Optical detection and manipulation of single electron spin coherence in a semiconductor quantum dot.

摘要

We demonstrate the ability to sequentially initialize, manipulate, and readout the state of a single electron spin in a quantum dot using all-optical techniques. The GaAs quantum dots are embedded in a diode structure to allow controllable charging of the quantum dots and positioned within a vertical optical cavity to enhance the small single spin signal. First, we demonstrate the detection of a single electron spin in a quantum dot using a time-averaged magnetooptical Kerr rotation measurement at T = 10 K. This technique provides a means to directly probe the spin off-resonance, thus minimally disturbing the system. Next, we have extended this technique into the time domain using pulsed pump and probe lasers, allowing for direct observation of the coherent evolution of a single electron spin-state. The coherent single spin precession in an applied magnetic field reveals the electron g-factor and a transverse spin lifetime of ∼ 10 ns. Additionally, the observed spin dynamics provide a sensitive probe of the local nuclear spin environment. Finally, by applying off-resonant optical pulses, we coherently rotate a single electron spin in a quantum dot up to pi radians on picosecond timescales. Measurements of the spin rotation as a function of laser detuning and intensity confirm that the optical Stark effect is the operative mechanism and the results are well-described by a model including the electron-nuclear spin interaction. Using short tipping pulses, this technique enables one to perform a large number of operations within the coherence time.;As an alternative system for single spin control, few Mn-ion spins in a GaAs quantum well were measured using polarized photoluminescence. A new mechanism for optically addressing and controlling small numbers of magnetic ions in semiconductors is demonstrated without the need for magnetic fields or magnetic materials. The polarized Mn-spins precess in a transverse magnetic field enabling Hanle measurements of the spin lifetimes. The observed Mn-ion spin lifetimes reach promising timescales in the low doping limit, demonstrating that individual magnetic spins in a solid are useful systems for coherent manipulation of spin information.