Scientists from the University of Chicago, in collaboration with partner institutions, have developed molecular qubits that are compatible with standard telecommunications networks. This advancement, detailed in a recent publication in Science, represents a significant step toward establishing a future quantum internet.
The newly designed molecular qubits use erbium, a rare-earth element valued for its clean absorption and emission of light and strong interactions with magnetic fields. The researchers note that these properties allow the molecules to act as a link between magnetism and optics at the nanoscale.
“These molecules can act as a nanoscale bridge between the world of magnetism and the world of optics,” said Leah Weiss, postdoctoral scholar at the UChicago Pritzker School of Molecular Engineering (UChicago PME) and co-first author on the paper. “Information could be encoded in the magnetic state of a molecule and then accessed with light at wavelengths compatible with well-developed technologies underlying optical fiber networks and silicon photonic circuits.”
Molecular qubits have potential uses as sensitive quantum sensors due to their small size and chemical adaptability. They could be embedded into various environments to measure magnetic fields, temperature, or pressure at very small scales. Because they are compatible with silicon photonics, there is also potential for direct integration into chips for compact quantum devices used in computing, communication, or sensing.
“Rare-earth chemistry provided a fortuitous combination of properties that allowed us to bring these capabilities to a molecular system,” said Grant Smith, graduate student at UChicago PME and another first author on the paper. “There were a lot of things pointing toward this as an exciting platform to advance the use of optical degrees of freedom in molecular spin qubits. One of the central focuses of this work, and the work in the lab more broadly, is that we want to really expand the gamut of quantum systems and materials that we can control and interact with.”
Smith added: “By doing this you can begin to think about new and unconventional ways to utilize and integrate them into technologies.”
The research team demonstrated through optical spectroscopy and microwave techniques that erbium molecular qubits operate at frequencies compatible with silicon photonics—technologies already widely used in telecommunications, high-performance computing, and advanced sensors. This compatibility may help speed up development of hybrid molecular–photonic platforms for quantum networks.
“By demonstrating the versatility of these erbium molecular qubits, we’re taking another step toward scalable quantum networks that can plug directly into today’s optical infrastructure,” said David Awschalom, Liew Family Professor of Molecular Engineering and Physics at UChicago and principal investigator on the study. “We’ve also demonstrated that these atomically engineered qubits have the capabilities necessary for multi-qubit architectures, which opens the door to a wide spectrum of applications, including quantum sensing and hybrid organic-inorganic quantum systems.”
The project involved close cooperation between scientists at UChicago; University of California Berkeley; Argonne National Laboratory; and Lawrence Berkeley National Laboratory. Both Weiss and Smith highlighted their collaboration with UC Berkeley chemists—especially co-first author Ryan Murphy from Prof. Jeffrey Long’s group—as essential to their progress.
“Synthetic molecular chemistry provides an opportunity for optimizing the electronic and optical properties of rare earth ions in ways that can be difficult to access in conventional solid-state substrates,” said Murphy. “This study is just scratching the surface of what we think we can accomplish.”
“Our work shows that synthetic chemistry can be used to design and control quantum materials at the molecular level,” said Long, co-principal investigator for the study. “This points to a powerful route for creating tailor-made quantum systems with applications in networking, sensing, and computation.”
Support for this research came from both Q-NEXT—a Department of Energy National Quantum Information Science Research Center—and funding from DOE’s Office of Science.