Quantum field theory for macroscopic and mesoscopic systems

1997 Fiscal Year Final Research Report Summary

• Project/Area Number: 08044097
• Research Category: Grant-in-Aid for international Scientific Research
• Allocation Type: Single-year Grants
• Section: Joint Research
• Research Field: 素粒子・核・宇宙線
• Research Institution: Waseda University
• Principal Investigator: NAKAZATO Hiromichi Waseda Univ., Dept.Phys., Assoc.Prof., 理工学部, 助教授 (00180266)
• Co-Investigator(Kenkyū-buntansha): PAOLO Cea Bari univ., Dept.Phys., Lect., 物理, 講師 ; SAVERIO Pascazio Bari Univ., Dept.Phys., Lect., 物理, 講師 ; OHBA Ichiro Waseda, Univ., Dept.Phys., Prof., 理工学部, 教授 (10063695)
• Project Period (FY): 1996 – 1997
• Keywords: quantum mechanics / measurement problem / dissipative process / tunneling phenomena / neutron experiments

Research Abstract

The final goal of this project shall be to understand both macroscopic and mesoscopic systems quantum mechanically. We have investigated such topics that are closely connected to some fundamental issues of quantum mechanics with special attention to the physical and mathematical realization of the micro-macro transition. Here is a summary of the project.
1. We have proposed a solvable dynamical model for the quantum measurement proces and scrutinized the mechanism of emergence of the Wiener stochastic process in the weak-coupling, macroscopic limit. It is shown explicitly taht the free Hamiltonian of the detecting macroscopic system plays the role of the Wiener process, which implies that the stchasticity in this model is ascribed to a quantum mechanical origin. 2. Temporal evolution of quantum systems has been reinvestigated in general. Furthermore, the time development of a wave packet was directly calculated for a simple quantum system, and for the hydrogen system the exact expression of the transition amplitude between different energy levels was derived. In the latter case, the characteristic time scale in the short time region was evaluated and the oscillatory behavior was found to persist in the survival probability. 3. A neutron spin-flip experiment which clarifies the occurrence of the quantum Zeno effect has been proposed and examined experimentally and theoretically. 4. Nelson's version of quantum mechanics has beeb applied to a quantum mechanical particle tunmneling through a potential. The behavior of the particle is numerically simulated and the tunneling time has been estimated. We have also tried to take the possible dissipation effect on such a particle into account in this formalism to obtain more realistic tunneling time.
5. We summarized our research on the decoherence mechanism in the quantum mechanical measurement process in the book, "Decoherence and Quantum Measurements, " (Singapore, 1998).