Crucial connection for ‘quantum Internet’ created for the first time

Researchers have produced, stored and retrieved quantum information for the first time, a critical step in creating quantum networks.

The ability to share quantum information is crucial to developing quantum networks for distributed computing and secure communication. Quantum computing will be useful in solving some important types of problems, such as optimizing financial risk, deciphering data, designing molecules, and studying material properties.

However, this development is being delayed because quantum information can be lost when transmitted over long distances. One way to overcome this barrier is to divide the network into smaller segments and link them all with a shared quantum state.

To do this requires a means to store the quantum information and retrieve it again: that is, a quantum memory device. This must “talk” to another device that allows the creation of quantum information in the first place.

For the first time, researchers have created a system that interconnects these two key components and uses regular optical fibers to transmit the quantum data.

The feat 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 in Scientific advances.

Co-lead author Dr Sarah Thomas, from the Department of Physics at Imperial College London, said: “Interconnecting two key devices is a crucial step forward in enabling the creation of quantum networks, and we are very excited to be the first team to have achieved it.” able to prove it.”

Co-first author Lukas Wagner of the University of Stuttgart added: “Enabling long-distance locations, and even quantum computers, to connect is a critical task for future quantum networks.”

long distance communication

In common telecommunications, such as the Internet or telephone lines, information can be lost over long distances. To combat this, these systems use ‘repeaters’ at regular points, which read and re-amplify the signal, ensuring it reaches its destination intact.

Classical repeaters, however, cannot be used with quantum information, since any attempt to read and copy the information would destroy it. This is an advantage in one sense, since quantum connections cannot be “exploited” without destroying information and alerting users. However, it is a challenge that needs to be addressed for long-distance quantum networks.

One way to overcome this problem is to share quantum information in the form of entangled light particles or photons. Entangled photons share properties such that one cannot be understood without the other. To share entanglement over long distances through a quantum network, two devices are needed: one to create the entangled photons and another to store them and allow them to be recovered later.

There are several devices used to create quantum information in the form of entangled photons and store it, but generating these photons on demand and having a compatible quantum memory in which to store them eluded researchers for a long time.

Photons have certain wavelengths (which, in visible light, create different colors), but the devices to create and store them are often tuned to operate at different wavelengths, preventing them from interacting.

To make the devices interact, the team created a system in which both devices used the same wavelength. A “quantum dot” produced (non-entangled) photons, which were then passed to a quantum memory system that stored the photons within a cloud of rubidium atoms. A laser turned the memory on and off, allowing photons to be stored and released on demand.

Not only did the wavelength of these two devices match, but it had the same wavelength as the telecommunications networks used today, allowing it to be transmitted with normal fiber optic cables familiar to everyday Internet connections.

European collaboration

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

While quantum dots and stand-alone quantum memories have been created that are more efficient than the new system, this is the first proof that devices can be made that interact at telecommunications wavelengths.

The team will now look to improve the system, including making sure all photons are produced at the same wavelength, improving the length of time photons can be stored, and making the entire system smaller.

However, as a proof of concept, this is an important step forward, says co-author Dr Patrick Ledingham from the University of Southampton. “Members of the quantum community have been actively trying this link for some time. This includes us, who have tried this experiment twice before with different memories and quantum dot devices, for more than five years, which shows how difficult it is to do.”

“The big breakthrough this time was bringing in experts to develop and execute each part of the experiment with specialized equipment and working together to synchronize the devices.”