October 2, 2026
Maureen Searcy
UChicago physicist proposes novel method to produce near-perfect quantum building blocks
A classical computer runs on billions of transistors, switched either on or off, a one or a zero. A quantum computer’s building blocks, called qubits, can be both at once until a measurement collapses them into one, like slapping a spinning coin down on a table.
That ability opens the door to solving certain types of problems that even the most powerful classical computers can’t. But quantum computers are not as robust as classical ones and need near-perfect hardware to function.
“You can use particles as qubits to perform computations that are not possible or extremely inefficient on classical computer technology,” said Zoe Yan, Neubauer Family Assistant Professor in UChicago’s Department of Physics. “The trade-off is that these qubits are very fragile, and they’re very susceptible to environmental noise.”
In a paper published in Physical Review Letters, Yan and collaborators Tijs Karman (Radboud University) and Sebastian Will (Columbia University) propose a way to build nearly perfect qubit arrays using ultracold, ultrapolar molecules that repel each other, creating a calm, controlled, and predictable system. Such a platform could help design building blocks for quantum computers, simulate complex materials, and test fundamental physics.
Bigger, better arrays
There are different approaches to building quantum computers, and one type uses atoms trapped by lasers in a grid. This arrangement is called an atom array, similar to a microchip in classical computing. Each trapped atom acts as a qubit when researchers designate two of its energy levels as the zero and the one and then manipulate the atoms with lasers. Current atom arrays range from hundreds to a few thousand qubits.
One way to create quantum arrays is by using optical tweezers: laser beams, each focused to a tiny spot, arranged in a grid and aimed into a cloud of cold gas. Atoms are drawn to the brightest part of each beam, so each focal spot acts as a trap meant to hold a single atom. The problem is that loading the traps requires some luck, and arrays are often left with defects like empty traps.
Researchers can rearrange atoms to fill the holes, and this has been successful for arrays with thousands of traps. The larger the array, the more useful it is for computing and other physics research.
For arrays to be useful, the qubits must interact with each other. Atoms typically have to be excited into an unstable, higher energy state to interact, which shortens their lifespan as qubits. Molecules, however, are more complex, so they can interact strongly in their ground energy states while remaining stable and keeping their quantum properties longer.
“We want to branch out to objects of higher and higher complexity,” said Yan. “While the experimental trade-off is more difficulty, greater complexity can buy you more bells and whistles in the quantum toolbox.”
Scientists have been exploring the use of molecules instead of atoms in quantum arrays, but they are tricky to capture. A trap has about an equal chance of being occupied as being left empty, and rearranging molecules has only been successful for arrays of about ten traps. Additionally, molecules that are trapped often keep jiggling, causing disorder.
A defect-free array as small as 100 molecules would be quite useful for fundamental sciences and quantum technology but has not yet been demonstrated.
Yan’s proposal would prevent the need to fill holes after the fact and would reduce the molecules’ motion. The team’s calculations suggest that each trap would be correctly loaded from the start, with nearly motionless molecules, more than 99% of the time, paving the way for larger arrays.
Musical chairs
The key to Yan’s design is repulsion, similar to how magnets with the same polarity push against each other. Repulsive molecules that fall into traps repel additional molecules from falling in, increasing the likelihood that every trap has only one occupant.
Yan compares it to a game of musical chairs: At the end of the song, every chair is occupied, and no chair has two people — not only because there isn’t room but because of “person-person interactions,” said Yan. You don’t want to sit on top of someone.
The premise starts with a new class of molecules that are ultracold and ultrapolar. The extremely low temperature helps calm the molecules down enough to be trapped by the optical tweezers. Lasers able to trap room-temperature, energetic molecules would have to be impractically powerful.
Polar molecules have one side that pulls electrons more strongly, so electrons from the other side gravitate toward it, creating negatively and positively charged ends. The lopsided nature of polar molecules helps them interact with other molecules more strongly and over longer distances than nonpolar molecules. The more lopsided the molecule, the stronger the effect.
“We’re working on building the world’s first so-called ultrapolar molecule,” said Yan. “No one has created this kind of molecule yet.”
Yan’s lab has achieved ultracold potassium and ultracold silver atoms. The goal is to create ultracold potassium-silver molecules, which would be highly polar. Yan proposes using microwaves to then make the ultrapolar molecules repel.
This repulsion helps fill the traps with only one molecule while also keeping the collisions between molecules gentle. Such gentle collisions transfer energy, allowing newly trapped molecules to settle down within the trap, like a ball coming to rest in a bucket instead of rolling around the sides.
Calculations suggest that repulsion and extremely low temperatures would allow molecules to get as close to a standstill as quantum mechanics allows, reducing disorder that would undermine the array’s usefulness.
Recently, the researchers saw the first signatures of the potassium-silver molecule. In the coming months, they hope to synthesize it at ultracold temperatures in its lowest-energy, most stable state.
The synthesis of this molecule is the next step before the team can see how well it loads into arrays. If successful, this approach could make much larger molecular arrays possible. Theoretical work suggests that as few as 10,000 qubits can meaningfully perform algorithms that have commercial and economic impact in a way that a classical computer cannot achieve.
Beyond computing
The improving ability to control molecules at the quantum mechanical level is beneficial to technology but also to basic sciences.
“There are a lot of questions that one could address by, for instance, putting these molecules in ordered lattices and using lasers to move them around,” said Yan. Such work could help scientists study physics relevant to our understanding of condensed matter.
Yan’s lab aims to simulate quantum materials by building matter from the ground up with these ultrapolar molecules. “Despite a century of quantum mechanics existing, there are still a lot of mysteries about why materials behave like they do,” said Yan. “For instance, why can’t superconductors currently work at room temperature, where they would be very useful? This is an inherently quantum mechanical problem. I think that quantum simulation, using these clean, bottom-up approaches, is one way to tackle these interesting questions.”
Citation: “Low-Entropy Arrays of Microwave-Shielded Molecules Prepared by Interaction Blockade,” Tijs Karman et al., Phys. Rev. Lett. 137, 113402 (2026).