Spin coherence in semiconductor quantum dots

Femtosecond-resolved Faraday rotation is used to probe spin dynamics in chemically synthesized CdSe quantum dots 22–80 Å in diameter from T=6–282 K. The precession of optically injected spins in a transverse magnetic field indicates that the measured relaxation lifetime of the spin polarization is dominated by inhomogeneous dephasing, ranging from ∼3 ns at zero field to <100 ps at 4 T. Fourier analysis reveals a multiperiodic Larmor precession, with several distinct g factors ranging from ∼1.1 to 1.7.