By a comparative analysis of the emission of highly charged ions and energetic electrons the interaction dynamics of intense femtosecond laser fields $({10}^{13}–{10}^{14}\mathrm{W}∕{\mathrm{cm}}^2)$ with nanometer-sized silver clusters is investigated. Using dual laser pulses with variable optical delay the time-dependent cluster response is resolved. A dramatic increase both in the atomic charge state of the ions and the maximum electron kinetic energy is observed for a certain delay of the pulses. Corresponding Vlasov calculations on a metal cluster model system indicate that enhanced cluster ionization as well as the generation of fast electrons coincide with resonant plasmon excitation.

We discuss the consequences of the Aharonov-Bohm (AB) effect in setups involving several charged particles, wherein none of the charged particles encloses a closed loop around the magnetic flux. We show that in such setups, the AB phase is encoded either in the relative phase of a bipartite or multipartite entangled photons states, or alternatively, gives rise to an overall AB phase that can be measured relative to another reference system. These setups involve processes of annihilation or creation of electron-hole pairs. We discuss the relevance of such effects in “vacuum birefringence" in QED, and comment on their connection to other known effects.

We solve the problem of the optimal cloning of pure entangled two-qubit states with a fixed degree of entanglement using local operations and classical communication. We show that, amazingly, classical communication between the parties can improve the fidelity of local cloning if and only if the initial entanglement is higher than a certain critical value. It is completely useless for weakly entangled states. We also show that bound entangled states with positive partial transpose are not useful as a resource to improve the best local cloning fidelity.

We present a method to find the decompositions of tripartite entangled pure states with one qubit which are smaller than two successive Schmidt decompositions. We use this method to get a classification of the entangled states according to their decompositions. Furthermore, we also use this method to classify the entangled states that can be interconverted through stochastic local operations and classical communication. More general tripartite systems are briefly discussed.

In this paper, we write down the separable Werner state in a two-qubit system explicitly as a convex combination of product states, which is different from the convex combination obtained by Wootters’ method. The Werner state in a two-qubit system has a single real parameter and varies from inseparable to separable according to the value of its parameter. We derive a hidden variable model that is induced by our decomposed form for the separable Werner state. From our explicit form of the convex combination of product states, we understand the following: The critical point of the parameter for separability of the Werner state comes from positivity of local density operators of the qubits.

We generalize Greenberger-Horne-Zeilinger (GHZ) nonlocality to every even-dimensional and odd-partite system. For the purpose we employ concurrent observables that are incompatible and nevertheless have a common eigenstate. It is remarkable that a tripartite system can exhibit the genuinely high-dimensional GHZ nonlocality.

We propose an approach to realize an $n$-qubit controlled-$U$ gate with superconducting quantum interference devices (SQUIDs) in cavity QED. In this approach, the two lowest levels of a SQUID represent the two logical states of a qubit while a higher-energy intermediate level serves the gate manipulation. Our method operates essentially by creating a single photon through one of the control SQUIDs and then performing an arbitrary unitary transformation on the target SQUID with the assistance of the cavity photon. In addition, we show that the method can be applied to implement an $n$-qubit controlled-$U$ gate with atomic qubits in cavity QED.

Hyperfine splittings in the $4d_1^{\prime }$, $4d_3$, $4d_4$, and $4d_5$ states of the $4p^{5}5d$ configuration of ${}^{83}\mathrm{Kr}(I=9∕2)$ have been measured using two-step laser excitation. The corresponding hyperfine coupling constants $A$ and $B$ are negative (with one exception) and range from $-400\text{to}+85\mathrm{MHz}$.

