High‑precision loss measurements reveal orbital‑resolved p‑wave recombination in ultracold ⁶Li
Physicists study ultracold lithium‑6 because it is a fermionic isotope of lithium: its nucleus contains three protons and three neutrons, giving it a half‑integer total spin. This makes lithium‑6 behave like other fundamental fermions such as electrons, protons, and neutrons, in contrast to lithium‑7, which has an integer spin and is a boson. According to the Pauli exclusion principle, fermions cannot occupy the same quantum state, so lithium‑6 provides a clean, controllable system for exploring how fermionic particles behave. It is also relatively easy to cool to ultracold temperatures, and its interactions can be tuned very precisely using magnetic fields. At these temperatures, atomic motion slows dramatically, allowing quantum mechanical effects to become directly observable.
In this work, the researchers studied three‑body recombination processes, where three atoms collide and two of them form a molecule while the third atom carries away the excess energy. The escaping atom has information about how the three atoms interacted. By tuning the interactions with a magnetic field using a Feshbach resonance, the researchers were able to access a p‑wave resonance (where atoms collide with orbital angular momentum) rather than the more common s‑wave (head‑on collisions). P‑wave interactions are especially important because they are linked to exotic quantum systems such as topological superfluidity and strongly correlated fermionic phases.
The researchers developed a highly stable technique to measure how often atoms are lost due to three‑body recombination for different orbital orientations of the collision. This high‑precision method allowed them to distinguish the orbital components, measure how the recombination rate changes with temperature and magnetic field and extract microscopic parameters that characterize p‑wave interactions. This work establishes a precise benchmark for p‑wave scattering theory, introduces a powerful method for probing direction‑dependent interactions, and lays the groundwork for exploring complex quantum phenomena such as anisotropic pairing, few‑body universality, and topological superfluidity relevant to future quantum technologies.
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Single atom detection in ultracold quantum gases: a review of current progress by Herwig Ott (2016)
