ABSTRACT
Superconductivity is a macroscopic quantum phenomena. This chapter examines Fritz London's ideas and describes some of the experiments establishing its validity. It was London's realization that electrodynamic behavior was a natural consequence of quantum condensation that led him to propose superconductivity as being fundamentally a macroscopic quantum phenomena. The chapter also discusses only those experiments immediately relevant to the concept of the Josephson junction as a quantum-phase detector for the purpose of experimentally examining the macroscopic quantum state. Because of the unusual voltage-dependent frequency the analysis of these effects is somewhat more complex than for the zero voltage current. However, at low frequencies it is usually adequate to describe the response simply as a complicated time modulation of the zero-voltage current. The existence of singularities within the macroscopic quantum state, however, leads to noise. Unless these singularities move with precision, a noise is developed associated with the random phase motion.
