Quantum entanglement is often described as a mysterious link between particles, but new research shows it may be even richer than scientists once imagined.
A team of researchers from University of the Witwatersrand and Huzhou University has discovered that a very common form of entanglement used in quantum optics hides an astonishing number of complex geometric structures, known as topologies.
These hidden structures appear in systems that many quantum laboratories around the world already use every day.
By carefully analyzing entangled light, the researchers found that what was thought to be a relatively simple quantum resource actually contains thousands of distinct “topological signatures.”
In their experiments, they identified entanglement spread across 48 dimensions, revealing more than 17,000 different topological patterns—the highest number ever observed in any physical system.
Most quantum optics labs create entangled photons using a process called spontaneous parametric downconversion, or SPDC.
In this process, a single photon is split into two lower-energy photons that remain linked to each other. These photons are naturally entangled in their spatial structure—the way the light is shaped as it travels through space.
What the researchers discovered is that hidden inside this spatial entanglement is a deep and previously unseen topological structure.
Topology is the branch of mathematics that studies properties of shapes that remain unchanged even when they are bent or stretched. In physics, topology is valued because it can protect information from noise and disturbances.
To reveal this hidden structure, the team focused on a property of light called orbital angular momentum, or OAM.
Light with OAM twists as it travels, like a corkscrew, and unlike many other properties, OAM can take on an unlimited number of values. By measuring the OAM of two entangled photons, the researchers showed that the entanglement itself has a topological character.
Previously, scientists believed that creating optical topologies required combining at least two properties of light, such as OAM and polarization. This new work overturns that idea. The researchers demonstrated that OAM alone is enough to generate complex topology. Because OAM is inherently high-dimensional, the resulting topologies are also high-dimensional—and incredibly numerous.
Another surprising result is that once the system moves beyond simple, two-dimensional cases, topology can no longer be described by a single number. Instead, a whole collection of numbers is needed to fully describe the structure, revealing a much richer internal organization than previously known.
One of the most exciting aspects of the discovery is its practicality. The required tools and equipment are already available in standard quantum optics laboratories.
No exotic materials or specialized quantum devices are needed. The topology, as the researchers put it, comes “for free” with spatial entanglement—it was always there, simply unnoticed.
This finding could have major implications for quantum communication and computing. High-dimensional topological structures offer a huge “alphabet” for encoding information and could make quantum systems far more resistant to errors caused by noise or environmental disturbances.
By rethinking a familiar quantum resource from a topological perspective, the study opens new pathways toward robust, real-world quantum technologies—and shows that even well-known quantum systems can still hold remarkable hidden surprises.
