We experimentally demonstrate a tunable hybrid qubit in a five-electron GaAs double quantum dot. The qubit is encoded in the (1,4) charge regime of the double dot and can be manipulated completely electrically. More importantly, dot anharmonicity leads to quasiparallel energy levels and a new anticrossing, which help preserve quantum coherence of the qubit and yield a useful working point. We have performed Larmor precession and Ramsey fringe experiments near the new working point and find that the qubit decoherence time is significantly improved over a charge qubit. This work shows a new way to encode a semiconductor qubit that is controllable and coherent.
@article{arxiv.1510.00895,
title = {Tunable Hybrid Qubit in a GaAs Double Quantum Dot},
author = {Gang Cao and Hai-Ou Li and Guo-Dong Yu and Bao-Chuan Wang and Bao-Bao Chen and Xiang-Xiang Song and Ming Xiao and Guang-Can Guo and Hong-Wen Jiang and Xuedong Hu and Guo-Ping Guo},
journal= {arXiv preprint arXiv:1510.00895},
year = {2016}
}