We employ the lowest-order radially polarized axicon fields of a Gaussian laser beam to demonstrate that electrons may be accelerated from rest in vacuum to a few GeV. Petawatt power laser beams focused onto micron-size focal spots result in multi-TeV/m electron energy gradients.

It is shown that, in the framework of classical electrodynamics and in some peculiar cases, an exhaustive description of rotational evolution of molecules driven by intense few-optical-cycle laser pulses should consider the electric field of the pulse rather than its intesity envelope. We show that, at moderate pulse intensities, nonlinear effects driven by the molecular hyperpolarizability play a significant role. These findings are illustrated by numerical simulations concerning the classical motion of several molecules exposed to few-cycle light pulses.

In this paper we describe an application of fermion molecular dynamics to the simulation of the behavior of $\mathrm{H}_2{}^{+}$ and ${\mathrm{H}}_2$ immersed in a strong laser field. The laser field consists of a single short pulse of linearly polarized long wavelength radiation; viz., $t_{\mathit{\text{pulse}}}\sim 100\mathrm{fs}$, $\lambda =758\mathrm{nm}$, and ${10}^{13}⩽I_0<{10}^{14}\mathrm{W}∕{\mathrm{cm}}^2$. Results are compared with data from recent laboratory measurements.

The Nambu-Goldstone mode (NGM), associated with vortex nucleation in a harmonically confined, two-dimensional dilute Bose-Einstein condensate is studied. We argue, based on exact diagonalization calculations, that the NGM manifests in the lowest-lying envelope of the quasidegenerate spectrum that emerges as the vortex is about to enter the condensate. The quasidegenerate states constitute a series of octupole-mode branches that originate primarily from pairwise repulsive interactions between octupole excitations and are distinguished by the number of admixed quadrupolar excitations. As the vortex approaches the center of the condensate and the system’s axisymmetry is restored, the NGM becomes massive due to its coupling to higher rotational bands. We clarify the mechanism of this mass acquisition by using a newly developed projection-operator method.

We report a theoretical study of the transition temperature of a trapped interacting dilute Bose gas. The system is treated like a two-fluid model consisting of a thermal component and a condensate component. Through the calculation of the energy spectra, the origins of various effects on the transition temperature are derived. We found that the interactive shift is affected by both the thermal component and the condensate component. The latter effect, which is about 34% of the former, has never been reported so far. With these two effects, our calculated interactive shift agrees very well with the recent measurement.

Two recent pump-probe experiments on the high-order harmonic generation (HHG) from partially aligned $\mathrm{C}{\mathrm{O}}_2$ molecules have shown that the HHG yields versus the ionization rates as functions of the pump-probe delay time exhibit inverted modulation. The inversion has been attributed to the quantum interference in the recombination process from the two oxygen centers. Using the Lewenstein model to calculate HHG from fixed $\mathrm{C}{\mathrm{O}}_2$ molecules and taking into account the partial alignment of the molecules versus the time delay, we interpret that the inversion is due to the degree of overlap between the partially aligned molecules and the angular dependence of the HHG yield. We also note that the harmonic order where inversion occurs may change with probe laser intensity due to the depletion of the ground state.

We present a scheme to conditionally engineer an optical quantum system via continuous-variable measurements. This scheme yields high-fidelity squeezed single photons and a superposition of coherent states, from input single- and two-photon Fock states, respectively. The input Fock state is interacted with an ancilla squeezed vacuum state using a beam splitter. We transform the quantum system by postselecting on the continuous-observable measurement outcome of the ancilla state. We experimentally demonstrate the principles of this scheme using coherent states and experimentally measure fidelities that are only achievable using quantum resources.

Measurements of the energy loss of $10\mathrm{keV}$ protons and helium ions in Al and Au as a function of the exit angle are presented, as well as model calculations and numerical simulations taking into account the polycrystalline nature of the target. The experimental results show significant differences in the angular dependence between hydrogen and helium ions. To analyze this phenomenon we have studied the angular behavior of the energy loss by two different approaches. The first one is based on a theoretical method described in previous works. The second is based on a simulation code which takes into account the interaction of the projectiles with all the nearest neighboring atoms simultaneously, and incorporates the real polycrystalline characteristics of the target as obtained by transmission electron microscopy. The results indicate that (a) the different angular behavior of helium ions is mainly due to an impact parameter dependence of the energy loss for these ions; and (b) additionally we find that the influence of the crystalline structure on the angular effects of the energy loss is small for protons and somewhat more significant for helium ions.

