Some quantum systems are so complex that even the most powerful supercomputers struggle to simulate their behavior. One solution is quantum simulation: building a controllable quantum system in the lab and tuning it to mimic the one researchers want to understand. In a trapped-ion simulator, a row of individual charged atoms, or ions, is held in place by electric fields inside a device called an ion trap. Lasers are used to make the ions interact in a manner that simulates the quantum system, then researchers measure the information encoded in the ions to reveal the system's properties.
Rice University's Guido Pagano , along with collaborators at Duke University and Translume Inc., has developed a new kind of trapped-ion simulator, called a monolithic segmented 3D ion trap. This trap allowed the team to study these complex systems using heavy ions like ytterbium. The work was recently published in Physical Review Applied .
"Trapped ion simulators can help us understand complex problems, like charge transfer in photosynthesis," said Pagano, an associate professor of physics and astronomy and senior author on this study. "With this new ion trap, we have combined some of the best features of the previous versions while overcoming engineering challenges inherent to integrating these features in a compact microfabricated monolithic architecture."
Ion traps using radio-frequency voltages have commonly fallen into two camps: blade-style traps and microfabricated chip traps. Blade-style ion traps offer high performance but are limited in geometric precision and difficult to reproduce, since they are assembled by hand. Microfabricated chip ion traps are typically two-dimensional traps that offer greater geometric precision, are highly modular and are easy to reproduce. In many ways, however, they are not as high-performing as blade-style ion traps. Monolithic three-dimensional ion traps sought to combine the best of blade and chip traps but, until now, were only available to work with light ions like calcium.
"In our monolithic ion trap, we wanted to combine the high-performance features and accessibility of the blade trap with the scalability and modularity of the chip trap in a way that was compatible with the heavier ions," said Abhishek Menon, a graduate student and the corresponding author on this study. "Solving the harder engineering problems with trapping heavier ionic species also helps simplify trapping lighter ionic species and further use of this trap for a variety of quantum technologies."
The research team came up with a design that started as a block of fusilica glass. They used lasers and chemicals to mark out and create channels for the ions and trenches for the electrodes that need to be installed before coating the trap with sputtered gold. The trenches were an important part of the design. They isolated the electrodes by design, preventing them not only from shorting during the gold sputtering process but also from undergoing dielectric breakdown under high-voltage conditions in vacuum.
"This really was an iterative process to design," Menon said. "Our first generation failed, although in a promising and informative way: It had a significant thermal and electrical management problem. The trap began to glow visibly when the desired high radio-frequency voltage was applied in a vacuum. The second generation fixed the previous generation's major flaws, but it had several problems, such as considerable axial micromotion and high ion-heating rates. It wasn't until the third generation that we had a viable trap."
While the glowing trap may have been the most dramatic problem, it wasn't the only engineering challenge the team faced. The trap had to balance the need for greater spacing between the ions while minimizing voltage in the system and maintaining appropriate heating rates of the ions without losing any of the qualities that made the ion trap so useful in the lab.
The third-generation ion trap had a better heat sink to move heat away from the ion trap, minimized axial micromotion of the ions and used a plasma-based surface treatment to help reduce ion-heating rates. Once the design was complete, Pagano's lab, along with collaborators at Duke, individually tested the ion traps. They were able to confirm that the ion traps both worked as intended and agreed with previously run computer simulations.
"The monolithic trap makes trapped-ion simulators more accessible to academic labs," said Roman Zhuravel, a senior author on this study and assistant research professor in Pagano's lab. "The traps allow researchers to simplify challenging quantum problems to problems we can solve, which we then map onto the bigger, more complex problems. The monolithic trap is suitable for many such applications, opening up new avenues for scientists interested in these problems."
This work was funded by the U.S. Department of Energy, Office of Science (DE-SC0023806, DE-SC0020553 and DE-SC0024504), the Welch Foundation Award (C-2154), the Office of Naval Research Young Investigator Program (N00014-22-1-2282), the National Science Foundation (PHY-2144910, OMA-2120757), the Office of Naval Research (N00014-23-1-2665 and N00014-24-1-2593), Army Research Office (W911NF21P0003) and the US Army Research Laboratory (W911QX21C0031).
