In a "massless" thruster, the theoretical maximum Thrust/Power ratio is 1/c = 0.0033 mN/KW if you don't want to break the conservation of momentum, special relativity or quantum mechanics. You could get this value with an ideal perfectly efficient laser beam. The latest NASA version proclaims (50 uN / 50 W) = 1 mN/KW that is 300x the theoretical maximum, so if it's not an experimental error, it must be breaking some of the currently supposed physic laws.
In a "massless" thruster, the theoretical maximum Thrust/Power ratio is 1/c = 0.0033 mN/KW if you don't want to break the conservation of momentum, special relativity or quantum mechanics. You could get this value with an ideal perfectly efficient laser beam. The latest NASA version proclaims (50 uN / 50 W) = 1 mN/KW that is 300x the theoretical maximum, so if it's not an experimental error, it must be breaking some of the currently supposed physic laws.