Physicists from the University of Southampton and ETH Zürich have reached a new threshold of light-matter coupling at the nanoscale.

The international research, published this week in Nature Photonics, combined theoretical and experimental findings to establish a fundamental limitation of our ability to confine and exploit light.

The collaboration focussed on photonic nano-antennas fabricated in ever reducing sizes on the top of a two-dimensional electron gas. The setup is commonly used in laboratories all over the world to explore the effect of intense electromagnetic coupling, taking advantage of the antennas? ability to trap and focus light close to electrons.

Professor Simone De Liberato, Director of the Quantum Theory and Technology group at the University of Southampton, says: "The fabrication of photonic resonators able to focus light in extremely small volumes is proving a key technology which is presently enabling advances in fields as different as material science, optoelectronics, chemistry, quantum technologies, and many others.

"In particular, the focussed light can be made to interact extremely strongly with matter, making electromagnetism non-perturbative. Light can then be used to modify the properties of the materials it interacts with, thus becoming a powerful tool for material science. Light can be effectively woven into novel materials."

Scientists discovered that light could no longer be confined in the system below a critical dimension, of the order of 250nm in the sample under study, when the experiment started exciting propagating plasmons. This caused waves of electrons to move away from the resonator and spill the energy of the photon.

Experiments performed in the group of Professors Jéréme Faist and Giacomo Scalari at ETH Zürich had obtained results that could not be interpreted with state-of-the-art understanding of light-matter coupling. The physicists approached Southampton?s School of Physics and Astronomy, where researchers led theoretical analysis and built a novel theory able to quantitatively reproduce the results.

Professor De Liberato believes the newfound limits could yet be exceeded by future experiments, unlocking dramatic technological advances that hinge on ultra-confined electromagnetic fields.

"It has been said that proofs of impossibility are only proofs of a lack of imagination," he explains. "This is not the first time that a 'fundamental limit' on how tightly we can focus light has been discovered. The most famous is the Abbe diffraction limit, from 19th century German physicist Ernst Abbe, which says light can't be confined in a volume smaller than a cubic wavelength.

"Nanophotonics is a very active and successful field of research that is studying different ways to break out of Abbe limit. I think the next step will be to use some ingenuity and look for novel ways to confine light, bypassing both Abbe limit and the one we have just discovered."

A ground-breaking innovation in quantum hardware has secured investment to spin out from the University of Southampton.

Aquark Technologies, launched by former postgraduate research students Dr Andrei Dragomir and Dr Alexander Jantzen, has created a miniaturised cold atom system following years of research.

Unlike modern electronics, which rely on the manipulation of electrons, quantum devices tap into and manipulate the wave-like properties of atoms and tiny changes in their energy levels. These devices use a cold atom chamber in which to manipulate the individual atoms.

Aquark Technologies' key innovation, the Aquark Cube, miniaturises the cold atom chamber by a factor of 100 to make this incredible, complex technology into a simple, portable plug-and-play system.

Andrei's postgraduate research focused on the miniaturisation of quantum systems in the School of Physics and Astronomy before continuing as a Research Fellow in the Quantum, Light and Matter Group. Alex, meanwhile, completed his PhD in optoelectronics focused on maturing early-stage optical technology for commercial use and joined Aquark from another successful Southampton spinout.

Dr Dragomir says: "Quantum technology has for many years offered increased performance over conventional technology, but it has been complicated to achieve and so applications have been limited. Mostly the tech has stayed hidden in research labs around the world; we want to make cold-atoms practical and accessible for wider use.

"By controlling a cloud of atoms at a temperature near absolute zero we can take extremely precise measurements for time, acceleration, gravity and rotation. As such, using this technology we could, for example, create a global navigation system that is accurate without a satellite connection."

Andrei believes the idea could replace bulky, power hungry and complicated sensors that are used regularly in laboratory environments. He adds: "Our core invention is a miniaturised cold atom system that reduces system size from that of an entire lab to the palm of a hand. This huge miniaturisation step will enable the commercialisation of all sensors, accelerating the development and capabilities of quantum technologies. Sensors made with cold atom systems at their core have been shown to significantly surpass their classical counterparts."

Aquark is one of a cohort of the University's most promising startups that unveiled technologies at a Demo Day for the Future Worlds on-campus accelerator on 10th June 2020. The spinout has received investment from angel investors in the Future Worlds network.

James Vernon, Aquark investor and Southampton alumnus, says: "Aquark's unique approach leverages novel research from the University of Southampton with the potential to unlock world-changing opportunities in the quantum market. As investors we are delighted to work with the team on what promises to be a very exciting journey ahead."

Professor Mark Sullivan, Head of Physics and Astronomy, says: "I'm hugely enthusiastic to see our fundamental research in quantum technologies translated into new commercial applications. Southampton's vibrant spirit of entrepreneurship provides an excellent platform to launch successful spinout companies to apply our world leading research to solve ambitious commercial challenges."

Diana Galpin, Director of Enterprise and Knowledge Exchange at the University, says: "It is great to see Aquark Technologies successfully spinout following the recent support from Research and Innovation Services (RIS), Space Research and Innovation Network for Technology (SPRINT), Seraphim Space Camp and EPSRC Impact Acceleration Account (IAA). Aquark Technologies is a promising company, and its enabling technology is poised to make a significant impact in the commercialisation of quantum technologies. We look forward to Aquark's continued success."

Ben Clark, Director of Future Worlds, says: "The founders pitching at Demo Day addressed some of the biggest challenges and most exciting opportunities in the world. Investors were impressed by the bold visions and world-changing potential they discovered. The investment in Aquark Technologies is an embodiment of the investors' belief in that potential."