Thermo-optical tuning of nonmonotonic Casimir potentials arising from the thermal expansion of a liquid

We demonstrate a thermo-optic switching of nonmonotonic Casimir potential with a local minimum, termed quantum trap, for Au plate immersed in ethanol and located above Teflon-coated Au substrate. Beyond a critical temperature of 420 K, the quantum trap is switched to monotonic attraction, due to the reversal of relative rankings of ethanol's and Teflon's dielectric functions. The effect originates from thermal expansion-induced decrease of ethanol's dielectric function, rather than temperature-related electronic transitions of interacting materials. In the case of barrierlike Casimir potential with a local maximum for suspended Teflon plate, while the barrier height reduces with temperature, no switching is allowed due to the stronger retardation effect at relatively farther unstable equilibria. The thermo-optic effect provides a viable route to control interobject interaction in liquid environment and modulate dynamic properties of nonmonotonic Casimir systems.