61 research outputs found
Micromotion-induced Limit to Atom-Ion Sympathetic Cooling in Paul Traps
We present and derive analytic expressions for a fundamental limit to the
sympathetic cooling of ions in radio-frequency traps using cold atoms. The
limit arises from the work done by the trap electric field during a long-range
ion-atom collision and applies even to cooling by a zero-temperature atomic gas
in a perfectly compensated trap. We conclude that in current experimental
implementations this collisional heating prevents access to the regimes of
single-partial-wave atom-ion interaction or quantized ion motion. We determine
conditions on the atom-ion mass ratio and on the trap parameters for reaching
the s-wave collision regime and the trap ground state
Interaction of trapped ions with trapped atoms
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 179-186).In this thesis, I present results from two Paul-trap based ion traps carried out in the VuletiÄ laboratory: the Atom-Ion trap for collision studies between cold atoms and cold ions, and the Cavity-Array trap for studying the interaction between ionic ensembles and photons. The Atom-Ion trap overlaps a surface-planar ion trap with a magneto-optical trap (MOT) for neutral atoms. The initial results of this system were loading of a shallow surface-planar ion trap at an unprecedented high rate of 4. 105 s-1 and isotopic purity by photoionization from the MOT. We demonstrate the first collisions between trapped atoms and trapped ions in the Langevin collision regime between Yb+ and Yb. A measurement of the Langevin rate constant through charge-exchange collisions between [alpha]Yb+ and [beta]Yb over three orders of magnitude in collision energy down to 3 yueV follows. The measured rate coefficient of 6 - 10-10 cm 3 s-1 is in good agreement with the Langevin model based on theoretical predictions of the polarizability of Yb. The theory and limits of sympathetic cooling of ions by localized cold atoms at low temperature is outlined. Measurements of momentum-transfer collisions between Yb+ and Rb are presented indicating that momentum-transfer collisions affect the ion energy at the Langevin rate. Finally, the fabrication and assembly of the Cavity-Array trap are presented. The Cavity-Array trap overlaps a high-finesse optical cavity with a linear array of Paul traps in order to reach the high co-operativity limit with trapped ions. Initial results from loading of the Cavity- Array trap are shown, indicating successful overlap of the optical cavity mode with the ion trapping region and the ability to load individual sites of the array ion trap.by Andrew T. Grier.Ph.D
Observation of Cold Collisions between Trapped Ions and Trapped Atoms
We demonstrate a double-trap system well suited to study cold collisions
between trapped ions and trapped atoms. Using Yb ions confined in a Paul
trap and Yb atoms in a magneto-optical trap, we investigate charge-exchange
collisions of several isotopes for collision energies down to 400 neV (5 mK).
The measured rate coefficient of cms, constant
over four orders of magnitude in collision energy, is in good agreement with
that derived from a semiclassical Langevin model for an atomic polarizability
of 143 a.u.Comment: 4 pages, 4 figures; Revision 1/V2: Revised in response to PRL
Referees' comment
One-dimensional array of ion chains coupled to an optical cavity
We present a novel hybrid system where an optical cavity is integrated with a
microfabricated planar-electrode ion trap. The trap electrodes produce a
tunable periodic potential allowing the trapping of up to 50 separate ion
chains spaced by 160 m along the cavity axis. Each chain can contain up to
20 individually addressable Yb\textsuperscript{+} ions coupled to the cavity
mode. We demonstrate deterministic distribution of ions between the sites of
the electrostatic periodic potential and control of the ion-cavity coupling.
The measured strength of this coupling should allow access to the strong
collective coupling regime with 10 ions. The optical cavity could
serve as a quantum information bus between ions or be used to generate a strong
wavelength-scale periodic optical potential.Comment: 15 pages, 6 figures, submitted to New Journal of Physic
Universal Loss Dynamics in a Unitary Bose Gas
The low temperature unitary Bose gas is a fundamental paradigm in few-body
and many-body physics, attracting wide theoretical and experimental interest.
