Theory of Macroscopic Quantum Phenomena

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* Macroscopic Quantum Pheniomena (of the second kind), to be abbreviated as MQP, are those phenomena which involve macroscopic number of degrees of freedom in a linear superposition of macroscopically distinct states and yet are characterised by an action of the order of Planck's constant. Fundamental ideas (basic concepts, classifications, phenomenological theories, detection methods and associated quantum measurement problem, and so on) were delineated in a form easily accessible for current and future workers.* Of crucial importance in describing MQP is the choice if collective degrees of freedom. Two systems were discussed in detail as typical examples :(a) Quantum nucleation in quantum fluids : Radius of the emerging nucleus as the collective degrees of freedom.・ Tentative estimate of the nucleation rate.・Limitation in the so-far standard phenomenology pointed out and remedied.(b) Quantum resonant oscillation between two chirality states of a ferromagnetic domain wall : Chirality as the collective degree of freedom. ・ Possibility of a magnetic version of the Cat ・ Semi-quantitative estimate of the resonance frequency.* Those quantum decay phenomena such as macroscopic quantum nucleation from an important class of MQP.Theoretical foundation of the bounce method, which is a method of evaluating the nucleation rate, had ben left obscure in spite of its popularity. The basic conditions needed to justify the method were clarified ; whether these conditions are actually met or not is a problem yet to be settled.* Some fundamental difficulties in the continuous-time formation of spin-coherent-state path integral, which had been (and still are) overwhelmingly used in dealing with quantum-mechanical behavior of a magnetic domain wall, were pointed out and a way out was suggested. Applications to concrete examples are left to future investigations.