Catastrophe Observation in a Josephson-Junction System

We report on experiments performed to probe quantum coherence in a system consisting of an rf-SQUID in which the Josephson junction is replaced by a small loop containing two junctions in parallel. At temperatures of the order of 10 mK the system may develop three potential energy wells, which modify the usual two well energy profile and thereby verify the qubit manipulation strategy. The appearance of the third potential well can be interpreted as evidence of a butterfly Catastrophe, namely, a catastrophe expected for a system described by four control parameters and one state variable.