• Advances in quantum computing could help us simulate large complex molecules.
  • These simulations could uncover new catalysts for carbon capture that are cheaper and more efficient than current models.
  • We can currently simulate small molecules up to a few dozen qubits but need to scale this to the order of 1 million.

Imagine being able to cheaply and easily “suck” carbon directly out of our atmosphere. Such a capability would be hugely powerful in the fight against climate change and advance us towards the ambitious global climate goals set.

Surely that’s science fiction? Well, maybe not. Quantum computing may be just the tool we need to design such a clean, safe and easy-to-deploy innovation.

In 1995 I first learned that quantum computing might bring about a revolution akin to the agricultural, industrial and digital ones we’ve already had. Back then it seemed far-fetched that quantum mechanics could be harnessed to such momentous effect; given recent events, it seems much, much more likely.

Quantum supremacy

Much excitement followed Google’s recent announcement of quantum supremacy: “[T]he point where quantum computers can do things that classical computers can’t, regardless of whether those tasks are useful”.

The question now is whether we can develop the large-scale, error-corrected quantum computers that are required to realize profoundly useful applications.

The good news is we already concretely know how to use such fully-fledged quantum computers for many important tasks across science and technology. One such task is the simulation of molecules to determine their properties, interactions, and reactions with other molecules – a.k.a. chemistry – the very essence of the material world we live in.

While simulating molecules may seem like an esoteric pastime for scientists, it does, in fact, underpin almost every aspect of the world and our activity in it. Understanding their properties unlocks powerful new pharmaceuticals, batteries, clean-energy devices and even innovations for carbon capture.

Quantum simulation

To date, we haven’t found a way to simulate large complex molecules – with conventional computers, we never will, because the problem is one that grows exponentially with the size or complexity of the molecules being simulated. Crudely speaking, if simulating a molecule with 10 atoms takes a minute, a molecule with 11 takes two minutes, one with 12 atoms takes four minutes and so on. This exponential scaling quickly renders a traditional computer useless: simulating a molecule with just 70 atoms would take longer than the lifetime of the universe (13 billion years).

This is infuriating, not just because we can’t simulate existing important molecules that we find (and use) in nature – including within our own body – and thereby understand their behaviour; but also because there is an infinite number of new molecules that we could design for new applications.

That’s where quantum computers could come to our rescue, thanks to the late, great physicist Richard Feynman. Back in 1981, he recognized that quantum computers could do that which would be impossible for classical computers when it comes to simulating molecules. Thanks to recent work by Microsoft and others we now have concrete recipes for performing these simulations.

A quantum catalyst to tackling climate change?

One area of urgent practical importance where quantum simulation could be hugely valuable is in meeting the SDGs – not only in health, energy, industry, innovation and infrastructure but also in climate action. Examples include room-temperature superconductors (that could reduce the 10% of energy production lost in transmission), more efficient processes to produce nitrogen-based fertilizers that feed the world’s population and new, far more efficient batteries.

One very powerful application of molecular simulation is in the design of new catalysts that speed up chemical reactions. It is estimated that 90% of all commercially produced chemical products involve catalysts (in living systems, they’re called enzymes).

Annual CO2 emissions globally in 2017
Annual CO2 emissions globally in 2017

A catalyst for “scrubbing” carbon dioxide directly from the atmosphere could be a powerful tool in tackling climate change. Although CO2 is captured naturally, by oceans and trees, CO2 production has exceeded these natural capture rates for many decades.

The best way to tackle CO2 is not releasing more CO2; the next best thing is capturing it. “While we can’t literally turn back time, [it] is a bit like rewinding the emissions clock,” according to Torben Daeneke at RMIT University.

There are known catalysts for carbon capture but most contain expensive precious metals or are difficult or expensive to produce and/or deploy. “We currently don’t know many cheap and readily available catalysts for CO2 reduction,” says Ulf-Peter Apfel of Ruhr-University Bochum.

Given the infinite number of candidate molecules that are available, we are right to be optimistic that there is a catalyst (or indeed many) to be found that will do the job cheaply and easily. Finding such a catalyst, however, is a daunting task without the ability to simulate the properties of candidate molecules.

And that’s where quantum computing could help.

We might even find a cheap catalyst that enables efficient carbon dioxide recycling and produces useful by-products like hydrogen (a fuel) or carbon monoxide (a common source material in the chemical industry).

Quantum computing to the rescue – what will it take?

We can currently simulate small molecules on prototype quantum computers with up to a few dozen qubits (the quantum equivalent of classical computer bits). But scaling this to useful tasks, like discovering new CO2 catalysts, will require error correction and simulation to the order of 1 million qubits.

It’s a challenge I have long believed will only be met on any human timescale – certainly by the 2030 target for the SDGs – if we use the existing manufacturing capability of the silicon chip industry.

The path forward

At a meeting of the World Economic Forum’s Global Future Councils last month a team of experts from across industry, academia and beyond assembled to discuss how quantum computing can help address global challenges, as highlighted by the SDGs, and climate in particular.

As co-chair of the Global Future Council on Quantum Computing, I was excited that we were unanimous in agreeing that the world should devote more resources, including in education, to developing the powerful quantum computing capability that could help tackle climate change, meet the SDGs more widely and much more. We enthusiastically called for more international cooperation to develop this important technology on the 2030 timescale to have an impact on delivering the SDGs, in particular climate.

So the real question for me is: can we do it in time? Will we make sufficiently powerful quantum computers on that timeframe? I believe so. There are, of course, many other things we can and should do to tackle climate change, but developing large-scale, error-corrected quantum computers is a hedge we cannot afford to go without.