• beam splitter
• quantum memory channel
• bosonic quantum communication
• quantum channel
• quantum information
• continuous-variable quantum information
• infinite-dimensional quantum channel
• memory effects
• quantum communication
• general attenuator
• entanglement-assisted capacity
• quantum capacity
• classical capacity
• environment-assisted capacity
• optical fiber
• quantum communication via optical fibers

In the context of Quantum Communication, a general attenuator is a noisy transmission line (e.g. optical fiber) that affects the input photonic signals through dissipative mechanisms. Mathematically, a general attenuator acts by combining the input state with an environment initialized in a given state through a beam splitter of fixed transmissivity.
The classical capacity of a transmission line is the maximum rate at which bits can be reliably transmitted from a sender to a receiver by using the line many times. In addition, if the sender and the receiver can exploit pre-shared entangled states in the design of their protocols, one defines the so-called entanglement-assisted capacities.
The first part of the Thesis focuses on the entanglement-assisted classical capacity of general attenuators. Most notably, we find that the entanglement resource and the appropriate control of the environment state make it possible to communicate with even better performance than the ideal case of absence of noise, even if the transmissivity is arbitrarily low.
In the second part of the Thesis, we introduce a protocol that give technological interest to the results of the first part. The protocol takes advantage of memory effects (which arise when the sender feeds signals into the line at a sufficiently high frequency) to boost the performance of the communication line. The idea is as follows: one sends trigger signals in order to transform the environment into a state that facilitates communication and subsequently sends the information-carrying signals. We show that by sending some trigger signals in a suitable entangled state, then the environment transforms into a state that activates the special performances discussed in the first part of the Thesis.