基于氢分子离子HD+振转光谱的精密测量确定质子电子质量比

The proton-electron mass ratio is a dimensionless fundamental physical constant. To determine this constant with high precision is of great importance both for the verifications and predictions of the basic physical theories. HD+ consists of one proton, one deuterium nucleus and one electron. And it is the simplest molecule, whose rovibrational transition frequencies strongly depend on the proton-electron mass ratio. Combining the precision measurements of the rovibrational spectroscopy and the quantum electrodynamics (QED) calculations, the proton-electron mass ration can be determined with high precision..In this project, the HD+ ions generated by the threshold photoionization method will be sympathetically cooled by the laser-cooled atomic ions to realize the accurate controlling of the internal and external degrees of freedom. Then, the HD+ ions, with the transitional kinetic energy around mK and in the ground state of the rovibration, can be obtained. The 991 nm overtone transition frequency from the rovibrational ground state to the 6th vibrational excited state will be measured by the precision spectroscopy method with the relative accuracy about 0.4.ppb, two to three times better than current measurements. Meanwhile, using QED theory, we will derive rigorously the equivalent operators for the high-order relativistic and radiation corrections, perform the high-precision numerical calculations for the expectation values of the operators. Together with the results of low-order QED corrections which have been finished by the applicant, the theoretical prediction of the rovibrational transition frequency is expected with the relative accuracy 0.1 ppb. Comparing the results from our experimental spectroscopy and theoretical prediction, the proton-electron mass ratio is expected to be determined with the relative accuracy better than 1ppb, to be accepted as reference data for CODATA.

质子-电子质量比是无量纲的基本物理常数，它的高精度确定对基本物理理论的验证及预言至关重要。HD+是由质子、氘核和电子构成的最简单的分子体系，其振转跃迁频率强烈依赖于质子-电子质量比，精密的振转光谱测量结合量子电动力学（QED）理论计算可以高精度地确定质子-电子质量比。. 本项目拟采用激光冷却的原子离子对由阈值光电离产生的HD+离子进行协同冷却，实现对HD+内外自由度的精确控制，获得平动能在mK量级、完全处于振转基态的HD+离子。进而对基态至第6振动激发态991nm泛频跃迁进行光谱测量，相对精度达到0.4ppb，较目前同类实验精度提高2到3倍；同时，利用QED理论严格导出描述高阶相对论与辐射修正的等效算符，实现算符期望值的高精度数值计算，实现对振转频率相对精度0.1ppb的理论预言；通过实验光谱与理论预言的比对，在优于1ppb相对精度上确定质子-电子质量比，成为CODATA参考值。

该项目本项目以提高质子-电子质量比直接测量精度为中心，开展HD+精密谱实验与理论研究，检验电子质量、质子质量、和它们比值这三个量之间的自洽性，探索新物理现象。研究目标精度达到CODATA2010推荐的精度（质量比目标精度 ：<1ppb）。理论方面，利用QED理论导出完备的高阶QED修正等效算子并实现满足目标要求的高精度数值计算（目标精度：0.1ppb）；实验方面，制备高纯度的HD+振转基态、降低离子温度、并测量多条振转超精细跃迁的频率，有效降低系统误差（光谱实验目标精度<0.4ppb）。在冷分子离子精密谱、氢分子离子振转光谱测量、少体束缚态QED理论计算方面取得了一系列重要研究成果，主要包括：建立了冷分子离子精密谱实验平台；开展分子精密谱光谱测量确定质子电子质量比研究；获得精度达1.6E-11的跃迁频率数据，达到项目预期目标。项目组共发表SCI论文10篇，其中包括Physical Review Letters 1篇，Physical Review A 5篇。获得国家发明专利1项。项目培养博士生6名，硕士4人。项目骨干1人入选中国科学院青年创新促进会。