The collisional, superelastic encounters at ultralow energies of ${\text{Li}}^{+}$ with ${\text{D}}_2$ are computed using the exact coupled-channel dynamics, and using an ab initio potential energy surface discussed in earlier work. The changes in the target rovibrational structure due to the isotopic substitution, and in its rovibrational wave functions, are seen to have a marked effect, under the collision conditions of vanishing relative energy, on the corresponding dynamical attributes, allowing one to make specific predictions on the possible use of isotopic variants in cold trap processes.

Free neutral potassium clusters of two different mean sizes were produced using a gas aggregation source. The $\text{K}3p$ core level was probed by means of synchrotron radiation based photoelectron spectroscopy. The absolute binding energy and the intensity ratio of the surface and bulk spectral features were used to obtain independent estimates of the cluster size. Plasmon satellites in core level spectra of free metallic clusters were observed. Surface and bulk plasmon energies were determined. The interplay between the core line and plasmon integrated intensities is discussed.

We study both numerically and analytically the possibility of using an adiabatic passage control method to construct a Mach-Zehnder interferometer (MZI) for Bose-Einstein condensates in the time domain, in exact one-to-one correspondence with the traditional optical MZI that involves two beam splitters and two mirrors. The interference fringes one obtains from such a minimum-disturbance setup clearly demonstrates that, fundamentally, an atom laser is not monochromatic due to interatomic interactions. We also consider how the amount of entanglement in the system correlates to the interference fringes.

Bose-Einstein condensates subject to short pulses (“kicks”) from standing waves of light represent a nonlinear analog of the well-known chaos paradigm, the quantum kicked rotor. Previous studies of the onset of dynamical instability (i.e., exponential proliferation of noncondensate particles) suggested that the transition to instability might be associated with a transition to chaos. Here we conclude instead that instability is due to resonant driving of Bogoliubov modes. We investigate the Bogoliubov spectrum for both the quantum kicked rotor (QKR) and a variant, the double kicked rotor (QKR-2). We present an analytical model, valid in the limit of weak impulses which correctly gives the scaling properties of the resonances and yields good agreement with mean-field numerics.

Using the model of the so-called “accessible solitons” in nonlocal nonlinear media, we introduce a species of two-dimensional stable spatial solitons featuring the shape of spinning “bearings” (ring beams periodically modulated in the azimuthal direction). They are generated by a superposition of concentric vortices with widely different topological charges. The superposition of two vortices with identical or opposite signs of their charges generates annular chains of quasicircular or oval eddies, respectively, whereas stable multilayered annular solitons are formed by the superposition of more than two vortices. Beams with this structure may form all-optical photonic crystal fibers, and suggest the creation of new matter-wave patterns in Bose-Einstein condensates.

In population trapping the occupation of a decaying quantum level keeps a constant nonzero value. We show that an atom-cavity system interacting with an environment characterized by a nonflat spectrum, in the non-Markovian limit, exhibits such a behavior, effectively realizing the preservation of nonclassical states against dissipation. Our results allow us to understand the role of cavity losses in hybrid solid state systems and pave the way to the proper description of leakage in the recently developed cavity quantum electrodynamic systems.

The local and nonlocal contents of nonlocal probability distributions are studied using the approach of Elitzur, Popescu, and Rohrlich [A. Elitzur, S. Popescu, and D. Rohrlich, Phys. Lett. A 162, 25 (1992)]. This work focuses on distributions that can be obtained by single-copy von Neumann measurements on bipartite quantum systems. For pure two-qubit states $|\Psi \left(\theta \right)⟩=\text{cos}\theta |00⟩+\text{sin}\theta |11⟩$ (with $\text{cos}\theta \ge \text{sin}\theta$), the local content of the corresponding probability distribution is found to lie between $1-\text{sin}2\theta$ and $\text{cos}2\theta$. For the family $|\Psi \left(\gamma \right)⟩=\left(|00⟩+|11⟩+\gamma |22⟩\right)/\sqrt{2+{\gamma }^2}$ of two-qutrit states, nonzero local content is found for $\gamma >2$.

