Magazine article Science News

Atomic Crowds Tied by Quantum Thread

Magazine article Science News

Atomic Crowds Tied by Quantum Thread

Article excerpt

Scientists have been predicting that the strangeness of quantum mechanics will lead to computing and communications devices of unprecedented power. In pursuit of those trophies, researchers have struggled to control the frail, fleeting quantum states of minuscule particles. Now, a relatively simple and robust way of manipulating quantum states may be at hand.

For years, physicists have been exploiting a quantum phenomenon, known as entanglement, to intertwine the quantum states of charged atoms, or ions. They've been able to entangle as many as four ions so far (SN: 4/15/00, p. 255).

Eugene S. Polzik and his colleagues at the University of Aarhus in Denmark have now entangled two gas clouds, each of about a trillion cesium atoms. That huge leap reflects the team's development of a type of entanglement of atoms that's different from that established in earlier work, the researchers say.

Entangled entities have a coordinated quantum state. For example, if one particle in an entangled pair has an upwardly oriented magnetic field, or so-called spin, its partner's spin points down. Which partner has which spin remains hidden until the spin of one of them is measured.

In the smaller-scale experiments, each ion was entangled with every other. However, in the Sept. 27 NATURE, the Aarhus team describes a technique that treats large atomic ensembles as single quantum entities.

In their experiment, Polzik and his colleagues first injected cesium gas into a pair of 3-centimeter-long glass capsules. Next, the scientists shot laser pulses through each cell to impart a different collective spin state onto each cloud. Then, the researchers fired another laser pulse of a carefully chosen wavelength through both clouds.

The orientation, or polarization, of that pulse's electromagnetic field is itself a quantum state. Once the pulse entered the capsules, it became entangled with the clouds' spins, creating the first photon-atom entanglements, Polzik says. …

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