冷氨碰撞中偶极-偶极动力学的演化
Evolution of dipole-dipole dynamics in cold ammonia collisions
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中文总结 AI 辅助
研究冷氨碰撞中偶极-偶极动力学演化，用新型束流合并器测量氨同位素分子态-态截面，发现低能下有效偶极矩可关闭，散射计算相符，还证明低能下偶极-偶极相互作用受抑制，为控制冷分子碰撞提供机会。
中文摘要 AI 辅助
冷极性分子为超冷化学和量子物理带来了迷人前景，如量子模拟或计算新平台。但其固有碰撞特性大多未知，因难以合并有显著偶极矩的分子束，难以在足够低能量和高精度下实验探测双偶极分子碰撞。本文用新型束流合并器报告了氨同位素分子在0.3至100cm⁻¹能量间碰撞的态-态截面测量结果。实验观察到截面局部最大值，表明低碰撞能量下有效偶极矩可关闭。散射计算重现该最大值并解释了与分子能级结构中宇称分裂能量的标度关系。对两个碰撞伙伴相关能量转移的测量直接证明了低能量下偶极-偶极相互作用的抑制。结果表明一类重要极性分子间的碰撞以反直觉方式从高温极限向超冷区域演化，对未来实验可行性和先前工作解释有重大影响，并为用外部场控制冷分子碰撞提供独特机会。
英文摘要
Cold polar molecules offer fascinating prospects for ultracold chemistry and quantum physics, including new platforms for quantum simulation or computation. However, their inherent collision properties remain largely unknown. It has proven extremely hard to experimentally probe collisions between two dipolar molecules at sufficiently low energies and high precision, as it appears fundamentally impossible to merge two beams of molecules with significant dipole moments. Here we report measurements of state-to-state cross sections for collisions between ammonia isotopologues at energies between 0.3 and 100 cm$^{-1}$ using a novel beam merger. We experimentally observed a local maximum in the cross sections that indicates the effective dipole moments can switch off at low collision energies. Scattering calculations reproduced this maximum in good agreement and explained the observed scaling with the parity splitting energies in the molecular energy level structures. Measurements of the correlated energy transfer in both collision partners yielded direct evidence of the suppression of the dipole-dipole interaction at low energies. Our results demonstrate how collisions between an important class of polar molecules evolve from the high temperature limit towards the ultracold regime in a counterintuitive way, have major consequences for the feasibility of future experiments and the interpretation of previous work, and offer distinctive opportunities to control cold molecular collisions with external fields.
