A protected vortex exciton qubit

We propose a protected qubit which is `dual' to a suggestion of a superconducting current mirror qubit [A. Kitaev, arXiv:0609441 (2006)]. Our construction can be regarded as the magnetic analogue of Kitaev's proposal: it inherits the intrinsic fault-tolerance of the current mirror qubit, but may perform better than it in the laboratory, since magnetic noise is generally less of a problem than electric noise. We adapt the scheme for universal fault-tolerant quantum computation proposed by Kitaev to our construction.