Magneto-optical Trap Research Articles

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.

Optical pumping of 5s4d1D2 strontium atoms for laser cooling and imaging

We present a faster repumping scheme for strontium magneto-optical traps operating on the broad 5s21S0−5s5p1P1 laser cooling transition. Contrary to existing repumping schemes, we directly address lost atoms that spontaneously decayed to the 5s4d1D2 state, sending them back into the laser cooling cycle by optical pumping on the 5s4d1D2−5s8p1P1 transition. We thus avoid the ∼100µs-slow decay path from 5s4d1D2 to the 5s5p3P1,2 states that is part of other repumping schemes. Using one low-cost external-cavity diode laser emitting at 448nm, we show our scheme increases the flux out of a 2D magneto-optical trap by 60% compared to without repumping. Furthermore, we perform spectroscopy on the 5s4d1D2−5s8p1P1 transition and measure its frequency νSr88=(668917515.3±4.0±25)MHz. We also measure the frequency shifts between the four stable isotopes of strontium and infer the specific mass and field shift factors, δνSMS88,86=−267(45)MHz and δνFS88,86=2(42)MHz. Finally, we measure the hyperfine splitting of the 5s8p1P1 state in fermionic strontium and deduce the magnetic dipole and electric quadrupole coupling coefficients A=−4(5)MHz and B=5(35)MHz. Our experimental demonstration shows that this simple and very fast scheme could improve the laser cooling and imaging performance of cold strontium atom devices, such as quantum computers based on strontium atoms in arrays of optical tweezers. Published by the American Physical Society 2024

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.

Progress toward ultra-cold Sr for the AION project—A red MOT and an optical-heterodyne diagnostic tool for injection-locked laser diodes

Long-baseline atom interferometers, such as the one to be built by the AION collaboration, require ultra-cold atomic clouds. These are produced by trapping the atoms in magneto-optical traps (MOTs) using high-power, narrow-linewidth lasers. We report on the laser and optical master–slave injection-locked system used to address the 1S0–3P1 strontium transition at 689 nm and on the trapping of strontium atoms in a narrowband MOT. We demonstrate the quality of the injection through the characterization of the injection lock using an easy-to-assemble method that uses a double-pass acousto-optic modulator to generate and detect a heterodyne beatnote. The reported system is used to produce an atomic cloud at a temperature of 812(43) nK in a narrowband red MOT.

Centralized design and production of the ultra-high vacuum and laser-stabilization systems for the AION ultra-cold strontium laboratories

This paper outlines the centralized design and production of the ultra-high-vacuum sidearm and laser-stabilization systems for the AION Ultra-Cold Strontium Laboratories. Commissioning data on the residual gas and steady-state pressures in the sidearm chambers, on magnetic field quality, on laser stabilization, and on the loading rate for the 3D magneto-optical trap are presented. Streamlining the design and production of the sidearm and laser stabilization systems enabled the AION Collaboration to build and equip in parallel five state-of-the-art Ultra-Cold Strontium Laboratories within 24 months by leveraging key expertise in the collaboration. This approach could serve as a model for the development and construction of other cold atom experiments, such as atomic clock experiments and neutral atom quantum computing systems, by establishing dedicated design and production units at national laboratories.

Continuous cold rubidium atomic beam with enhanced flux and tunable velocity.

We present a cold atomic beam source based on a two-dimensional (2D)+ magneto-optical trap (MOT), capable of generating a continuous cold beam of 87Rb atoms with a flux up to 4.3 × 109 s-1, a mean velocity of 10.96(2.20) m/s, and a transverse temperature of 16.90(1.56) µK. Investigating the influence of high cooling laser intensity, we observe a significant population loss of atoms to hyperfine-level dark states. To account for this, we employ a multiple hyperfine level model to calculate the cooling efficiency associated with the population in dark states, subsequently modifying the scattering force. Simulations of beam flux at different cooling and repumping laser intensities using the modified scattering force are in agreement with experimental results. Optimizing repumping and cooling intensities enhances the flux by 50%. The influence of phase modulation on both the pushing and cooling lasers is experimentally studied, revealing that the mean velocity of cold atoms can be tuned from 9.5 m/s to 14.6 m/s with a phase-modulated pushing laser. The versatility of this continuous beam source, featuring high flux, controlled velocity, and narrow transverse temperature, renders it valuable for applications in atom interferometers and clocks, ultimately enhancing bandwidth, sensitivity, and signal contrast in these devices.

