The photodetachment cross section of ${\mathrm{H}}^{-}$ in a static electric field near an elastic wall is investigated based on both a quantum approach and the semiclassical closed-orbit theory. It is found that the distance between the ion and wall is another factor to modulate the cross section of the photodetachment. For an elastic wall perpendicular to the electric field, the detachment spectrum displays an irregular staircase structure, contrasting with the smooth oscillation when only the electric field exists.

We calculate two-photon Raman spectra for fermionic atoms with interactions described by a single-mode mean-field BCS-BEC crossover theory. We compare calculated spectra of interacting and noninteracting systems and find that interactions lead to the appearance of correlated atomic pair signal due to Cooper pairs; splitting of peaks in the spectroscopic signal due to the gap in fermionic dispersion; and attenuation of signal due to the partial conversion of fermions into the corresponding single-mode dimer. By exploring the behavior of these effects, one can obtain quantitative estimates of the BCS parameters from the spectra.

We show that some two-party Bell inequalities with two-valued observables are stronger than the CHSH inequality for $3\otimes 3$ isotropic states in the sense that they are violated by some isotropic states in the $3\otimes 3$ system that do not violate the CHSH inequality. These Bell inequalities are obtained by applying triangular elimination to the list of known facet inequalities of the cut polytope on nine points. This gives a partial solution to an open problem posed by Collins and Gisin. The results of numerical optimization suggest that they are candidates for being stronger than the ${\mathrm{I}}_{3322}$ Bell inequality for $3\otimes 3$ isotropic states. On the other hand, we found no Bell inequalities stronger than the CHSH inequality for $2\otimes 2$ isotropic states. In addition, we illustrate an inclusion relation among some Bell inequalities derived by triangular elimination.

The von Neumann entropy of various quantum dissipative models is calculated in order to discuss the entanglement properties of these systems. First, integrable quantum dissipative models are discussed, i.e., the quantum Brownian motion and the quantum harmonic oscillator. In the case of the free particle, the related entanglement of formation shows no nonanalyticity. In the case of the dissipative harmonic oscillator, there is a nonanalyticity at the transition of underdamped to overdamped oscillations. We argue that this might be a general property of dissipative systems. We show that similar features arise in the dissipative two-level system and study different regimes using sub-Ohmic, Ohmic, and super-Ohmic baths, within a scaling approach.

We analyze an example of a photon in a superposition of different modes, and ask what is the degree of their entanglement with a vacuum. The problem turns out to be ill-posed since we do not know which representation of the algebra of canonical commutation relations (CCR) to choose for the field quantization. Once we make a choice, we can solve the question of entanglement unambiguously. So the difficulty is not with mathematics, but with physics of the problem. In order to make the discussion explicit we analyze from this perspective a popular argument based on a photon leaving a beam splitter and interacting with two two-level atoms. We first solve the problem algebraically in the Heisenberg picture, without any assumption about the form of representation of CCR. Then we take the $\infty$-representation and show in two ways that in two-mode states the modes are maximally entangled with the vacuum, but single-mode states are not entangled. Next we repeat the analysis in terms of the representation of CCR taken from Berezin’s book and show that two-mode states do not involve the mode-vacuum entanglement. Finally, we switch to a family of reducible representations of CCR recently investigated in the context of field quantization, and show that the entanglement with the vacuum is present even for single-mode states. Still, the degree of entanglement here is difficult to estimate, mainly because there are $N+2$ subsystems, with $N$ unspecified and large.

An experimental investigation of the Cs $6s{}^{2}S_{1∕2}\to 6p{}^{2}P_{3∕2}\to 10s{}^{2}S_{1∕2}$ double-resonance two-photon polarization spectrum has been made. In the investigation, a linear polarization degree was measured to extract the alignment depolarization cross section in the cesium $6p{}^{2}P_{3∕2}$ level due to collisions between ground-level argon and excited $6p{}^{2}P_{3∕2}$ cesium atoms over the Zeeman coherences. The spectra show strong depolarization of the Cs $6p{}^{2}P_{3∕2}$ level. The measured alignment depolarization cross section value of 186 $\left(58\right){\mathrm{\AA }}^2$ is in good agreement with the experiment and theoretical predictions.

