‘We are writing quantum algorithms for the imperfect quantum computers of today, to accelerate practical quantum advantage from decades away to years away,’ says Cat Mora, director of research operations at Phasecraft, one of the pioneers of the quantum revolution.

It’s an odd situation. Quantum chips are almost here. IBM, Quantum Motion, Infleqtion, D-Wave, and others, have prototypes with a few hundred to a few thousand qubits, able to run code. But they are unstable and ‘noisy’ in the industry parlance – prone to errors which require correction. The large-scale, high-performance fault-tolerant quantum chips that large swathes of the industry will require for many complex tasks are still three to five years away.

Which is why Phasecraft is so unusual. It’s one of the first quantum software firms: so early, the hardware isn’t ready yet. Founded in 2019 by academics from University College London and the University of Bristol, Phasecraft employs 30 researchers who are building the applications that aim to show the world what quantum chips can do, well before they reach the scale and size required for fault-tolerant computation.

The obvious question arises: how and why does Phasecraft create software if the chips aren’t ready?

‘They will exist soon!’ says Mora. ‘We are making sure useful stuff can be done on quantum computers as soon as possible. Quantum computers have been hypothetically thought about for 40 years. In the 1990s we had Shor’s algorithm and Grover’s algorithm, but then the focus switched to how to build the machines. There was an assumption we’d need billions of qubits to do anything useful. Our approach is to get our hands dirty and see what problems we can solve with as little quantum resource as possible.’

What problems is Phasecraft working on?

‘We work with a whole spectrum of companies,’ says Mora. ‘There are materials discovery companies, who want to improve industrial products; pharmaceutical companies researching molecules; and there are companies such as the National Grid working on optimisation problems. Classical computers don’t give good answers. So we try to build an algorithm which can solve them, and minimise the resources required so that it can run on a quantum computer in three or five years, without having to wait for the billion qubit fault-tolerant processor.’

At this juncture, a chipmaker might object. IBM launched the Condor quantum chip in December 2023, with 1,121 superconducting qubits – a big advance on its 433-qubit chip, and the 127-qubit chip in 2021. In January 2024, D-Wave unveiled the 1,200+ Advantage2. Xanadu has the Borealis chip. These exist and can run code.

Mora elaborates: ‘These quantum computers exist. The problem is the vulnerability to noise and their stability. In a classical computer error correction is built in. You can just run your program for as long as you need and not worry. In these quantum processors, you have a limited number of operations before things go pear-shaped.’

So the hardware is not able to run anything meaty. ‘We need thousands of operations to run our algorithms, and currently no chip can support what we need yet.’ Phasecraft’s work currently focuses on testing its algorithms on today’s current crop of quantum computers, including Google, IBM and Rigetti. The lessons Phasecraft gets from testing its algorithms are also shared with the hardware companies to help refine the technology.