Noise is disruptive, whether you're trying to get a good night’s sleep or working with the principles of quantum physics. While environmental noise is unavoidable, a team of scientists from the National Institute of Standards and Technology (NIST) may have discovered a new technique to cope with it at tiny scales where quantum physics rules. The study appeared in Physical Review Letters.
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Addressing this noise might result in the best sensors ever created, with applications ranging from healthcare to mineral exploration.
Researchers can harness quantum phenomena like superposition and entanglement to detect subtle changes in the environment, an approach that is valuable for applications ranging from geological studies to improving GPS accuracy. To do so, they must be able to see through surrounding noise, such as stray magnetic fields, to detect, for example, a crucial signal from the brain.
New results might allow interlinked groups of quantum objects, such as atoms, to better detect their surroundings in the midst of noise. A collection of unlinked quantum devices can already outperform a traditional sensor.
Linking them via quantum entanglement can improve their performance even further. However, entangling the group can leave it sensitive to external noise, resulting in mistakes and a loss of the group's enhanced sensing advantage.
The team's theoretical approach outlines how to prepare a set of quantum objects called qubits, the basic units of information in quantum computers, before using them for sensing applications.
Instead of training the group to correct all of the faults that the interlinked qubits suffer, the researchers discovered that correcting only part of the errors improves the sensor's robustness in the face of noise. The entangled qubits lose some sensitivity in the process, but the tradeoff is beneficial because the sensor outperforms unentangled qubits.
Usually in quantum error correction, you want to correct the error perfectly. But because we are using it for sensing, we only need to correct it approximately rather than exactly. As long as you prepare your entangled sensor the way we discovered, it will protect your sensor.
Cheng-Ju (Jacob) Lin, Study Author and Postdoctoral Fellow, Joint Center for Quantum Information and Computer Science (QuICS)
Qubits can exist in various energy levels, such as high and low, but they can also exist in a “superposition” of those states, appearing to be in all of them at the same time.
This superposition not only allows a quantum computer to solve problems that conventional computers cannot, but it also makes the qubit extremely sensitive to minute changes in its environment, such as the presence of a faint magnetic field, which would have a measurable effect on the qubit's energy state.
Quantum-enhanced measurement techniques like this offer greater precision than traditional sensing methods, making them especially useful for applications such as navigation.
However, qubits can become even more sensitive when they take advantage of an additional quantum property known as entanglement, where multiple particles share linked quantum states. In an entangled group, each qubit doesn’t just respond to a signal on its own; it also feels the signal through its quantum connection with the others. This amplifies the effect, allowing the group to detect subtle changes more effectively than unentangled qubits.
Increasing the number of entangled qubits boosts the group’s capabilities significantly. For example, 100 unentangled qubits would be ten times more sensitive than a single qubit in superposition, but 100 entangled qubits would be one hundred times more sensitive.
The problem is that entangling qubits often requires total isolation from external disturbances, such as mechanical vibrations or temperature variations. Such disruptions produce what quantum technology designers refer to as noise, which is a recurrent challenge for quantum computers and quantum sensors.
The researchers designed the group of entangled qubits to be resistant against certain types of noise-related errors. To bolster the group’s resistance to noise, the team applies quantum error correction codes, techniques originally developed to fix faulty data in quantum computers. Their approach builds on results from earlier experimental work by other researchers.
“In analyzing these error correction codes, we found that there is a family of codes that protects entangled sensors. One type of error correction code enables entangled qubits to detect magnetic fields with higher precision than unentangled qubits, even if some of the entangled qubits become corrupted with errors,” added Lin.
While previous teams’ experiments suggested the result, Lin claims that his group's study puts the findings on a more mathematically sound foundation.
“It may take time for technologists to create sensors that take advantage of the findings. However, the community’s understanding of quantum mechanics is good enough that we think the results will hold up under experiment, which we invite others to test in the lab,” concluded Lin.
Journal Reference:
Lin, C.-J., et al. (2025) Covariant Quantum Error-Correcting Codes with Metrological Entanglement Advantage. Physical Review Letters. doi.org/10.1103/dttc-ksdn