The new dual-frequency Paul trap developed by physicists at JGU and Helmholtz Institute Mainz can capture heavy calcium ions or light electrons.
Photo Credit: © Hendrik Bekker, JGU
Scientific Frontline: Extended "At a Glance" Summary: Dual-Frequency Paul Trap for Antihydrogen Synthesis
The Core Concept: The dual-frequency Paul trap is an advanced radiofrequency trap designed to capture and confine particles with vastly different mass profiles—such as heavy ions and light electrons—within the same apparatus.
Key Distinction/Mechanism: Unlike conventional Paul traps that operate on a single frequency and are limited to holding one particle type, this new apparatus utilizes a multi-layered printed circuit board (PCB) architecture. It generates both gigahertz (GHz) and megahertz (MHz) frequency fields simultaneously, allowing it to accommodate both low-mass particles (requiring high-frequency fields) and high-mass particles (requiring lower-frequency fields) in a single confinement zone.
Major Frameworks/Components:
- Layered PCB Architecture: Three stacked printed circuit boards separated by ceramic spacers to house the distinct electromagnetic fields.
- Coplanar Waveguide Resonator: Situated on the central board to generate the GHz-frequency field necessary for confining low-mass particles like electrons or positrons.
- Segmented DC Electrodes: Positioned on the top and bottom PCBs to apply the MHz-frequency field required for trapping heavy particles like calcium ions or antiprotons.
- Photo-Ionization Laser Scheme: A two-step laser system (using 423 nm and 390 nm wavelengths) utilized to ionize neutral atoms and generate the required particles for capture.
Branch of Science: Experimental Physics, Particle Physics, and Antimatter Research.
Future Application: The primary technological trajectory is the simultaneous trapping of antiprotons and positrons to successfully synthesize antihydrogen atoms. Additionally, the trap enables the experimental testing of theoretical physics models, such as analyzing the brief binding of positrons to atoms.
Why It Matters: The reliable synthesis of antihydrogen represents a "Holy Grail" in antimatter research. Because its counterpart, regular hydrogen, is the most thoroughly researched atom in physics, antihydrogen provides a perfectly simple and highly stable platform for precise comparative measurements, potentially unlocking answers to fundamental cosmological questions regarding matter-antimatter asymmetry.
Heavy calcium ions or light electrons captured in the same trap
A new type of radiofrequency trap can capture particles with extremely different requirements and could theoretically hold both types of particles at the same time. Researchers in the group of Professor Dmitry Budker from the PRISMA++ Cluster of Excellence and the Helmholtz Institute at Johannes Gutenberg University Mainz (JGU) were able to trap calcium ions or electrons in the same apparatus. The team’s findings, published in Physical Review A, show the potential of this technology for synthesizing antihydrogen.
“Radiofrequency traps, also called Paul traps, have long been used by physicists to trap specific particles,” Dr. Hendrik Bekker explained. “However, they are usually limited to a single frequency.” This means that only one type of particle can be captured at a time in a typical Paul trap. To synthesize antihydrogen, however, two types of particles – antiprotons and positrons – would need to be trapped together at the same time. Due to their low mass, positrons require GHz-frequency fields for stable confinement, while antiprotons are typically trapped with MHz-frequency fields. For their current study, the researchers at JGU used electrons and heavy calcium ions (\({^{40}\mathrm{Ca}}^{+}\)) as more readily available for stand-ins for antiprotons and positrons.
Catching two birds in the same cage
To trap the calcium ions and electrons, the dual-frequency Paul-trap, which is being developed in collaboration with Professor Ferdinand Schmidt-Kaler from JGU as well as the group of Professor Hartmut Häffner at UC Berkeley, must generate both GHz and MHz frequency fields. Hendrik Bekker and PhD candidate students Vladimir Mikhailovski and Natalija Rajeshri Sheth generate these fields by layering three printed circuit boards (PCB) and separating them with ceramic spacers. The central board is equipped with what is known as a coplanar waveguide resonator which generates the GHz frequency field to trap electrons. The top and bottom PCBs feature 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 nm and 390 nm).
The particles are then caught in the dual-frequency trap for various amounts of time, from milliseconds to several seconds, before extracting them via DC voltage pulses and detecting them. Bekker: “Using this technique, we stored electrons or ions. Trapping both at the same time proved challenging.” Electrons turn out to be highly sensitive to the amplitude of the lower-frequency field used for trapping the ions. The higher the amplitude, the more electrons are lost from the trap. Ions, on the other hand, have proven to be effectively unaffected by the amplitude of the high-frequency field.
Further challenges are posed on the mechanical side: roughness of surfaces, mechanical misalignments, and dielectric charging currently limit the effectiveness of the trap. Next-generation equipment will feature laser-etched, smoother electrodes with better thermal stability.
Diversifying the creation of antihydrogen
The ultimate goal of the researchers is to use their new dual-frequency trap to hold both antiprotons and positrons in order to combine them into antihydrogen. Currently, the only source for antiprotons, and thus antihydrogen, is the Antimatter Factory (AMF) at CERN in Switzerland. Bekker: “Antihydrogen is a kind of Holy Grail in antimatter research. Its uniquely simple makeup – just one antiproton and a positron – means we can generate it relatively easily compared to other antimatter.” And since its counterpart, hydrogen, is well-researched, measurements taken from antihydrogen have a strong point of comparison. The transport of antiprotons has recently been proven to work, which means that the chance of this becoming a reality rises. Professor Dmitry Budker is optimistic: “The recent success in transporting antiprotons using a truck has shown that delivering antiprotons to researchers far from CERN is feasible, although there are still technical challenges such as long-term cryogenic cooling to solve.”
Along with their own open questions and challenges, Dr. Hendrik Bekker and his team also look forward to scientific work along the way. “While we develop our trap further, we will be able to run a number of fascinating experiments,” said Bekker. “For example, theoretical physics tells us that positrons should be able to bind to atoms – even if for the briefest of moments. We might be able to test that theory in an experimental setting for the first time.”
Published in journal: Physical Review A
Title: Trapping of electrons and \({^{40}\mathrm{Ca}}^{+}\) ions in a dual-frequency Paul trap
Authors: Vladimir Mikhailovskii, Natalija Sheth, Guofeng Qu, Michal Hejduk, Niklas Vilhelm Lausti, K. T. Satyajith, Christian Smorra, Günther Werth, Neha Yadav, Qian Yu, Clemens Matthiesen, Hartmut Häffner, Ferdinand Schmidt-Kaler, Hendrik Bekker, and Dmitry Budker
Source/Credit: Johannes Gutenberg University Mainz
Reference Number: phy041026_01
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