  We study the dynamics of a particle tunneling between the ground states of a
symmetric double potential well system, in the presence of simultaneous
diagonal and non-diagonal couplings to an Ohmic oscillator bath. We use the
noninteracting-blip approximation to investigate coherence effects across a
wide range of system-environment coupling strengths at physiological
temperatures. We show how the presence of a non-diagonal coupling mechanism
significantly alters the dynamics of the tunneling particle, producing coherent
oscillations despite strong thermal fluctuations in the environment.
Fluctuations in both the particle's polarization, as well as tunneling
energies, lead to competing influences on the coherent nature of tunneling
particle dynamics, with non-diagonal couplings introducing a relatively
long-lived oscillatory mode in an otherwise incoherent setting.
