Seog Woo Nam

Excitons and polaritons in quasi-molecular eigenbasis of the excitation hopping system interacting with a photon field

We report studies of excitons and polaritons in the quasi-molecular eigenbasis of a nano-aggregate, in the model of excitation transfer with, or without, photon-exciton coupling. We evaluate the effective interaction between quasi-molecular subsystems in quasi-molecular eigenbasis representation, with its eigenenergies and eigenstates. From the analysis of the effective interaction Hamiltonian in the quasi-molecular eigenbasis representation, we see that the effective interaction between subsystems in quasi-molecular eigenbasis representation gives fertile points of view to understand the given system, and the dynamics of excitons and polaritons becomes simpler to understand, or to deal with, depending on the division of the whole system into specified subsystems.

Excitonic quantum interference in a quantum dot chain with rings

We demonstrate excitonic quantum interference in a closely spaced quantum dot chain with nanorings. In the resonant dipole-dipole interaction model with direct diagonalization method, we have found a peculiar feature that the excitation of specified quantum dots in the chain is completely inhibited, depending on the orientational configuration of the transition dipole moments and specified initial preparation of the excitation. In practice, these excited states facilitating quantum interference can provide a conceptual basis for quantum interference devices of excitonic hopping.

Phase correlation of ensemble of quantum emitters and timed Dicke state

We study the phase-correlated state which is introduced by the instantaneous excitation of an ensemble of identical two-level quantum emitters and its relation with the Dicke states. Under weak coupling regime, the time evolution of the phase-correlated system of the emitters is also derived to see the characteristics of the collective spontaneous emission of the emitters. It is found that the effective coupling of the ensemble in the phase-correlated state with the emitted field is directly determined by the collective phase of the system. Hence, the collective phase is considered for several specified distributions in brief.

Cooperative spontaneous emission of nano-emitters with inter-emitter coupling in a leaky microcavity

We study the spontaneous emission from a few two-level nano-emitters placed in a leaky microcavity with Lorentzian spectral density near a critically damped regime. Collective features of the spontaneous emission are investigated by numerical analysis of the excitation dynamics when initially one nano-emitter is totally excited but we do not know which one. The results show that there are three decay rates in the excitation dynamics, two for simple exponential decays and one for damped oscillatory decay. The excitation dynamics is found to critically depend on the regime of the system. It is shown that the spontaneous emission is enhanced or suppressed depending on whether the system is in the underdamped or overdamped regime, respectively. On the other hand, the cooperative spontaneous emission is suppressed in the underdamped while it is enhanced in the overdamped regime. Furthermore, the effect of the direct inter-emitter coupling on the breaking of the cooperativeness of the spontaneous emission is shown as well.