  Effects of both the dynamic nuclear polarization (DNP) created by circularly
polarized light and the fluctuations of average nuclear spin in a quantum dot
(QD) on the electron spin orientation are studied for singly negatively charged
InP QDs. From the dependence of the negative circular polarization of
photoluminescence on the applied longitudinal magnetic field, the hyperfine
field B_N of a few mT appearing due to DNP and the effective magnetic field B_f
of a few tens of mT arising from nuclear spin fluctuations (NSF) are estimated.
A lifetime of about 1 microsecond is estimated for NSF.
