From Quantum Tunnelling to Quantum Sensors: Can Quantum Physics Detect the Almost Undetectable?

The human heart produces electrical activity, but it also generates an extremely weak magnetic field.

Measuring that field is difficult. Detecting it from a considerable distance is even harder.

Yet scientists have developed quantum technologies capable of measuring incredibly small magnetic fields. Some rely on superconducting circuits, while others use specially engineered defects inside diamonds.

These technologies demonstrate how quantum mechanics can help us observe signals that conventional instruments may struggle to detect.

1. From quantum tunnelling to superconductivity

Quantum tunnelling allows a particle to have a non-zero probability of crossing an energy barrier that classical physics says it cannot overcome.

One important application involves Josephson junctions.

A superconductor is a material that, below its critical temperature, can carry electrical current without ordinary electrical resistance. In conventional superconductors, electrons form correlated pairs called Cooper pairs.

Now place two superconductors close together, separated by a very thin insulating barrier.

Although classical physics predicts that the insulator should block the current, Cooper pairs can tunnel through it. This is known as the Josephson effect, predicted by physicist Brian Josephson in 1962.

The discovery became important for superconducting electronics and extremely sensitive magnetic sensors.

2. SQUIDs: detecting tiny magnetic fields

One device built around the Josephson effect is the Superconducting Quantum Interference Device, or SQUID.

A SQUID contains a superconducting loop interrupted by Josephson junctions. When magnetic flux passes through the loop, it changes the quantum phase relationships within the circuit.

This affects the device's electrical response, allowing scientists to measure extremely small changes in magnetic flux.

 

 

 

SQUID magnetometers are used in research and biomedical applications, including:

• Magnetocardiography: measuring magnetic fields associated with the heart's electrical activity.
• Magnetoencephalography: measuring magnetic fields associated with brain activity.

Unlike ECG and EEG, which measure electrical potentials, these techniques measure magnetic fields.

SQUIDs are highly sensitive, but many require cryogenic cooling to maintain superconductivity. Researchers have therefore explored other quantum sensing technologies.

3. Why are scientists using diamonds?

Diamonds contain a useful type of atomic-scale defect called a nitrogen-vacancy (NV) centre.

It forms when a nitrogen atom replaces a carbon atom in the diamond crystal, next to a missing carbon atom.

This defect has electronic spin states that respond to external magnetic fields.

Scientists illuminate the diamond with green light and use microwave radiation to manipulate these spin states. A magnetic field changes the energy separation between certain states through an effect known as Zeeman splitting.

By measuring the resulting changes in the system's response, researchers can estimate the magnetic field.

One particularly interesting feature is that NV-centre sensors can operate at room temperature, depending on their design and measurement method.

This makes them promising tools for studying materials, magnetic devices and biological systems.

A tiny imperfection in a diamond can become an extremely sensitive scientific instrument.

4. Can quantum sensors detect a heartbeat?

The heart produces magnetic signals associated with its electrical activity. Sensitive instruments can measure these signals under suitable conditions.

Quantum magnetometers are among the technologies researchers investigate for biomedical sensing.

However, there is an important distinction: detecting a signal close to its source is very different from detecting it from kilometres away.

As distance increases, the magnetic signal becomes much weaker. Background interference from natural and human-made sources also complicates measurements.

A sensitive magnetometer does not automatically become a long-range detector.

5. The mysterious Ghost Murmur story

In 2026, reports circulated about a technology called Ghost Murmur, allegedly used to help locate a missing American airman in Iran.

The story suggested that the technology could detect the magnetic signal associated with a human heartbeat, with quantum magnetometry and artificial intelligence playing important roles.

It sounds extraordinary, but the claim requires careful examination.

Quantum magnetometers are real. Magnetic signals associated with the heart are real. AI can help analyse complex measurements.

However, the reported long-distance heartbeat-detection capability attracted scepticism from researchers. Detecting such a weak signal over a large distance would face serious physical and technical challenges.

Public reporting about the rescue does not independently establish that a quantum heartbeat detector was responsible.

Without independently verifiable technical evidence, the claimed capability should be treated as unconfirmed.

The real science is impressive enough without exaggerating what these instruments can do.

6. Can artificial intelligence improve quantum sensing?

AI can help researchers process complex sensor data, identify patterns, calibrate instruments and reduce certain types of measurement noise.

For example, machine-learning methods are being investigated to improve the readout of NV-centre magnetometers.

But AI has limitations.

It cannot guarantee that an extremely weak signal will be recovered if the sensor has not captured enough information. It can also mistake background patterns for genuine signals.

AI can improve data analysis, but it cannot simply remove the physical limitations imposed by distance, signal strength and interference.

 

7. What makes quantum sensing important?

Quantum sensing turns unusual quantum properties into practical scientific instruments.

Josephson junctions demonstrate how tunnelling can influence superconducting circuits. SQUIDs use quantum interference to detect tiny magnetic changes. Diamond NV centres use electron spin states to measure magnetic fields, even at room temperature.

These technologies are already valuable in physics, engineering and biomedical research.

The lesson is not that quantum technology can detect anything from anywhere. It is that carefully controlled quantum systems can help us measure things that are otherwise extremely difficult to observe.

The same quantum mechanics that explains particles crossing energy barriers is now helping scientists investigate the smallest magnetic signals in materials and living systems.

That is a remarkable connection between fundamental physics and real-world technology.

References

1. Nobel Prize – Brian D. Josephson
2. NIST – Diamond NV Centre Magnetometry
3. Casola et al. (2018) – Probing Condensed Matter Physics with Magnetometry Based on Nitrogen-Vacancy Centres in Diamond, Nature Reviews Materials.
4. Quantum-Based Magnetic Field Sensors for Biosensing (2023), Advanced Quantum Technologies.
5. Scientific American – What Is the Quantum 'Ghost Murmur' Purportedly Used in Iran?, April 2026.