Persistent current noise in normal and superconducting nanorings

We investigate fluctuations of persistent current (PC) in nanorings, both with and without dissipation and decoherence. We demonstrate that such PC fluctuations may persist down to zero temperature provided that there exists either interaction with an external environment or an external (periodic) potential produced, e.g., by quantum phase slips in superconducting nanorings. Provided that quantum coherence is maintained in the system, PC noise remains coherent and can be tuned by an external magnetic flux Φ_x piercing the ring. If quantum coherence gets suppressed by interactions with a dissipative bath, PC noise becomes incoherent and Φ_x-independent.