In semiconductors, the T2* coherence time of a single confined spin is limited either by the fluctuating magnetic environment (via the hyperfine interaction), or by charge fluctuations (via the spin-orbit interaction). We demonstrate that both limitations can be overcome simultaneously by using two exchange-coupled electron spins that realize a single decoherence-avoiding qubit. Using coherent population trapping, we generate a coherent superposition of the singlet and triplet states of an optically active quantum-dot molecule, and show that the corresponding T2* may exceed 200 nanoseconds.
@article{arxiv.1112.4710,
title = {Decoherence-avoiding spin qubits in optically active quantum dot molecules},
author = {K. M. Weiss and J. M. Elzerman and Y. L. Delley and J. Miguel-Sanchez and A. Imamoglu},
journal= {arXiv preprint arXiv:1112.4710},
year = {2012}
}