Universal nuclear focusing of confined electron spins

For spin-based quantum computation in semiconductors, dephasing of electron spins by a fluctuating background of nuclear spins is a main obstacle. It has been shown that in self-assembled InAs quantum dots, this nuclear background can be precisely controlled by periodically exciting single electron spins using optical laser pulses. A feedback mechanism between the electron spin polarization and the nuclear system focuses the electron spin precession frequency into discrete modes that are commensurate with the laser repetition rate. In such a spin-mode-locked system, the electron spin lifetime within individual dots can surpass the limit given by nuclear background fluctuations. Here we show that spin mode-locking is a universal phenomenon that also occurs in ensembles of lithographically-defined many-electron GaAs/AlGaAs dots [1]. This opens the door to achieve long electron spin coherence times also in systems that can be controlled in shape, size and position. We discuss possible mechanisms of spin mode-locking and show experiments that suggest that the optical Stark effect plays an important role in the nuclear focusing of our many-electron dots.

[1] S. Markmann, C. Reichl, W. Wegscheider and G. Salis, arXiv:1808.06571.