Using just a handful of quantum bits, researchers have used a quantum computer to simulate an infinite line of electron-like particles. The technique could be used to better understand the behaviour of molecules in materials

A quantum computer made of charged atoms can use only a handful of quantum bits to simulate how an infinitely long and chaotic line of interacting particles behaves over time.

The behaviour of special materials, like superconductors, and molecules undergoing interesting chemical reactions is often too complex to simulate even on supercomputers. Researchers have long thought that quantum computers would be better at such tasks if they could build one large enough.

Eli Chertkov at the quantum computing company Quantinuum in Colorado and his colleagues have now devised a simulation algorithm that gets around this size constraint, enabling a quantum computer to simulate an infinitely long chain of interacting electron-like particles with very few quantum bits (qubits).

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The researchers used qubits made of charged ytterbium atoms. They programmed them to run the new algorithm, which simulates a chain of particles that all interact with each other. The team set up the interactions in such a way that past mathematical analyses suggested would make the particles behave chaotically – a mathematical concept that means very small changes in the initial arrangement have a big impact later on.

Usually, the number of particles a quantum computer can simulate depends on the number of qubits it can use. Here, the researchers used just three to 11 qubits.

Chertkov says that the Quantinuum quantum computer could do this because the algorithm directed it to keep “recycling” qubits during the calculation. When the computer needed more qubits, it would choose one it had already used, reset it and then reuse it, all without disturbing other qubits involved in the ongoing calculation.

The researchers already knew how a line of particles should behave over time from previous calculations and that is what they saw in their simulation, suggesting that it works.

Miles Stoudenmire at the Flatiron Institute in New York says that the next test for the new algorithm would be to simulate a system that conventional computers can’t handle, such as particles in 2D materials rather than just in a line. Understanding what electrons in those materials do over time, for instance, could help develop more efficient electronics devices.

Kaden Hazzard at Rice University in Texas says that the chaotic element makes the simulation more relevant to the real world. If you just picked a system inspired by nature at random, it would probably be chaotic, he says.

**Reference:** Nature Physics, DOI:10.1038/s41567-022-01689-7

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