Qubit dissipation and contractions of Lie algebras

It is shown that the Kraus transformations and solutions of the evolution equations of the qubit dissipation are associated with contraction transformations of the Lie algebra su(2). The phase reversalchannel corresponds to the contraction of the uni tary algebra of qubit observables into the Euclideanalgebra e(2). The channel with amplitude attenuation is associated with the contraction of the algebrasu(2) into the Galilean (or the Heisenberg) algebrag(2). The contraction of the algebra of observablesinto the Abelian algebra corresponds to the depolarization channel, which means the loss of all quantum properties by the qubit. The interpretation of dissipation and decoherence processes in Lie algebraic terms is discussed.