Researchers have created, stored and retrieved quantum information for the first time, a critical step in quantum networks. The ability to share quantum information is critical to the development of quantum networks for distributed computing and secure communications. Quantum computing will be useful in solving some important types of problems, such as optimizing financial risks, decrypting data, designing molecules, and studying the properties of materials.

“Combining two important devices is a significant step forward in creating quantum networks, and we are thrilled to be the first team to demonstrate this.” — Dr. Sarah Thomas

However, this development is hampered because quantum information is lost when transmitted over long distances. One way to overcome this obstacle is to divide the network into smaller pieces and connect them all to a common quantum state.

This requires a means to store quantum information and retrieve it: namely, a quantum memory device. It needs to “talk” to another device, allowing quantum information to be created in the first place.

For the first time, researchers have created such a system that combines these two key components and uses traditional optical fibers to transmit quantum data. This achievement was achieved by researchers from Imperial College London, the University of Southampton and the universities of Stuttgart and Würzburg in Germany, and the results were published at: Science Developments.

Co-author Dr. from the Department of Physics at Imperial College London. Sarah Thomas said: “Combining two important devices is a significant step forward in creating quantum networks, and we are delighted to be the first team to be able to demonstrate this.”

Co-author Lucas Wagner from the University of Stuttgart added: “Allowing connections between remote locations and even quantum computers is a critical challenge for future quantum networks.”

long distance communication

With traditional telecommunications such as the Internet or phone lines, information can be lost over long distances. To combat this, these systems use “repeaters” at common points that read and re-amplify the signal, ensuring the signal reaches its destination intact.

But classical repeaters cannot be used with quantum information because any attempt to read and copy the information destroys it. On the one hand, this is an advantage, because quantum communications cannot be “interfered” without destroying information and alerting users. But for long-distance quantum networks, this is a challenge.

One way to overcome this problem is to exchange quantum information in the form of entangled particles of light, or photons. Entangled photons have such properties that it is impossible to understand one without the other. To share entanglement over long distances through a quantum network, you need two devices: one to create the entangled photons, and the other to store them and allow them to be retrieved later.

There are a variety of devices used to generate and store quantum information in the form of entangled photons, but generating these photons on demand and having a coherent quantum memory to store them has long eluded researchers.

Photons have a specific wavelength (producing different colors in visible light), but the devices that create and store them are usually set up to operate at different wavelengths, preventing them from interfering.

To interface between devices, the team created a system in which both devices use the same wavelength. He created “quantum dot” (unentangled) photons, which were then transferred to a quantum memory system that stored the photons in a cloud of rubidium atoms. The laser “turned on” and “turned off” the memory, allowing photons to be stored and released on demand.

The wavelengths of the two devices not only matched, but were also on the same wavelength as telecommunications networks in use today; this allowed it to be transmitted using common fiber optic cables familiar in everyday Internet connections.

European cooperation

The quantum point light source was created by researchers at the University of Stuttgart, with support from the University of Würzburg, and was then sent to the UK to interact with a quantum memory device created by Imperial and the Southampton team. The system was assembled in a laboratory in the basement of Imperial College London.

“The breakthrough this time was bringing together experts to design and run each part of the experiment using specialized equipment and work together to synchronize the devices.” —Dr. Patrick Ledingham

Although independent quantum dots and quantum memory have been created that are more efficient than the new system, this is the first evidence that devices can be created to interface at telecommunication wavelengths.

The team will now look to improve the system, including ensuring all photons are produced at the same wavelength, improving the storage time of photons, and making the entire system smaller.

However, co-author Dr. As a proof of concept, Patrick Ledingham says this is a significant step forward: “Members of the quantum community have been actively trying to connect for some time. This includes the fact that we tried this experiment twice with different memory devices and quantum dots as far back as five years ago, and This shows how difficult this is.

“The breakthrough this time was bringing together experts to design and run each part of the experiment using specialized equipment and work together to synchronize the devices.”