Superconducting circuits exhibit quantum properties on a macroscopic scale, and are natural candidates for solid state quantum computing. Their low-energy physics can be described in terms of the phase of the order parameter, a single collective degree of freedom associated with billions of coherently paired electrons. In practice, however, on top of the superfluid condensate there are single-particle excitations (quasiparticles) with a continuum energy spectrum; the quasiparticles are coupled to the phase degree of freedom. The presence of the quasiparticles in the system sets serious constraints on the performance of superconducting charge qubits.
In my talk, I will discuss the kinetics of superconducting quantum circuits in the presence of quasiparticles. First, I will consider the kinetics of quasiparticle trapping in a small superconducting island and talk about the statistics of quasiparticle capture and emission processes. Second, I will discuss the quasiparticle contribution to the energy and phase relaxation of a superconducting charge qubit.