Atomic magnetometers are the most precise magnetometers to date and are often used in applications ranging from medical to military uses. The use of atomic magnetometers is often limited in resolution when measuring low frequency signals due to short coherence time (mSec time scale). We have devised a magnetic field sensing method with long coherence time for static and time-dependent magnetic fields that enables high-sensitivity magnetometery.
The detection of magnetic signals at frequencies below 10Hz (Extremely Low Frequencies – ELF) is often limited in resolution and cannot be done by conventional atomic magnetometers. This is because the coherence time of magnetic sensitive atomic transitions is typically limited to the mSec times scale and therefore limits atomic detection to signals that vary fast as compared with the inverse of this time. Commercial magnetic detection at these frequencies relies on non-atomic devices such as SQUID (superconducting quantum interference devices), pick-up coils, Hall-effect sensors of flux gate sensors which are inferior to atomic magnetometers.
The group of Prof. Roee Ozeri developed a novel magnetometer based on an atomic transitions insensitive to magnetic field strength.
Atomic clock transitions have long coherence time (well above 1 msec) since they are, to first order, magnetic field insensitive. Prof. Roee Ozeri and his team invented a method to use these magnetic field insensitive transitions for the purpose of magnetic field detection resulting in improved sensitivity over conventional Zeeman-based atomic magnetometry, where coherency is restricted by sensitivity to magnetic fields. Instead of measuring magnetic fields strength in the direction of the quantization axis, as in Zeeman magnetometry, magnetic field strength is measured substantially orthogonal to the quantization axis, via determining the angular displacement of the quantization axis by the magnetic signal field, which is detected by changes in atomic state population as the quantization axis is rotated relative to the excitation polarization.
- Magnetoencephalography (MEG).
- Biological systems - detection of low frequency magnetic activity.
- ELF submarine communication systems.
- Atmospheric and climate sciences – Schumann resonance detection.
- Safety detection of magnetic fields emanating from electronic instruments and power grid.
- Enables higher accuracy of magnetic field measurements.
- Detects ELF magnetic field variations.
- Provides measurement and spectral analysis of time varying magnetic fields.
The team demonstrated magnetic field sensing method that is sensitive to signals perpendicular to the quantization field. They showed that atomic clock states, with an energy separation that is independent of the magnetic field, can nevertheless acquire a magnetic-field-dependent population difference and phase difference that appear due to a rotation of the magnetic field. This was experimentally demonstrated on an ensemble of optically trapped 87Rb atoms.
Magnetometry is an important tool prevalent in many applications such as material characterization, geological surveys, and biological imaging. The development of atomic magnetometer with increased coherence time will enable higher sensitivity for magnetometric devices in many industries.