Ultrafast Optical Spin Echo for Electron Spins in Semiconductors

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.