Quantum computers are expected to revolutionize material and drug development as well as information security. Among the key technologies driving this innovation are superconducting qubits, which offer easier control. A critical component of these qubits is the Josephson junction, enabling them to function by manipulating different energy levels.
While transmon qubits are popular, they face challenges due to low anharmonicity, making it difficult to integrate multiple qubits without interference. In contrast, flux qubits, utilizing three Josephson junctions, exhibit higher anharmonicity, mitigating interference issues. However, the need for special coils in flux qubits can introduce noise and require additional control lines, hindering scalability.
A collaborative effort between the National Institute of Information and Communications Technology (NICT), NTT Corporation, Tohoku University, and the Tokai National Higher Education and Research System Nagoya University has resulted in the development of a novel superconducting flux qubit that operates in a zero magnetic field. This breakthrough promises enhanced quantum computing performance and integration.
The newly devised superconducting flux qubit incorporates a ferromagnetic Josephson junction, known as a π-junction, which generates a 180-degree phase difference without external magnetic fields.
Superconducting material could someday power quantum computers
This unique qubit design enables independent optimal operation, potentially reducing external noise, simplifying circuits, and facilitating the integration of multiple qubits.
The research team combined NICT’s nitride superconducting qubit technology with ferromagnetic Josephson device technology to create a flux qubit featuring a Ï€-junction. The Ï€-junction qubit exhibited optimal performance at zero magnetic field, demonstrating promising coherence properties.
By leveraging palladium nickel (PdNi) instead of copper-nickel (CuNi) and incorporating NICT’s NbN/AlN/NbN junction technology with NTT’s advanced flux qubit design in 3D cavity resonators, the researchers achieved a coherence time of 1.45 microseconds, a significant improvement over previous Ï€-junction phase qubits.
This achievement marks a significant milestone in the development of flux qubits operating without external magnetic fields, boasting a microsecond-level coherence time. While further enhancements in quantum coherence are warranted, this technology represents a crucial advancement in miniaturizing and integrating quantum circuits. Eliminating the reliance on external magnetic fields streamlines designs, conserves energy, and reduces costs.
The authors stated, “Looking ahead, we aim to optimize the circuit structure and fabrication process to extend the coherence time further and enhance the uniformity of device characteristics, paving the way for future large-scale integration. Our objective is to develop a new quantum hardware platform surpassing the performance of conventional aluminum-based qubits.”
“Through improvements in materials and ferromagnetic junction structure, we aspire to create a Ï€-junction flux qubit with an extended coherence time capable of operating in zero magnetic fields. Such advancements could position it as a pivotal component in various quantum technologies, including quantum computer chips.”
Journal Reference:
- Kim, S., Abdurakhimov, L.V., Pham, D. et al. Superconducting flux qubit with ferromagnetic Josephson π-junction operating at zero magnetic field. Commun Mater 5, 216 (2024). DOI: 10.1038/s43246-024-00659-1
