Zero-point fluctuations and the quenching of the persistent current in normal metal rings

The ground state of a phase-coherent mesoscopic system is sensitive to its environment. We investigate the persistent current of a ring with a quantum dot which is capacitively coupled to ak external circuit with a dissipativ e impedance. At zero temperature, zero-point quantum fluctuations lead to a strong suppression of the persistent current with decreasing external impe dance. We emphasize the role of displacement currents in the dynamical fluc tuations of the persistent current and show that with decreasing external i mpedance the fluctuations exceed the average persistent current.