Researchers from Wits University and Universitat Autònoma de Barcelona show how controlling the structure of photons in space and time enables tailored quantum states for next-generation communication, sensing and imaging. Credit: Wits University

Researchers demonstrate that by shaping the spatial and temporal structure of photons, they can engineer customized quantum states suited for next-generation communication, sensing, and imaging technologies.

Researchers at the School of Physics at Wits University, working with colleagues from the Universitat Autònoma de Barcelona, have shown that quantum light can be shaped across space and time to produce quantum states with many dimensions. Their findings demonstrate that structured photons, which are photons whose spatial, temporal or spectral features are intentionally controlled, provide promising new options for high-capacity quantum communication and emerging quantum technologies.

The work appears in a review article in Nature Photonics, where the authors examine the rapid growth of methods used to generate, adjust, and measure quantum structured light. These methods include on-chip integrated photonics, nonlinear optical processes, and multiplane light conversion, all of which now form a versatile and increasingly powerful set of tools. Collectively, these improvements are pushing structured quantum states closer to practical use in areas such as imaging, sensing, and future quantum networks.

Two Decades of Transformation

According to Professor Andrew Forbes, corresponding author from Wits, the field has changed dramatically in two decades. “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.”

A key benefit of structuring photons is the ability to access high-dimensional encoding alphabets, enabling more information per photon and greater resilience to noise. This makes quantum structured light a promising platform for secure quantum communication.

However, the authors note that some real-world channels are still unfavorable to spatially structured photons, limiting long-distance transmission compared to more traditional degrees of freedom such as polarization. “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.”

Topological Approaches and Robust Quantum States

One emerging approach is to imbue quantum states with topological properties, offering inherent robustness to perturbations. “We have recently shown how quantum wave functions naturally have the potential to be topological, and this promises the preservation of quantum information even if the entanglement is fragile,” says Forbes.

The review article also documents rapid developments in multidimensional entanglement, ultrafast temporal structuring, nonlinear quantum detection schemes, and on-chip sources that can generate or process quantum light at higher dimensions than previously possible. Applications highlighted include high-resolution quantum imaging, precision metrology using structured photons, and quantum networks capable of carrying more information through multiple coupled channels.

The research points to an inflection point for the field. As the authors conclude, the future for quantum optics with quantum structured light “looks very bright indeed”—but further work is needed to increase dimensionality, boost photon numbers, and engineer states that survive realistic optical environments.

Reference: “Progress in quantum structured light” by Andrew Forbes, Fazilah Nothlawala and Adam Vallés, 21 November 2025, Nature Photonics. DOI: 10.1038/s41566-025-01795-x

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