Note 1 to entry: Superconducting qubits are classified into three different types depending on which quantum degrees of freedom they use. The first one uses states determined by the number of Cooper pairs (charge qubit), the second one uses the direction of a circulating persistent current in a superconducting loop (flux qubit), and the third one uses states determined by quantum oscillation of the phase difference between the electrodes of a Josephson junction (phase qubit).

Note 2 to entry: This entry was numbered 815-16-56 in IEC 60050-815:2015.