Using a technique based on production of ion Coulomb crystals, the isotope shifts of the $4s^2$ ${}^{1}S_0\to 4s5p$ ${}^{1}P_1$ transition for all naturally occurring isotopes of calcium as well as the hyperfine splitting of the $4s5p$ ${}^{1}P_1$ state in ${}^{43}\mathrm{Ca}$ have been measured. The field shift and specific mass shift coefficients as well as the hyperfine structure constants for ${}^{43}\mathrm{Ca}$ have been derived from the data.

The cross sections and rates for quenching of thermalized antiprotonic helium atoms in binary collisions with ordinary helium atoms are calculated in perturbation theory and in the coupled-channel formalism at the temperature and the number density of the helium gas, $T=6\mathrm{K}$ and $N={10}^{21}{\text{cm}}^{-3}$, respectively. It is shown that quenching is unlikely to be relevant for the metastable states of the antiprotonic helium atom with $32⩽n⩽40$. Comparison with experiment shows a good quantitative agreement for the $(n,l)=(39,35)$ state of antiprotonic helium and a large disagreement for the $(37,34)$ state. As a byproduct of this work, the existence of a series of bound states of the $\mathrm{He}–\overline{p}{}^4\mathrm{He}^{+}$ dimer is demonstrated numerically for $n⩾38$.

A Bose-Hubbard model, describing bosons in a harmonic trap with a superimposed optical lattice, is studied using a fast and accurate variational technique (MF+NRG): the Gutzwiller mean-field (MF) ansatz is combined with a numerical renormalization group (NRG) procedure in order to improve on both. Results are presented for one, two, and three dimensions, with particular attention to the experimentally accessible momentum distribution and possible satellite peaks in this distribution. In one dimension, a comparison is made with exact results obtained using stochastic series expansion.

We discuss the impact of thermally excited near fields on the coherent expansion of a condensate in a miniaturized electromagnetic trap. Monte Carlo simulations are compared with a kinetic two-component theory and indicate that atom interactions can slow down decoherence. This is explained by a simple theory in terms of the condensate dynamic structure factor.

Electromagnetically induced transparency and light storing are discussed in the case of an atomic medium in a double $\Lambda$ configuration. A polariton description of both phenomena is systematically introduced. Analytic expressions are given which allow one to predict the shapes and phases of both the transmitted pulses and the stored and released ones as well as the atomic coherence in the storage stage. A comparison of the numerical solutions of the Maxwell-Bloch equations with the results due to the polariton model proves a strong predictive power of the latter.

The problem of spontaneous emission of an excited atom inside a random medium formed by randomly distributed dipoles is theoretically discussed by explicitly calculating the decay rate of the atom. After averaging over all the density fluctuations of the medium, we obtain an analytical expression of the decay rate in the low-density limit, which shows that inside a random medium the relaxation of an excited state is enhanced due to the density-fluctuation correlations of the random medium.

We analyze the quantum limit to the sensitivity of the detection of small displacements. We focus on the case of free particles and harmonic oscillators as the systems experiencing the displacement. We show that the minimum displacement detectable is proportional to the inverse of the square root of the mean value of the energy in the state experiencing the displacement (Heisenberg limit). We present a measuring scheme that reaches this limit using semiclassical states. We examine the performance of this strategy under realistic practical conditions by computing the effect of imperfections such as losses and nonunit detection efficiencies. This analysis confirms the robustness of this measuring strategy by showing that the experimental imperfections can be suitably compensated by increasing the mean energy of the input state.

We report on calculations of the dipole-dipole dispersion coefficients for pairs of $n$-alkane molecules. The results are based on first-principles calculations of the molecular polarizabilities with a purely imaginary frequency argument and which were reported by us in a previous work [P. Norman, A. Jiemchooroj, and Bo E. Sernelius, J. Chem. Phys. 118, 9167 (2003)]. The results for the static polarizabilities and dispersion coefficients are compared to simple algebraic expressions in terms of the number of $\mathrm{C}\mathrm{C}$ and $\mathrm{C}\mathrm{H}$ bonds in the two weakly interacting species. The bond additivity procedure is shown to perform well in the present case, and bond polarizabilities of 4.256 and $3.964\text{a.u}$. are proposed for the $\mathrm{C}\mathrm{H}$ and the $\mathrm{C}\mathrm{C}$ bond, respectively.

