Using molecular-dynamics simulation, we study the impact of ${\left({\mathrm{N}}_2\right)}_{2869}$ clusters on a flat rigid wall. We study the cluster fragmentation process, the formation of lateral jets, the energy redistribution among the resulting fragments, and the ratio of internal and translational energy of the emerging free molecules as a function of cluster impact energy in the range of $0.076–1520\mathrm{meV}∕\text{molecule}$. We find the fragmentation threshold energy to be in agreement with that found previously for ${\left({\mathrm{N}}_2\right)}_{13}$ clusters; the (scaled) number of fragments, however, increases more slowly with impact energy. Also the energy redistribution of the cluster impact energy among the internal and translational energy of the fragments is similar to that found for the small cluster. This means in particular that free molecules show a strong nonequilibrium energy partitioning in which the internal degrees of freedom are considerably less excited than the translational degrees of freedom. We also find that at impact energies above the fragmentation threshold the angular distribution of fragments is peaked parallel to the surface—i.e., the formation of lateral surface jets.

Oscillations in the electron emission spectrum of atoms ionized by few-cycle laser pulses were recently identified as a time double-slit interference [F. Lindner et al., Phys. Rev. Lett. 95, 040401 (2005)]. We extend this analysis to three-dimensional momentum images. We show that different portions of the wave packet released at different times interfere, forming interference fringes in the momentum distributions. The complex interference pattern observable in momentum space maps out information on the scattering potential.

We extend and generalize previous work on the interference of light from independent cavities that began with the suggestion of Pfleegor and Mandel [Phys. Rev. 159, 1084 (1967)] that their observed interference of laser beams should not be associated too closely with particular states of the beams but more with the detection process itself. In particular we examine how the detection of interference induces a nonrandom-phase difference between internal cavity states with initial random phases for a much broader range of such states than has previously been considered. We find that a subsequent interference measurement should give results consistent with the induced phase difference. The inclusion of more cavities in the interference measurements enables the construction in principle of a laboratory in the sense used by Aharonov and Susskind, made up of cavity fields that can serve as frames of phase reference. We also show reasonably simply how intrinsic phase coherence of a beam of light leaking from a single cavity arises for any internal cavity state, even a photon number state. Although the work presented here may have some implications for the current controversy over whether or not a typical laboratory laser produces a coherent state, it is not the purpose of this paper to enter this controversy; rather it is to examine the interesting quantum physics that arises for cavities with more general internal states.

We obtain two stationary solutions for an intense optical pulse propagating in a Kerr-effect nonlinear ring cavity using elliptic functions associated with a parameter $m$. The solutions may be associated with distinct phases of the system, the transition from one to the other being dictated by an energy ratio. Semiclassical quantization reveals excitations that are quantized rotational states for the spatially constant solution and $N$-particle bound states for the soliton solution. On invoking periodic boundary conditions, a constraint relating the number of particles, wavelength, and $m$ emerges. This constraint fundamentally modifies the binding energy of the soliton for a large range of $m$. At the phase transition point, the energy undergoes a discontinuity in both value and derivative, a conclusion that differs markedly from results of a mean-field calculation.

A class of multiwavelength Fabry-Pérot lasers is introduced where the spectrum is tailored through a patterning of the cavity effective index. The cavity geometry is obtained using an inverse scattering approach and can be designed such that the spacing of discrete Fabry-Pérot lasing modes is limited only by the bandwidth of the inverted gain medium. A specific two-color semiconductor laser with a mode spacing in the THz region is designed, and measurements are presented demonstrating the simultaneous oscillation of the two wavelengths. The nonperiodic effective index profile of the particular two-color device considered is shown to be related to a Moiré or superstructure grating.

Using Maxwell-Bloch equations, we analyze the response of a two-component medium of two-level atoms driven by a two-cycle optical pulse beyond the traditional approach of slowly varying amplitudes and phases. We show that the notions of carrier, envelope, phase, and group velocities can be generalized to this situation. For optical pulses of a given duration, we show that the optical field can form a temporal soliton.

