Physicists at the University of the Witwatersrand in South Africa, working with colleagues from the Universitat Autònoma de Barcelona, have demonstrated how light at the quantum level can be deliberately shaped in both space and time to create high-dimensional quantum states.
By carefully controlling a photon’s spatial pattern, arrival time, and spectrum, the researchers can engineer what are known as structured photons. These tailored particles of light could open the door to higher-capacity quantum communication and a new generation of quantum technologies.
Their work appears in a review published in Nature Photonics, which surveys the rapid progress in creating, manipulating, and measuring structured quantum light.
The paper highlights several powerful tools now driving the field forward, including on-chip integrated photonics, nonlinear optics, and multiplane light conversion. Together, these approaches are helping move structured quantum states from theoretical ideas and lab experiments toward practical systems for imaging, sensing, and quantum networking.
From a Nearly Empty Toolbox to Advanced Quantum Control
According to Andrew Forbes, the corresponding author of the study, the progress made in the past two decades has been dramatic.
“The tailoring of quantum states—where quantum light is engineered for a specific purpose—has accelerated significantly in recent years and is finally beginning to show its full potential. Twenty years ago, the toolkit for doing this was almost empty. Today we have compact, efficient on-chip sources of structured quantum light that can create and control complex quantum states.”
One major advantage of shaping photons is that it allows scientists to use high-dimensional encoding. In simple terms, each photon can carry more information and can be more resistant to noise and interference. This makes structured quantum light particularly promising for secure quantum communication.
Challenges for Long-Distance Communication
Despite these advances, practical challenges remain. Some communication channels do not transmit spatially structured photons very well, which limits how far these signals can travel compared with more conventional properties such as polarization.
“Although we have made remarkable progress, significant challenges remain,” Forbes explains. “The distance that structured light—both classical and quantum—can travel is still quite limited. But this also creates an opportunity, pushing researchers to explore new and more abstract degrees of freedom.”
One possible solution involves giving quantum states topological properties, which could help protect quantum information from disturbances.
“We have recently shown that quantum wave functions naturally have the potential to be topological,” Forbes says. “This could help preserve quantum information even when entanglement itself is fragile.”
Multidimensional Entanglement and Future Technologies
The review also highlights rapid advances in areas such as multidimensional entanglement, ultrafast temporal structuring, improved nonlinear detection methods, and compact on-chip devices capable of producing higher-dimensional quantum light than ever before.
These developments could eventually lead to ultra-high-resolution quantum imaging, extremely precise measurement systems, and quantum networks able to transmit far more data across multiple interconnected channels.
Overall, researchers believe the field is approaching a key turning point. Structured quantum light is expected to play an increasingly important role in quantum optics and technology. Still, further work is needed to increase the dimensionality of quantum states, boost photon production, and design systems robust enough to operate in real-world optical environments.
Quantum Optics: An Introduction
"...a genuinely interesting experiment in undergraduate education could be put together on the basis of Fox's textbook." Physics Today