Yves Delley, ETH Zurich

Coherent electron-spin qubits in optically active InGaAs quantum dot molecules

Co-authors: K. M. Weiss, J. M. Elzerman, J. Miguel-Sanchez, A. Imamoglu

Department of Physics, ETH Zurich

The coherence time of single electron spins confined in semiconductors is limited by their fluctuating environment. Charge fluctuations affect the electron spin via the spin-orbit interaction, while nuclear spin fluctuations are coupled via the hyperfine interaction. We demonstrate that both limitations can be overcome simultaneously by using two exchange-coupled electron spins that realize a single decoherence-avoiding qubit.
We charge a coupled InGaAs quantum dot pair with exactly one electron each. Using coherent population trapping via a common optically excited state, we measure the coherence between the singlet and triplet state. In a small external magnetic field, these two states are to first order insensitive to magnetic fluctuations due to their vanishing spin projection along the external axis. By tuning the device to the so-called sweet spot where charge fluctuations are suppressed to first order as well, we show that the corresponding T2* time may exceed 200 nanoseconds.