Microscopic gyration of a Brownian ellipsoid

Abstract A Brownian gyrator requires anisotropic fluctuations to perform gyration in non-equilibrium conditions. In a typical set-up with an isotropic, colloidal particle, the anisotropy sets in by coupling the degrees of freedom, usually aided by the external, anisotropic potential confining the particle and the difference between the distinct temperatures along different degrees of freedom describing the dynamics of the particle. Contrary to this typical set-up, here we have considered an overdamped, Brownian ellipsoid, trapped by optical tweezers in an isotropic potential in two dimensions. Instead of the trap, the degrees of freedom are now coupled by the difference between the longitudinal and transverse frictional drags experienced by the ellipsoid, together with its finite mean orientation caused by a restoring torque acting on it. The torque on the ellipsoid is also due to its inherent anisotropic shape (i.e. bi-axiality) and the polarization of the laser used in the tweezer. The coupling is dissipative in origin and it is associated with the intrinsic properties of the ellipsoid itself. We have shown numerically as well as analytically that such an ellipsoid, when subjected to distinct temperatures along different translational degrees of freedom, exhibits a steady-state gyration even in an isotropic trap.