For quantum communication in a gravitational field, the properties of the Einstein-Podolsky-Rosen (EPR) correlation are studied within the framework of general relativity. Acceleration and gravity are shown to deteriorate the perfect anticorrelation of an EPR pair of spins in the same direction, and apparently decrease the degree of the violation of Bell’s inequality. To maintain the perfect EPR correlation and the maximal violation of Bell’s inequality, observers must measure the spins in appropriately chosen different directions which depend on the velocity of the particles, the curvature of the space-time, and the positions of the observers. Near the event horizon of a black hole, the appropriate directions depend so sensitively on the positions of the observers that even a very small uncertainty in the identification of the observers’ positions leads to a fatal error in quantum communication, unless the observers fall into the black hole together with the particles.

Using a method of characterizing entanglement in the framework of quantum field theory, we investigate the optical generation and quantitative characterizations of quantum entanglement in an electron-hole system, in presence of spin-orbit coupling, and especially make a theoretical analysis of a recent experimental result. Basically, such entanglement should be considered as between occupation numbers of single-particle basis states, and is essentially generated by coupling between different single-particle basis states in the second-quantized Hamiltonian. Interaction with two resonant light modes of different circular polarizations generically leads to a superposition of ground state and two heavy-hole excitonic states. When and only when the state is a superposition of only the two excitonic eigenstates, the entanglement reduces to that between two distinguishable particles, each with two degrees of freedom, namely, band index, as characterized by angular momentum, and orbit, as characterized by position or momentum. The band-index state, obtained by tracing over the orbital degree of freedom, is found to be a pure state, hence the band index and orbital degrees of freedom are separated in this state. We propose some basic ideas on spatially separating the electron and the hole, so that the entanglement of band indices, or angular momenta, is between spatially separated electron and hole.

This paper provides the theoretical basis for experimentation on van der Waals atom-surface energy as a manifestation of quantum zero-point energy, with a continuously variable parameterization by a Landau-quantizing magnetic field applied normal to the surface. Quantum magnetic field effects in the second-order van der Waals (vdW) atom-surface energy are fully analyzed. Focusing on the electrostatic nonretarded limit, we employ a random phase approximation (RPA) description of the dynamic, nonlocal polarizability of the mobile semi-infinite Landau quantized plasma behind a semiconductor surface. Our initial examination is carried out using a general low-wave-number approximation of the bounded plasma dielectric function both parallel and perpendicular to the surface, to expeditiously determine quantum magnetic field effects in the second-order vdW energy. Since the formulation calls for an integration over all wave numbers perpendicular to the surface, $p_z$, we subsequently eliminate the reasonable approximation of the RPA polarizability expanded in powers of $p_z$, and carry out a more accurate study in this respect. Explicit analytic results for quantum magnetic field effects in vdW energy due to a neutral atom in Coulombic interaction with a semi-infinite nonlocal, dynamic semiconductor plasma are obtained and presented in full detail.

Triggered single-photon sources produce the vacuum state with nonzero probability, but produce a much smaller multiphoton component. It is therefore reasonable to approximate the output of these photon sources as a mixture of the vacuum and single-photon states with probabilities $1-p$ and $p$, respectively. Here we are concerned with increasing the efficiency $p$ by directing multiple copies of the single-photon-vacuum mixture into a linear optical device and applying photodetection on some outputs. We prove that it is impossible, under certain conditions, to increase $p$ via linear optics and conditional preparation based on photodetection. We also establish a class of photodetection events for which $p$ can be improved, although with an added multiphoton component. In addition we prove that it is not possible to obtain perfect single-photon states via this method from imperfect $\left(p<1\right)$ inputs.

