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

We propose an implementation of a singlet-only spin qubit in a GaAs-based triple quantum dot with a (1, 4, 1) charge occupation. In the central multielectron dot, the interplay between Coulomb interaction and an out-of-plane magnetic field creates an energy spectrum with a tunable singlet-triplet splitting, which can be exploited to create a six-particle singlet-only qubit with a qubit splitting that can straightforwardly be tuned over tens of μ eV 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.