Just as modern microprocessors evolved from many decades of ever-improving electronic components before them, so too the movement towards quantum computers requires the development and integration of many devices to create a fully-functioning system. Now, in one more step on the road to this end, researchers at Harvard University and Sandia Ion Beam Laboratory claim to have created the very first quantum "bridge" that could effectively link strings of quantum computers together in a single networked unit.

Until now, small numbers of individual devices, such as IBM's online quantum processor, have been available to run small sets of simple algorithms or clusters of simple quantum computers can be employed to process very large, but individually uncomplicated, sets of equations, but no fully-functioning, multiple quantum computer system has been available.

"People have already built small quantum computers," said Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer but a connected cluster of small ones."

In this vein, the Harvard/Sandia collaboration aimed to produce a method to distribute quantum information across a bridge – or, more accurately, a network – that permits all of the atoms contained in the system to behave as if they were a single atom.

They began by using the focused-beam ion-implanter at Sandia Laboratories to replace one carbon atom in a diamond substrate with that of a larger silicon atom. Once the silicon atom was in place, it effectively crowded out its neighboring carbon atoms, leaving it buffered.

Because of this buffer, the material is useful for two reasons. First, the gap acts as an insulator from electrical currents that could be run through the diamond substrate. And second, Sandia says that the embedded silicon atoms behave as though they are suspended in a gas (even though they're in the solid diamond substrate), so "their electrons' response to quantum stimuli are not clouded by unwanted interactions with other matter."

Unlike the idea of a quantum data bus, the new quantum bridge eliminates the efficiencies of moving quantum bits individually over a distance. Instead, when laser-produced photons are pumped into the material, all of the silicon electrons are simultaneously excited into a higher atomic energy state so that, when the electrons revert to their lower energy state, they all emit groups of quantized photons that maintain 100 percent quantum integrity.

"What we've done is implant the silicon atoms exactly where we want them. We can create thousands of implanted locations, which all yield working quantum devices, because we plant the atoms well below the surface of the substrate and anneal them in place," said Comacho. "Before this, researchers had to search for emitter atoms among about 1,000 randomly occurring defects — that is, non-carbon atoms — in a diamond substrate of a few microns to find even one that emitted strongly enough to be useful at the single photon level."

With a much more robust and integral method to combine almost any number of quantum processors into a single unit, it is hoped that further research will lead directly to a method for producing effective, functional quantum computers.

The results of this research were recently published in the journal Science.

Source: Sandia National Laboratory