Researchers unveil the first fully programmable quantum computer with neutral atoms

While most quantum computers rely on the use of superconducting or trapped ion qubits, another approach involving ordinary atoms could have serious advantages.

Cesium atoms with a neutral charge

Unlike classical machines, which process data in the form of binary bits (0 or 1), those of quantum computers (known as qubits ) can exist in a simultaneous superposition of these two states. This translates into an exponential increase in their potential processing power.

The most powerful current devices use so-called superconducting or trapped ion qubits, but these have drawbacks: arranging them in such a way they can all communicate with each other is extremely complicated, and the maintenance of ultra-low temperatures is also necessary to operate superconducting systems.

In pre-published work on the arXiv server, Mark Saffman and his colleagues at the University of Wisconsin-Madison have designed an alternative quantum computer using six qubits made of charge-neutral cesium atoms, as opposed to to charged ions.

Trapped in a grid using lasers, these turn out to be far enough from each other not to interact. But when individual atoms are excited by a laser beam emitted at the right frequency, the electrons orbiting them move so far apart that they can become entangled with their neighbors. An essential phenomenon in the case of quantum computers.

A two-dimensional structure

This two-dimensional structure offers a significant advantage over the configuration of trapped ion machines, which are normally organized in rows to suppress unwanted interactions between charged particles. This limits their ability to communicate, and therefore to execute algorithms requiring high connectivity between qubits.

Presented as the first fully programmable neutral atom quantum machine, the system imagined by the American researchers is able to execute any quantum algorithm and could theoretically be scaled up to compete with other approaches peak.

"Since everything is done using laser beams, if you decide to run an algorithm involving different connectivity between qubits, you can easily reconfigure their positions," Charles Adams of Durham University comments at United Kingdom.

Steady progress

The new device is not the only one to demonstrate the potential of neutral atom machines. French start-up Pasqal has unveiled a processor with more than 100 qubits designed to perform complex simulations, while Harvard researchers have developed a machine that allows entanglements of distant qubits, although not fully programmable.

“The many advances made in recent years suggest that this approach will be able to compete with superconducting qubits and trapped ions in the relatively near future,” says Andrew Daley of the University of Strathclyde, UK.

Saffman also works for the company ColdQuanta, which is seeking to develop a neutral atom quantum computer for commercial use. According to the researcher, the development of larger (and therefore more powerful) fully programmable machines will notably require the integration of an error correction strategy.