Imroatul Nasiyah
Princeton engineers have achieved a groundbreaking advancement in quantum computing by developing a superconducting qubit that boasts a coherence time three times longer than the most robust designs currently available, marking a significant stride toward achieving practical quantum advantage and enabling the creation of reliably operating quantum computers. This pivotal development, detailed in a November 5th article in the prestigious journal Nature, addresses one of the most formidable obstacles hindering the widespread adoption of quantum technology: the ephemeral nature of quantum information. Andrew Houck, a leading figure in national quantum research and Princeton’s dean of engineering, emphasized the critical nature of this breakthrough, stating, "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. This is the next big jump forward."
The newly engineered qubit demonstrates an astonishing coherence time exceeding 1 millisecond, a figure that triples the longest previously documented lifetime in laboratory settings and represents a nearly fifteen-fold improvement over the standard coherence times found in industrial quantum processors. To validate their findings and underscore the practical implications of their work, the Princeton team successfully constructed a functional quantum chip employing their novel qubit design. This functional prototype not only showcased the qubit’s capacity for error correction but also validated its potential for scalability towards more complex quantum systems. The researchers further highlighted the compatibility of their qubit with established architectures used by industry giants like Google and IBM, projecting that integrating their design into Google’s Willow processor could yield a staggering thousandfold increase in performance. Houck elaborated on the synergistic benefits of this advancement, noting that as quantum systems grow in complexity and incorporate an ever-increasing number of qubits, the performance advantages conferred by their design escalate exponentially.
The significance of enhanced qubit stability cannot be overstated in the pursuit of quantum computing’s revolutionary potential. Quantum computers hold the promise of tackling intricate problems that lie beyond the computational grasp of even the most powerful classical machines. However, their current efficacy is severely curtailed by the inherent fragility of qubits, which tend to lose their delicate quantum states before complex calculations can be fully executed. Consequently, extending qubit coherence time is an indispensable prerequisite for the realization of truly practical quantum hardware. Princeton’s recent achievement represents the most substantial single gain in qubit coherence time observed in over a decade, a testament to its profound impact.
While numerous research institutions are exploring diverse qubit technologies, Princeton’s innovation builds upon the well-established and widely adopted transmon qubit architecture. Transmons, which function as superconducting circuits meticulously maintained at cryogenic temperatures, are lauded for their inherent resilience against environmental noise and their seamless integration with existing modern manufacturing processes. Despite these inherent advantages, augmenting the coherence times of transmon qubits has historically presented a formidable technical hurdle. Recent findings from Google, for instance, have identified material defects as the primary impediment to further performance enhancements in their most advanced processors.
Addressing these material-specific challenges, the Princeton team devised a sophisticated two-pronged strategy. Their approach first involved the strategic incorporation of tantalum, a metal renowned for its exceptional ability to retain energy within delicate circuits. Secondly, they revolutionized the substrate material, replacing the conventional sapphire with high-purity silicon, a material that forms the bedrock of the global computing industry. The direct deposition of tantalum onto a silicon substrate presented a series of intricate engineering challenges, primarily concerning the material interfaces and their interactions. However, the researchers successfully navigated these complexities, unlocking substantial performance benefits in the process. Nathalie de Leon, co-director of Princeton’s Quantum Initiative and a co-principal investigator on the project, expressed optimism about the new design, noting that the tantalum-silicon configuration not only surpasses previous approaches in performance but also offers a more streamlined and scalable manufacturing pathway. "Our results are really pushing the state of the art," she remarked.
Michel Devoret, Chief Scientist for Hardware at Google Quantum AI and a significant funder of the research, eloquently described the arduous journey of extending quantum circuit lifetimes, characterizing it as a "graveyard" of abandoned attempts. He lauded de Leon’s tenacity and innovative spirit, stating, "Nathalie really had the guts to pursue this strategy and make it work." Devoret, a distinguished figure in quantum physics and the recipient of the 2025 Nobel Prize in Physics, underscored the collaborative nature of scientific progress.
