481 research outputs found
Entanglement and Symmetry: A Case Study in Superselection Rules, Reference Frames, and Beyond
This paper concentrates on a particular example of a constraint imposed by
superselection rules (SSRs): that which applies when the parties (Alice and
Bob) cannot distinguish among certain quantum objects they have. This arises
naturally in the context of ensemble quantum information processing such as in
liquid NMR. We discuss how a SSR for the symmetric group can be applied, and
show how the extractable entanglement can be calculated analytically in certain
cases, with a maximum bipartite entanglement in an ensemble of N Bell-state
pairs scaling as log(N) as N goes to infinity . We discuss the apparent
disparity with the asymptotic (N >> 1) recovery of unconstrained entanglement
for other sorts of superselection rules, and show that the disparity disappears
when the correct notion of applying the symmetric group SSR to multiple copies
is used. Next we discuss reference frames in the context of this SSR, showing
the relation to the work of von Korff and Kempe [Phys. Rev. Lett. 93, 260502
(2004)]. The action of a reference frame can be regarded as the analog of
activation in mixed-state entanglement. We also discuss the analog of
distillation: there exist states such that one copy can act as an imperfect
reference frame for another copy. Finally we present an example of a stronger
operational constraint, that operations must be non-collective as well as
symmetric. Even under this stronger constraint we nevertheless show that
Bell-nonlocality (and hence entanglement) can be demonstrated for an ensemble
of N Bell-state pairs no matter how large N is. This last work is a
generalization of that of Mermin [Phys. Rev. D 22, 356 (1980)].Comment: 16 pages, 6 figures. v2 updated version published in Phys Rev
Space shuttle abort separation pressure investigation. Volume 2, Part B: Orbiter data at Mach 5
For abstract, see
Incomplete quantum state estimation: a comprehensive study
We present a detailed account of quantum state estimation by joint
maximization of the likelihood and the entropy. After establishing the
algorithms for both perfect and imperfect measurements, we apply the procedure
to data from simulated and actual experiments. We demonstrate that the
realistic situation of incomplete data from imperfect measurements can be
handled successfully.Comment: 11 pages, 10 figure
High-sensitivity force measurement using entangled probes
We show the possibility to improve the measurement sensitivity of a weak
force by using two meters in an entangled state. This latter can be achieved by
exploiting radiation pressure effects.Comment: ReVTeX file, 11 pages, 2 eps figure
A new mechanism for exchange processes observed in the compounds [M(η-C_5H_5)_2(exo-η-RCH = CH_2)H], M = Nb and Ta
Dynamic n.m.r. studies of the exchange processes in the complexes [M(η-C_5H_5)(exo-η-RCH=CH_2)H], M = Nb, Ta, lead to the proposal of a new mechanism involving intermediates with agostic bonding
Carbon Nanotube Electron Windmills: A Novel Design for Nanomotors
We propose a new drive mechanism for carbon nanotube (CNT) motors, based upon
the torque generated by a flux of electrons passing through a chiral nanotube.
The structure of interest comprises a double-walled CNT, formed from, for
example, an achiral outer tube encompassing a chiral inner tube. Through a
detailed analysis of electrons passing through such a "windmill", we find that
the current due to a potential difference applied to the outer CNT generates
sufficient torque to overcome the static and dynamic frictional forces that
exists between the inner and outer walls, thereby causing the inner tube to
rotate.Comment: 10 pages and 4 figure
Space shuttle abort separation pressure investigation. Volume 6: Orbiter data at Mach 2
For abstract, see
Investigation of the McDonnell-Douglas orbiter and booster shuttle models in proximity at Mach numbers 2.0 to 6.0. Volume 7: Proximity data at Mach 4 and 6, interference free and launch vehicle data
Aerodynamic data obtained from a space shuttle abort stage separation wind tunnel test are presented. The .00556 scale models of the orbiter and booster configuration were tested in close proximity using dual balances during the time period of April 21 to April 27 1971. Data were obtained for both booster and orbiter over an angle of attack range from -10 to 10 deg for zero degree sideslip angle. The models were tested at several relative incidence angles and separation distances and power conditions. Plug nozzles utilizing air were used to simulate booster and orbiter plumes at various altitudes along a nominal ascent trajectory. Powered conditions were 100, 50, 25 and 0 percent of full power for the orbiter and 100, 50 and 0 percent of full power for the booster. Pitch control effectiveness data were obtained for both booster and orbiter with power on and off. In addition, launch vehicle data with and without booster power were obtained utilizing a single balance in the booster model. Data were also obtained with the booster canard off in close proximity and for the launch configuration
Space shuttle abort separation pressure investigation. Volume 1, Part A: Booster data at Mach 5
Pressure data obtained from a joint Langley Research Center (LaRC)/Marshall Space Flight Center (MSFC) Space Shuttle about stage separation wind tunnel test are presented. The .00556 scale models of the McDonnell-Douglas orbiter and booster configurations were tested in proximity in Tunnel A of the Von Karman Facility (VKF), Arnold Engineering Development Center (AEDC). Mach numbers were 5.0, 3.0, and 2.0 and nominal Reynolds numbers were 1.09, 1.60, and 1.74 million per foot, respectively. Pressure data were obtained for the booster upper surface and orbiter lower surface at angles of attack of -10 deg, -5, 0, 5, and 10 deg for zero degrees sideslip. The models were tested at incidence angles of 0 and 5 deg for several separation distances and power conditions. Plug nozzles utilizing air were used to simulate booster and orbiter plumes at various altitudes along a nominal ascent trajectory. Powered conditions were 100, 50, and 0 percent of full power for the orbiter and 100, 50 and 0 percent of full power for the booster. Data were also obtained with the booster canard off in close proximity
Space shuttle abort separation pressure investigation. Volume 1, Part B: Booster data at Mach 5
For abstract, see
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