  Due to nontrivial orbital pairing symmetry, surfaces and interfaces of
high-Tc superconductors sup- port states which violate time-reversal (T -)
symmetry. Such naturally degenerate states, useful as work- ing states of a
qubit, are standard for atomic or molecular-size qubit prototypes (e.g. based
on nuclear spins), but exceptional for mesoscopic qubits. (In particular, they
hold promise of a better scalability.) In these lectures I review the physics
of T -breaking on surfaces and interfaces of high-Tc superconductors; then
describe existing proposals for high-Tc based qubits and the current state of
experiments; Finally, I discuss the decoherence sources in the system, open
questions, and future research directions.
