Memory cell based on a $varphi$ Josephson junction

The $varphi$ Josephson junction has a doubly degenerate ground state with the Josephson phases $pmvarphi$. We demonstrate the use of such a $varphi$ Josephson junction as a memory cell (classical bit), where writing is done by applying a magnetic field and reading by applying a bias current. In the store state, the junction does not require any bias or magnetic field, but just needs to stay cooled for permanent storage of the logical bit. Straightforward integration with Rapid Single Flux Quantum logic is possible.

Experimental evidence of a {phi} Josephson junction

We demonstrate experimentally the existence of Josephson junctions having a doubly degenerate ground state with an average Josephson phase psi=pm{phi}. The value of {phi} can be chosen by design in the interval 0<{phi}<pi. The junctions used in our experiments are fabricated as 0-{pi} Josephson junctions of moderate normalized length with asymmetric 0 and {pi} regions. We show that (a) these {phi} Josephson junctions have two critical currents, corresponding to the escape of the phase {psi} from -{phi} and +{phi} states; (b) the phase {psi} can be set to a particular state by tuning an external magnetic field or (c) by using a proper bias current sweep sequence. The experimental observations are in agreement with previous theoretical predictions.