Entanglement in composite systems due to external influences

2018 ◽  
Vol 33 (21) ◽  
pp. 1850128
Author(s):  
D. M. Gitman ◽  
M. S. Meireles ◽  
A. D. Levin ◽  
A. A. Shishmarev ◽  
R. A. Castro
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Density Operator ◽  
Time Dependent ◽  
Von Neumann Entropy ◽  
Entanglement Measure ◽  
Photon Beams ◽  
Von Neumann ◽  
Electron Positron ◽  
In The Beginning

In this paper, we consider two examples of an entanglement in two-qubit systems and an example of entanglement in quantum field theory (QFT). In the beginning, we study the entanglement of two spin states by a magnetic field. A nonzero entanglement appears for interacting spins. When the coupling between the spins is constant, we study the entanglement by several types of time-dependent magnetic fields. In the case of a constant difference between [Formula: see text] components of magnetic fields acting on each spin, we find several time-dependent coupling functions [Formula: see text] that also allow us to analyze analytically and numerically the entanglement measure. Considering two photons moving in an electron medium, we demonstrate that they can be entangled in a controlled way by applying an external magnetic field. The magnetic field affecting electrons of the medium affects photons and, thus, causes an entanglement of the photon beams. The third example is related to the effect of production of electron–positron pairs from the vacuum by a strong external electric field. Here, we have used a general nonperturbative expression for the density operator of the system under consideration. Applying a reduction procedure to this density operator, we construct mixed states of electron and positron subsystems. Calculating the von Neumann entropy of such states, we obtain the loss of information due to the reduction and, at the same time, the entanglement measure of electron and positron subsystems. This entanglement can be considered as an example of an entanglement in QFT.

scholarly journals PAIR PRODUCTION IN A TIME-DEPENDENT MAGNETIC FIELD

1999 ◽  
Vol 14 (18) ◽  
pp. 1183-1192 ◽  
Author(s):  
GIORGIO CALUCCI
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Pair Production ◽  
Rest Mass ◽  
Landau Levels ◽  
Time Dependent ◽  
Electron Positron ◽  
Astrophysical Objects ◽  
The Magnetic Field

The production of electron–positron pairs in a time-dependent magnetic field is estimated in the hypotheses that the magnetic field is uniform over large distances with respect to the pair localization and it is so strong that the spacing of the Landau levels is larger than the rest mass of the particles. This calculation is presented since it has been suggested that extremely intense and varying magnetic fields may be found around some astrophysical objects.

scholarly journals Hamiltonian Approach to Magnetic Fields with Toroidal Surfaces

1985 ◽  
Vol 40 (10) ◽  
pp. 959-967
Author(s):  
A. Salat
Keyword(s):  
Magnetic Field ◽  
Hamiltonian System ◽  
Magnetic Fields ◽  
Constant Pressure ◽  
Time Dependent ◽  
Hamiltonian Approach ◽  
One Dimensional ◽  
Mhd Equilibrium ◽  
Magnetic Surfaces ◽  
Rotational Transform

The equivalence of magnetic field line equations to a one-dimensional time-dependent Hamiltonian system is used to construct magnetic fields with arbitrary toroidal magnetic surfaces I = const. For this purpose Hamiltonians H which together with their invariants satisfy periodicity constraints have to be known. The choice of H fixes the rotational transform η(I). Arbitrary axisymmetric fields, and nonaxisymmetric fields with constant η(I) are considered in detail.Configurations with coinciding magnetic and current density surfaces are obtained. The approach used is not well suited, however, to satisfying the additional MHD equilibrium condition of constant pressure on magnetic surfaces.

An Interpretation on Kinetics of Martensitic Transformation

2011 ◽  
Vol 172-174 ◽  
pp. 90-98 ◽  
Author(s):  
Tomoyuki Kakeshita ◽  
Takashi Fukuda ◽  
Yong-Hee Lee
Keyword(s):  
Magnetic Field ◽  
Hydrostatic Pressure ◽  
Martensitic Transformation ◽  
Magnetic Fields ◽  
Martensitic Transformations ◽  
Phenomenological Theory ◽  
Time Dependent ◽  
Isothermal Process ◽  
Kinetics Of ◽  
Transformation Processes

