Scientists Discover Hidden Topological Universe Inside Entangled Light
A team of physicists has uncovered a hidden topological structure within one of the most widely used sources of quantum entanglement.
Researchers from the University of the Witwatersrand in South Africa, working together with scientists from Huzhou University, have identified an unexpected property in a widely used quantum optics technique. Experiments that routinely generate entangled photons in laboratories appear to contain hidden topological structures.
The team reports the highest level of topology observed in any physical system so far: structures spanning 48 dimensions and more than 17,000 distinct topological signatures. This vast set of patterns could function as a powerful new framework for encoding quantum information in ways that remain stable even in the presence of noise.
Hidden topology inside quantum light
In most quantum optics laboratories, entangled photons are produced using a process called spontaneous parametric downconversion (SPDC). This method naturally generates entanglement in the spatial properties of light. By examining these spatial degrees of freedom, the researchers discovered that the structure of entangled light contains previously unnoticed high-dimensional topologies.
These structures offer a new way to represent and protect information in quantum systems, potentially helping quantum signals resist noise and interference. The team demonstrated these features using the orbital angular momentum (OAM) of light, which can exist in two-dimensional states as well as in far higher-dimensional configurations.
The study, published in Nature Communications, shows that measuring the orbital angular momentum of two entangled photons reveals a topological structure embedded within the entanglement itself. Because OAM can assume an unlimited range of values, the possible topological configurations are also effectively limitless. “We report a major advance in this work: we only need one property of light (OAM) to make a topology, whereas previously it was assumed that at least two properties would be needed – usually OAM and polarization,” says Professor Andrew Forbes, from the Wits School of Physics.
“The consequence is that since OAM is high-dimensional, so too is the topology, and this let us report the highest topologies ever observed.” The researchers also found that once the topology extends beyond two dimensions, it can no longer be described with a single number. Instead, a range of topological numbers is required, reflecting the greater complexity that appears in higher-dimensional systems.
A universal resource in quantum optics
One of the most practical aspects of the discovery is that the necessary ingredients are already present in many existing laboratories. The experimental setup relies on resources that are standard in quantum optics research, meaning that scientists do not need specialized engineering systems to explore these effects. Pedro Ornelas explains, “You get the topology for free, from the entanglement in space. It was always there, it just had to be found.”
Prof. Robert de Mello Koch, lead author from Huzhou University explains further, “In high dimensions, it is not so obvious where to look for the topology. We used abstract notions from quantum field theory to predict where to look and what to look for – and found it in the experiment!”
Orbital angular momentum entanglement has long been investigated in many quantum experiments. However, its practical use has been limited because the quantum states can be fragile and sensitive to disturbance. The researchers now suggest that studying OAM entanglement through the lens of topology could provide a way to overcome that limitation. By focusing on these deeper structural features, scientists may open new paths toward stable quantum technologies capable of operating reliably outside laboratory conditions.
Source: SciTechDaily
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