Energy transfer, entanglement and decoherence in a molecular dimer interacting with a phonon bath

We study the dynamics of energy transfer and dephasing in a molecular dimer with degenerate energies interacting with an anti-correlated, collective vibrational bath. By diagonalizing the total Hamiltonian, we obtain an analytic expression for the dephasing rate as a function of temperature, resonance coupling, system-bath coupling and the spectrum of the bath. Eigenstates of the total Hamiltonian are identified as a natural basis set for studies of decoherence dynamics, and the study is motivated by observations of persistent coherence in two-dimensional (2D) photon echo experiments on photosynthetic light-harvesting proteins (Collini et al 2010 Nature 463 644-7). We find that, under the influence of a collective phonon bath, coherence survives longer in systems with weak electronic couplings, in agreement with observations of long-lasting coherence in weakly coupled multichromophoric systems.