Cavity enhanced Faraday rotation of semiconductor quantum dots

Dielectric vertical cavities are used to study the spin dynamics of molecularly self-assembled colloidal CdSe quantum dots (QDs). A quality factor dependent enhancement of Faraday rotation (∼25×) is observed and attributed to optically excited spins interacting with multiple passes of the cavity photons. This enables dynamical measurements at extremely low powers on relatively small numbers of quantum confined spins. In CdSe QDs, measurements reveal that spectroscopic contributions from exciton and electron spin precession depend on the power of excitation. We demonstrate that this scheme is amenable to chemically synthesized systems as a means to increase detection sensitivity.