I think this question makes two assumptions:
the system does not evolve intentionally (i.e., no gates or measurements are performed on it), and
there is no noise that would cause the system to evolve in an unintended way.
Of course, if you change the state of the system by applying some gates, or if the system is noisy, this will not be the case.
I think the subject matter of supercondcuting qubits is rather broad and diverse, making it challenging to accurately capture it in a 'brief explanation'.
With that said, this recent review (Krantz et al., Applied Physics Reviews 6, 021318 (2019)) - "A Quantum Engineer's Guide to Superconducting Qubits" (arXiv:1904.06560) from the MIT group may be a good ...