  Quantum mechanics offers the possibility of unconditionally secure
communication between multiple remote parties. Security proofs for such
protocols typically rely on bounding the capacity of the quantum channel in
use. In a similar manner, Cram\'er-Rao bounds in quantum metrology place limits
on how much information can be extracted from a given quantum state about some
unknown parameters of interest. In this work we establish a connection between
these two areas. We first demonstrate a three-party sensing protocol, where the
attainable precision is dependent on how many parties work together. This
protocol is then mapped to a secure access protocol, where only by working
together can the parties gain access to some high security asset. Finally, we
map the same task to a communication protocol where we demonstrate that a
higher mutual information can be achieved when the parties work collaboratively
compared to any party working in isolation.

Quantum Physics