  We study the quantum phase transition in a chain of superconducting grains,
coupled by Josephson junctions, with emphasis on the effects of gate charges
induced on the grains. At zero temperature the system is mapped onto a
two-dimensional classical Coulomb gas, where the gate charge plays the role of
an imaginary electric field. Such a field is found relevant in the
renormalization-group transformation and to change the nature of the
superconductor-insulator transition present in the system, tending to suppress
quantum fluctuations and helping establish superconductivity. On the basis of
this observation, we propose the zero-temperature phase diagram on the plane of
the gate charge and the energy ratio.
