As previous experiments have shown, when the second light beam is shut off while the first pulse is inside the vapor, the first pulse can be completely stopped (and be temporarily stored inside the vapor). Then, by starting up the second beam again, the first pulse can be recovered.
Here, the physicists used this method to capture, store, and restore complex 3D light fields. The scientists slowed images on a light pulse to a group velocity of 8,000 meters per second, a velocity that allowed the images to be stored in atomic vapor for several microseconds.
They directed two light beams to a 5-cm-long vapor cell containing 52°C rubidium gas and a neon gas for buffering. Once half of the first light pulse (containing the image) had exited the vapor cell, the researchers turned off the second beam, so that the remaining half of the image was stored in the vapor. As the researchers explained, during storage, the image was encoded in the quantum state of the ensemble of atoms. After 30 microseconds, the researchers turned the second pulse back on, and the image was then recovered as it left the vapor cell.
“During the storage time, there are no light fields in the experimental system,” Shuker explained. “All the information carried by the light (in our case the 3D intensity and phase pattern) is converted to the quantum state of the atoms in the vapor (specifically, the coherence between the sub-levels of the ground state). If it was easy to detect the coherence level of the quantum state of the atoms, we would notice that an effective ‘image’ exists – but this is not easily performed (maybe the easiest way is to convert it back to light – as we do in the restoring stage of the experiment).”