PhD defence: Spin-resolved Holography in Ultracold Sodium Gases Providing an insight into the magical world of spinor physics

PLEASE NOTE: The candidate gives a layman's talk, therefore the livestream will start fifteen minutes earlier.

To understand the world, we look at nature at its smallest scales. There, far below what we can see or touch, the familiar rules of everyday life no longer apply. Instead, matter and light follow a different set of laws called quantum mechanics. Once mainly a subject for theory, quantum mechanics now underpins most of modern technology and engineering, from computer chips, GPS clocks and lasers to MRI scanners, solar cells, and X-ray imaging.

Quantum effects are powerful but fundamentally difficult to study because they are small, weak, and fast. One of the key breakthroughs came just over a century ago, when Bose and Einstein predicted that when cooled to extremely low temperatures, millions of atoms could merge into a single quantum object called a Bose–Einstein condensate. This acts as a scaled-up version of a quantum system, a kind of quantum magnifying glass. It allows us to study the fundamental rules of the universe on objects the size of the dot at the end of this sentence.

One of the key areas such systems open up is magnetism, which arises from a tiny built-in magnetic property of atoms, which we call quantum spin. In everyday materials, these tiny magnetic effects combine to produce familiar magnetic behaviour, observed in permanent magnets on your fridge, as well in more complex electronic devices and magnetic storage. However, in typical materials, these microscopic processes are hidden inside solids and can usually only be studied indirectly. In Bose–Einstein condensates, spin becomes an active, observable part of the system, providing a clean and highly controlled way to study how magnetism emerges from quantum physics.

As part of my research, we developed a new non-destructive, spin-sensitive imaging technique. Beyond measuring the overall shape of the atomic cloud, it reveals its internal spin structure. Where researchers once had only a single black-and-white snapshot, we can now record a colour video that shows the quantum system in motion.