Magneto-optical Trap Research Articles

Apparatus for producing single strontium atoms in an optical tweezer array

Abstract We outline an experimental setup for efficiently preparing a tweezer array of $^{88}$Sr atoms. Our setup uses permanent magnets to maintain a steady-state two-dimensional magneto-optical trap (MOT) which results in a loading rate of up to $10^{8}$ s$^{-1}$ at 5 mK for the three-dimensional blue MOT. This enables us to trap $2\times10^{6}$ $^{88}$Sr atoms at 2 $\mu$K in a narrow-line red MOT with the $^{1}$S$_{0}$ $\rightarrow$ $^{3}$P$_{1}$ intercombination transition at 689 nm. With the Sisyphus cooling and pairwise loss processes, single atoms are trapped and imaged in 813 nm optical tweezers, exhibiting a lifetime of 2.5 minutes. We further investigate the survival fraction of a single atom in the tweezers and characterize the optical tweezer array using a release and recapture technique. Our experimental setup serves as an excellent reference for those engaged in experiments involving optical tweezer arrays, cold atom systems, and similar research.

Experimental realization of multiple frequency photoassociation in an optical dipole trap.

The generation of cold molecules is an important topic in the field of cold atoms and molecules and has received relevant advanced research attention in ultracold chemistry, quantum computation, and quantum metrology. With a high atomic phase space density, optical dipole traps have been widely used to prepare, trap, and study cold molecules. In this work, Rb2 molecules were photoassociated in a magneto-optical trap to obtain a precise rovibrational spectrum, which provided accurate numerical references for the realization of multiple frequency photoassociation. By meeting the harsh requirements of photoassociation in optical dipole traps, the cold molecule photoassociation process was well explored, and different photoassociation resonances were simultaneously addressed in a single optical dipole trap. This method can be universally extended to simultaneously photoassociate cold molecules with different internal states or atomic species in a single optical dipole trap, thus advancing generous cold molecule studies such as cold molecule collision dynamics.

Three-Dimensional Magneto-Optical Trapping of Barium Monofluoride.

As a heavy molecule, barium monofluoride (BaF) presents itself as a promising candidate for measuring permanent electric dipole moment. Here we report the realization of three-dimensional magneto-optical trapping (MOT) of BaF molecules. Through the repumping of all the vibrational states up to v=3, and rotational states up to N=3, we effectively close the transition to a leakage level lower than 10^{-5}. This approach enables molecules to scatter a sufficient number of photons required for laser cooling and trapping. By employing a technique that involves chirping the slowing laser frequency, BaF molecules are decelerated to near-zero velocity, resulting in the capture of approximately 3×10^{3} molecules in a MOT. Our findings represent a significant step towards the realization of ultracold BaF molecules and the conduct of precision measurements with cold molecules.

Reinforcement learning in cold atom experiments

Cold atom traps are at the heart of many quantum applications in science and technology. The preparation and control of atomic clouds involves complex optimization processes, that could be supported and accelerated by machine learning. In this work, we introduce reinforcement learning to cold atom experiments and demonstrate a flexible and adaptive approach to control a magneto-optical trap. Instead of following a set of predetermined rules to accomplish a specific task, the objectives are defined by a reward function. This approach not only optimizes the cooling of atoms just as an experimentalist would do, but also enables new operational modes such as the preparation of pre-defined numbers of atoms in a cloud. The machine control is trained to be robust against external perturbations and able to react to situations not seen during the training. Finally, we show that the time consuming training can be performed in-silico using a generic simulation and demonstrate successful transfer to the real world experiment.

