Theoretical Study of Macroscopic Quantum Coherence in SQUIDS : Condensed Matter and Statistical Physics

概要

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An investigation as to the possibility of the quantum phase coherence in a circuit containing the Josephson junction is made. In this study the primary part of the system is assumed to be a two-state system, and so the quantum oscillation between two states is expected. For an analysis of the influence exerted by an environment two types of environment are considered. One type has the Lorentzian spectral density and the other has the Ohmic one. In both types a total loss of the phase coherence is found when a strength of a coupling between the primary part of the system and the environment, α≡ <φ^2>^^^- / &plank; R_N (φ^^- ≃ φ_0), satisfies a condition √<α> ≫Δω_0τ_c. Here &plank;Δω_0 is a level splitting and τ_c a relaxation time of the environments. Furthermore, we find that the total loss of the phase coherence leads to a quantum tunneling governed by a Poisson process with a tunneling rate Ω^2/Γ(Ω is the renormalized natural frequency and Γ the damping constant.) It must be emphasized that the Ohmic spectral density of the environments gives rise to an instability in the primary part when the coupling strength α(√<α> ≫ Δω_0τ_c) exceeds some critical value.
理論物理学刊行会の論文
1988-12-25