Towards single electron spin resonance in a charge tunable quantum dot

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Optical detected electron spin resonance is a powerful tool to study the coherence properties of electron spin coherence properties. In particular for an electron trapped in a single self-assembled quantum dot (QD) the electron spin coherence is strongly influenced by the nuclear spin dynamics; The electron interacts via hyperfine interaction with ~300000 nuclear spins whose random fluctuating distripution usually lead to significant reduction of electron spin coherence.

In order to perform electron spin resonance of a single electron in a charge tunable QD a novel sample geometry was designed and fabricated allowing for simultaneous irradiation of the QD with microwave and optical fields. A coplanar waveguide was fabricated on the chip in order to generate an oscillating magnetic field as close as possible at the site of the QD. In a preliminary experiment the electric field of the microwave was coupled to the exciton in a QD which leads to the formation of photon sidebands (see fig 1.). The distribution of the exciton oscillator strength into the higher order sidenbands follows the Airy function and allows for a calibration of the microwave power at the QD. Future steps include further development of the sample structure in order to maximise the magnetic rather than the electric field at the QD. Also, collection efficiency of photons scattered off the QD will be enhanced with the goal to detect quantum jumps in the occupation of the QD electron spin states.

Fig.1: (a) Differential reflection signal of a single QD in the presence of a strong oscillating electric field (f=1.2GHz). With increasing microwave power the optical spectra develop sidebands and eventually the oscillator strength is completly redistributed leading a to suppression of the central resonance. (b) Normalized signal strength of the center resonance and the first and second arder sidebands. The amplitudes of the resonances follows the Airy function.