Imroatul Nasiyah
The core challenge in building practical quantum computers, as explained by Andrew Houck, a leader in national quantum research and Princeton’s dean of engineering, lies in the limited lifespan of qubits. "The real challenge, the thing that stops us from having useful quantum computers today, is that you build a qubit and the information just doesn’t last very long," Houck stated. "This is the next big jump forward." The Princeton team’s newly developed qubit boasts a coherence time exceeding 1 millisecond, a threefold increase over the longest previously documented lifetimes in laboratory settings and a staggering fifteenfold improvement compared to the standards employed in industrial quantum processors. To validate their findings, the researchers successfully constructed a functional quantum chip utilizing their novel qubit design, demonstrating its capability to support error correction and its scalability towards more complex systems.
Crucially, this new qubit architecture is fully compatible with the designs favored by industry giants like Google and IBM. The Princeton team’s analysis suggests that integrating their qubit technology into Google’s existing Willow processor could result in a thousand-fold performance enhancement. Houck further emphasized that the advantages of this design escalate exponentially as the number of qubits in a quantum system increases, promising an even more profound impact on future quantum computing capabilities.
The profound importance of improved qubit stability for quantum computing cannot be overstated. Quantum computers hold immense potential to tackle problems currently intractable for even the most powerful classical supercomputers. However, their practical application is severely hampered by the tendency of qubits to lose their quantum state, or coherence, before complex calculations can be completed. Extending this coherence time is therefore paramount for the development of functional quantum hardware. The advancement made by Princeton represents the most substantial single gain in qubit coherence time seen in over a decade.
While numerous research groups are exploring diverse qubit technologies, Princeton’s innovation builds upon the well-established and widely adopted transmon qubit approach. Transmons, which operate as superconducting circuits maintained at cryogenic temperatures, are favored for their inherent resilience to environmental noise and their compatibility with existing semiconductor manufacturing processes. Despite these advantages, enhancing the coherence time of transmon qubits has presented a persistent and difficult challenge. Recent findings from Google, for instance, have highlighted material defects as the primary impediment to further improvements in their most advanced processors.
Addressing these material-related challenges, the Princeton team implemented a sophisticated two-pronged strategy. The first element involved the integration of tantalum, a metal renowned for its ability to retain energy within delicate electronic circuits. The second, equally significant, innovation was the replacement of the conventional sapphire substrate with high-purity silicon, a material that forms the bedrock of the modern computing industry. The direct deposition of tantalum onto silicon necessitated overcoming several intricate technical hurdles related to their material interactions. However, the researchers successfully navigated these complexities, uncovering substantial performance benefits in the process.
Nathalie de Leon, co-director of Princeton’s Quantum Initiative and a co-principal investigator on the project, highlighted that their tantalum-silicon design not only outperforms previous approaches but is also more amenable to large-scale manufacturing. "Our results are really pushing the state of the art," de Leon remarked. Michel Devoret, chief scientist for hardware at Google Quantum AI, which provided partial funding for the research, underscored the formidable nature of extending quantum circuit lifetimes, describing the pursuit as a "graveyard" of failed attempts. Devoret, a recipient of the 2025 Nobel Prize in Physics, commended de Leon’s tenacity, stating, "Nathalie really had the guts to pursue this strategy and make it work."
The project received primary funding from the U.S. Department of Energy’s National Quantum Information Science Research Centers and the Co-design Center for Quantum Advantage (C2QA). Houck led C2QA from 2021 to 2025 and currently serves as its chief scientist. The research paper credits postdoctoral researcher Faranak Bahrami and graduate student Matthew P. Bland as co-lead authors.
