  We report transport and magnetic relaxation measurements in the mixed state
of strongly underdoped Y_{1-x}Pr_{x}Ba_{2}Cu_{3}O_{7} crystals. A transition
from thermally activated flux creep to temperature independent quantum flux
creep is observed in both transport and magnetic relaxation at temperatures T *
5 K. Flux transformer measurements indicate that the crossover to quantum creep
is preceded by a coupling transition. Based on these observations we argue that
below the coupling transition the current is confined within a very narrow
layer beneath the current contacts.
