2,499 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
Quantum Treatment of the Anderson-Hasegawa Model -- Effects of Superexchange and Polarons
We revisit the Anderson-Hasegawa double-exchange model and critically examine
its exact solution when the core spins are treated quantum mechanically.We show
that the quantum effects, in the presence of an additional superexchange
interaction between the core spins, yield a term, the significance of which has
been hitherto ignored. The quantum considerations further lead to new results
when polaronic effects, believed to be ubiquitous in manganites due to
electron-phonon coupling, are included. The consequence of these results for
the magnetic phase diagrams and the thermal heat capacity is also carefully
analysed.Comment: 18 pages, Revtex, 7 postscript 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
- …