If some energy input can produce some “reactionless” impulse of x N.s/J, is x a constant? If so, you can produce a free energy machine by having the quantum thruster move a mass along a track at some finite velocity- unless, as I suspect, the conversion factor makes the quantum drive power/thrust ratio identical to a photon drive.
Alas, if it works, it creates thrust no more efficiently than a flashlight.

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