Localization of the valence electron of endohedrally confined hydrogen, lithium and sodium in fullerene cages

The localization of the valence electron of $H$, $Li$ and $Na$ atoms enclosed by three different fullerene molecules is studied. The structure of the fullerene molecules is used to calculate the equilibrium position of the endohedrally atom as the minimum of the classical $(N+1)$-body Lennard-Jones potential. Once the position of the guest atom is determined, the fullerene cavity is modeled by a short range attractive shell according to molecule symmetry, and the enclosed atom is modeled by an effective one-electron potential. In order to examine whether the endohedral compound is formed by a neutral atom inside a neutral fullerene molecule $X@C_{N}$ or if the valence electron of the encapsulated atom localizes in the fullerene giving rise to a state with the form $X^{+}@C_{N}^{-}$, we analyze the electronic density, the projections onto free atomic states, and the weights of partial angular waves

Ground-state stability and criticality of two-electron atoms with screened Coulomb potentials using the B-splines basis set

We applied the finite-size scaling method using the B-splines basis set to construct the stability diagram for two-electron atoms with a screened Coulomb potential. The results of this method for two electron atoms are very accurate in comparison with previous calculations based on Gaussian, Hylleraas, and finite-element basis sets. The stability diagram for the screened two-electron atoms shows three distinct regions: a two-electron region, a one-electron region, and a zero-electron region, which correspond to stable, ionized and double ionized atoms. In previous studies, it was difficult to extend the finite size scaling calculations to large molecules and extended systems because of the computational cost and the lack of a simple way to increase the number of Gaussian basis elements in a systematic way. Motivated by recent studies showing how one can use B-splines to solve Hartree-Fock and Kohn-Sham equations, this combined finite size scaling using the B-splines basis set, might provide an effective systematic way to treat criticality of large molecules and extended systems. As benchmark calculations, the two-electron systems show the feasibility of this combined approach and provide an accurate reference for comparison

Near-threshold properties of the electronic density of layered quantum-dots

We present a way to manipulate an electron trapped in a layered quantum dot based on near-threshold properties of one-body potentials. We show that potentials with a simple global parameter allows the manipulation of the wave function changing its spatial extent. This phenomenon seems to be fairly general and could be implemented using current quantum-dot quantum wells technologies and materials if a proper layered quantum dot is designed. The layered quantum dot under consideration is similar to a quantum-dot quantum well device, i.e. consists of a spherical core surrounded by successive layers of different materials. The number of layers and the constituent material are chosen to highlight the near-threshold properties. In particular we show that the near-threshold phenomena can be observed using an effective mass approximation model that describes the layered quantum dot which is consistent with actual experimental parameters.Comment: 15 pages, 6 figures, regular articl

Quantum control of a model qubit based on a multi-layered quantum dot

In this work we present a model qubit whose basis states are eigenstates of a multi-layered quantum dot. We show that the proper design of the quantum dot results in qubit states that have excellent dynamical properties when a time-dependent driving is applied to it. In particular, it is shown that a simple sinusoidal driving is sufficient to obtain good quality Rabi oscillations between the qubit states. Moreover, the switching between states can be performed with very low leakage, even under off-resonance conditions. In this sense, the quantum control of the qubit is robust under some perturbations and achieved with simple means.Comment: 19 pages, 8 figure

The Effects of Privatization on Firms and on Social Welfare: The Chilean Case

Chile led the Latin American pack in launching its far-reaching privatization program, but the question of whether the process has made firms more profitable remains. Also unclear is whether society as a whole is better off because of privatization. This paper looks at the performance of several industries to gauge the effects of privatization on Chilean firms and social welfare. The authors’ research, which is both broad and deep, yields some surprising findings. For example, contrary to commonly-held perceptions of bloated state-run bureaucracies, the authors find that the employment ranks of regulated entities actually swelled after their ownership switched to private hands. The paper evaluates a wide range of aspects of the privatization process, from highway tolls to private pension fund returns to school vouchers, and concludes with some concrete recommendations for future improvements.

Comment on "towards a differential equation for the nonrelativistic ground-state electron density of the He-like sequence of atomic ions"

In a recent paper (Phys. Rev. A 71, 042501 (2005))Howard and March presented the exact ground state wave function of the spherical He-like atom, and many physical aspects of this solution were analyzed. We show that this function is not the exact solution of the modelFil: Serra, Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin

Quantum Confinement and Negative Heat Capacity

Thermodynamics dictates that the specific heat of a system is strictly non-negative. However, in finite classical systems there are well known theoretical and experimental cases where this rule is violated, in particular finite atomic clusters. Here, we show for the first time that negative heat capacity can also occur in finite quantum systems. The physical scenario on which this effect might be experimentally observed is discussed. Observing such an effect might lead to the design of new light harvesting nano devices, in particular a solar nano refrigerator.Comment: 8 pages, 5 figure

Exact finite reduced density matrix and von Neumann entropy for the Calogero model

The information content of continuous quantum variables systems is usually studied using a number of well known approximation methods. The approximations are made to obtain the spectrum, eigenfunctions or the reduced density matrices that are essential to calculate the entropy-like quantities that quantify the information. Even in the sparse cases where the spectrum and eigenfunctions are exactly known the entanglement spectrum, {\em i.e.} the spectrum of the reduced density matrices that characterize the problem, must be obtained in an approximate fashion. In this work, we obtain analytically a finite representation of the reduced density matrices of the fundamental state of the N-particle Calogero model for a discrete set of values of the interaction parameter. As a consequence, the exact entanglement spectrum and von Neumann entropy is worked out.Comment: Journal of Physics A (in press