Device-independent dimension leakage null test on qubits at low
  operational cost
We construct a null test of the two-level space of a qubit, which is both
device independent and needs a small number of different experiments. We
demonstrate its feasibility on IBM Quantum, with most qubits failing the test
by more than 10 standard deviations. The robustness of the test against common
technical imperfections, like decoherence and phase shifts, and supposedly
negligible leakage, indicates that the origin of deviations is beyond known
effects.
Tomasz Rybotycki Tomasz Białecki Josep Batle Adam Bednorz