  We describe macroscopic quantum memory devices based on type-II toroidal
superconductors and estimate in one case and compute in another the rates at
which quantum information stored in these devices ``degrades'' because of
thermal fluctuations. In the case when the entire solid torus is
superconducting, the Boltzmann factor in the rate corresponds to a well-defined
critical fluctuation, and the rate is suppressed exponentially with the linear
size of the system. In the case when superconductivity is confined to the
surface of the torus, the rate is determined by diffusive motion of vortices
around the torus and does not depend exponentially on the linear size; we find,
however, that when the two dimensions of the torus are comparable the rate does
not contain the usual volume enhancement factor, i.e. it does not grow with the
total surface area of the sample. We describe a possible way to write to and
read from this quantum memory.
