Recently, the Institute of Precision Measurement Science and Technology Innovation of the Chinese Academy of Sciences has cooperated with Australian and Canadian scientists to realize the precision calculation of the "invisible" atomic phantom zero wavelength, opening up a new method for testing the theory of quantum electrodynamics.
Quantum electrodynamics (QED) is a fundamental physical theory that describes the electromagnetic interaction between particles and is the cornerstone of the development of modern physics. Rigorous testing of QED theory helps to determine fundamental physical constants, explore the properties associated with nuclei, and explore new physics beyond the Standard Model. Therefore, since the QED theory was proposed nearly 80 years ago, people's tests of QED theory have never stopped. So far, the methods tested by QED theory have been the precise determination of the abnormal magnetic moment of electrons, but there are few studies of the precision spectra of electron atoms and molecules.
This time, Tang Liyan, researcher of the Atomic and Molecular Field Theory Group of the Institute of Precision Measurement Science and Technology Innovation of the Chinese Academy of Sciences, and Associate Researcher Zhang Yonghui cooperated with the Australian National University and the University of Windsor in Canada to realize the accurate calculation and precision measurement of the 413nm (nanometer) phantom zero wavelength of helium atoms, and opened up a new way to test QED theory by "invisible" atomic phantom zero wavelength precision measurement. The results of the research were published in the journal Science.
Image from Science
Different from the traditional energy spectrum measurement method for testing QED theory, this study uses the phantom zero wavelength of "stealth" atoms to test QEDs. Phantom zero wavelength refers to the fact that when the laser wavelength is modulated to a specific frequency, the Stark frequency of the individual energy states of the atom is shifted to zero, and the atom is invisible in the laser field.
The above-mentioned Chinese and foreign teams have changed the spatial oscillation frequency of Bose Einstein condensates in magnetic traps to measure the optical dipole potential by changing the spatial oscillation frequency of bose Einstein condensates in magnetic traps, and combined with high-precision atomic structure theory calculations, a new test of QED theory at the level of one part in three millions has been realized. The K. Baldwin Experimental Group of the Australian National University completed the experimental measurement of the phantom zero wavelength, and the team of the Institute of Precision Surveying of the Chinese Academy of Sciences and the Professor G.W.F. Drake of the University of Windsor were responsible for the theoretical calculations.
Experimental protocol, picture from the Institute of Precision Measurement Science and Technology Innovation, Chinese Academy of Sciences
The scheme of using phantom zero wavelength to test the theory of atomic QED was first proposed by Tang Liyan and Professor J. Mitroy of Charles Darwin University in Australia in 2013. In 2015, the K. Baldwin experimental team at the Australian National University worked with a theoretical team to achieve experimental measurements of helium atoms at a phantom zero wavelength of 5 ppm (a negative hexagon of ppm of 10, or one part per million) accuracy. There was a 134 ppm difference between experimental measurements and theoretical predictions at the time. In order to reveal this difference, the theoretical team independently developed a series of high-precision atomic structure calculation methods, realized the theoretical prediction of the accuracy of 0.1ppm level, and played a role in promoting a new round of international cooperation.
Since 2019, theoretical and experimental teams have collaborated again. This time, the researchers used the most sensitive method of measuring the light dipole potential to identify the peak potential energy of only 10 to the minus 35th power joule (J), and realized the experimental determination of the "invisible" helium atom phantom zero wavelength accuracy of up to 0.35 ppm, and the measurement accuracy was 20 times higher than that of the 2015 experiment. At the same time, the delay effect and the correction of the susceptibility to the phantom zero wavelength are theoretically calculated precisely, with an accuracy of 10 ppb (ppb is 10 to the power of negative 9, that is, one part of a billion). Through the comparison of experimental measurements and theoretical calculations, the sensitivity of phantom zero wavelength to QED correction and delay effects is confirmed, which confirms the theoretical predictions proposed by Tang Liyan and J. Mitroy.
The comparison between experimental uncertainty and theoretical calculation error, as well as the contribution of various corrections in theoretical calculation, is from the Institute of Precision Measurement Science and Technology Innovation of the Chinese Academy of Sciences
In the future, the measurement accuracy of the above experiments is expected to increase by an order of magnitude to the level of 30ppb. Under this precision, on the one hand, it can broaden people's understanding of QED theory, on the other hand, it may detect the relevant effects of atomic nuclei, which opens up a new research window for exploring the properties of nuclear structure from the perspective of "invisible" atoms.