Experimental Evidence of a φ Josephson Junction

We demonstrate experimentally the existence of Josephson junctions having a doubly degenerate ground state with an average Josephson phase psi = +/-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 c 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.