Abstract
It is shown, using the quasi-spin operator, that the BCS superconducting ground-state wave function is the direct product of single Cooper-pair SU(2) coherent state wave functions, and in certain conditions, is SU(2) coherent state wave function of the Cooper-pair system. If two superconductors, both in BCS ground state, are coupled together, the coupled system is also in SU(2) coherent state. Under the contraction of group SU(2) to harmonic-oscillator group, the SU(2) coherent states contract to Glauber coherent states. The quantum fluctuations, distributions, and second correlations of Cooper pairs and Josephson superfluidity in the two cases are discussed.
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