We theoretically analyze three-mode optoacoustic parametric interactions in a coupled Fabry-Perot cavity, where one acoustic mode interacts with two optical modes. We show explicitly that extra degrees of freedom in a coupled cavity allow explorations of both parametric instability and cooling regimes with high parametric gain in a single table top experiment. This work can motivate experimental realizations of the three-mode parametric instability which might be an issue in next-generation gravitational-wave detectors with high optical-power cavities, helping in the development of better models, and in developing techniques for controls. In addition, we show that the same scheme can be implemented in the resolved-sideband acoustic-mode cooling.

We propose a nonadiabatic change of the control-field amplitude to restore the temporal shape of a signal pulse, which usually experiences an appreciable temporal broadening in a conventional regime of electromagnetically-induced-transparency. This broadening sets a major limit on the maximum time delay achievable in a slow-light medium. A circumvention of this limit may be useful for the application of a slow-light medium as a practical, controllable delay line.

We study how photon addition and subtraction can be used to generate squeezed superpositions of coherent states (SSCSs) in free-traveling fields with high fidelities and large amplitudes. It is shown that an arbitrary $N$-photon subtraction results in the generation of a SSCS with nearly the perfect fidelity $(F>0.999)$ regardless of the number of photons subtracted. In this case, the amplitude of the SSCS increases as the number of the subtracted photons gets larger. For example, two-photon subtraction from a squeezed vacuum state of $6.1\mathrm{dB}$ can generate a SSCS of $\alpha =1.26$, while in the case of the four-photon subtraction a SSCS of a larger amplitude $\alpha =1.65$ is obtained under the same condition. When a photon is subtracted from a squeezed vacuum state and another photon is added subsequently, a SSCS with a lower fidelity $(F\approx 0.96)$ yet higher amplitude $(\alpha \approx 2)$ can be generated. We analyze some experimental imperfections including inefficiency of the detector used for the photon subtraction.

Doubly differential cross sections (DDCSs) for single ionization of molecular hydrogen by $75\text{−}\mathrm{keV}$ proton impact have been measured and calculated as a function of the projectile scattering angle and energy loss. Interference structures are observed in the scattering angular dependence of the DDCSs, which disappear, however, at electron speeds near the projectile speed. The comparison to our calculations shows that the projectile-target nucleus interaction plays a central role. Furthermore, our data suggest that for a given scattering angle, ionization favors well-defined molecular orientations.

We report on the creation of heterospecies bosonic molecules, associated from an ultracold Bose-Bose mixture of ${}^{41}\mathrm{K}$ and ${}^{87}\mathrm{Rb}$, by using a resonantly modulated magnetic field close to two Feshbach resonances. We measure the binding energy of the weakly bound molecular states versus the Feshbach field and compare our results to theoretical predictions. We observe the broadening and asymmetry of the association spectrum due to the thermal distribution of the atoms and a frequency shift occurring when the binding energy depends nonlinearly on the Feshbach field. A simple model is developed to quantitatively describe the association process. This work represents a required step toward Bose-Einstein condensates of dipolar molecules.

We investigate the Casimir force between two dissimilar plane mirrors, the material properties of which are described by Drude or Lorentz models. We calculate analytically the short and long distance asymptote of the force and relate its behavior to the influence of interacting surface plasmons. In particular, we discuss conditions under which Casimir repulsion could be achieved.

In quantum phase transitions induced by continuous level crossing, global-state fidelity drops to zero at every level crossing point, making finite-size scaling not applicable to study the criticality. In this paper, we calculate the partial-state fidelity in two models, i.e., the Lipkin-Meshkov-Glick (LMG) model and one-dimensional Heisenberg model. We show that it can spot the second-order phase transition point in the thermodynamic limit, where continuous level crossing occurs. The finite-size scaling shows the partial-state fidelity susceptibility diverges as $N$ for the isotropic LMG model and $N^3$ for the Heisenberg model.

We study a parametrically driven nanomechanical resonator capacitively coupled to a microwave cavity. If the nanoresonator can be cooled to near its quantum ground state then quantum squeezing of a quadrature of the nanoresonator motion becomes feasible. We consider the adiabatic limit in which the cavity mode is slaved to the nanoresonator mode. By driving the cavity on its red-detuned sideband, the squeezing can be coupled into the microwave field at the cavity resonance. The red-detuned sideband drive is also compatible with the goal of ground state cooling. Squeezing of the output microwave field may be inferred using a technique similar to that used to infer squeezing of the field produced by a Josephson parametric amplifier, and subsequently, squeezing of the nanoresonator motion may be inferred. We have calculated the output field microwave squeezing spectra and related this to squeezing of the nanoresonator motion, both at zero and finite temperature. Driving the cavity on the blue-detuned sideband, and on both the blue and red sidebands, have also been considered within the same formalism.

