Quantum mixtures of ultracold gases of neutral atoms
Year: 2024
Authors: Baroni C., Lamporesi G., Zaccanti M.
Autors Affiliation: Univ Trento, CNR, INO, Pitaevskii BEC Ctr, Trento, Italy; Univ Trento, Dipartimento Fis, Trento, Italy; Austrian Acad Sci, Inst Quantum Opt & Quantum Informat IQOQI, Innsbruck, Austria; Consiglio Nazl Ric CNR INO, Ist Nazl Ott, Sesto Fiorentino, Italy; Univ Firenze, European Lab Nonlinear Spect LENS, Sesto Fiorentino, Italy.
Abstract: After decades of improvements in cooling techniques of several atomic species and in finding methods for the achievement of stable quantum mixtures, the field is now ready for an extensive use of such a versatile experimental platform for the investigation of various physical problems. Among them, relevant examples are the dynamics of impurities in a quantum gas, the miscibility condition of different gases, the study of exotic topological structures, the interplay between magnetism and superfluidity, the formation of artificial molecules or new few-body states. We illustrate the differences among possible quantum mixtures – whether homonuclear spin mixtures or heteronuclear ones – and show how they can be exploited to investigate a plethora of topics from the few-body to the many-body regime. In particular, we discuss quantum mixtures of ultracold gases under three different perspectives: systems made of a few atoms of different kinds, single impurities immersed in a host quantum gas and quantum mixtures of two interacting gases. We restrict the discussion to single harmonic or flat traps, predominantly in a 3D configuration. A selection of results on recent experiments and possible interesting future directions are given. Three-dimensional, quantum mixtures of ultracold gases of neutral atoms are ideal platforms for probing the physics of many-body systems because the interparticle interactions can be fine-tuned externally. This Review introduces a range of active topics under investigation: topological defects, the interplay of superconductivity and magnetism, novel few-body states and more. Mixtures of atoms can be realized either using different ’spin’ states of the same atomic species (homonuclear mixtures), or using different atomic species or isotopes (heteronuclear mixtures). The main differences concern the different levels of experimental complexity, the possibility to independently manipulate the two components, the quantum statistics and mass ratio of the constituents, and the interconversion between the two components of the mixture.The combination of ultralow collision energies, quantum statistics of the scattering particles and their mass asymmetry promotes the appearance of various novel few-particle cluster states, exhibiting different types of spatial correlations and spectral properties.When one atom (impurity) is embedded in a bath of different particles with which it interacts, it dresses itself with excitations of the bath and can be described in terms of a quasiparticle (polaron), which is an object that behaves as a free particle but with renormalized properties, such as energy and mass.The behaviour of two bosonic gases is mainly given by the combination of their two-body interaction strengths, with interesting features for small values of intercomponent interactions. For repulsive interspecies interaction, the gases can mix and self-organize in spatially separated domains, whereas for increasing attractive ones they can either form stable solitons or quantum droplets or collapse.The physics of two distinguishable fermionic gases is dominated by the crossover from a superfluid of tightly bound molecules to a superfluid of loosely bounded pairs while passing from strongly repulsive to strongly attractive intercomponent interactions.
Journal/Review: NATURE REVIEWS PHYSICS
Volume: 6 (12) Pages from: 736 to: 752
More Information: The authors thank the members of the LENS Quantum Gases group in Florence and of the Pitaevskii BEC Center in Trento for fruitful discussions. The authors thank R. Grimm for his scientific support and X. Cui, D.S. Petrov and P. Massignan for their critical reading of the manuscript and insightful discussions. The authors also acknowledge financial support by the PE0000023-NQSTI project by the Italian Ministry of University and Research, co-funded by the European Union – NextGeneration EU. C.B. and G.L. acknowledge financial support from Provincia Autonoma di Trento, and M.Z. acknowledges financial support from the ’Integrated Infrastructure Initiative in Photonic and Quantum Sciences’ I-PHOQS (CUP B53C22001750006).KeyWords: Bose-einstein Condensation; Fermi Gas; Phase-separation; Feshbach Resonances; Critical Field; Edge States; Single-ion; Scattering; Molecules; DynamicsDOI: 10.1038/s42254-024-00773-6