In collaboration with the Australian National University and the University of Windsor, Canada, tang Liyan, associate professor of Atomic and Molecular Field Theory at the Institute of Precision Measurement Science and Technology Innovation, Chinese Academy of Sciences, and Zhang Yonghui, associate professor of atomic and Molecular Field Theory at the Institute of Precision Measurement Science and Technology Innovation, Chinese Academy of Sciences, have recently realized the precise calculation and measurement of the phantom zero wavelength of helium atom at 413 nm. It opens up a new way to test quantum electrodynamics (QED) theory by precise measurement of phantom zero wavelength of “invisible” atom. Measurement of a Helium Tune-out Frequency: An Independent Test of Quantum Electrodynamics was published in The journal Science.

QED is a basic physical theory describing the electromagnetic interaction between particles, which is the foundation of modern physics development. Rigorous testing of QED theory has been ongoing since it was first proposed nearly 80 years ago, helping to determine fundamental physical constants, explore properties related to atomic nuclei, and explore new physics beyond the standard Model. So far, QED theory has been tested by precise determination of electron anomalous magnetic moment and precise spectral study of small electron atoms and molecules.

Unlike traditional energy spectrum measurement methods, which test QED theory, this study uses phantom zero wavelengths of “invisible” atoms to test QED. Phantom zero wavelength refers to the fact that when the laser wavelength is modulated to a specific frequency, the stark frequency shift of the individual atomic energy states is zero, and the atom is invisible in the laser field. The team achieved a new test of the QED theory at the 3 millionth level by changing the spatial oscillation frequency of the bose Einstein condensates of helium atoms in magnetic traps to measure the optical dipole potential, combined with high-precision atomic structure theoretical calculations. K. Baldwin experimental group of Australian National University completed the experimental measurement of phantom zero wavelength, while Liyan Tang, Yonghui Zhang and PROFESSOR G. W. F. Drake of University of Windsor, Canada were responsible for the theoretical calculation.

In 2013, professors J. Mitroy and Tang Liyan from Charles Darwin University in Australia proposed A new scheme of “using magic zero wavelength to test atomic QED theory” for the first time [Phys. Rev. A 88, 052515 (2013)]. Rev.lett. 115, 043004 (2015). Experimental measurements of helium atoms with a phantom zero wavelength of 5 PPM (~10-6) were performed by k. Baldwin experimental group and theoretical group in 2015. There was a gap of 134 PPM between experimental measurements and theoretical predictions at the time. In order to explain this difference, the theoretical team independently developed A series of high-precision atomic structure calculation methods, and realized the theoretical prediction with accuracy of 0.1ppm level [Phys. Rev. A 99, 040502(R) (2019)], which played A positive role in promoting A new round of international cooperation.

Since 2019, scientists have been working together to identify peak potential energies of only 10-35 J using the most sensitive method to date for measuring optical dipole potential (Figure 1), achieving an experimental determination of phantom zero wavelength accuracy of 0.35 PPM for “invisible” helium atoms, 20 times higher than the experimental measurement in 2015. Theoretically, the correction of the phantom zero wavelength by the delay effect and magnetic susceptibility is calculated accurately to the level of 10 PPB (~10-9). The comparison between experimental measurements and theoretical calculations confirms the sensitivity of phantom zero wavelength to QED correction and delay effect (FIG. 2), which confirms the theoretical prediction proposed by J. Mitroy and Tang Liyan. In the future, the experimental measurement accuracy is expected to be improved by an order of magnitude to the level of 30 PPB. Under this precision, on the one hand, scientists can broaden their understanding of QED theory, and on the other hand, nuclear related effects can be detected, which opens up a new research window for exploring nuclear structure and properties from the perspective of “invisible” atoms.

The research work was supported by the National Key RESEARCH and Development Program, the National Natural Science Foundation of China and the Strategic Priority Science and Technology Special Project of cas.

Paper Link & NBSP;

Experimental scheme. (A) The magnetically captured metastable HELIUM BEC condensates are illuminated with frequency-modulated probe light, and A series of atomic laser pulses are coupled from the BEC to sample the oscillations; (B) The average velocity Vx of each pulse in the X direction is used to track the oscillation over time (red dots) and to extract the oscillation frequency from the decaying sine wave fitting (solid lines); (C) The square of the frequency of the probe beam well is obtained by separate measurement of the magnetic trap frequency. The phantom zero wavelength is determined by linear fitting (solid black line) to find the intersection of the square of the frequency of the probe beam well and the X axis.

Comparison between experimental uncertainty and theoretical calculation error, and the contribution of various modifications in theoretical calculation & NBSP;