This experiment is a novel setup for a very versatile two species Bose-Fermi mixture quantum gas experiment for87Rb and40K in optical potentials. Development of improved new technologies are emphasised in this project and cover self-made vacuum chambers realised with different techniques, a miniaturised, ultra stable laser system and a compact oil-cooled coil design for magnetic trapping and transport of ultracold atom clouds.
This experiment is a novel setup for a very versatile two species Bose-Fermi mixture quantum gas experiment for87Rb and40K in optical potentials. Development of improved new technologies are emphasised in this project and cover self-made vacuum chambers realised with different techniques, a miniaturised, ultra stable laser system and a compact oil-cooled coil design for magnetic trapping and transport of ultracold atom clouds.
A cold atom experiment can be used to simulate analogous solid-state systems. This provides the bene�t of having a high degree of control over the system parameters and allowing direct detection methods. Disordered transport is one example of where such a system has much to o�er. This thesis concerns the development of a Bose-Fermi mixture experiment for study of two-dimensional optical lattice systems. To achieve single site resolution of the lattice, the experiment makes use of a double microscope set-up. One microscope provides imaging and the second is used to image a spatial light modulator onto the atomic plane. This provides an extremely versatile potential landscape for a trapped cloud. This thesis presents an overview of the set-up of the experiment including progress towards condensation. Particular focus is given to the design and characterisation of the vacuum system and the combined double microscope and spatial light modulator system. The vacuum system design requires a narrow magneto-optical trapping chamber. A novel epoxy sealing technique has been developed, allowing construction of a chamber of just 36mm thickness whilst maintaining high optical access. To provide illumination for the spatial light modulator a technique for homogenising the output of multi-mode �bre has been developed.
The study of low density, ultracold atomic Fermi gases is a promising avenue to understand fermion superfluidity from first principles. One technique currently used to bring Fermi gases in the degenerate regime is sympathetic cooling through a reservoir made of an ultracold Bose gas. We discuss a proposal for trapping and cooling of two-species Fermi-Bose mixtures into optical dipole traps made from combinations of laser beams having two different wavelengths. In these bichromatic traps it is possible, by a proper choice of the relative laser powers, to selectively trap the two species in such a way that fermions experience a stronger confinement than bosons. As a consequence, a deep Fermi degeneracy can be reached having at the same time a softer degenerate regime for the Bose gas. This leads to an increase in the sympathetic cooling efficiency and allows for higher precision thermometry of the Fermi - Bose mixture.
During my PhD, I participated in the full setup from scratch of an experiment that aims at cooling down and manipulating two fermionic alkaline atomic species, 6Li and 40K. Our goal is to study ultracold Fermi mixtures with mass imbalance, and to realize a flexible quantum analog simulator. In fact, for certain quantum many-body problems, such as high critical temperature superconductivity and frustrated anti-ferromagnetism, there is neither complete analytical nor numerical solution. Therefore, cold atoms systems, due to their purity and their high degree of tunability, even on their interaction itself, offer an interesting complementary point of view in the study of those phenomena. As far as the experimental setup is concerned, we built an ultra-high vacuum system, a complete and stable laser source for each species, as well as two performing atomic sources, a 6Li Zeeman slower and a 40K bidimensionnal magneto-optical trap; most of the optical and electrical quantities, as well as the imaging diagnostics, being computer controlled. Once those preliminary steps have been performed and optimized, we could obtain an efficient double magneto-optical trap, containing typically 5x10^9 atoms of 6Li and 8x10^9 atoms of 40K. In this configuration, we produced the first 6Li40K* heteronuclear molecules by photoassociation, for which we identified 70 rovibrational lines. In a second part, I describe in detail the magnetic transport of the atomic mixture, between the magneto-optical trap chamber and a science cell, located in an ultra-high vacuum region with large optical access. The complete setup, from its design to its experimental implementation and optimization, as well as the development of the program and the useful numerical diagnostics, are the heart of my work. The transport efficiency could be tested and optimized, allowing for an efficient transfer of the mixture in the science cell. Thus, after this thesis, all the experimental tools are operational in order to allow for evaporative cooling of the mixture in an optically plugged magnetic trap. Therefore, the field is open for quantum simulation and understanding of many-body problems in ultracold Fermi mixtures.
We give an overview on our current experiments with Bose-Fermi degenerate mixtures in a one dimensional (ID) optical lattice. Our system consists of a Fermi gas of 40 K atoms and a Bose-Einstein condensate of 87 Rb. The two species are simultaneously trapped in a combined magnetic and optical lattice potential. We have investigated the thermodynamical properties of the mixture in a tight lattice and observed a change in the density of states. This is a signature of a quasi two dimensional confinement of the atoms in the lattice sites. We also discuss the mechanical stability of the mixture in presence of the 1D lattice.
Ultracold atomic gases can be prepared in laboratory environments with unrivaled control and purity. In one and a half decades the field has evolved from the first Bose condensates in dilute alkali gases to multiple species mixtures and degenerate Fermi systems. Combining quantum degenerate fermions and optical lattices enables the simulation of relevant condensed matter systems. By observing the final state of an atomic sample in a tailored optical potential the system can be used as an analog quantum computer to evaluate Hamiltonians that are computationally impossible to tackle on classical computers. A versatile optical dipole trap has been constructed and characterized. The trap can be converted to an optical lattice, allowing for the investigation of the phase diagram of the two-component, one-dimensional, imbalanced Fermi gas.
I have been one of the main responsible for building a new laboratory for Bose-Einstein condensation with 87Rb. In particular, the experimental setup has been designed for performing experiments with Bose-Einstein condensates load into optical lattices of variable geometries. All parts essential for Bose-Einstein condensation are in place. Atoms are collected in a magneto-optical trap, transferred to another vacuum chamber, with better vacuum, and trapped in another magneto-optical trap. Atoms are successfully transferred to a dark magnetic trap, and system for diagnostics with absorption imaging has been realized. We have not yet been able to form a Bose-Einstein condensate, due to a range of technical difficulties. Equipment for alignment of optical lattices with flexible geometry has been designed, built, and tested. This tool has been proven to work as desired, and there is a great potential for a range of unique experiments with Bose-Einstein condensates in optical lattices of various geometries, including superlattices and quasi-periodic lattices. Numerical studies have been made on anisotropic optical lattices, and the existence of a transition between a 2D superfluid phase and a 1D Mott-insulating phase has been confirmed. We have shown that the transition is of Berezinskii-Kosterlitz-Thouless type. In another numerical study it has been shown that using stimulated Raman transitions is a practical method for transferring atoms between states in a double optical lattice. Thus, it will be possible to transfer populations between the lattices, with further applications in qubit read/write operations.