1,367 research outputs found
From Doubled Chern-Simons-Maxwell Lattice Gauge Theory to Extensions of the Toric Code
We regularize compact and non-compact Abelian Chern-Simons-Maxwell theories
on a spatial lattice using the Hamiltonian formulation. We consider a doubled
theory with gauge fields living on a lattice and its dual lattice. The Hilbert
space of the theory is a product of local Hilbert spaces, each associated with
a link and the corresponding dual link. The two electric field operators
associated with the link-pair do not commute. In the non-compact case with
gauge group , each local Hilbert space is analogous to the one of a
charged "particle" moving in the link-pair group space in a
constant "magnetic" background field. In the compact case, the link-pair group
space is a torus threaded by units of quantized "magnetic" flux,
with being the level of the Chern-Simons theory. The holonomies of the
torus give rise to two self-adjoint extension parameters, which form
two non-dynamical background lattice gauge fields that explicitly break the
manifest gauge symmetry from to . The local Hilbert space
of a link-pair then decomposes into representations of a magnetic translation
group. In the pure Chern-Simons limit of a large "photon" mass, this results in
a -symmetric variant of Kitaev's toric code, self-adjointly
extended by the two non-dynamical background lattice gauge fields. Electric
charges on the original lattice and on the dual lattice obey mutually anyonic
statistics with the statistics angle . Non-Abelian
Berry gauge fields that arise from the self-adjoint extension parameters may be
interesting in the context of quantum information processing.Comment: 38 pages, 4 figure
Graphical Tensor Product Reduction Scheme for the Lie Algebras so(5) = sp(2), su(3), and g(2)
We develop in detail a graphical tensor product reduction scheme, first
described by Antoine and Speiser, for the simple rank 2 Lie algebras so(5) =
sp(2), su(3), and g(2). This leads to an efficient practical method to reduce
tensor products of irreducible representations into sums of such
representations. For this purpose, the 2-dimensional weight diagram of a given
representation is placed in a "landscape" of irreducible representations. We
provide both the landscapes and the weight diagrams for a large number of
representations for the three simple rank 2 Lie algebras. We also apply the
algebraic "girdle" method, which is much less efficient for calculations by
hand for moderately large representations. Computer code for reducing tensor
products, based on the graphical method, has been developed as well and is
available from the authors upon request.Comment: 43 pages, 18 figure
Antiferromagnetically coupled CoFeB/Ru/CoFeB trilayers
This work reports on the magnetic interlayer coupling between two amorphous
CoFeB layers, separated by a thin Ru spacer. We observe an antiferromagnetic
coupling which oscillates as a function of the Ru thickness x, with the second
antiferromagnetic maximum found for x=1.0 to 1.1 nm. We have studied the
switching of a CoFeB/Ru/CoFeB trilayer for a Ru thickness of 1.1 nm and found
that the coercivity depends on the net magnetic moment, i.e. the thickness
difference of the two CoFeB layers. The antiferromagnetic coupling is almost
independent on the annealing temperatures up to 300 degree C while an annealing
at 350 degree C reduces the coupling and increases the coercivity, indicating
the onset of crystallization. Used as a soft electrode in a magnetic tunnel
junction, a high tunneling magnetoresistance of about 50%, a well defined
plateau and a rectangular switching behavior is achieved.Comment: 3 pages, 3 figure
Design Considerations for a Dedicated Gravity Recovery Satellite Mission Consisting of Two Pairs of Satellites
Future satellite missions dedicated to measuring time-variable gravity will need to address the concern of temporal aliasing errors; i.e., errors due to high-frequency mass variations. These errors have been shown to be a limiting error source for future missions with improved sensors. One method of reducing them is to fly multiple satellite pairs, thus increasing the sampling frequency of the mission. While one could imagine a system architecture consisting of dozens of satellite pairs, this paper explores the more economically feasible option of optimizing the orbits of two pairs of satellites. While the search space for this problem is infinite by nature, steps have been made to reduce it via proper assumptions regarding some parameters and a large number of numerical simulations exploring appropriate ranges for other parameters. A search space originally consisting of 15 variables is reduced to two variables with the utmost impact on mission performance: the repeat period of both pairs of satellites (shown to be near-optimal when they are equal to each other), as well as the inclination of one of the satellite pairs (the other pair is assumed to be in a polar orbit). To arrive at this conclusion, we assume circular orbits, repeat groundtracks for both pairs of satellites, a 100-km inter-satellite separation distance, and a minimum allowable operational satellite altitude of 290 km based on a projected 10-year mission lifetime. Given the scientific objectives of determining time-variable hydrology, ice mass variations, and ocean bottom pressure signals with higher spatial resolution, we find that an optimal architecture consists of a polar pair of satellites coupled with a pair inclined at 72deg, both in 13-day repeating orbits. This architecture provides a 67% reduction in error over one pair of satellites, in addition to reducing the longitudinal striping to such a level that minimal post-processing is required, permitting a substantial increase in the spatial resolution of the gravity field products. It should be emphasized that given different sets of scientific objectives for the mission, or a different minimum allowable satellite altitude, different architectures might be selected
