4 ms·

Smells like absolute BS to me.

alsaaro 6mo ago
Same. But perhaps the underlying technology is a superconducting SQUID. The ability to detect a heartbeat from distance is far fetched though.
- kuhsaft 6mo ago
  So is cm resolution with satellite imagery, but the NRO does have those capabilities.
  - quietsegfault 6mo ago
    The photons arriving at the satellite from a ground target aren’t getting weaker due to distance in any way that defeats you, because the sun is illuminating the target and the NRO just needs to collect enough of the reflected photons. SQUID sensors (the most sensitive magnetometers that exist) require magnetically shielded rooms to record cardiac signals at centimeter range.
    - kuhsaft 6mo ago
      They require a shielded room to increase the SNR. SQUID sensors are sensitive enough to record cardiac signals at distance. The issue is SNR. What they are saying is that they produced a low noise sensor array and managed to increase the SNR through computation. They also stated that it was an ideal environment with no other electrical/magnetic interference.
      - xavieralexandre 6mo ago
        > They require a shielded room to increase the SNR. Not anymore. That is exactly the purpose of Darpa Ambient program: https://www.darpa.mil/research/programs/atomic-magnetometer-for-biological-imaging-in-earths-native-terrain https://www.darpa.mil/research/programs/atomic-magnetometer-... Demo from 2022: https://www.youtube.com/watch?v=VTnIXWCBYTw https://www.youtube.com/watch?v=VTnIXWCBYTw
        quietsegfault 6mo ago
        AMBIIENT’s goal was biological imaging.. sensors near a body for medical/neuroscience applications. The range being discussed is still on the order of meters at best, not miles.
        kuhsaft 6mo ago
        > AMBIIENT’s goal was biological imaging.. sensors near a body for medical/neuroscience applications. As with all DARPA projects, there is a civilian use-case and a military use-case. That demo was at a conference, in a city, surrounded by electronics and RF noise. The fact that it worked at all in that environment is surprising. As the subject got closer to the apparatus, the signal became larger than the background noise. So, I think the distance is limited mostly by background noise. The press release did state that it was an optimal environment for locating their target, i.e., an isolated person with only geomagnetic noise and known signatures of the aircraft.
        quietsegfault 6mo ago
        If background noise was the factor, which it's not, but if it was, the background noise to combat would be the thermal noise floor of any physical conductor at any temperature above absolute zero. But that's not the factor. You're assuming the cardiac field is like a radio signal being transmitted rather than a local field effect. A magnetic dipole doesn't radiate energy outward the way a radio antenna does. It creates a static field that exists in the space around it, and that field geometrically collapses with distance. I ran the numbers on Wolfram Alpha, and at 1 meter from your chest the field is around 100 femtotesla. At 10 meters it's around 100 attotesla. At 5 kilometers it's around 10^-27 tesla. Oh, but you say that you simply cool the sensor to 0K. Cooling helps, but you're still many orders of magnitude short even at near 0K, and you're doing this in Iranian mountains, not a dilution refrigerator.
        kuhsaft 6mo ago
        You’re calculating based on classical mechanics. The sensors are optical-atomic magnetometers, using quantum mechanics to measure magnetic vector potentials (MVP), which behave differently and can produce seemingly non-local effects (Aharonov–Bohm effect). > A magnetic dipole doesn't radiate energy outward the way a radio antenna does. See Section 15-5 of https://www.feynmanlectures.caltech.edu/II_15.html#Ch15-S5 https://www.feynmanlectures.caltech.edu/II_15.html#Ch15-S5 Veritasium has a video on the weirdness of MVP: https://m.youtube.com/watch?v=XKSjCOKDtpk https://m.youtube.com/watch?v=XKSjCOKDtpk See https://pubs.aip.org/aip/adv/article/13/2/025127/2877320/Differential-behavior-of-magnetic-field-and https://pubs.aip.org/aip/adv/article/13/2/025127/2877320/Dif... for an experiment measuring MVP with an optical-atomic magnetometer. > Oh, but you say that you simply cool the sensor to 0K. These sensors do not require cryogenics and have been developed with sensitivities of 10s of fT/√Hz, so approaching the quantum noise limit. Essentially, you can think of it as measuring the energy of a magnetic dipole in space instead of measuring a magnetic field.
- r58lf 6mo ago
  It's not a SQUID. There is new technology (quantum magnetometry) that measures slight shifts in molecular energy levels inside defects in synthetic diamonds. One of the google/alphabet spinouts from their quantum computing research is commercializing the technology (SandboxAQ). The have a non contact MCG, like a EKG, but no electrical contacts. They can definitely "see" the heart beating from a few feet away. SandboxAQ is also developing a navigation version. Put this sensitive magnetometer on a plane. You get very sensitive measurements of the local magnetic field. Once they have a region mapped, you can get exact positioning just from measuring magnetic fields. You can extrapolate from SandboxAQ and get long range detection of a human heart. I don't know if it's real, but if so it's probably came out of that research effort.
  - kuhsaft 6mo ago
    You are correct, it is not based on SQUID. But, I think SQUID is technically a class of quantum magnetometer? Quantum magnetometry is pretty vague, since most high-end magnetometers use some sort of quantum mechanics. I think the term you're looking for is atomic-optical magnetometer. Someone posted a DARPA project (AMBIIENT), that uses one. What's special about the atomic-optical magnetometer, is that it measures the gradient directly. With SQUID, if you have two SQUIDs in a uniform magnetic field, you can't determine the vector of the field. But, with atomic-optical magnetometry you can.

