A team led by researchers at the University of Science and Technology of China (USTC) entangled two quantum memories based on atomic ensembles through 260 miles (420 kilometers) of optical fiber.<\/p>\n
Each memory consisted of a laser-cooled cloud of rubidium atoms. Unlike demonstrations that distribute entangled photons alone, the experiment entangled matter-based memories capable of storing quantum states for subsequent network operations.<\/p>\n
Both memories were in the same laboratory, with the transmission path incorporating coiled fiber and a 6.2-mile deployed link. The experiment tested an intercity-scale optical path rather than establishing entanglement between nodes located 260 miles apart.<\/p>\n
Direct quantum transmission over fiber becomes exponentially less successful as distance and signal loss increase. Quantum memories could help overcome this problem by holding entanglement established on individual network segments while connections are created across other segments. This capability is considered essential for quantum repeaters and wide-area quantum networks.<\/p>\n
The researchers used the Duan-Lukin-Cirac-Zoller protocol, in which photons emitted by the two memories travel to a middle node and interfere. A photon detection at the middle node signals that entanglement has been established between the memories.<\/p>\n
The experiment\u2019s entangling probability scaled with the square root of the channel transmittance, while direct entangled-photon distribution scales with transmittance itself. The researchers reported exceeding the Pirandola-Laurenza-Ottaviani-Banchi (PLOB) bound at losses corresponding to fiber distances greater than approximately 132 miles in their setup.<\/p>\n
The PLOB bound defines the maximum rate at which quantum information can be distributed through a lossy channel without quantum repeaters. Exceeding it demonstrates that memory-based methods can outperform direct transmission as losses increase.<\/p>\n
Photons emitted by the rubidium memories do not naturally occupy a low-loss telecommunications band. The team converted them to the telecom S-band at a wavelength of 1,522 nanometers, where the fiber loss was approximately 0.17 decibels per kilometer.<\/p>\n
Single-photon interference also requires the optical paths to maintain a stable relative phase. The researchers combined continuous, far-off-resonant locking to suppress rapid noise with intermittent dual-band locking to correct slower drift.<\/p>\n
They verified entanglement at 260 miles, reporting a concurrence of 0.046, with an uncertainty of 0.022. Concurrence is a measure of entanglement, with a value above zero indicating that the two memories shared an entangled state.<\/p>\n
The researchers said their phase-stabilization approach could be adapted to nodes separated by a comparable geographical distance. They also proposed using Rydberg blockade techniques to improve the fidelity of the remote entanglement.<\/p>\n
The work builds on the group\u2019s 2024 three-node metropolitan network, which generated entanglement between atomic quantum memories separated by up to 7.7 miles. Potential applications for longer-distance memory entanglement include quantum communications, distributed quantum computing, and networked sensing.<\/p>\n","protected":false},"excerpt":{"rendered":"A team led by researchers at the University of Science and Technology of China (USTC) entangled two quantum…\n","protected":false},"author":2,"featured_media":597131,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6],"tags":[61,60,80],"class_list":["post-597130","post","type-post","status-publish","format-standard","has-post-thumbnail","category-technology","tag-ie","tag-ireland","tag-technology"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/posts\/597130","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/comments?post=597130"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/posts\/597130\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/media\/597131"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/media?parent=597130"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/categories?post=597130"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/tags?post=597130"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}