  Resonant laser scattering along with photon correlation measurements have
established the atom-like character of quantum dots. Here, we present
measurements which challenge this identification for a wide range of
experimental parameters: the absorption lineshapes that we measure at magnetic
fields exceeding 1 Tesla indicate that the nuclear spins polarize by an amount
that ensures locking of the quantum dot resonances to the incident laser
frequency. In contrast to earlier experiments, this nuclear spin polarization
is bi-directional, allowing the electron+nuclear spin system to track the
changes in laser frequency dynamically on both sides of the quantum dot
resonance. Our measurements reveal that the confluence of the laser excitation
and nuclear spin polarization suppresses the fluctuations in the resonant
absorption signal. A master equation analysis shows narrowing of the nuclear
Overhauser field variance, pointing to potential applications in quantum
information processing.
