Highlights:
- Researchers have developed a method to fabricate superconducting qubits on 300 mm wafers using CMOS technology.
- The qubits achieved relaxation and coherence times exceeding 100 µs, marking a significant breakthrough in quantum computing.
- The fabrication method involves optical lithography and reactive-ion etching, offering high-yield and performance scalability.
- This development sets the stage for producing million-qubit quantum processors, essential for future quantum computing breakthroughs.
TLDR: Researchers have demonstrated a scalable method to manufacture superconducting qubits on 300 mm silicon wafers using CMOS processes. This industrial-scale approach enables high-coherence qubits with relaxation times over 100 µs, offering significant potential for the development of large-scale quantum processors.
In the quest to build practical quantum computers, one of the most significant hurdles is producing stable and scalable qubits. A new study from researchers at Imec and KU Leuven presents a significant leap forward by demonstrating the large-scale manufacturing of superconducting qubits on 300 mm wafers using Complementary Metal-Oxide-Semiconductor (CMOS) technology. Their innovative fabrication method marks a shift from traditional lab-based techniques, offering an alternative approach that could revolutionize quantum computing hardware by supporting the creation of million-qubit processors.
A New Era for Quantum Fabrication
Traditionally, the construction of superconducting qubits has relied on bespoke laboratory techniques, such as electron-beam lithography and metal lift-off processes. While these methods have been effective in producing small-scale, high-coherence qubits, they are not suited for large-scale production. With quantum processors expected to require millions of qubits for fault-tolerant computation, a more scalable approach is necessary. This is where the team’s work shines.
Using a 300 mm CMOS pilot line, the researchers fabricated superconducting transmon qubits using optical lithography and reactive-ion etching. These techniques are widely employed in the semiconductor industry, providing the precision and control required for quantum computing hardware. The qubits produced using this method showed relaxation times exceeding 100 µs, a key metric for determining qubit stability and performance. High coherence is essential for reliable quantum operations, as it means the qubits can maintain their quantum states for longer periods, enabling more complex computations.
Superior Control and Uniformity
One of the most impressive aspects of this new fabrication process is its yield and uniformity. The researchers analyzed over 400 qubits and 12,840 Josephson Junction (JJ) test structures, revealing exceptional consistency in qubit performance across the entire wafer. This uniformity is crucial for the eventual production of large-scale quantum processors, where variability in qubit performance could lead to significant computational errors.
A notable feature of this approach is the ability to maintain high coherence times despite the use of industrial-scale manufacturing methods. The qubits produced showed across-wafer relaxation times ranging from 42 µs at the edge to 113 µs at the center, with a median value of 75 µs. This level of performance is comparable to, and in some cases better than, traditional qubit fabrication methods.
Overcoming Coherence Limitations
Achieving high-coherence qubits in an industrial setting presents several challenges, particularly in managing interface defects that can limit qubit performance. The research team tackled this by designing qubits with varying capacitor geometries, allowing them to identify and mitigate sources of decoherence. Their analysis revealed that two-level system (TLS) defects at capacitor interfaces were the dominant source of energy loss, limiting qubit relaxation times. By fine-tuning the fabrication process, particularly through the use of argon milling and controlled oxidation, the team was able to minimize these losses.
The study also identified that further improvements in qubit performance could be achieved by refining the oxidation process used in the fabrication of Josephson junctions. This step is crucial, as it directly impacts the qubit’s operating frequency and coherence time.
Long-Term Stability and Potential for Scale-Up
An important aspect of this research is the long-term stability of the qubits produced. Over a period of 151 days, the team monitored the aging of the qubits and found that their performance remained stable, with only a 3.7% reduction in normal resistance over this time. This demonstrates the robustness of the fabrication process and suggests that qubits produced in this way could maintain their performance for extended periods, a critical factor for the development of practical quantum computers.
The industrial-scale methods used in this study, such as optical lithography and subtractive dry etching, are already highly optimized in the semiconductor industry. This means that further refinements could push qubit performance even higher, potentially achieving sub-millisecond coherence times in the future. Additionally, the integration of three-dimensional (3D) packaging techniques could enable the construction of even more complex and densely packed quantum processors.
Looking Ahead: Million-Qubit Processors
The implications of this research are far-reaching. By demonstrating that CMOS-compatible processes can produce high-coherence qubits with excellent yield, the team has opened the door to the large-scale fabrication of quantum processors. With further refinements in process control, the techniques outlined in this study could be used to produce quantum processors with millions of qubits, a critical milestone on the road to achieving quantum supremacy and fault-tolerant quantum computing.
In summary, this breakthrough sets the stage for a new era in quantum computing hardware. By leveraging existing semiconductor manufacturing techniques, researchers have taken a significant step towards the industrial-scale production of quantum processors, bringing us closer to the dream of practical, large-scale quantum computing.
Source: Van Damme, J., Massar, S., Acharya, R., Ivanov, Ts., Perez Lozano, D., Canvel, Y., Demarets, M., Vangoidsenhoven, D., Hermans, Y., Lai, J. G., Vadiraj, A. M., Mongillo, M., Wan, D., De Boeck, J., & De Greve, K. (2024). Advanced CMOS manufacturing of superconducting qubits on 300 mm wafers. Nature. https://doi.org/10.1038/s41586-024-07941-9