&Cartridge; physics 15, p.132
Researchers produce analogues of difficult-to-study quantum phenomena in a gas of strontium atoms near absolute zero.
Recently, researchers have started using ultracold atomic gases to simulate phenomena that are difficult to study in their natural environment. Using electromagnetic fields, for example, they can orchestrate interatomic interactions analogous to interactions in condensed matter systems, which they can then study with greater experimental control than the real examples allow. Now, David Wilkowski of Nanyang Technological University in Singapore and colleagues are using an ultracold atomic gas to simulate the spin dynamics of a condensed matter system .
Wilkowski’s team cools a gas of strontium-87 atoms to 30 nK. Then they drive the gas through different transitions with three convergent laser beams until the atoms populate two so-called dark states, in which quantum mechanics forbids the atoms from spontaneous emission.
The relationship between the two dark states is analogous to the relationship between opposite quantum spin states: just as particles with different spins move differently in a magnetic field, atoms in different dark states move differently in the laser field. As the atoms collectively evolve between different superpositions of these dark states, their interaction with the field induces a “wobbling” motion of their center of mass. This interaction reproduces the phenomenon of spin-orbit coupling, with the dark state representing the spin and the motion of the atoms representing the orbital angular momentum. This analogy with spin systems goes further: in the experiment, the direction of the gas’s wiggling motion is perpendicular to its average momentum—a velocity-momentum relationship that corresponds to the spin Hall effect in condensed-matter systems in which a charge current induces a perpendicular spin current. Next, the researchers plan to use more complex interactions between atoms and laser fields to mimic high-energy particle systems.
Sophia Chen is a freelance science writer based in Columbus, Ohio.
- M Hasan et al.“Wave packet dynamics in synthetic non-Abelian gauge fields”, physics Rev. Lett. 129130402 (2022).