Physics World Top 10 Breakthroughs of the Year 2025 for coherent control of antimatter

Imperial physicists are part of an international team behind one of Physics World’s Top 10 Breakthroughs of the year 2025, awarded to the BASE experiment at CERN.

The Baryon Antibaryon Symmetry Experiment (BASE) was recognised for being the first to achieve coherent control of the spin of a single trapped antiproton. The experiment represents a major advance in antimatter physics and our ability to perform precision tests of the fundamental laws that govern the universe.

These findings, first published last year in Nature, were recognised as one of Physics World’s annual Top 10 Breakthroughs in early December.

Controlling a single antiproton

Particles such as the antiproton, which has the same mass but opposite electrical charge to a proton, behave like magnets that can “point” in one of two directions depending on the direction of their quantum spin.

Spin is a fundamental property in quantum mechanics and determines a particle’s magnetic behaviour, so controlling it is essential for precision measurements of a particle’s magnetic properties.

In the award-winning experiment, researchers demonstrated for the first time that they could precisely control the spin of an individual antiproton, holding it stable long enough to perform multiple “flips” of the spin direction.

To achieve this, the team trapped the antiproton inside a cryogenic Penning trap, where it could be isolated from external disturbances and held for months or years. Using finely tuned electromagnetic fields, they induced Rabi oscillations, making the spin flip back and forth between its two states in a controlled and repeatable way.

In quantum mechanics, this is called a two-level system, the simplest possible quantum system with only two states. "Some of the earliest experiments in quantum science involved achieving a high degree of control over the direction of spins in atoms and molecules” says BASE member and Imperial researcher Dr. Jack Devlin. “Now, for the first time, the BASE team have been able to do the same for an antiproton."  

Crucially, the team were able to demonstrate that the antiproton’s spin remained coherent for more than 50 seconds, long enough to observe multiple oscillations between the two spin states.

This new technique promises at least 16-fold improved measurements of the antiproton magnetic properties. In the long term, this promises dramatic improvements in determining the antiproton g-factor, one of the most precisely testable quantities in particle physics.

Testing the Standard Model

The BASE experiment tackles one of the biggest unanswered questions in physics: why the universe contains far more matter than antimatter. According to the Standard Model, matter and antimatter should have been created in almost equal amounts during the Big Bang, yet today antimatter is extremely rare.

By trapping a single antiproton and measuring its magnetic properties with record breaking precision, the team has taken a major step toward testing whether matter and antimatter are truly identical, as theory predicts. Any tiny difference between these properties could point to a new physics beyond the Standard Model and help explain why matter came to dominate the universe.

 “This opens up the prospect of applying the entire set of coherent spectroscopy methods to single matter and antimatter systems in precision experiments.” says BASE founder and spokesperson Prof. Stefan Ulmer from Heinrich Heine University Düsseldorf. “Most importantly, it will help BASE to perform antiproton moment measurements in future experiments with 10- to 100-fold improved precision.”

Achieving this level of control over antimatter is extremely challenging and represents both a fundamental advance in knowledge and a technical milestone in precision quantum experiments.

A successful year for BASE

The 2025 Physics World recognition caps off a particularly successful year for the BASE collaboration. In a separate breakthrough, the BASE-STEP team led by Dr. Christian Smorra also demonstrated the first transportable trap for antimatter.

In this first demonstration, protons were loaded into a trap, lifted by crane, driven around CERN for four hours, and then successfully returned to the antimatter factory.

This confirms the feasibility of transporting antiprotons to low-noise laboratories with stable magnetic fields, enabling even more precise measurements in the future.

About the BASE collaboration

The BASE collaboration was established in 2012 and is 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: RIKEN, Wako, Japan; Max Planck Institute for Nuclear Physics, Heidelberg, Germany; European Organisation for Nuclear Research (CERN), Geneva, Switzerland; Heinrich Heine University Düsseldorf, Germany; Leibniz University Hanover, Germany; National Metrology Institute of Germany (PTB), Braunschweig, Germany; Swiss Federal Institute of Technology in Zurich, Switzerland; GSI Helmholtz Centre for Heavy Ion Research GmbH, Darmstadt, Germany; Imperial College London, UK; Johannes Gutenberg University Mainz, Germany; The University of Tokyo, Japan.

Imperial has been a collaborating institute in BASE since 2022. Current members involved in this research include Jack Devlin, BASE member since 2018, and Natakala Dakshesh, who is currently working on an upgrade to the cryogenic and electronic components of the experiment at CERN. The links between BASE and Imperial physics are part of a wider programme of research in Quantum Tests of Fundamental Physics underway in the Physics Department, which uses advanced quantum techniques to probe the most basic principles of nature, and forms a key part of QuEST, Imperial’s Centre for Quantum Engineering, Science and Technology.