The development of modular and versatile quantum interconnect hardware is a
key next step in the scaling of quantum information platforms to larger size
and greater functionality. For superconducting quantum systems, fast and
well-controlled tunable circuit couplers will be paramount for achieving high
fidelity and resource efficient connectivity, whether for performing two-qubit
gate operations, encoding or decoding a quantum data bus, or interfacing across
modalities. Here we propose a versatile and internally-tunable double-transmon
coupler (DTC) architecture that implements tunable coupling via flux-controlled
interference in a three-junction dcSQUID. Crucially, the DTC possesses an
internally defined zero-coupling state that is independent of the coupled data
qubits or circuit resonators. This makes it particular attractive as a modular
and versatile design element for realizing fast and robust linear coupling in
several applications such as high-fidelity two-qubit gate operations, qubit
readout, and quantum bus interfacing