Exotic Atoms Successfully Employed to Authenticate Quantum Electrodynamics

by Amir Hussein
5 comments
Quantum Electrodynamics Verification

Muonic atoms and quantum electrodynamic (QED) effects demonstrated in a conceptual illustration. Credit: RIKEN

A multinational research team, featuring participants from the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), has achieved a groundbreaking experiment to confirm strong-field quantum electrodynamics in exotic atoms, as detailed in a recent paper published in Physical Review Letters. This landmark success was realized via the high-precision examination of the energy spectrum of characteristic X-rays radiated from muonic atoms, utilizing a complex X-ray detector.

The accomplishment of this experiment signifies a vital step forward in the substantiation of core physical laws within the scope of intense electric fields, a domain humans have yet to synthetically create. The highly accurate and efficient technique for determining X-ray energy, shown through state-of-the-art quantum technology in this study, is predicted to be employed across different research sectors, like non-destructive elemental analysis procedures using muonic atoms.

Scientific exploration to unearth physical laws has long been a pursuit of researchers. These laws have been discovered or suggested to explicate observed phenomena that existing theories cannot comprehend.

Often, unearthing new physics necessitates the innovation of fresh experimental methods and enhanced accuracy of measurements. Quantum ElectroDynamics (QED), the theory that illustrates the microscale interactions between charged particles and light, is the most rigorously tested physical law. Researchers continually strive to test the boundaries of QED’s accuracy in describing our physical universe.

In the study, the collaborative team, inclusive of Dr. Takuma Okumura (former Postdoctoral Researcher at RIKEN, presently Assistant Professor at Tokyo Metropolitan University), Professor Toshiyuki Azuma (Chief Scientist, RIKEN), Dr. Tadashi Hashimoto (Assistant Principal Researcher at Japan Atomic Energy Agency), Visiting Researcher Hideyuki Tatsuno of Tokyo Metropolitan University, Associate Professor Shinya Yamada of Rikkyo University, Professor Paul Indelicato of the Kastler-Brossel Laboratory, Professor Tadayuki Takahashi of Kavli IPMU, the University of Tokyo, Professor Koichiro Shimomura of Institute for Materials Structure Science, KEK, Professor Shinji Okada of Chubu University, introduced a slow-moving negative muon beam from the J-PARC facility into neon gas. The energy of the characteristic X-rays emitted from the resulting muonic neon (Ne) atoms was accurately measured using a superconducting Transition-Edge Sensor (TES) detector.

Leveraging the exceptional energy resolution of the TES detector, the energy of the muonic characteristic X-rays was determined with an absolute uncertainty of less than 1/10,000, and the contributions from vacuum polarization in strong-field quantum electrodynamics were successfully verified with a high precision of 5.8 %.

The TES detector, initially designed for space X-ray observation, has been employed in unprecedented cross-disciplinary research led by Takahashi at Kavli IPMU. His research group comprises Kavli IPMU Project Assistant Professor Shin’ichiro Takeda, Project Researcher Miho Katsuragawa, and graduate student Kairi Mine, who participated in the muon experiments.

The collaboration’s demonstration of the experimental technique employing muonic atoms is anticipated to catalyze significant advancements in the investigation of QED verification within strong electric fields.

The details of the study were made available online (27 April 2023 Japan time) before its publication in the scientific journal Physical Review Letters (27 April 2023 Japan time).

Background

The influence of QED is more visible in strong electric field settings, but theoretical calculations become increasingly challenging in this scenario. Hence, the environment of a strong electric field is essential for QED validation.

For several years, experiments using highly charged ions (HCIs), or atoms that have lost multiple electrons, have been carried out as a strategy to establish a strong electric field environment. In HCIs, as the atomic number increases and more electrons are stripped off, the electric field experienced by the bound electrons strengthens and the shielding effect is reduced.

HCI research with large accelerators continues robustly. However, even for HCIs with large atomic numbers, the impact of the nucleus’s finite size cannot be disregarded. It has been suggested that this effect is not precisely known, and thus the accuracy of QED verification, which compares experimental results with theory, is substantially undermined.

Research Methodology and Results

International research groups have focused on “exotic atoms” to verify QED under strong electric fields differently than with HCIs. In these unique atoms, a negatively charged particle is bound to the nucleus in place of the electron. Of the various exotic atoms, muonic atoms consist of negative muons (fundamental particles about 200 times heavier than electrons) and nuclei. Negative muons can presently be extracted as beams from large accelerators.

Muonic atoms are distinct due to the exceptionally close proximity of the negative muon to the nucleus, with the bound muon’s orbital radius being roughly 1/200th that of a bound electron. This results in the muon experiencing an electric field about 40,000 times stronger than the electric field experienced by a bound electron of the same quantum level in an HCI, leading to a massive QED effect.