Direct observation of domain wall structures in curved permalloy wires containing an antinotch
The formation and field response of head-to-head domain walls in curved permalloy wires, fabricated to contain a single antinotch, have been investigated using Lorentz microscopy. High spatial resolution maps of the vector induction distribution in domain walls close to the antinotch have been derived and compared with micromagnetic simulations. In wires of 10 nm thickness the walls are typically of a modified asymmetric transverse wall type. Their response to applied fields tangential to the wire at the antinotch location was studied. The way the wall structure changes depends on whether the field moves the wall away from or further into the notch. Higher fields are needed and much more distorted wall structures are observed in the latter case, indicating that the antinotch acts as an energy barrier for the domain wal
A quantum Monte Carlo algorithm realizing an intrinsic relaxation
We propose a new quantum Monte Carlo algorithm which realizes a relaxation
intrinsic to the original quantum system. The Monte Carlo dynamics satisfies
the dynamic scaling relation and is independent of the Trotter
number. Finiteness of the Trotter number just appears as the finite-size
effect. An infinite Trotter number version of the algorithm is also formulated,
which enables us to observe a true relaxation of the original system. The
strategy of the algorithm is a compromise between the conventional worldline
local flip and the modern cluster loop flip. It is a local flip in the
real-space direction and is a cluster flip in the Trotter direction. The new
algorithm is tested by the transverse-field Ising model in two dimensions. An
accurate phase diagram is obtained.Comment: 9 pages, 4 figure
Photodetachment study of He^- quartet resonances below the He(n=3) thresholds
The photodetachment cross section of He^- has been measured in the photon
energy range 2.9 eV to 3.3 eV in order to investigate doubly excited states.
Measurements were made channel specific by selectively detecting the residual
He atoms left in a particular excited state following detachment. Three
Feshbach resonances were found in the He(1s2p ^3P)+e^-(epsilon p) partial cross
section: a ^4S resonance below the He(1s3s ^3S) threshold and two ^4P
resonances below the He(1s3p ^3P) threshold. The measured energies of these
doubly excited states are 2.959260(6) eV, 3.072(7) eV and 3.26487(4) eV. The
corresponding widths are found to be 0.20(2) meV, 50(5) meV and 0.61(5) meV.
The measured energies agree well with recent theoretical predictions for the
1s3s4s ^4S, 1s3p^2 ^4P and 1s3p4p ^4P states, respectively, but the widths
deviate noticeably from calculations for 1s3p^2 ^4P and 1s3p4p ^4P states.Comment: 10 pages, 3 figures, LaTeX2e scrartcl, amsmath. Accepted by Journal
of Physics B; minor changes after referee repor
Probabilistic Phase Space Trajectory Description for Anomalous Polymer Dynamics
It has been recently shown that the phase space trajectories for the
anomalous dynamics of a tagged monomer of a polymer --- for single polymeric
systems such as phantom Rouse, self-avoiding Rouse, Zimm, reptation, and
translocation through a narrow pore in a membrane; as well as for
many-polymeric system such as polymer melts in the entangled regime --- is
robustly described by the Generalized Langevin Equation (GLE). Here I show that
the probability distribution of phase space trajectories for all these
classical anomalous dynamics for single polymers is that of a fractional
Brownian motion (fBm), while the dynamics for polymer melts between the
entangled regime and the eventual diffusive regime exhibits small, but
systematic deviations from that of a fBm.Comment: 8 pages, two figures, 3 eps figure files, minor changes,
supplementary material included moved to the appendix, references expanded,
to appear in J. Phys.: Condens. Matte
Dual Monte Carlo and Cluster Algorithms
We discuss the development of cluster algorithms from the viewpoint of
probability theory and not from the usual viewpoint of a particular model. By
using the perspective of probability theory, we detail the nature of a cluster
algorithm, make explicit the assumptions embodied in all clusters of which we
are aware, and define the construction of free cluster algorithms. We also
illustrate these procedures by rederiving the Swendsen-Wang algorithm,
presenting the details of the loop algorithm for a worldline simulation of a
quantum 1/2 model, and proposing a free cluster version of the
Swendsen-Wang replica method for the random Ising model. How the principle of
maximum entropy might be used to aid the construction of cluster algorithms is
also discussed.Comment: 25 pages, 4 figures, to appear in Phys.Rev.
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