Session E04: Next-Generation Platforms for Trapping and Cooling

NASA's Cold Atom Lab Operating Onboard the Intertnational Space Station

The Cold Atom Lab (CAL) launched to the International Space Station (ISS) in May 2018, and has been operating since that time as the world’s first multi-user facility for the study of ultra-cold atoms in space. The unique microgravity environment of the ISS is utilized with CAL by a national group of principal investigators to achieve exceptionally low temperature gases, to study and utilize their quantum properties in an environment free from the perturbing force of gravity, and to observe and interact with these gases in the essentially limitless free-fall of orbit. In addition to the toolbox of capabilities originally built into CAL, an upgrade in 2020 enabled the study of atom interferometry in orbit, a 2021 upgrade and repair enabled studies with dual-species rubiduim-potassium bosonic gases, and planning is ongoing for a near-term upgrade to further enable novel science with quantum gases in space. We will give an overview of the microgravity enabled quantum gas research explored with CAL to date and discuss near-term projects to study dual-species gases using both rubidium and potassium quantum gases. The impact from this work, and potential for follow-on studies, will also be reviewed in the context of future space-based fundamental physics missions.

    

An optical dipole trap in a drop tower - the PRIMUS-project

The application of matter wave interferometry in a microgravity (µg) environment offers the potential of largely extended interferometer times and thereby highly increased sensitivities in precision measurements, e.g. of the universality of free fall. While most µg-based cold atom experiments use magnetic trapping on an atom chip, we develop an optical dipole trap as an alternative source for matter wave interferometry in weightlessness. Solely using optical potentials offers unique advantages like improved trap symmetry, trapping of all magnetic sub-levels and the accessibility of Feshbach resonances. Equipping a 50W trapping laser at a wavelength of 1064nm we implement a cold atom experiment for use in the drop tower at ZARM in Bremen, a free fall tower with a height of 110m offering 4.7s of microgravity time with excellent microgravity quaity. We demonstrated Bose-Einstein condensation of Rubidium in a compact setup on ground while now focusing on a fast, efficient preparation in microgravity using painted optical potentials. Within this talk we will report on the current status and latest results of the experiment.   

Single-beam laser cooling and magnetic trapping using a nano-structured atom chip

Bose-Einstein condensates (BECs) are interesting sources for a wide range of research areas due to their unique quantum properties. They are typically created using evaporative cooling in high frequency atomic traps. In particular, atom chips have proven their ability to create BECs very efficiently, even in challenging environmental conditions such as sounding rockets or the international space station. With the recent realization of grating magneto-optical traps (gMOTs), an exciting route to further improve such devices has opened: Since all required MOT beams are generated by diffraction from the grating, a single input beam suffices which promises greater long-term stability at reduced complexity.

We present the implementation of a nano-structured atom chip with results on magneto-optical trapping, sub-Doppler cooling, and magnetic trapping. These results pave the way towards a compact single-beam BEC apparatus for general use and transportable applications.   

Diffraction gratings for atom cooling produced by direct laser writing

We report the use of a direct laser-writing process to fabricate a 2D diffraction grating that can form a magneto-optical trap from a single laser  beam. This approach significantly speeds up the fabrication process of these gratings compared to the conventionally used electron-beam lithography approach [1]. We also discuss the effects of imperfect suppression of higher-order diffractions — arising from the resolution limits of the direct laser writer — on the trapping and cooling region of the MOT.

[1] A surface-patterned chip as a strong source of

ultracold atoms for quantum technologies, C. C. Nshii1, M. Vangeleyn1, J. P. Cotter2, P. F. Griffin, E. A. Hinds, C. N. Ironside, P. See, A. G. Sinclair, E. Riis and A. S. Arnold   

A New Platform for Programmable Arrays of Strontium Atoms

We report on a new apparatus for trapping ultracold strontium in optical tweezer arrays. Our platform is exciting due to its small footprint, simple optical setup, and adaptability for strontium-based experiments. Using a novel 2D MOT design based on dispensers, we prepare cold atoms for single-atom trapping. We also present progress towards the magic wavelength trapping of strontium in arbitrary optical patterns produced by holographic metasurfaces. A goal of this setup is the investigation of subradiance in ordered atomic arrays. The platform is suitable for a broad range of applications spanning quantum optics, quantum simulation, and quantum computation experiments.   

