'Spooky' science points to quantum internet

'Entanglement' breakthrough made at University of Michigan

Robert Jaques, vnunet.com 06 Sep 2007

Physicists at the University of Michigan have demonstrated how two separate atoms can communicate with a sort of 'quantum intuition' which Albert Einstein referred to as "spooky".

In doing so, the researchers have made an advance towards super-fast quantum computing and even a quantum internet.

The scientists used light to establish an "entanglement" between two atoms, which were trapped one metre apart in separate enclosures.

"This link between remote atoms could be the fundamental piece of a radically new quantum computer architecture," said Professor Christopher Monroe, the principal investigator on the project who is now at the University of Maryland.

"Now that the technique has been demonstrated, it should be possible to scale it up to networks of many interconnected components that will eventually be necessary for quantum information processing."

David Moehring, the lead author of the paper who performed the research as a University of Michigan graduate student, explained that the most important aspect of the experiment is the distance between the two atoms.

"The separation of the quantum bits [qubits] in our entangled state is the most important feature," he said.

"Localised entanglement has been performed in ion trap qubits in the past, but to build a scalable quantum computer network (or a quantum internet) the creation of entanglement schemes between remotely entangled qubit memories is necessary."

The researchers used two atoms to function as qubits storing a piece of information in their electron configuration. They then excited each atom, inducing electrons to fall into a lower energy state and emit one photon, or one particle of light, in the process.

The atoms, which were actually ions of the rare-earth element ytterbium, are capable of emitting two different types of photons of different wavelengths.

The type of photon released by each atom indicates the particular state of the atom. Because of this, each photon was entangled with its atom.

By manipulating the photons emitted from each of the two atoms and guiding them to interact along a fibre-optic thread, the researchers were able to detect the resulting photon clicks and entangle the atoms.

Professor Monroe explained that the fibre-optic thread was necessary to establish entanglement of the atoms. But the fibre could be severed and the two atoms would remain entangled, even if one were "carefully taken to Jupiter".

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