The standard oracle operator corresponding to a function $f$ is a unitary operator that computes this function coherently, i.e., it maintains superpositions. This operator acts on a bipartite system, where the subsystems are the input and output registers. In distributed quantum computation, these subsystems may be spatially separated, in which case we will be interested in its classical and entangling capacities. For an arbitrary function $f$, we show that the unidirectional classical and entangling capacities of this operator are ${\log }_2\left(n_f\right)$ bits (ebits) where $n_f$ is the number of different values this function can take. An optimal procedure for bidirectional classical communication with a standard oracle operator corresponding to a permutation on ${\mathbb{Z}}_M$ is given. The bidirectional classical capacity of such an operator is found to be $2{\log }_2\left(M\right)$ bits. The proofs of these capacities are facilitated by an optimal distributed protocol for the implementation of an arbitrary standard oracle operator.

The properties of a helium atom confined inside an endohedral cavity, such as a fullerene, are studied. The fullerene cavity is modeled by a potential well and the strength of this potential is varied in order to understand the collapse of different atomic wave functions into the fullerene cage. Three theoretical calculation methods have been developed: a relaxation method, a Sturmian basis method, and a variational method. The first two methods are nonperturbative. The three methods allow inclusion of full correlations among the two electrons. Results showing mirror collapse effects are presented for an $S$-wave model, in which all the angular quantum numbers are set to zero.

The spectra of vanadium $K\alpha$ x rays excited in targets of vanadium metal, VO, ${\mathrm{V}}_2{\mathrm{O}}_4$, and ${\mathrm{V}}_2{\mathrm{O}}_5$ by $15\mathrm{MeV}∕\mathrm{amu}$ projectiles of Ne, Ar, Kr, Ag, and Ho have been measured with a curved-crystal spectrometer. The spectra were analyzed to extract the relative intensities and energies of $K\alpha$ satellites and hypersatellites emitted in the decay of states having single and double $K$ vacancies, respectively, plus additional vacancies in the $L$ shell ranging from zero to seven. The intensity distributions, energies, and hypersatellite to satellite intensity ratios were examined for chemical effects. The parameters of a “universal” scaling function were obtained for the description of $K\alpha$ x-ray hypersatellite intensity distributions excited by heavy-ion collisions in solid targets.

We study single- and two-atom van der Waals interactions of ground-state atoms which are both polarizable and paramagnetizable in the presence of magnetoelectric bodies within the framework of macroscopic quantum electrodynamics. Starting from an interaction Hamiltonian that includes particle spins, we use leading-order perturbation theory to express the van der Waals potentials in terms of the polarizability and magnetizability of the atom(s). To allow for atoms embedded in media, we also include local-field corrections via the real-cavity model. The general theory is applied to the potential of a single atom near a half space and that of two atoms embedded in a bulk medium or placed near a sphere, respectively.

An efficient method to generate a short attosecond pulse is presented by using intense few-cycle shaped infrared (ir) laser in combination with an ultraviolet (uv) attosecond (as) pulse. We show that high-order harmonic generation (HHG) plateau near the cutoff is enhanced by one order of magnitude compared with the shaped laser case and the HHG supercontinuum spectrum is generated by adding a uv attosecond pulse to the few-cycle shaped ir laser at a proper time. By enhancing the long quantum path and suppressing the short one corresponding to one major return, an isolated 57-as pulse with a bandwidth of $62\mathrm{eV}$ is obtained directly. The time-frequency characteristics of the HHG are analyzed in detail by means of the wavelet transform of the time-dependent induced dipole acceleration. In addition, we also perform classical trajectory simulation of the strong-field electron dynamics and electron return map.

We investigate high-order harmonic generation in a sequence of icosahedral fullerenes using the extension of the so-called three-step or Lewenstein model to the molecular case. The high harmonic spectra obtained at midinfrared wavelengths show modulations in the plateau region. These modulations are due to the coherent superposition of the contributions from the atomic centers in the molecule to the dipole moment. Results of test calculations, in which the interference effects between the atomic contributions are deliberately neglected, show a “flat” plateau, as it is known from high-order harmonic generation in atoms. It is shown that the characteristic modulations are present in ensembles of aligned fullerenes as well as randomly oriented ones. We further show that in the case of the larger fullerenes the radius can be determined from the positions of the interference minima in the high harmonic spectra using a spherical model.

