We are carrying out two projects that will advance the state-of-the-art for disordered quantum gases, thus enabling new methods for attacking outstanding questions related to condensed matter physics and materials science. First, we are developing a technique to directly measure compressibility for ultra-cold gases trapped in 3D disordered optical lattices. We will apply this method to identify the nature of a disorder-induced insulator that we discovered, potentially detecting a Bose-glass phase using atoms unambiguously for the first time. Second, we are adding a cubic optical lattice to our disordered Fermi gas apparatus to achieve the first realization of the disordered Fermi-Hubbard model using ultra-cold atoms.
In these experiments, trapped atom gases are cooled to nanoKelvin temperatures using a combination of lasers and magnetic fields. A disordered optical lattice is superimposed on the gas by slowly turning on three pairs of counter-propagating infrared lattice laser beams and a green optical speckle field. The equivalent of material parameters, such as the disorder strength and tunneling energy, are smoothly tuned by adjusting the laser intensities. To measure compressibility, two laser beams (tuned near an electronic transition) applied to a Rubdium-87 gas will be used to image only the atoms located in the middle of the disordered lattice as the confining trap is changed. To create a disordered lattice for fermionic Potassium-40 atoms, additional lattice laser beams will be applied to an ultra-cold gas. We will measure the velocity of the gas as a force is applied in order to search for a predicted metal-insulator transition in the disordered lattice.
The interplay of disorder and strong interactions is one of the key outstanding problems in condensed matter physics. Fundamental questions center on how disorder and interactions either cooperate or compete to create localized phases in equilibrium and the influence of disorder on dynamical properties. The impact of disorder on quantum materials is also of prime importance to technological applications. Insight gained from our experiments may lead to improvements in materials with superlative properties that are important to energy applications, such as the high-temperature superconducting cuprates. Enhanced understanding of how disorder and interactions influence material properties may also enable new applications for strongly correlated materials in functions such as thermoelectric power generation.
