Quantum VenTuring
Home · Brief

Quantum sensing: diamond NV to cold atoms

What actually sets sensitivity and dynamic range? A field-ready way to think about specs — with examples that aren’t just abstract.

Where it shows up

Non-destructive PCB/IC testing

NV magnetometry images current paths to find shorts & opens without probes.

Underground mapping

Cold-atom gravimeters locate voids/tunnels for civil engineering and geology.

GPS-denied navigation (MagNav)

Airborne magnetometers track Earth-field gradients to aid navigation; requires high sample rates with good sensitivity.

Decode the spec sheet

  • Sensitivity (η) in T/√Hz — Sometimes referred to as noise density, the sensor’s noise floor per √bandwidth. A lower sensitivity is what everyone wants.
  • Bandwidth (BW) The range of frequencies of the magnetic field that can be detected. Application specific.
  • Coherence (T2*) How long the sensor can maintain its coherence-enhanced magnetic sensitivity. A higher coherence time lowers sensitivity
  • Dynamic range The range in the strength of the magnetic field that can be detected. Application specific.

SNR vs time (play with it)

SNR(T): — (linear)
SNR(T): — dB
Bmin(T,BW) = —

Model: for white noise, SNR grows as SNR ≈ (Signal/η) · √(T/BW). Here η is noise density in T/√Hz, BW is measurement bandwidth (Hz), and T is your averaging/integration time (s). The minimum detectable field at SNR≈1 is Bmin(T,BW) = η · √(BW/T).

Sensitivity 101: why T/√Hz matters (and MagNav)

T/√Hz is a convenient way to quote a sensor’s fundamental noise, and thus sensitivity. If you average for time T, white noise falls as 1/√T. If you need higher sample rate (larger BW), noise rises as √BW. That's why a longer measurement time results in the ability to detect smaller magnetic fields. An application that requires a high sampling rate will increase the minimum detectable magnetic field (1×√(10/1)), but only ~1 nT at 100 Hz BW — and much worse at 1 kHz.

MagNav implication: an aircraft moving quickly needs ≥100–1000 samples/s to resolve geologic/urban gradients without aliasing. This high requirement for the sampling rate often requires non-sequential vector readout. Practically: pick a magnetometer with the lowest η you can afford and validate Bmin(T,BW) at the mission’s sample rate to ensure you can detect the target signal.

What to measure in a pilot

  • In-field noise density vs temperature and vibration
  • Calibration drift over hours; re-zero procedure and time
  • Packaging and alignment stability (optics, vacuum)