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Quantum technologies, systems that operate leveraging quantum mechanical effects, have the potential to outperform classical technologies in some specific tasks. Over the past decades, some researchers have also been trying to realize quantum networks, systems comprised of multiple connected quantum devices.

So far, photons have been the most widely used particles for carrying quantum information across different devices in quantum networks. The main reasons for this are that photons can travel at remarkable speeds, while weakly interacting with their surrounding environment, which helps to preserve the quantum states they are carrying.

To successfully employ photons in quantum networks, however, physicists and engineers need to be able to confirm that they are stored successfully without destroying them.

Heralded storage is a promising technique to achieve this, as it entails the storage of photons accompanied by the production of a signal (i.e., 'herald') that confirms that their storage was successful.

Researchers at the University of Science and Technology recently demonstrated the heralded storage of photons in a Rydberg superatom (i.e., a cloud of atoms that behave as an individual quantum system under certain conditions).

Using newly proposed experimental methods, which were outlined in a paper published in , they were able to successfully demonstrate the heralded storage of photons without relying on traditional high-finesse optical cavities, as done in earlier works.

"Prior to this work, , which we used to demonstrate the generation of atom-photon entanglement, and ," Xiao-Hui Bao, co-senior author of the paper, told Â鶹ÒùÔº.

"In subsequent discussions, we explored new potential applications of this technique, leading to the idea of heralded storage."

Bao and his colleagues have been trying to identify more promising techniques and experimental platforms for the realization of large-scale quantum networks for years. Their recent study was aimed at realizing the heralded storage of photons in Rydberg superatoms, quantum systems that they often employed in their earlier experiments.

"In our initial proposal for demonstrating heralded storage, we planned to use two Rydberg superatom setups, with the input photonic qubit encoded in the spatial degree of freedom," explained Bao.

"While this scheme appeared straightforward, its implementation demanded extensive experimental resources and introduced considerable complexity."

Bao and his colleagues found that demonstrating heralded storage using two Rydberg superatoms was more challenging than they had originally anticipated, thus they devised a new and simpler approach.

The scheme they employed relies on a single superatom and entails the encoding of individual qubits in the time-bin degree of freedom (i.e., in the time in which a photon arrives, as opposed to its location or its polarization).

"Heralded storage has traditionally been considered a capability unique to cavity-QED systems," said Bao. "However, our scheme and experimental results demonstrate that a Rydberg superatom can perform this task effectively as well."

This work introduces a new promising and viable scheme for realizing entanglement between two remote superatoms via the heralded storage of photons. In the future, their proposed methods could contribute to the advancement and up-scaling of quantum networks.

"As an application, our current experiment demonstrates the generation of two-node entanglement via heralded storage, eliminating the need for an intermediate node," added Bao. "In the near future, we plan to incorporate this technique into a metropolitan-scale quantum network."

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