  The laws of quantum physics endow superior performance and security for
information processing: quantum sensing harnesses nonclassical resources to
enable measurement precision unmatched by classical sensing, whereas quantum
cryptography aims to unconditionally protect the secrecy of the processed
information. Here, we present the theory and experiment for
entanglement-enhanced covert sensing, a paradigm that simultaneously offers
high measurement precision and data integrity by concealing the probe signal in
an ambient noise background so that the execution of the protocol is
undetectable with a high probability. We show that entanglement offers a
performance boost in estimating the imparted phase by a probed object, as
compared to a classical protocol at the same covertness level. The implemented
entanglement-enhanced covert sensing protocol operates close to the fundamental
quantum limit by virtue of its near-optimum entanglement source and quantum
receiver. Our work is expected to create ample opportunities for quantum
information processing at unprecedented security and performance levels.
