357,193 research outputs found
Vortex-vortex control in exciton-polariton condensates
Vortices are widely studied in fields ranging from nonlinear optics to
magnetic systems and superconductors. A vortex carries a binary information
corresponding to its topological charge, `plus' or `minus', that can be used
for information storage and processing. In spatially extended optical and
condensed many-particle systems, achieving full control over vortex formation
and its charge is particularly difficult and is not easily extended to systems
of multiple vortices. Here we demonstrate the optical creation of multiplets of
phase-locked vortices in polariton condensates using off-resonant excitation
with ring-shaped pump beams. We find that the vorticity of one vortex can be
controlled solely using the phase-locking with other nearby vortices. Using
this mechanism, we demonstrate how an existing vortex with a specific
topological charge can be inverted to the oppositely charged state, and how the
charge state of one reference vortex can be copied to a neighboring vortex.
This way we can optically encode any set of binary information onto a chain of
vortices. We further show that this information can be modified later by using
the possibility to address and manipulate each vortex in the chain
individually.Comment: Physical Review B, in pres
Quantization effects and convergence properties of rigid formation control systems with quantized distance measurements
In this paper, we discuss quantization effects in rigid formation control
systems when target formations are described by inter-agent distances. Because
of practical sensing and measurement constraints, we consider in this paper
distance measurements in their quantized forms. We show that under
gradient-based formation control, in the case of uniform quantization, the
distance errors converge locally to a bounded set whose size depends on the
quantization error, while in the case of logarithmic quantization, all distance
errors converge locally to zero. A special quantizer involving the signum
function is then considered with which all agents can only measure coarse
distances in terms of binary information. In this case, the formation converges
locally to a target formation within a finite time. Lastly, we discuss the
effect of asymmetric uniform quantization on rigid formation control.Comment: 29 pages, International Journal of Robust and Nonlinear Control 201
Detection and Characterization of Planets in Binary and Multiple Systems
Moderately close binaries are a special class of targets for planet searches.
From a theoretical standpoint, their hospitality to giant planets is
uncertain and debated. From an observational standpoint, many of these systems
present technical difficulties for precise radial-velocity measurements and
classical Doppler surveys avoid them accordingly. In spite of these adverse
factors, present data support the idea that giant planets residing in binary
and hierarchical systems provide unique observational constraints on the
processes of planet formation and evolution. The interest and the importance of
including various types of binary stars in extrasolar planet studies have thus
grown over time and significant efforts have recently been put into: (i)
searching for stellar companions to the known planet-host stars using direct
imaging, and (ii) extending Doppler planet searches to spectroscopic and
moderately close visual binaries. In this contribution we review the
observational progresses made over the past years to detect and study
extrasolar planets in binary systems, putting special emphasis on the two
developments mentioned above.Comment: 20 pages, 4 figures, review to appear in Extrasolar Planets in
Multi-Body Systems: Theory and Observations, ed. K. Gozdziewski, A.
Niedzielski, and J. Schneider, EAS Publications Serie
Causality and defect formation in the dynamics of an engineered quantum phase transition in a coupled binary Bose-Einstein condensate
Continuous phase transitions occur in a wide range of physical systems, and
provide a context for the study of non-equilibrium dynamics and the formation
of topological defects. The Kibble-Zurek (KZ) mechanism predicts the scaling of
the resulting density of defects as a function of the quench rate through a
critical point, and this can provide an estimate of the critical exponents of a
phase transition. In this work we extend our previous study of the
miscible-immiscible phase transition of a binary Bose-Einstein condensate (BEC)
composed of two hyperfine states in which the spin dynamics are confined to one
dimension [J. Sabbatini et al., Phys. Rev. Lett. 107, 230402 (2011)]. The
transition is engineered by controlling a Hamiltonian quench of the coupling
amplitude of the two hyperfine states, and results in the formation of a random
pattern of spatial domains. Using the numerical truncated Wigner phase space
method, we show that in a ring BEC the number of domains formed in the phase
transitions scales as predicted by the KZ theory. We also consider the same
experiment performed with a harmonically trapped BEC, and investigate how the
density inhomogeneity modifies the dynamics of the phase transition and the KZ
scaling law for the number of domains. We then make use of the symmetry between
inhomogeneous phase transitions in anisotropic systems, and an inhomogeneous
quench in a homogeneous system, to engineer coupling quenches that allow us to
quantify several aspects of inhomogeneous phase transitions. In particular, we
quantify the effect of causality in the propagation of the phase transition
front on the resulting formation of domain walls, and find indications that the
density of defects is determined during the impulse to adiabatic transition
after the crossing of the critical point.Comment: 23 pages, 10 figures. Minor corrections, typos, additional referenc
Two computational primitives for algorithmic self-assembly: Copying and counting
Copying and counting are useful primitive operations for computation and construction. We have made DNA crystals that copy and crystals that count as they grow. For counting, 16 oligonucleotides assemble into four DNA Wang tiles that subsequently crystallize on a polymeric nucleating scaffold strand, arranging themselves in a binary counting pattern that could serve as a template for a molecular electronic demultiplexing circuit. Although the yield of counting crystals is low, and per-tile error rates in such crystals is roughly 10%, this work demonstrates the potential of algorithmic self-assembly to create complex nanoscale patterns of technological interest. A subset of the tiles for counting form information-bearing DNA tubes that copy bit strings from layer to layer along their length
Quantifying Triadic Closure in Multi-Edge Social Networks
Multi-edge networks capture repeated interactions between individuals. In
social networks, such edges often form closed triangles, or triads. Standard
approaches to measure this triadic closure, however, fail for multi-edge
networks, because they do not consider that triads can be formed by edges of
different multiplicity. We propose a novel measure of triadic closure for
multi-edge networks of social interactions based on a shared partner statistic.
We demonstrate that our operalization is able to detect meaningful closure in
synthetic and empirical multi-edge networks, where common approaches fail. This
is a cornerstone in driving inferential network analyses from the analysis of
binary networks towards the analyses of multi-edge and weighted networks, which
offer a more realistic representation of social interactions and relations.Comment: 19 pages, 5 figures, 6 table
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