  Using the numerical path integral method we investigate the decoherence and
relaxation of qubits coupled to an Ohmic bath directly and via an intermediate
harmonic oscillator (IHO). Here, we suppose the oscillation frequencies of the
bath modes are higher than the IHO's. When we choose suitable parameters the
qubits in the two models may have almost same decoherence and relaxation times.
However, the decoherence and relaxation times of the qubit in the
qubit-IHO-bath model can be modulated through changing the coupling
coefficients of the qubit-IHO and IHO-bath and the oscillation frequency of the
IHO.
