| Quantum coherence is a quantum interference phenomenon arising from the interaction between light and atoms,which has been the focus of attention during the development of quantum optics.The physical mechanism of quantum coherence is that different quantum transition channels can produce interference effects when the different quantum states are associated with action of coherent light.Owing to the optical response of the medium can be significantly changed by the quantum coherence effects,the effects are extensively employed in nonlinear optics,quantum state manipulation,quantum information storage,and quantum precision measurement.Rydberg atoms are high-excited atoms,whose electron is excited to a high quantum state with large principal quantum number n.It is an important research content in atomic and molecular physics due to the Rydberg atomic excellent characteristics of large radius,long radiation lifetime,large polarizability,transition dipole moment and strong interatomic interactions.In recent years,the study of quantum coherent system based on Rydberg atoms has attracted attention,which has brought new vitality in the fields of high precision spectroscopy,external field measurement and quantum sensing because of its superior advantages such as long coherence time,and extreme sensitivity to external fields.At present,the Rydberg atoms have become ideal mediums for analyzing various quantum coherence effects,and high-resolution Rydberg atomic coherence spectroscopy is an important technical tool for investigating the Rydberg atomic energy level structure,interactions between coherent fields,and precise measurements of external fields.In this paper,we construct Rydberg atomic systems of multiple energy level structures and focus the studies of high-resolution multi-energy Rydberg atomic coherence spectroscopy,and weak external field measurements traceable to the International Standard System of Units.The main research contents and innovations are as follows:1、The quantum coherence effects are theoretically analyzed by the Rydberg atomic system models of multiple energy level structures by using the atomic density matrix theory.The Rydberg atomic system models of multiple energy level structures are established.The steady-state solution and Rydberg atomic polarizability corresponding to each energy level structure when the system is in equilibrium are obtained by solving the density matrix equations.The theoretical simulations of the coherence spectra in the Rydberg atomic systems of different energy level structures are realized.2、The high-resolution coherent spectra of Rydberg atoms are obtained experimentally by constructing Rydberg atomic systems of multiple energy level structures.The Rydberg atoms are obtained by two-photon transition,and the coherent spectra are obtained by the interaction of two different microwave fields with the Rydberg atoms.In the experiment,the basic properties of Autler-Townes effect and coherent population transfer effect are investigated,and the effects of the microwave field power and frequency on the coherent spectra are analyzed.With the optimal experimental parameters,the transfer efficiency of the coherent population transfer effect can be increased to 2.9%.3、The resolutions of Rydberg atomic coherence spectra under weak field conditions are improved experimentally by multi-microwave-assisted quantum coherence effects.The effects of two microwave field powers on the resolution of the Rydberg atomic coherence spectra under weak field conditions are investigated.With the optimal power ratio between auxiliary microwave field and target microwave field,the measurements of target microwave field strength below 0.20 m V cm-1 can be achieved.The minimum measurable field strength of this method is about 6.71V cm-1,which is an improvement of about 33 times compared to the case without an auxiliary microwave field. |
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