Single-spin system breaks quantum symmetry

Researchers say they have observed parity-time symmetry breaking for the first time in an experiment. The result was obtained using a “dilation” technique on a single-spin system – a nitrogen-vacancy centre in diamond. The system could be used as a platform for studying new and exotic physics, such as new topological variants, quantum thermodynamics and quantum criticality, in non-Hermitian quantum systems.

According to current physics theories, the universe is governed by certain fundamental symmetries. One of these looks at the relation between parity (P) or “handedness” and time (T) and describes the oddness or evenness of a quantum particle and whether it is moving forwards or backwards in time. When a PT transformation is applied to a quantum system it appears the same as the original.

Physicists are always on the look-out for signs of PT-violation, however, because this would indicate the presence of new physics. They would also like to be able to break the symmetry of quantum systems, like those containing single spins. This would allow them to control these systems – something that should be important for understanding quantum interactions and developing novel devices (such as quantum simulators and quantum sensors) based on these interactions.

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