Physics / mechanism
Cold-atom interferometry exploits matter-wave phase shifts induced by gravitational acceleration. Atoms (typically Rb-87 or Cs-133) are laser-cooled to µK, launched in free-fall, and interrogated with three Raman or Bragg pulses in a Mach-Zehnder geometry. Phase shift Δφ = k_eff · g · T² encodes local gravity; longer interrogation time T and larger effective wavevector k_eff drive sensitivity. State-of-art lab systems reach <1 µGal (10⁻⁸ m/s²); fieldable units (AOSense, Muquans, Q-NEXT spinouts) are at ~10 µGal. Key engineering constraints: vibration isolation, magnetic shielding, laser coherence length, and vacuum lifetime. MEMS gravimeters (Scintrex, Sercel) hold the ruggedized baseline at ~5 µGal but lack the drift-free absolute accuracy cold-atom devices offer.
Competitive landscape
Classical gravimetry: MEMS/spring-mass (Scintrex CG-6, iGrav SG) and superconducting gravimeters dominate deployed installations. Superconducting devices hit <0.1 µGal but require LHe, ruling out field use. Gravity gradiometry (full-tensor, e.g. ARKeX/Lumens) extracts gradient tensor for sharper subsurface contrast. GNSS-derived gravity is coarse (~mGal). Optical clocks offer an orthogonal relativistic gravimetry path (redshift = Δg·h/c²) at comparable sensitivity but with entirely different infrastructure requirements.
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.