Vortices in Granular Superconducting Films Exhibit Quantum Two-Level Behaviour

Vortices trapped in granular superconducting films can behave as two-level systems with microsecond-range quantum coherence and energy relaxation times that reach fractions of a millisecond, according to a paper published in Nature. A defining characteristic of superconductors is their tendency to expel magnetic fields.

Above a critical threshold, magnetic flux penetrates superconductors in discrete quanta carried by Abrikosov vortices.

The superconducting gap is completely suppressed at the vortex core, rendering them dissipative, semi-classical entities. Abrikosov vortices impact applications from high-current-density wires to quantum devices. Material disorder can drive a crossover to vortices that preserve an energy gap at the core, owing to intrinsic or emergent granularity on the scale of the coherence length.

Quantum vortex behaviour could emerge in the effective tunnel-junction regime. Coherent manipulation of vortex states has remained elusive prior to the reported work. Using the tools of circuit quantum electrodynamics, researchers performed coherent manipulation and quantum non-demolition readout of vortex states in granular aluminium microwave resonators.

The current paper is titled 'Quantum coherent manipulation and readout of superconducting vortex states'. @Nature reported that the experiments demonstrate vortices trapped in granular superconducting films can behave as two-level systems exhibiting the measured coherence and relaxation properties.

The work heralds future directions for quantum information processing, materials characterization and sensing.