"The 1.2mN/kW1.2mN/kW performance parameter is over two orders of magnitude higher than other forms of “zero-propellant” propulsion, such as light sails,"
I have a question: What the smurf does this mean? Seriously?
Are we talking about a ground-based laser pushing it? In which case, the idiocy of comparing a system that you have to lift into space, in which every gram is critical, versus something here that can be hooked up to the power grid, is beyond belief.
Are we talking about a solar sail that is simply power by the sun? In which case, given the power source is external, and unending (well, good for the next 5 billion years or so), how do you make a claim that something is 'two orders of magnitude higher' in 'performance parameters' than the solar sail? Calculations?
When the paper is 'proof of concept', but a) they don't actually do any experimentation to see what would change performance, b) have lots of explanations for all the possible sources of error ... but, again, don't actually monkey around with said sources, to see if their hand-wavium is correct (apart from the torsion pendulum), .... and c) finish with a unsupported statement claiming superiority over 'other' zero-propellant system ... honestly, they did some great science is some respects, and utterly abysmal in others.
To be fair, they could easily be using previously published numbers on solar-sail efficiency. And their numbers could all be spot on, not to mention their conclusions. But failing to have a paper proof-read by someone NOT familiar with the subject is bad (and all too common).
And they could have made the paper better, but some decent editing. OK, so you start with a thrust-to-power ratio of 1.2 mN/kW. The error margin, ±6 N, is buried way, way down. Seriously, putting the two together would give some real validation to the idea the thrust they got was far more than the (calculated) error margin.