We have investigated athermal and isothermal martensitic transformations (typical displacive transformations) in Fe–Ni, Fe–Ni–Cr, and Ni-Co-Mn-In alloys under magnetic fields and hydrostatic pressures in order to understand the time-dependent nature of martensitic transformation, that is, the kinetics of martensitic transformation. We have confirmed that the two transformation processes are closely related to each other, that is, the athermal process changes to the isothermal process and the isothermal process changes to the athermal one under a hydrostatic pressure or a magnetic field. These findings can be explained by the phenomenological theory, which gives a unified explanation for the two transformation processes previously proposed by our group.

scholarly journals Magnetic dominance of axion electrodynamics: photon capture effect and anisotropy of Coulomb potential

2021 ◽  
Vol 81 (4) ◽  
Author(s):  
S. Villalba-Chávez ◽  
A. E. Shabad ◽  
C. Müller
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Strong Magnetic Field ◽  
Coulomb Potential ◽  
Heat Radiation ◽  
Radiation Mechanism ◽  
Electron Positron ◽  
Coulomb Singularity ◽  
Relativistic Hydrogen ◽  
The Magnetic Field

AbstractFor magnetic fields larger than the characteristic scale linked to axion-electrodynamics, quantum vacuum fluctuations due to axion-like fields can dominate over those associated with the electron-positron fields. This conjecture is explored by investigating both the axion-modified photon capture by a strong magnetic field and the Coulomb potential of a static pointlike charge. We show that in magnetic fields characteristic of neutron stars $$\sim 10^{13}$$ ∼ 10 13 –$$10^{15}\;\mathrm{G}$$ 10 15 G , the capture of gamma photons prior to the production of a pair can prevent the existence of an electron-positron plasma, essential for explaining the pulsar radiation mechanism. This incompatibility is used to limit the axion parameter space. Our bounds improve existing outcomes in the region of mass $$m\sim 10^{-10}$$ m ∼ 10 - 10 –$$10^{-5}\;{\mathrm{eV}}$$ 10 - 5 eV . The effect of capture, known in QED as relating to gamma-quanta, is extended in axion electrodynamics to include X-ray photons with the result that a specially polarized part of the heat radiation from the surface is canalized along the magnetic field. Besides, we find that in the regime in which the dominance takes place, the running QED coupling depends on the field strength and the modified Coulomb potential is of Yukawa-type in the direction perpendicular to the magnetic field at distances much smaller than the axion Compton wavelength, while along the field it follows approximately the Coulomb law at any length scale. Despite the Coulomb singularity manifested in the latter case, we argue that the ground-state energy of a non-relativistic hydrogen atom placed in a strong magnetic field turns out to be bounded due to the nonrenormalizable feature of axion-electrodynamics.

scholarly journals Quantum Weak Invariants: Dynamical Evolution of Fluctuations and Correlations

Entropy ◽  
2020 ◽  
Vol 22 (11) ◽  
pp. 1219
Author(s):  
Zeyi Shi ◽  
Sumiyoshi Abe
Keyword(s):  
Time Evolution ◽  
Open Quantum System ◽  
Dynamical Evolution ◽  
Time Dependent ◽  
Von Neumann Entropy ◽  
Completely Positive Map ◽  
Expectation Values ◽  
Completely Positive ◽  
Temporal Asymmetry ◽  
Von Neumann

Weak invariants are time-dependent observables with conserved expectation values. Their fluctuations, however, do not remain constant in time. On the assumption that time evolution of the state of an open quantum system is given in terms of a completely positive map, the fluctuations monotonically grow even if the map is not unital, in contrast to the fact that monotonic increases of both the von Neumann entropy and Rényi entropy require the map to be unital. In this way, the weak invariants describe temporal asymmetry in a manner different from the entropies. A formula is presented for time evolution of the covariance matrix associated with the weak invariants in cases where the system density matrix obeys the Gorini–Kossakowski–Lindblad–Sudarshan equation.

scholarly journals Time-variability of the Crab Nebula wisps

2000 ◽  
Vol 177 ◽  
pp. 507-508 ◽  
Author(s):  
Anatoly Spitkovsky ◽  
Jonathan Arons
Keyword(s):  
Magnetic Field ◽  
Crab Nebula ◽  
Propagation Speed ◽  
Time Dependent ◽  
Time Variability ◽  
Electron Positron ◽  
Pair Density ◽  
Pulsar Wind ◽  
The Crab Nebula ◽  
The Waves

AbstractWe present results of time-dependent numerical modeling of the internal structure of the collisionless shock terminating the pulsar wind in Crab Nebula. We treat the equatorial relativistic wind as composed of ions and electron-positron plasma with an embedded toroidal magnetic field. Relativistic cyclotron instability of the ion ring downstream from the shock is found to launch outward propagating magnetosonic waves. Due to the fresh supply of ions crossing the shock, the time-dependent process achieves a limit-cycle pattern, in which the waves are launched with periodicity on the order of the ion Larmor time. Compressions in magnetic field and pair density associated with these waves as well as their propagation speed qualitatively reproduce the features observed in the wisps.

