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arXiv 0907.3727physics.atom-ph
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超精细相互作用和磁场诱导的玻色-爱因斯坦统计抑制双光子跃迁

Hyperfine-interaction- and magnetic-field-induced Bose-Einstein-statistics suppressed two-photon transitions

M. G. Kozlov, D. English, D. Budker

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摘要：

当光子具有相同的能量时，在总电子角动量$J_a=0$和$J_b=1$的原子态之间的双光子跃迁是被禁止的。这个选择规则类似于粒子物理学中的朗道-杨定理，该定理禁止矢量粒子衰变为两个光子。它的出现是因为不可能构造出两个光子的总角动量$J_{2γ}=1$量子力学态，它是排列对称的，正如玻色-爱因斯坦统计所要求的那样。在具有非零核自旋的原子中，由于超精细相互作用，选择规则可以被违反。两种不同的机制负责的超精细诱导的双光子跃迁被确定，和诱导跃迁的超精细结构进行了评估。通过外加磁场，即使对于零核自旋原子，选择规则也被放宽了。再一次，有两个类似的机制在起作用：中间态子能级的塞曼分裂，以及末态中具有不同总电子角动量的状态的非对角混合。目前的理论治疗是相关的正在进行的实验研究可能的玻色-爱因斯坦统计违反使用双光子跃迁钡，其中超精细诱导的过渡最近已被观察到，和磁场诱导的过渡被认为是一种可能的系统效应，并作为一种方式来校准测量。

英文摘要：

Two-photon transitions between atomic states of total electronic angular momentum $J_a=0$ and $J_b=1$ are forbidden when the photons are of the same energy. This selection rule is analogous to the Landau-Yang theorem in particle physics that forbids decays of vector particle into two photons. It arises because it is impossible to construct a total angular momentum $J_{2γ}=1$ quantum-mechanical state of two photons that is permutation symmetric, as required by Bose-Einstein statistics. In atoms with non-zero nuclear spin, the selection rule can be violated due to hyperfine interactions. Two distinct mechanisms responsible for the hyperfine-induced two-photon transitions are identified, and the hyperfine structure of the induced transitions is evaluated. The selection rule is also relaxed, even for zero-nuclear-spin atoms, by application of an external magnetic field. Once again, there are two similar mechanisms at play: Zeeman splitting of the intermediate-state sublevels, and off-diagonal mixing of states with different total electronic angular momentum in the final state. The present theoretical treatment is relevant to the ongoing experimental search for a possible Bose-Einstein-statistics violation using two-photon transitions in barium, where the hyperfine-induced transitions have been recently observed, and the magnetic-field-induced transitions are being considered both as a possible systematic effect, and as a way to calibrate the measurement.

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