A realization of Yangian and its applications to the bi-spin system

Yangian $Y(sl(2))$ is realized in the bi-spin system coupled with a time-dependent external magnetic field. It is shown that $Y(sl(2))$ generators can describe the transitions between the ``spin triplet'' and the ``spin singlet'' that evolve with time. Furthermore, new transition operators between the states with Berry phase factor and those between the states of Nuclear Magnetic Resonance (NMR) are presented.