  A key to achieving ultra-long electron spin memory in quantum dots (QDs) at
0~$T$ is the polarization of the nuclei, such that the electron spin is
stabilized along the nuclear magnetic field. We demonstrate that spin-polarized
electrons in n-doped QDs align the nuclear field via the hyperfine interaction.
A feedback onto the electrons occurs, leading to stabilization of electron
polarization. We suggest that the coupled electron-nuclear system forms a rigid
nuclear spin polaron state as predicted by I.A.~Merkulov, for which spin memory
is retained over millisecond lifetimes.
