  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 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 use the gate for remote entanglement
creation of all four Bell states. Our non-local quantum-logic gate could be
extended both to multiple qubits and many modules for a tailor-made multi-qubit
computing register.
