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Register a new userTrapping of ultra cold atoms in a 3He/4He dilution refrigerator
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We describe the preparation of ultra cold atomic clouds in a dilution refrigerator. The closed cycle 3He/4He cryostat was custom made to provide optical access for laser cooling, optical manipulation and detection of atoms. We show that the cryostat meets the requirements for cold atom experiments, specifically in terms of operating a magneto-optical trap, magnetic traps and magnetic transport under ultra high vacuum conditions. The presented system is a step towards the creation of a quantum hybrid system combining ultra cold atoms and solid state quantum devices.
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We experimentally and numerically study the temporal dynamics of light scattered by large clouds of cold atoms after the exciting laser is switched off in the low intensity (linear optics) regime. Radiation trapping due to multiple scattering as well as subradiance lead to decay much slower than the single atom fluorescence decay. These two effects have already been observed separately, but the interplay between them remained to be understood. Here, we show that with well chosen parameters of the driving field, the two effects can occur at the same time, but follow different scaling behaviors. The subradiant decay is observed at late time and its rate is independent of the detuning, while the radiation trapping decay is observed at intermediate time and depends on the detuning through the optical depth of the sample. Numerical simulations based on random walk process and coupled-dipole equations support our interpretations. Our study clarifies the different interpretations and physical mechanisms at the origin of slow temporal dynamics of light in cold atoms.
We store and control ultra-cold atoms in a new type of trap using magnetic fields of vortices in a high temperature superconducting micro-structure. This is the first time ultra-cold atoms have been trapped in the field of magnetic flux quanta. We generate the attractive trapping potential for the atoms by combining the magnetic field of a superconductor in the remanent state with external homogeneous magnetic fields. We show the control of crucial atom trap characteristics such as an efficient intrinsic loading mechanism, spatial positioning of the trapped atoms and the vortex density in the superconductor. The measured trap characteristics are in good agreement with our numerical simulations.
We measure the temperature of ultra-cold Rb-87 gases transferred into an optical lattice and compare to non-interacting thermodynamics for a combined lattice--parabolic potential. Absolute temperature is determined at low temperature by fitting quasimomentum distributions obtained using bandmapping, i.e., turning off the lattice potential slowly compared with the bandgap. We show that distributions obtained at high temperature employing this technique are not quasimomentum distributions through numerical simulations. To overcome this limitation, we extract temperature using the in-trap size of the gas.
We studied light assisted collisions of Tm atoms in a magneto optical trap (MOT) for the first time, working on a weak cooling transition at 530.7 nm $(4f^{13}(^2F^0)6s^2,J=7/2,F=4$ to $4f^{12}(^3H_6)5d_{5/2}6s^2,J=9/2,F=5)$. We observed a strong influence from radiation trapping and light assisted collisions on the dynamics of this trap. We carefully separated these two contributions and measured the binary loss rate constant at different laser powers and detuning frequencies near the cooling transition. Analyzing losses from the MOT, we found the light assisted inelastic binary loss rate constant to reach values of up to $beta=10^{-9}$ cm$^3$/s and gave the upper bound on a branching ratio $k<0.8times 10^{-6}$ for the 530.7 nm transition.
We trap cold, ground-state, argon atoms in a deep optical dipole trap produced by a build-up cavity. The atoms, which are a general source for the sympathetic cooling of molecules, are loaded in the trap by quenching them from a cloud of laser-cooled metastable argon atoms. Although the ground state atoms cannot be directly probed, we detect them by observing the collisional loss of co-trapped metastable argon atoms using a new type of parametric loss spectroscopy. Using this technique we also determine the polarizability ratio between the ground and the metastable 4s[3/2]$_2$ state to be 40$pm6$ and find a polarisability of (7.3$pm$1.1) $times$10$^{-39}$ Cm$^2/$V for the metastable state. Finally, Penning and associative losses of metastable atoms, in the absence of light assisted collisions, are determined to be $(3.3pm 0.8) times 10^{-10}$ cm$^3$s$^{-1}$.
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