Quantum Computing Advances At MIT - Trapping Rubidium Atoms In A Lattice Of Light
April 11, 2014

New Light Lattice Technique Could Advance Quantum Computing

redOrbit Staff & Wire Reports - Your Universe Online

Scientists at MIT and Harvard University have developed a light lattice that traps atoms, a technique they say could aid in the creation of powerful quantum computing systems.

The researchers used a laser to place individual atoms of the metal rubidium near the surface of a lattice of light, allowing them to couple a lone atom with a single photon, or light particle. The system 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.

The scientists said they believe their technique, described in a paper published this week in the journal Nature, will allow them to increase the number of useful interactions occurring within a tiny space, thereby increasing the amount of quantum computing processing available.

“This is a major advance of this system,” said study co-author Vladan Vuletić, a professor in MIT’s Department of Physics and Research Laboratory for Electronics (RLE), in an interview with MIT News.

“We have demonstrated basically an atom can switch the phase of a photon. And the photon can switch the phase of an atom.”

Photons can have two polarization 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.

This means the atom-photon coupling can serve as a quantum switch to transmit information – the equivalent of a transistor in a classical computing system. Furthermore, by placing many atoms within the same field of light, the researchers could possibly build networks that can process quantum information even more effectively.

“You can now imagine having several atoms placed there, to make several of these devices — which are only a few hundred nanometers thick, 1,000 times thinner than a human hair — and couple them together to make them exchange information,” Vuletić said.

Quantum computing could enable the rapid performance of calculations by harnessing 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. Such particles, known as qubits, could thus contain more information than particles at classical scales, and allow for faster computing.

But researchers are only in the nascent stages of determining which materials best allow for quantum-scale computing. The MIT and Harvard researchers have been investigating photons as a candidate material, since photons rarely interact with other particles. For this reason, an optical quantum computing system using photons could be harder to disrupt out of its fragile alignment. However, since photons rarely interact with other bits of matter, they are difficult to manipulate.

In the current study, the researchers used a laser to place a rubidium atom very close to the surface of a photonic crystal cavity, a structure of light. The atoms were placed no more than 100 or 200 nanometers from the edge of the cavity. At these tiny distances, there is a strong attractive force between the atom and the surface of the light field, which the researchers used to trap the atom in place.

“In some sense, it was a big surprise how simple this solution was compared to the different techniques you might envision of getting the atoms there,” Vuletić said.

The result is what he calls a “hybrid quantum system,” where individual atoms are coupled to microscopic fabricated devices, and in which atoms and photons can be controlled in productive ways. The researchers also found that the new device serves as a kind of router separating photons from each other.

“The idea is to combine different things that have different strengths and weaknesses in such a way to generate something new,” Vuletić said. “This is an advance in technology. Of course, whether this will be the technology remains to be seen.”