Gaussian States Minimize the Output Entropy of the One-Mode Quantum Attenuator

Understand

We prove that Gaussian thermal input states minimize the output von Neumann entropy of the one-mode Gaussian quantum-limited attenuator for fixed input entropy.

• The Gaussian quantum-limited attenuator models the attenuation of an electromagnetic signal in the quantum regime.
• The Shannon entropy of an attenuated real-valued classical signal is a simple function of the entropy of the original signal.
• A striking consequence of energy quantization is that the output von Neumann entropy of the quantum-limited attenuator is no more a function of the input entropy alone.