Scientists from South Africa’s University of the Witwatersrand, in collaboration with collaborators from Huzhou University, have discovered a surprising feature in one of the most widely used tools in quantum optics. They discovered that standard methods of producing entangled photons may involve topological structures never seen before. In their experiments, these structures reached a record 48 dimensions and contained more than 17,000 different topological features, creating a vast new “alphabet” for encoding stable quantum information.
Most quantum optics labs generate entangled photons using a technique called spontaneous parametric downconversion (SPDC). This process creates a natural entanglement in the spatial properties of light. Researchers have discovered hidden regions of higher-dimensional topology within this spatial structure. These complex patterns could provide new ways to store and protect information and make quantum systems more noise-tolerant.
The research team demonstrated this effect using the orbital angular momentum (OAM) of light. OAM can range from simple two-dimensional cases to very high dimensions. This flexibility allows for a much richer set of structures than previously realized.
Topology emerges from a single property
The survey results are nature communicationswe show that measuring the OAM of two entangled photons reveals a unique topology, a fundamental feature of entanglement itself. Because OAM can take on an unlimited range of values, the associated topology can also be extended to very high dimensions.
Professor Andrew Forbes, from the Wits School of Physics, said: “We report a major advance in this research. Only one optical property (OAM) is required to create the topology, whereas previously it was thought that at least two properties were required, usually OAM and polarization.” “As a result, because OAM is high-dimensional, the topology is also high-dimensional, so we can report the best topology ever observed.”
The researchers also discovered that once the topology exceeds two dimensions, it can no longer be explained by a single number. Instead, a set of topological values is required that reflects a much richer and more complex structure than standard optical systems.
Discoveries hidden in plain sight
One of the most notable aspects of this breakthrough is its accessibility. The necessary resources already exist in most quantum optics labs, and no special equipment or “quantum engineers” are required to take advantage of the effects.
Pedro Ornelas explains, “You can get topology for free from Entanglement of the Universe. It’s always been there, you just had to find it.”
Guided by theory, confirmed by experiment
According to lead author Robert de Melo Kok, a professor at Huzhou University, identifying these structures was not easy. “In higher dimensions, it’s not so obvious where to look for topology. We used the abstract concepts of quantum field theory to predict where and what to look for, and we found it in experiments.”
Towards more robust quantum technology
Orbital angular momentum entanglement has been widely studied but has been considered fragile. Researchers now suggest that looking at it through a topological lens could change that view. By leveraging these newly discovered structures, scientists can develop more reliable quantum systems, potentially opening the door to practical real-world applications.
