MIT Researchers Achieve Record-Breaking Fidelity in Superconducting Qubit Control
A team of researchers at the Massachusetts Institute of Technology (MIT) has made a significant breakthrough in the field of quantum computing by developing new control methods that enable record-setting fidelity in superconducting qubits. This advancement has the potential to significantly reduce the resource overhead needed for error correction in quantum systems.
Quantum computing, which relies on the principles of quantum mechanics to perform calculations exponentially faster than classical computers, faces challenges due to the sensitivity of qubits to noise and control imperfections. These factors introduce errors, which limit the complexity and stability of quantum operations.
MIT researchers from the Department of Physics, the Research Laboratory of Electronics (RLE), and the Department of Electrical Engineering and Computer Science (EECS) have focused on improving qubit performance. In their recent work, they used a superconducting qubit called fluxonium and developed two innovative control techniques, achieving a single-qubit fidelity of 99.998 percent—setting a new world record. This result builds on past achievements, including a 99.92 percent two-qubit gate fidelity demonstrated by a former MIT researcher, Leon Ding.
The research paper’s senior authors include David Rower PhD ’24, a former physics postdoc in MIT’s Engineering Quantum Systems (EQuS) group and now a research scientist at Google Quantum AI; Leon Ding PhD ’23 from EQuS, now leading the Calibration team at Atlantic Quantum; and William D. Oliver, the Henry Ellis Warren Professor of EECS, professor of physics, leader of EQuS, director of the Center for Quantum Engineering, and RLE associate director. The paper, titled “Suppressing Counter-Rotating Errors for Fast Single-Qubit Gates with Fluxonium,” was recently published in the journal PRX Quantum.
Tackling Decoherence and Counter-Rotating Errors
One of the main challenges in quantum computation is decoherence—the loss of quantum information due to environmental noise. Superconducting qubits, like fluxonium, are especially prone to decoherence, which hinders the realization of high-fidelity quantum gates. To address this, MIT researchers have developed techniques that make quantum gates faster, minimizing the impact of decoherence.
However, faster gates can introduce another type of error—counter-rotating errors—caused by the interaction between qubits and electromagnetic waves. Traditional single-qubit gates use resonant pulses that induce Rabi oscillations. When these pulses are applied too rapidly, they lead to inconsistent results due to unwanted errors from counter-rotating effects.
David Rower explains, “Initially, Leon had the idea to utilize circularly polarized microwave drives, but we realized that this alone wasn’t sufficient to fully eliminate counter-rotating errors.”
The breakthrough came when the team introduced a concept they call “commensurate pulses.” By carefully timing the application of pulses according to specific intervals determined by the qubit frequency, they were able to correct counter-rotating errors in a consistent and automatic manner. This technique requires no additional calibration overhead and can be applied to any qubit that suffers from counter-rotating errors.
“This project makes it clear that counter-rotating errors can be dealt with easily,” says Rower. “It’s a simple yet effective method, and it works across various superconducting qubits, including fluxonium.”
The Promise of Fluxonium
Fluxonium is a type of superconducting qubit that combines a capacitor and Josephson junction with a large “superinductor,” which protects the qubit from environmental noise. This design results in high coherence and accuracy in logical operations.
Despite its advantages, fluxonium qubits typically have lower frequencies, leading to longer gates. However, the MIT team’s work demonstrates that fluxonium can achieve extremely fast and high-fidelity gates.
Leon Ding, one of the paper’s co-authors, states, “Our experiments show that fluxonium not only performs well in physical exploration but also delivers exceptional engineering results. It’s proving to be a promising qubit for quantum computing.”
The researchers aim to continue their work to refine these techniques further and uncover new limitations, potentially leading to even faster and more reliable quantum gates.
“This research demonstrates how deep collaboration between physics and electrical engineering can lead to remarkable advancements,” says William Oliver. “Our results push the boundaries of what is possible in quantum computing and provide a pathway toward practical, fault-tolerant quantum computation.”
This research was supported by funding from the U.S. Army Research Office, the U.S. Department of Energy Office of Science, National Quantum Information Science Research Centers, and other U.S. government agencies.
Related Contributors
The research team includes MIT’s Helin Zhang, Max Hays, Patrick M. Harrington, Ilan T. Rosen, Simon Gustavsson, Kyle Serniak, Jeffrey A. Grover, and Junyoung An, as well as researchers from MIT Lincoln Laboratory: Jeffrey M. Gertler, Thomas M. Hazard, Bethany M. Niedzielski, and Mollie E. Schwartz.
This advancement in quantum control methods represents a major step forward in the quest to realize high-fidelity quantum computing, which could lead to transformative applications in fields such as cryptography, machine learning, and beyond.
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