Study of ultrafast system-bath interactions and excitation energy transfer using photon echoes

Suguru Sangu, Kiyoshi Kobayashi, Akira Shojiguchi +2 more

Energy transfer and exciton population dynamics in a two-quantum dot system coupled with a phonon heat-bath system are examined using the density matrix formalism. In such a system, optical near-field interactions induce energy transfer between quantum dots, and exciton–phonon interactions guarantee the unidirectional excitation energy transfer. Our theoretical investigation shows that the population dynamics change drastically depending on the coupling strengths due to optical near-field interactions and exciton–phonon heat-bath interactions. The temperature effect promotes frequent energy back-transfer from the heat-bath to the quantum dot system. Applying our theoretical formulation, we numerically calculate the time evolution of populations, and estimate energy transfer time or state-filling time for a CuCl quantum dot system. The estimated time is suitable for the elements in our proposed optical nano-switch and nano-photonic devices.

Carrie S. Cornish

Thomas Steffen, Yoshitaka Tanimura

The quantum Fokker-Planck equation is derived for a system nonlinearly coupled to a harmonic oscillator bath. The system-bath interaction is assumed to be linear in the bath coordinates but quadratic in the system coordinate. The relaxation induced dynamics of a harmonic system are investigated by simulating the higher-order correlation functions of the Raman polarizability and the dipole moment, which represent the nonlinear optical responses of Raman or infrared spectroscopy. The 5th-order Raman response shows that, in addition to the frequency fluctuations induced by the bath, higher-order energy transfer between the system and bath plays a role. The nonlinearity of the system-bath interaction yields also an interesting feature in the 7th-order Raman echo or the 3rd-order infrared photon echo response: The calculations predict a finite signal for the case of a harmonic potential and a linear coordinate dependence of the polarizability or dipole while for linear system-bath coupling this response vanishes completely due to destructive interference of different Liouville space pathways.

Aleksander K. Rebane, Mikhail A. Drobizhev, Christophe Sigel +2 more

James L. Skinner, Hans C. Andersen, M. D. Fayer

We present the theory of the photon echo and stimulated photon echo from a four level system that results from a pair of weakly coupled two level systems. This model describes an impurity dimer in a molecular crystal. We include the effect of relaxation processes, focusing on energy transfer between delocalized states. We find that both the photon and stimulated echoes contain information about static level splittings and dynamic energy transfer processes. Moreover, these observables show a dramatic dependence on the excitation power. We discuss implications of our results for recent experiments on concentration dependent dephasing of impurities in molecular crystals. Our analysis casts considerable doubt on the intermolecular interaction interpretation of these experiments.

Maxim S. Pshenichnikov, Wim P. de Boeij, D. A. Wiersma