Ingrid Fadelli is a writer for the website Phys.org.
Physicists don't reach exact solutions or conclusions in more than one study. There are instances in which the quantum background is not an acting Fermi gas.
Over the last decade or so, the Fermi polaron problem has been studied a lot. It has been difficult to predict the quasi-particle properties of Fermi polarons.
A model that could be used to predict the exact quasi-particle properties of a heavy polaron was recently introduced by researchers. Their paper introduces a theoretical solution for a many-body system, which could be tested and realized in experimental settings.
One of the team's papers was published in Physical Review A. This past work focused on the different types of polaron.
"Our previous work and many other theoretical studies of polarons using various approximation methods give some universal features, such as the existence of attractive/repulsive polarons and a dark continuum," said one of the researchers. The mechanism behind these features is believed to be the suppression of multiple quasiparticles.
The recoil energy of a mobile impurity or the existence of an energy gap in a superfluid are believed to be the mechanisms underpinning the universal features of Fermi polarons. They had to represent their hypothesis theoretically in order for it to be verified in an experiment.
Wang said that the paper studied immobile impurities in non-Interacting Fermi gases. The model is easy to solve using the FDA method. There are no polarons in such systems due to Anderson's catastrophe. The polaron resonance is destroyed by the existence of multiple particle-hole excitations.
The polaron can be suppressed by the presence of a superfluid gap. They wanted to extend the FDA method to their superfluid system.
Wang said that they wanted to investigate the topic of superfluids. Several experiments have recently realized that another species of atoms can play a role in a superfluid. The polaron spectrum of impurities can be used to measure features of the background superfluid spectrum in accessible systems.
Wang and his colleagues use a good approximation of heavy impurities in the calculations they carry out. Physicists should be able to use a deep optical lattice to get to the root of the problem.
The study was a theoretical one. A system of immobile impurity is considered in our model. We assume that the impurity has two internal states, one interacting with the superfluid and the other not.
The researchers were able to reveal all the universal polaron features with a simple calculation. The achievement is remarkable, as previous studies had been unable to prove all the properties of the system.
Wang said that the probability of the impurity absorbing a photon and switch to the strongly interacting state was calculated using the photon frequencies. The existence of a quasiparticle with energy is called heavy crossover polaron.
The theoretical work done by this team of researchers could lead to lab experiments with cold atoms. Physicists could draw inspiration from their paper to conduct Ramsey-Interference-type experiments, which involve some of the processes and technical details outlined in their paper.
The theory presented by Wang and his colleagues could be applied to many different systems. The team suggests an experimental realization of their proposed system using heavy 133Cs impurities in a superfluid which had already been realized in some previous works.
Wang said that the work's contributions are twofold. We looked at a model that could be solved and gave all the features of the Fermi polarons. These features have only been calculated in a few studies, but our analysis shows they are the result of suppression of multiple particle holes. There is a magnetic impurity that interacts with the two components of the superfluid with different strengths.
The subgap Yu-Shiba-Rusinov bound state was shown when the researchers conducted their calculations. They could soon be tested in different physics labs around the world.
This is the first study to apply polaron-related theory to investigate subgap Yu-Shiba-Rusinov bound states in ultracold gases. We plan to investigate heavy polarons in other superfluids. Our method will help us to understand the background medium's phase transition.
More information: Jia Wang et al, Exact Quasiparticle Properties of a Heavy Polaron in BCS Fermi Superfluids, Physical Review Letters (2022). DOI: 10.1103/PhysRevLett.128.175301There are heavy polarons in ultracold atomic Fermi superfluids. There is a DOI titled "10.103/PhysRevA.105.043320".
Journal information: Physical Review A , Physical Review LettersThere is a science network.
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