  Extending the qubit coherence times is a crucial task in building quantum
information processing devices. In the three-dimensional cavity implementations
of circuit QED, the coherence of superconducting qubits was improved
dramatically due to cutting the losses associated with the photon emission.
Next frontier in improving the coherence includes the mitigation of the adverse
effects of superconducting quasiparticles. In these lectures, we review the
basics of the quasiparticles dynamics, their interaction with the qubit degree
of freedom, their contribution to the qubit relaxation rates, and approaches to
control their effect.
