[jbob2000]

They're using light to heat the bottom of a thin material. Bottom of material heats up, heats up the air underneath the material, hot air expands and makes it float. Controlling the strength of the light controls how much heat the disc generates and thus controls its height. Heating one side of the disc causes it to heat unevenly and move in the opposite direction.

Do I have that right? Hot air rises, so if you stick something light on the plume of hot air, it will also rise? I think birds discovered this millions of years ago.

[Gatsky]

The temperature of the material is the same on the top and bottom (less than 0.1K difference they say). The mechanism is rather that the air molecules are entrapped in the nanotube coated under surface and heat up more, so depart with a higher velocity than the upper surface. This creates lift.

Quite a cool effect, reminiscent of an army of Laplace's demons kicking air molecules off the bottom of the surface to make it fly.