Conceptual illustration of an entangled Skyrmion topology. Each photon contributes to the formation of an emerging topology that exists only as a combined entity of two photons. Credit: University of the Witwatersrand.
For the first time, the researchers demonstrated the extraordinary ability to perturbate spatially separated but interconnected pairs of quantically entangled particles without altering their shared properties.
The team includes researchers from the Structured Light Laboratory (School of Physics) at the University of the Witwatersrand in South Africa, led by Professor Andrew Forbes, in collaboration with Robert De Mello Koch (formerly from the University of the Witwatersrand) at Huzhou University in China.
We achieved this experimental milestone by entangling two identical photons and customizing the wave function they share, i.e., their topology or structure only becomes apparent when the photons are treated as a unified entity," explains lead author Pedro Ornelas, a master's student in the Structured Light Laboratory.
This connection between photons is established through quantum entanglement, often referred to as "ghosting at a distance", which enables particles to influence each other's measurements, even at great distances. The study was published in the journal Nature Photonics on January 8, 2024.
In this work, the role of topology and its ability to retain properties can be likened to how a coffee cup is reshaped into the shape of a doughnut;Although the appearance and shape change during the transformation, the singular holes, a topological feature, remain unchanged and unchanging. In this way, the two objects are topologically equivalent. "The entanglement between our photons is malleable, like clay in the potter's hands, but during the molding process, some features are preserved," Forbes explains.
The properties of the topology studied here, known as Skyrmion topology, were first explored by Tony Skyrme in the 1980s as a field configuration to display particle-like features. In this case, topology refers to a global property of a field, similar to a piece of fabric (wave function), whose texture (topology) remains unchanged regardless of which direction it is pushed.
Since then, these concepts have been realized in modern magnetic materials, liquid crystals, and even as optical analogues using classical laser beams. In the field of condensed matter physics, sgormions are highly regarded for their stability and noise immunity, leading to breakthroughs in high-density data storage devices. "We aspire to see our quantum entanglement sigminons have a similarly transformative impact," Forbes said.
Previous studies have described these skyrmions as confined to one location. "Our work presents a paradigm shift: topologies that were traditionally thought to exist in a single local configuration are now non-local, or shared between spatially separated entities," Ornelas said.
On the basis of this concept, researchers use topology as a framework to classify or distinguish entangled states. They envision that "this new perspective could serve as a labeling system for entangled states, similar to the alphabet," said co-researcher Dr. Isaac Nape.
Similar to spheres, doughnuts and handcuffs that are distinguished by the number of holes they contain, our quantum sgmions can be distinguished by their topological aspects in the same way," Nape said. The team hopes this could be a powerful tool to pave the way for new quantum communication protocols that use topology as an alphabet for quantum information processing across entanglement-based channels.
The findings reported in the article are crucial because researchers have been working for decades to develop techniques to protect entangled states. The fact that the topology remains intact even with entanglement attenuation suggests a potential new encoding mechanism that utilizes entanglement, even with minimal entanglement failure of traditional encoding protocols.
We will focus our research on defining these new protocols and expanding the landscape of topological non-local quantum states," Forbes said.
More information: Pedro Ornelas et al., Nonlocal Skyrmions as a Topological Elastic Quantum Entangled State of Light, Nature Photonics (2024). doi： 10.1038/s41566-023-01360-4