Highly tunable exchange-only singlet-only qubit in a GaAs triple quantum dot

Quantum-dot based exchange-only spin qubits offer fast manipulation and full electric control but decohere rapidly in the presence of Zeeman field gradients, such as those resulting from the hyperfine interaction with randomly polarized nuclear-spin ensembles in the dots. A solution is to encode the qubit in the decoherence-free subspace spanned by two four-particle singlet states in a quadruple-dot setup [1].

Here we propose an implementation of this singlet-only qubit in a triple quantum dot with a (1,4,1) charge occupation. In the central multi-electron dot, the interplay between Coulomb interaction and an out-of-plane magnetic field creates an energy spectrum with a tunable singlet-triplet splitting and this feature can be exploited to create a six-particle singlet-only qubit with a qubit splitting that can straightforwardly be tuned over several μeV by adjusting the external magnetic field. We confirm the full exchange-based electric control of the qubit and demonstrate its superior coherence properties due to its singlet-only nature.

[1] A. Sala and J. Danon, Phys. Rev. B 95, 241303(R) (2017)