Manfred Bartz wrote:

I think emerging nano technology will still provide us with a few
surprises. At the nano scale there may yet be some undiscovered
physical properties in some materials.

The quantum effect mentioned might be small, but if harnessed by a
trillion nano devices in parallel it may become significant enough
to be useful for inter-planetary or even inter-stellar, propellant-
less propulsion.

Do be aware that reactionless propulsion is mathematically equivalent
to a perpetual motion machine of the first kind (if the phenomenon
occurs the same way in any inertia reference frame.)

Paul