Coherent control of electron spins in semiconductor quantum wells .

摘要

Electron spin states in semiconductors feature long coherence lifetimes, which have stimulated intense interest in the use of these spins for applications in spin based electronics and quantum information processing (QIP). A principal requirement for these spins to be viable candidates in QIP is the ability to coherently control the spins on timescales much faster than the decoherence times. The ability to optically control the spin state can meet this requirement. The spin states of electrons exhibit strong radiative coupling to negatively charged exciton (trion) states, and this radiative coupling makes coherent optical control of spin states possible.;This dissertation presents experimental demonstration of coherent control of an electron spin ensemble in a two-dimensional electron gas in a CdTe quantum well. We present two complimentary techniques to optically manipulate these electron spins using a Raman transition. The first demonstration is with a single off-resonant ultrafast optical pulse. This ultrafast pulse acts like an effective magnetic field in the propagation direction of the optical pulse. The second experiment utilizes phase-locked Raman resonant pulse pairs to coherently rotate the quantum state, where the relative phase of the pulse pair sets the axis of rotation. The Raman pulse pair acts like a microwave field driving the spin states.;This research demonstrates two significant contributions to the field of coherent optical interactions with semiconductors. First, we have advanced the potential use of electron spin ensembles in semiconductors for optics based quantum information processing hardware through our demonstration of coherent spin flips and complete coherent control. Second, we have experimentally realized full coherent control through the use of phase-locked Raman pulse pairs that overcomes inherent limitations of the single-pulse optical rotation technique, which is the current standard technique used in coherent control.;This dissertation includes previously published and unpublished co-authored material.