2,117 research outputs found
Dephasing of a Qubit due to Quantum and Classical Noise
The qubit (or a system of two quantum dots) has become a standard paradigm
for studying quantum information processes. Our focus is Decoherence due to
interaction of the qubit with its environment, leading to noise. We consider
quantum noise generated by a dissipative quantum bath. A detailed comparative
study with the results for a classical noise source such as generated by a
telegraph process, enables us to set limits on the applicability of this
process vis a vis its quantum counterpart, as well as lend handle on the
parameters that can be tuned for analyzing decoherence. Both Ohmic and
non-Ohmic dissipations are treated and appropriate limits are analyzed for
facilitating comparison with the telegraph process.Comment: 12 pages, 8 figure
Landau diamagnetism revisited
The problem of diamagnetism, solved by Landau, continues to pose fascinating
issues which have relevance even today. These issues relate to inherent quantum
nature of the problem, the role of boundary and dissipation, the meaning of
thermodynamic limits, and above all, the quantum-classical crossover occasioned
by environment-induced decoherence. The Landau Diamagnetism provides a unique
paradigm for discussing these issues, the significance of which are
far-reaching. Our central result is a remarkable one as it connects the mean
orbital magnetic moment, a thermodynamic property, with the electrical
resistivity, which characterizes transport properties of materials.Comment: 4 pages, 1 figur
Memory in nanomagnetic systems: Superparamagnetism versus Spinglass behavior
The slow dynamics and concomitant memory (aging) effects seen in nanomagnetic
systems are analyzed on the basis of two separate paradigms : superparamagnets
and spinglasses. It is argued that in a large class of aging phenomena it
suffices to invoke superparamagnetic relaxation of individual single domain
particles but with a distribution of their sizes. Cases in which interactions
and randomness are important in view of distinctive experimental signatures,
are also discussed.Comment: 11 pages and 19 figure
Domain Growth in Random Magnets
We study the kinetics of domain growth in ferromagnets with random exchange
interactions. We present detailed Monte Carlo results for the nonconserved
random-bond Ising model, which are consistent with power-law growth with a
variable exponent. These results are interpreted in the context of disorder
barriers with a logarithmic dependence on the domain size. Further, we clarify
the implications of logarithmic barriers for both nonconserved and conserved
domain growth.Comment: 7 pages, 4 figure
Hysteresis in a magnetic bead and its applications
We study hysteresis in a micron-sized bead: a non-magnetic matrix embedded
with super- paramagnetic nanoparticles. These hold tremendous promise in
therapeutic applications as heat generating machines. The theoretical
formulation uses a mean-field theory to account for dipolar interactions
between the supermoments. The study enables manipulation of heat dissipation by
a compatible selection of commercially available beads and the frequency f and
amplitude ho of the applied oscillating field in the labortory. We also
introduce the possibility of utilizing return point memory for gradual heating
of a local region.Comment: 8 pages, 4 figure
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