Demonstration of Entanglement of Electrostatically Coupled

†These authors contributed equally to this work. Quantum computers have the potential to solve certain interesting problems significantly faster than classical computers. To exploit the power of a quantum computation it is necessary to perform inter-qubit operations and generate entangled states. Spin qubits are a promising candidate for implement-ing a quantum processor due to their potential for scalability and miniaturization. However, their weak interactions with the environment, which leads to their long coherence times, makes inter-qubit operations challenging. We perform a controlled two-qubit operation between singlet-triplet qubits using a dynamically decoupled sequence that maintains the two-qubit coupling while decoupling each qubit from its fluctuating environment. Using state tomography we measure the full density matrix of the system and determine the concurrence and the fidelity of the generated state, providing proof of entanglement. Singlet-triplet (S-T0) qubits, a particular realization of spin qubits[1–7], store quantum information in the joint spin state of two electrons[8–10]. The basis states for the S-T0 qubit can be constructed from the eigenstates of a single electron spin, | ↑ 〉 and | ↓〉. We choose |S 〉 = 1p 2 ( | ↑↓〉 − | ↓↑〉) and |T0 〉 = 1p2 ( | ↑↓〉+ | ↓↑〉) for the logical subspace of the S-T0 qubit because these states are insensitive to uniform fluctuations in the magnetic field. The qubit can then be described as a two level system with a representation on a Bloch sphere shown in Fig. 1a. 1 a