  We measure the strength and the sign of hyperfine interaction of a heavy-hole
with nuclear spins in single self-assembled quantum dots. Our experiments
utilize the locking of a quantum dot resonance to an incident laser frequency
to generate nuclear spin polarization. By monitoring the resulting Overhauser
shift of optical transitions that are split either by electron or exciton
Zeeman energy with respect to the locked transition using resonance
fluorescence, we find that the ratio of the heavy-hole and electron hyperfine
interactions is -0.09 +/- 0.02 in two QDs. Since hyperfine interactions
constitute the principal decoherence source for spin qubits, we expect our
results to be important for efforts aimed at using heavy-hole spins in
solid-state quantum information processing. The novel spectroscopic technique
we develop also brings new insights to the nuclear-spin mediated locking
mechanism in quantum dots.
