UIUC researchers to develop new interconnects as important step in enabling quantum networks

In the future, there may be a “quantum Internet” that comprises a network of quantum devices that enable security, privacy, and processing capabilities that are not possible with today’s Internet. It’s just one of the technological triumphs that could eventually be achieved if several scientific challenges are solved.

Among them is the development of efficient and robust quantum interconnects, which are the quantum version of the “wires” that serve as the nervous system for electronic devices. These wires would be used to transmit the quantum information that serves as the foundation of these future applications. However, creating good interconnects for quantum systems has proven to be difficult.

Recently, researchers at the University of Illinois Urbana-Champaign were awarded a grant to begin developing interconnects that, if successful, could serve as linkages in a network of quantum processors and other elements. The new project, called “QuIC-TAQS: Interconnects for a Superconducting-Atomic Hybrid Quantum Network,” has been funded at $2.5 million for four years by the National Science Foundation.

“Transduction” is the process of converting one type of energy to another, and scientists have struggled to achieve good transduction across quantum devices that work at very different frequencies, as needed to create effective interconnects. One thrust of the research will center around creating efficient protocols for transduction that can tolerate imperfections in device fabrication, and that operate over a wide range of parameters.

“Quantum processors and memory devices operate at fairly low frequencies (comparable to wireless networks) in the so-called microwave regime, whereas quantum repeaters (communication stations that extend the signal range across long distances) would use optical photons, which are comparable to telecommunications frequencies,” said Wolfgang Pfaff, assistant professor of physics at UIUC and the project’s principal investigator.

“When we try to convert between the two, we lose energy,” Pfaff said. “The problem is that quantum information can barely tolerate loss, otherwise its essential quantum properties are lost.”

The UIUC team will seek to create more efficient transfer using a “trick” borrowed from the field of nonlinear optics, says Pfaff. They will use a special type of crystal, which serves as a medium that can be used to change the frequency of electromagnetic information. The crystal and radiation will serve as a sort of mixing bowl, where the microwave and optical photons can be spun and converted into the same signal.

In technical terms, the team will work to establish a suite of pair-wise interconnects across a rare-earth spin ensemble memory, superconducting quantum information processors, opto-mechanical frequency converters, and an ytterbium atom array. Doing so would enable transmission of quantum signals between a long-lived microwave “quantum memory” at cryogenic temperatures and an atom processor that may be used as a quantum repeater. Such a quantum link would be a crucial stepping-stone towards an ability to link microwave quantum processors across long distances, so a successful outcome would represent important progress toward the realization of large-scale quantum networks, such as the quantum Internet.

In addition to Pfaff, the research team includes Jacob P. Covey (an assistant professor of physics), Kejie Fang (an assistant professor of electrical & computer engineering), and Elizabeth A. Goldschmidt (an assistant professor of physics) of UIUC, and Liang Jiang, a professor of molecular engineering at the University of Chicago. The UIUC faculty are all researchers in the Illinois Quantum Information Science and Technology Center (IQUIST), which is home to Illinois’ quantum science research, education, and collaboration efforts.