  Starting from a quantum Langevin equation (QLE) of a charged particle coupled
to a heat bath in the presence of an external magnetic field, we present a
fully dynamical calculation of the susceptibility tensor. We further evaluate
the position autocorrelation function by using the Gibbs ensemble approach.
This quantity is shown to be related to the imaginary part of the dynamical
susceptibility, thereby validating the fluctuation-dissipation theorem in the
context of dissipative diamagnetism. Finally we present an overview of
coherence-to-decoherence transition in the realm of dissipative diamagnetism at
zero temperature. The analysis underscores the importance of the details of the
relevant physical quantity, as far as coherence to decoherence transition is
concerned.
