Consequences of nonuniqueness in spin-relaxation theory

Abstract

Various aspects of a general theorem, which asserts the lack of uniqueness of the density operator ρA for a composite system having subsystems B and C, are exploited in a systematic manner to obtain the maximum simplification in the equation of motion for the density operator ρB describing the subsystem. In particular, these ideas are applied to relaxation in spin systems in which only the second order terms in the interaction between subsystems B and C are retained in the master equation.