Suppressing electron-phonon interactions in semiconductor quantum dot systems by engineering the electronic wavefunctions

It is well-known that decoherence deteriorates the efficiency of cavity QED systems containing quantum dots (QDs), and that a major contribution stems from the coupling between the electrical carriers in the QD and acoustic phonons [1]. Employing a recently published model [2], we demonstrate how a proper matching between the electronic wavefuntion and the phonon-induced energy shift of valence and conduction band may be exploited to change the decoherence and decay properties of the QD by suppressing the phonon-induced processes.

This effect may be addressed in a photoluminescence experiment, where a CW laser excites a two-level QD which interacts with a non-Markovian reservoir of acoustical phonons, see Fig. 1a. We assume a simple harmonic confinement of the electronic carriers, resulting in Gaussian wavefunctions, (r) / exp[−r2/(2W2 )], withWe (Wg) being the width of the electron (hole) wavefunction.

In Fig. 1b we plot the stationary QD population vs. the laser frequency. We observe that for non-equal electron and hole wavefunction, the phonon-induced effect on the population surprisingly is fully suppressed at specific detunings. In a coupled QD–cavity system [2, 3], see Fig. 2a, this effect causes the QD lifetime to be unaffected by phonon processes at specific QD-cavity detunings.

Furthermore, as shown in Fig. 2b, a proper choice of the QD wavefunction minimizes the phonon-induced pure dephasing rate, both in terms of the short-time magnitude and the long-time constant value. Furthermore we show, that even for realistic QDs, where We and Wg are determined by the QD shape and material composition, a significant suppression of phonon-induced processes is possible.

Thus, more efficient quantum systems may be obtained if the QD wavefunctions are properly matched with the phononic properties of the surroundings.