Quantum structured light could transform secure communication and computing

The researchers describe how controlling several properties of light at once, including polarization, spatial modes, and frequency, makes it possible to create high-dimensional quantum states. In this framework, standard qubits (two-dimensional, with photons in superposition of two quantum states) are replaced by qudits (with more than two dimensions). This shift greatly expands what quantum systems can do and opens new paths across many areas of science and technology.

In quantum communication, these high-dimensional photons increase security by packing more information into each particle of light. They also allow many communication channels to operate at the same time while improving tolerance to errors and background noise. For quantum computing, structured light can simplify circuit designs and speed up processing, while enabling the creation of complex quantum states needed for advanced simulations.

Advances in Imaging, Sensing, and Materials Research

Quantum structured light is also driving progress in imaging and measurement. Researchers point to improved resolution techniques -- such as the recent development of the holographic quantum microscope, which allows obtaining images of delicate biological samples -- along with extremely sensitive sensors that rely on quantum correlations. Beyond these applications, structured light can be used to simulate complex quantum systems, helping scientists model how molecules interact within networks and potentially guiding the discovery of new materials.

Two Decades of Rapid Progress

According to Professor Andrew Forbes, corresponding author from the University of the Witwatersrand, at Johannesburg, the field has evolved dramatically over the past 20 years. "The tailoring of quantum states, where quantum light is engineered for a particular purpose, has gathered pace of late, finally starting to show its full potential. Twenty years ago the toolkit for this was virtually empty. Today we have on-chip sources of quantum structured light that are compact and efficient, able to create and control quantum states."

Despite this momentum, challenges remain. "Although we have made amazing progress, there are still challenging issues," says Forbes. "The distance reach with structured light, both classical and quantum, remains very low, but this is also an opportunity, stimulating the search for more abstract degrees of freedom to exploit."

From Scientific Curiosity to Practical Tool

Researcher Adam Vallés, from the Optics Group of the UAB Department of Physics, says the field has reached a critical moment. "We are at a turning point: quantum structured light is no longer just a scientific curiosity, but a tool with real potential to transform communication, computing and image processing." Vallés emphasizes UAB's role as a major contributor to this progress through its collaboration with Forbes, citing "advances of great international impact, such as the stimulated teleportation of quantum information encoded in high dimensions, the design of laser cavities to generate complex states of high purity and, in the field of cryptography, the distribution of robust quantum keys in the face of obstacles that block communication channels."

A Global Collaboration Backed by Catalonia

The review article, featured as the cover article on the November 2025 issue of Nature Photonics, reflects a long-running partnership between Vallés and the structured light research group led by Forbes at the Faculty of Physics of the University of the Witwatersrand in Johannesburg, South Africa. The work was also supported by the Catalonia Quantum Academy (CQA), a collaborative initiative coordinated by the Institut de Ciències Fotòniques (ICFO) and promoted by the Government of Catalonia, which aims to strengthen education and talent development in quantum sciences and technologies across the region.