Coherent Spin Dynamics

Well defined spin states of carriers or excitons can be readily prepared, manipulated and read-out in semiconductors. Their coherent dynamics is quite different from the intra- and interband dynamics of carriers or excitons. Reasons are, e.g., the effect of motional narrowing and that a coupling to some angular momentum is required for relaxation. In quantum structures the spin can be well shielded from interaction which yields spin coherence times long enough for many qubit operations. We start with the preparation of a coherent superposition of spin states and its optical detection via spin quantum beats in order to determine the size of the spin splitting, the particle Landé g-factor and the spin relaxation dynamics. We then discuss the main processes leading to spin decoherence and relaxation of electrons, holes and excitons in different scenarios. Particular attention is give to spin coherence in quantum dots due to the possible applications in spintronics. We describe the experimental tools to monitor the spin dynamics and introduce efficient realization concepts to initiate (e.g., Schottky diodes) and manipulate (e.g., \(\varLambda \) systems involving trions in charged QDs) the spins. We shortly discuss recent developments like Si-based spin systems or valleytronics. This chapter includes a description of the experimental technique of spin quantum beat spectroscopy as well as time-resolved Faraday or Kerr rotation.