Quantum forces in solids with two-state systems: Example of molecular magnets

Two-state systems may exhibit mechanical forces of quantum origin that have no counterpart in classical physics. We show that such forces must exist in molecular magnets due to quantum tunneling between classically degenerate magnetic states. They can be observed in the presence of a microwave field when the magnet is placed in a static magnetic field with a gradient. At low temperature, the force is proportional to the tunnel splitting and it disappears on raising the temperature.

Figure 1

Oscillating force normalized by its value at $t=0$ for $\epsilon =0.1$ and $\omega /{\Omega }_0=100$. The inset shows oscillations. The envelope line shows analytical result for the amplitude of the force at long times.

Figure 2

Oscillating force normalized by its value at $t=0$ for $\epsilon =1$ and $\omega /{\Omega }_0=10$.