Entanglement of Two Singlet-Triplet Qubits

Semiconductor spin qubits are promising candidates for quantum computation because of their potential for scalability. However, their weak interaction with the environment, which leads to long coherence times, makes two-qubit operations challenging. We perform the first two-qubit operation between singlet-triplet qubits. The two qubit operation relies on the capacitive coupling between two adjacent qubits to generate a CPHASE gate. In order to combat low frequency noise we use a dynamically decoupled gate that maintains the two-qubit coupling while decoupling each qubit from its fluctuating environment. Using state tomography we measure the two-qubit density matrix and show that the operation produces the expected state. We extract a concurrence of 0.44 and a Bell state fidelity of 0.72, each providing definitive proof of entanglement.