  This work addresses the dynamical quantum problem of a driven discrete energy
level coupled to a semi-infinite continuum whose density of states has a
square-root-type singularity, such as states of a free particle in one
dimension or quasiparticle states in a BCS superconductor. The system dynamics
is strongly affected by the quantum-mechanical repulsion between the discrete
level and the singularity, which gives rise to a bound state, suppresses the
decay into the continuum, and can produce Stueckelberg oscillations. This
quantum coherence effect may limit the performance of mesoscopic
superconducting devices, such as quantum electron turnstile.
