Multipartite Mixed-Species Entanglement over a Quantum Network

Abstract

We generate multipartite entangled states of two, three and four matter qubits, where the entanglement is distributed over macroscopic distances via a photonic network link. Trapped-ion ${}^{88}{\text{Sr}}^{+}$ qubits are entangled directly via the optical fibre link, and the entanglement is subsequently extended to ${}^{43}{\text{Ca}}^{+}$ memory qubits co-trapped in each network node, using local mixed-species logic gates. We create remotely entangled ${\text{Sr}}^{+}$-${\text{Ca}}^{+}$ and ${\text{Ca}}^{+}$-${\text{Ca}}^{+}$ states, as well as mixed-species Greenberger-Horne-Zeilinger (GHZ) states of up to four qubits. We demonstrate storage of the remotely-entangled memory qubits for $\sim 10\text{s}$, more than $100\times$ the creation time.