Use of the 5P3/2→6P3/2 electric dipole forbidden transition in Rb as a non-perturbing probe of atom dynamics in an operating magneto-optical trap

Abstract Results of spectroscopy experiments using the $5P_{3/2} \to 6P_{3/2}$ electric dipole forbidden transition in cold rubidium atoms are presented. Production of this forbidden transition is detected by observing the emission of the $420 $ nm fluorescence photons that result from the decay of the $6P_{3/2} $ state into the ground state. The experiments are performed under the steady state operation conditions of a magneto-optical trap (MOT), and thus provide non-perturbing information on the atom-light system. The hyperfine structure of the $6P_{3/2}$ level is completely resolved, and the fluorescence peaks show the expected Autler-Townes (AT) splitting of the emission lines. This hyperfine structure is used to calibrate the frequency scale of all spectra recorded. A combination of this absolute frequency scale and an expression for the AT profile allows an absolute determination of the effective Rabi frequency and detuning of the MOT. The behavior of these AT doublets is studied as a function of frequency detuning and also as a function of the trapping light intensity.
The experiments also take full advantage of the strong polarization dependence of the relative intensities of the hyperfine fluorescence components.
This study results in a sensitive probe of the relative populations of the magnetic sublevel projections relative to the trapping magnetic field gradient.
An almost isotropic population distribution was found, but small deviations from isotropy could be determined with this electric dipole forbidden probe.

Ratchet loading and multi-ensemble operation in an optical lattice clock

We demonstrate programmable control over the spatial distribution of ultra-cold atoms confined in an optical lattice. The control is facilitated through a combination of spatial manipulation of the magneto-optical trap and atomic population shelving to a metastable state. We first employ the technique to load an extended (5 mm) atomic sample with uniform density in an optical lattice clock (OLC), reducing atomic interactions and realizing remarkable frequency homogeneity across the atomic cloud. We also prepare multiple spatially separated atomic ensembles, and realize multi-ensemble clock operation within the standard one-dimensional (1D) OLC architecture. Leveraging this technique, we prepare two oppositely spin-polarized ensembles that are independently addressable, offering a platform for implementing spectroscopic protocols for enhanced tracking of local oscillator phase. Finally, we demonstrate a relative fractional frequency instability at one second of 2.4(1)×10−17 between two ensembles, useful for characterization of intra-lattice differential systematics.

Realization of a single-beam, detachable, cascaded 2D magneto-optical trap based modular cesium source

We present a detachable, cascaded modular cesium loading source based on a 2D magneto-optical trap (MOT). Our design utilizes only a single beam of mixed cooling and repumping light that is split evenly into five discrete trapping regions, each with horizontal and vertical beams. The pre-aligned, single-beam design makes our module suitable for miniaturization. The generated cold atomic beam serves to load a 3D MOT, whose loading rate we use to characterize the efficiency of our design. The effect of individual trapping regions relative to the differential tube and to each other on the loading rate has also been examined. Experimental results were compared with a numerical simulation. We are able to obtain an experimental loading rate of nearly 8×107atoms/s and a vapor density of about 3×1015atoms/m3 in our 2D MOT module.

Realization of a chip-based hybrid trapping setup for 87Rb atoms and Yb+ ion crystals.

Hybrid quantum systems integrate laser-cooled trapped ions and ultracold quantum gases within a single experimental configuration, offering vast potential for applications in quantum chemistry, polaron physics, quantum information processing, and quantum simulations. In this study, we introduce the development and experimental validation of an ion trap chip that incorporates a flat atomic chip trap directly beneath it. This innovative design addresses specific challenges associated with hybrid atom-ion traps by providing precisely aligned and stable components, facilitating independent adjustments of the depth of the atomic trapping potential, and positioning trapped ions. Our findings include the simultaneous loading of the ion trap with linear Yb+ ion crystals and the loading of neutral 87Rb atoms into a mirror magneto-optical trap.

Effect of light-assisted tunable interaction on the position response function of cold atoms.

The position response of a particle subjected to a perturbation is of general interest in physics. We study the modification of the position response function of an ensemble of cold atoms in a magneto-optical trap (MOT) in the presence of tunable light-assisted interactions. We subject the cold atoms to an intense laser light tuned near the photoassociation (PA) resonance and observe the position response of the atoms subjected to a sudden displacement. Surprisingly, we observe that the entire cold atomic cloud undergoes collective oscillations. We use a generalized quantum Langevin approach to theoretically analyze the results of the experiments and find good agreement.

