159,950 research outputs found
Entanglement Distillation Protocols and Number Theory
We show that the analysis of entanglement distillation protocols for qudits
of arbitrary dimension benefits from applying basic concepts from number
theory, since the set \zdn associated to Bell diagonal states is a module
rather than a vector space. We find that a partition of \zdn into divisor
classes characterizes the invariant properties of mixed Bell diagonal states
under local permutations. We construct a very general class of recursion
protocols by means of unitary operations implementing these local permutations.
We study these distillation protocols depending on whether we use twirling
operations in the intermediate steps or not, and we study them both
analitically and numerically with Monte Carlo methods. In the absence of
twirling operations, we construct extensions of the quantum privacy algorithms
valid for secure communications with qudits of any dimension . When is a
prime number, we show that distillation protocols are optimal both
qualitatively and quantitatively.Comment: REVTEX4 file, 7 color figures, 2 table
Charge Fluctuations in the Edge States of N-S hybrid Nano-Structures
In this work we show how to calculate the equilibrium and non-equilibrium
charge fluctuations in a gated normal mesoscopic conductor which is attached to
one normal lead and one superconducting lead. We then consider an example where
the structure is placed in a high magnetic field, such that the transport is
dominated by edge states. We calculate the equilibrium and non-equilibrium
charge fluctuations in the gate, for a single edge state, comparing our results
to those for the same system, but with two normal leads. We then consider the
specific example of a quantum point contact and calculate the charge
fluctuations in the gate for more than one edge state.Comment: 4 pages with 1 figure. In published version the high magnetic field
dynamics of the holes is treated incorrectly. An erratum is in preparatio
Keck Observations of the Hidden Quasar IRAS P09104+4109
We present imaging and spectro- polarimetric observations of the
ultraluminous infrared galaxy IRAS P09104+4109 using the Keck 10-m Telescope.
We detect the clear presence of broad Hb, Hg, and MgII 2800 emission lines in
the polarized flux spectra of the nucleus and of an extranuclear emission
region ~ 4" away, confirming the presence of a hidden central quasar. The
polarization of the broad Mg II emission line is high (~ 29%), consistent with
the remarkably high polarization (~ 30%-40%) observed in the extended continuum
emission. The narrow emission lines are polarized in a stratified fashion, with
the high ionization lines being polarized 0.7%-1.7% and [O II] essentially
unpolarized. The line polarizations are positively correlated with critical
density, ionization potential, and velocity width of the emission lines. This
indicates that the NLR may be partially shadowed by the putative torus, with
the higher ionization lines originating closer to the nucleus. One notable
characteristic of the extranuclear knot is that all species of Fe are markedly
absent in its spectrum, while they appear prominently in the nucleus. Our
favored interpretation is that there is a large amount of dust in the
extranuclear regions, allowing gaseous refractory metals to deposit. The
extended emission regions are most likely material shredded from nearby cluster
members and not gas condensed from the cooling flow or expelled from the
obscured quasar. Our data provide strong evidence for matter-bounded clouds in
addition to ionization-bounded clouds in the NLR. Ionization by pure velocity
shocks can be ruled out. Shocks with photoionizing precursors may be present,
but are probably not a dominant contributor to the energy input.Comment: 32 pages, including 9 figs and 2 tables, to be published in the
Astronomical Journa
A Design Strategy for Deadlock-Free Concurrent Systems
When building concurrent systems, it would be useful to have a collection of reusable processes
to perform standard tasks. However, without knowing certain details of the inner workings of
these components, one can never be sure that they will not cause deadlock when connected to
some particular network.
Here we describe a hierarchical method for designing complex networks of communicating
processeswhich are deadlock-free.We use this to define a safe and simple method for specifying
the communication interface to third party software components. This work is presented using
the CSP model of concurrency and the occam2.1 programming language
The infrared counterpart to the magnetar 1RXS J170849.0-400910
We have analyzed both archival and new infrared imaging observations of the
field of the Anomalous X-ray Pulsar 1RXS J170849.0-400910, in search of the
infrared counterpart. This field has been previously investigated, and one of
the sources consistent with the position of the AXP suggested as the
counterpart. We, however, find that this object is more likely a background
star, while another object within the positional error circle has non-stellar
colors and shows evidence for variability. These two pieces of evidence, along
with a consistency argument for the X-ray-to-infrared flux ratio, point to the
second source being the more likely infrared counterpart to the AXP.Comment: 19 pages AASTEX, 4 figure. Accepted for publication in ApJ. Full
resolution figures at: http://www.astro.utoronto.ca/~durant/1708.ps.g
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