The Experts below are selected from a list of 1245603 Experts worldwide ranked by ideXlab platform
C. Wetterich - One of the best experts on this subject based on the ideXlab platform.
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Spontaneous Symmetry breaking origin for the difference between time and space
Physical Review Letters, 2005Co-Authors: C. WetterichAbstract:We suggest that the difference between time and space is due to spontaneous Symmetry breaking. In a theory with spinors the signature of the metric is related to the signature of the Lorentz group. We discuss a higher Symmetry that contains pseudo-orthogonal groups with an arbitrary signature as subgroups. The fundamental aSymmetry between time and space can then result as a property of the ground state rather than being put into the formulation of the theory a priori. We show how the complex structure of quantum field theory as well as gravitational field equations arise from spinor gravity--a fundamental spinor theory without a metric.
Mary Bomberger Brown - One of the best experts on this subject based on the ideXlab platform.
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natural selection on tail and bill morphology in barn swallows hirundo rustica during severe weather
Ibis, 2008Co-Authors: Charles R Brown, Mary Bomberger BrownAbstract:An unusual six-day period of cold, rainy weather caused mortality among Barn Swallows Hirundo rustica in southwestern Nebraska, USA, in May 1996. We compared birds that died during the cold to those still alive when the severe weather ended. Among males, survivors had significantly longer culmens and significantly less variance in outer-tail aSymmetry than non-survivors. Among females, survivors had significantly longer outer tails and significantly less variance in outer-tail length, overall body size and outer-tail aSymmetry than non-survivors. Larger birds in general and those with less aSymmetry in wing and outer tail tended to be favoured during this weather event. Long tails may reflect condition in females and, along with high levels of Symmetry in wing and outer tail, improve foraging efficiency during extreme conditions. Males with long tails did not appear to suffer survival costs. Larger size probably allows more fat to be stored and may confer thermal benefits to swallows during late spring cold snaps. Similar mortality events have apparently occurred in the study area on only one other occasion since 1875.
Iman Marvian - One of the best experts on this subject based on the ideXlab platform.
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Quantum speed limits, coherence, and aSymmetry
Physical Review A, 2016Co-Authors: Iman Marvian, Robert W Spekkens, Paolo ZanardiAbstract:The resource theory of aSymmetry is a framework for classifying and quantifying the Symmetry-breaking properties of both states and operations relative to a given Symmetry. In the special case where the Symmetry is the set of translations generated by a fixed observable, aSymmetry can be interpreted as coherence relative to the observable eigenbasis, and the resource theory of aSymmetry provides a framework to study this notion of coherence. We here show that this notion of coherence naturally arises in the context of quantum speed limits. Indeed, the very concept of speed of evolution, i.e., the inverse of the minimum time it takes the system to evolve to another (partially) distinguishable state, is a measure of aSymmetry relative to the time translations generated by the system Hamiltonian. Furthermore, the celebrated Mandelstam-Tamm and Margolus-Levitin speed limits can be interpreted as upper bounds on this measure of aSymmetry by functions which are themselves measures of aSymmetry in the special case of pure states. Using measures of aSymmetry that are not restricted to pure states, such as the Wigner-Yanase skew information, we obtain extensions of the Mandelstam-Tamm bound which are significantly tighter in the case of mixed states. We also clarify some confusions in the literature about coherence and aSymmetry, and show that measures of coherence are a proper subset of measures of aSymmetry.
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the theory of manipulations of pure state aSymmetry i basic tools equivalence classes and single copy transformations
New Journal of Physics, 2013Co-Authors: Iman Marvian, Robert W SpekkensAbstract:If a system undergoes symmetric dynamics, then the final state of the system can only break the Symmetry in ways in which it was broken by the initial state, and its measure of aSymmetry can be no greater than that of the initial state. It follows that for the purpose of understanding the consequences of symmetries of dynamics, in particular, complicated and open-system dynamics, it is useful to introduce the notion of a state's aSymmetry properties, which includes the type and measure of its aSymmetry. We demonstrate and exploit the fact that the aSymmetry properties of a state can also be understood in terms of information-theoretic concepts, for instance in terms of the state's ability to encode information about an element of the Symmetry group. We show that the aSymmetry properties of a pure state ψ relative to the Symmetry group G are completely specified by the characteristic function of the state, defined as χψ(g) ≡ 〈ψ|U(g)|ψ〉 where g∈G and U is the unitary representation of interest. For a Symmetry described by a compact Lie group G, we show that two pure states can be reversibly interconverted one to the other by symmetric operations if and only if their characteristic functions are equal up to a one-dimensional representation of the group. Characteristic functions also allow us to easily identify the conditions for one pure state to be converted to another by symmetric operations (in general irreversibly) for the various paradigms of single-copy transformations: deterministic, state-to-ensemble, stochastic and catalyzed.
