In November, the Department of Energy Office of Science renewed the Superconducting Quantum Materials and Systems Center (SQMS), hosted by Fermi National Accelerator Laboratory, with $125 million over the next five years to accelerate breakthroughs in quantum information science.
The investment continues to unite more than 300 experts from 43 partner institutions across national laboratories, universities and industry to advance the next generation of quantum computing, communication and sensing technologies. Lawrence Livermore National Laboratory (LLNL) is one of those partners, bringing a deep expertise in materials and microwave cavities to the table.
As part of this collaboration, LLNL scientist Keith Ray is studying niobium and tantalum, materials used to create 3D cavities and 2D resonators for superconducting qubits.
"Regardless of the institution you're at or the qubit design you're working on, you want more information about the materials that you're employing," he said. "It's great to see a bunch of experimental and theoretical work coming out of SQMS that's focused on materials for quantum computers. The more data I have on these materials, the more refined my models can be, and the more informative and relevant they can be."
Niobium cavity superconducting qubits work by trapping single photons inside a hollow chamber, where they resonate with a particular frequency. For those photons to function as qubits and store useful information, they need to bounce back and forth off the cavity while dissipating as little energy as possible. In other words, the niobium surface must be free from imperfections.
"We've developed methods to look at these interfaces and what causes loss in superconducting qubits," said Ray. "A lot of effort has been undertaken on other projects here at Livermore to develop those methods, and we can now apply them to interfaces and materials that are useful for SQMS and potentially leverage our work to do very targeted things for the collaboration."
SQMS is focused on developing these cavity-based quantum computing platforms. And LLNL's work on the Axion Dark Matter eXperiment (ADMX) - which uses similar types of 3D cavities to search for axions, a candidate particle for dark matter - provides insights beyond the materials and into the cavities themselves.
"My role with SQMS is to help with the cavity design," said LLNL scientist Gianpaolo Carosi. "So far, one of their cavities was able to get a photon to exist in that cavity for on the order of a few seconds. It's kind of crazy, a little trapped photon bouncing around for actual seconds."
The longer a photon sticks around in the cavity, the more time to compute and the lower the error rate.
This quantum technology also goes beyond computing, circling back to improve the hunt for axions and extending out to a search for "dark photons," another dark matter candidate. The cavities could also detect gravitational waves, which would physically squeeze and stretch the chamber, changing its resonant frequency.
"I am really curious to see how the designs they have for gravitational wave sensing could be used for other types of sensing that may be applicable to national security," said Carosi. "I think SQMS has the ability to bring an interesting set of resources together to try and tackle things at a pretty large scale."
Ray and Carosi emphasized that there are many projects at LLNL that could tie in further with SQMS and its mission. This resonance and potential for amplification, they said, is exciting.
"We can all share ideas to develop better models and simulations to describe these materials and cavities," said Ray. "All of this adds up to better quantum computers in the long run."