We have investigated collisions of $\mathrm{Ca}\left(4s^2\right)$ with ${\mathrm{H}}^{+}$ in the energy range of $200\mathrm{eV}∕\mathrm{u}-10\mathrm{keV}∕\mathrm{u}$ using the semiclassical molecular-orbital close-coupling (MOCC) method with 18 coupled molecular states ($11{}^1\Sigma ^{+}$ and seven ${}^1\Pi ^{+}$ states) to determine charge-transfer cross sections. Except for the incoming channel $6{}^1\Sigma ^{+}$, the molecular states all correspond to charge-transfer channels. Inclusion of ${\mathrm{Ca}}^{2+}\text{−}{\mathrm{H}}^{-}$ is crucial in the configuration-interaction calculation for generating the molecular wave functions and potentials. Because of the Coulomb attraction, the state separating to ${\mathrm{Ca}}^{2+}\text{−}{\mathrm{H}}^{-}$ creates many avoided crossings, even though at infinite separation it lies energetically above all other states that we included. Because of the avoided crossings between the incoming channel $6{}^1\Sigma ^{+}$ and the energetically close charge-transfer channel $7{}^1\Sigma ^{+}$ the charge-transfer interaction occurs at long range. This makes calculations of charge-transfer cross sections by the MOCC method very challenging. The total charge-transfer cross sections increase monotonically from $3.4\times {10}^{-15}{\mathrm{cm}}^2$ at $200\mathrm{eV}∕\mathrm{u}$ to $4.5\times {10}^{-15}{\mathrm{cm}}^2$ at $10\mathrm{keV}∕\mathrm{u}$. Charge transfer occurs mostly to the excited ${\mathrm{Ca}}^{+}\left(5p\right)$ state in the entire energy range, which is the sum of the charge transfer to $7{}^1\Sigma ^{+}$ and $4{}^1\Pi ^{+}$. It accounts for $\sim 47\%$ of the total charge transfer cross sections at $200\mathrm{eV}∕\mathrm{u}$. However, as the energy increases, transfer to ${\mathrm{Ca}}^{+}\left(4d\right)$ increases, and at $10\mathrm{keV}∕\mathrm{u}$ the charge-transfer cross sections for ${\mathrm{Ca}}^{+}\left(5p\right)$ and ${\mathrm{Ca}}^{+}\left(4d\right)$ become comparable, each giving $\sim 38\%$ of the total cross section.

We study Coulomb explosions of fast $\mathrm{H}_2{}^{+}$ molecules under the channeling conditions through a single-wall carbon nanotube by solving the classical equations of motion for the fragment ions, involving both the repulsive continuum potential of the nanotube wall and the dynamically screened Coulomb repulsion between the two ions. Dynamic polarization of the nanotube electrons, described by a two-dimensional hydrodynamic model, gives rise to the correlated energy losses, a wakelike interaction between the fragment ions, as well as the dynamical image force on each ion. The explosion dynamics is dominated by the bare Coulomb repulsion and it mostly proceeds in the longitudinal direction, accompanied with the radially constrained oscillations of the fragment ions. Strong vicinage effects are found in both the molecule self-energy and its stopping power in the early stages of explosions, but they quickly diminish with the increasing dwell time in a manner which depends on the impact molecule speed and its axis orientation.

Two-component Fermi gases with tunable repulsive or attractive interactions inside quasi-one-dimensional (Q1D) harmonic wells may soon become the cleanest laboratory realizations of strongly correlated Luttiger and Luther-Emery liquids under confinement. We present a microscopic Kohn-Sham density-functional theory of these systems, with specific attention to a gas on the approach to a confinement-induced Feshbach resonance. The theory employs the one-dimensional Gaudin-Yang model as the reference system and transfers the appropriate Q1D ground-state correlations to the confined inhomogeneous gas via a suitable local-density approximation to the exchange and correlation energy functional. Quantitative understanding of the role of the interactions in the bulk shell structure of the axial density profile is thereby achieved. While repulsive intercomponent interactions depress the amplitude of the shell structure of the noninteracting gas, attractive interactions stabilize atomic-density waves through spin pairing. These should be clearly observable in atomic clouds containing of the order of up to 100 atoms.

Atom-surface interactions can significantly modify the intensity and phase of atom de Broglie waves diffracted by a silicon nitride grating. This affects the operation of a material grating as a coherent beam splitter. The phase shifts induced by diffraction are measured by comparing the relative phases of several interfering paths in a Mach-Zehnder Na atom interferometer formed by three material gratings. The values of the diffraction phases are consistent with a simple model which includes a van der Waals atom-surface interaction between the Na atoms and the silicon nitride grating bars.

We employ mean-field, Bogoliubov and many-body theories to study critical fluctuations in the position and momentum of a Bose-Einstein condensate whose translation symmetry is spontaneously broken due to attractive interactions. In a homogeneous system, the many-body ground state of the symmetry-preserving Hamiltonian is very fragile against superposition of low-lying states, while the mean-field theory predicts a stable bright soliton which spontaneously breaks translation symmetry. We show that weak symmetry-breaking perturbations cause the translation-symmetric many-body ground state to cross over to a many-body bright soliton. We argue that the center-of-mass fluctuations in the soliton state arise primarily from the depletion of the condensate to translation modes. We develop an extended mean-field theory to analytically reproduce these results obtained by the exact diagonalization method.

