Quantum precision measurement advances in experimental test of time-reversal symmetry

A team of Prof. Zhengtian Lu at the University of Science and Technology of China (USTC) has made the first measurement of the intrinsic electric dipole moment of ytterbium-171 atoms (Yb-171) using the laser cold-atom method, and obtained an upper limit of the electric dipole moment less than 1.5 x 10-26e cm, and set an upper limit on the Schiff's moment of the Yb-171 nucleus. The results, entitled "Measurement of the Electric Dipole Moment of171Yb Atoms in an Optical Dipole Trap," were published on August 19 in Physical Review Letters [Phys. Rev. Lett. 129, 083001, (2022)].

EDM violates time-reversal symmetry

Spin is prevalent in atoms and nuclei, and the flow of charges in a spinning atom forms a coil, resulting in the intrinsic magnetic dipole moment of the atom, which is a familiar endogenous property of atoms. However, do the positive and negative charges within an atom separate along the spin direction to produce an intrinsic electric dipole moment? Since Zhengdao Li and Chen-Ning Yang proposed the idea of cosmic non-conservation in the 1950s, people have been searching for the intrinsic electric dipole moments of particles, nuclei and atoms. This physical phenomenon breaks both spatial inversion symmetry (i.e., "cosymmetry") and temporal inversion symmetry, and is closely related to fundamental physical problems such as CP breaking and matter-antimatter asymmetry. Particle physics theory postulates that the study of electric dipole moments is a promising pathway to new physics beyond the Standard Model, and generations of experiments have been searching for electric dipole moment signals for half a century, with increasing precision, but so far all measurements have yielded only upper limits.

Schematic diagram of the experimental scheme

The intrinsic electric dipole moment of an atom causes the spin-in frequency to vary depending on the applied electric field. Researchers at the Chinese University of Science and Technology (CSU) have used a laser to cool and imprison Yb-171 atoms and observe the spin-in phenomenon of atoms in optical traps. They developed a quantum non-destructive measurement method for atomic spin states using the principle of embellished light, which greatly improves the measurement efficiency of spin states by suppressing the technical noise in the measurement to below the quantum projection noise limit. At the same time, the coherence time of the spin-feed is increased to more than 300 s, and finally a measurement accuracy of the order of 100 nHz is achieved for a spin-feed frequency of 15 Hz. With the significant improvement in accuracy, the researchers observed the cosmic mixing effect in the optical trap for the first time and successfully suppressed the systematic errors associated with the optical trap by precise manipulation of the optical trap.

Tao Zheng and Yang Yang, PhD students of NSRM, are the co-first authors of the paper, and Dr. Tim Xia and Prof. Zhengtian Lu are the co-corresponding authors. This research work was supported by the National Natural Science Foundation of China, the Chinese Academy of Sciences Pioneer Program, and Anhui Province.

Link to the paper：

https://link.aps.org/doi/10.1103/PhysRevLett.129.083001