Collisional stability of a three-component degenerate Fermi gas

We report on the creation of a degenerate Fermi gas consisting of a balanced mixture of atoms in three different hyperfine states of $^6$Li. This new system consists of three distinguishable Fermions with different and tunable interparticle scattering lengths $a_{12}$, $a_{13}$ and $a_{23}$. We are able to prepare samples containing $5 \cdot 10^4$ atoms in each state at a temperature of about $215$nK, which corresponds to $T/T_F \approx 0.37$. We investigated the collisional stability of the gas for magnetic fields between 0 and 600 G and found a prominent loss feature at 130 G. From lifetime measurements we determined three-body loss coefficients, which vary over nearly three orders of magnitude

Atom-Dimer Scattering in a Three-Component Fermi Gas

Ultracold gases of three distinguishable particles with large scattering lengths are expected to show rich few-body physics related to the Efimov effect. We have created three different mixtures of ultracold 6Li atoms and weakly bound 6Li2 dimers consisting of atoms in three different hyperfine states and studied their inelastic decay via atom-dimer collisions. We have found resonant enhancement of the decay due to the crossing of Efimov-like trimer states with the atom-dimer continuum in one mixture as well as minima of the decay in another mixture, which we interpret as a suppression of exchange reactions of the type |12>+|3> -> |23>+|1>. Such a suppression is caused by interference between different decay paths and demonstrates the possiblity to use Efimov physics to control the rate constants for molecular exchange reactions in the ultracold regime.Comment: 5 pages, 3 figure

Preliminary navigation accuracy analysis for the TDRSS Onboard Navigation System (TONS) experiment on EP/EUVE

A Tracking and Data Relay Satellite System (TDRSS) Onboard Navigation System (TONS) is currently being developed by NASA to provide a high accuracy autonomous navigation capability for users of TDRSS and its successor, the Advanced TDRSS (ATDRSS). The fully autonomous user onboard navigation system will support orbit determination, time determination, and frequency determination, based on observation of a continuously available, unscheduled navigation beacon signal. A TONS experiment will be performed in conjunction with the Explorer Platform (EP) Extreme Ultraviolet Explorer (EUVE) mission to flight quality TONS Block 1. An overview is presented of TONS and a preliminary analysis of the navigation accuracy anticipated for the TONS experiment. Descriptions of the TONS experiment and the associated navigation objectives, as well as a description of the onboard navigation algorithms, are provided. The accuracy of the selected algorithms is evaluated based on the processing of realistic simulated TDRSS one way forward link Doppler measurements. The analysis process is discussed and the associated navigation accuracy results are presented

High-resolution imaging of ultracold fermions in microscopically tailored optical potentials

We report on the local probing and preparation of an ultracold Fermi gas on the length scale of one micrometer, i.e. of the order of the Fermi wavelength. The essential tool of our experimental setup is a pair of identical, high-resolution microscope objectives. One of the microscope objectives allows local imaging of the trapped Fermi gas of 6Li atoms with a maximum resolution of 660 nm, while the other enables the generation of arbitrary optical dipole potentials on the same length scale. Employing a 2D acousto-optical deflector, we demonstrate the formation of several trapping geometries including a tightly focussed single optical dipole trap, a 4x4-site two-dimensional optical lattice and a 8-site ring lattice configuration. Furthermore, we show the ability to load and detect a small number of atoms in these trapping potentials. A site separation of down to one micrometer in combination with the low mass of 6Li results in tunneling rates which are sufficiently large for the implementation of Hubbard-models with the designed geometries.Comment: 15 pages, 6 figure

Deterministic Preparation of a Tunable Few-Fermion System

Systems consisting of few interacting fermions are the building blocks of matter with atoms and nuclei being the most prominent examples. We have created an artificial few-body quantum system with complete control over the system's quantum state using ultracold fermionic atoms in an optical dipole trap. We deterministically prepare ground state systems consisting of one to ten particles with fidelities of ~ 90%. We can tune the inter-particle interactions to arbitrary values using a Feshbach resonance and have observed the interaction-induced energy shift for a pair of repulsively interacting atoms. With this work, quantum simulation of strongly correlated fewbody systems has become possible. In addition, these microscopic quantum systems can be used as building blocks for scalable quantum information processing.Comment: 8 pages, 6 figure

A Universal Trimer in a Three-Component Fermi Gas

We show that the recently measured magnetic field dependence of three-body loss in a three-component mixture of ultracold $^6$Li atoms [1,2] can be explained by the presence of a universal trimer state. Previous work suggested a universal trimer state as a probable explanation, yet failed to get good agreement between theory and experiment over the whole range of magnetic fields. For our description we adapt the theory of Braaten and Hammer [3] for three identical bosons to the case of three distinguishable fermions by combining the three scattering lengths $a_{12},$ $a_{23}$ and $a_{13}$ between the three components to an effective interaction parameter $a_m$. We show that taking into account a magnetic field variation of the lifetime of the trimer state is essential to obtain a complete understanding of the observed decay rates.Comment: 5 pages, 3 figure

Density profiles and density oscillations of an interacting three-component normal Fermi gas

We use a semiclassical approximation to investigate density variations and dipole oscillations of an interacting three-component normal Fermi gas in a harmonic trap. We consider both attractive and repulsive interactions between different pairs of fermions and study the effect of population imbalance on densities. We find that the density profiles significantly deviate from those of non-interacting profiles and extremely sensitive to interactions and population imbalance. Unlike for a two-component Fermi system, we find density imbalance even for balanced populations. For some range of parameters, one component completely repels from the trap center giving rise a donut shape density profile. Further, we find that the in-phase dipole oscillation frequency is consistent with Kohn's theorem and other two dipole mode frequencies are strongly effected by the interactions and the number of atoms in the harmonic trap.Comment: Total seven pages with five figures. Published versio

Orbit Determination and Navigation of the Solar Terrestrial Relations Observatory (STEREO)

This paper provides an overview of the required upgrades necessary for navigation of NASA's twin heliocentric science missions, Solar TErestrial RElations Observatory (STEREO) Ahead and Behind. The orbit determination of the STEREO spacecraft was provided by the NASA Goddard Space Flight Center's (GSFC) Flight Dynamics Facility (FDF) in support of the mission operations activities performed by the Johns Hopkins University Applied Physics Laboratory (APL). The changes to FDF's orbit determination software included modeling upgrades as well as modifications required to process the Deep Space Network X-band tracking data used for STEREO. Orbit results as well as comparisons to independently computed solutions are also included. The successful orbit determination support aided in maneuvering the STEREO spacecraft, launched on October 26, 2006 (00:52 Z), to target the lunar gravity assists required to place the spacecraft into their final heliocentric drift-away orbits where they are providing stereo imaging of the Sun

Observation of an Efimov spectrum in an atomic system

In 1970 V. Efimov predicted a puzzling quantum-mechanical effect that is still of great interest today. He found that three particles subjected to a resonant pairwise interaction can join into an infinite number of loosely bound states even though each particle pair cannot bind. Interestingly, the properties of these aggregates, such as the peculiar geometric scaling of their energy spectrum, are universal, i.e. independent of the microscopic details of their components. Despite an extensive search in many different physical systems, including atoms, molecules and nuclei, the characteristic spectrum of Efimov trimer states still eludes observation. Here we report on the discovery of two bound trimer states of potassium atoms very close to the Efimov scenario, which we reveal by studying three-particle collisions in an ultracold gas. Our observation provides the first evidence of an Efimov spectrum and allows a direct test of its scaling behaviour, shedding new light onto the physics of few-body systems.Comment: 10 pages, 3 figures, 1 tabl