Defect-Free Arbitrary-Geometry Assembly of Mixed-Species Atom Arrays

Optically trapped mixed-species single atom arrays with arbitrary geometry are an attractive and promising platform for various applications, because tunable quantum systems with multiple components provide extra degrees of freedom for experimental control. Here, we report the first demonstration of two-dimensional $6\times 4$ dual-species atom assembly of ${}^{85}\mathrm{Rb}$ (${}^{87}\mathrm{Rb}$) atoms with a filling fraction of 0.88 (0.89). This mixed-species atomic synthesis is achieved via rearranging initially randomly distributed atoms by a sorting algorithm (heuristic heteronuclear algorithm) which is designed for bottom-up atom assembly with both user-defined geometries and two-species atom number ratios. Our fully tunable hybrid-atom systems with scalable advantages are a good starting point for high-fidelity quantum logic, many-body quantum simulation, and single molecule array formation.

Figure 1

Protocol for creating mixed-species atom array. (a) Simplified schematics of the experimental setup. (b) Fluorescence count distribution for 64 tweezers during 80 ms of exposure of ${}^{85}\mathrm{Rb}$ (top) and ${}^{87}\mathrm{Rb}$ (down) atoms. (c) The loading rates of ${}^{85}\mathrm{Rb}$ and ${}^{87}\mathrm{Rb}$ as a function of the frequency of ${}^{85}\mathrm{Rb}$ cooling beam. The frequency of ${}^{87}\mathrm{Rb}$ cooling beam is fixed to 15 MHz detuned by $|5S_{1/2},F=2⟩\to |5P_{3/2},F=3⟩$ and the loading ratios are tuned by the frequency of ${}^{85}\mathrm{Rb}$ cooling beam detuned by $|5S_{1/2},F=3⟩\to |5P_{3/2},F=4⟩$. The optical intensity of ${}^{85}\mathrm{Rb}$ and ${}^{87}\mathrm{Rb}$ cooling (repumping) beams are almost the same. The frequency value is set to the intersection of the two lines when we prepare the atom arrays with equal ${}^{85}\mathrm{Rb}$ and ${}^{87}\mathrm{Rb}$ atom numbers. The tunability is also essential for arrays with imbalanced two-species atom numbers such as “embedded lattice” configuration. (d) Pulse diagram of the experimental sequence. (e) Images of various defect-free mixed-species atom arrays. Each one is synthesized by one image of ${}^{85}\mathrm{Rb}$ atoms and one image of ${}^{87}\mathrm{Rb}$ atoms. The distance of the neighboring sites is $5\mu \mathrm{m}$.

Figure 2

Assembling of a mixed-species atom array using the HHA. (a) Schematic diagrams of the HHA. The sorting process is from left to right. The blue (red) disks denote single atoms of ${}^{87}\mathrm{Rb}$ (${}^{85}\mathrm{Rb}$) and the blue (red) dashed line circles denote the target sites of ${}^{87}\mathrm{Rb}$ (${}^{85}\mathrm{Rb}$). The green regions represent the routes connected to the reservoir tweezers and the sites with “$+$” symbols are the innermost sites in the routes to be filled. (b) The number of moves as a function of the number of filled sites for dual-species atom arrays. The averaged simulation results are repeated by 100 000 times with randomly initial configurations for the $N\times N$ arrays, which are enlarged by increasing the $N$. The inset shows the histogram of the number of moves of preparing a $5\times 6$ single-species atom array and a $5\times 6$ dual-species atom array in zebra stripes configuration.

Figure 3

Filling fraction and configuration entropy of the dual-species atom array. (a) Filling fraction of ${}^{85}\mathrm{Rb}$ and ${}^{87}\mathrm{Rb}$ as a function of the number of atom pairs. Inset: Green circles show the cumulative success rate of obtaining a defect-free atom array with several atom pairs; the dashed line shows the result corresponding to random loading for dual-species atoms. The cumulative success rates $P_n=2^{-2n}$ for randomly loading dual-species array, where $n$ is the number of filled sites, if the loading ratios are 25% for both two-species atoms. The number of atom pairs is accumulated through a path marked by the color gradient of purple dashed rectangles. (b) Configuration entropy decreasing in the process of rearrangement. Each entropy distribution is measured by repeating the experiment for 100 times. The left (right) one is the result of initial (final) atom array and the red (blue) one is the result of region A (B). The middle one represents the entropy with half of the total transport moves. The values of entropy during the sorting process in region A and B are 2.0(5), 1.5(4), $0.4(3)k_B$ and 2.0(4), 1.4(4), $0.4(2)k_B$, respectively.