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arXiv:2103.02387 · Review of Scientific Instruments

Long distance optical transport of ultracold atoms: A compact setup using a Moiré lens

Govind Unnikrishnan, Charly Beulenkamp, De-Chao Zhang, Krzysztof P. Zamarski, Manuele Landini, Hanns‐Christoph Nägerl

Published Jun 1, 2021• 13 citations
arXivHTMLPDF

Abstract

We present a compact and robust setup to optically transport ultracold atoms over long distances. Using a focus-tunable moiré lens that has recently appeared in the market, we demonstrate transport of up to a distance of 465 mm. A transfer efficiency of 70% is achieved with a negligible temperature change at 11 μK. With its high thermal stability and low astigmatism, the moiré lens is superior to fluid-based varifocal lenses. It is much more compact and stable than a lens mounted on a linear translation stage, allowing for simplified experimental setups.

DOI
10.1063/5.0049320

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We present a compact and robust setup to optically transport ultracold atoms over long distances. Using a focus-tunable moiré lens that has recently appeared in the market, we demonstrate transport of up to a distance of 465 mm. A transfer efficiency of 70% is achieved with a negligible temperature change at 11 μK. With its high thermal stability and low astigmatism, the moiré lens is superior to fluid-based varifocal lenses. It is much more compact and stable than a lens mounted on a linear translation stage, allowing for simplified experimental setups.
Abstract Optically trapped laser-cooled polar molecules hold promise for new science and technology in quantum information and quantum simulation. Large numerical aperture optical access and long trap lifetimes are needed for many studies, but these requirements are challenging to achieve in a magneto-optical trap (MOT) vacuum chamber that is connected to a cryogenic buffer gas beam source, as is the case for all molecule laser cooling experiments so far. Long distance transport of molecules greatly eases fulfilling these requirements as molecules are placed into a region separate from the MOT chamber. We realize a fast transport method for ultracold molecules based on an electronically focus-tunable lens combined with an optical lattice. The high transport speed is achieved by the 1D red-detuned optical lattice, which is generated by interference of a focus-tunable laser beam and a focus-fixed laser beam. Efficiency of 48(8)% is realized in the transport of ultracold calcium monofluoride (CaF) molecules over 46 cm distance in 50 ms, with a moderate heating from 32(2) μK to 53(4) μK. Positional stability of the molecular cloud allows for stable loading of an optical tweezer array with single molecules.
At temperatures near absolute zero, bosons form a macroscopic quantum state that can be manipulated and imaged in a very controlled and tunable way. To reach these extreme temperatures near absolute zero, advanced methods in cooling, including laser and evaporative cooling, must be used. In addition to these techniques for cooling, atoms must also be held up against the constant pull of gravity, so additional trapping techniques using lasers and magnets are used. In our lab at University of San Diego, we are implementing a tunable lens system (TLS) to optically transfer atoms to a more optically accessible location. A tunable lens (TL) is a lens where the curvature of the lens can be adjusted through an applied electrical current, thus translating where the focus of a lens is in a controlled way. This research aims to discover the optimal setup for a TLS to be used in the transportation of ultracold atoms in our system. In this research, I will report on the building of the TLS within the lab and the adjustment of various systems pertaining to the TL.
We present an optical setup with focus-tunable lenses to dynamically control the waist and focus position of a laser beam, in which we transport a trapped ultracold cloud of 87 Rb over a distance of . The scheme allows us to shift the focus position at constant waist, providing uniform trapping conditions over the full transport length. The fraction of atoms that are transported over the entire distance comes near to unity, while the heating of the cloud is in the range of a few microkelvin. We characterize the position stability of the focus and show that residual drift rates in focus position can be compensated for by counteracting with the tunable lenses. Beyond being a compact and robust scheme to transport ultracold atoms, the reported control of laser beams makes dynamic tailoring of trapping potentials possible. As an example, we steer the size of the atomic cloud by changing the waist size of the dipole beam.
We report the design and application of an optically compensated zoom lens supporting a moving optical dipole trap for transporting cold atoms. The proposed zoom lens is designed to have tunable magnification in a compact form factor which can significantly reduce the required long optical path lengths in conventional moving optical dipole trap systems. Without the need of mechanical cams for zooming, the optically compensated zoom lens has the ability to control the position of the trap along the optical axis with high precision while maintaining a constant trap depth by conserving the numerical aperture of the laser beam focus during the transport. We experimentally comprise an optically compensated zoom lens having dimensions of $\ensuremath{\lesssim}20$ cm in length, which can be readily configured to suit a wide range of desired transport lengths from 0.15 to 3 m and displacement magnifications from 7 to 100. The performance of our moving optical dipole trap is tested for a target transport length of 600 mm using a 532 nm laser beam on laser-cooled ytterbium atoms. The atoms can be transported to an adjacent vacuum chamber using this optically compensated zoom lens with $\ensuremath{\sim}89%$ efficiency.
Transporting cold atoms between distant sections of a vacuum system is a central ingredient in many quantum simulation experiments, in particular in setups, where large optical access and precise control over magnetic fields is needed. In this work, we demonstrate optical transport of cold cesium atoms over a total transfer distance of about 43 cm in less than 30ms30\phantom{\rule{0.16em}{0ex}}\mathrm{ms}30ms. The high speed is facilitated by a moving lattice, which is generated via the interference of a Bessel and a Gaussian laser beam. We transport about $3\ifmmode\times\else\texttimes\fi{}{10}^{6}$ atoms at a temperature of a few microkelvins with a transport efficiency of about 7575%75. We provide a detailed study of the transport efficiency for different accelerations and lattice depths and find that the transport efficiency is mainly limited by a fast initial loss most likely due to the sudden onset of the acceleration and the potential depth along the direction of gravity. To highlight the suitability of the optical-transport setup for quantum simulation experiments, we demonstrate the generation of a pure Bose-Einstein condensate with about $2\ifmmode\times\else\texttimes\fi{}{10}^{4}$ atoms. We find a robust final atom number within 22%2 over a duration of 2.5 h with a standard deviation of <5<5%<5 between individual experimental realizations.
We present a novel method for transporting ultracold atoms in a focused optical lattice over macroscopic distances of many Rayleigh ranges. With this method ultracold atoms were transported over 5 cm in 250 ms without significant atom loss or heating. By translating the interference pattern together with the beam geometry, the trap parameters are maintained over the full transport range. Thus, the presented method is well suited for tightly focused optical lattices that have sufficient trap depth only close to the focus. Tight focusing is usually required for far-detuned optical traps or traps that require high laser intensity for other reasons. The transport time is short and thus compatible with the operation of an optical lattice clock in which atoms are probed in a well-designed environment spatially separated from the preparation and detection region.