Sensitivity enhancement of Pulsed Atomic Magnetometer for Minute Changes in Ambient Magnetic Field

We developed and patented a novel methodology to measure minute changes in ambient magnetic field. A sensitivity of less than 10 pT/Sqrt(Hz) at 1 Hz has been demonstrated using a Cesium unshielded pulsed optical scalar magnetometer operated at 1 kHz of 170 ns pump pulses and 5s data acquisition time. The demonstrated dynamic range of our magnetometer is 0.2 – 500 Hz. The purpose of this research proposal is to improve the performance of our pulsed magnetometer towards sensitivity below 1pT/Sqrt(Hz), with a dynamic range going down below 0.05 Hz and an operational temperature of 4-50oC. In a 'pulsed magnetometer' the pump laser is a pulsed laser operated at high repetition rate (1-10 kHz) of very short pulses (100-200 ns). The spin-polarization of the optically pumped atoms undergoes a Free Induction Decay (FID) relaxation while rotating at the Larmor frequency. Based on direct Larmor frequency differences measurement, the measured magnetic field Signal to Noise Ratio (SNR) is almost independent of temperature and signal amplitude. The pulsed magnetometer offers several essential advantages over the CW pumping: low power consumption, no need for laser cooling, fast rise-time with a well-defined starting point, high rep-rate enabling multiple-pulse averaging, high peak-power for high polarization, compact size, low cost. The signal analysis requires intense data processing and digital filtering, regarded as a 'logic shielding'. Data processing used well-understood physics and modeling. The vapor cell of our magnetometer contains 5 torr of N2, 10 torr of Ne and a drop of Cs. We propose to reach the challenging goals of this proposal by investigating magnetometer performance with other alkali atoms like Rb and K besides Cs. We propose to investigate the contribution of buffer gas pressure and mixture to magnetometer sensitivity and Signal-to-Noise Ratio (SNR). The magnetometer SNR will be experimentally investigated in a shielded environment in our lab and finally modeled for future development and applications. Improved optical designs, gradiometric configurations as well as temporal continuous data acquisition with higher accuracy (~14 bit), and new processing and analysis algorithms will be part of this research. Atomic Physics Quantum calculations of the dynamics within the magnetometer will accompany the experiments, including modeling of the Cs atoms as three levels system and calculating time dependent Hamiltonian, related density matrices, Atom Correlations, Spin Squeezing etc. Enhanced performance proportional to the square of the atomic density is expected due to inter-atomic correlations. Spin Squeezing may reduce Quantum Noise. The outcomes of this research effort could lead to advanced 'logic shielding' algorithms, and establish a starting point to new, higher sensitivity pulsed magnetometers. Relevance to ONR: the possibility to detect minute changes in the ambient magnetic field with bandwidth down to 0.05 Hz enables one to monitor the presence of moving objects carrying ferromagnetic materials across buried or submerged detector lines. There are no US collaborators in this research. We propose a three-year program to be performed by 1.5 manpower/year of our Quantum Magnetometry Group including 5 researchers, on a budget of k$100/year. The budget is for salaries, travel and expendables. The outcome of this research: scientific reports, conference presentations and journal articles.