We theoretically analyze the interaction of a quantum system with a single ground state and three excited states that interacts with a pulsed laser field. The three excited states decay outside of the system to the same state. The dynamics of the system is studied by solving the coupled Maxwell-Schrödinger equations. We first present conditions for obtaining dark states of the system. These dark states lead to the phenomenon of coherent population trapping for strong applied fields. In addition, the existence of dark states leads to transparency at two different frequencies of a probe field. Slow light, at two different frequencies, can also occur. We present analytical results and verify those results with numerical solutions of the coupled Maxwell-Schrödinger equations.

We report an immediate generalization of the argument by Sen(De) and Sen proving that quantum dynamics, if linear, must be unitary, under the hypothesis of no-faster-than-light signaling between noninteracting entangled parties. The assumption of linearity is unnecessary and the conclusion is even stronger: not only are supraquantum cloning or deleting machines forbidden by the no signaling condition, but also any nonuniversal trace-preserving evolution.

We have produced a Bose-Einstein condensate of metastable helium $\left({}^4\mathrm{He}^{*}\right)$ containing over $1.5\times {10}^7$ atoms, which is a factor of 25 higher than previously achieved. The improved starting conditions for evaporative cooling are obtained by applying one-dimensional Doppler cooling inside a magnetic trap. The same technique is successfully used to cool the spin-polarized fermionic isotope $\left({}^3\mathrm{He}^{*}\right)$, for which thermalizing collisions are highly suppressed. Our detection techniques include absorption imaging, time-of-flight measurements on a microchannel plate detector, and ion counting to monitor the formation and decay of the condensate.

We demonstrate that parity-nonconserving interaction due to the nuclear weak charge $Q_W$ leads to a nonlinear magnetoelectric effect in centrosymmetric paramagnetic crystals. It is shown that the effect exists only in crystals with special symmetry axis $\mathbf{k}$. Kinematically, the correlation (correction to energy) has the form $H_{\mathrm{PNC}}\propto Q_W\mathbf{E}\bullet [\mathbf{B}\times \mathbf{k}](\mathbf{B}\bullet \mathbf{k})$, where $\mathbf{B}$ and $\mathbf{E}$ are external magnetic and electric fields. This gives rise to the magnetic induction ${\mathbf{M}}_{\mathrm{PNC}}\propto Q_W\{\mathbf{k}(\mathbf{B}\bullet [\mathbf{k}\times \mathbf{E}])+[\mathbf{k}\times \mathbf{E}](\mathbf{B}\bullet \mathbf{k})\}$. To be specific, we consider rare-earth-metal trifluorides and, in particular, dysprosium trifluoride which looks the most suitable for experiment. We estimate the optimal temperature for the experiment to be of a few kelvin. For the magnetic field $B=1\mathrm{T}$ and the electric field $E=10\mathrm{kV}∕\mathrm{cm}$, the expected magnetic induction is $4\pi M_{\mathrm{PNC}}\sim 0.5\times {10}^{-11}\mathrm{G}$, six orders of magnitude larger than the best sensitivity currently under discussion. Dysprosium has several stable isotopes, and so comparison of the effects for different isotopes provides the possibility for precise measurement of the Weinberg angle.

Suppose that Alice and Bob define their coordinate axes differently, and the change of reference frame between them is given by a probability distribution $\mu$ over SO(3). We show that this uncertainty of reference frame is of no use for bit commitment when $\mu$ is uniformly distributed over a (sub)group of SO(3), but other choices of $\mu$ can give rise to a partially or even arbitrarily secure bit commitment.

The multiphoton states generated by high-gain spontaneous parametric down-conversion (SPDC) in the presence of large losses are investigated theoretically and experimentally. The explicit form for the two-photon output state has been found to exhibit a Werner structure very resilient to losses for any value of the nonlinear gain parameter $g$. The theoretical results are found to be in agreement with experimental data obtained by “entanglement witness” methods and by the quantum tomography of the state generated by a high-$g$ SPDC.