  Modular networks are a promising paradigm for increasingly complex quantum
devices based on the ability to transfer qubits and generate entanglement
between modules. These tasks require a low-loss, high-speed intermodule link
that enables extensible network connectivity. Satisfying these demands
simultaneously remains an outstanding goal for long-range optical quantum
networks as well as modular superconducting processors within a single
cryostat. We demonstrate communication and entanglement in a superconducting
network with a microwave-actuated beamsplitter transformation between two
bosonic qubits, which are housed in separate modules and joined by a
demountable coaxial bus resonator. We transfer a qubit in a multi-photon
encoding and track photon loss events to improve the fidelity, making it as
high as in a single-photon encoding. Furthermore, generating entanglement with
two-photon interference and postselection against loss errors produces a Bell
state with success probability 79% and fidelity 0.94, halving the error
obtained with a single photon. These capabilities demonstrate several promising
methods for faithful operations between modules, including novel possibilities
for resource-efficient direct gates.
