Four-terminal SQUID: Magnetic Flux Switching in Bistable State and Noise

The effect of thermal fluctuations on the behaviuor of a 4-terminal SQUID is investigated. The studied system consists of the Josephson 4-terminal junction with two terminals short-circuited by a superconducting ring and other two form the transport circuit. The behaviour of a 4-terminal SQUID is controlled by external parameters, the applied magnetic flux and the transport current. They determine the voltage in the transport channel and the magnetic flux embraced in the ring. Within the numerical model the noise-rounded current-voltage characteristics and the time dependence of the magnetic flux have been calculated. In some region of the control parameters the 4-terminal SQUID is in the bistable state with two magnetic flux values. The switching of the flux in bistable state produced by the thermal noise or by the transport current is studied.