  A stable suspension of nanoscale particles due to the Casimir force is of
great interest for many applications such as sensing, non-contract
nano-machines. However, the suspension properties are difficult to change once
the devices are fabricated. Vanadium dioxide (VO$_2$) is a phase change
material, which undergoes a transition from a low-temperature insulating phase
to a high-temperature metallic phase around a temperature of 340 K. In this
work, we study Casimir forces between a nanoplate (gold or Teflon) and a
layered structure containing a VO$_2$ film. It is found that stable Casimir
suspensions of nanoplates can be realized in a liquid environment, and the
equilibrium distances are determined, not only by the layer thicknesses but
also by the matter phases of VO$_2$. Under proper designs, a switch from
quantum trapping of the gold nanoplate ("on" state) to its release ("off"
state) as a result of the metal-to-insulator transition of VO$_2$, is revealed.
On the other hand, the quantum trapping and release of a Teflon nanoplate is
found under the insulator-to-metal transition of VO$_2 $. Our findings offer
the possibility of designing switchable devices for applications in micro-and
nano-electromechanical systems.