The project received substantial backing from the U.S. Department of Energy National Quantum Information Science Research Centers and the Co-design Center for Quantum Advantage (C2QA). Houck, who directed C2QA from 2021 to 2025 and now serves as its chief scientist, highlighted the collaborative effort that underpinned this success. The seminal paper, titled "Millisecond lifetimes and coherence times in 2D transmon qubits," lists postdoctoral researcher Faranak Bahrami and graduate student Matthew P. Bland as co-lead authors, underscoring the contributions of early-career scientists.
The enhancement of qubit stability through the use of tantalum is rooted in fundamental principles of quantum computing. Houck, the Anthony H.P. Lee ’79 P11 P14 Professor of Electrical and Computer Engineering, explained that a quantum computer’s overall capability hinges on two critical factors: the sheer number of interconnected qubits and the number of error-free operations each qubit can perform. Improvements in the durability of individual qubits directly bolster both these aspects, enabling greater scalability and more robust error correction protocols. Energy loss, often stemming from microscopic surface defects in metallic components, is a primary culprit for qubit failures during computation. These errors are amplified as the number of qubits increases. Tantalum’s inherent advantage lies in its significantly lower density of such defects compared to commonly used metals like aluminum, thereby minimizing error generation and simplifying the complex process of error mitigation.
This pioneering application of tantalum for superconducting chips was initially conceptualized in 2021 by Houck and de Leon, with crucial insights provided by Princeton chemist Robert Cava, the Russell Wellman Moore Professor of Chemistry. Cava, a renowned expert in superconducting materials, was drawn to the challenge after attending one of de Leon’s presentations, subsequently suggesting tantalum as a promising candidate. "Then she went and did it," Cava remarked, marveling at the successful implementation. Building upon this foundational idea, researchers across three distinct labs collaborated to construct a tantalum-based superconducting circuit on a sapphire substrate, which yielded a significant boost in coherence time, nearly matching the prior world record. Bahrami further elaborated on tantalum’s unique properties, noting its exceptional durability and resistance to the harsh chemical cleaning processes essential for fabricating contamination-free circuits. "You can put tantalum in acid, and still the properties don’t change," she asserted.
Subsequent analysis revealed that the sapphire substrate was a significant contributor to residual energy losses. The team’s decision to transition to a high-purity silicon substrate effectively eliminated this persistent source of error. The synergistic combination of tantalum and silicon, coupled with refined fabrication techniques, resulted in one of the most substantial advancements ever recorded for a transmon qubit. Houck aptly described this outcome as "a major breakthrough on the path to enabling useful quantum computing." He further emphasized the exponential benefits of this design for larger systems, projecting that replacing current industry-leading qubits with the Princeton version could elevate the effectiveness of a theoretical 1,000-qubit computer by an astounding factor of one billion.
The silicon-based design not only promises superior performance but also lays the groundwork for industry-scale growth. This multidisciplinary triumph is a direct result of the synergistic integration of expertise from three distinct research groups. Houck’s team specialized in the intricate design and optimization of superconducting circuits. De Leon’s laboratory focused on quantum metrology, alongside the crucial materials and fabrication methodologies that dictate qubit performance. Cava’s group brought decades of experience in the development of advanced superconducting materials. By pooling their collective knowledge and capabilities, the team achieved results that would have been unattainable by any single group working in isolation. This groundbreaking work has already garnered considerable attention from the quantum computing industry.
Devoret highlighted the indispensable role of collaborations between academic institutions and commercial enterprises in propelling advanced technologies forward, noting the "rather harmonious relationship between industry and academic research." He explained that university researchers are ideally positioned to explore the fundamental limits of quantum performance, while industry partners can then translate these discoveries into practical, large-scale applications. De Leon expressed confidence in the scalability of their findings, stating, "We’ve shown that it’s possible in silicon. 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 comprehensive research findings, detailed in the paper "Millisecond lifetimes and coherence times in 2D transmon qubits," were published in Nature on November 5th. The author list 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, in addition to the previously mentioned de Leon, Houck, Cava, Bahrami, and Bland. This transformative research received primary funding 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 supplementary support from Google Quantum AI.
