Researchers in Germany have moved closer to synthesizing antihydrogen after successfully confining heavy calcium ions and lightweight electrons within the same trap, despite their vastly different requirements.

The team, led by Dmitry Budker, PhD, a researcher and physics professor at the Johannes Gutenberg University Mainz (JGU Mainz), developed a dual frequency trap that can successfully confine the two particle types at the same time.

“Radiofrequency traps, also called Paul traps, have long been used by physicists to trap specific particles,” Hendrik Bekker, PhD, a senior scientist at the Helmholtz Institute in Mainz, said. “However, they are usually limited to a single frequency.”

The find could enable antihydrogen production outside of facilities like CERN, as creating it requires trapping antiprotons and positrons simultaneously. CERN’s Antimatter Factory (AMF) is currently the only lab in the world that produces and traps significant amounts of antihydrogen for research.

A dual-frequency design

Particle traps, often called Paul traps, are used to confine charged particles using oscillating electric fields in three-dimensional space. However, these systems run at a single frequency, which limits them to trapping one type of particle at a time.

This poses a challenge for antimatter research, as creating antihydrogen requires bringing together antiprotons and positrons, which differ in mass and behavior.

Due to their low mass, positrons need high-frequency (gigahertz) fields to remain stable. Meanwhile, antiprotons are confined using much lower frequencies in the megahertz range.

To address the challenge, the team engineered a trap capable of generating both frequency regimes. The scientists used electrons and heavy calcium ions as more readily available stand-ins for antiprotons and positrons.

For the fields, Bekker and his colleagues layered three printed circuit boards (PCB) and separated them with ceramic spacers. The central board featured a coplanar waveguide resonator that produces the GHz frequency field required for tapping electrons.

The top and bottom PCBs had segmented DC electrodes used to apply the lower MHz frequency field used for catching ions. Both types of particles are generated by photo-ionizing neutral calcium atoms using a two-step laser scheme (423 and 390 nanometers).

Inside the trap

Bekker said the particles are caught in the dual trap for milliseconds or seconds and are then extracted with DC pulses for detection. “Using this technique, we stored electrons or ions,” he stressed. “Trapping both at the same time proved challenging.”

While the team successfully trapped electrons and ions separately, keeping both in the trap at the same time remained a challenge. Electrons are sensitive to the amplitude of the lower-frequency field used for ions, with higher amplitudes leading to significant losses.

Ions, by contrast, appear largely unaffected by the high-frequency field. Moreover mechanical limitations such as surface roughness, slight misalignments, as well as dielectric charging effects can also reduce trapping efficiency.

Despite the difficulties, the team aims to use the trap to combine antiprotons and positrons into antihydrogen. “Antihydrogen is a kind of Holy Grail in antimatter research,” Bekker stared.

“Its uniquely simple makeup, just one antiproton and a positron, means we can generate it relatively easily compared to other antimatter,” he added. Moreover, the concept could also be utilized to explore other fundamental questions.

“For example, theoretical physics tells us that positrons should be able to bind to atoms – even if for the briefest of moments,” Bekker concluded in a press release. “We might be able to test that theory in an experimental setting for the first time.”

The study has been published in the journal Physical Review A.

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