Modular entanglement of atomic qubits using photons and phonons

Quantum entanglement is the central resource behind quantum information science, from quantum computation and simulation(1,2) to enhanced metrology(3) and secure communication(1). These applications require the quantum control of large networks of qubits to realize gains and speed increases over conventional devices. However, propagating entanglement becomes difficult or impossible as the system grows in size. Here, we demonstrate the first step in a modular approach(4) to scaling entanglement by using complementary quantum buses on a collection of three atomic ion qubits stored in two remote ion trap modules. Entanglement within a module is achieved with deterministic near-field interactions through phonons(5), and remote entanglement between modules is achieved with a probabilistic interaction through photons(6). This minimal system allows us to address generic issues in the synchronization of entanglement with multiple buses. It points the way towards a modular large-scale quantum information architecture that promises less spectral crowding and thus potentially less decoherence as the number of qubits increases(4). We generate this modular entanglement faster than the observed remotely entangled qubit-decoherence rate, showing that entanglement can be scaled simply by adding more modules.