5,527 research outputs found
Circuit complexity for free fermions
We study circuit complexity for free fermionic field theories and Gaussian
states. Our definition of circuit complexity is based on the notion of geodesic
distance on the Lie group of special orthogonal transformations equipped with a
right-invariant metric. After analyzing the differences and similarities to
bosonic circuit complexity, we develop a comprehensive mathematical framework
to compute circuit complexity between arbitrary fermionic Gaussian states. We
apply this framework to the free Dirac field in four dimensions where we
compute the circuit complexity of the Dirac ground state with respect to
several classes of spatially unentangled reference states. Moreover, we show
that our methods can also be applied to compute the complexity of excited
states. Finally, we discuss the relation of our results to alternative
approaches based on the Fubini-Study metric, the relevance to holography and
possible extensions.Comment: 84 pages, 10 figures, 1 tabl
Testing chameleon gravity with the Coma cluster
We propose a novel method to test the gravitational interactions in the
outskirts of galaxy clusters. When gravity is modified, this is typically
accompanied by the introduction of an additional scalar degree of freedom,
which mediates an attractive fifth force. The presence of an extra
gravitational coupling, however, is tightly constrained by local measurements.
In chameleon modifications of gravity, local tests can be evaded by employing a
screening mechanism that suppresses the fifth force in dense environments.
While the chameleon field may be screened in the interior of the cluster, its
outer region can still be affected by the extra force, introducing a deviation
between the hydrostatic and lensing mass of the cluster. Thus, the chameleon
modification can be tested by combining the gas and lensing measurements of the
cluster. We demonstrate the operability of our method with the Coma cluster,
for which both a lensing measurement and gas observations from the X-ray
surface brightness, the X-ray temperature, and the Sunyaev-Zel'dovich effect
are available. Using the joint observational data set, we perform a Markov
chain Monte Carlo analysis of the parameter space describing the different
profiles in both the Newtonian and chameleon scenarios. We report competitive
constraints on the chameleon field amplitude and its coupling strength to
matter. In the case of f(R) gravity, corresponding to a specific choice of the
coupling, we find an upper bound on the background field amplitude of
|f_{R0}|<6*10^{-5}, which is currently the tightest constraint on cosmological
scales.Comment: 27 pages, 8 figures, version accepted for publication in JCA
Analysis of 2009 International Energy Conservation Code Requirements for Residential Buildings in Utah
The 2009 International Energy Conservation Code (IECC) contains several major improvements in energy efficiency over the current Utah code, the 2006 IECC. The most notable changes are improved duct sealing and efficient lighting requirements. A limited analysis of these changes resulted in estimated savings of 188 for an average new house in Utah at recent fuel prices
Quantum control in foundational experiments
We describe a new class of experiments designed to probe the foundations of
quantum mechanics. Using quantum controlling devices, we show how to attain a
freedom in temporal ordering of the control and detection of various phenomena.
We consider wave-particle duality in the context of quantum-controlled and the
entanglement-assisted delayed-choice experiments. Then we discuss a
quantum-controlled CHSH experiment and measurement of photon's transversal
position and momentum in a single set-up.Comment: Contribution to the Proceedings of the workshop Horizons of Quantum
Physics, Taipei, 14-18.10.2012. Published version: two new authors, modified
and streamlined presentation, new section on quantum control in complementary
position/momentum measurement
Laparoscopic Resection of a Small Bowel Lipoma with Incidental Intussusception
Small bowel lipomas, which can cause intussusception and gastrointestinal bleeding, can be managed with laparoscopic resection when diagnosed preoperatively
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