Quantum holography The researchers (Christopher R. Moon, Laila S. Mattos, Brian K. Foster, Gabriel Zeltzer and Hari C. Manoharan) an interdisciplinary team from the departments of Physics, Electrical Engineering and Applied Physics at Stanford, used a gas of 2D surface state electrons held on the face of a copper crystal. Using atomic manipulation the team place individual electrons in closed quantum corrals - a common research tool.
The tricky part was encoding a specific pattern around the electrons. Using simulated annealing, they controlled the amplitude and phase of the electrons to encode the bits.
Since the writing "surface" is a gas, the team was then able to encode holograms in the same space by embedding them volumetrically in 3D. Here's a picture: