On perspectives of INTERMAGNET observatories usage for fundamental research in spin-gravitational interactions and cosmology.
V. Sapunov 1, J. Rasson 2, A. Denisov 1, D. Saveliev 1, E. Narkhov 1, B. Rubinstein 3
Quantum magnetometry laboratory of Ural federal university, Mira str. 21, Ekaterinburg, Russia Institut Royal Mуtуorologique Centre de Physique du Globe Rue du Centre de Physique, Belgium Stowers Institute for Medical Research, 1000 East 50th St., Kansas City, MO 64110, USA
The recent LIGO project successful proof of the basic statements of Einstein theory on existence of the gravitational waves was a major motive of this proposal. Similar to magnetic field that appears to be a consequence of the electrical field relativistic transformation under condition of speed of light invariance, experimental proof of the gravitational waves leads to a conclusion of existence of the quasi-magnetic gravitational field initiated by accelerated motion of masses . The extremely high cost of the developed network of the LIGO laser detectors naturally leads to increased attention to alternatives methods for gravitational waves detection based on high precision nuclear magnetometers and theoretically predicted spin-gravitational effects. High precision atomic magnetometers can be used for other fundamental research including spin-gravity coupling, tests of Lorentz and CPT violations, detection of dark matter and dark energy [3-5]. In particular, in  it is discussed a use of so-called comagnetometers made of two scalar magnetometers, for example, built on a pair of nuclear magnetometers, or nuclear (proton) and electron optical quantum magnetometers. The best known application of such devices is high precision gyroscope sensors based on the observation that the proton precession frequency changes significantly due to sensor rotation . A short incomplete list of the requirements to such systems and magnetometers is presented below:
* Minimal possible level of industrial magnetic interferences
* Maximal homogeneity and stability of a weak magnetic field in which the nuclear and electron precession is measured
* Network of spin-gravitational sensors placed at maximal large distances with data transmission to a single data center
* High precision measurement synchronization (for example, using the GPS)
* Long term (multiyear) data accumulation in a single (or cloud) data center with public access for independent processing
* Highly qualified research and management personnel servicing spin-gravitational sensors and data processing of high precision multi-parameter measurements
It is easy to see that these requirements are completely satisfied by the existing network of magnetic observatories INTERMAGNET (including some magnetometer sensor types).
The developers of magnetometer spin-gravitational sensors are working on resolving difficult scientific and technical problems from industrial interference magnetic shielding to sensor deployment in space. Various sensors are under development, including those analogous to optical potassium or cesium magnetometers, and nuclear magnetoresonant sensors with nuclear magnetization amplification based on hyperpolarization (including Overhauser nuclear dynamical polarization). The above considerations lead to a proposal of development of a network for cosmological spin-gravity effects detection based on existing network of magnetic observatories. The development cost of such network (with insignificant hard- and software tuning and access to the original measurements database for data analysis using specialized algorithms) will be much lower compared to the LIGO project.
An existence of the IAGA developed network of seismic observation bases supports the proposed network of spin-gravitational sensors which in its turn might appear a powerful tool for global seismic prognosis as ground-based spin-gravitational sensor measurements are significantly dependent on geolocation and Earth rotation parameters.
It is assumed that the spin-gravitational effect signal would of the order of magnitude of few fT with the registration time of 100 s and over. Such a signal can be easily detected by K optical magnetometer and potentially by the Overhauser magnetometer with large volume sensors and special algorithms for the signal accumulation. It requires synchronous operation of multiple pairs of magnetometers to eliminate gyroscopic and seismic effects and mutual verification.
The report shows that the magnetometer equipment GEM employed in INTERMAGNET network might satisfy the required parameters after some tuning aimed to direct output of the original electron and proton precession signals to the specialized registration device resolution. It will allow significant increase of magnetic field measurements. A multiyear signal accumulation will make possible to reach the precision level of a few fT in measurement of gradient between Overhauser and potassium magnetometers.
We discuss development of the Overhauser POS magnetometer with GPS synchronization of the proton precession signal. The signal processing algorithm also includes a possibility of real time output time series of the zero crossing for data accumulation and significant increase measurement sensitivity and bit depth. We also describe a regime of precession wide-band registration  of several nuclei simultaneously. Simultaneous Overhauser polarization of these nuclei is also possible with the coefficients of an order of (gyromagnetic electron ratio/gyromagnetic nucleus ratio). This option can be useful for development and design of new types of gyroscope and spin-gravitational sensors.
In other words, the rotating Earth is just a float bobbing in a gravitational wave and the INTERMAGNET network can serve as a fishing net for the gravitational waves.
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