Singlet-Triplet Dephasing in Asymmetric Quantum Dot Molecules

Abstract

Dephasing of singlet-triplet superpositions in twoelectron quantum dot molecules is important for a possible implementation of quantum information processing in semiconductor systems [1]. In a recent work [2], we showed that elastic phonon scattering via virtual transitions to doubly occupied states, which is only possible in a singlet configuration, induces distinguishability of spin configurations and, therefore, leads to pure dephasing of spin superpositions. In Ref. [2], we studied a system of two identical dots. However, as quantum dots are artificial systems, one has to take into account unavoidable inhomogeneity of dot parameters when modeling the properties of the system. Therefore, in the present contribution, we generalize our previous result and study the phonon-induced dephasing process in an asymmetric QDM. We show that in the asymmetric QDM, an additional dephasing channel appears, as compared to the symmetric one. Nonetheless, the dephasing rate is very weakly affected by the asymmetry unless the latter becomes very strong. The system under consideration is composed of two electrons in an asymmetric quantum dot molecule (QDM) built from two different gate-defined quantum dots [3, 4]. The electrons are coupled to phonons by the usual charge-phonon interactions (deformation potential and piezoelectric couplings). We do not take any spin-environment interactions into account (neither direct, with nuclear spins, nor indirect, via spin-orbit coupling). The Hamiltonian of the system is then