  We present an optomechanical model that describes the stochastic motion of an
overdamped chiral nanoparticle diffusing in the optical bistable potential
formed in the standing-wave of two counter-propagating Gaussian beams. We show
how chiral optical environments can be induced in the standing-wave with no
modification of the initial bistability by controlling the polarizations of
each beam. Under this control, optical chiral densities and/or an optical
chiral fluxes are generated, associated respectively with reactive vs.
dissipative chiral optical forces exerted on the diffusing chiral nanoparticle.
This optomechanical chiral coupling bias the thermodynamics of the thermal
activation of the barrier crossing, in ways that depend on the nanoparticle
enantiomer and on the optical field enantiomorph. We show that reactive chiral
forces, being conservative, contribute to a global, enantiospecific, change of
the Helmholtz free energy bistable landscape. In contrast, when the chiral
nanoparticle is immersed in a dissipative chiral environment, the symmetry of
the bistable potential is broken by non-conservative chiral optical forces. In
this case, the chiral electromagnetic fields continuously transfer, through
dissipation, mechanical energy to the chiral nanoparticle. For this chiral
nonequilibrium steady-state, the thermodynamic changes of the barrier crossing
take the form of heat transferred to the thermal bath and yield chiral
deracemization schemes that can be explicitly calculated within the framework
of our model. Three-dimensional stochastic simulations confirm and further
illustrate the thermodynamic impact of chirality. Our results reveal how chiral
degrees of freedom both of the nanoparticle and of the optical fields can be
transformed into true thermodynamics control parameters, thereby demonstrating
the significance of optomechanical chiral coupling in stochastic
thermodynamics.
