{"id":5234,"date":"2024-08-11T08:50:04","date_gmt":"2024-08-11T12:50:04","guid":{"rendered":"https:\/\/www.ecoticias.com\/en\/teleporting-light-quantum-communication\/5234\/"},"modified":"2026-10-28T04:06:11","modified_gmt":"2026-10-28T08:06:11","slug":"teleporting-light-quantum-communication","status":"publish","type":"post","link":"https:\/\/www.ecoticias.com\/en\/teleporting-light-quantum-communication\/5234\/","title":{"rendered":"Physicists in Barcelona teleported a photon’s quantum state into a crystal memory over 1 kilometer of lab fiber, without breaking the speed of light"},"content":{"rendered":"\n

In April 2023, physicists at the Institute of Photonic Sciences (ICFO) in Castelldefels, near Barcelona, led by ICREA professor Hugues de Riedmatten, reported in Nature Communications<\/a> that they had teleported the quantum state of a telecom-wavelength photon onto a qubit stored in a solid-state memory, across 0.62 miles (1 kilometer) of fiber spooled up in the lab.<\/p>\n\n\n\n

Nothing traveled faster than light, though. In teleportation the quantum information is destroyed at one end and shows up at the other without physically crossing the gap, but the protocol only works alongside ordinary classical bits, and those move at normal speed.<\/p>\n\n\n\n

“Here we demonstrate long distance quantum teleportation from a photonic qubit at telecom wavelength to a matter qubit, stored as a collective excitation in a solid-state quantum memory,” write the researchers in the study.<\/p>\n\n\n\n

The work built on a 2021 experiment in which the same group entangled two multimode quantum memories placed 33 feet (10 meters) apart, with a telecom photon announcing each success.<\/p>\n\n\n\n

The setups at either end of the spool were called Alice and Bob. At Alice, a crystal generated pairs of entangled photons, a ‘signal’ photon at 606 nanometers and an ‘idler’ at 1,436 nanometers, which suits telecom networks.<\/p>\n\n\n\n

“[W]e kept the first 606 nm photon at Alice and stored it in a multiplexed solid-state quantum memory, holding it in the memory for future processing,” says ICFO researcher Dario Lago-Rivera, the first author.<\/p>\n\n\n\n

The memory is a Pr3+:Y2SiO5 crystal (doped with praseodymium) that stores light with an atomic frequency comb protocol. At Bob, a second crystal prepared the qubit to be teleported. ICFO’s press release<\/a> calls this the third photon; in the paper it’s a pair of weak coherent pulses 420 nanoseconds apart, with 0.02 photons per qubit on average.<\/p>\n\n\n\n

Bob’s qubit and the idler met on a beam splitter in front of superconducting nanowire detectors for a Bell state measurement (BSM). When the BSM succeeds, the state of Bob’s qubit passes to the photon waiting in Alice’s memory.<\/p>\n\n\n\n

“[W]e are capable of transferring information between two photons that were never in contact before, but connected through a third photon that was indeed entangled with the first,” say Lago-Rivera and fellow ICFO researcher Jelena Rakonjac.<\/p>\n\n\n\n

“[W]e employed a multiplexed quantum memory capable of storing the first photon for long enough such that by the time Alice found out that the interaction had happened, we were still able to process the teleported information as the protocol requires.”<\/p>\n\n\n\n

The idler needed 5 microseconds to get through the spool, and an electronic delay of another 5 microseconds stood in for the reply, so Alice waited 10 microseconds for the BSM result. The memory held the stored photon for 17.5 microseconds. Depending on the outcome, the team then shifted its phase on the way out of the memory (active feed-forward), which means the same state comes out each time; without it, half of the events would be discarded.<\/p>\n\n\n\n

Average fidelity over the kilometer was 86 percent, plus or minus 4. A classical strategy can’t beat 66.7 percent for a single qubit, or 75 percent with these weak pulses at 1 kilometer.<\/p>\n\n\n\n

What’s more, a single-mode memory at that distance is capped at 100,000 attempts per second. ICFO’s ran at 133 to 323 kHz with no change in fidelity, roughly three times that cap, and the control electronics set the ceiling.<\/p>\n\n\n\n

There are caveats. Storage-and-retrieval efficiency at 1 kilometer was 12.2 percent, and heralded teleportation events came in at about one per second. The spool didn’t leave the lab, either.<\/p>\n\n\n\n

“The additional bit flip required to recover the original qubit (not performed in this experiment) could be implemented using an unbalanced Mach-Zehnder interferometer,” write the researchers.<\/p>\n\n\n\n

A 2014 experiment published in Nature Photonics had already teleported a telecom photon’s state into a solid-state memory, with storage times short compared with the communication time. ICFO says no earlier setup brought together three requirements: compatibility with telecom networks, active feed-forward (which needs a receiving memory that keeps the qubit until the final operation) and multiplexing.<\/p>\n\n\n\n

In December 2023, in Optica Quantum, Rakonjac, Lago-Rivera, F\u00e9licien Appas and colleagues sent light-matter entanglement through two fibers of the metropolitan network, from ICFO to the Telecommunication Centre of Catalunya (CTTI) in L’Hospitalet de Llobregat, a loop of 31 miles (50 kilometers) to central Barcelona and back, and the light’s quantum features came through without a substantial drop. That wasn’t teleportation; it distributed entanglement.<\/p>\n\n\n\n

“Demonstrating it in the installed fiber network is a first step towards realizing a test-bed for quantum repeater technologies in the Barcelona area,” de Riedmatten says in material reproduced by eeNews Europe<\/a>.<\/p>\n\n\n\n

Then in October 2025 the group described in Physical Review X a heralded entangled link between two solid-state memories with on-demand retrieval, meant as a building block for quantum repeaters. According to ICFO<\/a>, a link of a few kilometers is already within reach, and the researchers expect further improvements could stretch that to several tens of kilometers, eventually linking distant cities.<\/p>\n\n\n\n

“These results establish our architecture as a prime candidate for the implementation of the future quantum internet,” says Appas, one of the first co-authors.<\/p>\n\n\n\n

This article was first published on August 11, 2024, under a headline saying the experiment traveled faster than light, which it didn’t. It was rewritten and updated with verified sources on October 28, 2026.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

In April 2023, physicists at the Institute of Photonic Sciences (ICFO) in Castelldefels, near Barcelona, led by ICREA professor Hugues … <\/p>\n

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