Persistent Josephson Phase-Slip Memory with Topological Protection

Abstract

Superconducting computing promises enhanced computational power in both classical and quantum approaches. Yet, efficient schemes for scalable and fast superconducting memories are still missing. On the one hand, the large inductance required in magnetic flux-controlled Josephson memories impedes device miniaturization. On the other hand, the use of ferromagnetic order to store information often degrades superconductivity, and limits the operation speed to the magnetization switching rate of a few GHz. Here, we overcome the above limitations through a fully superconducting memory cell based on the topological transition driven by hysteretic phase slips existing in aluminum nanowire Josephson junctions. Our direct and non-destructive read-out scheme, based on local tunneling spectroscopy, ensures reduced dissipation ($\lesssim 40$ fW) and estimated response time below $\lesssim 30$ ps thereby yielding a maximum energy per bit consumption as low as $\sim 10^{-24}$ J. In addition, the memory topological index can be directly read by robust phase measurements thus further lowering dissipation whilst maximizing the stability against magnetic noise. The memory, measured over several days, showed no evidence of information degradation up to $\sim 1.1$ K, i.e., $\sim 85\%$ of the critical temperature of aluminum. The ease of operation combined with remarkable performance elects the Josephson phase-slip memory as an attractive storage cell to be exploited in advanced superconducting logic architectures.