Narrow-Line Cooling and Imaging of Ytterbium Atoms in an Optical Tweezer Array

S. Saskin, J. T. Wilson, B. Grinkemeyer, and J. D. Thompson

Phys. Rev. Lett. 122, 143002 – Published 10 April 2019

Abstract

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 $1 0^{4}$ 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.

Received 25 October 2018

DOI:https://doi.org/10.1103/PhysRevLett.122.143002

Physics Subject Headings (PhySH)

Atom & ion cooling Optical lattices & traps

Atomic ensemble Atoms

Atomic, Molecular & Optical

Authors & Affiliations

S. Saskin^1,2,*, J. T. Wilson^1,*, B. Grinkemeyer¹, and J. D. Thompson^1,†

¹Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08540, USA
²Department of Physics, Princeton University, Princeton, New Jersey 08540, USA

^*These authors contributed equally to this work.
^†jdthompson@princeton.edu

Article Text (Subscription Required)

Click to Expand

Supplemental Material (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 122, Iss. 14 — 12 April 2019

Reuse & Permissions

Access Options

Article Available via CHORUS

Download Accepted Manuscript

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
(a) Relevant energy levels for ${}^{174}{Yb}$ , with transition wavelengths ( $λ$ ) and linewidths ( $Γ$ ) indicated. (b) Diagram of experimental setup indicating the geometry of the cooling, imaging, and trapping beams. Two of the 3D MOT beams are in the $x y$ plane, while the third propagates through the objective lens along the $z$ axis. The angled imaging beam is in the $x z$ plane. For other details, see text. (c) Average and (d) single-shot images of atoms in a $4 \times 4$ tweezer array, with $6 μ m$ spacing (35 ms exposure time). The color bar indicates the number of detected photons on each pixel.
Reuse & Permissions
Figure 2
(a) Differential light shift of the ${}^{1}{S_{0}} − {}^{3}{P_{1}}$ transition as a function of the ground state optical tweezer depth. The tensor light shift lifts the degeneracy of the ${}^{3}{P_{1}}$ $m_{J}$ levels, resulting in different potentials for the $m_{J} = 0$ (black) and $m_{J} = \pm 1$ (red) excited states. The light shift for the ${}^{1}{S_{0}} − {}^{3}{P_{1}}$ $m_{J} = 0$ transition is 1.6% of the ground state trap depth, corresponding to a shift of only $Γ_{556} / 2$ under typical trapping conditions. The horizontal axis is calibrated using the previously measured value of the ${}^{3}{P_{1}}$ $m_{J} = \pm 1$ polarizability at 532 nm [28]. (b) Lifetime and scattering rate of trapped atoms under various imaging intensities at a typical imaging detuning of $Δ \approx - 1.5 Γ_{556}$ . The black curve is a fit to a saturation model. The lifetime decreases exponentially with increasing imaging power above $I / I_{sat} \approx 4$ (red line guides the eye). We find $I / I_{sat} \approx 3$ to be the optimal balance of photon scattering rate and lifetime for this detuning.
Reuse & Permissions
Figure 3
(a) Histogram of detected photons at a single site for an exposure time of 30 ms ( $\sim 136, 000$ images), revealing clear separation between fluorescence counts for 0 and 1 atom occupancy. Inset: Typical image of single atom, with integration region indicated. (b) Imaging fidelity, quantified by the probability of disagreement between two subsequent images of the same array. Two event types are classified: blue points show the probability of bright sites appearing dark in the next image [ $P_{b \to d} = P (n_{i + 1} = d | n_{i} = b)$ , where $n_{i} = {d, b}$ denotes the state in image $i$ ] and black points show the probability of a dark site appearing bright in the next image [ $P_{d \to b} = P (n_{i + 1} = b | n_{i} = d)$ ]. The light blue symbols show the classification using a simple count threshold, while the other points (blue, black, red) use a pixel-wise Bayesian classifier that has approximately half the error rate. For exposure times greater than 20 ms, $P_{b \to d}$ is dominated by atom loss, consistent with the independently measured lifetime (7.2 s) for these imaging conditions (blue curve). $P_{d \to b}$ reaches a floor below $1 \times 10^{- 4}$ that originates from quantum jumps out of a metastable state. A representative jump event is shown in panel (c): a tweezer initially loaded with an atom goes dark, but spontaneously becomes bright one second later, though the MOT is off the entire time. The duration of these events [panel (d)] is consistent with a metastable state lifetime of $τ_{m} = 0.54 (7) s$ (exponential fit is shown in black). The black dashed curve in (b) is a fit to $P_{m} (1 - e^{- t / τ_{m}})$ , which describes the rate of these events for an average metastable state population $P_{m}$ , which we infer to be $P_{m} = 4 \times 10^{- 3}$ . The red points in (b) show $P_{d \to b}$ with conclusively identified quantum jump events removed.
Reuse & Permissions
Figure 4
(a) Average and (b) single-shot images of a $12 \times 12$ tweezer array, with $6 μ m$ spacing, using simultaneous ${}^{1}{P_{1}}$ imaging and ${}^{3}{P_{1}}$ cooling. The detected photon rate is much lower for this imaging method, so the exposure time is 500 ms. The color bar indicates the number of detected photons on each pixel. Over repeated single-shot images, the average (worst) site has loading probability $p = 0.49$ ( $p = 0.35$ ).
Reuse & Permissions

Physical Review Letters