A Quantum-Logic Gate between Distant Quantum-Network Modules

Scaling up the number of individually addressable qubits on a quantum processing unit is one of the main challenges towards the realization of functional quantum computers. A solution is to embed smaller qubit modules into a non-local quantum network that, in essence, forms a large quantum machine. Such a distributed architecture, however, requires the capability to execute quantum-logic gates between distant qubits. Here I will present our recent realization [Daiss et al. Science vol. 371 614-617 (2021)] of such a gate between two single-qubit cavity-QED modules separated by a distance of 60m. We employ an ancillary photon that we successively reflect from two remote qubit modules, followed by a heralding photon detection which triggers a final qubit rotation. We demonstrate that the gate is capable of generating all the four Bell states. As outlook, I will discuss the extension of our scheme to multiple-qubits modules and to many modules in a complex quantum network.