Publication in the scientific journal “Nature”: Milestone in antimatter research
23.07.2025 |
This news is based on a press release by Heinrich-Heine-University Düsseldorf (HHU)
The BASE collaboration at the European Organization for Nuclear Research CERN in Geneva has achieved a breakthrough in antimatter research: For the first time, the researchers were able to let a single antiproton – the antimatter counterpart of a proton – oscillate between two spin quantum states in a controlled manner for almost a minute. The collaboration includes scientists from numerous international institutions, including researchers from Heinrich Heine University Düsseldorf (HHU) and GSI/FAIR. The study, which has now been published in the journal Nature, marks the world’s first realization of an antimatter quantum bit (qubit for short). “This is a milestone that will enable much more precise tests of fundamental symmetries in the future,” says HHU physics professor and BASE spokesperson Stefan Ulmer.
Compared to a proton, antiprotons have the same mass but the opposite electrical charge. Both particles behave like miniature rod magnets. Their so-called spin – comparable to a compass needle – points in one of two directions. The precise measurement of the associated magnetic moment, in particular a controlled “flipping” of the spin, is one of the central tools of modern quantum measurements. It enables high precision tests of fundamental laws of nature.
The study presented in Nature used the method of “coherent spin quantum transition spectroscopy”. This enables the high-precision manipulation and observation of individual spin states. The measurements are motivated by tests of the so-called CPT symmetry (charge, parity, time reversal) which requires that matter and antimatter – apart from their opposite charges – behave in exactly the same way. As a consequence, they should also appear with the same quantity in our universe. However, the real world shows a considerable asymmetry: it consists almost entirely of matter. This is still an unsolved mystery of modern physics.
So far, such coherent quantum transitions have been observed, for example, in macroscopic particle ensembles or in the hyperfine structure of stored ions. The BASE collaboration has now for the first time demonstrated and observed such coherent flips of a single free nuclear spin of an antiproton – which is an enormous physical and technical challenge.
“A good analogy for this is a child’s playground swing,” explains BASE spokesperson Professor Stefan Ulmer from the Institute of Experimental Physics at HHU. “With the right push, the swing arcs back and forth in a perfect rhythm. In our case, the swing is the spin of a single antiproton, which we set into motion in a controlled manner using electromagnetic fields. On top of that, we achieved a coherence time of 50 seconds.”
The antiprotons, required for the experiment, were produced by CERN's Antimatter Factory (AMF) and stored in Penning traps - high-precision electromagnetic instruments for exact particle control. The antiprotons were then individually transferred to a separate multi-trap system in which their spin states could be measured and manipulated. “This is nothing else than a qubit based on a single antiproton spin,” emphasizes CERN scientist Dr. Barbara Maria Latacz, first author of the publication.
The BASE collaboration has previously been able to show that the magnitudes of the magnetic moments of protons and antiprotons are identical within a just few parts-per-billion. But is there still a tiny difference? An essential question, because even the slightest difference would break CPT symmetry and thus point to new physics beyond the Standard Model of particle physics. Dr. Christian Smorra from HHU: "At that time, however, incoherent spectroscopic methods were used, in which magnetic field fluctuations and technical perturbations affected the spin dynamics. This ultimately limited the accuracy."
Substantial upgrades of the experimental setup have now made it possible to systematically suppress these decoherence mechanisms and enable the first coherent spectroscopy of an antiproton spin. The research team thus not only created a stable antimatter qubit, but also unlocked new measurement methods.
“This work gives us the opportunity to apply the entire spectrum of coherent spectroscopy methods to single particles of antimatter for the first time,” emphasizes Ulmer, adding: “Specifically, we expect to be able to determine the magnetic moment of the antiproton with ten times improved precision in the future, and in the long term with up to a hundred times greater accuracy, for example in dedicated laboratories that we are currently developing at HHU.”
The next big leap is already planned: Using the newly developed BASE-STEP system, antiprotons will in future be transferred with transportable traps from the AMF to highly-stable precision laboratories. There, significantly longer spin coherence times can be achieved and thus a much higher measurement accuracy.
“Once it is fully operational, our new offline precision Penning trap system, which will be supplied with antiprotons transported by BASE-STEP, could allow us to achieve spin coherence times maybe even ten times longer than in current experiments, which will be a game-changer for baryonic antimatter research,” says Barbara Latacz.
GSI/FAIR is also involved in the BASE collaboration. For instance, the GSI/FAIR workshop under the direction of Markus Romig and Stephan Teich has manufactured precision components for the Penning trap setup, and Dr. Wolfgang Quint from the Atomic Physics Department of GSI/FAIR is supervising a PhD student who is working for BASE at CERN and whose position is funded by GSI/FAIR. (HHU/BP)
The BASE collaboration
Established in 2013 and based at the Antimatter Factory (AMF) at CERN, research institutes in Germany, Japan, the United Kingdom and Switzerland are involved in the collaboration. These include CERN – European Organisation for Nuclear Research, Geneva; ETH – Eidgenössische Technische Hochschule, Zürich; GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt; HHU – Heinrich Heine University Düsseldorf; ICL – Imperial College London; JGU – Johannes Gutenberg University Mainz; LU – Leibniz University Hannover; MPIK – Max Planck Institute for Nuclear Physics, Heidelberg: PTB – National Metrology Institute of Germany; RIKEN, Institute for Physical and Chemical Research, Wako, Japan; University of Tokyo. Professor Stefan Ulmer from the Institute for Experimental Physics at HHU and Chief Scientist at RIKEN in Japan, is the founder and spokesperson of the collaboration.
More information
Publication in the journal "Nature"