The most powerful modern computers, supercomputers, are a multitude of computing nodes interconnected by special bridges and high-speed data buses, the so-called interconnects. The same will be true for future quantum computers, which should be a functionally complete system integrated with many additional devices. Researchers at Harvard University and the Ion Beam Laboratory, part of Sandia National Laboratory, have taken a big step toward integrating quantum computing systems. They have created a first-of-its-kind quantum “bridge” capable of efficiently integrating multiple quantum computers into a single networked computing system.
Currently, there are only the simplest quantum computing systems in the world, for example, IBM Quantum Experience, which can only perform simple algorithms. For some time scientists are trying to create systems consisting of several simple quantum computers, which together can solve more complicated problems. But unfortunately, despite all these efforts, attempts to create fully functioning “multiprocessor” quantum systems have not yet succeeded.
“People have already built simple quantum computers long enough,” says Ryan Camacho, a researcher at Sandia Labs, “And it is likely that the next step is not to build one large and powerful quantum computer, but an entire system made up of interconnected simple quantum computers.”
In order to link quantum computers as a whole, a bridge capable of sharing quantum information between multiple devices is required. In other words, this bridge must make all atoms (quantum bits, qubits) contained in the system behave as if they were one single atom.
Using a focused-beam ion implantation facility in Sandia’s lab, scientists replaced one carbon atom in the crystal lattice of a diamond base with a larger silicon atom. Once this was done, the silicon atom “squeezed” the neighboring carbon atoms, creating a kind of buffer zone around itself. This buffer zone acts as an insulator from the electric current affecting the diamond crystal. And, secondly, the silicon atom in the center of the buffer zone behaves as if it were in a vacuum rather than confined inside a solid crystal. This allows the necessary “response of the atom’s electrons to quantum phenomena, which is not affected by unwanted interactions with other particles of matter.
When pumped by laser light photons, all silicon atoms go into an excited energy state, their electrons jumping to higher energy orbits. But when these electrons return to their initial state, they emit “packs” of photons of light whose quantum parameters with 100 percent probability correspond to the current quantum state of the silicon atom.
“The first thing we managed to do was to place silicon atoms in strictly defined places of the crystal lattice, located far below the surface level. Now we are already able to create thousands of such “silicon defects”, which will be arranged in a strict order” – says Ryan Camacho – “If before we had to be able to isolate photons from one of thousands of randomly scattered light sources, now we can tell exactly which silicon atom was emitted by any of the photons”.
With the development and implementation of some additional methods, including already created “quantum detectors”, such an ordered matrix of “silicon defects” can become a bridge, which will unite into a single whole almost infinite number of quantum processors. And scientists are going to continue working in this direction, which sooner or later will lead to efficient and functional quantum computing systems.