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Optoelectronics & Communications

Physicists demonstrate quantum entanglement

Researchers at the National Institute for Standards and Technology (NIST) have synchronized the motions of two nano-pendulums by virtue of a quantum phenomenon called entanglement.  Quantum entanglement keeps atoms, electrons and photons in synchronized states no matter how far they are moved apart. Their work was reported in the latest issue of Nature.

The team developed a means to entangle the actual motions of two pairs of atoms: a more tangible and visual property of a system than electron spins and photon polarisations.

"What we wanted to do was to perform this entanglement in the sort of system that people can relate to, a mechanical system that pervades nature everywhere: a vibrating violin string, the pendulum on a clock, the quartz crystal in your digital watch," lead author John Jost told BBC News.

The results further bridge the gap between the world of quantum mechanics and the laws of everyday experience. Entanglement could be exploited in future quantum computers, because the inherent probability-based nature of quantum systems means they can compute certain kinds of problems significantly more quickly than current "classical" computers.

The intertwining involved four electrically charged atoms, or ions - two beryllium and two magnesium ions. These are prepared in a device called an ion trap that uses electric fields to manipulate the charged particles.

The positively charged ions repel one other, and behave as if they are connected by a spring. This "spring" has a natural resonant frequency, just like a pendulum, which can be excited with the "kick" of a laser of just the right colour.

First, a laser is used to entangle the internal energy states - the "spins" - of the two beryllium ions.

The four ions are then separated into two pairs, each made up of a beryllium and a magnesium ion four micrometres apart. The pairs themselves are separated by 240 micrometres - just a few hairs' breadths, but an enormous distance in the atomic world.

The magnesium ions are cooled with lasers, which in turn removes excess energy from the beryllium ions. Further laser pulses then provide an energetic "kick" to ensure the beryllium ions are no longer entangled via their spin states, but are now entangled via their motions. The entangled pairs move in perfect unison despite their separation distance.

Read full article on BBC News