Superfluidity in Mixtures of Fermionic Dy and K Atoms

Elementary particles can be divided into two fundamental classes bosons and fermions. In the quantum world, bosons like to get together in large groups, whereas fermions tend to avoid each other as described by Paulis famous exclusion principle. Fermions are the basic building blocks of matter (electrons, protons, neutrons, quarks etc.) and the Pauli principle is essential for its stabilization. The exclusion principle is responsible for the electrons filling the shells around an atomic nucleus and also for the stability of neutron stars against a gravitational collapse. Based on a subtle mechanism, fermions can bypass Paulis principle. If two fermions pair up as a result of interaction, a composite particle is formed, which has bosonic character. This can drastically change the whole physical behavior of a particle system. A striking effect is the emergence of superfluidity (or superconductivity with charged particles), where particles can move without any friction. Such systems challenge our fundamental understanding of matter under quantum conditions, and they are of great interest for possible applications in lossless transport of electric energy. Superfluid systems can be studied with ultracold atomic quantum gases, which are produced in the laboratory at temperatures only a few billionths of a degree above absolute zero. Such systems are exceptionally pure and they can be very well controlled, manipulated, and detected. They thus offer ideal properties to create model systems for studying the fundamental behavior of many-body quantum systems. Superfluidity has been studied in such ultracold systems for two decades. This includes fermions of a single atomic species, where pairing is restricted to particles of the same mass. Our project aims at the realization of novel regimes of superfluidity in mixtures of two different fermionic species. Theoretical work has predicted that different masses can support novel pairing mechanisms and corresponding novel regimes of superfluidity. Such phenomena have attracted great attention in the theoretical literature, but they have been elusive to experimental observations. In our laboratory, we combine a fermionic dysprosium isotope (161Dy) with fermionic potassium (40K) and realize an ultracold quantum mixture. In previous work, we have demonstrated that these two isotopes can strongly interact via a quantum-mechanical resonance and how this can be controlled by a magnetic field. The present project aims at the creation and detection of novel superfluids in such mixtures of Dy and K atoms, and will thus break new ground in our understanding of strongly interacting fermion systems.