During this project, several tasks of both technical and scientific nature have been undertaken in parallel, in order to reach the planned objectives.
- We have developed and characterized various technical advances to the experimental setup, which can produce Fermi gases and paired superfluids trapped in nearly arbitrary sub-micrometer optical structures and imaged in situ with high optical resolution. Absorption imaging with sub-micrometer resolution is afforded by a newly implemented optical system, featuring a bi-chromatic microscope objective that has been characterized before integration into the experimental machine. Arbitrary potentials are imprinted onto the quantum gas by projecting DMD patterns (see Fig. 1). The pattern fed to the DMD array is optimized through a newly developed feedback algorithm, which compensates the imperfections of the illumination field and of the optical setup. The DMD setup performance has been characterized before integration into the main experimental apparatus, as summarized in Ref. [1]. The setup has been already shown to produce binary-disorder potentials with sub-micrometer correlation length (see Fig. 2).
- We have made important and necessary steps towards the reliable production of quasi-two-dimensional atomic Fermi gases. First, we have implemented and characterized a new optical setup for creating a single quasi-two-dimensional optical trap to confine the atomic gas in a single two-dimensional layer. The setup generates a highly anisotropic TEM01-mode Gaussian beam (see Fig. 3 and Ref. [2]), which satisfies the pointing and intensity stability requirements. Second, we have designed, built and characterized a novel large-spacing optical lattice, based on a minimal interferometric scheme, featuring exceptional intrinsic fringe stability < d/20 over several hours (see Fig. 4 and Ref. [3]). Both these potentials are presently undergoing integration into the main apparatus. The combination of the realized setups will also allow in the future to study individual one-dimensional Fermi systems with unprecedented in-situ resolution and probing capabilities.
- We have developed a fast RF spectroscopic technique with resolution < 100Hz, allowing a rapid, accurate manipulation of the Fermi gas spin composition and the coherent control over lithium lowest hyperfine levels. This tool has been already exploited to explore the still debated physics of strongly repulsive Fermi gases. In particular, in a first study we have probed the properties of repulsive spin impurities immersed in a Fermi gas (see Ref. [4]), characterizing the so-called polaron quasiparticles. More recently, we have investigated the dynamics of a balanced spin mixture undergoing a sudden change of interparticle interactions, using a RF pump-probe spectroscopy scheme (see Fig. 5 and Ref. [5]).
- As a fundamental issue in itself, and in preparation to the study of superfluid transport in two dimensions, we have studied the relation between dissipative transport and superfluid excitations in a planar Josephson junction-like geometry in three dimensions. We have found that vortex-induced phase slippage is the dominant microscopic source of dissipation across the BEC-BCS crossover. The results of this study are published in Ref. [6].
[1] G. Del Pace, Master Thesis (University of Florence, 2017)
[2] M. Bertrand, Research internship report (ESPCI, Paris and LENS, Florence, 2016)
[3] E. Lippi, Master Thesis (University of Florence, 2017)
[4] F. Scazza et al., Phys. Rev. Lett. 118, 083602 (2017)
[5] A. Amico et al., Phys. Rev. Lett. 121, 253602 (2018)
[6] A. Burchianti et al., Phys. Rev. Lett. 120, 025302 (2018)
