We can build a quantum computer today. But it’ll be as big as a stadium.

Nature pores over the blueprints drawn up using today’s technology… and a $126 million budget… for the next big step in computing power:

“Yes it will be big, yes it will be expensive — but it absolutely can be built right now,” says quantum physicist Winfried Hensinger of the University of Sussex in Brighton, UK, who leads the team that published the blueprint in Science Advances on 1 February.

Quantum computers promise to exploit the remarkable properties of quantum particles to carry out certain calculations exponentially faster than their classical counterparts. Teams around the world are competing to build them on the scale required for them to be useful, but most designs so far have targeted a few dozen quantum bits, or qubits. Many thousands are probably needed to do useful calculations, such as finding the prime factors of large numbers, a crucial problem in encryption.

Hensinger’s team suggests using ions trapped by magnetic fields to create its qubits — an approach that physicists have been working on for more than 20 years. Most of the components necessary to build a trapped-ion quantum computer have already been demonstrated, Monroe says. “Our community needs a systems-engineering push to simply build it.”

In Hensinger’s blueprint, thousands of hand-sized square modules could be yoked together to produce — in theory — a quantum computer of any size. Key to the design is how to overcome practical problems, such as the need to dissipate heat produced by the machine.

In each module, around 2,500 trapped-ion qubits would be suspended in magnetic fields, protected from interference that would affect their delicate quantum states. To perform operations, ions interact with their neighbours by shuttling around an x-shaped grid, like Pac-Man characters.

The ions themselves would hop from chip to chip to transmit information between the modules — a technique that produces inter-chip connection speeds 100,000 times those of systems that use light waves and optical fibres, says Hensinger. The individual modules would be replaceable, built on silicon bases that could be manufactured using techniques available in the conventional electronics industry, he adds.