Chiral Thermodynamics in Tailored Chiral Optical Environments

The stochastic motion of Brownian particles out of equilibrium yields rich thermodynamic landscapes studied on a great variety of systems through many different research fields. Here, we study within the field of stochastic thermodynamics the dynamics and energetics of an overdamped Brownian chiral nanoparticle diffusing in a symmetric bistable optical potential formed in the standing wave of two counterpropagating Gaussian beams. Control on the polarizations of each beam creates chiral optical environments by endowing the standing wave with optical chiral densities or optical chiral fluxes without modifying the initial bistability. These chiral densities and fluxes are associated, respectively, with reactive or dissipative chiral optical forces exerted on the diffusing chiral nanoparticle. This optomechanical chiral coupling leads to a modification of the thermal activation process in ways that depend on the nanoparticle enantiomer and on the enantiomorphism of the optical field. Reactive chiral forces contribute to a global enantiospecific change of the Helmholtz free energy, but preserving the symmetry of the bistable potential. Dissipative chiral forces correspond to a nonequilibrium steady state where the barrier-crossing rates become asymmetric while leaving unaffected the initial potential. This symmetry breaking is associated with heat transferred to the thermal bath that can be evaluated. The symmetry breaking yields chiral deracemization schemes that can be explicitly calculated and simulated. Our results reveal how chiral degrees of freedom of both the nanoparticle and the optical field transform into true thermodynamic control parameters. The resulting optomechanical model gives way to new opportunities in the context of chiral sensing at the single-nanoparticle level and to original strategies for chiral discrimination at the nanoscale using the observables associated with the thermodynamics at play, such as escape rates or probability density functions.