Based on quantum electrodynamics, we reexamine the two-photon decay of one-electron atoms. Special attention is paid to the calculation of the (two-photon) total decay rates which can be viewed as the imaginary part of the two-loop self-energy. We argue that our approach can be easily applied to the cases with a virtual state having an intermediate energy between the initial and the final state of the decay process leading, thus, to the resonance peaks in the two-photon energy distribution. In order to illustrate our approach, we obtain fully relativistic results, resolved into electric and magnetic multipole components, for the two-photon decay rates of the $3S_{1/2}\to 1S_{1/2}$ transition in neutral hydrogen as well as in various hydrogenlike ions.

A purification procedure that simultaneously corrects the $N$- and $S$-representability main defects of a second-order reduced density matrix (2RDM), second-order hole reduced density matrix (2HRDM), and second-order $\mathcal{G}$ matrix is presented here. In this purifying procedure, the generalized unitarily invariant second-order matrix decomposition [D. R. Alcoba, Int. J. Quantum Chem. 97, 776 (2004)] for the 2RDM and the 2HRDM as well as for the $\mathcal{G}$ matrix is combined with the $S$-representability conditions. In particular, here we will focus our attention on the RDMs corresponding to doublet states. We will thus explicitly give the $S$-representability conditions that a two-body correlation matrix has to satisfy when an $N$-electron system is in a doublet spin-state in the spin-component of maximum projection. Furthermore, as a consequence of the $\mathcal{G}$-matrix spin properties (which directly affect the $S$-representability of the 2RDM), we show that a different contracting form for the 2RDM is possible. The numerical results presented in this work confirm the efficiency of our purifying procedure.

Exact soliton solutions containing only a few cycles are found within the framework of a nonlinear full wave equation in a Kerr medium. It is proven numerically that they are stable and play a fundamental role in the pulse propagation dynamics. These wave solitons cover the range from the fundamental Schrödinger solitons, which occur for long pulses involving many field oscillations, to extremely short pulses, which contain only one optical period.

We propose a method for amplification of complex localized ultrashort wave packets ($\mathsf{X}$ pulses or $\mathsf{X}$ waves). We present an analytical derivation and numerical simulations of broadband parametric amplification of chirped $\mathsf{X}$ pulses in a noncentrosymmetric medium with quadratic nonlinearity. Our results suggest that $\mathsf{X}$ pulses with particular spatial and temporal chirps can be efficiently amplified in an optical parametric amplifier and compressed down to a few tens of femtoseconds during free-space propagation.

We show that a superresolution process with 100% visibility is characterized by the formation of a point of phase singularity in free space outside a metamaterial in the form of a saddle with topological charge equal to $-1$. The saddle point is connected to two vortices at the end boundaries of the lens, and the two vortices are in turn connected to another saddle point inside the lens. The structure saddle-vortices-saddle is topologically stable. The formation of the saddle point in free space explains also the negative flux of energy present in a certain region of space outside the lens. The circulation strength of the power flow can be controlled by varying the position of the object plane with respect to the lens.

The acetylene-vinylidene isomerization and the dissociation of the ${\text{C}}_2\text{H}_2{}^{2+}$ dication formed in the inner-shell ionization by electron impact have been studied via Auger-electron–ion and Auger-electron–ion–ion coincidence experiments. The occurrence of the isomerization is proved by measuring the production of the $\text{CH}_2{}^{+}$ fragment ion as well as by detecting the ${\text{C}}^{+}-\text{CH}_2{}^{+}$ ion pair in coincidence. The state selectivity of the technique shows that isomerization mainly takes place in the three $1{\pi }_u^{-2}$ lower states of the acetylene dication.

The local-density approximation is used to study the ground state superfluid properties of harmonically trapped $p$-wave Fermi gases as a function of fermion-fermion attraction strength. While the density distribution is bimodal on the weakly attracting BCS side, it becomes unimodal with increasing attraction and saturates towards the Bose-Einstein condensate (BEC) side. This nonmonotonic evolution is related to the topological gapless-to-gapped phase transition, and may be observed via radio-frequency spectroscopy since quasiparticle transfer current requires a finite threshold only on the BEC side.