The Coulomb deexcitation of the pionic hydrogen atom in collisions with the hydrogen atom has been studied in the quantum mechanical close-coupling approach. The total Coulomb deexcitation cross sections of $nl\to n^{\prime }{l}^{\prime }$ transitions and $l$-averaged cross sections are calculated for initial states with $n=3–8$ and at relative energies $E=0.01-100\mathrm{eV}$. The strong interaction and vacuum polarization shifts of $ns$ states are taken into account. It is shown that the $\Delta n>1$ transitions are very important and make up a substantial fraction of the Coulomb deexcitation cross section (up to $\sim 47\%$).

Trapped ultracold Fermi gases provide a system that can be tuned between the BCS and Bose-Einstein condensation regimes by means of a magnetic-field Feshbach resonance. Condensation of fermionic atom pairs in a ${}^{40}\mathrm{K}$ gas was demonstrated experimentally by a sweep technique that pairwise projects fermionic atoms onto molecules. In this paper, we examine previous data obtained with this technique that probed the phase boundary in the temperature-magnetic field plane. Comparison of the ${}^{40}\mathrm{K}$ data to a theoretically computed phase diagram demonstrates good agreement between the two.

The architecture proposed by Duan, Lukin, Cirac, and Zoller (DLCZ) for long-distance quantum communication with atomic ensembles is analyzed. Its fidelity and throughput in entanglement distribution, entanglement swapping, and quantum teleportation is derived within a framework that accounts for multiple excitations in the ensembles as well as loss and asymmetries in the channel. The DLCZ performance metrics that are obtained are compared to the corresponding results for the trapped-atom quantum communication architecture that has been proposed by a team from the Massachusetts Institute of Technology and Northwestern University (MIT and NU). Both systems are found to be capable of high-fidelity entanglement distribution. However, the DLCZ scheme only provides conditional teleportation and repeater operation, whereas the MIT-NU architecture affords full Bell-state measurements on its trapped atoms. Moreover, it is shown that achieving unity conditional fidelity in DLCZ teleportation and repeater operation requires ideal photon-number resolving detectors. The maximum conditional fidelities for DLCZ teleportation and repeater operation that can be realized with nonresolving detectors are 1/2 and 2/3, respectively.

We present a simple protocol to purify a coherent-state superposition that has undergone a linear lossy channel. The scheme constitutes only a single beam splitter and a homodyne detector, and thus is experimentally feasible. In practice, a superposition of coherent states is transformed into a classical mixture of coherent states by linear loss, which is usually the dominant decoherence mechanism in optical systems. We also address the possibility of producing a larger amplitude superposition state from decohered states, and show that in most cases the decoherence of the states are amplified along with the amplitude.

Measurements within 10% accuracy of the dynamic dipole polarizabilities $\alpha \left(\lambda \right)$ for five nonrefractory metal atoms (Mg, Ag, Al, Cu, and Au) at laser wavelengths of $\lambda =532$ and $1064\mathrm{nm}$ are presented using electrical explosion of thin wires in vacuum and a novel laser probing integrated-phase technique. The technique is based on single-wavelength interferometry and does not require axial symmetry of the tested object. Theoretical prediction of $\alpha \left(\lambda \right)$ for wavelengths $\lambda =355$, 532, and $1064\mathrm{nm}$, as well as the static dipole polarizabilities ${\alpha }_{\mathrm{st}}$, are also presented. An agreement within 20% was obtained between calculated data, recommended static polarizabilities ${\alpha }_{\mathrm{st}}$, and the measured dynamic polarizabilities $\alpha \left(532\mathrm{nm}\right)$ and $\alpha \left(1064\mathrm{nm}\right)$.

