Scientists from the MIT and Harvard have figured out a way to connect individual atoms of rubidium using lasers. This new technique could further accelerate the development of ultra-powerful quantum computers in the future.
"This is a major advance of this system," said MIT Department of Physics and Research Laboratory for Electronics (RLE) professor Vladan Vuletić. "We have demonstrated basically an atom can switch the phase of a photon. And the photon can switch the phase of an atom." Vuletić is also one of the co-authors of a paper describing the technique. Vuletić and his colleagues published their findings in the online journal Nature.
As a concept, quantum computing has been around 30 years. However, the development of this type of technology has both been slow and tedious. Unlike traditional computing, quantum computers revolve around quantum mechanics, which theoretically means that quantum computers will be more powerful compared with today's crop of computers.
The technique uses lasers to connect atoms of rubidium with light. This means that scientists can now bind individual metallic rubidium atoms with individual photons. This pairing could be used for quantum computing processes since both of the paired particles can change each other's quantum states.
"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.
The devices described by Vuletić have the potential to deal with vast amounts of information. With normal computers, the basic unit of information is called a bit. A bit can only have two possible values, either a 0 or a 1. With quantum computers, the basic unit of information is called a quantum bit or a qubit. And because of the sometimes weird and fantastical properties of quantum mechanics, a qubit actually allows for a superposition of two possible states.
"The idea is to combine different things that have different strengths and weaknesses in such a way to generate something new," said Vuletić. "This is an advance in technology. Of course, whether this will be the technology remains to be seen."
Taking the polarization of light as an example, the two possible states could either be horizontal polarization or vertical polarization. A single photon could either be vertically polarized or horizontally polarized. This means that the qubit is still a two-state system but the photon could also experience a superposition, both states existing at the same time.
The new technique developed by the researchers uses the polarization of light and the quantum states of the rubidium atoms. The interaction of the paired particles can cause the quantum state of individual rubidium atoms to change from the "ground" state to the "excited" state. The paired particles can essentially serve as a "transistor" for a quantum mechanical computer, a quantum switch.
"For me what is still amazing, after working in this for 20 years," Vuletić reflects, "is that we can hold onto a single atom, we can see it, we can move it around, we can prepare quantum superpositions of atoms, we can detect them one by one."
