  We use a floating tunable coupler to mediate interactions between qubits on
separate chips to build a modular architecture. We demonstrate three different
designs of multi-chip tunable couplers using vacuum gap capacitors or
superconducting indium bump bonds to connect the coupler to a microwave line on
a common substrate and then connect to the qubit on the next chip. We show that
the zero-coupling condition between qubits on separate chips can be achieved in
each design and that the relaxation rates for the coupler and qubits are not
noticeably affected by the extra circuit elements. Finally, we demonstrate
two-qubit gate operations with fidelity at the same level as qubits with a
tunable coupler on a single chip. Using one or more indium bonds does not
degrade qubit coherence or impact the performance of two-qubit gates.