Die Wirkung eines homogenen Magnetfeldes auf das Wachstum von Micrococcus denitrificans / The Influence of Homogeneous Magnetic Fields on the Growth of Micrococcus denitrificans

1970 ◽  
Vol 25 (9) ◽  
pp. 1020-1023 ◽  
Author(s):  
Wolfram Thiemann ◽  
Erich Wagner
Keyword(s):  
Magnetic Field ◽  
Saccharomyces Cerevisiae ◽  
Growth Rate ◽  
Magnetic Fields ◽  
The Other ◽  
Anaerobic Conditions ◽  
Inhibition Of Growth ◽  
Significant Acceleration ◽  
In The Beginning ◽  
The Magnetic Field

The influence of strong homogeneous magnetic fields in the range of 5000 to 8000 Gauss on the growth of Saccharomyces cerevisiae and Micrococcus denitrificans was studied. In the case of yeast growing under nearly anaerobic conditions an inhibition of growth rate was observed in the beginning of incubaton while some hours later the growth accelerated and surpassed the control. M. denitrificans on the other hand grew with the same rate as the controls during the first 2 - 3 hours of experiment; thereafter the magnetic field resulted in a significant acceleration of growth rate measured by a 5.8 to 13.3% increase of oxygen consumption after 5 - 6 hours run of experiment. Until now only inhibition of bacterial growths by magnetic fields is reported elsewhere in the literature.

scholarly journals PARTICLE ACCELERATION, MAGNETIC FIELD GENERATION, AND ASSOCIATED EMISSION IN COLLISIONLESS RELATIVISTIC JETS

2008 ◽  
Vol 17 (10) ◽  
pp. 1761-1767 ◽  
Author(s):  
K.-I. NISHIKAWA ◽  
Y. MIZUNO ◽  
G. J. FISHMAN ◽  
P. HARDEE
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Small Scale ◽  
Spectral Structure ◽  
Relativistic Jets ◽  
Weibel Instability ◽  
Electron Positron ◽  
Jitter Radiation

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and galactic microquasar systems usually have power-law emission spectra. Recent PIC simulations using injected relativistic electron-ion (electron-positron) jets show that acceleration occurs within the downstream jet. Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electrons' transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties to synchrotron radiation which assumes a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

Solidification of AlSi Alloys in the ARTEMIS and ARTEX Facilities Including Rotating Magnetic Fields – A Combined Experimental and Numerical Analysis

2006 ◽  
Vol 508 ◽  
pp. 199-204 ◽  
Author(s):  
Marc Hainke ◽  
Sonja Steinbach ◽  
Johannes Dagner ◽  
Lorenz Ratke ◽  
Georg Müller
Keyword(s):  
Magnetic Field ◽  
Numerical Modeling ◽  
Numerical Analysis ◽  
Temperature Gradient ◽  
Magnetic Fields ◽  
Time Dependent ◽  
Flow Conditions ◽  
Rotating Magnetic Fields ◽  
Microstructural Parameters ◽  
Wide Range

The solidification microstructure is the consequence of a wide range of process parameters, like the growth velocity, the temperature gradient and the composition. Although the influence of these parameters is nowadays considerably well understood, an overall theory of the influence of convection on microstructural features is still lacking. The application of time dependent magnetic fields during directional solidification offers the possibility to create defined solidification and flow conditions. In this work, we report about solidification experiments in the ARTEMIS and ARTEX facilities including rotating magnetic fields (RMF). The effect of the forced melt flow on microstructural parameters like the primary and secondary dendrite arm spacing is analyzed for a wide range of magnetic field parameters. The experimental analysis is supported by a rigorous application of numerical modeling. An important issue is hereby the prediction of the resulting macrosegregation, i.e., differences in the composition on the scale of the sample (macroscale) due to the RMF. For the considered configuration and parameters an axial enrichment of Si is found beyond a certain magnetic field strength. The results are compared to available theories and their applicability is discussed.

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