Ultra-slow orbital and spin dynamics in an electrically tunable quantum dot molecule

TL;DR

This study demonstrates the ability to electrically tune and control long-lived spin states in quantum dot molecules, advancing their potential for quantum information applications.

Contribution

It introduces a method for sequential optical charging and tuning of two-electron spins in a quantum dot molecule with detailed analysis of spin relaxation dynamics.

Findings

Observed spin relaxation times exceeding 100 microseconds.

Achieved electrical tuning of orbital state couplings.

Qualitative agreement with phonon-mediated relaxation models.

Abstract

Tunnel-coupled optically active quantum dot molecules (QDMs), have the potential to operate as spin-photon-interfaces with coupled spins that interact with two different photon frequencies at the same time. A prerequisite is to deterministically prepare two (electron or hole) spins in the QDM and be able to electrically tune the orbital state couplings. Here, we demonstrate the sequential optical charging of a single QDM with two electron spins while simultaneously maintaining the ability to widely tune orbital couplings using static electric fields and optically drive the system for quantum light generation. We optically prepare one- and two-spin states, initialize via optical pumping and explore orbital and spin relaxation dynamics for one and two-spin states as a function of the energy detuning and hybridization of orbital states. For two-spin states, remarkably long S-T relaxation times are observed extending beyond $\sim 100\mu s$ with strong dependence on the relative energy of ground and excited two-spin states. Qualitative agreement is observed with $\mathbf{k \cdot p}$ calculations of phonon-mediated spin-relaxation. Our results provide new quantitative understanding of the dynamics of one and two-spin states and confirm their suitability of QDMs for creating multidimensional photonic cluster states by exploiting tunable spin-spin exchange couplings at zero magnetic fields combined with optical driving.