  The study of decoherence plays a key role in our understanding of the
transition from the quantum to the classical world. Typically, one considers a
system coupled to an external bath which forms a model for an open quantum
system. While most of the studies pertain to a position coupling between the
system and the environment, some involve a momentum coupling, giving rise to an
anomalous diffusive model. Here we have gone beyond existing studies and
analysed the quantum Langevin dynamics of a harmonically oscillating charged
Brownian particle in the presence of a magnetic field and coupled to an Ohmic
heat bath via both position and momentum couplings. The presence of both
position and momentum couplings leads to a stronger interaction with the
environment, resulting in a faster loss of coherence compared to a situation
where only position coupling is present. The rate of decoherence can be tuned
by controlling the relative strengths of the position and momentum coupling
parameters. In addition, the magnetic field results in the slowing down of the
loss of information from the system, irrespective of the nature of coupling
between the system and the bath. Our results can be experimentally verified by
designing a suitable ion trap setup.
