Electron spin polarization and detection in InAs quantum dots through p-shell trions

We perform two-color time-resolved spectroscopy of spin dynamics in an ensemble of InAs quantum dots, demonstrating that an electron spin polarization in negatively charged quantum dots can be efficiently generated or detected with pulses tuned to p-shell trions. Due to the polarization selection rules and exchange splitting of the electron spin triplet and singlet trion states, the absorption probability of circularly polarized light depends strongly on the spin state of the resident electron in the quantum dot. This leads to spin selective excitation of electrons to the p-shell trion states, generating a spin polarization in the ensemble of unexcited resident electrons. Manipulating spin states through the excited trion states allows for separation of the excitation wavelength from the emission wavelength for control of the spatial extent of the excited-state wave function. ©2010 The American Physical Society