  We experimentally demonstrate the operation of a Josephson magnetic random
access memory unit cell, built with a Ni_80Fe_20/Cu/Ni pseudo spin-valve
Josephson junction with Nb electrodes and an integrated readout SQUID in a
fully planarized Nb fabrication process. We show that the parallel and
anti-parallel 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 work represents a first step towards a scalable,
dense, and power-efficient cryogenic memory for superconducting
high-performance digital computing.
