For the first time, physicists from the Universities of Innsbruck, Austria, and Paris-Saclay, France, have integrated all the essential features of a distant quantum network in a single device. Using this technology, scientists were able to send quantum information across a distance of 50 kilometers in a proof-of-principle experiment. This suggests that the components of large-scale, realistic quantum networks may soon be achievable. The system is termed a repeater node.
Repetition without pause or interruption:
Although they can’t be used directly, quantum repeaters can give this increase. Repeaters cannot just replicate the signal that receive and send it to the next node because of restrictions imposed by quantum physics on the copy of entangled states. Rather, data must be sent via BSM , which involves storing the data in a so-called quantum memory.
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Some practical conditions must also be met by a fully functional quantum repeater. In order for quantum signals to be sent across optical fibers with minimal loss, they must first be at wavelengths that are utilized in telecommunications. Second, the quantum memory’s storage duration should be longer than the time required to produce entanglement. Ultimately, every stage in the procedure must be deterministic, which means that signals must be generated following each successful phase.
Everything in one:
All three of the practical conditions are met in a single experiment by the most recent study, which is reported in Physical Review Letters. 2 trapped calcium ions release one photon each in the first series of events, creating two entangled pairs of photons and ions. In this case, the trapped ions function as qubits, and the quantum network distributes their quantum states. Following conversion to the telecom wavelength of 1550 nm, the photons of these pairs are sent via two distinct 25-km-long optical fibers to two different nodes. Thus, there are 50 kilometers between each node overall.
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The status of each entangled ion is saved in the ion’s protected memory states whenever a photon arrives at its assigned node. Then, the system tries again to transmit a second photon to another node that is entangled with another ion. The experimenters apply a BSM to convert the ion states into the corresponding entangled photons at each node once photons have been identified at both.(Source: Physics World)