  Considering a multi-pathway structure in a light-harvesting complex of
photosynthesis, we investigate the role of energy-level mismatches between
antenna molecules in transferring the absorbed energy to a reaction center. We
find a condition in which the antenna molecules faithfully play their roles:
Their effective absorption ratios are larger than those of the receiver
molecule directly coupled to the reaction center. In the absence of
energy-level mismatches and dephasing noise, there arises quantum destructive
interference between multiple paths that restricts the energy transfer. On the
other hand, the destructive interference diminishes as asymmetrically biasing
the energy-level mismatches and/or introducing quantum noise of dephasing for
the antenna molecules, so that the transfer efficiency is greatly enhanced to
near unity. Remarkably, the near-unity efficiency can be achieved at a wide
range of asymmetric energy-level mismatches. Temporal characteristics are also
optimized at the energy-level mismatches where the transfer efficiency is near
unity. We discuss these effects, in particular, for the Fenna-Matthews-Olson
complex.
