The world of quantum technology, which seeks to harness the strange properties of quantum mechanics for applications in computing, communication, and sensing, has just gained an exciting new player in its arsenal. Researchers have discovered that spinel, a gemstone long admired for its vivid colors resembling rubies and sapphires, can store quantum information, opening the door to new possibilities in the field. This groundbreaking development, published in the journal Applied Physics Express, comes from a collaboration between researchers from Tohoku University, the University of Chicago, and Argonne National Laboratory.
The research marks the first published results from the Chicago–Tohoku Quantum Alliance, an academic and research partnership formed in June 2023. Its goal is to strengthen ties between academic institutions in the U.S. and Japan while fostering closer collaborations with industry and government. As the first breakthrough from this collaborative effort, the discovery of spinel’s potential as a viable material for quantum information storage offers a fresh perspective on the role of gemstones in quantum systems.
The Unlikely Candidate: Spinel
Spinel (MgAl₂O₄) is a naturally occurring mineral often seen in a spectrum of bright colors, from red to blue and purple. It is known for its brilliant aesthetic properties, which have made it a sought-after gemstone. Yet, beyond its aesthetic allure, spinel possesses some intriguing physical characteristics that were previously underexplored from a quantum computing perspective.
The critical aspect of spinel’s potential in quantum technologies lies in its ability to host defects at the atomic level that trap electron spins, which are fundamental to the operation of quantum bits, or qubits. Qubits are the building blocks of quantum information systems, which leverage quantum mechanical phenomena like superposition and entanglement to process information in ways classical systems cannot.
While materials like diamond and moissanite have been at the forefront of solid-state spin qubit research, the discovery of spinel as a functional qubit material offers an exciting new path for development. Professor David Awschalom, one of the study’s co-leaders and the Liew Family Professor and Vice Dean for Research at the University of Chicago’s Pritzker School of Molecular Engineering, praised this finding for both its scientific significance and its potential for real-world applications.
“This discovery highlights the incredible potential of materials like spinel, which have long been prized for their aesthetic qualities but are now revealing profound scientific capabilities,” said Awschalom. “By leveraging its unique properties, we’re not only advancing our understanding of qubit systems but also expanding the toolkit for quantum technologies in ways that were previously unimagined.”
Quantum Technologies and Qubits
Quantum information technology represents a paradigm shift in computing. Whereas classical systems store and process information in binary form (0s and 1s), quantum systems utilize qubits that can exist in multiple states simultaneously, thanks to quantum superposition. This allows quantum systems to perform complex computations at an exponentially faster rate than classical computers.
At the heart of quantum technology is the challenge of creating stable and controllable qubits. While the theory behind qubits is well-established, making these systems operational and scalable is a far more complex task. One approach to stabilizing qubits is embedding them within materials that have precise atomic defects capable of trapping and manipulating electron spins.
Materials like diamond, in particular, have been frequently explored due to the stability of defects that host spin states. However, as the field of quantum information expands, researchers are looking for additional materials that can host spin qubits at higher temperatures, in more diverse environments, and with the flexibility needed for a wider variety of quantum applications.
How Spinel Works as a Quantum Material
The team’s research led them to examine spinel for its potential as a quantum material due to its structural and optical properties. Spinel possesses an intriguing defect center—specifically, the presence of cerium (Ce), a rare-earth metal atom. The cerium atom is capable of hosting electron spins, which makes spinel a promising candidate for quantum information processing.
The researchers employed a method that used a laser beam to excite the spinel material and then measured the photoluminescence—the light emitted by the material when returning to its lower-energy state. This technique allows the scientists to probe and measure the behavior of qubits with great precision.
“What we found was that the cerium (Ce) centers in the spinel material were able to hold qubit information at extremely low temperatures—down to 4 Kelvin (about -269°C)—in the presence of a 500 mT magnetic field,” explained Shun Kanai, a professor at RIEC, Tohoku University, and co-lead of the study.
The team’s optical measurements demonstrated that spinel could successfully initialize and read qubit states. Initialization refers to preparing a qubit in a known state, while readout refers to extracting information from the qubit. These are two of the most critical functions required for a functioning qubit system.
What’s Next for Spinel and Quantum Technologies?
While this is a significant breakthrough in material science, the journey is far from complete. As with other qubit materials, spinel must prove its ability to also manipulate qubit states for it to be fully operational. The control of qubits—entailing precise interactions to modify the qubit’s state—is crucial for all quantum applications.
“Our next steps will focus on manipulating the qubit states in spinel,” said Awschalom. “The long-term goal is to implement and test qubit control schemes that will allow quantum sensors, communications, and computing applications to flourish.”
The ability to manipulate qubits reliably, as well as maintain their coherence (the stability of their quantum states), is essential to moving from fundamental research to functional devices. The next stages of research will likely delve into applying electric and magnetic fields to control qubit spins more efficiently and accurately.
Moreover, spinel’s promising features—such as its resilience at extremely low temperatures—make it a potential candidate for quantum sensing applications, which could offer unprecedented sensitivity to external factors like electromagnetic fields. This could have profound implications not only for quantum computing but also for precision sensing in fields such as material science, biology, and environmental monitoring.
The Path Ahead: Quantum Applications
While researchers are excited by spinel’s potential for quantum information technology, it remains one step among many in what will likely be a decade-long journey to build large-scale quantum devices. If spinel can demonstrate full qubit manipulation alongside initialization and readout capabilities, its applications may soon expand beyond quantum computing into areas like quantum communication and quantum sensing.
As more breakthroughs in materials science and quantum theory unfold, researchers anticipate the rise of various quantum technologies—from quantum encryption for secure communications to quantum sensors capable of detecting gravitational waves or mapping the brain. These are enormous challenges, but spinel could prove to be a piece of the puzzle that bridges the gap between lab-based demonstrations and the practical implementation of quantum systems in real-world scenarios.
Ultimately, the discovery of spinel’s utility as a quantum material is part of a larger, ongoing effort to develop the tools necessary to push the boundaries of human understanding and technological innovation. The collaboration between Tohoku University, the University of Chicago, and Argonne National Laboratory, along with similar partnerships, stands as an example of how cross-disciplinary and cross-border efforts are vital in shaping the future of quantum technologies.
Conclusion
The work on spinel’s potential in quantum technology opens up a new realm of possibilities in the rapidly advancing field of quantum computing. While still early in its development, spinel’s ability to store and manipulate quantum information represents an exciting advancement in materials science. By continuing to refine the manipulation of spin qubits within spinel, researchers aim to unlock new applications that could revolutionize sectors such as computing, communication, and beyond. As the Chicago–Tohoku Quantum Alliance continues to foster these international collaborations, we can expect many more breakthroughs to emerge, bringing the promises of quantum technology closer to reality.
Reference: Manato Kawahara et al, Polarization-dependent photoluminescence of Ce-implanted MgO and MgAl2O4, Applied Physics Express (2024). DOI: 10.35848/1882-0786/ad59f4