  It is well known that entanglement can benefit quantum information processing
tasks. Quantum illumination, when first proposed, is surprising as
entanglement's benefit survives entanglement-breaking noise. Since then, many
efforts have been devoted to study quantum sensing in noisy scenarios. The
applicability of such schemes, however, is limited to a binary quantum
hypothesis testing scenario. In terms of target detection, such schemes
interrogate a single polarization-azimuth-elevation-range-Doppler resolution
bin at a time, limiting the impact to radar detection. We resolve this
binary-hypothesis limitation by proposing a quantum ranging protocol enhanced
by entanglement. By formulating a ranging task as a multiary hypothesis testing
problem, we show that entanglement enables a 6-dB advantage in the error
exponent against the optimal classical scheme. Moreover, the proposed ranging
protocol can also be utilized to implement a pulse-position modulated
entanglement-assisted communication protocol. Our ranging protocol reveals
entanglement's potential in general quantum hypothesis testing tasks and paves
the way towards a quantum-ranging radar with a provable quantum advantage.
