CERN did something truly quantum with antimatter that was never pulled off before

Scientists from the BASE collaboration at CERN have achieved a major breakthrough in antimatter research by creating the first antimatter quantum bit, or qubit. In a paper published in Nature, the team explained how they kept a single antiproton switching smoothly between two quantum spin states for nearly a minute while it was held inside a trap.

An antiproton is the antimatter version of a proton. It has the same mass as a proton but the opposite electric charge. Like tiny magnets, antiprotons have a property called spin, which can point in one of two directions. Watching these spins change is important for quantum sensing and extremely precise measurements. It also helps scientists test whether matter and antimatter truly behave the same way under the laws of physics, including a principle known as CPT symmetry.

CPT symmetry is a fundamental principle in particle physics stating that the laws of physics remain unchanged if three transformations occur together: charge reversal (C), spatial inversion or parity flip (P), and time reversal (T). The Standard Model predicts that particles and antiparticles should have identical masses and lifetimes, differing mainly in charge-related properties. Experiments at CERN test CPT symmetry by comparing matter and antimatter with extreme precision.

To carry out the experiment, the researchers used a method called coherent quantum transition spectroscopy. This technique lets them study changes between spin states while reducing interference from outside noise. The same method is already used in fields such as metrology, quantum information processing, magnetometry, and precision tests of the Standard Model. Earlier experiments with protons and deuterons using this approach achieved maser spectroscopy measurements with sub-parts-per-trillion resolution.

In the past, this kind of spectroscopy was usually done using large groups of particles. The BASE team managed to do it with just one free nuclear spin. Using a cryogenic Penning-trap system, the researchers first measured the antiproton’s spin state through the continuous Stern–Gerlach effect. They then moved the particle into a precision trap with a very stable magnetic field, where they created and studied its coherent quantum behaviour using quantum-projection measurements.

For the first time, the team also observed Rabi oscillations in an antiproton spin. Rabi oscillations are the periodic transitions of a quantum system between two energy states when driven by an oscillating electromagnetic field at or near resonance. The oscillation frequency, called the Rabi frequency, depends on the strength of the interaction. This effect is central to quantum computing, magnetic resonance, and atomic physics because it enables precise control of quantum states in atoms, ions, and qubits.

In time-series measurements, they reached spin-inversion probabilities above 80% with spin coherence times of around 50 seconds. Tests of single-particle spin resonances showed inversions above 70%, while the transition linewidths were 16 times narrower than in earlier measurements. The main limit came from decoherence linked to cyclotron frequency measurements.

The BASE collaboration had already shown in earlier work that the magnetic moments of protons and antiprotons match to within a few parts per billion. According to Stefan Ulmer, future experiments could improve the precision of antiproton magnetic moment measurements by “10- to 100-fold improved precision”.

Even though qubits are best known as the basic units of quantum computers, this antimatter qubit is not expected to lead to immediate technology applications. Its real importance is in helping scientists study antimatter in much greater detail and compare it more accurately with ordinary matter.

Lead author Barbara Latacz said the team is also looking toward BASE-STEP, a system designed to transport trapped antiprotons into quieter magnetic environments. This could increase spin coherence times by as much as ten times compared with current experiments, which would be a major step forward for baryonic antimatter research.

By combining advanced quantum-control techniques with highly precise measurements, the BASE collaboration has pushed antimatter research into new territory and moved scientists closer to understanding why the universe appears to contain far more matter than antimatter.

Source: CERN, Nature

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