Composite pulse sequences designed for nuclear magnetic resonance experiments are currently being applied in many quantum information processing technologies. We present an analysis of a family of composite pulse sequences used to address systematic pulse-length errors in the execution of quantum gates. It has been demonstrated by Cummins et al. [Phys. Rev. A 67, 042308 (2003)] that for this family of composite pulse sequences, the fidelity of the resulting unitary operation compared with the ideal unitary operation is $1-C{ϵ}^6$, where $ϵ$ is the fractional error in the length of the pulse. We derive an exact expression for the sixth-order coefficient $C$ and from this deduce conditions under which this sixth-order dependence is observed. We also present pulse sequences which achieve the same fidelity.

We explore a generalization of quantum secret sharing (QSS) in which classical shares play a complementary role to quantum shares, exploring further consequences of an idea first studied by Nascimento, Mueller-Quade, and Imai [Phys. Rev. A 64, 042311 (2001)]. We examine three ways, termed inflation, compression, and twin thresholding, by which the proportion of classical shares can be augmented. This has the important application that it reduces quantum (information processing) players by replacing them with their classical counterparts, thereby making quantum secret sharing considerably easier and less expensive to implement in a practical setting. In compression, a QSS scheme is turned into an equivalent scheme with fewer quantum players, compensated for by suitable classical shares. In inflation, a QSS scheme is enlarged by adding only classical shares and players. In a twin-threshold scheme, we invoke two separate thresholds for classical and quantum shares based on the idea of information dilution.

We present the derivation of the effective higher-order Hamiltonian, which gives an $m{\alpha }^6$ contribution to the energy levels of an arbitrary light atom. The derivation is based on the Foldy-Wouthuysen transformation of the one-particle Dirac Hamiltonian followed by perturbative expansion of the many-particle Green function. The obtained results can be used for the high precision calculation of relativistic effects in atomic systems.

A problem of collisions of atoms with two-channel zero-range interaction in an atomic waveguide is solved by using of a renormalization procedure. A matching of the solution to a solution of the related one-dimensional problem leads to relation between the one-dimensional and three-dimensional scattering parameters. The scattering amplitude and bound states for the confined system demonstrate differences from the related free and one-dimensional systems.

Collisions between $\mathrm{H}_2{}^{+}$ ion projectiles with H targets have been investigated in the $2.5–1000\mathrm{keV}$ energy range by means of classical-trajectory Monte Carlo calculations. It has been possible to simulate classically a dynamical $\mathrm{H}_2{}^{+}$ molecule and, therefore, the approach includes all the Coulomb interactions between the five classical particles. Particular attention is paid to the description of the $\mathrm{H}_2{}^{+}$ ion projectile, initially in its first vibration $(\mathrm{v}=0)$ ground state, and to the identification of the various reaction products after collision. Total cross sections for all the possible reaction channels are calculated, and are found in fair agreement with recent experimental data in the $20–100\mathrm{keV}$ energy range. Final $n$-state distributions for the hydrogen fragments are also determined.

We have investigated collisions involving fast, excited Cs atoms produced by photodissociating ${\mathrm{Cs}}_2$ molecules with a pulsed dye laser. The velocities of the atoms in the $5D$ state formed by the process ${\mathrm{Cs}}_2\left(X{}^1\Sigma _g^{+}\right)+\hslash {\omega }_{\text{pump}}\to {\mathrm{Cs}}_2^{*}\to \mathrm{Cs}\left(5D\right)+\mathrm{Cs}\left(6S\right)$ are much greater than typical thermal velocities associated with the cell temperature. Using a narrow-band cw probe laser to observe the increased Doppler broadening of the $5D_{3∕2}\to 5F_{5∕2}$ excitation line shape, we are able to monitor the time evolution of the velocity distribution of these $5D$ atoms. We analyze the data using a model that predicts the time-dependent excitation line shape of the fast atoms. Because the photons used to dissociate the molecules have a well-defined energy, the velocity distribution of the excited atoms in the early time after they are produced can be fairly well determined. Over time, velocity-changing collisions with ground-state Cs atoms cause the velocity distribution of excited atoms to approach the thermal limit. An analysis based on the strong-collision model leads to a prediction that the observed line shape at intermediate times will be a linear combination of contributions from distinct “fast” and “thermalized” atomic populations. By fitting our data to this model, a rate coefficient for velocity-changing collisions of fast $\mathrm{Cs}\left(5D_{3∕2}\right)$ atoms with ground-state Cs atoms has been determined. The result $k_{\mathrm{VCC}}=(6.1\pm 1.2)\times {10}^{-10}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ corresponds to an effective velocity-changing collision cross section of ${\sigma }_{\mathrm{VCC}}^{\mathrm{Cs},\mathrm{eff}}=(1.2\pm 0.2)\times {10}^{-14}{\mathrm{cm}}^2$.