Inner-shell ionization of xenon $4d$ electrons have been studied by the binary $(e,2e)$ spectroscopy at the impact energies of 1200, 1600, and $2400\mathrm{eV}$. Experimental energy-momentum densities and the impact-energy dependence of momentum distributions of $4d_{5∕2}$ and $4d_{3∕2}$ are reported, the results are compared with the distorted-wave impulse approximation and the distorted-wave Born approximation. Moreover, the cross-section ratios of $4d_{5∕2}$ to $4d_{3∕2}$ are further provided at these different impact energies, which clearly manifest the relativistic effects. Some similarities and dissimilarities are observed on the impact-energy dependence of momentum distributions of $4d_{5∕2}$ and $4d_{3∕2}$ states and their cross-section ratios.

A complete experimental study of the production and transport of long-lifetime excited states has been done for ${\mathrm{Ar}}^{18+}$ on solid C targets, at a velocity of $23\mathrm{a.u.}$, and for a range of thickness allowing us to vary the transport conditions from single collision to equilibrium $(3.5\text{to}201\mu \mathrm{g}∕{\mathrm{cm}}^2)$. A systematic determination of ${\mathrm{Ar}}^{17+}$ Rydberg $\ell$- and $2s$-state populations has been performed using the x-ray spectroscopy technique. Results are compared with predictions of different transport simulations (developed on either a quantum or a classical phase space), which take into account multiple collisions and the strong polarization induced by the incoming ion (the wakefield). Using the continuum distorted-wave approximation for modeling the initial capture process, very good agreement is found between experimental Rydberg-state populations and theoretical approaches limited to the effect of multiple collisions. On the contrary, the transport of the metastable $2s$ state exhibits strong sensitivity to Stark mixing induced by the wakefield. The limitation of each theoretical approach is discussed with respect to the different experimental observables.

We have shown that the whole time-dependent vibrational wave packet of ${{\mathrm{D}}_2}^{+}$ ions can be reconstructed from the kinetic energy release of the ${\mathrm{D}}^{+}$ ion pairs when it is probed with an attosecond xuv pulse. Such a full interrogation of the wave packet will pave the way for controlling the generation of tailor-designed wave packets for favorable chemical reaction paths, as well as for probing the time evolution of their interaction with the medium.

We present an exact solution for a quantum spin chain driven through its critical points. Our approach is based on a many-body generalization of the Landau-Zener transition theory, applied to a fermionized spin Hamiltonian. The resulting nonequilibrium state of the system, while being a pure quantum state, has local properties of a mixed state characterized by finite entropy density associated with Kibble-Zurek defects. The entropy and the finite spin correlation length are functions of the rate of sweep through the critical point. We analyze the anisotropic $XY$ spin-$1∕2$ model evolved with a full many-body evolution operator. With the help of Toeplitz determinant calculus, we obtain an exact form of correlation functions. The properties of the evolved system undergo an abrupt change at a certain critical sweep rate, signaling the formation of ordered domains. We link this phenomenon to the behavior of complex singularities of the Toeplitz generating function.

The creation of TE-mode photons in a three-dimensional perfectly conducting cavity with one resonantly vibrating wall is studied numerically. We show that the creation of TE-mode photons in a rectangular cavity is related to the production of massive scalar particles on a time-dependent interval. The equations of motion are solved numerically which allows us to take into account the intermode coupling. We compare the numerical results with analytical predictions and discuss the effects of the intermode coupling in detail. The numerical simulations reveal that photon creation in a three-dimensional resonantly vibrating cavity can be maximized by arranging the size of the cavity such that certain conditions are realized. In particular, the creation of TE-mode photons in the lowest-frequency mode $(1,1,1)$ is most efficient in a noncubic cavity where the size of the nondynamical dimensions is roughly 11 times larger than the size of the dynamical dimension. We discuss this effect and its relation to the intermode coupling in detail.

