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Scientists have so far been able to entangle large groups of atoms, although most attempts have only generated entanglement between pairs in a group. Only one team has successfully entangled 100 atoms—the largest mutual entanglement to date, and only a small fraction of the whole atomic ensemble.
Now Vuletic and his colleagues have successfully created a mutual entanglement among 3,000 atoms, virtually all the atoms in the ensemble, using very weak laser light—down to pulses containing a single photon. The weaker the light, the better, Vuletic says, as it is less likely to disrupt the cloud. "The system remains in a relatively clean quantum state," he says.
The researchers first cooled a cloud of atoms, then trapped them in a laser trap, and sent a weak laser pulse through the cloud. They then set up a detector to look for a particular photon within the beam. Vuletic reasoned that if a photon has passed through the atom cloud without event, its polarization, or direction of oscillation, would remain the same. If, however, a photon has interacted with the atoms, its polarization rotates just slightly—a sign that it was affected by quantum "noise" in the ensemble of spinning atoms, with the noise being the difference in the number of atoms spinning clockwise and counterclockwise.
originally posted by: Autorico
a reply to: lostbook
Pardon my ignorance, are atoms not bigger than photons?