QZFM coupled to a magnetic guide

[Adrià Barbecho Barrado]

Dear Sir/Madam,

We are working on an experiment where we use a QZFM gen-2 coupled to a magnetic guide made of a conical ferrite core covered by a superconductor-strip-tape operating inside a Magnetically Shielded Chamber (Zero Gauss Chamber), with a degaussing coil controlled by a proper degaussing unit.

A first approach is done in https://iopscience.iop.org/article/10.1088/1367-2630/acb37a, but now we are studying the system to optimize the measurements and counteract the effect of the magnetic guide. In order to take all parts correctly we would like to ask, if it is possible, for some of the parameters and functioning of the OPM.

 Since the magnetometer is coupled to the magnetic guide, we would like to understand how different magnetic fields coming from the internal coils of the QZFM. Concerning this, we are having problems in the zeroing stage and it is not converging correctly. We would like to know which technique is used in the feedback loop controlling this process and which is the frequency of the currents in this compensation coils. Once the system has converged, the current in compensation coils is fixed for the following stages? When the system has been calibrated, does the OPM adding some DC signal in the modulation field to optimize the sensibility?

Another parameter we are interested to is the frequency of the modulation field. In the paper  https://iopscience.iop.org/article/10.1088/1361-6501/aa58b4 it is commented to be 926 Hz. Is this the modulation frequency for all cases?

Finally, so to consider correct values, at least orders of magnitude, of the impact on the sensibility of field inhomogeneities could you give us the pressure of buffer gases and the power of the laser?  In https://iopscience.iop.org/article/10.1088/1361-6501/aa58b4 the pressure is said to be around 1 amagat and in https://www.nature.com/articles/nphoton.2007.201 the power is around 0.35mW , is this correct? 

Thank you in advance,
Adrià