The contribution of the detector dynamics to the weak measurement is analyzed. According to the usual theory [Y. Aharonov, D. Z. Albert, and L. Vaidman, Phys. Rev. Lett. 60, 1351 (1988)] the outcome of a weak measurement with preselection and postselection can be expressed as the real part of a complex number: the weak value. By accounting for the Hamiltonian evolution of the detector, here we find that there is a contribution proportional to the imaginary part of the weak value to the outcome of the weak measurement. This is due to the coherence of the probe being essential for the concept of complex weak value to be meaningful. As a particular example, we consider the measurement of a spin component and find that the contribution of the imaginary part of the weak value is sizable.

Repeated observations of a quantum system interacting with another one can drive the latter toward a particular quantum state, irrespective of its initial condition, because of an effective nonunitary evolution. If the target state is a pure one, the degree of purity of the system approaches unity, even when the initial condition of the system is a mixed state. In this paper we study the behavior of the purity from the initial value to the final one, that is, unity. Depending on the parameters, after a finite number of measurements, the purity exhibits oscillations that brings about a lower purity than that of the initial state, which is a point to be taken care of in concrete applications.

Entropic uncertainty relations place nontrivial lower bounds to the sum of Shannon information entropies for noncommuting observables. Here we obtain a lower bound on the entropy sum for general pairs of observables in finite-dimensional Hilbert space, which improves on the best bound known to date [H. Maassen and J. B. M. Uffink, Phys. Rev. Lett. 60, 1103 (1988)] for a wide class of observables. This result follows from another formulation of the uncertainty principle, the Landau-Pollak inequality, whose relationship to the Maassen-Uffink entropic uncertainty relation is discussed.

We analyze the problem of finding sets of quantum states that can be deterministically discriminated. From a geometric point of view, this problem is equivalent to that of embedding a simplex of points whose distances are maximal with respect to the Bures distance (or trace distance). We derive upper and lower bounds for the trace distance and for the fidelity between two quantum states, which imply bounds for the Bures distance between the unitary orbits of both states. We thus show that, when analyzing minimal and maximal distances between states of fixed spectra, it is sufficient to consider diagonal states only. Hence when optimal discrimination is considered, given freedom up to unitary orbits, it is sufficient to consider diagonal states. This is illustrated geometrically in terms of Weyl chambers.

The existing theory of decoy-state quantum cryptography assumes the exact control of each state from Alice’s source. Such exact control is impossible in practice. We develop the theory of decoy-state method so that it is unconditionally secure even if there are state errors of sources, if the range of a few parameters in the states are known. This theory simplifies the practical implementation of the decoy-state quantum key distribution because the unconditional security can be achieved with a slightly shortened final key, even though the small errors of pulses are not corrected.

The mixing time of a discrete-time quantum walk on the hypercube is considered. The mean probability distribution of a Markov chain on a hypercube is known to mix to a uniform distribution in time $O\left(n\text{log}n\right)$. We show that the mean probability distribution of a discrete-time quantum walk on a hypercube mixes to a (generally nonuniform) distribution $\pi \left(x\right)$ in time $O\left(n\right)$, and the stationary distribution is determined by the initial state of the walk. An explicit expression for $\pi \left(x\right)$ is derived for the particular case of a symmetric walk. These results are consistent with those obtained previously for a continuous-time quantum walk. The effect of decoherence due to randomly breaking links between connected sites in the hypercube is also considered. We find that the probability distribution mixes to the uniform distribution as expected. However, the mixing time has a minimum at a critical decoherence rate $p\approx 0.1$. A similar effect was previously reported for a quantum walk on an $N$-cycle with decoherence from repeated measurements of position. A controlled amount of decoherence helps in obtaining—and preserving—a uniform distribution over the $2^n$ sites of the hypercube in the shortest possible time.