Additionally, utilizing negative muons, which occupy high angular momentum quantum levels with minimal overlap with the nucleus, it becomes possible to conduct experiments where the nucleus’s finite size’s effect is considerably suppressed. By accurately measuring the energy of muonic characteristic X-rays emitted when muonic atoms deexcite from a specific level to lower ones, QED can be verified under a strong electric field.

Therefore, muonic atoms present a promising experimental target for strong-field QED verification. Nevertheless, several challenges must be overcome. The most significant is that a considerable number of isolated muonic atoms must be prepared. The presence of other atoms or molecules near the muonic atoms might cause rapid electron transfer and alter the energy of the muonic characteristic X-rays. The solution is to use dilute gas targets with a low number density (low pressure), but this reduces the number of produced muonic atoms and the intensity of the resulting muonic characteristic X-rays.

The international research group carried out experiments at the Japan Proton Accelerator Research Complex (J-PARC) in Tokai-mura, Ibaraki, where the world’s most powerful slow-velocity muon beam is available. To ascertain energy with sufficient accuracy even with low-intensity muonic characteristic X-rays, the experiment was performed with a superconducting transition edge sensor (TES) microcalorimeter, a highly efficient and high-resolution X-ray detector.

Employing rare gas neon (10Ne) atoms as the target, they achieved an energy resolution ten times higher than that of traditional semiconductor detectors under dilute conditions of 0.1 atm and successfully measured the muonic characteristic X-rays. The displayed peaks primarily result from the overlap of muonic characteristic X-rays from six different transitions, and the energy of the muonic characteristic X-rays was determined with a high accuracy of 0.002% by analyzing contributions from each.

They performed the measurements at varying pressures of the neon gas target and confirmed that the energy of the muonic X-rays is constant within experimental error regardless of the neon gas target’s pressure, thus concluding that the muonic neon atoms were in an isolated environment.

They compared the latest theoretical calculations with the experimental results and confirmed

Frequently Asked Questions (FAQs) about Quantum Electrodynamics Verification

What was the primary aim of the international team of researchers’ experiment?

The main aim of this experiment was to verify strong-field quantum electrodynamics within exotic atoms. The researchers accomplished this through high-precision measurement of the energy spectrum of muonic characteristic X-rays.

Who were the key participants in this research?

Key participants included members from the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), Dr. Takuma Okumura, Professor Toshiyuki Azuma, Dr. Tadashi Hashimoto, and several other experts from various universities and institutes across the globe.

What is Quantum ElectroDynamics (QED)?

Quantum ElectroDynamics (QED) is the most precisely tested theory of physical laws, which describes the microscopic interactions between charged particles and light.

What are the implications of this successful experiment?

This successful experiment signifies a crucial advancement in the verification of key physical laws within the context of strong electric fields. The highly precise method for determining X-ray energy that was demonstrated in this study is expected to be utilized across various research areas.

What are muonic atoms and why are they important in this research?

Muonic atoms are exotic atoms composed of negative muons (elementary particles about 200 times heavier than electrons) and nuclei. They are important in this research because they experience an electric field about 40,000 times stronger than the electric field felt by a bound electron of the same quantum level in a highly charged ion. This results in a massive QED effect, which is essential for the verification of QED under strong electric fields.

What were the experimental methods used in this research?

The researchers used a low-velocity negative muon beam from the J-PARC facility injected into neon gas. The energy of characteristic X-rays emitted from the resulting muonic neon atoms was then precisely measured using a superconducting Transition-Edge Sensor (TES) detector.

What was the key finding of the research?

The team was able to precisely measure the energy of muonic characteristic X-rays with an absolute uncertainty of less than 1/10,000, and they successfully verified contributions from vacuum polarization in strong-field quantum electrodynamics with a high precision of 5.8%.

Where were the findings of this research published?

The findings were published in the scientific journal Physical Review Letters in April 2023.

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5 comments

EnergySpectrum July 15, 2023 - 1:56 am

This just goes to show how far we’ve come in terms of technology and scientific understanding. Exciting times we’re living in!

Reply
QuantumBob July 15, 2023 - 3:07 am

wow, thats some next level stuff right there. Never thought i’d see the day we could measure x-rays so precisely. Science is amazing!

Reply
PhysicsFan101 July 15, 2023 - 4:11 am

These scientists are doing some seriously cool stuff with muonic atoms. The future of quantum physics is here, people!

Reply
AtomicAva July 15, 2023 - 5:06 am

can’t wrap my head around this… Muonic atoms and x-rays. sounds like something out of a sci-fi movie! Keep pushing the limits, scientists!

Reply
EinsteinReturns July 15, 2023 - 11:00 am

i must say, I am very impressed by this. QED in strong electric fields… Didn’t think it would be possible to confirm it like this.

Reply

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