A key challenge on the way to a powerful quantum computer is to interconnect millions of quantum bits, or qubits for short, in such a way that they interact reliably with one another. So far, quantum computers are still working on a fairly rudimentary 100-qubit scale. Scientists at the University of Sussex in the UK have now succeeded in connecting two microchips together via a special quantum matter link and transferring qubits between neighboring modules. This is what the group around the quantum physicist Mariam Akhtar reports in the journal »Nature Communications«. Both the speed and accuracy are superior to anything previously achieved with ion trap technology. This shows that quantum computers can be scaled beyond the physical limits of a microchip.
Of all the different ways in which qubits can be realized for future quantum computers, the ion trap is one of the most promising concepts. Ions, i.e. electrically charged atoms or molecules, are held in place using electric and magnetic fields and manipulated with lasers. The quantum state remains stable over a comparatively long period of time, the calculation precision is higher than with other qubit systems and the microchip has to be cooled a little less than the superconducting circuits that IBM and Google use for their quantum chips.
In their experiment, the researchers developed a special technique to transport the ions. With the help of electric fields, they controlled the ion movement in such a way that a single ion qubit could be physically moved back and forth between the modules. “Using this method, we were able to achieve a success rate of 99.999993 percent and a connection rate of 2424 connections per second over a total distance of 684 microns,” they write in the paper. The fragile quantum state remained stable over the entire transport period. This opens up the potential for putting hundreds or even thousands of quantum microchips together and connecting them like pieces of a puzzle.