  One long-standing difficult problem in quantum dissipative dynamics is to
solve the spin-boson model in a non-Markovian regime where a tractable
systematic master equation does not exist. The spin-boson model is particularly
important due to its crucial applications in quantum noise control and
manipulation as well as its central role in developing quantum theories of open
systems. Here we solve this important model by developing a non-Markovian
quantum Langevin approach. By projecting the quantum Langevin equation onto the
coherent states of the bath, we can derivie a set of non-Markovian quantum
Bloch equations containing no explicit noise variables. This special feature
offers a tremendous advantage over the existing stochastic Schr\"odinger
equations in numerical simulations. The physical significance and generality of
our approach are briefly discussed.
