RESUMO
Spin-based quantum computing and magnetic resonance techniques rely on the ability to measure the coherence time T(2) of a spin system. We report on the experimental implementation of all-optical spin echo to determine the T(2) time of a semiconductor electron-spin system. We use three ultrafast optical pulses to rotate spins an arbitrary angle and measure an echo signal as the time between pulses is lengthened. Unlike previous spin-echo techniques using microwaves, ultrafast optical pulses allow clean T(2) measurements of systems with dephasing times (T_{2};{*}) fast in comparison to the time scale for microwave control. This demonstration provides a step toward ultrafast optical dynamic decoupling of spin-based qubits.
RESUMO
In high-purity n-type GaAs under a strong magnetic field, we are able to isolate a lambda system composed of two Zeeman states of neutral-donor-bound electrons and the lowest Zeeman state of bound excitons. When the two-photon detuning of this system is zero, we observe a pronounced dip in the excited-state photoluminescence, indicating the creation of the coherent population-trapped state. Our data are consistent with a steady-state three-level density-matrix model. The observation of coherent population trapping in GaAs indicates that this and similar semiconductor systems could be used for various electromagnetically induced transparency type experiments.
