Summary:

Who and why? In their pioneering work carried out at Berkeley in the mid-1980s, the laureates, John Clarke John Martinis and Michel Devoret, first demonstrated that a collective electrical variable, namely the phase difference across a Josephson junction, obeys the rules of quantum mechanics, an issue raised by A.J Leggett. They measured the so-called macroscopic quantum tunneling rate of the junction out of its zero-voltage state, and they demonstrated that the phase has well defined quantum states between which transitions can be induced by applying a resonant microwave signal. These results triggered a huge activity in the field of superconducting quantum circuits for first making quantum bits, and later quantum processors and quantum sensors. I will review some of the main results obtained in this area, and noticeably those of our Quantronics group at CEA Saclay.