We observe the build-up of a matter wave interference pattern from single atom detection events in a double-slit experiment. The interference arises from two overlapping atom laser beams extracted from a rubidium Bose-Einstein condensate. Our detector is a high-finesse optical cavity which realizes a quantum measurement of the presence of an atom and thereby projects delocalized atoms into a state with zero or one atom in the resonator. The experiment reveals simultaneously the granular and the wave nature of matter. We present a setup which is suited for applications in atom interferometry and cavity QED.

Čerenkov radiation from cavities has been analyzed by quantum electrodynamic theory. Analytical expressions of basic radiation properties such as the Einstein’s $A$ and $B$ coefficients are derived and shown to be directly modified by the cavities. The analysis leads to the conclusion that the coherent radiation from the Čerenkov radiation devices is due to super radiance of spontaneous emission instead of stimulated emission. Coherent and incoherent radiations are analyzed in the THz radiation range.

We analytically study the linear propagation of arbitrarily shaped light pulses through an absorbing medium with a narrow transparency window or through a resonant amplifying medium. We point out that, under certain general conditions, the pulse acquires a nearly Gaussian shape, irrespective of its initial shape and of the spectral profile of the line. We explicitly derive in this case the pulse parameters, including its skewness, responsible for a deviation of the delay of the pulse maximum from the group delay. We illustrate our general results by analyzing the slow-light experiments having demonstrated the largest fractional pulse delays.

The Groverian entanglement measure, introduced earlier for pure quantum states of multiple qubits [O. Biham, M.A. Nielsen, and T. Osborne, Phys. Rev. A 65, 062312 (2002)], is generalized to the case of mixed states. The Groverian measure of a mixed state of $n$ qubits is obtained by a purification procedure into a pure state of $2n$ qubits, followed by an optimization process, before the resulting state is fed into Grover’s search algorithm. It is expressed in terms of the maximal success probability of the algorithm and in this sense provides an operational measure of entanglement.

Three-body systems of scalar bosons are covariantly described in the framework of relativistic constraint dynamics. With help of a change of variables followed by a change of wave function, two redundant degrees of freedom get eliminated and the mass-shell constraints can be reduced to a three-dimensional eigenvalue problem. In general, the reduced equation obtained by this procedure involves the spectral parameter in a nonconventional manner, but for three equal masses a drastic simplification arises at the first post-Galilean order: the reduced wave equation becomes a conventional eigenvalue problem that we treat perturbatively, computing a first-order correction beyond the nonrelativistic limit. The harmonic interaction is displayed as a toy model.

The conditional shift in the evolution operator of a quantum walk generates entanglement between the coin and position degrees of freedom. This entanglement can be quantified by the von Neumman entropy of the reduced density operator (entropy of entanglement). We show analytically that for a Hadamard walk with local initial conditions the asymptotic entanglement is 0.872 for all initial coin states. When nonlocal initial conditions are considered, the asymptotic entanglement varies smoothly between almost complete entanglement and no entanglement (product state). An exact expression for the asymptotic (long-time) entanglement is obtained for initial conditions in the position subspace spanned by $\mid \pm 1⟩$.

Metastable channel of doubly ionized carbon monoxide, ${\mathrm{CO}}^{2+}$, was scantly seen in previous strong-field experiments at the visible wavelength region, but was commonly observed using single high-energy photon or electron excitation. For the first time with near-IR ultrashort-pulse radiation, we observe an abundance of ${\mathrm{CO}}^{2+}$. We show that ${\mathrm{CO}}^{2+}$ results from nonsequential double ionization, while its dissociation counterpart, ${\mathrm{C}}^{+}+{\mathrm{O}}^{+}$, results from sequential processes, and ${\mathrm{CO}}^{2+}$ can be obtained through either single high-energy photon or electron excitation or multiphoton ionization with ultrashort pulses before a critical internuclear distance is reached. Our study demonstrates the experimental conditions to converge the outcomes from two vastly different regimes, namely, multiphoton excitation and ionization in strong fields and single high-energy photon or electron excitation and ionization in weak fields.