scholarly journals Mean-field quantum dynamics with magnetic fields

2012 ◽  
Vol 53 (2) ◽  
pp. 022105 ◽  
Author(s):  
Jonas Lührmann
Keyword(s):  
Magnetic Fields ◽  
Quantum Dynamics ◽  
Mean Field

scholarly journals Global MHD phenomena and their importance for stellar surfaces

2010 ◽  
Vol 6 (S273) ◽  
pp. 141-147
Author(s):  
Rainer Arlt
Keyword(s):  
Magnetic Fields ◽  
Mean Field ◽  
Momentum Equation ◽  
Small Scale ◽  
Dynamo Action ◽  
Complex Activity ◽  
Mhd Instabilities ◽  
Stellar Magnetic Fields ◽  
Mean Field Dynamo

AbstractThis review is an attempt to elucidate MHD phenomena relevant for stellar magnetic fields. The full MHD treatment of a star is a problem which is numerically too demanding. Mean-field dynamo models use an approximation of the dynamo action from the small-scale motions and deliver global magnetic modes which can be cyclic, stationary, axisymmetric, and non-axisymmetric. Due to the lack of a momentum equation, MHD instabilities are not visible in this picture. However, magnetic instabilities must set in as a result of growing magnetic fields and/or buoyancy. Instabilities deliver new timescales, saturation limits and topologies to the system probably providing a key to the complex activity features observed on stars.

scholarly journals Dynamics of an orbital polarization of twisted electron beams in electric and magnetic fields

2019 ◽  
Vol 204 ◽  
pp. 10008
Author(s):  
Alexander J. Silenko ◽  
Pengming Zhang ◽  
Liping Zou
Keyword(s):  
Magnetic Field ◽  
Electron Beam ◽  
Magnetic Fields ◽  
Quantum Dynamics ◽  
Electron Beams ◽  
Equations Of Motion ◽  
Vortex Beam ◽  
Dirac Particles ◽  
Electric And Magnetic Fields ◽  
Average Projection

Relativistic classical and quantum dynamics of twisted (vortex) Dirac particles in arbitrary electric and magnetic fields is constructed. The relativistic Hamiltonian and equations of motion in the Foldy-Wouthuysen representation are derived. Methods for the extraction of an electron vortex beam with a given orbital polarization and for the manipulation of such a beam are developed. The new effect of a radiative orbital polarization of a twisted electron beam in a magnetic field resulting in a nonzero average projection of the intrinsic orbital angular momentum on the field direction is predicted.

Mean-field results for the Kondo lattices at high magnetic fields

1992 ◽  
Vol 46 (1) ◽  
pp. 231-236 ◽  
Author(s):  
T. M. Hong ◽  
G. A. Gehring
Keyword(s):  
Magnetic Fields ◽  
Mean Field ◽  
High Magnetic Fields

Quantum dynamics of molecular magnets in ultra-fast sweeping magnetic fields

2004 ◽  
Vol 346-347 ◽  
pp. 216-220 ◽  
Author(s):  
Hiroyuki Nojiri ◽  
Tomohiro Taniguchi ◽  
Yoshitami Ajiro ◽  
Achim Müller ◽  
Bernard Barbara
Keyword(s):  
Magnetic Fields ◽  
Quantum Dynamics ◽  
Molecular Magnets ◽  
Fast Sweeping

scholarly journals SYMMETRIES OF THE NEAR HORIZON OF A BLACKHOLE BY GROUP THEORETIC METHODS

2007 ◽  
Vol 22 (08n09) ◽  
pp. 1717-1726
Author(s):  
K. MAHARANA
Keyword(s):  
Black Hole ◽  
Charged Particle ◽  
Magnetic Fields ◽  
Lie Algebras ◽  
Quantum Dynamics ◽  
Equations Of Motion ◽  
Scalar Particle ◽  
Lie Point Symmetries

We use group theoretic methods to obtain the extended Lie point symmetries of the quantum dynamics of a scalar particle probing the near horizon structure of a black hole. Symmetries of the classical equations of motion for a charged particle in the field of an inverse square potential and a monopole, in the presence of certain model magnetic fields and potentials are also studied. Our analysis gives the generators and Lie algebras generating the inherent symmetries.

scholarly journals Long-time Dynamics of Spontaneous Parametric Down-conversion and Quantum Limitations of Conversion Efficiency

1999 ◽  
Vol 54 (1) ◽  
pp. 57-62 ◽  
Author(s):  
Michael Fleischhauer ◽  
Oliver Veits
Keyword(s):  
Quantum Dynamics ◽  
Equations Of Motion ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Time Dynamics ◽  
Pendulum Equation ◽  
Parametric Down Conversion ◽  
Long Time ◽  
Down Conversion

Abstract We analyze the long-time quantum dynamics of degenerate parametric down-conversion from an initial sub-harmonic vacuum (spontaenous down-conversion). Standard linearization of the Heisenberg equations of motion fails in this case, since it is based on an expansion around an unstable classical solution and neglects pump depletion. Introducing a mean-field approximation we find a periodic exchange of energy between the pump and subharmonic mode goverened by an anharmonic pendulum equation. From this equation the optimum interaction time or crystal length for maximum conversion can be determined. A numerical integration of the 2-mode Schrödinger equation using a dynamically optimized basis of displaced and squeezed number states verifies the characteristic times predicted by the mean-field approximation. In contrast to semiclassical and mean-field predictions it is found that quantum fluctuations of the pump mode lead to a substantial limitation of the efficiency of parametric down-conversion.

scholarly journals Synthesizing Observations and Theory to Understand Galactic Magnetic Fields: Progress and Challenges

Galaxies ◽  
2019 ◽  
Vol 8 (1) ◽  
pp. 4 ◽  
Author(s):  
Rainer Beck ◽  
Luke Chamandy ◽  
Ed Elson ◽  
Eric G. Blackman
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Mean Field ◽  
Large Data ◽  
Data Sets ◽  
Dynamo Theory ◽  
Galactic Magnetic Fields ◽  
Ngc 6946 ◽  
Upper Limits ◽  
New Instruments

Constraining dynamo theories of magnetic field origin by observation is indispensable but challenging, in part because the basic quantities measured by observers and predicted by modelers are different. We clarify these differences and sketch out ways to bridge the divide. Based on archival and previously unpublished data, we then compile various important properties of galactic magnetic fields for nearby spiral galaxies. We consistently compute strengths of total, ordered, and regular fields, pitch angles of ordered and regular fields, and we summarize the present knowledge on azimuthal modes, field parities, and the properties of non-axisymmetric spiral features called magnetic arms. We review related aspects of dynamo theory, with a focus on mean-field models and their predictions for large-scale magnetic fields in galactic discs and halos. Furthermore, we measure the velocity dispersion of H i gas in arm and inter-arm regions in three galaxies, M 51, M 74, and NGC 6946, since spiral modulation of the root-mean-square turbulent speed has been proposed as a driver of non-axisymmetry in large-scale dynamos. We find no evidence for such a modulation and place upper limits on its strength, helping to narrow down the list of mechanisms to explain magnetic arms. Successes and remaining challenges of dynamo models with respect to explaining observations are briefly summarized, and possible strategies are suggested. With new instruments like the Square Kilometre Array (SKA), large data sets of magnetic and non-magnetic properties from thousands of galaxies will become available, to be compared with theory.

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