Optimal design and quantum benchmarks for coherent state amplifiers

TL;DR

This paper determines the fundamental quantum limits for amplifying unknown coherent states, providing benchmarks for experimental quantum amplification that surpass classical methods, applicable to finite photon numbers.

Contribution

It establishes the ultimate quantum limits for both deterministic and probabilistic coherent state amplification with finite photon numbers, and offers benchmarks for experimental validation.

Findings

Quantum limits for coherent state amplification are derived.

Benchmarks for surpassing classical amplification are provided.

Quantum amplification is feasible for all finite photon numbers.

Abstract

We establish the ultimate quantum limits to the amplification of an unknown coherent state, both in the deterministic and probabilistic case, investigating the realistic scenario where the expected photon number is finite. In addition, we provide the benchmark that experimental realizations have to surpass in order to beat all classical amplification strategies and to demonstrate genuine quantum amplification. Our result guarantees that a successful demonstration is in principle possible for every finite value of the expected photon number.