Same. But perhaps the underlying technology is a superconducting SQUID. The ability to detect a heartbeat from distance is far fetched though.

kuhsaft 6mo ago
So is cm resolution with satellite imagery, but the NRO does have those capabilities.
- quietsegfault 6mo ago
  The photons arriving at the satellite from a ground target aren’t getting weaker due to distance in any way that defeats you, because the sun is illuminating the target and the NRO just needs to collect enough of the reflected photons. SQUID sensors (the most sensitive magnetometers that exist) require magnetically shielded rooms to record cardiac signals at centimeter range.
  - kuhsaft 6mo ago
    They require a shielded room to increase the SNR. SQUID sensors are sensitive enough to record cardiac signals at distance. The issue is SNR. What they are saying is that they produced a low noise sensor array and managed to increase the SNR through computation. They also stated that it was an ideal environment with no other electrical/magnetic interference.
    - xavieralexandre 6mo ago
      > They require a shielded room to increase the SNR. Not anymore. That is exactly the purpose of Darpa Ambient program: https://www.darpa.mil/research/programs/atomic-magnetometer-for-biological-imaging-in-earths-native-terrain https://www.darpa.mil/research/programs/atomic-magnetometer-... Demo from 2022: https://www.youtube.com/watch?v=VTnIXWCBYTw https://www.youtube.com/watch?v=VTnIXWCBYTw
      - quietsegfault 6mo ago
        AMBIIENT’s goal was biological imaging.. sensors near a body for medical/neuroscience applications. The range being discussed is still on the order of meters at best, not miles.
        kuhsaft 6mo ago
        > AMBIIENT’s goal was biological imaging.. sensors near a body for medical/neuroscience applications. As with all DARPA projects, there is a civilian use-case and a military use-case. That demo was at a conference, in a city, surrounded by electronics and RF noise. The fact that it worked at all in that environment is surprising. As the subject got closer to the apparatus, the signal became larger than the background noise. So, I think the distance is limited mostly by background noise. The press release did state that it was an optimal environment for locating their target, i.e., an isolated person with only geomagnetic noise and known signatures of the aircraft.
        quietsegfault 6mo ago
        If background noise was the factor, which it's not, but if it was, the background noise to combat would be the thermal noise floor of any physical conductor at any temperature above absolute zero. But that's not the factor. You're assuming the cardiac field is like a radio signal being transmitted rather than a local field effect. A magnetic dipole doesn't radiate energy outward the way a radio antenna does. It creates a static field that exists in the space around it, and that field geometrically collapses with distance. I ran the numbers on Wolfram Alpha, and at 1 meter from your chest the field is around 100 femtotesla. At 10 meters it's around 100 attotesla. At 5 kilometers it's around 10^-27 tesla. Oh, but you say that you simply cool the sensor to 0K. Cooling helps, but you're still many orders of magnitude short even at near 0K, and you're doing this in Iranian mountains, not a dilution refrigerator.
        kuhsaft 6mo ago
        You’re calculating based on classical mechanics. The sensors are optical-atomic magnetometers, using quantum mechanics to measure magnetic vector potentials (MVP), which behave differently and can produce seemingly non-local effects (Aharonov–Bohm effect). > A magnetic dipole doesn't radiate energy outward the way a radio antenna does. See Section 15-5 of https://www.feynmanlectures.caltech.edu/II_15.html#Ch15-S5 https://www.feynmanlectures.caltech.edu/II_15.html#Ch15-S5 Veritasium has a video on the weirdness of MVP: https://m.youtube.com/watch?v=XKSjCOKDtpk https://m.youtube.com/watch?v=XKSjCOKDtpk See https://pubs.aip.org/aip/adv/article/13/2/025127/2877320/Differential-behavior-of-magnetic-field-and https://pubs.aip.org/aip/adv/article/13/2/025127/2877320/Dif... for an experiment measuring MVP with an optical-atomic magnetometer. > Oh, but you say that you simply cool the sensor to 0K. These sensors do not require cryogenics and have been developed with sensitivities of 10s of fT/√Hz, so approaching the quantum noise limit. Essentially, you can think of it as measuring the energy of a magnetic dipole in space instead of measuring a magnetic field.
r58lf 6mo ago
It's not a SQUID. There is new technology (quantum magnetometry) that measures slight shifts in molecular energy levels inside defects in synthetic diamonds. One of the google/alphabet spinouts from their quantum computing research is commercializing the technology (SandboxAQ). The have a non contact MCG, like a EKG, but no electrical contacts. They can definitely "see" the heart beating from a few feet away. SandboxAQ is also developing a navigation version. Put this sensitive magnetometer on a plane. You get very sensitive measurements of the local magnetic field. Once they have a region mapped, you can get exact positioning just from measuring magnetic fields. You can extrapolate from SandboxAQ and get long range detection of a human heart. I don't know if it's real, but if so it's probably came out of that research effort.
- kuhsaft 6mo ago
  You are correct, it is not based on SQUID. But, I think SQUID is technically a class of quantum magnetometer? Quantum magnetometry is pretty vague, since most high-end magnetometers use some sort of quantum mechanics. I think the term you're looking for is atomic-optical magnetometer. Someone posted a DARPA project (AMBIIENT), that uses one. What's special about the atomic-optical magnetometer, is that it measures the gradient directly. With SQUID, if you have two SQUIDs in a uniform magnetic field, you can't determine the vector of the field. But, with atomic-optical magnetometry you can.