atomic interactions: period doubling.

We investigate the effects of a nearly uniform Bose-Einstein condensate (BEC) on the properties of immersed trapped impurity atoms. Using a weak-coupling expansion in the BEC-impurity interaction strength, we derive a model describing polarons, i.e., impurities dressed by a coherent state of Bogoliubov phonons, and apply it to ultracold bosonic atoms in an optical lattice. We show that, with increasing BEC temperature, the transport properties of the impurities change from coherent to diffusive. Furthermore, stable polaron clusters are formed via a phonon-mediated off-site attraction.

In this paper, we consider teleportation capability, distillability, and nonlocality on three-qubit states. In order to investigate some relations among them, we first find the explicit formulas of the quantities about the maximal teleportation fidelity on three-qubit states. We show that if any three-qubit state is useful for three-qubit teleportation then the three-qubit state is distillable into a Greenberger-Horne-Zeilinger state, and that if any three-qubit state violates a specific form of Mermin inequality then the three-qubit state is useful for three-qubit teleportation.

We consider a possible detector-efficiency loophole in experiments that detect entanglement via the local measurement of witness operators. Here, only local properties of the detectors are known. We derive a general threshold for the detector efficiencies which guarantees that a negative expectation value of a witness is due to entanglement, rather than to erroneous detectors. This threshold depends on the local decomposition of the witness and its measured expectation value. For two-qubit witnesses, we find the local operator decomposition that is optimal with respect to closing the loophole.