8,258 research outputs found
VISTAS Interdisciplinary Colloquium on Emerging Research on Education, Economy and Community
Abstracts of presentations given at the VISTAS Interdisciplinary Colloquium on Emerging Research on Education, Economy and Communit
An information and field theoretic approach to the grand canonical ensemble
We present a novel derivation of the constraints required to obtain the
underlying principles of statistical mechanics using a maximum entropy
framework. We derive the mean value constraints by use of the central limit
theorem and the scaling properties of Lagrange multipliers. We then arrive at
the same result using a quantum free field theory and the Ward identities. The
work provides a principled footing for maximum entropy methods in statistical
physics, adding the body of work aligned to Jaynes's vision of statistical
mechanics as a form of inference rather than a physical theory dependent on
ergodicity, metric transitivity and equal a priori probabilities. We show that
statistical independence, in the macroscopic limit, is the unifying concept
that leads to all these derivations.Comment: 7 pages, 3 pages of Appendi
Symmetry-protected self-correcting quantum memories
A self-correcting quantum memory can store and protect quantum information
for a time that increases without bound with the system size and without the
need for active error correction. We demonstrate that symmetry can lead to
self-correction in 3D spin-lattice models. In particular, we investigate codes
given by 2D symmetry-enriched topological (SET) phases that appear naturally on
the boundary of 3D symmetry-protected topological (SPT) phases. We find that
while conventional on-site symmetries are not sufficient to allow for
self-correction in commuting Hamiltonian models of this form, a generalized
type of symmetry known as a 1-form symmetry is enough to guarantee
self-correction. We illustrate this fact with the 3D "cluster-state" model from
the theory of quantum computing. This model is a self-correcting memory, where
information is encoded in a 2D SET-ordered phase on the boundary that is
protected by the thermally stable SPT ordering of the bulk. We also investigate
the gauge color code in this context. Finally, noting that a 1-form symmetry is
a very strong constraint, we argue that topologically ordered systems can
possess emergent 1-form symmetries, i.e., models where the symmetry appears
naturally, without needing to be enforced externally.Comment: 39 pages, 16 figures, comments welcome; v2 includes much more
explicit detail on the main example model, including boundary conditions and
implementations of logical operators through local moves; v3 published
versio
Statistics of Stellar Variability from Kepler - I: Revisiting Quarter 1 with an Astrophysically Robust Systematics Correction
We investigate the variability properties of main sequence stars in the first
month of Kepler data, using a new astrophysically robust systematics
correction, and find that 60% of stars are more variable then the active Sun.
We define low and high variability samples, with a cut corresponding to twice
the variability level of the active Sun, and compare the properties of the
stars belonging to each sample. We show tentative evidence that the more active
stars have lower proper motions and may be located closer to the galactic
plane. We also investigate the frequency content of the variability, finding
clear evidence for periodic or quasi-periodic behaviour in 16% of stars, and
showing that there exist significant differences in the nature of variability
between spectral types. Of the periodic objects, most A and F stars have short
periods (< 2 days) and highly sinusoidal variability, suggestive of pulsations,
whilst G, K and M stars tend to have longer periods (> 5 days, with a trend
towards longer periods at later spectral types) and show a mixture of periodic
and stochastic variability, indicative of activity. Finally, we use
auto-regressive models to characterise the stochastic component of the
variability, and show that its typical amplitude and time-scale both increase
towards later spectral types, which we interpret as a corresponding increase in
the characteristic size and life-time of active regions.Comment: Accepted A&A, 13 pages, 13 figures, 4 table
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