Optical Tweezer Arrays Created by Holographic Metasurfaces

We report on the creation of optical tweezer arrays generated by holographic metasurfaces. Metasurfaces allow full holographic control over light fields, enabling the creation of arbitrary optical trapping geometries. We have designed and fabricated patterns spanning 1D to 3D, featuring quasicrystal, twisted bilayer honeycomb, and 3D cubic lattice structures. We have characterized the metasurfaces with a 520 nm laser, studying the thermal response under high power, trap homogeneity, and position accuracy. In addition, we have created and characterized metasurfaces that can switch between two trapping geometries via polarization tuning. We are working towards trapping strontium atoms using this novel nanophotonic platform.   

Optical trapping of 88Sr around a nanotapered optical fiber

Interfacing ultracold atoms with the large evanescent fields around a nanotapered optical fiber offers a rich toolbox for quantum science, such as probing subtle quantum effects. In particular, strontium is an excellent candidate for high-resolution spectroscopy on such platforms due to its 7.6 kHz-linewidth intercombination transition. However, the high-intensity optical fields required for trapping at the nanotapered region can introduce unwanted position- and state-dependent energy shifts on the atoms. Employing magic wavelengths with proper polarization of the evanescent fields ensures the atomic transition is insensitive to the trap. We demonstrate optical trapping of ⁸⁸Sr atoms in a two-color, state-insensitive trap around a 215-nm diameter tapered fiber at well-defined distances of hundreds of nanometers from the fiber surface. In this two-color trap, adjusting the attractive and repulsive intensities can precisely tune the atom-surface separation. This platform opens the door to performing high-resolution spectroscopy measurements of the Casimir-Polder interaction between the trapped atoms and the fiber dielectric surface.   

An electro-optical trap for polar molecules

A detailed treatment of an electro-optical trap/tweezer for polar molecules, realized by embedding an optical trap within a uniform electrostatic field, is presented and the trap's  properties discussed. The electro-optical trap offers significant advantages over an optical trap that include an increased trap depth and conversion of alignment of the trapped molecules to marked orientation. Tilting the polarization plane of the optical field with respect to the electrostatic field lifts the degeneracy of the M  states of the trapped molecules. These and other features of the electro-optical trap are explained in terms of the eigenproperties of the polar and polarizable molecules subject to the combined permanent and induced electric dipole interactions at play.   

A Novel individual addressing system for ions in a micro-fabricated trap

Trapped ions are one of the most promising platforms for the large-scale implementation of quantum information processing. For the realization of such a device, control over the state of individual qubits is necessary. Current implementations rely on acousto-optic deflectors, multi-channel acousto-optic modulators (AOMs) or micromirror devices for holographic beam shaping. Such implementations either suffer from high crosstalk, lack parallel addressing or the ability to control the frequency and phase of each beam. Here we describe the novel individual addressing system of our trapped-ion computer currently under construction. The system is designed for enabling Raman-based gates on 16 Ba+ ions. It consists of an array of laser-written waveguides that split the light into 16 channels and couple each into single mode fibers. Fiber-based AOMs provide control over the frequency, phase and amplitude of each channel and a micro-lens-based telescope maps the light from each fiber channel to an ion in the trap with low crosstalk. The use of such technology is enabled by the desirable energy level structure of Ba+, namely the visible S- to P-shell transition used for Raman operations.    

Advancements toward Cryogenic System for Electric Gradient Gates and Molecular Qubits

Dipolar molecular ions possess an expansive state space which offers a unique platform for qubit operations. An application was proposed recently to enable laser free qubit manipulation of molecular ions by applying sub-gigahertz quadrupole RF fields to the electrodes of the ion trap (PhysRevA. 2021, 104, 042605). Addressing the molecular states with this method enables qubit control independent of the ion motional state, in contrast to the optical Lamb-Dicke limit. To provide greater control over the molecular qubit states and suppress unwanted chemical reactions, we have developed a new cryogenic system that is capable of reaching 6K with minimal vibrations. With the aid of this new trap, we are posed to co-trap Ca⁺ with HCl⁺ and pursue non-destructive state readout as a SPAM for molecular quantum computing.