  The observed prevalence of oscillatory signals in the spectroscopy of
biological light-harvesting complexes at ambient temperatures has led to a
search for mechanisms supporting coherent transport through larger molecules in
noisy environments. We demonstrate a generic mechanism supporting long-lasting
electronic coherence up to 0.3 ps at a temperature of 277 K. The mechanism
relies on two properties of the spectral density: (i) a large dissipative
coupling to a continuum of higher-frequency vibrations required for efficient
transport and (ii) a small slope of the spectral density at zero frequency.
