Singlet-singlet qubit with two spins in a triple quantum dot

Encoded qubits in semiconductor spin systems offer efficient electrical control of qubit operations, making them a promising candidate for scalable quantum devices. In this work, we propose a novel encoded qubit based on a triple quantum dot system containing two electrons. By leveraging both spin and charge degrees of freedom, we encode the qubit within a subspace spanned by two spin-singlet states. Unlike single-spin or exchange-only qubits, the singlet-singlet encoded qubit is intrinsically robust against magnetic noise. We identify sweet spots where the qubit is also immune to detuning fluctuations caused by charge noise. We demonstrate how single-qubit gate operations can be implemented by electrically controlling the tunneling between quantum dots and the detunings of the quantum dot energy levels. Our results highlight the singlet-singlet qubit as a promising path forward for scalable quantum computing on semiconductor platforms.