University of Nottingham: New research twists elusive ‘exotic’ quantum particles

New research using a highly controllable quantum processor has provided new insights into ‘exotic’ states of matter that could lead to new ways to improve quantum computers.

Scientists from the University of Nottingham and Technical University of Munich (TUM) collaborated with the Google Quantum AI team and used a highly controllable quantum processor to simulate the ground state of a so-called toric code Hamiltonian – an archetypical model system in modern condensed matter physics, which was originally proposed in the context of quantum error correction.

Google’s ‘Sycamore’ quantum processor
While the number of qubits and the stability of quantum states are still limiting actual quantum computing devices, there are questions where these processors are already able to leverage their enormous computing power. This new research published today in Science helps to understand this.

What would it be like if we lived in a flat two-dimensional world? Physicists predict that quantum mechanics is even stranger in that case and results in exotic particles — so-called “anyons”— that cannot exist in the three-dimensional world we live in. This unfamiliar world is not just a curiosity but may be key to unlocking quantum materials and technologies of the future. The research team used a highly controllable quantum processor to simulate these states of quantum matter.

Emergent quantum particles in two dimensional systems

All particles in our universe come in two flavors, bosons or fermions. In the three-dimensional world we live in, this observation stands firm. However, it was theoretically predicted almost 50 years ago that other types of particles, dubbed anyons, could exist when matter is confined to two dimensions.

Twisting pairs of these anyons by moving them around one another unveils their exotic properties—physicists call it braiding statistics
Dr Adam Smith from the University of Nottingham
While these anyons do not appear as elementary particles in our universe, it turns out that anyonic particles can emerge as collective excitations in so-called topological phases of matter, for which the Nobel prize was awarded in 2016.

A simple picture for these collective excitations is “the wave” in a stadium crowd–it has a well-defined position, but it cannot exist without the thousands of people that make up the crowd. However, realizing and simulating such topologically ordered states experimentally has proven to be extremely challenging.

Quantum processors as a platform for controlled quantum simulations

In landmark experiments, the researchers programmed Google’s quantum processor to simulate these two-dimensional states of quantum matter. “Google’s quantum processor named ‘Sycamore’ can be precisely controlled and is a well-isolated quantum system, which are key requirements for performing quantum computations,” says Kevin Satzinger, a scientist from the Google team.

The researchers came up with a quantum algorithm to realize a state with topological order, which was confirmed by simulating the creation of anyon excitations and twisting them around one another. Fingerprints from long-range quantum entanglement could be confirmed in their study. As a possible application, such topologically ordered states can be used to improve quantum computers by realizing new ways of error correction. First steps toward this goal have already been achieved in their work.

“Near term quantum processors represent an ideal platform to explore the physics of exotic quantum phases matter,” says Prof. Frank Pollmann from TUM. In the near future, quantum processors promise to solve problems that are beyond the reach of current classical supercomputers. In particular, they offer new opportunities to unlock the mysteries of novel quantum materials.

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