Fractional Quantum Hall Physics with Ultracold Atoms

Harvard University, Cambridge MA

Investigators

Abstract

This project is aimed at finding and exploring new states of matter, particularly "quantum matter" in which the counterintuitive and surprising effects of the theory of quantum mechanics plays a crucial role. In condensed matter materials such as conductors, superconductors, and magnets, atoms are arranged in regular crystals, and the electric and magnetic properties of the material emerge from the motion of electrons within that crystal. The physics of this motion is very complex, and many associated fundamental questions are unanswered. In order to better understand this physics, the scientists working on this project are building an enlarged model system of such matter: they are using atoms instead of electrons, and these atoms move in crystals formed by light. The atoms have to be at extremely cold temperatures, only a billionth of a degree above absolute zero. This way they behave quantum mechanically like the electrons in condensed matter systems. One strange feature of the ultracold system is that each atom is at many places at the same time. This synthetic condensed matter system can be very well characterized and directly compared to theory using a "Quantum Gas Microscope" (invented during the previous cycle of NSF funding to this research group) to image every single atom with perfect fidelity. The particular focus of this work is to create "Bosonic fractional quantum hall states"--states of matter whose behavior is dictated by "Entanglement," the most non-classical manifestation of quantum mechanics, famously described by Albert Einstein as "Spooky action in a distance." By addressing open questions linked to these materials, the researchers supported by this grant are working to advance science towards the ultimate goal of tailoring new quantum materials from scratch with yet unknown properties. Such materials could find applications in quantum information devices, and in quantum metrology. This project trains students and postdocs in a broad range of physics and in many modern technologies such as laser optics. Fractional quantum Hall states represent new states of matter that contain topological order. While Fermionic fractional quantum Hall states of electrons have been previously observed in 2D electron materials, the work supported by this grant work aims to experimentally realize and explore fractional quantum Hall states with small ensembles of strongly interacting bosonic atoms that quickly rotate in a two-dimensional harmonic trap. Such ensembles experience a gauge field, and are expected to adiabatically transition into the bosonic fractional quantum Hall state. While the particle number in such ensembles is small, on the order of 4-10 particles, the quantum gas microscope will enable the researchers to detect every single particle with near unity fidelity. Therefore, they can carry out a complete quantum limited measurement of the mesoscopic many- body system. In particular they seek to directly measure particle correlation functions in momentum space, which would give very direct evidence of the highly entangled many-body states.