In a breakthrough for antimatter research, CERN scientists have successfully maintained an antiproton in a state of oscillation between two distinct quantum states for nearly a minute while it was trapped.
Performed under the BASE experiment, this achievement marks the first demonstration of an antimatter quantum bit, or qubit, and paves the way for substantially improved comparisons between the behaviour of matter and antimatter.
The demonstration also paves the way for substantially improved tests of nature’s fundamental symmetries.
How do antiprotons behave?
Particles such as the antiproton, which has the same mass but opposite electrical charge to a proton, behave like miniature bar magnets that can “point” in one of two directions depending on their underlying quantum mechanical spin.
Measuring the way these so-called magnetic moments flip, using a technique called coherent quantum transition spectroscopy, is a powerful tool in quantum sensing and information processing.
It also enables high-precision tests of the fundamental laws of nature, including charge-parity-time symmetry. This symmetry rules that matter and antimatter behave identically, which is at odds with the observation that matter vastly outweighs antimatter in the Universe.
Preserving quantum coherent transitions
Particles have quantum characteristics that defy our common sense, such as the characteristic of interfering with themselves, as demonstrated in the double slit experiment. Interactions with the surrounding environment can quickly suppress these interference effects through a process known as quantum decoherence.
Preserving coherence is essential for controlling and tracking the evolution of quantum systems, like the transitions between the spin states of a single antiproton.
Although coherent quantum transitions have been observed before in large collections of particles and trapped ions, they have never been seen for a single free nuclear magnetic moment until now.
CERN researchers achieved this using a sophisticated system of electromagnetic traps to give an antiproton the right “push” at the right time. Since this swing has quantum properties, the antimatter spin-qubit can even point in different directions at the same time when unobserved.
Identifying magnetic moments of protons and antiprotons
The experiment studied antiprotons produced at CERN’s antimatter factory by storing them in electromagnetic Penning traps and feeding them one by one into a second multi-trap system to, among other things, measure and change their spin states.
Any slight difference in their magnitudes would break charge-parity-time symmetry and point to new physics beyond the Standard Model of particle physics.
“This represents the first antimatter qubit and opens up the prospect of applying the entire set of coherent spectroscopy methods to single matter and antimatter systems in precision experiments,” explains BASE spokesperson Stefan Ulmer.
“Most importantly, it will help BASE to perform antiproton moment measurements in future experiments with 10- to 100-fold improved precision.”
The future of antimatter research
While qubits are the basic building blocks of quantum computers, where they allow information to be stored not just in one of two states but via a potentially limitless superposition of those states, the antimatter qubit demonstrated by BASE is unlikely to have immediate applications outside fundamental physics.
An even bigger leap in the precision of antiproton measurements is expected using BASE-STEP, which was designed to allow trapped antiparticles to be transported by road to magnetic environments that are “calmer” than the antimatter factory.
Barbara Latacz, who led the research, concluded: “Once it is fully operational, our new offline precision Penning trap system, which will be supplied with antiprotons transported by BASE-STEP.
“This 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.”
