[OPTICAL REVIEW Vol. 6, No. 3 (1999) 227-231]

## Quantum Phase Dynamics of Interaction between Photon Field and Magnetic System: Effects of Magnetic Quantum Tunnelling*

Hidemi NAGAO, Masayoshi NAKANO, Yasuteru SHIGETA and Kizashi YAMAGUCHI

Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043 Japan

(Received December 7, 1998; Accepted December 28, 1998)

We investigate the dynamics of probability distributions of an initially one-mode coherent field interacting with a four-state molecular system, which is a single magnet with a tunneling across an anisotropic barrier, using a numerically exact approach. The population for each state, the phase properties of <cos^{2}ψ^> and *Δ cos ^{2} ψ(≡<cos^{2}ψ^>−<cos ψ^>^{2}), and the entropy are calculated for a model system. The model predicts that the molecule and field become asymptotically disentangled at half of the revival time, and that optical Schrödinger-cat and magnetic Schrödinger-cat states are generated.*

Key words : quantum phase dynamics, magnetic quantum tunnelling, collapse and rivival, phase properties, Jaynes-Cummings model