Compact magneto-optical traps using planar optics

Abstract Magneto-optical traps (MOTs) composed of magnetic fields and light fields have been widely utilized to cool and confine microscopic particles. Practical technology applications require miniaturized MOTs. The advancement of planar optics has promoted the development of compact MOTs. In this article, we review the development of compact MOTs based on planar optics. First, we introduce the standard MOTs. We then introduce the grating MOTs with micron structures, which have been used to build cold atomic clocks, cold atomic interferometers, and ultra-cold sources. Further, we introduce the integrated MOTs based on nano-scale metasurfaces. These new compact MOTs greatly reduce volume and power consumption, and provide new opportunities for fundamental research and practical applications.

Measurements of cesium PJ-series quantum defect with the microwave spectroscopy

High-precision microwave spectroscopy has been used to measure the transition frequency of nS1/2 → nPJ (n is the principle quantum number) and further the quantum defect of nPJ states in a standard cesium magneto-optical trap. A microwave field with 30-μs duration coupling the nS1/2 → nP1/2,3/2 transition yields a narrow linewidth microwave spectroscopy with the linewidth approaching the Fourier limit. After carefully compensating the stray electric and magnetic field and using the diluted atomic gas, we extract improved quantum defects of nPJ state, δ0(nP1/2) = 3.59159091(19), δ2(nP1/2) = 0.36092(35) and δ0(nP3/2) = 3.55907153(25), δ2(nP3/2) = 0.37344(47).

Compact structures for single-beam magneto-optical trapping of ytterbium.

At present, the best optical lattice clocks are based on the spectroscopy of trapped alkaline-earth-like atoms such as ytterbium and strontium. The development of mobile or even space-borne clocks necessitates concepts for the compact laser-cooling and trapping of these atoms with reduced laser requirements. Here, we present two compact and robust achromatic mirror structures for single-beam magneto-optical trapping of alkaline-earth-like atoms using two widely separated optical cooling frequencies. We have compared the trapping and cooling performance of a monolithic aluminum structure that generates a conventional trap geometry to a quasi-planar platform based on a periodic mirror structure for different isotopes of Yb. Compared to prior work with strontium in non-conventional traps, where only bosons were trapped on a narrow line transition, we demonstrate two-stage cooling and trapping of a fermionic alkaline-earth-like isotope in a single-beam quasi-planar structure.

Blue-Detuned Magneto-optical Trap of CaF Molecules.

A key method to produce trapped and laser-cooled molecules is the magneto-optical trap (MOT), which is conventionally created using light red detuned from an optical transition. In this work, we report a MOT for CaF molecules created using blue-detuned light. The blue-detuned MOT (BDM) achieves temperatures well below the Doppler limit and provides the highest densities and phase-space densities reported to date in CaF MOTs. Our results suggest that BDMs are likely achievable in many relatively light molecules including polyatomic ones, but our measurements suggest that BDMs will be challenging to realize in substantially heavier molecules due to sub-mK trap depths. In addition to record temperatures and densities, we find that the BDM substantially simplifies and enhances the loading of molecules into optical tweezer arrays, which are a promising platform for quantum simulation and quantum information processing. Notably, the BDM reduces molecular number requirements ninefold compared to a conventional red-detuned MOT, while not requiring additional hardware. Our work therefore substantially simplifies preparing large-scale molecular tweezer arrays, which are a novel platform for simulation of quantum many-body dynamics and quantum information processing with molecular qubits.

Cavity-based nondestructive detection of photoassociation in a dark magneto-optical trap

Cavity-based nondestructive detection of photoassociation in a dark magneto-optical trap

Development of a pyramidal magneto-optical trap for pressure sensing application

Development of a pyramidal magneto-optical trap for pressure sensing application

Review and experimental benchmarking of machine learning algorithms for efficient optimization of cold atom experiments

The generation of cold atom clouds is a complex process which involves the optimization of noisy data in high dimensional parameter spaces. Optimization can be challenging both in and especially outside of the lab due to lack of time, expertise, or access for lengthy manual optimization. In recent years, it was demonstrated that machine learning offers a solution since it can optimize high dimensional problems quickly, without knowledge of the experiment itself. In this paper we present results showing the benchmarking of nine different optimization techniques and implementations, alongside their ability to optimize a rubidium (Rb) cold atom experiment. The investigations are performed on a 3D 87Rb molasses with 10 and 18 adjustable parameters, respectively, where the atom number obtained by absorption imaging was chosen as the test problem. We further compare the best performing optimizers under different effective noise conditions by reducing the signal-to-noise ratio of the images via adapting the atomic vapor pressure in the 2D+ magneto-optical trap and the detection laser frequency stability.

