A quantum-logic gate between distant quantum-network modules

Quantum gating at a distance The processing of quantum information is reliant on the encoding and manipulation of quantum states of a qubit. Superconducting circuits are the most advanced platform at present, but there is an issue with cross-talk between the qubits and the challenge of error correction as the systems are scaled up. Another approach being pursued is a modular platform in which the qubits are spatially separated. Daiss et al. demonstrate the operation of a quantum gate in which one qubit conditionally controls the state of another qubit spatially separated by 60 meters (see the Perspective by Hunger). Because the approach is platform independent, it could be extended from the demonstrated neutral atoms to ions, impurity vacancy centers, or even a combination of these qubits. Science, this issue p. 614; see also p. 576 A quantum gate is demonstrated for qubits spatially separated by 60 meters. The big challenge in quantum computing is to realize scalable multi-qubit systems with cross-talk–free addressability and efficient coupling of arbitrarily selected qubits. Quantum networks promise a solution by integrating smaller qubit modules to a larger computing cluster. Such a distributed architecture, however, requires the capability to execute quantum-logic gates between distant qubits. Here we experimentally realize such a gate over a distance of 60 meters. 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 use the gate for remote entanglement creation of all four Bell states. Our nonlocal quantum-logic gate could be extended both to multiple qubits and many modules for a tailor-made multi-qubit computing register.