Energy transfer in finite-size exciton-phonon systems: Confinement-enhanced quantum decoherence

Abstract

Based on the operatorial formulation of the perturbation theory, the exciton-phonon problem is revisited for investigating exciton-mediated energy flow in a finite-size lattice. Within this method, the exciton-phonon entanglement is taken into account through a dual dressing mechanism so that exciton and phonons are treated on an equal footing. In a marked contrast with what happens in an infinite lattice, it is shown that the dynamics of the exciton density is governed by several time scales. The density evolves coherently in the short-time limit whereas a relaxation mechanism occurs over intermediated time scales. Consequently, in the long-time limit, the density converges toward a nearly uniform distributed equilibrium distribution. Such a behavior results from quantum decoherence that originates in the fact that the phonons evolve differently depending on the path followed by the exciton to tunnel along the lattice. Although the relaxation rate increases with the temperature and with the coupling, it decreases with the lattice size, suggesting that the decoherence is inherent to the confinement.

The excitonic qubit coupled with a phonon bath on a star graph: anomalous decoherence and coherence revivals

“…Its knowledge provides key information on the way the phonon bath modifies the excitonic coherences either in the local basis or in the eigenbasis (by performing a change of basis). As detailed previously [49][50][51][52], it can be evaluated quite straightforwardly using PT. To proceed, we first introduce U and diagonalize H in Eq.…”

“…To overcome this problem, a powerful method based on the operatorial formulation of perturbation theory (PT) has been introduced and used in the case of one-dimensional lattices [49][50][51][52]. Provided that the exciton-phonon coupling remains sufficiently weak, this method treats the exciton and the phonons on an equal footing.…”

A qubit coupled with confined phonons: The interplay between true and fake decoherence

“…(3) is the simplest quantum nondemolition interaction that allows the description of fake decoherence which results from exciton-induced phonon frequency shift. When the coupling depends linearly on the phonon coordinates, such a shift arises only when the exciton is allowed to move [29][30][31][32] . To recover this feature with a localized exciton, it is thus necessary to introduce an additional interaction that depends quadratically on the phonon coordinates.…”

“…Recently [29][30][31][32] , the exciton-phonon problem was revisited to account for finite-size effects. In a confined lattice, the phonons no longer form a reservoir 33 .…”

“…Although many strategies exist to overcome such problems [36][37][38][39][40] , we have developed a quite powerful unitary transformation-based method [29][30][31][32] . Within this method, the exciton and the phonons are treated on an equal footing to estimate the system eigenstates and to go beyond the Born approximation.…”