Quantum Precision Measurement Of The Electric Dipole Moment Of Ytterbium Atoms

CP violation is an essential phenomenon in particle physics,indicating matter and antimatter asymmetry.However,the magnitude of CP violation in the Standard Model of particle physics cannot explain the matter-antimatter asymmetry on a cosmic scale.Finding new sources of CP violation is a significant direction in the search for new physics beyond the Standard Model.CP violation can lead to permanent electric dipole moments(EDMs)in particles,representing an asymmetric charge distribution along the direction of particle spin.The expected values of EDMs in the Standard Model are far below current experimental sensitivities,while some extensions to the Standard Model provide larger expected values.Therefore,improving the experimental sensitivities of EDMs can search for new sources of CP violation beyond the Standard Model.The EDMs of diamagnetic atoms are mainly sensitive to the CP-violating effects of the hadronic and semileptonic types,such as the EDMs of quarks and the CP-violating pion-nucleon and electron-nucleus interactions.Measuring the EDMs of diamagnetic atoms can effectively limit the relevant CP-violating parameters.The goal of this study is to realize the precision measurement of the atomic EDM of optically trapped ytterbium-171(171Yb)atoms,with a sensitivity on the order of 10-27 e cm,and to limit the relevant CP-violating parameters.We aim to develop related techniques of quantum precision measurement to improve EDM sensitivity further.This study includes the laser cooling and trapping of ytterbium atoms,the realization of long-lived atomic confinement,the implementation of high-stability magnetic fields and high electric field strength,the efficient measurement of the ground-state nuclear spin of ytterbium atoms,and the observation of Larmor precession with long coherence time.We also aim to achieve coherent quantum control of the ground-state nuclear spin of ytterbium atoms and magnetic-field sensitivity beyond the standard quantum limit.To these ends,we have constructed two independent experimental setups for laser cooling and trapping of Yb atoms.We have achieved precision measurements of the EDM of 171Yb atoms based on laser cooling and trapping.Ytterbium atoms in a thermal atomic beam are firstly slowed using the technique of Zeeman slowing and then loaded into a two-stage magnetooptical trap and cooled to about 20μK.The cold atoms are transferred to an optical dipole trap and then transported to the position between a pair of high-voltage electrodes in a magnetically shielded area,where the electric field strength reaches 73 kV/cm.We develop a quantum non-demolition(QND)measurement method based on optical dressing,enabling quantum-projection-noise-limited detection of atomic nuclear spins.This QND measurement is based on the condition of the magic wavelength of the probe transition,which is first experimentally determined in this work.The atomic spins are initially polarized,and a Larmor precession phase is accumulated under two conditions with the electric field parallel or antiparallel with the magnetic field.Then the precession phase is determined by measuring the atomic spin states.The number of atoms in the experiment is about 5 × 104,and the duration of the Larmor precession is about 100 s.The experimental value of the EDM of 171 Yb atoms is measured to be dA(171 Yb)=(-6.8±5.1stat±1.2syst)× 10-27 e cm,and the resulting experimental upper limit is |dA(171Yb)|<1.5 × 10-26 e cm(95%confidence).In addition,to achieve EDM sensitivity at the quantum-projection-noise level,we plan to develop a 171 Yb/173Yb co-magnetometer to suppress the effect of magnetic field noise.Utilizing the a.c.Stark effect,we have realized coherent quantum control of the 1/2 nuclear spin of 171Yb atoms and the 5/2 nuclear spin of 173Yb atoms and prepared a Schrodinger’s cat state of the 5/2 nuclear spin.With the nuclear spin state prepared in the decoherence-free subspace,the cat state is immune to the decoherence effect of the optical trap.In a Ramsey experiment with the cat state,the decoherence time reached T2*=1.4(2)× 103 s,the longest lifetime among Schr(?)dinger cat states;the magneticfield sensitivity surpasses the standard quantum limit and reaches the Heisenberg limit.The techniques of quantum precision measurement of EDM developed in this work can be applied to other cold atom systels,such as the rare radioactive 225Ra atoms,whose expected value of EDM in the Standard Model is about three orders of magnitude higher than that of 171Yb.Furthermore,the method of the coherent quantum control of nuclear spin can be used to realize a dual-species cold-atom co-magnetometer,which can be used as a probe of new physics,such as testing Lorentz invariance or searching for EDM,fifth forces,and dark matter.