Charles R Brown - One of the best experts on this subject based on the ideXlab platform.
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natural selection on tail and bill morphology in barn swallows hirundo rustica during severe weather
Ibis, 2008Co-Authors: Charles R Brown, Mary Bomberger BrownAbstract:An unusual six-day period of cold, rainy weather caused mortality among Barn Swallows Hirundo rustica in southwestern Nebraska, USA, in May 1996. We compared birds that died during the cold to those still alive when the severe weather ended. Among males, survivors had significantly longer culmens and significantly less variance in outer-tail aSymmetry than non-survivors. Among females, survivors had significantly longer outer tails and significantly less variance in outer-tail length, overall body size and outer-tail aSymmetry than non-survivors. Larger birds in general and those with less aSymmetry in wing and outer tail tended to be favoured during this weather event. Long tails may reflect condition in females and, along with high levels of Symmetry in wing and outer tail, improve foraging efficiency during extreme conditions. Males with long tails did not appear to suffer survival costs. Larger size probably allows more fat to be stored and may confer thermal benefits to swallows during late spring cold snaps. Similar mortality events have apparently occurred in the study area on only one other occasion since 1875.
Robert W Spekkens - One of the best experts on this subject based on the ideXlab platform.
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Quantum speed limits, coherence, and aSymmetry
Physical Review A, 2016Co-Authors: Iman Marvian, Robert W Spekkens, Paolo ZanardiAbstract:The resource theory of aSymmetry is a framework for classifying and quantifying the Symmetry-breaking properties of both states and operations relative to a given Symmetry. In the special case where the Symmetry is the set of translations generated by a fixed observable, aSymmetry can be interpreted as coherence relative to the observable eigenbasis, and the resource theory of aSymmetry provides a framework to study this notion of coherence. We here show that this notion of coherence naturally arises in the context of quantum speed limits. Indeed, the very concept of speed of evolution, i.e., the inverse of the minimum time it takes the system to evolve to another (partially) distinguishable state, is a measure of aSymmetry relative to the time translations generated by the system Hamiltonian. Furthermore, the celebrated Mandelstam-Tamm and Margolus-Levitin speed limits can be interpreted as upper bounds on this measure of aSymmetry by functions which are themselves measures of aSymmetry in the special case of pure states. Using measures of aSymmetry that are not restricted to pure states, such as the Wigner-Yanase skew information, we obtain extensions of the Mandelstam-Tamm bound which are significantly tighter in the case of mixed states. We also clarify some confusions in the literature about coherence and aSymmetry, and show that measures of coherence are a proper subset of measures of aSymmetry.
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the theory of manipulations of pure state aSymmetry i basic tools equivalence classes and single copy transformations
New Journal of Physics, 2013Co-Authors: Iman Marvian, Robert W SpekkensAbstract:If a system undergoes symmetric dynamics, then the final state of the system can only break the Symmetry in ways in which it was broken by the initial state, and its measure of aSymmetry can be no greater than that of the initial state. It follows that for the purpose of understanding the consequences of symmetries of dynamics, in particular, complicated and open-system dynamics, it is useful to introduce the notion of a state's aSymmetry properties, which includes the type and measure of its aSymmetry. We demonstrate and exploit the fact that the aSymmetry properties of a state can also be understood in terms of information-theoretic concepts, for instance in terms of the state's ability to encode information about an element of the Symmetry group. We show that the aSymmetry properties of a pure state ψ relative to the Symmetry group G are completely specified by the characteristic function of the state, defined as χψ(g) ≡ 〈ψ|U(g)|ψ〉 where g∈G and U is the unitary representation of interest. For a Symmetry described by a compact Lie group G, we show that two pure states can be reversibly interconverted one to the other by symmetric operations if and only if their characteristic functions are equal up to a one-dimensional representation of the group. Characteristic functions also allow us to easily identify the conditions for one pure state to be converted to another by symmetric operations (in general irreversibly) for the various paradigms of single-copy transformations: deterministic, state-to-ensemble, stochastic and catalyzed.