Spectroscopy of the 5s5p3P0→5s5d3D1 transition of strontium using laser cooled atoms

This article presents spectroscopy results of the 5s5p3P0→5s5d3D1 transition in all isotopes of laser cooled Sr atoms and the utility of this transition for repumping application. By employing the 5s5p3P0→5s5d3D1 (483 nm) transition in combination with the excitation of 5s5p3P2→5s6s3S1 (707 nm) transition, we observe a significant increase (∼13 fold) in the steady state number of atoms in the magneto-optic trap. This enhancement is attributed to the efficient repumping of Sr atoms that have decayed into the dark 5s5p3P2 state by returning them to the ground state 5s21S0 without any loss into the other states. The absolute transition frequencies were measured with an absolute accuracy of 30 MHz. To support our measurements, we performed Fock-space relativistic coupled-cluster calculations of the relevant parameters in Sr To further increase the accuracy of the calculated properties, corrections from the Breit, quantum electrodynamical and perturbative triples were also included. The calculated branching ratio for the repumping state confirms the significantly increased population in the 3P1 state. Thereby, leading to an increase of population of atoms trapped due to the enhanced repumping. Our calculated hyperfine-splitting energies are in excellent agreement with the measured values. Moreover, our calculated isotope shifts in the transition frequencies are in good agreement with our measured values.

High Density Loading and Collisional Loss of Laser-Cooled Molecules in an Optical Trap.

We report optical trapping of laser-cooled molecules at sufficient density to observe molecule-molecule collisions for the first time in a bulk gas. SrF molecules from a red-detuned magneto-optical trap (MOT) are compressed and cooled in a blue-detuned MOT. Roughly 30% of these molecules are loaded into an optical dipole trap with peak number density n_{0}≈3×10^{10} cm^{-3} and temperature T≈40 μK. We observe two-body loss with rate coefficient β=2.7_{-0.8}^{+1.2}×10^{-10} cm^{3} s^{-1}. Achieving this density and temperature opens a path to evaporative cooling towards quantum degeneracy of laser-cooled molecules.

High flux strontium atom source

We present a novel cold strontium atom source designed for quantum sensors. We optimized the deceleration process to capture a large velocity class of atoms emitted from an oven and achieved a compact and low-power setup capable of generating a high atomic flux. Our approach involves velocity-dependent transverse capture of atoms using a two-dimensional magneto-optical trap. To enhance the atomic flux, we employ tailored magnetic fields that minimize radial beam expansion and incorporate a cascaded Zeeman-slowing configuration utilizing two optical frequencies. The performance is comparable to that of conventional Zeeman slower sources, and the scheme is applicable to other atomic species. Our results represent a significant advancement towards the deployment of portable and, possibly, space-based cold atom sensors.

Steady-State Ultracold Plasma Created by Continuous Photoionization of Laser Cooled Atoms.

In this Letter we discuss our approach that makes possible creation of the steady-state ultracold plasma having various densities and temperatures by means of continuous two-step optical excitation of calcium atoms in the magneto-optical trap. A strongly coupled ultracold plasma can be used as an excellent test platform for studying many-body interactions associated with various plasma phenomena. The parameters of the plasma are studied using laser-induced fluorescence of calcium ions. The experimental results are well described by a simple theoretical model involving equilibration of the continuous source of charged particles by the hydrodynamical ion outflux and three-body recombination. The ultracold plasma with the peak ion density of 2.7×10^{6} cm^{-3} and the minimum electron temperature near 2K has been prepared. Our steady-state approach in combination with the strong magnetic confinement of the plasma will make it possible to reach extremely strong coupling in such system.