We present here a scheme that relates seemingly two different kinds of physical impossibilities of quantum information processing. We derive, exact flipping of three arbitrary states not lying in one great circle is not possible with certainty, by using the existence of incomparable states which are not interconvertible deterministically by local operations and classical communications. In contrast, considering the nonexistence of exact universal flipper, the incomparability of a pair of bipartite pure entangled states can be established.

V. I. Usachenko and S.-I. Chu [Phys. Rev. A, 71, 063410 (2005)] discuss the molecular strong-field approximation in the velocity gauge formulation and indicate that some of our earlier velocity gauge calculations are inaccurate. Here we comment on the results of Usachenko and Chu. First, we show that the molecular orbitals used by Usachenko and Chu do not have the correct symmetry, and second, that it is an oversimplification to describe the molecular orbitals in terms of just a single linear combination of two atomic orbitals. Finally, some values for the generalized Bessel function are given for comparison.

We acknowledge the criticism of the preceding Comment related to imperfect composition of our model $3{\sigma }_g$ molecular state [V. I. Usachenko and S.-I. Chu, Phys. Rev. A 71, 063410 (2005)]. However, we cannot agree with the authors suggesting this critique also as an irrefutable argument and evidence in support and justification of their opposite and incorrect (viz. inconsistent with relevant experiment) orientation dependence of ${\mathrm{N}}_2$ ionization rate calculated within the velocity gauge version of molecular strong-field approximation. We demonstrate that appropriately composed $3{\sigma }_g$ state (modified according to the Comment's critique) rather confirm the alternative calculation [A. Jaron-Becker, A. Becker, and F. H. M. Faisal, Phys. Rev. A 69, 023410 (2004)], which suggests correct orientation dependence of ${\mathrm{N}}_2$ ionization, contrary to respective results of the Comment’s authors applying the same approach and procedure of $3{\sigma }_g$ composition.

We report the observation of multiple laser thresholds in the many-atom cavity QED microlaser. Traveling-wave coupling and a supersonic atom beam are used to create a well-defined atom-cavity interaction. Multiple thresholds are observed as jumps in photon number due to oscillatory gain. Although the number of intracavity atoms is large, up to $N\sim {10}^3$, the dynamics of the microlaser agree with a single-atom theory. This agreement is supported by quantum trajectory simulations of a many-atom microlaser and a semiclassical microlaser theory. We discuss the relation of the microlaser with the micromaser and conventional lasers.

We study the solutions for a one-dimensional electrostatic potential in the Dirac equation when the incoming wave packet exhibits the Klein paradox (pair production). With a barrier potential we demonstrate the existence of multiple reflections (and transmissions). The antiparticle solutions which are necessarily localized within the barrier region create new pairs with each reflection at the potential walls. Consequently we encounter a new “paradox” for the barrier because successive outgoing wave amplitudes grow geometrically.

We study switching between period-two states of an underdamped quantum oscillator modulated at nearly twice its natural frequency. For all temperatures and parameter values switching occurs via quantum activation: it is determined by diffusion over oscillator quasienergy, provided the relaxation rate exceeds the rate of interstate tunneling. The diffusion has quantum origin and accompanies relaxation to the stable state. We find the semiclassical distribution over quasienergy. For $T=0$, where the system has detailed balance, this distribution differs from the distribution for $T\to 0$; the $T=0$ distribution is also destroyed by small dephasing of the oscillator. The characteristic quantum activation energy of switching displays a typical dependence on temperature and scaling behavior near the bifurcation point where period doubling occurs.

We derive a version of information-disturbance theorems for mutually unbiased observables. We show that the information gain by Eve inevitably makes the outcomes by Bob in the conjugate basis not only erroneous but random.