Protocol overcomes the quantum sensing decoherence barrier
In a study, researchers from the University of Southern California (USC) demonstrated a new quantum sensing technique that mitigates the decoherence limitation and widely surpasses conventional methods. This technique could potentially accelerate advances in fields ranging from medical imaging to foundational physics research.
Until now, the performance of quantum sensors has been limited by decoherence, which refers to the unpredictable behaviour caused by environmental noise. “Decoherence causes the state of a quantum system to become randomly scrambled, erasing any quantum sensing signal,” said Eli Levenson-Falk, senior author of the study.
Quantum sensing measures physical quantities with exceptional precision, often exceeding the capabilities of classical sensors by utilising properties such as superposition, entanglement, and coherence to detect minute signals that would otherwise be obscured by noise.
“Think of it as trying to hear a faint whisper in a noisy space,” said Malida Hecht, lead author of the study. “Quantum sensing devices detect things that are too small or faint for normal measuring tools to notice.”
In the new study, the research team temporarily counteracted the long-standing problem of decoherence by utilising a new pre-determined coherence-stabilized protocol in their experiment’s qubit, thereby stabilising one key property of the quantum state. The protocol was based on theory derived by co-authors Daniel Lidar and Kumar Saurav. This experiment significantly enhanced the measurement of small frequency shifts in quantum systems. Levenson-Falk said the study’s coherence-stabilized sensing protocol enables the sensing signal, which manifests as a change in the quantum state, to grow larger than it would with the standard protocol sensing measurement.
This stabilisation could prove crucial for applications where detecting subtle signals is essential. “The larger signal is easier to detect, giving improved sensitivity,” Levenson-Falk said. “Our study gives the best sensitivity for detecting a qubit’s frequency to date. Most importantly, our protocol requires no feedback and no extra control or measurement resources, making it immediately applicable across various quantum computing and quantum sensor technologies.”
The researchers demonstrated their protocol on a superconducting qubit, achieving up to 1.65 times better efficacy per measurement compared to the standard protocol known as Ramsey interferometry. Theoretical analysis indicated potential improvements of up to 1.96 times in some systems.
Levenson-Falk said his experimental demonstration of sensing with a stabilised state shows that there are ways to improve quantum sensors without resorting to complicated techniques like real-time feedback or entangling many sensors. “It also shows that we have not yet extracted all the possible information from these types of measurements. Even better sensing protocols are out there, and we could use them to make immediate real-world impacts.”
Image: The qubit state decays toward the “north pole” of the sphere due to decoherence. Using the study’s coherence-stabilized sensing protocol, the researchers temporarily counteracted the decay, resulting in a larger sensing signal (y component) in the study’s protocol (blue) than in the standard protocol (red). Credit Eli Levenson-Falk/USC.
The study was authored by Matilda O. Hecht, Kumar Saurav, Evangelos Vlachos, Daniel A. Lidar and Eli M. Levenson-Falk, all of USC.
Eli Levenson-Falk holds the posts of associate professor of physics and astronomy at the USC Dornsife College of Letters, Arts and Sciences and associate professor of electrical and computer engineering at the USC Viterbi School of Engineering.
Daniel Lidar holds the post of Viterbi Professor of Engineering and professor of chemistry, physics and astronomy at USC). Kumar Saurav is a doctoral student in electrical engineering at USC Viterbi, and Malida Hecht is a doctoral student in physics at USC Dornsife.
https://doi.org/10.1038/s41467-025-58947-4
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