  A major challenge in the field of quantum computing is the construction of
scalable qubit coupling architectures. Here, we demonstrate a novel tuneable
coupling circuit that allows superconducting qubits to be coupled over long
distances. We show that the inter-qubit coupling strength can be arbitrarily
tuned over nanosecond timescales within a sequence that mimics actual use in an
algorithm. The coupler has a measured on/off ratio of 1000. The design is
self-contained and physically separate from the qubits, allowing the coupler to
be used as a module to connect a variety of elements such as qubits,
resonators, amplifiers, and readout circuitry over long distances. Such design
flexibility is likely to be essential for a scalable quantum computer.
