The concept of building a quantum computer with topological qubits had been knocking around Microsoft for nearly 15 years.
At the company’s Redmond campus, later expanding into its Station Q centre at the University of California, researchers investigated this “complex, yet beautiful mathematical theory” as Microsoft’s quantum guru Michael Freedman once described it.
It remained just that – a beautiful theory – for years. Then something changed.
Suddenly in late 2016, Microsoft announced Station Q would expand to eight labs worldwide including one at the Quantum Nanoscience Laboratory at the University of Sydney. Four heavyweight academic hires were made. An 'inflection point' had been reached, a release stated.
“Why are they now switching on? How much should I read into that?” says Professor David Reilly, director of Station Q’s new Sydney lab. “I think you can read plenty into that.”
Is Anyon out there?
The topological approach to forming qubits uses quasiparticles called non-abellian anyons.
“We've realised that the only way to really scale is to build much better qubits. Qubits that are inherently, intrinsically immune to noise and immune to disturbances from the environment,” says Reilly.
In most approaches to building quantum systems, information is encoded in the properties of particles. That makes the systems very fragile as any disturbances from the environment can destroy a particle’s quantum state.
According to Microsoft, topological qubits are better able to withstand heat and electrical noise, which allows them to remain in a stable quantum state for longer. By encoding the information not on the quasiparticle but in the order the positions of the anyons are swapped around (called braiding), topological qubits offer a more viable way to make a scalable, usable quantum computer.
The quasiparticles themselves remain something of a riddle. Non-abellian anyons can’t be seen with any kind of microscope but they can be measured with high-precision devices. Probably. Certainly there is no consensus among physicists as to whether they are real or not.
As Microsoft’s Alex Bocharov confidently put it to Nature, the company is “pretty sure” that they exist.
“We reached a point where the experiments were convincing enough that now we should actually try and construct technology from it. And that's where we are today,” Reilly adds.
Faith at scale
Backing topological qubits is as much about belief in the approach, Reilly says, as doubt in all the others.
“It's a double-edged sword. For me personally some of the decision to go in this direction is born out of a pessimistic view. It's faith in this approach and the reality is it's pessimism that the other existing approaches can really go the distance,” he says.
Google and IBM back the superconducting loop approach to building qubits, while Intel and the Commonwealth Bank and Telstra backed Centre for Quantum Computation and Communication Technology at UNSW in Sydney, are pursuing a silicon-based method.
“The difference between demonstrating the basic operation of one single device in a university lab and publishing a very nice paper, and what it's going to take to bring that technology to scale – I think these are vastly different activities,” Reilly says. “It becomes pretty depressing and I don't see it.”
The ability to scale is key to Microsoft’s quantum efforts. Its ambition goes way beyond the lab.
“It's all about having the fundamental building blocks that can take you to millions of qubits,” Reilly says. “It's all about going the distance.”