  We aim to devise feasible, efficient verification schemes for bosonic
channels. To this end, we construct an average-fidelity witness that yields a
tight lower bound for average fidelity plus a general framework for verifying
optimal quantum channels. For both multi-mode unitary Gaussian channels and
single-mode amplification channels, we present experimentally feasible
average-fidelity witnesses and reliable verification schemes, for which sample
complexity scales polynomially with respect to all channel specification
parameters. Our verification scheme provides an approach to benchmark the
performance of bosonic channels on a set of Gaussian-distributed coherent
states by employing only two-mode squeezed vacuum states and local homodyne
detections. Our results demonstrate how to perform feasible tests of quantum
components designed for continuous-variable quantum information processing.
