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arXiv:1811.06014 · Physical Review Letters

2000-Times Repeated Imaging of Strontium Atoms in Clock-Magic Tweezer Arrays

Jacob P. Covey, Ivaylo S. Madjarov, Alexandre Cooper, Manuel Endres

Published May 1, 2019• 136 citations
arXivHTMLPDF

Abstract

We demonstrate single-atom resolved imaging with a survival probability of 0.99932(8) and a fidelity of 0.99991(1), enabling us to perform repeated high-fidelity imaging of single atoms in tweezers thousands of times. We further observe lifetimes under laser cooling of more than seven minutes, an order of magnitude longer than in previous tweezer studies. Experiments are performed with strontium atoms in 813.4 nm tweezer arrays, which is at a magic wavelength for the clock transition. Tuning to this wavelength is enabled by off-magic Sisyphus cooling on the intercombination line, which lets us choose the tweezer wavelength almost arbitrarily. We find that a single not retroreflected cooling beam in the radial direction is sufficient for mitigating recoil heating during imaging. Moreover, this cooling technique yields temperatures below 5 μK, as measured by release and recapture. Finally, we demonstrate clock-state resolved detection with average survival probability of 0.996(1) and average state detection fidelity of 0.981(1). Our work paves the way for atom-by-atom assembly of large defect-free arrays of alkaline-earth atoms, in which repeated interrogation of the clock transition is an imminent possibility.

