原子nD里德堡态量子亏损的精密测量

Precision Measurements of Quantum Defects of Cesium nD Rydberg States

量子亏损是碱金属原子低轨道角动量的特有性质,它主要源于最外层电子轨道与离子实相互作用所引起的能量变化,导致碱金属低轨道角动量态的能量与氢原子相应能级相比产生较大的频移。在里德堡原子波函数的数值计算过程中,量子亏损会影响里德堡能级的精确值,从而影响波函数的计算精确度,对于里德堡原子的极化率计算、基于里德堡原子的微波电场测量等理论研究和实验测量精确度的提高有重要的意义。原子的电磁诱导透明效应(Electromagnetically-Induced-Transparency,EIT)提供了一种实现精密测量里德堡能级的技术手段。通过双光子激发方法将室温蒸汽池中的原子激发到里德堡态,利用电磁诱导透明光谱测量了nD_(5/2)和nD_(3/2)态(50≤n≤70)的精细结构分裂,进而拟合获得了原子nD里德堡态的量子亏损。通过分析里德堡原子nD态精细结构分裂的测量误差,去除了里德堡原子相互作用引起的能级频移,提高了里德堡nD态量子亏损测量的精确度。

Objective Quantum defect is a unique property of the low-orbit angular momentum of alkali metal atoms,which is mainly due to the energy change caused by the interaction between the outermost electron orbital and the ionic core,resulting in a large frequency shift between the energy of the low-orbit angular momentum state of alkali metal and the corresponding energy level of hydrogen atoms.In the numerical calculation of the Rydberg atomic wave function,the quantum defect affects the exact value of the Rydberg energy level,which in turn affects the calculation accuracy of the wave function.It is of great significance value of the Rydberg energy level,which in turn affects the calculation accuracy of the wave function.It is of great significance for both theoretical research and improvement of experimental measurement accuracy such as the calculation of polarizability of Rydberg atom and the measurement of microwave electric field utilizing Rydberg atom.Methods The electromagnetically-induced-transparency(EIT)of atoms provides an effective method to achieve precise measurement of the Rydberg energy level.EIT is a typical quantum interference effect,and the non-destructive detection of Rydberg atoms can be realized based on the EIT effect of the stepped three-level system.We used the double-sided band frequency stabilization technology based on ultra-stable cavity to detect the optical frequency locking to ensure the stability and accuracy of frequency measurement,and the atoms in the room temperature steam pool were stably excited to the Rydberg state by the twophoton excitation method,and the fine structure splitting of nD_(5/2)and nD_(3/2)states(50≤n≤70)had been measured by electromagnetic-induced transparency spectroscopy,and then the quantum defect of the Rydberg state of the cesium atom nD was obtained by fitting.The low-noise,narrow-linewidth laser system is the most important part of the experimental system.Reducing the frequency noise and intensity noise of the laser system is the basis for achieving highly sensitive fine structure measurements,and stable laser systems and accurate frequency scanning are the prerequisites for accurate measurements.In order to reduce the laser frequency noise,we use an active feedback scheme(PDH frequency stabilization)to suppress the frequency noise of the laser and improve the long-term stability of the laser.Then,two Fiber-Electro-Optical-Modulator(FEOM)are used to modulate the laser frequency in two stages,so that the laser frequency can be locked and a wide range of adjustment can be realized.In addition,we also analyzed the measurement error caused by the photoinduced AC-Stark frequency shift and the frequency shift caused by the strong interaction of Rydberg atoms,and optimized the influence of the strong interaction of cesium Rydberg atoms on the measurements,so as to accurately measure the quantum loss of the Rydberg state of the cesium atom nD.Results and Discussions By this method,we measure the quantum defect value aan of nDsn to be 2.47519(74),bsn to-0.21626(54),the quantum defect of nDsn to be 2.46560(32),and the quantum defect of nDsn to be 0.78345(75).The a-value of our experimental results is very close to the theoretical calculation of a-value,and the theoretical and experimental errors of our experimental results are controlled within±1.8 MHz,which fully proves the accuracy of the quantum defect measured by our experiments.The results lay a physical foundation for the accurate measurement of the microwave electric field based on the Rydberg atom and the precise control of the Rydberg state of the cesium atom.