The notion of weak-degradability of quantum channels is introduced by generalizing the degradability definition given by Devetak and Shor. Exploiting the unitary equivalence with beam-splitter/amplifier channels we then prove that a large class of one-mode Bosonic Gaussian channels are either weakly degradable or anti-degradable. In the latter case this implies that their quantum capacity $Q$ is null. In the former case instead, this allows us to establish the additivity of the coherent information for those maps which admit unitary representation with single-mode pure environment.

We present measurements of the loss-rate coefficients $K_{\mathit{am}}$ and $K_{\mathit{mm}}$ caused by inelastic atom-molecule and molecule-molecule collisions. A thermal cloud of atomic ${}^{87}\mathrm{Rb}$ is prepared in an optical dipole trap. A magnetic field is ramped across the Feshbach resonance at $1007.4\mathrm{G}$. This associates atom pairs to molecules. A measurement of the molecule loss at $1005.8\mathrm{G}$ yields $K_{\mathit{am}}=2\times {10}^{-10}{\mathrm{cm}}^3∕\mathrm{s}$. Additionally, the atoms can be removed with blast light. In this case, the measured molecule loss yields $K_{\mathit{mm}}=3\times {10}^{-10}{\mathrm{cm}}^3∕\mathrm{s}$.

We investigate the nonlinear self-trapping phenomenon of a Bose-Einstein condensate (BEC) in a symmetric double well, emphasizing its underlying dynamical phase transition. As the nonlinear parameter characterizing the interaction between the degenerate atoms increases, the BEC becomes self-trapped, manifesting an asymmetric distribution of the atomic density profile. The essence of this phenomenon is revealed to be a continuous phase transition and the underlying critical behavior is studied analytically and found to follow a logarithmic scaling law. We then go beyond the mean-field treatment and extend our treatment to discuss the effect of many-body quantum fluctuations on the transition. It is found that the transition point is shifted and the scaling law is broken. In particular, the quantum phase transition is accompanied by a change of the entanglement entropy, which is found to reach a maximum at the transition point. The underlying physics is revealed.

We study the thermodynamics of ultracold Bose atoms in optical lattices by numerically diagonalizing the mean-field Hamiltonian of the Bose-Hubbard model. This method well describes the behavior of long-range correlations and therefore is valid deep in the superfluid phase. For the homogeneous Bose-Hubbard model, we draw the finite-temperature phase diagram and calculate the superfluid density at unity filling. We evaluate the finite-temperature effects in a recent experiment probing number fluctuation [Phys. Rev. Lett. 96 090401 (2006)], and find that our finite-temperature curves give a better fitting to the experimental data, implying non-negligible temperature effects in this experiment.

We propose a feasible method of coherent-state information concentration and purification utilizing quantum memory. The method allows us to optimally concentrate and purify information carried by many noisy copies of an unknown coherent state (randomly distributed in time) to a single copy. Thus nonclassical resources and operations can be saved, if we compare information processing with many noisy copies and a single copy with concentrated and purified information.

In this work, a sensitivity of the rate of relaxation of ground-state atomic coherences to magnetic-field inhomogeneities is studied. Such coherences give rise to many interesting phenomena in light-atom interactions, and their lifetimes are a limiting factor for achieving better sensitivity, resolution, or contrast in many applications. For atoms contained in a vapor cell, some of the coherence-relaxation mechanisms are related to magnetic-field inhomogeneities. We present a simple model describing relaxation due to such inhomogeneities in a buffer-gas-free antirelaxation-coated cell. A relation is given between relaxation rate and magnetic-field inhomogeneities including the dependence on cell size and atomic species. Experimental results, which confirm predictions of the model, are presented. Different regimes, in which the relaxation rate is equally sensitive to the gradients in any direction and in which it is insensitive to gradients transverse to the bias magnetic field, are predicted and demonstrated experimentally.

The wealth of quantum coherence effects depending on the orientation of external magnetic field, the polarization of coupling and probe lights, and the Rabi frequency of the coupling beam are studied in transition $F_e=2\leftrightarrow F_g=3$ of Cs ${\mathrm{D}}_2$ line. The split of electromagnetically induced transparency (EIT) resonances on two or three resonances determined by the different combination of the polarization of interaction lights and the direction of applied magnetic fields is obtained. The shifting and widening of the EIT resonances with the strength of the magnetic field (i.e., Zeeman splitting in the upper and lower levels) and Rabi frequency of the coupling beam increasing are also discussed. It may develop into the potential application for tunable multichannel optical information storage. On the other hand, an explanation of observed asymmetry of spectra by laser frequency offset from the optical resonance is given with theoretical calculation, which is in good agreement with the experimental results.