In previous papers [; ], electron-hydrogen and electron- -wave scattering phase shifts were calculated using the optical potential approach. This method is now extended to the singlet and triplet electron-hydrogen -wave scattering in the elastic region. Phase shifts are calculated using Hylleraas-type correlation functions with up to 220 terms. Results are rigorous lower bounds to the exact phase shifts and they are compared to phase shifts obtained from previous calculations.

We derive the equilibrium conditions for a thermal atom-molecule mixture near a Feshbach resonance. Under the assumption of low collisional loss, thermodynamical properties are calculated and compared to the measurements of a recent experiment on thermal fermionic lithium atoms. We discuss and evaluate possible collision mechanisms which can lead to atom-molecule conversion. Finally, we propose a novel evaporative cooling scheme to efficiently cool the molecules toward Bose-Einstein condensation.

It is shown that entangling two-qubit phase gates for quantum computation with atoms inside a resonant optical cavity can be generated via common laser addressing, essentially, within one step. The obtained dynamical or geometrical phases are produced by an evolution that is robust against dissipation in form of spontaneous emission from the atoms and the cavity and demonstrates resilience against fluctuations of control parameters. This is achieved by using the setup introduced by Pachos and Walther [Phys. Rev. Lett. 89, 187903 (2002)] and employing entangling Raman- or STIRAP-like transitions that restrict the time evolution of the system onto stable ground states.

We examine Maris’ [J. Low. Temp. Phys. 120, 173 (2000)] recent suggestion that the fission of electron-inhabited bubbles in liquid helium may give rise to a new form of electron fractionization. We introduce a one-dimensional toy model—a simplified analog of the helium system—which may be analyzed using the Born-Oppenheimer approximation. We find that none of the model’s low-lying energy eigenstates have the form suggested by Maris’ computations, in which the bubbles were treated completely classically. Instead, the eigenstates are quantum-mechanically entangled superposition states, which the classical treatment overlooks.

The influence of the geometric phase, in particular the Berry phase, on an entangled spin-$\frac{1}{2}$ system is studied. We discuss in detail the case, where the geometric phase is generated only by one part of the Hilbert space. We are able to cancel the effects of the dynamical phase by using the “spin-echo” method. We analyze how the Berry phase affects the Bell angles and the maximal violation of a Bell inequality. Furthermore we suggest an experimental realization of our setup within neutron interferometry.

We report, to our knowledge, the first relativistic calculation for many-electron atoms complete through the fourth order of many-body perturbation theory. Owing to an overwhelmingly large number of underlying diagrams, the calculations are aided by our suite of symbolic algebra tools. We augment all-order single-double excitation method with 1648 omitted fourth-order diagrams and compute amplitudes of principal transitions in Na. The resulting ab initio relativistic electric dipole amplitudes are in an excellent agreement with $0.05\%$-accurate experimental values. Analysis of previously unmanageable classes of diagrams provides a useful guide to a design of even more accurate, yet practical, many-body methods.

Fragment ions from ${\mathrm{C}}_{60}$ induced by $2\text{MeV}$ $\left(v=1.7\mathrm{a}\text{.u.}\right)$ ${\text{Si}}^{2+}$ impacts are measured in coincidence with the number distributions of secondary electrons under conditions of single-electron loss and single-electron capture collisions. Multifragmentation, leading to disintegration of cage structure, is found to occur at surprisingly low charge states of $r\simeq 3$. Also, we find that mass distributions of fragment ions are nearly the same for loss and capture collisions provided that the number of electrons ejected, due to electronic energy deposition from an incident ion, are the same. Present results indicate evidently that the internal excitation, rather than the charge state $r$ of transiently formed prefragmented parent ions $\mathrm{C}_{60}{}^{r+\ast \ast }$, plays the essential role in ${\mathrm{C}}_{60}$ fragmentation in fast heavy ion collisions.