Low power consumption grating magneto-optical trap based on planar elements.

The grating-based magneto-optical trap (GMOT) is a promising approach for miniaturizing cold-atom systems. However, the power consumption of a GMOT system dominates its feasibility in practical applications. In this study, we demonstrated a GMOT system based on planar elements that can operate with low power consumption. A high-diffraction-efficiency grating chip was used to cool atoms with a single incident beam. A planar coil chip was designed and fabricated with a low power consumption nested architecture. The grating and coil chips were adapted to a passive pump vacuum chamber, and up to 106 87Rb atoms were trapped. These elements effectively reduce the power consumption of the GMOT and have great potential for applications in practical cold-atom-based devices.

A versatile apparatus for simultaneous trapping of multiple species of ultracold atoms and ions to enable studies of low energy collisions and cold chemistry.

We describe an apparatus where many species of ultracold atoms can be simultaneously trapped and overlapped with many species of ions in a Paul trap. Several design innovations are made to increase the versatility of the apparatus while keeping the size and cost reasonable. We demonstrate the operation of a three-dimensional (3D) magneto-optical trap (MOT) of 7Li using a single external cavity diode laser. The 7Li MOT is loaded from an atomic beam, with atoms slowed using a Zeeman slower designed to work simultaneously for Li and Sr. The operation of a 3D MOT of 133Cs, loaded from a 2D MOT, is demonstrated, and provisions for MOTs of Rb and K in the same vacuum manifold exist. We demonstrate the trapping of 7Li+ and 133Cs+ at different settings of the Paul trap and their detection using an integrated time-of-flight mass spectrometer. We present results on low energy neutral-neutral collisions (133Cs-133Cs, 7Li-7Li, and 133Cs-7Li collisions) and charge-neutral collisions (133Cs+-133Cs and 7Li+-7Li collisions). We show evidence of sympathetic cooling of 7Li+ (133Cs+) due to collisions with the ultracold 7Li (133Cs).

Sub-Doppler laser cooling and magnetic trapping of natural-abundance fermionic potassium

We demonstrate the largest number of 40K atoms that has ever been cooled to deeply sub-Doppler temperatures in a single-chamber apparatus without using an enriched source of potassium. With gray molasses cooling on the D 1-line following a standard D 2-line magneto-optical trap, we obtain 3×105 atoms at 10(2) µK. We reach densities high enough to measure the temperature via absorption imaging using the time-of-flight method. We magnetically trap a mixture of mF=−3/2,−5/2 and −7/2 Zeeman states of the F=7/2 hyperfine ground state confining 5×104 atoms with a lifetime of 0.6 s or ∼103 atoms with a lifetime of 2.8 s—depending on whether the temperature of the potassium dispensers was chosen to maximize the atom number or the lifetime. The background pressure-limited lifetime of 0.6 s is a reasonable starting point for proof-of-principle experiments with atoms and/or molecules in optical tweezers as well as for sympathetic cooling with another species if transport to a secondary chamber is implemented. Our results show that unenriched potassium can be used to optimize experimental setups containing 40K in the initial stages of their construction, which can effectively extend the lifetime of enriched sources. Moreover, the demonstration of sub-Doppler cooling and magnetic trapping of a relatively small number of potassium atoms might influence experiments with laser-cooled radioactive isotopes of potassium.

