Inhomogeneous dynamic nuclear polarization and suppression of electron polarization decay in a quantum dot

• Nuclear spin polarization is highly inhomogeneous after a dynamic nuclear polarization (DNP) process.
• The DNP process is well described by an analytical model based on the independent spin approximation.
• The highly inhomogeneous nuclear polarization significantly prolongs the electron spin coherence time.

We investigate the dynamic nuclear polarization in a quantum dot. Due to the suppression of direct dipolar and indirect electron-mediated nuclear spin interactions by frequently injected electron spins, our analytical results under independent spin approximation agree well with quantum numerical simulations for a small number of nuclear spins. We find that the acquired nuclear polarization is highly inhomogeneous, proportional to the square of the local electron-nuclear hyperfine interaction constant. Starting from the inhomogeneously polarized nuclear spins, we further show that the electron polarization decay time can be extended 100 times even at a relatively low nuclear polarization.