Recently we developed a technique for producing cold molecules from a supersonic molecular beam via single collisions with a supersonic atomic beam [M. S. Elioff, J. J. Valentini, and D. W. Chandler, Science 302, 1940 (2003)]. This cooling technique necessarily produces the cold molecules at the relatively high density crossing of the atomic and molecular beams. In previous reports, secondary glancing collisions with the remnant atomic and molecular beams lead to rapid depletion of the cold molecules limiting the observation time to less than $10\mu \mathrm{s}$ with an estimated temperature of $440\mathrm{mK}$. Here we present experimental conditions for the kinematic cooling technique which overcome the limitations of the previous experiments. We demonstrate the success of this experiment for the production of cold nitric oxide (NO) in the ground vibrational, $j=7.5$ rotational, state in order to compare with our previously reported data. With the present setup, we are able to extract the cold molecules from the pulsed molecular and atomic beams and we observe these cold $\mathrm{NO}{\left(X\right)}_{j=7.5}$ persisting for over $150\mu \mathrm{s}$. This long observation time demonstrates our ability to temporally and spatially separate the cold molecules from the parent atomic and molecular beams, simultaneously allowing for a better measurement of the final average velocity for the kinematically cooled molecules. From the data we find a final average velocity of the $\mathrm{NO}{\left(X\right)}_{j=7.5}$ of approximately $4.5\mathrm{m}∕\mathrm{s}$, consistent with simulations. The final observed average velocity is equated to a temperature of approximately $35\mathrm{mK}$, over an order of magnitude colder than our previous measurements.

We study stability of the first excited state of quasi-one-dimensional Bose-Einstein condensates in a double-well potential, which is called “$\pi$ state.” The density notch in the $\pi$ state can be regarded as a standing dark soliton. From the excitation spectrum, we determine the critical barrier height, above which the $\pi$ state is dynamically unstable. We find that the critical barrier height decreases monotonically as the number of condensate atoms increases. We also simulate the dynamics of the $\pi$ state by solving the time-dependent Gross-Pitaevskii equation. We show that due to the dynamical instability the dark soliton starts to move away from the trap center and exhibits a large-amplitude oscillation.

The diffractive resolution on a collisionless shock formed along the spatial profile of a beam in a nematic liquid crystal is considered, this material being an example of a self-focusing, nonlocal medium. It is found that the shock is resolved through the formation of an undular bore structure which persists for experimentally relevant propagation distances due to nonlocality delaying the onset of modulational instability. Both $1+1$ and $2+1$ dimensional bores with circular symmetry are considered (termed line and circular bores, respectively). A semianalytical solution is developed for the line undular bore, approximating it as a train of uniform solitary waves. The predictions of this semianalytical theory are found to be in excellent agreement with numerical solutions of the governing equations, both for line and circular bores. The method presented here yields semianalytical results for a bore in focusing media.

Using an improved value for the energy splitting between the $1s^{-1}3s{}^{1}S_0$ and $1s^{-1}3p{}^{1}P_1$ states, electromagnetically induced transparency for x rays at the $1s\to 3p$ resonance in Ne is reassessed. The energy splitting between the $1s^{-1}3s{}^{1}S_0$ and $1s^{-1}3p{}^{1}P_1$ states is calculated with two independent approaches. In the first approach, first-order nonrelativistic many-body perturbation theory is employed. In the second approach, the Dirac-Fock method is combined with the relativistic configuration interaction method. Both approaches give an energy splitting of $1.88\mathrm{eV}$. The calculated x-ray absorption near-edge structure of laser-dressed Ne agrees closely with an earlier prediction. It may therefore be expected that at a laser intensity of ${10}^{13}\mathrm{W}∕{\mathrm{cm}}^2$, the $1s\to 3p$ x-ray absorption cross section of Ne is suppressed by more than an order of magnitude.

One of the most important and still unresolved problems in the field of dispersion forces, is that of determining the influence of temperature on the Casimir force between two metallic plates. While alternative theoretical approaches lead to contradictory predictions for the magnitude of the effect, no experiment has yet detected the thermal correction to the Casimir force. In this paper we show that a superconducting cavity provides a new opportunity to investigate the problem of the thermal dependence of the Casimir force in real materials, by looking at the change of the Casimir force determined by a small change of temperature. The actual feasibility of the proposed scheme is briefly discussed.