Charge carrier correlation in the electron-doped t-J model

We study the t-t'-t''-J model with parameters chosen to model an electron-doped high temperature superconductor. The model with one, two and four charge carriers is solved on a 32-site lattice using exact diagonalization. Our results demonstrate that at doping levels up to x=0.125 the model possesses robust antiferromagnetic correlation. When doped with one charge carrier, the ground state has momenta (\pm\pi,0) and (0,\pm\pi). On further doping, charge carriers are unbound and the momentum distribution function can be constructed from that of the single-carrier ground state. The Fermi surface resembles that of small pockets at single charge carrier ground state momenta, which is the expected result in a lightly doped antiferromagnet. This feature persists upon doping up to the largest doping level we achieved. We therefore do not observe the Fermi surface changing shape at doping levels up to 0.125

Continuous-time Diffusion Monte Carlo and the Quantum Dimer Model

A continuous-time formulation of the Diffusion Monte Carlo method for lattice models is presented. In its simplest version, without the explicit use of trial wavefunctions for importance sampling, the method is an excellent tool for investigating quantum lattice models in parameter regions close to generalized Rokhsar-Kivelson points. This is illustrated by showing results for the quantum dimer model on both triangular and square lattices. The potential energy of two test monomers as a function of their separation is computed at zero temperature. The existence of deconfined monomers in the triangular lattice is confirmed. The method allows also the study of dynamic monomers. A finite fraction of dynamic monomers is found to destroy the confined phase on the square lattice when the hopping parameter increases beyond a finite critical value. The phase boundary between the monomer confined and deconfined phases is obtained.Comment: 4 pages, 4 figures, revtex; Added a figure showing the confinement/deconfinement phase boundary for the doped quantum dimer mode

Improving the Fidelity of Optical Zeno Gates via Distillation

We have modelled the Zeno effect Control-Sign gate of Franson et al (PRA 70, 062302, 2004) and shown that high two-photon to one-photon absorption ratios, $\kappa$, are needed for high fidelity free standing operation. Hence we instead employ this gate for cluster state fusion, where the requirement for $\kappa$ is less restrictive. With the help of partially offline one-photon and two-photon distillations, we can achieve a fusion gate with unity fidelity but non-unit probability of success. We conclude that for $\kappa > 2200$, the Zeno fusion gate will out perform the equivalent linear optics gate.Comment: 6 pages, 11 figures, Submitted to PR

Normal Approximation in Large Network Models

We develop a methodology for proving central limit theorems in network models with strategic interactions and homophilous agents. Since data often consists of observations on a single large network, we consider an asymptotic framework in which the network size tends to infinity. In the presence of strategic interactions, network moments are generally complex functions of components, where a node's component consists of all alters to which it is directly or indirectly connected. We find that a modification of "exponential stabilization" conditions from the stochastic geometry literature provides a useful formulation of weak dependence for moments of this type. We establish a CLT for a network moments satisfying stabilization and provide a methodology for deriving primitive sufficient conditions for stabilization using results in branching process theory. We apply the methodology to static and dynamic models of network formation

Hole correlation and antiferromagnetic order in the t-J model

We study the t-J model with four holes on a 32-site square lattice using exact diagonalization. This system corresponds to doping level x=1/8. At the ``realistic'' parameter J/t=0.3, holes in the ground state of this system are unbound. They have short range repulsion due to lowering of kinetic energy. There is no antiferromagnetic spin order and the electron momentum distribution function resembles hole pockets. Furthermore, we show evidence that in case antiferromagnetic order exists, holes form d-wave bound pairs and there is mutual repulsion among hole pairs. This presumably will occur at low doping level. This scenario is compatible with a checkerboard-type charge density state proposed to explain the ``1/8 anomaly'' in the LSCO family, except that it is the ground state only when the system possesses strong antiferromagnetic order

Galileo internal electrostatic discharge program

The Galileo spacecraft which will orbit Jupiter in 1988 will encounter a very harsh environment of energetic electrons. These electrons will have sufficient energy to penetrate the spacecraft shielding, consequently depositing charges in the dielectric insulating materials or ungrounded conductors. The resulting electric field could exceed the breakdown strength of the insulating materials, producing discharges. The transients produced from these Internal Electrostatic Discharges (IESD) could, depending on their relative location, be coupled to nearby cables and circuits. These transients could change the state of logic circuits or degrade or even damage spacecraft components, consequently disrupting the operation of subsystems and systems of the Galileo spacecraft during its expected mission life. An extensive testing program was initiated for the purpose of understanding the potential threats associated with these IESD events. Data obtained from these tests were used to define design guidelines