Phase-tuned entangled state generation between distant spin qubits

Quantum entanglement between distant qubits is an important feature of quantum networks. Distribution of entanglement over long distances can be enabled through coherently interfacing qubit pairs via photonic channels. Here, we report the realization of optically generated quantum entanglement between electron spin qubits confined in two distant semiconductor quantum dots. The protocol relies on spin-photon entanglement in the trionic $Λ$-system and quantum erasure of the Raman-photon path. The measurement of a single Raman photon is used to project the spin qubits into a joint quantum state with an interferometrically stabilized and tunable relative phase. We report an average Bell-state fidelity for $|ψ^{(+)}\rangle$ and $|ψ^{(-)}\rangle$ states of $61.6\pm2.3\%$ and a record-high entanglement generation rate of 7.3 kHz between distant qubits.