  Quantum transducers convert quantum signals through hybrid interfaces of
physical platforms in quantum networks. Modeled as quantum communication
channels, performance of unidirectional quantum transduction can be measured by
the quantum channel capacity. However, characterizing performance of quantum
transducers used for duplex quantum transduction where signals are converted
bidirectionally remains an open question. Here, we propose rate regions to
characterize the performance of duplex quantum transduction. Using this tool,
we find that quantum transducers optimized for simultaneous duplex transduction
can outperform strategies based on the standard protocol of time-shared
unidirectional transduction. Integrated over the frequency domain, we
demonstrate that rate region can also characterize quantum transducers with
finite bandwidth.
