Researchers have engineered a new technique to trap ions in 3D structures using modified electric fields in Penning traps, forming stable bilayer crystals.
This innovation paves the way for more complex quantum devices and could revolutionize recent write up about the paper. “We started to explore ways to realize such structures in a specific type of ion trap called a Penning trap, because these traps are good at storing large numbers of ions, typically many hundreds to thousands.”
In a Penning trap, ions can be forced to self-ensemble into crystalline structures generated by the competition between repulsive Coulomb interactions and the confinement potential—the combined electric and magnetic force that keeps ions securely trapped in a specific region of space.
“Confinement is achieved via electromagnetic forces created by a stack of electrodes and by making the ions rotate in a powerful magnetic field,” explains Carter.
For physicists, Penning traps are particularly useful because they can store a large number of ions, making them a good option for experimenting with more complex, three-dimensional structures. Penning traps have been used to arrange ions into a single, two-dimensional layer or more rounded, three-dimensional shapes. The rounded, three-dimensional shape happens because the confining electric field in these traps usually increases linearly with distance from the trap’s center, like that of an ideal spring, naturally guiding the ions into these simpler, rounded formations.
However, the researchers, including Prakriti Shahi of the Indian Institute of Technology Bombay, tried modifying the trap’s electric field to be more nuanced and dependent on the distance from the center of the trap. This subtle change allowed them to coax the ions into forming a new kind of structure—a bilayer crystal, where two flat layers of ions were stacked one above the other.
The team conducted extensive numerical simulations to validate their new approach, showing that this bilayer configuration could be stabilized under certain conditions and even suggesting the potential to extend the method to create crystals with more than two layers.
“We’re excited to try forming bi-layer crystals in the lab with our current Penning trap set-up,” says John Bollinger, an experimental physicist and co-author of the publication. “In the longer term I think this idea will motivate a redesign of the detailed electrode structure of our traps.”
A New Frontier for Ion Trapping
Shifting ion trapping from 2D to 3D has significant implications for the future of quantum devices such as sensors or quantum computers.
“Bilayer crystals open up several new capabilities for quantum information processing that are not straightforward with 1D chains or 2D planes,” Dr. Athreya Shankar, a postdoctoral researcher at the Indian Institute of Science, said in a recent statement about the study. “For instance, the generation of quantum entanglement between large sub-systems separated by a distance, such as the two layers in this system, is a sought-after capability across all quantum hardware.”
The team is eager to test these findings experimentally in their Penning traps. If successful, this could lead to new quantum hardware architectures that make more efficient use of 3D space, thus increasing the scalability and robustness of quantum technologies.
Besides hardware opportunities, the bilayers open new quantum simulations and sensing possibilities.
“For example, the normal modes of the ions in a bilayer can couple both vertical and radial degrees of freedom, favoring the clock over anti-clockwise circulation or vice versa,” Rey elaborates. “This could be used to imitate rich behaviors experienced by electrons in strong magnetic fields but under fully controllable settings. Moreover, having more ions can enhance signal-to-noise in measurement and thus enable more precise estimation of quantities such as time, electric fields, or accelerations, which can be very important for discovering new physics.”
This partnership between researchers in India, Austria, and the USA is critical as the field of quantum technology continues to evolve. Innovations like these will be vital in realizing the full potential of quantum computing, sensing, and beyond.
Reference: “Bilayer Crystals of Trapped Ions for Quantum Information Processing” by Samarth Hawaldar, Prakriti Shahi, Allison L. Carter, Ana Maria Rey, John J. Bollinger and Athreya Shankar, 16 August 2024, Physical Review X.
DOI: 10.1103/PhysRevX.14.031030
This work was supported by the U.S. Department of Energy’s Office of Science, The National Quantum Initiative (NQI) Science Research Centers, and the Quantum Systems Accelerator (QSA).