A defining characteristic of superconductors is their tendency to expel magnetic fields, yet above a critical threshold, magnetic flux penetrates in discrete quanta carried by Abrikosov vortices1. The superconducting gap is completely suppressed at the vortex core, rendering them dissipative, semi-classical entities that 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 core2–4, owing to intrinsic5 or emergent granularity on the scale of the coherence length2,6. Although quantum vortex behaviour could emerge in this effective tunnel-junction regime7, and signatures have been observed in diverse systems8–10, coherent manipulation of vortex states has remained elusive. Here we present evidence that vortices trapped in granular superconducting films can behave as two-level systems, exhibiting microsecond-range quantum coherence and energy relaxation times that reach fractions of a millisecond. Using the tools of circuit quantum electrodynamics11, we perform coherent manipulation and quantum non-demolition readout of vortex states in granular aluminium microwave resonators, heralding future directions for quantum information processing, materials characterization and sensing. Vortices trapped in superconducting granular aluminium films can behave as a quantum two-level system that can be manipulated and read out, suggesting that they could be used for future quantum technologies.

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Nature

Researchers demonstrate that vortices trapped in granular aluminium (grAl) superconducting microwave resonators can behave as quantum two-level systems (vortex qubits, VQs). Using circuit quantum electrodynamics techniques, they achieve coherent manipulation and quantum non-demolition readout of these vortex states. The VQs exhibit microsecond-range quantum coherence (T2* = 440 ns, T2echo = 1.2 μs) and energy relaxation times up to ~300 μs, comparable to engineered superconducting qubits. The behavior is modeled as vortex tunnelling between pinning sites in a field-tunable double-well potential, described by an asymmetric quantum Rabi model. VQ states remain stable for weeks, opening potential avenues for quantum information processing, materials characterization, and nanoscale sensing.

Quantum coherent manipulation and readout of superconducting vortex states