Ipsa Tripathy
Bhubaneswar: Earth is surrounded by a magnetic field generated primarily by the movement of electrically conducting molten iron in its outer core. This field is relatively weak at the surface, yet it contains valuable information about the planet, its geology and even the environment around it. Measuring such fields accurately requires sensitive magnetometers, and quantum sensors are emerging as one of the most precise technologies for magnetic-field measurement.
Quantum magnetometry is not based on a single technology. It includes atomic magnetometers, nitrogen-vacancy (NV) centres in diamond, superconducting sensors and other quantum systems. Each has different strengths and limitations. The important question is therefore not simply whether quantum sensors can detect Earth’s magnetic field or they can but how precisely, compactly and reliably they can measure it for different applications.
What Makes a Quantum Sensor Different?
Conventional magnetic sensors measure magnetic fields through effects such as changes in electrical resistance or mechanical motion. Quantum sensors instead exploit precisely controlled quantum properties of atoms, electrons or other systems.
One important property is quantum spin. Particles such as electrons possess intrinsic angular momentum associated with spin, and their magnetic moments respond to external magnetic fields. Measuring changes in their quantum states can therefore provide information about the field being measured. This is particularly useful because quantum energy levels can be measured with very high precision. A small change in a magnetic field can produce a measurable change in the quantum state of the sensing system.
Atomic Magnetometers
One established form of quantum magnetometer uses a vapour of atoms, commonly rubidium or caesium. In an atomic magnetometer, laser light prepares the spins of atoms in a particular orientation. When the atoms are exposed to an external magnetic field, their spins respond to that field. The resulting change can be detected optically and used to determine the magnetic-field strength.
Atomic magnetometers have been developed for decades and can achieve extremely high sensitivity. Modern devices can detect magnetic fields below one-billionth of the field produced by a typical refrigerator magnet, according to the U.S. National Institute of Standards and Technology (NIST). Some atomic magnetometers have demonstrated sensitivities approaching those of superconducting quantum sensors under suitable conditions. Their ability to operate near room temperature is an important practical advantage over superconducting sensors that require cryogenic cooling.
The Nitrogen-Vacancy Diamond Sensor
Another important quantum technology uses tiny defects inside diamond called nitrogen-vacancy (NV) centres. An NV centre consists of a nitrogen atom replacing a carbon atom in the diamond lattice, next to a missing carbon atom. The electron spin associated with the defect has quantum energy levels that respond to an external magnetic field. Scientists can illuminate the diamond with green light and observe red fluorescence from the NV centres. Microwave radiation is then used to manipulate the quantum states. The microwave frequency at which the spin state changes depends on the magnetic field, allowing the field to be measured. This technique has an important advantage: NV centres can operate under a broad range of temperatures and pressures, including ordinary room-temperature conditions. Diamond is also mechanically robust, allowing sensors to be made small and durable.
Can They Measure Earth’s Magnetic Field?
Yes. Quantum magnetometers can measure Earth’s magnetic field, including its strength and, in some systems, its direction. However, greater sensitivity does not automatically mean that one quantum sensor is better for every application.
For example, atomic magnetometers and SQUIDs remain highly sensitive choices for detecting extremely weak magnetic signals. NV-centre sensors currently do not generally match the ultimate sensitivity of the best atomic and superconducting magnetometers. Their strength lies elsewhere: they can offer compactness, robustness, directional information and very high spatial resolution. This distinction is important when discussing the future of quantum sensing.
Why Earth’s Magnetic Field Is Scientifically Useful
Earth’s magnetic field is not perfectly uniform. Small variations occur because of differences in the magnetic properties of rocks and geological structures. These variations create a magnetic map of Earth’s crust. Highly sensitive magnetometers can detect these variations and use them for geological investigations.
Quantum magnetometers could therefore help researchers study:
- Magnetic minerals in rocks
- Geological structures
- Subsurface features
- Changes in Earth’s magnetic environment
NIST is also investigating NV-centre magnetometers for navigation without dependence on GPS. An aircraft or drone could measure variations in Earth’s crustal magnetic field and compare them with existing magnetic maps to estimate its position and direction.
GPS depends on signals received from satellites and can be disrupted by interference or deliberate jamming. Magnetic navigation works differently. A magnetometer measures naturally occurring variations in Earth’s magnetic field and compares them with a reference magnetic map. NV-centre magnetometers are being investigated for this purpose because they can measure both the strength and direction of a magnetic field. Their compact size and robustness could make them suitable for aircraft, drones and other mobile platforms. However, this remains a developing technology rather than a universal replacement for GPS.
What Could Happen in the Future?
One major research direction is miniaturisation. Researchers are working toward quantum sensors that are smaller, more robust and easier to integrate into electronic systems. Another is the development of arrays of quantum sensors. Instead of measuring the magnetic field at a single point, an array could measure spatial variations simultaneously. Recent research has demonstrated photonic-integrated NV-centre sensor arrays for microscale magnetic localisation, showing the continuing movement toward integrated quantum sensing systems.
Researchers are also investigating improved control of multiple quantum systems. A 2025 Nature study demonstrated multi-qubit nanoscale sensing using NV centres, including approaches in which entanglement can be used as a sensing resource. Such developments could eventually contribute to improved measurement capabilities, although they should not be interpreted as an immediate improvement to Earth’s large-scale magnetic-field mapping.
Beyond Navigation
The same quantum-sensing technologies have applications far beyond Earth’s magnetic field. Atomic magnetometers can measure extremely weak magnetic signals produced by biological activity, including electrical activity in the brain and heart. NV-centre sensors can measure magnetic fields with very high spatial resolution, including fields produced by microscopic systems. This demonstrates the broader value of quantum magnetometry: the same physical principles can be used to study phenomena ranging from Earth’s crust to individual cells and microscopic materials.
Quantum sensors are not perfect. Their performance can be affected by temperature, environmental magnetic noise, sensor imperfections and the stability of the quantum state. Different technologies also have different requirements. Some atomic systems require lasers and carefully controlled environments, while NV-centre systems require optical and microwave control. Achieving laboratory-level sensitivity in a small, inexpensive and field-ready instrument remains an engineering challenge.
Therefore, the future is unlikely to involve a single universal quantum magnetometer. Instead, different quantum technologies will probably find applications where their particular combination of sensitivity, spatial resolution, operating temperature, size and robustness provides an advantage.
The Future of Magnetic Measurement
Quantum sensors have already demonstrated that quantum properties can be used to measure extraordinarily small magnetic fields. Atomic magnetometers provide exceptional sensitivity, while NV-centre diamond sensors offer a combination of compactness, robustness and high spatial resolution.
For Earth’s magnetic field, their future importance could extend from geological mapping and scientific observation to GPS-independent navigation and environmental sensing. The technology is still developing, but the underlying principle is established: the behaviour of quantum systems can be used as an extremely precise ruler for measuring magnetic fields. The remaining challenge is to transform that precision into instruments that are practical, affordable and reliable outside the laboratory.