Hole spin precession in a (In,Ga)As quantum dot ensemble: From resonant spin amplification to spin mode locking.

Coherent collective phenomena of hole spins confined in an ensemble of (In,Ga)As quantum dots are studied by monitoring their Larmor precession about a magnetic field. Variation of the field strength drives the hole spins from a regime of resonant spin amplification, in which their precession frequency is a unique multiple of the laser repetition rate, to spin mode locking, in which several precession modes are commensurable with the laser repetition rate. In this regime the spin coherence time of individual holes is determined to be 0.7 µs. In contrast, electron spins in the quantum dots are always trapped in the mode-locking regime due to the strong hyperfine interaction with nuclear spins. [ABSTRACT FROM AUTHOR]