The mechanism by which tantalum enhances qubit stability is rooted in fundamental principles of quantum computing. Houck, the Anthony H.P. Lee ’79 P11 P14 Professor of Electrical and Computer Engineering, elucidated that a quantum computer’s efficacy hinges on two key factors: the number of interconnected qubits and the number of operations each qubit can perform before accumulating errors. Improvements in the durability of individual qubits directly bolster both these aspects, as extended coherence times facilitate scalability and more robust error correction. Energy loss is identified as the predominant cause of failure in these sensitive systems. Microscopic surface imperfections within metallic components can trap energy, disrupting qubit operations during computations. These disruptions are amplified as more qubits are integrated into a system. Tantalum proves particularly advantageous due to its inherently lower concentration of such defects compared to metals like aluminum. A reduction in defects translates to fewer errors and a simplified process for correcting the residual errors.
Houck and de Leon first proposed the use of tantalum for superconducting chips in 2021, with critical contributions from Princeton chemist Robert Cava, the Russell Wellman Moore Professor of Chemistry. Cava, an expert in superconducting materials, became intrigued by the problem after attending one of de Leon’s presentations. Their subsequent discussions led him to suggest tantalum as a promising candidate material. "Then she went and did it," Cava commented. "That’s the amazing part."
Researchers across three laboratories adopted this concept, constructing a tantalum-based superconducting circuit on a sapphire substrate. This initial iteration demonstrated a significant enhancement in coherence time, nearing the prior world record. Bahrami pointed out that tantalum’s exceptional durability is a key asset, enabling it to withstand the rigorous cleaning processes essential for removing contamination during fabrication. "You can put tantalum in acid, and still the properties don’t change," she noted.
Following meticulous contaminant removal, the team analyzed the remaining sources of energy loss. They identified the sapphire substrate as the primary contributor to these persistent issues. The switch to high-purity silicon effectively eliminated this loss mechanism. The synergistic combination of tantalum and silicon, coupled with refined fabrication techniques, culminated in one of the most substantial improvements ever recorded for a transmon qubit. Houck characterized the outcome as "a major breakthrough on the path to enabling useful quantum computing." He further elaborated that given the exponential increase in benefits as quantum systems scale, replacing current industry-leading qubits with Princeton’s design could theoretically yield a thousand-qubit computer operating approximately one billion times more effectively.
The silicon-based design is poised to support industry-scale growth due to its inherent compatibility with existing semiconductor manufacturing infrastructure. The success of this project is a testament to the power of interdisciplinary collaboration, drawing on expertise from three distinct areas. Houck’s group specializes in the design and optimization of superconducting circuits, while de Leon’s lab focuses on quantum metrology, materials science, and fabrication methods critical for qubit performance. Cava’s group brings decades of experience in developing advanced superconducting materials. The fusion of these complementary strengths enabled the team to achieve results unattainable by any single group. This significant advancement has already garnered considerable interest from the quantum computing industry.
Devoret emphasized the indispensable role of collaborations between academia and industry in propelling advanced technologies forward. "There is a rather harmonious relationship between industry and academic research," he observed. University researchers are adept at exploring the fundamental limits of quantum performance, while industrial partners are instrumental in translating these discoveries into practical, large-scale systems. "We’ve shown that it’s possible in silicon," de Leon affirmed. "The fact that we’ve shown what the critical steps are, and the important underlying characteristics that will enable these kinds of coherence times, now makes it pretty easy for anyone who’s working on scaled processors to adopt."
The paper, titled "Millisecond lifetimes and coherence times in 2D transmon qubits," was published in Nature on November 5th. Alongside de Leon, Houck, Cava, Bahrami, and Bland, the authorship includes Jeronimo G.C. Martinez, Paal H. Prestegaard, Basil M. Smitham, Atharv Joshi, Elizabeth Hedrick, Alex Pakpour-Tabrizi, Shashwat Kumar, Apoorv Jindal, Ray D. Chang, Ambrose Yang, Guangming Cheng, and Nan Yao. This groundbreaking research received primary support from the U.S. Department of Energy, Office of Science, National Quantum Information Science Research Centers, and the Co-design Center for Quantum Advantage (C2QA), with partial support from Google Quantum AI.
