  Nuclear quadrupole interaction extends the limits imposed by hyperfine
interaction on the spin coherence of the electron and nuclei in a quantum dot.
The strain-induced nuclear quadrupole interaction suppresses the nuclear spin
flip and makes possible the zero-field dynamic nuclear polarization in
self-organized InP/InGaP quantum dots. The direction of the effective nuclear
magnetic field is fixed in space, thus quenching the magnetic depolarization of
the electron spin in the quantum dot. The quadrupole interaction suppresses the
zero-field electron spin decoherence also for the case of non-polarized nuclei.
These results provide a new vision of the role of the nuclear quadrupole
interaction in nanostructures: it elongates the spin memory of the
electron-nuclear system.
