One of the biggest hurdles in building quantum networks is showing that quantum information can be transferred between devices that are not inherently compatible. But one Europe-wide research collaboration has now demonstrated teleportation between photons generated by two independent and physically dissimilar quantum dot emitters.

Quantum teleportation transfers the state of one quantum particle to another without physically sending the particle. Previously, all semiconductor quantum dot demonstrations have used a single emitter. In this work, the team demonstrated that two independent emitters, each with distinct electronic and optical properties, can be tuned and synchronized well enough to teleport a polarization qubit across a campus-scale network.

Professor Klaus Jöns of Paderborn University said the move from single to separate emitters is what elevates the work from a controlled research demonstration to a building block for true networks. 

“We used two remote quantum emitters. Beforehand, the same source was used for teleportation of a polarization state emitted by a quantum dot. Now we can actually separate the sources and harvest the idea of teleportation, that we can transmit quantum information over larger distances,” Jöns said. “That is the reason why this paper is such a milestone for quantum dots as sources for quantum networks and quantum communication.”

To make two naturally different emitters behave closely enough for teleportation, the researchers used advanced nanophotonic structures designed to boost photon output and tuning mechanisms to precisely match the color and properties of the photons each dot produced. They also applied external controls to align the two sources, a step that ensured their photons could interfere in the way the teleportation protocol requires.

The team conducted the experiment over a hybrid network with fiber links and a 270-meter free-space channel between two university buildings. They chose this path to mirror the conditions that future quantum communication systems will face.

“Free space quantum links suffer tremendously from environmental conditions such as heat, air quality, rain, and sunlight, thus it was very challenging to stabilize, synchronize, and maintain the link over long measurement times,” Jöns said.

“The main challenge was maintaining alignment and signal quality under real-world conditions,” said postdoctoral researcher Alessandro Laneve and Professor Rinaldo Trotta of Sapienza University of Rome, whose team coordinated and carried out the on-campus free-space experiment.

Synchronization is one of the toughest challenges in long-distance quantum communication. To keep the two emitters synchronized, the team used a GPS-disciplined oscillator that provided a precise frequency and time reference. That level of coordination enabled them to reach a teleportation fidelity of 82%, well past the classical threshold.

“Fidelity below the classical threshold would mean you could get the same results with classical particles. So it is mandatory to be above the classical threshold,” Jöns said.

“The teleportation protocol itself proved more resilient to loss and noise than direct photon transmission, helping us maintain high fidelity even in a challenging urban environment,” the Sapienza team added.

The next target is entanglement swapping between two remote quantum dots, a prerequisite for a functional quantum relay. 

“Swapping requires at least a four-photon coincidence measurement compared to three for teleportation, making it much harder,” Jöns said. He added that he expects continued improvements in emitter brightness and indistinguishability to make that possible, “hopefully next year.”

The milestone adds momentum to a broader architectural shift in the industry. IBM and Cisco recently emphasized that teleportation and entanglement distribution between separated systems will be essential for distributed quantum computing. 

The team’s results, published in Nature Communications, show that solid-state photonic sources are maturing in parallel, positioning the networking and computing stacks to meet in the middle as the first generation of quantum networks takes shape.