Quantum electrodynamics verified with exotic atoms

An international collaboration of researchers, including the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) has succeeded in a proof-of-principle experiment to verify strong-field quantum electrodynamics ...
The group's results are a significant step toward verifying fundamental physical laws under , which humankind has not yet been able to create artificially. The highly efficient and accurate X-ray energy determination method using state-of-the-art quantum technology demonstrated in this research is expected to be applied to various research fields, such as non-destructive elemental analysis methods using muonic atoms.

It has always been a dream of scientists to discover physical laws. They have been found or proposed to explain observed phenomena that cannot be understood by existing theories. In many cases, the discovery of new physics requires the development of new experimental techniques and improved accuracy of measurements. The most precisely tested theory of physical laws is Quantum ElectroDynamics (QED), which describes the microscopic interactions between charged particles and light. Scientists are constantly pushing the limits of how far QED accurately describes our physical reality.
In this paper, the collaboration injected a low-velocity negative muon beam from the J-PARC facility into , and the energy of characteristic X-rays emitted from the resulting muonic neon (Ne) atoms was precisely measured using a superconducting Transition-Edge Sensor (TES) detector. By taking full advantage of the excellent 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 contributions from vacuum polarization in strong-field quantum electrodynamics were successfully verified with a high precision of 5.8 %.

Conceptual diagram showing muonic atoms and quantum electrodynamic (QED) effects Credit: RIKEN

Figure 1. Conceptual diagram showing muonic atoms and quantum electrodynamic (QED) effects. In a muonic atom, the negative muon (μ^-) is bound to the nucleus and orbits around it. According to quantum electrodynamics, the bound negative muon continues its orbital motion while repeatedly emitting and absorbing virtual photons (self-energy: SE ). In addition, there is an electrostatic attraction between the neon nucleus (Ne^10+) and the negative muon, and the photons propagating through this interaction continuously repeat the creation and annihilation of virtual electron-positron (e^±) pairs (vacuum polarization: VP ). In this study, we precisely measured the energy of muonic characteristic X-rays emitted when the negative muon deexcites to a lower state. Credit: Okumura et al

Figure 2. Spectrum of emitted muonic characteristic X-rays emitted from muonic neon atoms (a) Muonic characteristic X-rays emitted from muonic neon atoms appearing around 6300 eV at a neon gas target pressure of 0.1 atm. This peak is formed by the superposition of six different transitions. The peak energy was determined to an accuracy of 0.002% by fitting with respect to each contribution. (b) The residuals (difference between theoretical and measured values) from the fitting. The residuals are sufficiently small, indicating that the fitting was done with high accuracy. Credit: Okumura et al

Figure 3. Dependence of muonic characteristic X-ray energy on neon gas pressure and comparison with the latest theoretical calculation. Credit: Okumura et al