445 research outputs found
Thermal state entanglement in harmonic lattices
We investigate the entanglement properties of thermal states of the harmonic
lattice in one, two and three dimensions. We establish the value of the
critical temperature for entanglement between neighbouring sites and give
physical reasons. Further sites are shown to be entangled only due to boundary
effects. Other forms of entanglement are addressed in the second part of the
paper by using the energy as witness of entanglement. We close with a
comprehensive diagram showing the different phases of entanglement versus
complete separability and propose techniques to swap and tune entanglement
experimentally.Comment: 9 pages, 4 figure
L1551NE - Discovery of a Binary Companion
L1551NE is a very young (class 0 or I) low-mass protostar located close to
the well-studied L1551 IRS5. We present here evidence, from 1.3mm continuum
interferometric observations at ~1'' resolution, for a binary companion to
L1551NE. The companion, whose 1.3mm flux density is ~1/3 that of the primary
component, is located 1.43'' (~230 A.U. at 160pc) to the southeast. The
millimeterwave emission from the primary component may have been just barely
resolved, with deconvolved size ~0.82"x0.70" (~131x112 A.U.). The companion
emission was unresolved (<100 A.U.). The pair is embedded within a flattened
circum-binary envelope of size ~5.4'' x 2.3'' (~860 x 370 A.U.). The masses of
the three components (i.e. from the cicumstellar material of the primary star
and its companion, and the envelope) are approximately 0.044, 0.014 and 0.023
Mo respectively.Comment: 8 pages, 1 figur
The detection of the J = 3-2 lines of HCN, HNC, and HCO^+ in the Orion molecular cloud
We report the first measurements of the 1.1 mm (J = 3-2) lines of HCN, HNC, and HCO^+ in the Orion molecular cloud. The low-intensity broad velocity wings seen in the (1-0) lines of HCN and HCO^+ are greatly enhanced in the HCN (3-2) line but not in HCO^+ (3-2). No broad wings are seen in the HNC (3-2) line. The HCN observations suggest molecular hydrogen densities ~ 10^6 cm^(-3) in the broad wing source, and the differences between the lines of HCN and HCO^+ suggest that the lines may be formed in different regions within the source
On the Green's Function of the almost-Mathieu Operator
The square tight-binding model in a magnetic field leads to the
almost-Mathieu operator which, for rational fields, reduces to a
matrix depending on the components , of the wave vector in the
magnetic Brillouinzone. We calculate the corresponding Green's function without
explicit knowledge of eigenvalues and eigenfunctions and obtain analytical
expressions for the diagonal and the first off-diagonal elements; the results
which are consistent with the zero magnetic field case can be used to calculate
several quantities of physical interest (e. g. the density of states over the
entire spectrum, impurity levels in a magnetic field).Comment: 9 pages, 3 figures corrected some minor errors and typo
Exponential Complexity of the Quantum Adiabatic Algorithm for certain Satisfiability Problems
We determine the complexity of several constraint satisfaction problems using
the quantum adiabatic algorithm in its simplest implementation. We do so by
studying the size dependence of the gap to the first excited state of "typical"
instances. We find that at large sizes N, the complexity increases
exponentially for all models that we study. We also compare our results against
the complexity of the analogous classical algorithm WalkSAT and show that the
harder the problem is for the classical algorithm the harder it is also for the
quantum adiabatic algorithm.Comment: 9 pages, 7 figure
Electric Dipole Radiation from Spinning Dust Grains
We discuss the rotational excitation of small interstellar grains and the
resulting electric dipole radiation from spinning dust. Attention is given to
excitation and damping of rotation by: collisions with neutrals; collisions
with ions; plasma drag; emission of infrared radiation; emission of microwave
radiation; photoelectric emission; and formation of H_2 on the grain surface.
We introduce dimensionless functions F and G which allow direct comparison of
the contributions of different mechanisms to rotational drag and excitation.
Emissivities are estimated for dust in different phases of the interstellar
medium, including diffuse HI, warm HI, low-density photoionized gas, and cold
molecular gas. Spinning dust grains can explain much, and perhaps all, of the
14-50 GHz background component recently observed in CBR studies. It should be
possible to detect rotational emission from small grains by ground-based
observations of molecular clouds.Comment: 59 pages, 19 eps figures, uses aaspp4.sty . Submitted to Ap.
Conductivity of 2D lattice electrons in an incommensurate magnetic field
We consider conductivities of two-dimensional lattice electrons in a magnetic
field. We focus on systems where the flux per plaquette is irrational
(incommensurate flux). To realize the system with the incommensurate flux, we
consider a series of systems with commensurate fluxes which converge to the
irrational value. We have calculated a real part of the longitudinal
conductivity . Using a scaling analysis, we have found
behaves as \,
when and the Fermi energy is near
zero. This behavior is closely related to the known scaling behavior of the
spectrum.Comment: 16 pages, postscript files are available on reques
The Nature of the IRAS Ring G159.6−18.5 in Perseus and Its Exciting Star HD 278942
We discuss an extended feature in the Perseus molecular cloud complex, most prominent in the IRAS database as an almost complete ring of radius 0.75 degrees, but also clearly seen in optical surveys and in radio continuum emission
Time Periodic Behavior of Multiband Superlattices in Static Electric Fields
We use an analytic perturbation expansion for the two-band system of tight
binding electrons to discuss Bloch oscillations and Zener tunneling within this
model. We make comparison with recent numerical results and predict
analytically the frequency of radiation expected from Zener tunneling,
including its disappearance, as a function of the system parameters.Comment: 12 pages, no figure include
Reply to the Comment by B. Andresen
All the comments made by Andresen's comments are replied and are shown not to
be pertinent. The original discussions [ABE S., Europhys. Lett. 90 (2010)
50004] about the absence of nonextensive statistical mechanics with q-entropies
for classical continuous systems are reinforced.Comment: 5 pages. This is Reply to B. Andresen's Comment on the paper entitled
"Essential discreteness in generalized thermostatistics with non-logarithmic
entropy", Europhys. Lett. 90 (2010) 5000
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