DOI
10.1103/physrevlett.122.173201

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We demonstrate single-atom resolved imaging with a survival probability of 0.99932(8) and a fidelity of 0.99991(1), enabling us to perform repeated high-fidelity imaging of single atoms in tweezers thousands of times. We further observe lifetimes under laser cooling of more than seven minutes, an order of magnitude longer than in previous tweezer studies. Experiments are performed with strontium atoms in 813.4 nm tweezer arrays, which is at a magic wavelength for the clock transition. Tuning to this wavelength is enabled by off-magic Sisyphus cooling on the intercombination line, which lets us choose the tweezer wavelength almost arbitrarily. We find that a single not retroreflected cooling beam in the radial direction is sufficient for mitigating recoil heating during imaging. Moreover, this cooling technique yields temperatures below 5 μK, as measured by release and recapture. Finally, we demonstrate clock-state resolved detection with average survival probability of 0.996(1) and average state detection fidelity of 0.981(1). Our work paves the way for atom-by-atom assembly of large defect-free arrays of alkaline-earth atoms, in which repeated interrogation of the clock transition is an imminent possibility.
Recent advances in quantum simulation based on neutral atoms have largely benefited from high-resolution, single-atom sensitive imaging techniques. A variety of approaches have been developed to achieve such local detection of atoms in optical lattices or optical tweezers. For alkaline-earth and alkaline-earth-like atoms, the presence of narrow optical transitions opens up the possibility of performing novel types of Sisyphus cooling, where the cooling mechanism originates from the capability to spatially resolve the differential optical level shifts in the trap potential. Up to now, it has been an open question whether high-fidelity imaging could be achieved in a "repulsive Sisyphus" configuration, where the trap depth of the ground state exceeds that of the excited state involved in cooling. Here, we demonstrate high-fidelity (99.971(1)%) and high-survival (99.80(5)%) imaging of strontium atoms using repulsive Sisyphus cooling. We use an optical lattice as a pinning potential for atoms in a large-scale tweezer array with up to 399 tweezers and show repeated, high-fidelity lattice-tweezer-lattice transfers. We furthermore demonstrate loading the lattice with approximately 10 000 atoms directly from the MOT and scalable imaging over >10 000 lattice sites with a combined survival probability and classification fidelity better than 99.2%. Our lattice thus serves as a locally addressable and sortable reservoir for continuous refilling of optical tweezer arrays in the future.
Single strontium atoms held in optical tweezers have so far only been imaged using the broad ${}^{1}{S}_{0}{\text{\ensuremath{-}}}^{1}{P}_{1}\phantom{\rule{0.16em}{0ex}}$transition. For Yb, use of the narrow (183-kHz wide) ${}^{1}{S}_{0}{\text{\ensuremath{-}}}^{3}{P}_{1}\phantom{\rule{0.16em}{0ex}}$transition for simultaneous imaging and cooling has been demonstrated in tweezers with a magic wavelength for the imaging transition. We demonstrate high-fidelity imaging of single Sr atoms using its even narrower (7.4-kHz wide) ${}^{1}{S}_{0}{\text{\ensuremath{-}}}^{3}{P}_{1}\phantom{\rule{0.16em}{0ex}}$transition. The atoms are trapped in nonmagic-wavelength tweezers. We detect the photons scattered during Sisyphus cooling, thus keeping the atoms near the motional ground state of the tweezer throughout imaging. The fidelity of detection is 0.9991(4) with a survival probability of 0.97(2). An atom in a tweezer can be held under imaging conditions for 79(3) seconds allowing for hundreds of images to be taken, limited mainly by background gas collisions. The use of a fully closed (cycling) transition for imaging will provide a useful tool for state specific detection. We detect atoms in an array of 36 tweezers with 813.4-nm light and trap depths of 135(20) $\ensuremath{\mu}$K. This trap depth is three times shallower than typically used for imaging on the broad ${}^{1}{S}_{0}{\text{\ensuremath{-}}}^{1}{P}_{1}\phantom{\rule{0.16em}{0ex}}$transition. Narrow-line imaging opens the possibility to even further reduce this trap depth, as long as all trap frequencies are kept larger than the imaging transition linewidth. Imaging using a narrow-linewidth transition in a nonmagic-wavelength tweezer also allows for selective imaging of a given tweezer. As a demonstration, we selectively image (hide) a single tweezer from the array. This provides a useful tool for quantum error correction protocols.
Optical tweezer arrays of neutral atoms have emerged as a versatile and powerful platform for quantum simulation and quantum information processing. In this thesis, I present the realization of an experimental platform for quantum simulation based on individually trapped strontium atoms in optical tweezer arrays. The experiment combines precise laser cooling, optical control, and high-resolution imaging to enable the manipulation and high fidelity detection of single atoms. I developed and optimized a two-stage three-dimensional magneto-optical trap (3D-MOT) that produces cold and dense samples of strontium atoms from a thermal beam. In the f irst stage, atoms are captured and precooled using the dipole-allowed 1S0 → 1P1 transition at 461nm (which has a linewidth of !=2ω ↑ 32MHz). The second stage employs the 1S0 → 3P1 narrow intercombination transition at 689nm (with a linewidth of !=2ω ↑7.5kHz) to further cool and compress the atomic cloud. By optimizing the trapping parameters, I achieved clouds with temperatures around 5μK and densities above 1010cm→3, providing ideal initial conditions for e!cient loading into optical tweezers. A 3↑3 array of 360μK deep optical tweezers is generated by spatially modulating an 813.4nm laser beam using two crossed acousto-optic deflectors. The deflected beams are relayed and focused into the science chamber using a high–numericalaperture objective, which simultaneously serves as the collection optics for atomic f luorescence. The fluorescence light emitted by the atoms is imaged onto a scientific qCMOS camera, enabling site-resolved detection of individual atoms. I implemented and optimized the in-trap cooling dynamics to prevent atom loss during imaging and to minimize residual thermal motion. In addition, by precisely tuning lightassisted collisions, multiple atoms occupancies are removed from the traps and a single-atom regime is reached in the array, with a filling fraction of about 50%. I have demonstrated a single-atom detection fidelity of 99,986(1)% and a survival probability of 97(2)% between subsequent image acquisition, comparable to other current state-of-the-art experiments. To characterize the platform, I carried out release-and-recapture experiments, from which it is possible to measure a temperature for the individually trapped atoms of 12.95(5)μK. These results demonstrate the successful implementation of a robust and high-fidelity platform for optical trapping and imaging of single strontium atoms. The apparatus provides the foundation for future quantum simulation experiments with alkalineearth atoms excited to the Rydberg state, o"ering precise control over individual particles and the ability to scale towards larger, programmable atomic arrays.
Engineering controllable, strongly interacting many-body quantum systems is at the frontier of quantum simulation and quantum information processing. Arrays of laser-cooled neutral atoms in optical tweezers have emerged as a promising platform because of their flexibility and the potential for strong interactions via Rydberg states. Existing neutral atom array experiments utilize alkali atoms, but alkaline-earth atoms offer many advantages in terms of coherence and control, and also open the door to new applications in precision measurement and time keeping. In this Letter, we present a technique to trap individual alkaline-earth-like ytterbium (Yb) atoms in optical tweezer arrays. The narrow ^{1}S_{0}-^{3}P_{1} intercombination line is used for both cooling and imaging in a magic-wavelength optical tweezer at 532 nm. The low Doppler temperature allows for imaging near the saturation intensity, resulting in a very high atom detection fidelity. We demonstrate the imaging fidelity concretely by observing rare (<1 in 10^{4} images) spontaneous quantum jumps into and out of a metastable state. We also demonstrate stochastic loading of atoms into a two-dimensional, 144-site tweezer array. This platform will enable advances in quantum information processing, quantum simulation, and precision measurement. The demonstrated narrow-line Doppler imaging may also be applied in tweezer arrays or quantum gas microscopes using other atoms with similar transitions, such as erbium and dysprosium.
Abstract We outline an experimental setup for efficiently preparing a tweezer array of 88Sr 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 108 s−1 at 5 mK for the three-dimensional blue MOT. This enables us to trap 2 × 106 88Sr atoms at 2 μK in a narrow-line red MOT with the 1S0 → 3P1 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 min. 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.
Subwavelength atomic tweezer arrays, in which atoms can be positioned at distances smaller than their emission wavelength, have been proposed as a versatile platform to study collective emission phenomena, such as superradiance and subradiance. Experimentally, the realization of such arrays has been a challenge as typical emission wavelengths in the visible or near-infrared are short compared to typical tweezer spacings in the micrometer range. Here, we use 88^{88}88Sr atoms in optical tweezer arrays to access a mid-infrared transition at 2,923 nm (5s5p 3P2→ 5s4d 3D35s5p\:^{3}P_{2} \rightarrow\, 5s4d\:^{3}D_{3}5s5p3P2​→5s4d3D3​). We identify a magic trapping wavelength at 597.14(3) nm and demonstrate single-atom preparation and imaging with high fidelity. In addition, using 2,923 nm light, we demonstrate resolved-sideband cooling of tweezer-trapped strontium. Beyond enabling studies of collective emission phenomena in flexible arrangements of atoms, our platform opens novel opportunities for dipolar many-body physics and enhanced control over Rydberg dynamics and the strontium fine-structure qubit.