20,580 research outputs found
Einstein-Podolsky-Rosen paradox and quantum steering in pulsed optomechanics
We describe how to generate an Einstein-Podolsky-Rosen (EPR) paradox between
a mesoscopic mechanical oscillator and an optical pulse. We find two types of
paradox, defined by whether it is the oscillator or the pulse that shows the
effect Schrodinger called "steering". Only the oscillator paradox addresses the
question of mesoscopic local reality for a massive system. In that case, EPR's
"elements of reality" are defined for the oscillator, and it is these elements
of reality that are falsified (if quantum mechanics is complete). For this sort
of paradox, we show that a thermal barrier exists, meaning that a threshold
level of pulse-oscillator interaction is required for a given thermal
occupation n_0 of the oscillator. We find there is no equivalent thermal
barrier for the entanglement of the pulse with the oscillator, nor for the EPR
paradox that addresses the local reality of the optical system. Finally, we
examine the possibility of an EPR paradox between two entangled oscillators.
Our work highlights the asymmetrical effect of thermal noise on quantum
nonlocality.Comment: 9 pages, 7 figure
A Trigonometric Parallax of Sgr B2
We have measured the positions of water masers in Sgr B2, a massive star
forming region in the Galactic center, relative to an extragalactic radio
source with the Very Long Baseline Array. The positions measured at 12 epochs
over a time span of one year yield the trigonometric parallax of Sgr B2 and
hence a distance to the Galactic center of Ro=7.9 (+0.8/-0.7) kpc. The proper
motion of Sgr B2 relative to Sgr A* suggests that Sgr B2 is about 0.13 kpc
nearer than the Galactic center, assuming a low-eccentricity Galactic orbit.Comment: Submitted to ApJ; 4 tables; 3 figures. Version 2 corrects Fig. 2
which was missing some dat
Zirconium carbide as an electrocatalyst for the chromous-chromic redox couple
Zirconium carbide is used as a catalyst in a REDOX cell for the oxidation of chromous ions to chromic ions and for the reduction of chromic ions to chromous ions. The zirconium carbide is coated on an inert electronically conductive electrode which is present in the anode fluid of the cell
The Megamaser Cosmology Project. V. An Angular Diameter Distance to NGC 6264 at 140 Mpc
We present the direct measurement of the Hubble constant, yielding the direct
measurement of the angular-diameter distance to NGC 6264 using the HO
megamaser technique. Our measurement is based on sensitive observations of the
circumnuclear megamaser disk from four observations with the Very Long Baseline
Array, the Green Bank Telescope and the Effelsberg Telescope. We also monitored
the maser spectral profile for 2.3 years using the Green Bank Telescope to
measure accelerations of maser lines by tracking their line-of-sight velocities
as they change with time. The measured accelerations suggest that the systemic
maser spots have a significantly wider radial distribution than in the
archetypal megamaser in NGC 4258. We model the maser emission as arising from a
circumnuclear disk with orbits dominated by the central black hole. The best
fit of the data gives a Hubble constant of 689 km s
Mpc, which corresponds to an angular-diameter distance of 14419
Mpc. In addition, the fit also gives a mass of the central black hole of
(3.090.42) . The result demonstrates the
feasibility of measuring distances to galaxies located well into the Hubble
flow by using circumnuclear megamaser disks.Comment: 29 pages, 8 figures, Accepted by Ap
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