Inducing electron spin coherence in GaAs quantum well waveguides: Spin coherence without spin precession

We demonstrate the generation and detection of electron spin coherence in a quantum well waveguide without either an external or internal dc magnetic field. In the absence of spin precession, the induced spin coherence is detected through effects of quantum interference in the spectral domain coherent nonlinear optical response. We interpret the experimental results qualitatively using a few-level model with optical selection rules as its basic ingredient.

Figure 1

(Color online) (a) Optical selection rule for dipole transitions between the conduction and the HH and LH valence bands in a GaAs QW. (b) and (c) Linear transmission spectra of the QW waveguide for TE and TM polarized fields.

Figure 2

(Color online) DT response obtained with $I_{\mathrm{pump}}=2\mathrm{m}\mathrm{W}$ and $I_{\mathrm{probe}}=0.25\mathrm{m}\mathrm{W}$. The pump and probe are TE and TM polarized, respectively. The solid line is a fit to Lorentzian.

Figure 3

DT response obtained with $I_{\mathrm{pump}}=2\mathrm{m}\mathrm{W}$ and $I_{\mathrm{probe}}=0.25\mathrm{m}\mathrm{W}$ and with an external magnetic field $(B=0.25\mathrm{T})$ applied along the growth direction. For (a) and (b), the pump and probe are TE and TM polarized, respectively. For (c), both the pump and probe are TE polarized.

Figure 4

Calculated DT response. (a) Pump is TE polarized and probe is TM polarized. (b) Both pump and probe are TE polarized. See text for parameters used.