Here we first present a theoretical model that describes the dynamic
competition between two-body evaporation and three-body re-combination in a
harmonically trapped unitary atomic gas above the condensation temperature. We
identify a universal magic trap depth where, within some parameter range,
evaporative cooling is balanced by recombination heating and the gas
temperature stays constant. Our model is developed for the usual
three-dimensional evaporation regime as well as the 2D evaporation case.
Experiments performed with unitary 133 Cs and 7 Li atoms fully support our
predictions and enable quantitative measurements of the 3-body recombination
rate in the low temperature domain. In particular, we measure for the first
time the Efimov inelasticity parameter * = 0.098(7) for the 47.8-G
d-wave Feshbach resonance in 133 Cs. Combined 133 Cs and 7 Li experimental data
allow investigations of loss dynamics over two orders of magnitude in
temperature and four orders of magnitude in three-body loss. We confirm the 1/T
2 temperature universality law up to the constant *
Single-atom imaging of fermions in a quantum-gas microscope
Single-atom-resolved detection in optical lattices using quantum-gas
microscopes has enabled a new generation of experiments in the field of quantum
simulation. Fluorescence imaging of individual atoms has so far been achieved
for bosonic species with optical molasses cooling, whereas detection of
fermionic alkaline atoms in optical lattices by this method has proven more
challenging. Here we demonstrate single-site- and single-atom-resolved
fluorescence imaging of fermionic potassium-40 atoms in a quantum-gas
microscope setup using electromagnetically-induced-transparency cooling. We
detected on average 1000 fluorescence photons from a single atom within 1.5s,
while keeping it close to the vibrational ground state of the optical lattice.
Our results will enable the study of strongly correlated fermionic quantum
systems in optical lattices with resolution at the single-atom level, and give
access to observables such as the local entropy distribution and individual
defects in fermionic Mott insulators or anti-ferromagnetically ordered phases.Comment: 7 pages, 5 figures; Nature Physics, published online 13 July 201
Signature-Based Small Molecule Screening Identifies Cytosine Arabinoside as an EWS/FLI Modulator in Ewing Sarcoma
BACKGROUND: The presence of tumor-specific mutations in the cancer genome represents a potential opportunity for pharmacologic intervention to therapeutic benefit. Unfortunately, many classes of oncoproteins (e.g., transcription factors) are not amenable to conventional small-molecule screening. Despite the identification of tumor-specific somatic mutations, most cancer therapy still utilizes nonspecific, cytotoxic drugs. One illustrative example is the treatment of Ewing sarcoma. Although the EWS/FLI oncoprotein, present in the vast majority of Ewing tumors, was characterized over ten years ago, it has never been exploited as a target of therapy. Previously, this target has been intractable to modulation with traditional small-molecule library screening approaches. Here we describe a gene expressionâbased approach to identify compounds that induce a signature of EWS/FLI attenuation. We hypothesize that screening small-molecule libraries highly enriched for FDA-approved drugs will provide a more rapid path to clinical application. METHODS AND FINDINGS: A gene expression signature for the EWS/FLI off state was determined with microarray expression profiling of Ewing sarcoma cell lines with EWS/FLI-directed RNA interference. A small-molecule library enriched for FDA-approved drugs was screened with a high-throughput, ligation-mediated amplification assay with a fluorescent, bead-based detection. Screening identified cytosine arabinoside (ARA-C) as a modulator of EWS/FLI. ARA-C reduced EWS/FLI protein abundance and accordingly diminished cell viability and transformation and abrogated tumor growth in a xenograft model. Given the poor outcomes of many patients with Ewing sarcoma and the well-established ARA-C safety profile, clinical trials testing ARA-C are warranted. CONCLUSIONS: We demonstrate that a gene expressionâbased approach to small-molecule library screening can identify, for rapid clinical testing, candidate drugs that modulate previously intractable targets. Furthermore, this is a generic approach that can, in principle, be applied to the identification of modulators of any tumor-associated oncoprotein in the rare pediatric malignancies, but also in the more common adult cancers
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