Phonon influence on the measurement of spin states in double quantum dots using the quantum point contact

Abstract

We study the influence of phonon scattering on the noise characteristics of a quantum point contact coupled to a two-electron system in a double quantum dot, as proposed for a singlet-triplet measurement scheme in a double-dot system. We point out that at low temperatures phonon-induced relaxation to the ground state suppresses transitions to doubly occupied singlet states which are the source of detectable current fluctuations in this measurement scheme. Thus, for a relatively strong electron-phonon interaction present in the system, the two configurations display the same noise characteristics. In this way, coupling to phonons reduces the distinguishability between the singlet and triplet configurations. Under such conditions, the proposed measurement scheme is no longer valid even though the times of the measurement-induced decoherence of an initial singlet-triplet superposition and of the localization into the singlet or triplet subspace remain essentially unchanged.