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Energy transfer in quantum molecular chain -- two models of inhomogeneity

We study a linear chain of oscillators with inhomogeneity in their interactions with phonon bath. In a previous work on the Markovian master equation of the system, we investigated a model in which the difference in the site-phonon coupling between adjacent oscillators is the same throughout the chain. Here we look into another model in which the oscillators are coupled to the phonon bath with alternating strength at successive sites. Whereas in the first model all exciton modes are connected, in the second model they are coupled in pairs that are not connected to each other. Owing to this special structure in the coupling, the excitation numbers of different modes can be solved exactly in the steady state. In the first model, the minima of the excitation profile in the site basis occur at the edges of the chain, whereas in the second model the maxima occur at the edges. The energy transfer efficiency in the first model is affected by the source power whereas in the second model the efficiency is independent of it. A distinct feature in the second model is that a sink placed at the middle of the chain is able to distinguish between chains with even and odd number of sites. The energy transfer efficiency in a chain with even number of sites is higher than a chain with odd number of sites. Therefore, it reveals the discrete nature of the chain. In the limit of very long chain when the discreteness of the chain is less evident, the efficiencies approach each other.