Anderson localization (AL) is a ubiquitous interference phenomenon in which waves fail to propagate in a disordered medium. We observe three-dimensional AL of noninteracting ultracold matter by allowing a spin-polarized atomic Fermi gas to expand into a disordered potential. A two-component density distribution emerges consisting of an expanding mobile component and a nondiffusing localized component. We extract a mobility edge that increases with the disorder strength, whereas the thermally averaged localization length is shown to decrease with disorder strength and increase with particle energy. These measurements provide a benchmark for more sophisticated theories of AL.

We observe the emergence of a disorder-induced insulating state in a strongly interacting atomic Fermi gas trapped in an optical lattice. This closed quantum system free of a thermal reservoir realizes the disordered Fermi-Hubbard model, which is a minimal model for strongly correlated electronic solids. In measurements of disorder-induced localization obtained via mass transport, we detect interaction-driven delocalization and localization that persists as the temperature of the gas is raised. These behaviors are consistent with many-body localization, which is a novel paradigm for understanding localization in interacting quantum systems at non-zero temperature.PACS numbers: 37.10.Jk,71.23.AnThe impact of inter-particle interactions on localization of disordered quantum systems has been the subject of intense scrutiny for decades (see [1][2][3][4][5] and references therein). Obtaining new insights into the interplay of interactions and disorder is critical to improving our understanding of quantum electronic solids such as the high-temperature superconducting cuprates and materials that exhibit colossal magnetoresistance, such as the manganites [4,6,7]. Despite the application of a wide variety of sophisticated theoretical and numerical approaches, consensus regarding the nature of metalinsulator transitions and localization in strongly correlated systems has not been achieved. A recent theoretical approach to these questions is many-body localization (MBL) [8][9][10][11], which overturns the conventional view holding that materials above zero temperature have nonzero conductivity in the presence of interactions. In a many-body localized state, a quantum system can remain an Anderson-localized insulator at non-zero temperature because the inter-particle interactions fail to generate thermally activated conductivity.We investigate localization using an ultracold atomic gas trapped in a disordered optical lattice. This precisely controllable system, which realizes the disordered FermiHubbard model (DFHM) [12]-the minimal model for strongly correlated, disordered electronic solids-is free of a heat bath, such as phonons, that can lead to finite conductivity at nonzero temperature and foils direct tests of theories such as MBL in the solid state. The seminal theoretical work by Basko et al. on MBL [8] explored the weakly interacting regime of a spinless DFHM; we investigate the strongly correlated limit which is challenging for theory and numerical approaches. We probe disorder-induced metal-insulator transitions using mass transport measurements. The disorder ∆ c required to localize the gas and produce an insulating state is determined for different ratios of the Hubbard interaction to tunneling energies. We find that increased interactions stabilize the metal against localization and lead to an insulator-metal transition. We also show that localization occurs across a range of thermal energy densities at fixed disorder strength by varying the temperature of the gas.In our experiment, fermionic 40 K atoms cooled...

Electrical current in conventional metals is carried by electrons that retain their individual character. Bad metals, such as the normal state of some high-temperature superconductors, violate this scenario, and the complete picture for their behavior remains unresolved. Here, we report phenomena consistent with bad-metal behaviour in an optical-lattice Hubbard model by measuring the transport lifetime for a mass current excited by stimulated Raman transitions. We demonstrate incompatibility with weak-scattering theory and key characteristics of bad metals: anomalous resistivity scaling consistent with T -linear behavior, the onset of incoherent transport, and the approach to the Mott–Ioffe–Regel limit. Our work demonstrates a direct method for determining the transport lifetime, which is critical to theory but difficult to measure in materials, and exposes minimal ingredients for bad-metal behavior.

Laser-cooled atoms are a key technology for many calibration-free measurement platforms—including clocks, gyroscopes, and gravimeters—and are a promising system for quantum networking and quantum computing. The optics and vacuum hardware required to prepare these gases are often bulky and not amenable to large-volume manufacturing, limiting the practical realization of devices benefiting from the properties of cold atoms. Planar, lithographically produced optics including photonic integrated circuits, optical metasurfaces (MSs), and gratings offer a pathway to develop chip-scale, manufacturable devices utilizing cold atoms. As a demonstration of this technology, we have realized laser cooling of atomic Rb in a grating-type magneto-optical trap (MOT) using planar optics for beam launching, beam shaping, and polarization control. Efficient use of available light is accomplished using MS-enabled beam shaping, and the performance of the planar optics MOT is competitive with Gaussian-beam illuminated grating MOTs.