Grating magneto-optical trap optimization and drift-mitigation based on Bayesian learning

The grating magneto-optical trap (GMOT) is a promising approach for miniaturizing cold-atom systems. We demonstrated a real-time parameter optimization and drift-mitigation method for a GMOT system based on Bayesian learning. In a remarkable short convergence period, optimal numbers of cold atoms reached up to 7.7 × 106, which was nearly four times better than with manual optimization. The parameters included not only physical parameters but also mechanical parameters that can control the critical optical alignment. The results experimentally demonstrate that our work can efficiently optimize multiple parameters for a GMOT system and for the atom-based systems that need fine control. The machine learner employed a dual layer Bayesian learning, which could suppress the cost function drift due to the instability of the experimental parameters and environmental factors of the GMOT. The proposed approach validates the feasibility of Bayesian optimization in multiparameter cold-atom systems and can be applied to rapidly determine optimal parameters and high stability of general cold atom-based physical systems.

Historical foreword: Jean Dalibard, the magneto-optical trap, and the ascent of physics with cold atomic gases

Historical foreword: Jean Dalibard, the magneto-optical trap, and the ascent of physics with cold atomic gases

Atom Chip and Diffraction Grating for the Laser Cooling of Ytterbium Atoms

The possibility of using an atom chip and a diffraction grating to form a compact magneto-optical trap for ytterbium atoms, which can be used to develop compact atomic interferometers and optical clocks based on ultracold atoms, has been studied. An experiment on the laser cooling of the 171Yb and 174Yb isotopes in a first‑stage magneto-optical trap has been carried out to determine initial requirements for the mentioned elements. The design of the atom chip forming a magnetic field gradient up to 60 G/cm has been calculated. The optimal configurations of the diffraction grating that allow forming both the first- and second-stage magneto-optical traps have been evaluated.

Superradiance of ultracold cesium Rydberg |65D5/2〉 → |66P3/2〉

We investigate Rydberg |65D5/2〉 → |66P3/2〉 superradiance in dense ultracold cesium atoms, where the ground atoms are excited to |65D5/2〉 Rydberg states via two-photon excitation in a standard magneto-optical trap. The superradiant spectrum of |65D5/2〉 → |66P3/2〉 is obtained using the state-selective field ionization technique. We observe its dynamic evolution process by varying the delay time of ionization field t d. The results show that the evolution process of |65D5/2〉 → |66P3/2〉 is much shorter than its radiation lifetime at room temperature, which verifies the superradiance effect. The dependence of the superradiance process on Rydberg atoms number N e and principal quantum number n is investigated. The results show that the superradiance becomes faster with increasing N e, while it is suppressed for stronger van der Waals (vdW) interactions. Superradiance has potential applications in quantum technologies, and the Rydberg atom is an ideal medium for superradiance. Our system is effective for studying the strong two-body interaction between Rydberg atoms.

A cold-atom Ramsey clock with a low volume physics package

We demonstrate a Ramsey-type microwave clock interrogating the 6.835 GHz ground-state transition in cold 87\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{87}$$\\end{document}Rb atoms loaded from a grating magneto-optical trap (GMOT) enclosed in an additively manufactured loop-gap resonator microwave cavity. A short-term stability of 1.5×10-11τ-1/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1.5 \ imes 10^{-11} \ au ^{-1/2}$$\\end{document} is demonstrated, in reasonable agreement with predictions from the signal-to-noise ratio of the measured Ramsey fringes. The cavity-grating package has a volume of ≈\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\approx $$\\end{document}67 cm3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{3}$$\\end{document}, ensuring an inherently compact system while the use of a GMOT drastically simplifies the optical requirements for laser cooled atoms. This work is another step towards the realisation of highly compact portable cold-atom frequency standards.

Efficient Loading of an Atom Chip from a Low-Velocity Atomic Beam

Various regimes of the loading of a magneto-optical trap formed near an atom chip, such as loading from thermal atomic vapors and from a low-velocity atomic beam, have been studied on an example of 87Rb atoms. The possibility of controlling the loading of the magneto-optical trap by spatially controlling the atomic beam has been demonstrated. This has made it possible to increase the loading rate of atoms into the magneto-optical trap with keeping ultrahigh vacuum near the atom chip. The maximum number of atoms in the magneto-optical trap at optimal loading regimes is 4.9 × 107. In this case, the measured lifetime of atoms in the magneto-optical trap is 4.1 s.