China Tests Drone-Mounted Quantum Sensor That Could Reshape Submarine Detection

Chinese scientists tested a drone-mounted quantum sensor system that could detect submarines with high sensitivity, overcoming blind spots found in traditional detectors.
Offshore trials demonstrated high accuracy and stability, with potential applications in underwater resource mapping as well as military surveillance.

Researchers noted the need for further testing in harsher conditions before the system could be considered operational.
Chinese researchers have developed and tested a drone-mounted quantum sensor that could allow faster and more accurate detection of submarines and underwater features, according to a study published April 16 in the Chinese Journal of Scientific Instrument.

Led by Wang Xuefeng at the Quantum Engineering Research Centre of China Aerospace Science and Technology Corporation (CASC), the team designed a system to overcome a major flaw in traditional magnetic anomaly detectors, as reported by the South China Morning Post. In low-latitude regions like the South China Sea, Earth’s magnetic field runs nearly parallel to the surface, causing blind zones where conventional sensors lose effectiveness.

The new system uses a Coherent Population Trapping (CPT) atomic magnetometer, which leverages quantum interference effects in rubidium atoms, according to SCMP. Magnetic fields cause shifts in the atoms’ energy levels, generating seven distinct microwave resonance signals. By measuring these resonances, the device can infer the strength and direction of a magnetic field, without depending on the sensor’s physical orientation.

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The researchers connected the CPT magnetometer to a rotor drone using a 20-meter cable to reduce electromagnetic interference. Additional instruments, including a fluxgate magnetometer for heading corrections and GPS-linked ground stations, processed the raw data to remove noise and account for daily variations in Earth’s magnetic field.

OFFSHORE TRIALS
In offshore trials near Weihai, Shandong province, the system surveyed a 400-meter by 300-meter grid, according to SCMP. Raw measurements showed a magnetic anomaly detection accuracy of 2.517 nanotesla (nT), which improved to 0.849 nT after correction. Two independent surveys of the same area produced results with a 99.8 percent correlation, with a root mean square error of just 1.149 nT.

The researchers described the outcome as evidence of the system’s real-world stability. In simpler terms, the system could detect incredibly tiny changes in Earth’s magnetic field — roughly a billion times smaller than the strength of a typical refrigerator magnet. After correcting for noise and other small errors, the measurements were highly consistent across multiple test runs, suggesting that the sensor could reliably spot even faint magnetic clues left by objects.

In the case of locating submarines, these underwater vehicles are made of metal and carry powerful engines, both of which slightly disturb Earth’s natural magnetic field as they move underwater. The quantum sensor looks for these tiny disturbances — invisible to the eye but detectable as small magnetic “ripples” — and maps them out. By spotting unusual magnetic patterns that don’t match the surrounding environment, the system can reveal the presence of a hidden submarine, even if it is deep below the surface.

Based on what is known about similar magnetic detection systems, the drone would likely need to pass within several hundred meters to about a kilometer of a submarine to reliably detect it, depending on the size of the vessel, its depth and local magnetic noise.

MATCHES NATO SYSTEM PERFORMANCE
The CPT-based design matches the sensitivity of the sophisticated MAD-XR system used by NATO allies but operates at significantly lower cost and complexity. Unlike MAD-XR, which uses multiple probes to avoid blind spots, the Chinese sensor achieves full directional coverage with a single unit. This could make it more feasible for broad deployment in contested or resource-rich waters at low latitudes.

The researchers also noted that the sensor’s precision could support civilian applications, including mapping oil fields, locating shipwrecks, and studying tectonic activity beneath the seafloor.

LIMITATIONS
Despite the promising test results, the research team acknowledged that the system is not yet operationally ready. Offshore trials were conducted under relatively stable and controlled conditions, far from the harsher, noisy environments typical of real-world military operations.

By contrast, the MAD-XR system has been validated through years of operational use by the United States, Japan and allied forces, offering a significant advantage in battle-tested reliability.

The Chinese system’s ability to maintain precision while facing factors such as ocean currents, drone movement instability, and electromagnetic clutter from ships or coastal activity remains unproven based on the available trial data.

Additionally, although the sensor achieved picotesla sensitivity, other technologies such as Spin-Exchange Relaxation-Free (SERF) magnetometers promise even greater sensitivity at femtotesla levels, albeit with their own engineering challenges.

FUTURE RESEARCH DIRECTIONS
There are likely several key areas for future development.

First, additional testing under operationally realistic conditions—including rough seas, mobile targets, and high background noise—is required to verify the system’s reliability in combat environments.

Further miniaturization and ruggedization of the CPT sensor system may also be necessary to allow easier deployment across a wider range of aerial and maritime platforms. It’s likely that integrating the drone-mounted system with broader surveillance networks, including sonar and satellite tracking, would enhance detection capabilities and operational flexibility.

The team suggested the possibility of developing enhanced CPT sensors capable of higher sensitivity, potentially by incorporating emerging atomic magnetometer technologies or more advanced noise-cancellation algorithms.

Because the journal was not — easily — found online, the specifications of the device was taken from The South China Morning Post article.