Experimental evidence of a {\phi} Josephson junction

TL;DR

This paper experimentally demonstrates Josephson junctions with a tunable doubly degenerate ground state phase, showing controllable switching between two states, aligning with theoretical predictions.

Contribution

First experimental realization of {} Josephson junctions with a controllable doubly degenerate ground state phase.

Findings

Existence of two critical currents corresponding to phase escape from -{} and +{} states.

Ability to set the phase {} using magnetic field or bias current.

Experimental results agree with theoretical models.

Abstract

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.