Two new methods to power interstellar travel are being tested by NASA: an EmDrive, which uses only electricity to power space travel, and (believe it or not) warp drive. More here: http://www.ajc.com/news/news/national/nasa-about-crack-interstellar-travel/nk75M/
Don't hold your breath. It's likely an experimental error. They measured the same minuscule thrust in both the experimental engine as well as in the "dummy" (the one not supposed to generate thrust). So yeah, either that or they broke the laws of physics.