We made regionally specific measurement of the hyperfine polarization $⟨\mathit{S}\bullet \mathit{I}⟩$ of Rb atoms in the vicinity $(\sim {10}^{-5}\mathrm{cm})$ of coated and uncoated Pyrex glass surfaces in optical pumping cells. This is in contrast to the previous hyperfine polarization studies, where the quantity measured is the bulk hyperfine polarization, which depends on surface interactions averaged over the entire cell surfaces. We probe the hyperfine polarization of the Rb atoms in the vicinity of cell surfaces using the evanescent wave of a weak laser beam. We find that the polarization in the vicinity of uncoated surfaces is significantly lower than that in the bulk. The polarization decreases rapidly with decreasing distance from the surface. By contrast, the polarization in the vicinity of a silicone-coated Pyrex glass surface is independent of the distance from the cell surface and is equal to the bulk polarization. Regionally specific measurement of the hyperfine polarization as a function of the penetration depth of the evanescent wave allows us to deduce the hyperfine polarization, its normal gradient, as well as the normal gradient coefficient ${\mu }_{\mathit{S}\bullet \mathit{I}}$ at the cell surface. We present the values of these quantities for three representative uncoated cells.

We have performed high-resolution measurements of photoelectrons emitted from the valence shell of ${\mathrm{C}}_{60}$, for both gas phase and solid state, in order to obtain branching ratios, partial cross sections, and the angular distribution anisotropy parameters of the two highest occupied molecular orbitals. The analysis is based on the Fourier transform of the cross-section oscillations and the results are corroborated by different theoretical models. In contrast to this good overall agreement between theory and experiment there is a striking disagreement with respect to predicted discrete resonance structures in the partial cross sections. Possible reasons for this behavior are discussed.

A systematic study is presented for $\mathrm{OH}\bullet {\left({\mathrm{H}}_2\mathrm{O}\right)}_7$ clusters derived from the cubic ${\left({\mathrm{H}}_2\mathrm{O}\right)}_8$ octamer by replacing one water with a hydroxyl radical. The system is a prototype for atmospheric water clusters containing the environmentally important OH species, and for OH adsorbed at the surface of ice. The full set of 39 symmetry-distinct cubic $\mathrm{OH}\bullet {\left({\mathrm{H}}_2\mathrm{O}\right)}_7$ clusters is enumerated, and the structures are determined using ab initio quantum chemical methods. Graph invariants are employed to obtain a unified analysis of the stability and structure of cubic ${\left({\mathrm{H}}_2\mathrm{O}\right)}_8$ and $\mathrm{OH}\bullet {\left({\mathrm{H}}_2\mathrm{O}\right)}_7$, relating these physical properties to the various hydrogen-bond topologies present in these clusters. To accomplish this the graph invariant formalism is extended to treat a hydrogen bonding impurity within a pure water network.

We theoretically investigate how the photoelectron angular distribution is altered by the introduction of a dressing laser. The physical mechanism underlying this alteration is the so-called laser-induced continuum structure; namely, a strong dressing laser induces quantum mechanical interference, the degree of which is different for different ionization channels. Therefore the branching ratio into different ionization channels changes as a function of laser detuning, and accordingly the photoelectron angular distribution is altered. After a general argument, we present specific theoretical results for the K atom, which indeed exhibit significant modification of the photoelectron angular distribution.

