Bendkowsky Vera, Butscher Björn, Nipper Johannes, Shaffer James P, Löw Robert, Pfau Tilman
5. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany.
Nature. 2009 Apr 23;458(7241):1005-8. doi: 10.1038/nature07945.
Rydberg atoms have an electron in a state with a very high principal quantum number, and as a result can exhibit unusually long-range interactions. One example is the bonding of two such atoms by multipole forces to form Rydberg-Rydberg molecules with very large internuclear distances. Notably, bonding interactions can also arise from the low-energy scattering of a Rydberg electron with negative scattering length from a ground-state atom. In this case, the scattering-induced attractive interaction binds the ground-state atom to the Rydberg atom at a well-localized position within the Rydberg electron wavefunction and thereby yields giant molecules that can have internuclear separations of several thousand Bohr radii. Here we report the spectroscopic characterization of such exotic molecular states formed by rubidium Rydberg atoms that are in the spherically symmetric s state and have principal quantum numbers, n, between 34 and 40. We find that the spectra of the vibrational ground state and of the first excited state of the Rydberg molecule, the rubidium dimer Rb(5s)-Rb(ns), agree well with simple model predictions. The data allow us to extract the s-wave scattering length for scattering between the Rydberg electron and the ground-state atom, Rb(5s), in the low-energy regime (kinetic energy, <100 meV), and to determine the lifetimes and the polarizabilities of the Rydberg molecules. Given our successful characterization of s-wave bound Rydberg states, we anticipate that p-wave bound states, trimer states and bound states involving a Rydberg electron with large angular momentum-so-called trilobite molecules-will also be realized and directly probed in the near future.
里德堡原子的一个电子处于主量子数非常高的状态，因此可以表现出异常长程的相互作用。一个例子是两个这样的原子通过多极作用力结合形成具有非常大核间距的里德堡 - 里德堡分子。值得注意的是，键合相互作用也可能源于里德堡电子与基态原子的低能散射，且散射长度为负。在这种情况下，散射诱导的吸引相互作用将基态原子在里德堡电子波函数内的一个良好定位位置处与里德堡原子结合，从而产生核间距可达数千玻尔半径的巨型分子。在此，我们报告了由处于球对称s态且主量子数n在34至40之间的铷里德堡原子形成的此类奇异分子态的光谱表征。我们发现里德堡分子（铷二聚体Rb(5s)-Rb(ns)）的振动基态和第一激发态的光谱与简单模型预测吻合良好。这些数据使我们能够提取里德堡电子与基态原子Rb(5s)在低能区（动能<100毫电子伏特）散射的s波散射长度，并确定里德堡分子的寿命和极化率。鉴于我们成功地表征了s波束缚的里德堡态，我们预计在不久的将来，p波束缚态、三聚体态以及涉及具有大角动量的里德堡电子的束缚态（即所谓的三叶虫分子）也将被实现并直接探测到。
