We study the electronic relaxation in a quantum dot within the polaron approach by focusing on thereversible anharmonic decay of longitudinal optical LO phonons forming the polaron into longitudinalacoustic LA phonons. The coherent coupling between the LO and LA phonons is treated within a mean-fieldapproach.We derive a temperature-dependent interlevel coupling parameter, related to the Grüneisen parameterand the thermal-expansion coefficient, which characterizes an effective decay channel for the electronic orexcitonic states. Within this theory, we obtain a characteristic anharmonic decay time of 1 ns, 2–3 orders ofmagnitude longer than previous predictions based on the Fermi’s Golden Rule. We suggest that coherentrelaxation due to carrier-carrier interaction is an efficient alternative to the (too slow) polaron decay.
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