  The experimentally demonstration of Casimir force transition from attraction
to repulsion is still challenging. Herein, the Casimir forces for a sphere
above a plate immersed in different liquids were precisely measured using
Atomic force microscope, and the long-range repulsive Casimir force in the
gold-cyclohexane-PTFE system is observed for the first time. The experimental
data are consistent with the calculation by Lifshitz theory, which offers the
direct evidence for the system of {\epsilon}1<{\epsilon}3<{\epsilon}2. It
further verifies the reasonability of van Zwol et al. dielectric model to
describe the intervening fluids. This study is promising for potential
applications on quantum levitation and frictionless devices in MEMS and NEMS by
Casimir repulsion.
