  Protocols of quantum information processing are the foundation of quantum
technology, allowing to share secrets at a distance for secure communication
(quantum key distribution), to teleport quantum states, and to implement
quantum computation. While various protocols have already been realized, and
even commercialized, the throughput and processing speed of standard protocols
is generally low, limited by the narrow electronic bandwidth of the measurement
apparatus in the MHz-to-GHz range, which is orders-of-magnitude lower than the
optical bandwidth of available quantum optical sources (10-100 THz). We present
a general concept and methods to process quantum information in parallel over
multiplexed frequency channels using parametric homodyne detection for
measurement of all the channels simultaneously, thereby harnessing the optical
bandwidth for quantum information in an efficient manner. We exemplify the
concept through two basic protocols: Multiplexed Continuous-Variable Quantum
Key Distribution (CV-QKD) and multiplexed continuous-variable quantum
teleportation. We demonstrate the multiplexed CV-QKD protocol in a
proof-of-principle experiment, where we successfully carry out QKD over 23
uncorrelated spectral channels, with capability to detect eavesdropping in any
channel. These multiplexed methods (and similar) will enable to carry out
quantum processing in parallel over hundreds of channels, potentially
increasing the throughput of quantum protocols by orders of magnitude.
