Quantum computers could create completely new forms of matter

The way we can tweak interactions between qubits in quantum computers means the machines could help us create novel structures with weird properties we have never seen in nature.

Quantum computers could create a new form of matter with strange structures and qualities not seen in nature, which could one day help unlock exotic properties similar to superconductivity.

Most solid materials are made up of atoms or molecules that are influenced by short-range forces from their near neighbours, a principle known as locality. This gives rise to the common lattice structures seen in compounds like ice or salt. But the workings of quantum computers aren’t tied by this constraint, so the machines might be able to manipulate matter to defy locality.

To investigate this possibility, Joseph Tindall at the University of Oxford and his colleagues created a mathematical model that describes systems of quantum particles that are free to interact with any other particle, not just with their neighbours.

The team then used a field of mathematics called graph theory to figure out whether such a system could really arise, by looking at constraints from systems that exist in the real world.

“In order to actually have proper, many-body quantum physics, you can’t just have any geometry you want, you actually have to have some very strong restrictions on your geometry,” says Tindall. “Our work demonstrates that actually, you need either these kinds of lattice structures that people know, or you can go in a completely different direction.”

Unusual geometry

The process revealed a new class of structures that had unusual geometries – how their atoms were connected – with some particles within them partially interacting with others and some being isolated. Using computational algorithms to calculate some of the properties of these particles revealed a structure that changed its magnetic properties in a way unlike anything found in nature.

It is unclear how this property might manifest in the real world, or how it would be useful, but it might be possible to create the phenomenon on a quantum computer.

“There are certain computing platforms, like ion-trap quantum computers, where you can almost apply interactions between any qubits you want,” says Tindall. “So, in principle, these sorts of irregular structures that we talked about in our paper could then be realised.”

The application of graph theory to quantum systems in this way is novel, says Stephen Clark at the University of Bristol, UK. “It’s a very interesting result and may tell us about new types of systems and connectivity that we’ve not even thought about before because they wouldn’t normally occur in nature.”

Exotic behaviours

Understanding how these systems would function in the real world is difficult, says Clark, because the structures that Tindall’s team looked at don’t have a notion of distance factored in – only the connections between particles. It would be very interesting if they give rise to exotic qualities, similar to superconductivity, he says.

We aren’t yet at the stage where we can create matter with these properties, says Thomas Elliott at Imperial College London. “Actually building materials is still more than a few years away, because you need the next stage of the theory to come out actually looking at potential types of graphs that give rise to various exotic behaviours – but this is the first stepping stone towards that.”

The next step will be to move from static calculations to looking at how these systems might evolve over time, says Tindall.


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