Researchers from Sorbonne University in Paris have achieved a highly efficient transfer of quantum entanglement into and out of two quantum memory devices. This achievement brings a key ingredient for the scalability of a future quantum internet.

A quantum internet that connects multiple locations is a key step in quantum technology roadmaps worldwide. In this context, the European Quantum Flagship Programme launched the Quantum Internet Alliance in 2018. This consortium coordinated by Stephanie Wehner (QuTech-Delft) consists of 12 leading research groups at universities from eight European countries, in close cooperation with over 20 companies and institutes. They combined their resources and areas of expertise to develop a blueprint for a future quantum internet and the required technologies.

A quantum internet uses an intriguing quantum phenomenon to connect different nodes in a network together. In a normal network connection, nodes exchange information by sending electrons or photons back and forth, making them vulnerable to eavesdropping. In a quantum network, the nodes are connected by entanglement, Einstein’s famous “spooky action at a distance.” These non-classical correlations at large distances would allow not only secure communications beyond direct transmission but also distributed quantum computing or enhanced sensing.

Optical computing, which uses photons instead of electrons, has been one of the great promises of this field for decades.

According to Moore’s law —actually more like a forecast, formulated in 1965 by Intel co-founder Gordon Moore— the number of transistors in a microprocessor doubles about every two years, boosting the power of the chips without increasing their energy consumption. For half a century, Moore’s prescient vision has presided over the spectacular progress made in the world of computing. However, by 2015, the engineer himself predicted that we are reaching a saturation point in current technology. Today, quantum computing holds out hope for a new technological leap, but there is another option on which many are pinning their hopes: optical computing, which replaces electronics (electrons) with light (photons).

The end of Moore’s law is a natural consequence of physics: to pack more transistors into the same space they have to be shrunk down, which increases their speed while simultaneously reducing their energy consumption. The miniaturisation of silicon transistors has succeeded in breaking the 7-nanometre barrier, which used to be considered the limit, but this reduction cannot continue indefinitely. And although more powerful systems can always be obtained by increasing the number of transistors, in doing so the processing speed will decrease and the heat of the chips will rise.

The hybridization of electronics and optics

Hence the promise of optical computing: photons move at the speed of light, faster than electrons in a wire. Optical technology is also not a newcomer to our lives: the vast global traffic on the information highways today travels on fibre optic channels, and for years we have used optical readers to burn and read our CDs, DVDs and Blu-Ray discs. However, in the guts of our systems, the photons coming through the fibre optic cable must be converted into electrons in the microchips, and in turn these electrons must be converted to photons in the optical readers, slowing down the process.