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

One of the largest challenges for GaAs-based spin qubits is decoherence caused by the random nuclear field of the host material. A potential solution to mitigate this source of decoherence is to encode the qubit in a singlet-only subspace, where the qubit states are insensitive to the nuclear field to lowest order. We propose an implementation of such a singlet-only 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 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.