Spin state tomography of optically injected electrons in a semiconductor

Spin-state tomography Many proposed quantum information processing schemes rely on electron spin as the basic (quantum) unit of information. For this approach, careful preparation and read-out of the electron spin state, which can be done optically, are essential operations. Since coherence of the spin state is a manifestation of its quantum nature, both the preparation and read-out should be spin coherent. The traditional technique to measure spin coherence, based on the magneto-optical Kerr effect, measures spin population by the rotation of the reflected light polarization, but it requires an extra step of spin manipulation to project a measurement onto a fixed basis which is defined by the direction of the probe light beam. Kosaka et al. have developed a more straightforward and general scheme still based on Kerr rotation but modified so that a spin projection measurement can be done on an arbitrary set of basis states. This allows them to perform a direct tomographic measurement of electron spin precession in a semiconductor structure. The authors propose that the developed scheme offers a universal tool for performing preparation and read-out of a spin quantum state in a solid.