330 research outputs found
Electron spin phase relaxation of phosphorus donors in nuclear spin enriched silicon
We report a pulsed EPR study of the phase relaxation of electron spins bound
to phosphorus donors in isotopically purified 29^Si and natural abundance Si
single crystals measured at 8 K.Comment: 5 pages, 3 figure
Nonequilibrium electron spin polarization in a double quantum dot. Lande mechanism
In moderately strong magnetic fields, the difference in Lande g-factors in
each of the dots of a coupled double quantum dot device may induce oscillations
between singlet and triplet states of the entangled electron pair and lead to a
nonequilibrium electron spin polarization. We will show that this polarization
may partially survive the rapid inhomogeneous decoherence due to random nuclear
magnetic fields.Comment: New version contains figures. New title better reflects the content
of the pape
Time evolution of spin state of radical ion pair in microwave field: An analytical solution
The paper reports an exact solution for the problem of spin evolution of
radical ion pair in static magnetic and resonant microwave field taking into
account Zeeman and hyperfine interactions and spin relaxation. The values of
parameters that provide one of the four possible types of solution are
analysed. It is demonstrated that in the absence of spin relaxation, besides
the zero field invariant an invariant at large amplitudes of the resonant
microwave field can be found. The two invariants open the possibility for
simple calculation of microwave pulses to control quantum state of the radical
pair. The effect of relaxation on the invariants is analysed and it is shown
that changes in the high field invariant are induced by phase relaxation.Comment: 18 pages, 7 figure
Hyperfine interaction and magnetoresistance in organic semiconductors
We explore the possibility that hyperfine interaction causes the recently
discovered organic magnetoresistance (OMAR) effect. Our study employs both
experiment and theoretical modelling. An excitonic pair mechanism model based
on hyperfine interaction, previously suggested by others to explain magnetic
field effects in organics, is examined. Whereas this model can explain a few
key aspects of the experimental data, we, however, uncover several fundamental
contradictions as well. By varying the injection efficiency for minority
carriers in the devices, we show experimentally that OMAR is only weakly
dependent on the ratio between excitons formed and carriers injected, likely
excluding any excitonic effect as the origin of OMAR.Comment: 10 pages, 7 figures, 1 tabl
Stochastic Dynamics of Magnetosomes in Cytoskeleton
Rotations of microscopic magnetic particles, magnetosomes, embedded into the
cytoskeleton and subjected to the influence of an ac magnetic field and thermal
noise are considered. Magnetosome dynamics is shown to comply with the
conditions of the stochastic resonance under not-too-tight constraints on the
character of the particle's fastening. The excursion of regular rotations
attains the value of order of radian that facilitates explaining the biological
effects of low-frequency weak magnetic fields and geomagnetic fluctuations.
Such 1-rad rotations are effectively controlled by slow magnetic field
variations of the order of 200 nT.Comment: LaTeX2e, 7 pages with 3 figure
EPR imaging study of paramagnetic centre distribution in thiokol-epoxy hermetics
The distribution of paramagnetic centres in carbon black filler in the interphase layer of the thiokol-epoxy hermetics on the border of brass or glass substrate was studied using EPR-imaging method. It was shown that the relative content of radicals decreases near the hermetic-"rigid" surface contact border. The thickness of the layer with a low concentration of radicals is estimated as 0.5±0.3 mm. The inhomogeneous distribution of radicals is more obvious in the case of hermetic hardening on a brass surface. These results are explained by a catalytic acceleration of the thiokol-epoxy polymerization reaction in the region of hermetic-metal surface contact. © 1996 Springer
Upper bounds on the error probabilities and asymptotic error exponents in quantum multiple state discrimination
We consider the multiple hypothesis testing problem for symmetric quantum
state discrimination between r given states \sigma_1,...,\sigma_r. By splitting
up the overall test into multiple binary tests in various ways we obtain a
number of upper bounds on the optimal error probability in terms of the binary
error probabilities. These upper bounds allow us to deduce various bounds on
the asymptotic error rate, for which it has been hypothesised that it is given
by the multi-hypothesis quantum Chernoff bound (or Chernoff divergence)
C(\sigma_1,...,\sigma_r), as recently introduced by Nussbaum and Szko{\l}a in
analogy with Salikhov's classical multi-hypothesis Chernoff bound. This
quantity is defined as the minimum of the pairwise binary Chernoff divergences
min_{j<k}C(\sigma_j,\sigma_k). It was known already that the optimal asymptotic
rate must lie between C/3 and C, and that for certain classes of sets of states
the bound is actually achieved. It was known to be achieved, in particular,
when the state pair that is closest together in Chernoff divergence is more
than 6 times closer than the next closest pair. Our results improve on this in
two ways. Firstly, we show that the optimal asymptotic rate must lie between
C/2 and C. Secondly, we show that the Chernoff bound is already achieved when
the closest state pair is more than 2 times closer than the next closest pair.
We also show that the Chernoff bound is achieved when at least of the
states are pure, improving on a previous result by Nussbaum and Szko{\l}a.
Finally, we indicate a number of potential pathways along which a proof (or
disproof) may eventually be found that the multi-hypothesis quantum Chernoff
bound is always achieved.Comment: 50 pages. v3: Slightly restructured, main results unchanged,
connection to Barnum and Knill's result (arXiv:quant-ph/0004088) clarified.
Accepted for JM
Single Electron Spin Decoherence by Nuclear Spin Bath: Linked Cluster Expansion Approach
We develop a theoretical model for transverse dynamics of a single electron
spin interacting with a nuclear spin bath. The approach allows a simple
diagrammatic representation and analytical expressions of different nuclear
spin excitation processes contributing to electron spin decoherence and
dynamical phase fluctuations. It accounts for nuclear spin dynamics beyond
conventional pair correlation models. As an illustration of the theory, we
evaluated the coherence dynamics of a P donor electron spin in a Si crystal.Comment: 37 pages, 13 figure
Spin exchange between charged paramagnetic particles in dilute solutions
© Springer-Verlag Wien 2014. Kinetic equations for the spin density matrix which take into account binary collisions and a method of calculating the spin exchange effective radius have been generalized to the case of dilute solutions of charged paramagnetic particles. The effective radius of the spin exchange and rate constant of the bimolecular spin exchange between charged paramagnetic particles in solutions have been calculated numerically. Calculations have been performed under the assumption that the exchange interaction is isotropic and decays exponentially with the increase in the distance between radicals, and the solution has a given dielectric permittivity and Debye screening radius. Dependences of the spin exchange rate constant on the mutual diffusion coefficient, exchange and electrostatic interactions parameters have been found numerically. The theory has been applied to experimental results taken from the literature. The rate constant of the spin exchange between radicals of like charge found from the experiment and calculated within the developed theory are in good qualitative agreement
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