  A simplified Bogoliubov transform reduces a fully-interacting many-fermion
spin-1/2 system-plus-environment to a more tractable many-to-one variant. The
transform additionally yields exact solutions for bosonic multi-particle
interactions sans the approximation introduced by using discrete time steps to
deal with quantum parallelism. The decohering effect of relatively general
finite environments is therewith modeled and compared to the decohering effect
of an infinite environmental "bath." The anti-symmetric singlet state formed by
two maximally-entangled two-state particles is shown to be inherently
decoherence-free. As a quantum bit ("qubit") it is thus potentially superior to
any single-particle state.
