Quantum computer creates quasiparticles with their own memory

Particles with unusual properties, called anyons, are sought after because they can serve as building blocks for advanced quantum computers. Now researchers have found one, using a quantum computer.

A mysterious particle that can remember its past has been created using a quantum computer. This anyon could improve the performance of quantum computers in the future.

The anyon is unlike any other particle we know of because it keeps a sort of list of where it has been. Normally, particles, such as electrons or photons (particles of light), are identical, so it is impossible to tell if a pair has been swapped.

But in the 1970s, physicists realized that this was not the case for certain quasiparticles that can only exist in two dimensions. Later they were called anyen. Quasiparticles, as the name implies, are not real particles. They arise from collective behaviour, such as vibrations of large numbers of real particles, which behave together as if they were particles.

Non-abelian

Unlike other particles, swapping two anys fundamentally changes the pair, with the number of swaps affecting the way they vibrate. Groups of a certain kind of these quasiparticles, called non-abelian anyones, carry memories of the order in which they were swapped, just as a braided piece of rope carries information about the order in which the strands were crossed. But where the threads of a rope influence each other physically, anyons influence each other via the quantum phenomenon of entanglement.

This inherent memory and the quantum nature of the quasiparticles make non-abelian anyons an attractive candidate for quantum calculations. But their existence had never been proven experimentally.

Quantum processor

Now say theoretical quantum physicist Henry Dryer from quantum computer company Quantinuum and his colleagues that they have done that in an unpeer-reviewed preprint. The researchers developed a new quantum processor, called H2, that uses ytterbium and barium ions captured with magnetic fields and lasers to create qubits, or quantum bits, the building blocks of a quantum computer.

They then intertwined these qubits in a formation called a Kagome lattice, a pattern of interlocking stars that is also used in traditional Japanese basket weaving. This gave the qubits quantum mechanical properties that fit anyons. The team then modified the interactions between the qubits in such a way that it corresponds to moving anyons. This allowed them to test and confirm the characteristic changes that occur during exchanges.

Simulation

‘This is the first convincing trial capable of doing this. So this would be the first case of what you could call non-abelian topological order,” says physicist Steve Simon from the University of Oxford. The fact that you can play with the anyones with a quantum computer is also useful for researchers who want to better understand this exotic state of matter, he says.

But others argue that Quantinuum simulated non-abelian anyons rather than actually creating them. “I know they are very enthusiastic about their work, and they should be, but it remains a simulation,” says theoretical physicist Jiannis Pachos from the University of Leeds. This means that certain properties of real anyones may be missing.

Dryer takes a different view, saying that the quasiparticle nature of anyons means that a simulation is the same as a “real” quasiparticle. ‘A counterintuitive feature of these anyones is that they are not physical. It doesn’t matter what they’re made of,” says Dryer. ‘It’s only about the information and quantum entanglement. So if you have a system that can create that kind of entanglement, you can also create the corresponding anyons.’