An experiment has shown that quantum teleportation and classical communication signals can coexist in the same optical cable. Researchers from Northwestern University in the United States have successfully transmitted quantum states invisibly for 30 kilometers using ordinary optical cables. This brings new possibilities for the combination of quantum communication and existing Internet optical cables, and greatly simplifies the infrastructure required for distributed quantum sensing or computing applications. The relevant paper was published in the latest issue of the journal Optics.

Quantum teleportation is only limited by the speed of light, allowing for almost instantaneous communication. This process utilizes quantum entanglement technology, which means that two particles, no matter how far apart they are, can exchange information without physical transmission.

In optical communication, all signals are converted into light. The traditional signal of classical communication is usually composed of millions of light particles, while quantum information uses a single photon.

Traditionally, it is believed that a single photon would be “submerged” in a fiber optic cable carrying millions of optical particles for classical communication. It’s like a thin bicycle struggling through a narrow tunnel filled with speeding heavy trucks.

However, researchers have found a way to help fragile photons avoid busy “traffic”. After in-depth research on how light scatters in optical cables, researchers have discovered a less crowded wavelength of light to accommodate photons. Then, they added special filters to reduce noise from regular Internet traffic.

To test this new method, researchers set up a 30 kilometer long optical cable with one photon at each end. Then, they send quantum information and regular Internet traffic through this optical cable at the same time. Finally, they measured the quality of quantum information at the receiving end while executing the teleportation protocol. The results show that quantum information can be successfully transmitted even when the Internet traffic is busy.

Research has shown that quantum teleportation can provide secure quantum connections between geographically distant nodes, and next-generation quantum networks and traditional networks can share the same optical fiber.

Next, the researchers plan to extend the experimental distance and use two pairs of entangled photons to demonstrate entanglement swapping, which is an important milestone in achieving distributed quantum applications.