Abstract
We describe the creation of a long-lived spin-orbit-coupled gas of quantum degenerate atoms using the most magnetic fermionic element, dysprosium. Spin-orbit coupling arises from a synthetic gauge field created by the adiabatic following of degenerate dressed states composed of optically coupled components of an atomic spin. Because of dysprosium’s large electronic orbital angular momentum and large magnetic moment, the lifetime of the gas is limited not by spontaneous emission from the light-matter coupling, as for gases of alkali-metal atoms, but by dipolar relaxation of the spin. This relaxation is suppressed at large magnetic fields due to Fermi statistics. We observe lifetimes up to 400 ms, which exceeds that of spin-orbit-coupled fermionic alkali atoms by a factor of 10–100 and is close to the value obtained from a theoretical model. Elastic dipolar interactions are also observed to influence the Rabi evolution of the spin, revealing an interacting fermionic system. The long lifetime of this weakly interacting spin-orbit-coupled degenerate Fermi gas will facilitate the study of quantum many-body phenomena manifest at longer time scales, with exciting implications for the exploration of exotic topological quantum liquids.
- Received 10 May 2016
DOI:https://doi.org/10.1103/PhysRevX.6.031022
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Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
The tight locking of the spin of an electron to its motion (or orbit) is known as spin-orbit coupling. This coupling is a key component of recently discovered materials exhibiting topologically nontrivial behavior at relatively high temperatures. Such behavior arises because of large spin-orbit coupling, making novel technological applications possible. Using laser light to generate spin-orbit coupling in neutral ultracold gases also makes it possible to study the quantum effects of spin-orbit coupling with very precise control and tunability. One can even produce phases of matter not observable in the solid state. Previous experiments attempting these studies with quantum gases of fermionic alkali-metal atoms have been limited to lifetimes too short to explore the full range of spin-orbit-coupling physics, but here we show that much longer lifetimes—10 to 100 times longer—can be achieved using fermionic quantum gases of dysprosium, a lanthanide atom.
Here, we focus on an ensemble of roughly 15,000 ultracold atoms. Because of the electronic configuration of dysprosium and its large electronic orbital angular momentum, lasers can produce spin-orbit coupling without the heating that plagues alkali gases. However, the magnetic interaction between the dysprosium atoms—Dy is the most magnetic fermionic element—introduces a new instability due to inelastic dipolar collisions. We measure loss rates in dysprosium gases under spin-orbit coupling and find that quantum Fermi statistics suppress these destructive collisions. We also observe that elastic dipolar collisions can affect spin dynamics, demonstrating the presence of interactions in a spin-orbit-coupled Fermi gas.
We expect that the long lifetime of spin-orbit-coupled fermionic dysprosium gases—400 ms—will enable novel studies of interacting topological Fermi gases and topological superfluids.
