In quantum entanglement, particles are correlated so that a change in one will instantaneously induce a change in others—even if they are at opposite ends of the universe. The classic example is a pair of entangled particles: If one changes its spin to clockwise, the other simultaneously flips to counterclockwise.
Entangling particles, especially large numbers of them, is no easy task. MIT and University of Belgrade scientists report in Nature that they managed to entangle 3,000 particles trapped in a supercooled cloud. The key was using very weak light, as weak as a single photon of light, which is less likely to disturb the cloud than a strong beam. The photon bounced thousands of times between two mirrors, passing back and forth through the cloud of atoms. This was enough to entangle the atoms, which LiveScience explains:
If a photon in a pulse interacted with the cloud’s atoms, the polarization of the photon would rotate slightly. Strangely, in the realm of quantum physics, the act of measurement can dramatically influence the object getting measured, and the act of detecting a photon that interacted with these atoms can essentially generate entanglement between those atoms.
So why does this matter? One possible application is quantum clocks—the more atoms are entangled, the more accurate the clock. This technique might even be used to get around the uncertainty of quantum measurements. (Physics World has a great technical explanation of how.) Atomic clocks are used to keep track of GPS systems.
This could also be a step toward complex entangled states that can give us quantum computing and quantum encryption. But it’s also just pretty damn cool to push the limits of what’s possible. [Nature, LiveScience, MIT]
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