Strongly Interacting Quantum Mixtures of Ultracold Atoms

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

When many particles interact, they can form collective states of matter, the most common of which are the solid, liquid and gaseous state. The present project will search for new states of matter at ultralow temperatures, using gases of atoms with freely tunable interactions as the starting point. At these low temperatures, quantum mechanics takes center stage, and the intrinsic uncertainty in where each particle is – the Heisenberg uncertainty – strongly affects the behavior of the collection of particles. They commonly form a quantum liquid, but they may enter a superfluid state, where atoms flow without any friction. Understanding such superfluid states is crucial for the understanding of yet another “super” state, namely superconductors, which carry electricity without any heat. The atoms in the experiment will be imaged with single-atom resolution, enabling an unprecedented view into the microscopic origins of various phases of matter. In particular, the research aims to find evidence for a state that is at the same time a superfluid and a solid. These experiments will enhance our understanding of collective phenomena and states of matter. The work will provide excellent training for graduate and undergraduate students on lasers and optics, computer control, vacuum assemblies, high magnetic fields, radiofrequency and microwave electronics, thereby combining research with education objectives. The PI and the team will use ultracold sodium and lithium atoms trapped in two and three dimensions to investigate the thermodynamics of quantum gases. Sodium is a boson, a particle with integer spin, while lithium-6 with its half-integer spin is a fermion. Mixtures of bosons and fermions realize an important ingredient of the standard model of physics. Fermi-Fermi mixtures can mimic the behavior of electrons in high-temperature superconductors or the dilute neutron matter in the crust of neutron stars. The PI will embed impurities of one species into a host bath of the other, and thereby study the fate of impurities in a quantum bath, expecting the formation of polarons, dressed quasi-particles. For the first time, these polarons will be able to be imaged with single-atom resolution. The experiments address long-standing questions on the ground state of fermionic superfluids in the presence of spin imbalance and of Bose-Fermi mixtures, on the existence and nature of boson-induced pairing, and on the role of dimensionality. The research will lead to a better understanding of superfluidity and superconductivity. Precision measurements of thermodynamics and interparticle correlations enable the validation of novel theoretical tools. These can then be employed with confidence in other strongly interacting Fermi systems, relevant to diverse fields of physics: From studies of high-temperature superconductors in condensed matter physics, to the Coulomb gas governing chemistry, to the quark-gluon plasma of the early universe and the behavior of neutron matter in nuclear physics. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.