New 'switch' may bring quantum computers closer

Scientists have developed a new method of trapping rubidium atoms in a lattice of light, a finding that could bring super-fast quantum computers closer to reality.
The technique created by scientists at the Massachusetts Institute of Technology (MIT) and Harvard University allows researchers to couple a lone atom of rubidium, a metal, with a single photon, or light particle.
This allows both the atom and photon to switch the quantum state of the other particle, providing a mechanism through which quantum-level computing operations could take place, researchers said.
Moreover, the scientists believe their technique will allow them to increase the number of useful interactions occurring within a small space, thus scaling up the amount of quantum computing processing available.

"This is a major advance of this system," said Vladan Vuletic, a professor in MIT's Department of Physics and Research Laboratory for Electronics (RLE).
"We have demonstrated basically an atom can switch the phase of a photon. And the photon can switch the phase of an atom," said Vuletic, a co-author of the paper.

Photons can have two polarisation states, and interaction with the atom can change the photon from one state to another; conversely, interaction with the photon can change the atom's phase, which is equivalent to changing the quantum state of the atom from its "ground" state to its "excited" state.

In this way the atom-photon coupling can serve as a quantum switch to transmit information - the equivalent of a transistor in a classical computing system.
And by placing many atoms within the same field of light, the researchers may be able to build networks that can process quantum information more effectively.
"You can now imagine having several atoms placed there, to make several of these devices - which are only a few hundred nanometres thick, 1,000 times thinner than a human hair - and couple them together to make them exchange information," Vuletic added.
Quantum computing could enable the rapid performance of calculations by taking advantage of the distinctive quantum-level properties of particles.

Some particles can be in a condition of superposition, appearing to exist in two places at the same time.
Particles in superposition, known as qubits, could thus contain more information than particles at classical scales, and allow for faster computing.
The study was published in the journal Nature.