84 research outputs found
Criteria for Continuous-Variable Quantum Teleportation
We derive an experimentally testable criterion for the teleportation of
quantum states of continuous variables. This criterion is especially relevant
to the recent experiment of Furusawa et al. [Science 282, 706-709 (1998)] where
an input-output fidelity of was achieved for optical coherent
states. Our derivation demonstrates that fidelities greater than 1/2 could not
have been achieved through the use of a classical channel alone; quantum
entanglement was a crucial ingredient in the experiment.Comment: 12 pages, to appear in Journal of Modern Optic
Crystalline Assemblies and Densest Packings of a Family of Truncated Tetrahedra and the Role of Directional Entropic Forces
Polyhedra and their arrangements have intrigued humankind since the ancient
Greeks and are today important motifs in condensed matter, with application to
many classes of liquids and solids. Yet, little is known about the
thermodynamically stable phases of polyhedrally-shaped building blocks, such as
faceted nanoparticles and colloids. Although hard particles are known to
organize due to entropy alone, and some unusual phases are reported in the
literature, the role of entropic forces in connection with polyhedral shape is
not well understood. Here, we study thermodynamic self-assembly of a family of
truncated tetrahedra and report several atomic crystal isostructures, including
diamond, {\beta}-tin, and high- pressure lithium, as the polyhedron shape
varies from tetrahedral to octahedral. We compare our findings with the densest
packings of the truncated tetrahedron family obtained by numerical compression
and report a new space filling polyhedron, which has been overlooked in
previous searches. Interestingly, the self-assembled structures differ from the
densest packings. We show that the self-assembled crystal structures can be
understood as a tendency for polyhedra to maximize face-to-face alignment,
which can be generalized as directional entropic forces.Comment: Article + supplementary information. 23 pages, 10 figures, 2 table
Ozone-Activated Nanoporous Gold: A Stable and Storable Material for Catalytic Oxidation
We
report a new method for facile and reproducible activation of
nanoporous gold (npAu) materials of different forms for the catalytic
selective partial oxidation of alcohols under ambient pressure, steady
flow conditions. This method, based on the surface cleaning of npAu
ingots with ozone to remove carbon documented in ultrahigh vacuum
conditions, produces active npAu catalysts from ingots, foils, and
shells by flowing an ozone/dioxygen mixture over the catalyst at 150
°C, followed by a temperature ramp from 50 to 150 °C in
a flowing stream of 10% methanol and 20% oxygen. With this treatment,
all three materials (ingots, foils, and shells) can be reproducibly
activated, despite potential carbonaceous poisons resulting from their
synthesis, and are highly active for the selective oxidation of primary
alcohols over prolonged periods of time. The npAu materials activated
in this manner exhibit catalytic behavior substantially different
from those activated under different conditions previously reported.
Once activated in this manner, they can be stored and easily reactivated
by flow of reactant gases at 150 °C for a few hours. They possess
improved selectivity for the coupling of higher alcohols, such as
1-butanol, and are not active for carbon monoxide oxidation. This
ozone-treated npAu is a functionally new catalytic material
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