Yung Lit Hung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves p. [122]-124). / Text in English; abstracts in English and Chinese. / Yung Lit Hung. / Abstract --- p.i / Acknowledgements --- p.ii / List of Figures --- p.v / List of Tables --- p.vii / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Dissipative two-state system --- p.3 / Chapter 2.1 --- Introduction --- p.3 / Chapter 2.2 --- A two-state system viewed as a spin --- p.4 / Chapter 2.3 --- Rotation of spin operators --- p.5 / Chapter 2.4 --- Dissipative two state system --- p.7 / Chapter 2.5 --- The model in consideration --- p.8 / Chapter 2.5.1 --- gk= 0 --- p.8 / Chapter 2.5.2 --- Δ0 = 0 --- p.8 / Chapter 2.5.3 --- dispersionless phonon case with constant coupling --- p.10 / Chapter 3 --- Linearized spin-wave approximation and mean-field method --- p.13 / Chapter 3.1 --- Holstein Primakoff Transformation --- p.13 / Chapter 3.2 --- Application of linearized spin-wave approxmation to our system --- p.14 / Chapter 3.3 --- Mean-field method --- p.24 / Chapter 4 --- Variational method for optical phonons with constant coupling --- p.35 / Chapter 4.1 --- Introduction --- p.35 / Chapter 4.2 --- Variational Principle --- p.35 / Chapter 4.3 --- Variational Principle applied to optical phonon case --- p.36 / Chapter 4.4 --- Results --- p.41 / Chapter 4.5 --- Conclusion --- p.54 / Chapter 5 --- Variational method for acoustic phonons with ohmic dissipation --- p.56 / Chapter 5.1 --- Introduction --- p.56 / Chapter 5.2 --- Variational Principle applied to acoustic phonon case --- p.57 / Chapter 5.3 --- μk= 0 case --- p.59 / Chapter 5.4 --- Search for any μk≠ 0 solution --- p.60 / Chapter 5.5 --- Results --- p.62 / Chapter 5.6 --- Conclusion --- p.70 / Chapter 6 --- Coupled Cluster Method --- p.72 / Chapter 6.1 --- Introduction --- p.72 / Chapter 6.2 --- Coupled Cluster Method --- p.73 / Chapter 6.2.1 --- Zeroth Level --- p.74 / Chapter 6.2.2 --- First Level --- p.74 / Chapter 6.2.3 --- The bra-state --- p.75 / Chapter 6.3 --- Coupled cluster method applied to our system --- p.76 / Chapter 6.4 --- Coupled cluster method applied to optical phonon case --- p.78 / Chapter 6.4.1 --- First Level --- p.79 / Chapter 6.4.2 --- Second Level --- p.81 / Chapter 6.5 --- Coupled cluster method applied to acoustic phonon case --- p.90 / Chapter 6.5.1 --- First Level --- p.90 / Chapter 6.5.2 --- Second Level --- p.92 / Chapter 6.6 --- Conclusion --- p.98 / Chapter 7 --- Spin system interacting with a photon field --- p.99 / Chapter 7.1 --- Rotation wave approximation --- p.100 / Chapter 7.2 --- Spin system interacting with an optical field --- p.101 / Chapter 7.3 --- Heisenberg equation of motion --- p.102 / Chapter 7.4 --- Brogoliubov transformation approach --- p.104 / Chapter 7.5 --- Conclusion --- p.106 / Chapter A --- Supplementary calculations --- p.107 / Chapter A.1 --- First level calculation for optical photon --- p.107 / Chapter A.2 --- Second level calculation for optical photon --- p.111 / Chapter A.3 --- First level calculation for acoustic photon --- p.114 / Chapter A.4 --- Second level calculation for acoustic photon --- p.118 / Bibliography --- p.121