A breakthrough experiment led by a team from the University of Stuttgart in Germany brings a quantum internet a step closer, with physicists teleporting a quantum state between photons produced by separate light sources for the first time.
The achievement allows engineers to bounce quantum information through repeating stations consisting of 'quantum dots' over long distances without loss or disruption.
Sending signals over a distance puts it at risk of losing critical elements of information. In a standard broadband internet cable, light signals carrying data are boosted using amplifiers, but boosting quantum information requires sources of light that can produce virtually identical photons.
Special semiconductors that emit photons with a high level of control could do the job. Known as quantum dots, they are able to emit light waves at incredibly precise frequencies, making photons from different dots impossible to tell apart.
Related: Quantum Teleportation Was Achieved Over The Internet For The First Time
Researchers have now teleported quantum information between photons from two separate quantum dots, proof that this can indeed work as a way of keeping quantum data safe and secure across networks.
"For the first time worldwide, we have succeeded in transferring quantum information among photons originating from two different quantum dots," says physicist Peter Michler, from the University of Stuttgart.
While teleportation is the term quantum physicists use for these kinds of experiments, what's actually being transferred here is a quantum state – there aren't actually any photons popping out of existence in one place and materializing in another.
For a quantum state to be transferred between a pair of photons, the two particles must be in a fuzzy quantum form. More importantly, they must be otherwise indistinguishable.
These qualities can be achieved easily when they share the same source. Yet different sources risk producing photons with subtly different characteristics.
Quantum dots restrict these characteristics, allowing teleportation to occur between completely separate locations using different sources.
What's more, the experiments run by the researchers used a standard optical fiber cable like those used in online networks today. The use of existing infrastructure is going to be key to getting the quantum internet up and running.
"Transferring quantum information between photons from different quantum dots is a crucial step toward bridging greater distances," says Michler.
Scientists are still figuring out how much of the quantum internet might rely on our existing technology, but the quantum layer will be essential for security and integrity – if we're able to get it working across long enough distances. The setup for the current study involved an optical fiber around 10 meters (nearly 33 feet) in length.
There's lots more work to do, and the researchers are keen to increase the distance that this can work over, as well as improve the teleportation success rate, which currently stands at a little over 70 percent.
"These results demonstrate the maturity of quantum dot-based technology, showing an important building block for future quantum communication," the researchers conclude.
The research has been published in Nature Communications.