Dynamics of an asymmetric nondestructive read out memory cell

In single flux quantum interferometer memory cells the information can be stored without bias current, if the interferometer inductance L is chosen sufficiently large (λ = 2₀/Φ₀ = 2π) to allow for three stable states (-1-, 0-, 1-mode) at zero control and gate current. In this case the binary informations are represented by the -1- and 0-mode of the interferometer. The nondestructive read out operation of a binary "1" is performed without a transition into another mode or into the voltage state. The binary "1" corresponds to no sense signal. Nondestructive read out of the binary "0" is achieved in switching to the voltage state and in returning to the 0-mode after the end of the drive currents. In this paper the dynamics of switching back into the zero voltage state are investigated by simulations of trajectories in the order parameter phase plane. It is shown that for realistic fabrication tolerances the interferometer settles in the wanted 0-mode and not in the -1- or 1-mode even under severe gate or control current disturbs, if the maximum Josephson currents of the two Josephson junctions are unequal (2:1) and if the McCumber damping factor is sufficiently large (β ≈ 100).