Experimental quantum repeater without quantum memory

Abstract

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.

Fundamental building block for all-optical scalable quantum networks

“…All-optical quantum repeaters, categorized also as 3rd generation, have been proposed recently [31,32] and some preliminary models are experimentally demonstrated [41,42]. A repeater protocol based on optical systems provides some advantages as discussed in [31,32]: it can be performed by photon sources, linear optical elements, and photon detectors.…”

Secure Quantum Communication Technologies and Systems: From Labs to Markets

“…One should note that in all-photonic quantum repeaters, the quantum information is instead encoded and protected in multi-photon entangled states, so they operate, in principle, at room temperature. This approach and the related protocol require only two coupled quantum emitters, as described in [118][119][120].…”

Optical Quantum Memory and its Applications in Quantum Communication Systems

“…However, it requires many multiple entangled photon sources and photon interferometers, which is technically very challenging. To date, only a 2 × 2 parallel all-photonic quantum repeater has been demonstrated [54]. It is believed that some combination of the all-photonic protocols and the quantum memory-based protocols could one day enable a practical quantum repeater.…”