Creating the complex entangled states needed for these technologies has traditionally required sophisticated equipment and carefully designed experimental systems.

Researchers at the University of Chicago Pritzker School of Molecular Engineering have now proposed a much simpler approach. Their new theoretical method can generate and control a wide range of entangled quantum states using tools that are already common in many quantum physics laboratories.

The work, published in Physical Review X, could help advance ultra precise quantum sensing and open new opportunities for exploring fundamental physics.

"We wanted to take simple ingredients that you find in a lot of physical platforms and put these together in a minimal way to get something interesting, complex and powerful," said Aashish Clerk, professor of molecular engineering at UChicago PME and senior author of the new study.

The research was supported by Q-NEXT, a U.S. Department of Energy National Quantum Information Science Research Center led by DOE's Argonne National Laboratory.

Rethinking Cavity QED Systems

The team's approach is based on cavity quantum electrodynamics, commonly known as cavity QED. In these experiments, atoms or other particles are placed inside an optical cavity, which consists of two mirrors that trap light between them. The particles then interact with the confined light inside the cavity.

A limitation of many cavity QED systems is that all of the atoms interact with the light in exactly the same way. Because the atoms are effectively indistinguishable, the range of quantum states that can be produced is restricted.

"The challenge has always been that these systems have too much symmetry. All the atoms are talking to light in the same way," Clerk said. "That really restricts what kind of entangled states you get."

In a typical cavity QED setup, each atom has a ground state and an excited state separated by a specific energy difference.

The researchers found a straightforward way to reduce the system's symmetry. While all atoms continue to be driven by the same laser, additional lasers or magnetic fields are used to shift the excited state energies of different groups of atoms. The atoms are arranged so that each one is paired with another atom that has an equal but opposite energy offset.

This simple modification allows atoms to behave differently from one another while preserving enough structure for the system to remain controllable and predictable. By changing which atoms receive particular energy shifts, scientists can tune the system to produce a variety of entangled states without altering the physical hardware.