Distributed quantum metrology aims to surpass classical methods in estimating multiple distributed parameters. However, existing schemes often require entangled resources with photon numbers exceeding or equaling the parameter count. This paper presents a distributed quantum sensing protocol achieving quantum-enhanced sensitivity using fewer photons than parameters. A two-photon entangled state is used to experimentally estimate four phases distributed 3 km from a central node, demonstrating a 2.2 dB sensitivity enhancement over the standard quantum limit. This work suggests a pathway for large-scale distributed quantum sensing using currently available entangled sources.

Dong-Hyun Kim, Seongjin Hong, Yong-Su Kim, Yosep Kim, Seung-Woo Lee, Raphael C. Pooser, Kyunghwan Oh, Su-Yong Lee, Changhyoup Lee, Hyang-Tag Lim