Collisional cooling of ultracold molecules
Collisional cooling of ultracold molecules
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DOI：
10.1038/s41586-020-2141-z
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发表时间：
2019-07
期刊：
影响因子：
64.8
通讯作者：
H. Son;Juliana J. Park;W. Ketterle;A. Jamison
中科院分区：
文献类型：
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作者：
H. Son;Juliana J. Park;W. Ketterle;A. Jamison
自从玻色-爱因斯坦凝聚的最初工作以来，原子的量子简并气体的使用使得凝聚态和核物理中重要系统的量子模拟成为可能，以及在其他物理领域没有类似物的多体状态的研究。由于与原子相比具有丰富的内部自由度，微米和纳米开尔文体系中的超冷分子有望为量子仿真和量子计算带来强大的能力，并促进精确测量和量子化学研究。超冷原子的量子气体可以使用基于碰撞的冷却方案（如蒸发冷却）来产生，但热化和碰撞冷却尚未实现。其他技术，例如使用超音速射流和低温缓冲气体，已经达到限制在10毫开尔文以上的温度。在这里，我们展示了通过与超冷Na原子碰撞，将NaLi分子冷却到微米和纳米开尔文温度，分子和原子都在其拉伸的超精细自旋状态下制备。我们发现弹性与非弹性分子-原子碰撞的比率的下限大于50-大到足以支持持续的碰撞冷却。通过采用两个阶段的蒸发，我们将分子的相空间密度增加了20倍，实现了低至220纳开尔文的温度。Na-NaLi系统的有利碰撞特性可以使深度量子简并偶极分子的产生成为可能，并提高了在其他分子的冷却中使用拉伸自旋态的可能性。
Since the original work on Bose–Einstein condensation,, the use of quantum degenerate gases of atoms has enabled the quantum emulation of important systems in condensed matter and nuclear physics, as well as the study of many-body states that have no analogue in other fields of physics. Ultracold molecules in the micro- and nanokelvin regimes are expected to bring powerful capabilities to quantum emulation and quantum computing, owing to their rich internal degrees of freedom compared to atoms, and to facilitate precision measurement and the study of quantum chemistry. Quantum gases of ultracold atoms can be created using collision-based cooling schemes such as evaporative cooling, but thermalization and collisional cooling have not yet been realized for ultracold molecules. Other techniques, such as the use of supersonic jets and cryogenic buffer gases, have reached temperatures limited to above 10 millikelvin,. Here we show cooling of NaLi molecules to micro- and nanokelvin temperatures through collisions with ultracold Na atoms, with both molecules and atoms prepared in their stretched hyperfine spin states. We find a lower bound on the ratio of elastic to inelastic molecule–atom collisions that is greater than 50—large enough to support sustained collisional cooling. By employing two stages of evaporation, we increase the phase-space density of the molecules by a factor of 20, achieving temperatures as low as 220 nanokelvin. The favourable collisional properties of the Na–NaLi system could enable the creation of deeply quantum degenerate dipolar molecules and raises the possibility of using stretched spin states in the cooling of other molecules.