20,676 research outputs found
Spin-guides and spin-splitters: Waveguide analogies in one-dimensional spin chains
Here we show a direct mapping between waveguide theory and spin chain
transport, opening an alternative approach to quantum information transport in
the solid-state. By applying temporally varying control profiles to a spin
chain, we design a virtual waveguide or 'spin-guide' to conduct individual spin
excitations along defined space-time trajectories of the chain. We explicitly
show that the concepts of confinement, adiabatic bend loss and beamsplitting
can be mapped from optical waveguide theory to spin-guides (and hence
'spin-splitters'). Importantly, the spatial scale of applied control pulses is
required to be large compared to the inter-spin spacing, and thereby allowing
the design of scalable control architectures.Comment: 5 figure
Quantum phase transitions in photonic cavities with two-level systems
Systems of coupled photonic cavities have been predicted to exhibit quantum
phase transitions by analogy with the Hubbard model. To this end, we have
studied topologies of few (up to six) photonic cavities each containing a
single two-level system. Quantum phase space diagrams are produced for these
systems, and compared to mean-field results. We also consider finite effective
temperature, and compare this to the notion of disorder. We find the extent of
the Mott lobes shrink analogously to the conventional Bose-Hubbard model.Comment: 11 pages, 11 figures, updated typo
Quantum System Identification by Bayesian Analysis of Noisy Data: Beyond Hamiltonian Tomography
We consider how to characterize the dynamics of a quantum system from a
restricted set of initial states and measurements using Bayesian analysis.
Previous work has shown that Hamiltonian systems can be well estimated from
analysis of noisy data. Here we show how to generalize this approach to systems
with moderate dephasing in the eigenbasis of the Hamiltonian. We illustrate the
process for a range of three-level quantum systems. The results suggest that
the Bayesian estimation of the frequencies and dephasing rates is generally
highly accurate and the main source of errors are errors in the reconstructed
Hamiltonian basis.Comment: 6 pages, 3 figure
How the asymmetry of internal potential influences the shape of I-V characteristic of nanochannels
Ion transport in biological and synthetic nanochannels is characterized by
such phenomena as ion current fluctuations, rectification, and pumping.
Recently, it has been shown that the nanofabricated synthetic pores could be
considered as analogous to biological channels with respect to their transport
characteristics \cite{Apel, Siwy}. The ion current rectification is analyzed.
Ion transport through cylindrical nanopores is described by the Smoluchowski
equation. The model is considering the symmetric nanopore with asymmetric
charge distribution. In this model, the current rectification in asymmetrically
charged nanochannels shows a diode-like shape of characteristic. It is
shown that this feature may be induced by the coupling between the degree of
asymmetry and the depth of internal electric potential well. The role of
concentration gradient is discussed
Infrared luminosities of galaxies in the Local Volume
Near-infrared properties of 451 galaxies with distances D \leq 10 Mpc are
considered basing on the all-sky two micron survey (2MASS). A luminosity
function of the galaxies in the K-band is derived within [-25,-11] mag. The
local (D < 8 Mpc) luminosity density is estimated to be 6.8*10^8 L_sun/Mpc^3
that exceeds (1.5+-0.1) times the global cosmic density in the K-band. Virial
mass-to-K-luminosity ratios are determined for nearby groups and clusters. In
the luminosity range of (5*10^{10} - 2*10^{13})L_sun, the groups and clusters
follow the relation \lg(M/L_K) propto (0.27+-0.03) lg(L_K) with a scatter of
\~0.1 comparable to errors of the observables. The mean ratio ~=
(20-25) M_sun/L_sun for the galaxy systems turns out to be significantly lower
than the global ratio, (80-90)M_sun/L_sun, expected in the standard
cosmological model with the matter density of Omega_m =0.27. This discrepancy
can be resolved if most of dark matter in the universe is not associated with
galaxies and their systems.Comment: 15 pages, 7 figures. Astronomy Letters, submitte
Measurement of Jets and Jet Suppression in sqrt(s_NN)=2.76 TeV Lead-Lead Collisions with the ATLAS detector at the LHC
The first results of single jet observables in Pb+Pb collisions at
sqrt(s_NN)=2.76 TeV measured with the ATLAS detector at the LHC are presented.
Full jets are reconstructed with the anti-kt algorithm with R= 0.2 and 0.4,
using an event-by-event subtraction procedure to correct for the effects of the
underlying event including elliptic flow. The geometrically-scaled ratio of jet
yields in central and peripheral events,Rcp, indicates a clear suppression of
jets with ET >100 GeV. The transverse and longitudinal distributions of jet
fragments is also presented. We find little no substantial change to the
fragmentation properties and no significant change in the level of suppression
when moving to the larger jet definition.Comment: 5 pages, 6 figures, proceedings for Quark Matter 2011, Annecy,
France, May 23-28, 201
The Impact of Vegetation Structure and Spatial Heterogeneity on Invertebrate Biodiversity Within Upland Landscapes
Livestock grazing influences vegetation structure and composition at both the patch and wider landscape scale (Milne et al., 1998), and this may have effects on upland invertebrate communities, which in turn influence bird abundance and distribution (Fuller & Gough, 1999; Cole et al., 2002). Of particular importance are open grasslands and wet flushes where invertebrates are abundant and more accessible to birds. However, there have been few studies of invertebrates associated with upland habitats, and most of these have focused on heather moorland, blanket bog, or very fine-scaled structure within grasslands (Dennis et al. 1997; 1998; 2001). This study addresses the relationship between upland invertebrate biodiversity and the spatial and structural diversity of vegetation
Galaxy Clustering and Large-Scale Structure from z = 0.2 to z = 0.5 in Two Norris Redshift Surveys
(abridged) We present a study of the nature and evolution of large-scale
structure based on two independent redshift surveys of faint field galaxies
conducted with the 176-fiber Norris Spectrograph on the Palomar 200-inch
telescope. The two surveys together sparsely cover ~20 sq. degrees and contain
835 r < 21 mag galaxies with redshifts 0.2 < z < 0.5. Both surveys have a
median redshift of z = 0.30. In order to obtain a rough estimate of the cosmic
variance, we analyze the two surveys independently. We measure the comoving
correlation length to be 3.70 +/- 0.13 h^-1 Mpc at z = 0.30 with a power-law
slope gamma = 1.77 +/- 0.05. Dividing the sample into low (0.2 < z < 0.3) and
high (0.32 < z < 0.5) redshift intervals, we see no evidence for a change in
the comoving correlation length over the redshift range 0.2 < z < 0.5. Similar
to the well-established results in the local universe, we find that
intrinsically bright galaxies are more strongly clustered than intrinsically
faint galaxies and that galaxies with little ongoing star formation, as judged
from the rest-frame equivalent width of the [OII]3727, are more strongly
clustered than galaxies with significant ongoing star formation. The rest-frame
pairwise velocity dispersion of the sample is 326^+67_-52 km s^-1, ~25% lower
than typical values measured locally. The appearance of the galaxy
distribution, particularly in the more densely sampled Abell 104 field, is
quite striking. The pattern of sheets and voids which has been observed locally
continues at least to z ~ 0.5. A friends-of-friends analysis of the galaxy
distribution supports the visual impression that > 90% of all galaxies at z <
0.5 are part of larger structures with overdensities of > 5.Comment: 40 pages including 26 Postscript figures; revised version to match
version accepted by Ap
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