We show how to generate quadratic and biquadratic phonon-photon interactions through a driven three-level ion inside a cavity. With such a system it is possible to squeeze the cavity-field state, the ion motional state, or even the entangled phonon-photon state. We present a detailed analysis of the cavity-field squeezing process, distinguishing three different regimes of this amplification mechanism: the subcritical, critical, and supercritical regimes, which depend, apart from the coupling parameters, on the excitation of the vibrational state. As an application of the engineered Hamiltonians, we show how to implement a Fock-state filter for the vibrational mode. Different aspects of the technique of adiabatic elimination emerge in this analysis.

We present a protocol that allows us to obtain the concurrence of any two-qubit pure state by performing a minimal and optimal tomography of one of the subsystems through measuring a single observable of an ancillary four-dimensional qudit. An implementation for a system of trapped ions is also proposed, which can be achieved with present-day experimental techniques.

We investigated the quantum-state distribution in nonadiabatic rotational excitation induced by a nonresonant intense laser field. NO molecules, initially prepared in the lowest $J=0.5$ state, were rotationally excited to states with up to $J=8.5$ at a laser intensity of $2.5\times {10}^{13}\mathrm{W}∕{\mathrm{cm}}^2$. The characteristics in the observed state distribution were quantitatively reproduced by a quantum dynamical calculation, and excitation pathways typical to molecules in a doubly degenerate state were identified.

We proposed a scheme of continuous-variable quantum key distribution, in which the bright Einstein-Podolsky-Rosen entangled optical beams are utilized. The source of the entangled beams is placed inside the receiving station, where half of the entangled beams are transmitted with round trip and the other half are retained by the receiver. The amplitude and phase signals modulated on the signal beam by the sender are simultaneously extracted by the authorized receiver with the scheme of the dense-coding correlation measurement for continuous quantum variables, thus the channel capacity is significantly improved. Two kinds of possible eavesdropping are discussed. The mutual information and the secret key rates are calculated and compared with those of unidirectional transmission schemes.

In a previous paper [Phys. Rev. Lett. 96, 123401 (2006)] we have shown by means of three-dimensional particle-in-cell simulations and a simple rigid-sphere model that nonlinear resonance absorption is the dominant collisionless absorption mechanism in the intense, short-pulse laser cluster interaction. In this paper we present a more detailed account of the matter. In particular we show that the absorption efficiency is almost independent of the laser polarization. In the rigid-sphere model, the absorbed energy increases by many orders of magnitude at a certain threshold laser intensity. The particle-in-cell results display maximum fractional absorption around the same intensity. We calculate the threshold intensity and show that it is underestimated by the common overbarrier ionization estimate.

We present analytical stationary solutions for the Gross-Pitaevskii equation (GPE) of a Bose-Einstein condensate (BECs) trapped in a double-well potential. These solutions are compared to those described by [Mahmud et al., Phys. Rev. A 66, 063607 (2002)]. In particular, we provide further evidence that symmetry preserving stationary solutions can be reduced to the eigenstates of the corresponding linear Schrödinger equation. Moreover, we have found that the symmetry-breaking solutions can emerge not only from bifurcations, but also from isolated points in the chemical potential–nonlinear interaction diagram. We also have found that there are some moving nodes in the symmetry-breaking solutions.

In the present paper we investigate the influence of measurements on the quantum dynamics of degenerate Bose atoms gases in a symmetric double well. We show that continuous measurements enhance asymmetry on the density distribution of the atoms and broaden the parameter regime for self-trapping. We term this phenomenon as nonlinear quantum Zeno effect in analog to the celebrated Zeno effect in a linear quantum system. Under discontinuous measurements, the self-trapping due to the atomic interaction in the degenerate bosons is shown to be destroyed completely. Underlying physics is revealed and possible experimental realization is discussed.