Quantum repeaters -important components of a scalable quantum internet -enable the entanglement to be distributed over long distances. The standard paradigm for a quantum repeater relies on a necessary demanding requirement of quantum memory. Despite significant progress, the limited performance of quantum memory makes practical quantum repeaters still a great challenge. Remarkably, a proposed allphotonic quantum repeater avoids the need for quantum memory by harnessing the graph states in the repeater nodes. Here we perform an experimental demonstration of an all-photonic quantum repeater using linear optics. By manipulating a 12-photon interferometer, we implement a 2×2 parallel all-photonic quantum repeater, and observe an 89% enhancement of entanglement-generation rate over the standard parallel entanglement swapping. These results open a new way towards designing repeaters with efficient single-photon sources and photonic graph states, and suggest that the all-photonic scheme represents an alternative path -parallel to that of matter-memory-based schemes -towards realizing practical quantum repeaters.Recent years have seen enormous interest in quantum communication driven by its remarkable features of secure communication [1], quantum teleportation [2] and distributed quantum computing [3]. Photons are considered to be the optimal medium for quantum communication because of their flying nature and compatibility with current telecommunications networks. However the maximum communication distance is currently severely limited by photon loss in quantum channels, such as optical fibres. One viable solution is to use satellites as relays to transmit photons over a free-space channel [4,5]. In fibre-based telecommunications networks, quantum repeaters are believed to be the most promising way to overcome the distance limit [6]. The standard paradigm for a quantum repeater [7,8] consists of three basic technologies namely entanglement swapping [9, 10], entanglement purification [11,12] and quantum memory [13][14][15]. Recently, significant progress has been made both theoretically [16][17][18] and experimentally [19][20][21]. However, the limited performance of current quantum memories [22] remains a major obstacle in realizing practical quantum repeaters unless there is a future experimental breakthrough.

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Distributed quantum metrology can enhance the sensitivity for sensing spatially distributed parameters beyond the classical limits. Here we demonstrate distributed quantum phase estimation with discrete variables to achieve Heisenberg limit phase measurements. Based on parallel entanglement in modes and particles, we demonstrate distributed quantum sensing for both individual phase shifts and an averaged phase shift, with an error reduction up to 1.4 dB and 2.7 dB below the shot-noise limit. Furthermore, we demonstrate a combined strategy with parallel mode entanglement and multiple passes of the phase shifter in each mode. In particular, our experiment uses six entangled photons with each photon passing the phase shifter up to six times, and achieves a total number of photon passes N = 21 at an error reduction up to 4.7 dB below the shot-noise limit. Our research provides a faithful 1