In the race to build large-scale quantum computers, two contrasting strategies – one based on trapping ions, the other on more conventional technology – have drawn neck-and-neck. Both sides can now create simple devices that run multiple varieties of quantum software.
Early endeavours had focused on trying to run a single quantum algorithm, such as Shor’s algorithm for factoring numbers. A large enough quantum device running these algorithms should massively outperform ordinary computers. But the strategy is limited in scope – if ordinary computers were designed like this, you’d need a different laptop for every app you wanted to run.
That’s why attention has now turned to creating programmable quantum computers. In May this year, IBM announced it was making such a device available for anyone to use over the internet. Its computer has five quantum bits, or qubits, so can only handle relatively small problems – but it’s programmable just like a regular PC. Researchers at Google have developed a similar device, although have not made it accessible to the public.
Both of these computers use superconducting qubits built using techniques from the conventional computer chip industry. Now, a team at the University of Maryland has succeeded with its own quite different approach to making a programmable five-qubit computer.
Their qubits are made from ytterbium ions held in place by magnetic fields and lasers, a technology with its origins in atomic clocks. “Ions are nature’s quantum units,” says team member Shantanu Debnath. “If you have a bunch of them in a processor, all of them are identical, and that is a significant advantage.”
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