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Here’s How to Build the First Large-Scale Quantum Computer

The only thing that remains is to actually build it.

Daniel Oberhaus

Daniel Oberhaus

Image: University of Sussex

In what may best be described as a quantum leap, a group of researchers from the University of Sussex have unveiled what they claim is the first realistic blueprint for the construction of a large scale quantum computer.

As detailed in a paper published Wednesday in Science Advances, the quantum computer designed by the Sussex team leverages a new device they've created that allows quantum information to pass from one microchip of the quantum computer, to another using electric fields instead of fiber optic cables. This would allow for connection speeds between the microchips that are up to 100,000 times faster than those currently achievable using fiber optics.

"There have been many studies where people made certain innovations to put us one step closer to a quantum computers," Winfried Hensinger, the head of the Ion Quantum Technology Group at the University of Sussex, told me. "But what we have done is quite a bit different: we've developed a nuts and bolts construction plan to build a large scale quantum computer."

In other words, the Sussex group has taken a number of separate innovations in the field of quantum computing and brought them together to create a fine-grained blueprint for what is needed to build the first large scale quantum computer, covering everything from the back-of-house electronics to the power requirements for the machine.

A large scale quantum computer would revolutionize the world of computing due to its ability to perform calculations that are impossible for a classical, binary computer to solve. This is a result of the way that quantum computers process information—unlike a classical computer, which stores information in bits (either a 1 or a 0), a quantum computer traffics in qubits, which can either be a 0, 1, or a combination of these two states at the same time (a property known as superposition). Experts worry that quantum computers will be able to easily break some of our most widely used forms of encryption today, and are preparing for that eventuality now.

There are a number of proposals for how to actually go about building a quantum computer, but the most promising—and the kind described by the Sussex blueprint—is known as a trapped ion quantum computer. As its name suggests, this type of quantum computer makes use of ions (an atom or molecule with an electric charge) that are 'trapped' in electromagnetic fields.

By changing the state of these ions—using microwaves to move an atom's electrons from one energy level to another—researchers make them function as qubits, or vessels of quantum information. To create a quantum computer, these qubits must interact with one another either by being physically moved from one location to another with lasers, or by emitting photons which are then transported through a fiber optic cable.

In the Sussex blueprint, the quantum computer consists of a collection of hand-sized microchip modules, each of which, according to Hensinger, will be capable of trapping around 2,500 ions. When voltages are applied to these microchips, they create the electric field which traps the ions and levitates them above the microchip. Yet rather than having ions from one microchip interact with ions on another microchip using a complicated setup involving lasers or fiber optic cables, Hensinger and his colleagues have invented a device which uses the electric field itself to transport the ions from one microchip to an adjacent microchip.

"They're trying to make the mechanisms for controlling and manipulating the qubits a lot easier," said Michele Mosca, a co-founder of the Institute for Quantum Computing at the University of Waterloo, who was not involved with the blueprint. "So instead of having countless lasers addressing individual ions, they want to use this [electric field] approach. It's impressive work."

A prototype of the core of a trapped ion quantum computer. Image: University of Sussex

Aside from a much faster connection speed than using fiber optics to connect the microchip modules, the Sussex team's device offers another key improvement: much simpler and cheaper technology. Lasers work great when you're talking about a quantum computer that is only manipulating a handful of ions, but a large scale quantum computer that would be capable of, say, breaking the encryption standards used today would consist of millions of ions. This in turn would require millions of lasers, making it impractical with current technologies. Indeed, so far researchers have struggled to build trapped ion devices which are capable of manipulating more than about a dozen qubits.

The Sussex blueprint, on the other hand, should be achievable with currently available technologies and able to manipulate far more qubits. Hesinger hopes that he and his colleagues will be able to build a small prototype over the next two years to prove the feasibility of their design. The prototype would only consist of only two microchips, but if it works, it could be the basis of a large scale quantum computer consisting of millions of ions and occupying a space the size of a football field (not to mention costing upwards of $120 million).

How long it will take to get to a large scale quantum computer is anybody's guess. Just as a classical computer wasn't made in a day, the quantum computer will emerge in increments—the point, according to Hesinger, is that it's time to start building it.

"This is not something we can do overnight, but our blueprint specifies what needs to be done," said Hesinger. "It won't be cheap or easy, but I think we're at a place now where we can think about engineering we need to do to build this machine."

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