Did a quantum sensor really find a missing pilot?

Why the physics and engineering challenges should make you deeply sceptical...

Image generated by ChatGPT

Quantum sensing is an interesting technology that could enable some interesting and commercially viable use cases. Recently, there have been stories in the media about the US government having a capability called “Ghost Murmur”. This is apparently some sort of quantum magnetic sensor, being used to locate and rescue a pilot who had come down in Iran, by being able to detect his heartbeat at a distance. How realistic is this?

What have we been told?

Comments were made by President Trump and John Ratcliffe (CIA Director) in a press conference after rescuing an American pilot who had been downed over Iran. They talked vaguely of classified CIA technology that enabled them to find the pilot, with Trump talking of an initial detection from 40 miles away. The New York Post subsequently claimed it had been told by a source that this was done using a quantum magnetic sensor to detect the pilot’s heartbeat. The sensor, called “Ghost Murmur” had apparently been developed by a group called “Skunk Works”. Its astonishing capabilities were also apparently powered by some sort of AI-based signal processing.

How realistic is this?

In order for this to work in practice, three key factors to consider are the intrinsic sensitivity of the sensor, being able to package up to the system to be used where it is required, and whether it will be affected by environmental noise in practical situations. Let’s consider each of these in turn.

Sensitivity

Quantum sensors have been shown to be able to detect the magnetic field from a human heartbeat. This has been suggested for medical applications, where the main advantage may be that it can do this detection in a non-contact manner. However, the latest published research from Harvard seems to show the sensor has to be very close to the patient - of order a few centimetres in a recent paper. Let’s make a generous assumption that this could be stretched to work at maybe up to a metre’s distance with tweaking and tuning.

The problem with extrapolating to further distance is that the magnetic field from something like a heartbeat falls off as the cube of the distance. This means that if we go 10 times further away, the signal we are trying to detect is 1000 times weaker. This means that going from a 1m detection range to a 40 mile detection range means being able to detect a signal that is about 100 trillion times weaker. Even if we ignored the “40 mile range” claim, to be useful for a search and rescue mission when you’re not close enough to detect a beacon, or use thermal imaging or other techniques, it probably still needs to work at around 1km distance. This means the sensor needs to be a mere billion times more sensitive than a generous interpretation of the typical state of the art in scientific publications.

That’s not just some incremental classified “Skunk Works” improvements, or even a single innovative change - that would need to be completely different science.

Deploying to the field

One of the biggest challenges of quantum sensors today is how to move them from a lab setup, with various pieces of equipment set up on a bench in a well controlled, stable environment. Being able to deploy them for practical applications means building an integrated system that contains all the components you need to go from the sensor to a useful output, in this case for those conducting the search and rescue mission. In this case, the system would need to be completely self contained and portable. For this sort of mission, you might need to make sure you can fit everything into a backpack, but more likely it would need to be something that can work on a plane or the back of a truck. Making the system work in places like that, overcoming challenges of vibration, dust, temperature variations etc would be a challenge, but maybe this is what something like Skunkworks can do. However doing so, while still maintaining a billion-fold improvement in sensitivity would probably require further miraculous inventions.

Environmental noise limitations

Even if you could make a sensor a billion times more sensitive, and make it work in the back of truck, any mission still comes up against the problem of environmental noise - if the change you are trying to detect is smaller than other random changes in the same place you are sensing, you’ll never succeed. To use an analogy I’ve used before, imagine you are in a busy multi-storey office building, and have a microphone guaranteed to pick up anyone talking anywhere in the building. However, unless you are using it late at night, you are very unlikely to hear someone in a far away office, because at any one time it’s likely many other people are talking as well.

In this case, the New York Post story claims:

It was “about as clean an environment as you could ask for” because of low electromagnetic interference, “almost no competing human signatures…”

However, we have to wonder - for example what about animals in the same area? Remember the challenges of how the signal falls off with this distance - something else that is 500m away would have a signal that is almost 10 times bigger, swamping that from something a kilometre away.

Maybe with some clever signal processing you could distinguish a human heartbeat from the background, but that would probably require measuring over a long time period. Elsewhere in the article it says the airman was only found because he came out of a crevice for a quick moment to send a radio beacon signal.

In conclusion

To be able to effectively detect a human heartbeat for a search and rescue mission would require a sensor that is at least a billion, maybe a trillion times more sensitive than publicly known technology, able to be packaged up and used in a military environment, and a very fortuitous environment with no other noise sources.

It seems highly unlikely that this is what happened. More likely, the other techniques the article mentions - a radio beacon and thermal imaging were decisive. Maybe someone was field-trialling a quantum sensor, maybe when up close there was small flicker that correlated with a thermal image detection, but I’d be very surprised if it played any decisive part in the mission.

Whether this was misinformation, disinformation, or some over-enthusiastic marketing, I’ll leave others to speculate.

If you remember nothing else

Quantum sensors aren’t miracles that make the world transparent and observable by anyone, anywhere. “Quantum advantage” in sensing will probably be for specific niche use cases, where one or more of the specific differences that a quantum sensor provides are critical.

And when you read quantum stories in the media, apply a sceptical angle - for example, has any scientist been consulted as part of the story? Understanding a complex topic like quantum technology requires deep technical expertise in order to explain it and use it properly!

MDR Quantum provides consulting services to help organisations prepare for the risks and opportunities of quantum technology. We can provide executive briefings, market surveys, strategy development, assistance in selecting and evaluating solutions, and support delivery of pilot projects. Please get in touch if you’re interested in working with us.