Experimental Demonstration of a Josephson Magnetic Memory Cell With a Programmable $\pi$-Junction

We experimentally demonstrate the operation of a Josephson magnetic random access memory unit cell, built with a Ni $_{80}$ Fe $_{20}$ /Cu/Ni pseudo-spin-valve Josephson junction with Nb electrodes and an integrated readout superconducting quantum interference device in a fully planarized Nb fabrication process. We show that the parallel and antiparallel memory states of the spin valve can be mapped onto a junction equilibrium phase of either zero or $\pi$ by appropriate choice of the ferromagnet thicknesses, and that the magnetic Josephson junction can be written to either a zero-junction or $\pi$ -junction state by application of write fields of approximately 5 mT. This letter represents a first step toward a scalable, dense, and power-efficient cryogenic memory for superconducting high-performance digital computing.