  The quantum states of flux qubit is suggested to observe with the help of a
new device, the superconducting differential double contour interferometer
(DDCI). The flux qubit and the superconducting quantum interference device
(DC-SQUID) are connected in the DDCI through the phase of the wave function
rather than through magnetic flux. The critical current of DC-SQUID should
change to the maximum value at the change of the flux qubit state thanks to
this phase coupling. A large jump in the critical current and voltage enables
to observe continuously the change in time the state of the flux qubit. This
observation can have fundamental importance for the investigation of the
superposition of macroscopic quantum states.
