Levitating in midair, a fleck of diamond just 100 nanometers across glows brightly in a green laser beam. “This nanodiamond is just suspended in free space, and the way we hold it in place isn't with tweezers or our fingers,” says optical physicist Nick Vamivakas of the University of Rochester. Instead Vamivakas and his colleagues use a second laser, with an invisible infrared beam, to produce an electric field that traps the diamond in place.
Nestled inside the specially engineered crystal are hundreds of so-called nitrogen vacancy (NV) centers—nitrogen atoms adjoining gaps in the carbon lattice. The green laser excites the NV centers, which then emit reddish photons by photoluminescence, the team recently reported in Optics Letters. The red glow is too faint to see, but the demonstration shows that lasers can manipulate quantum states inside the hovering crystal. Vamivakas says that physicists could even exploit the quirks of quantum mechanics to trap a levitating nanodiamond in two places at once.