The University of Science and Technology of China has made progress in the experimental test of the symmetry of time inversion

Professor Lu Zhengtian’s team at the University of Science and Technology of China used the laser cold atom method to make the first measurement of the inherent electric dipole moment of the ytterbium-171 atom (Yb-171), obtained the upper limit of the electric dipole moment of less than 1.5 x 10-26e cm, and set the upper limit on the Schiff pole moment of the ytterbium-171 nucleus. The results were published in the Physical Review Letters on August 19.


The inherent electric dipole moment violates the symmetry of time inversion. Courtesy of The University of Science and Technology of China

The phenomenon of spin is common in atoms and nuclei, and the flow of charge in rotating atoms forms a coil, which produces the inherent magnetic dipole moment of the atom, which is a property we are familiar with in the atom. However, will the positive and negative charges inside the atom separate along the direction of the spin and produce an inherent electric dipole moment?

Since the 1950s, when Lee Jeong-do and Yang Zhenning proposed the idea of non-conservation of cosmology, people have begun to look for particles, nuclei and the inherent electric dipole moments of atoms. This physical phenomenon not only destroys the spatial inversion symmetry (i.e., the “cosmology”), but also destroys the time inversion symmetry, and is closely related to basic physical problems such as CP destruction and matter-antimatter asymmetry.

Particle physics theory speculates that electric dipole moment research is a promising way to explore new physics outside the Standard Model, and generation after generation of experiments for half a century have been looking for electric dipole moment signals, and the measurement accuracy has been continuously improved, but so far all measurements have only been capped.


Schematic diagram of the protocol. Courtesy of The University of Science and Technology of China

The inherent electric dipole moment of an atom causes the spin precession frequency to vary due to an applied electric field. Researchers at the University of Science and Technology of China used lasers to cool and imprison Yb-171 atoms and observe the spin precession of the primary quantum in the light trap. They used the principle of embellishment light to develop a quantum non-destructive measurement method for the spin state of atoms, which suppressed the technical noise in the measurement below the noise limit of quantum projection, thereby greatly improving the measurement efficiency of the spin state. At the same time, the coherence time of the spin precession is increased to more than 300 seconds, and the measurement accuracy of the spin precession frequency of 15 Hz is finally achieved in the order of 100 nanograms.

Under the premise of greatly improved accuracy, the researchers observed the cosmic mixing effect in the light trap for the first time, and successfully suppressed the systematic errors associated with the light trap through the precise manipulation of the light well.

Zheng Tao and Yang Yang, phD students of Hefei National Research Center for Physical Sciences at the Microscale, are the co-first authors of the paper, and Dr. Xia Tian and Professor Lu Zhengtian are co-corresponding authors. (Source: China Science Daily Wang Min)

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