The silicon vacancy in silicon carbide is a strong emergent candidate for applications in quantum information processing and sensing. We perform room temperature optically-detected magnetic resonance and spin echo measurements on an ensemble of vacan
cies and find the properties depend strongly on magnetic field. The spin echo decay time varies from less than 10 $mu$s at low fields to 80 $mu$s at 68 mT, and a strong field-dependent spin echo modulation is also observed. The modulation is attributed to the interaction with nuclear spins and is well-described by a theoretical model.
We show that detuned optical pulse trains with a modest spectral width can polarize nuclear spins in InAs quantum dots. The pulse bandwidth is large enough to excite a coherent superposition of both electron spin eigenstates in these negatively charg
ed dots but narrow enough to give partial spectral selectivity between the eigenstates. The coherent precession of electron spin states and periodic excitation focuses the nuclear spin distribution, producing a discrete set of precession modes. The spectral selectivity generates a net nuclear polarization, through a mechanism that relies on optical spin rotations rather than electron spin relaxation.
We find that detuning an optical pulse train from electronic transitions in quantum dots controls the direction of nuclear spin flips. The optical pulse train generates electron spins that precess about an applied magnetic field, with a spin componen
t parallel to the field only for detuned pulses. This component leads to asymmetry in the nuclear spin flips, providing a way to produce a stable and precise value of the nuclear spin polarization. This effect is observed using two-color, time-resolved Faraday rotation and ellipticity.