We present temperature-dependent measurements of the EPR frequency shifts for Na, K, and Rb interacting with polarized ${}^3\mathrm{He}$. K and Na frequency shifts were measured via comparison with Rb frequency shifts (well known at low temperatures) in $\mathrm{Na}-\mathrm{Rb}-{}^3\mathrm{He}$ and $\mathrm{K}-\mathrm{Rb}-{}^3\mathrm{He}$ spin-exchange cells. The lowered Rb vapor pressure of these “hybrid” spin-exchange cells also allowed us to extend the measured temperature dependence of the Rb EPR frequency shifts up to $350°\mathrm{C}$. This work presents measurements of the EPR frequency shift for Na in ${}^3\mathrm{He}$ and significantly extends the temperature range of previous Rb and K EPR frequency shift measurements. These results are critical to the performance of accurate ${}^3\mathrm{He}$ EPR polarimetry in spin-exchange cells.

We use intense few-cycle laser pulses to ionize molecules to the point of Coulomb explosion. We use Coulomb’s law or ab initio potentials to reconstruct the molecular structure of ${\mathrm{D}}_2\mathrm{O}$ and $\mathrm{S}{\mathrm{O}}_2$ from the correlated momenta of exploded fragments. For ${\mathrm{D}}_2\mathrm{O}$, a light and fast system, we observed about $0.3\mathrm{\AA }$ and 15° deviation from the known bond length and bond angle. By simulating the Coulomb explosion for equilibrium geometry, we showed that this deviation is mainly caused by ion motion during ionization. Measuring three-dimensional structure with half bond length resolution is sufficient to observe large-scale rearrangements of small molecules such as isomerization processes.

We have studied the behavior of cold Rydberg atoms embedded in an ultracold plasma. We demonstrate that even deeply bound Rydberg atoms are completely ionized in such an environment, due to electron collisions. Using a fast pulse extraction of the electrons from the plasma we found that the number of excess positive charges, which is directly related to the electron temperature $T_e$, is not strongly affected by the ionization of the Rydberg atoms. Assuming a Michie-King equilibrium distribution, in analogy with globular star cluster dynamics, we estimate $T_e$. Without concluding on heating or cooling of the plasma by the Rydberg atoms, we discuss the range for changing the plasma temperature by adding Rydberg atoms.

We investigate the “twist” mode (rotation of the upper against the lower hemisphere) of a dilute atomic Fermi gas in a spherical trap. The normal and superfluid phases are considered. The linear response to this external perturbation is calculated within the microscopic Hartree-Fock-Bogoliubov approach. In the normal phase the excitation spectrum is concentrated in a rather narrow peak very close to the trapping frequency. In the superfluid phase the strength starts to be damped and fragmented and the collectivity of the mode is progressively lost when the temperature decreases. In the weak-pairing regime some reminiscence of the collective motion still exists, whereas in the strong-pairing regime the twist mode is completely washed out. The disappearance of the twist mode in the strong-pairing regime with decreasing temperature is interpreted in the framework of the two-fluid model.

We propose the implementation of selective interactions of atom-motion subspaces in trapped ions. These interactions yield resonant exchange of population inside a selected subspace, leaving the others in a highly dispersive regime. Selectivity allows us to generate motional Fock (and other nonclassical) states with high purity out of a wide class of initial states, and becomes an unconventional cooling mechanism when the ground state is chosen. Individual population of number states can be distinctively measured, as well as the motional Wigner function. Furthermore, a protocol for implementing quantum logic through a suitable control of selective subspaces is presented.

Within the framework of macroscopic quantum electrodynamics, general expressions for the Casimir force acting on linearly and causally responding magnetodielectric bodies that can be embedded in another linear and causal magnetodielectric medium are derived. Consistency with microscopic harmonic-oscillator models of the matter is shown. The theory is applied to planar structures, and proper generalizations of Casimir’s and Lifshitz-type formulas are given.

The decay properties of an above-threshold resonance in core-ionized water, which is difficult to identify with usual spectroscopic methods, have been analyzed by resonant Auger spectroscopy. The resonance is shown to correspond to a doubly excited neutral state embedded in the O $1s$ ionization continuum. The main result of the experiments is the assessment on the dissociative nature of the intermediate state, with a consequent fragmentation in H neutral plus $\mathrm{O}*\mathrm{H}$ core excited. This dissociation takes place on the same time scale as electron decay, and therefore is categorized as an ultrafast dissociation process.