Characterization of the magnetic field through the three-body loss near a narrow Feshbach resonance

Abstract

The narrow $s$-wave Feshbach resonance of a $^{6}\mathrm{Li}$ Fermi gas shows strong three-body loss, which is proposed to be used to measure the minute change of a magnetic field around the resonance. However, the eddy effect will cause ultracold atom experiencing a magnetic field delay to the desired magnetic field from the current of the magnetic coils. The elimination of the eddy effect will play a key role in any experiments that are motivated to measure the magnetic field to the precision of a parts per million stability. Here, we apply a method to correct the eddy effect for precision measurement of the magnetic field. We first record the three-body loss influenced by the induced eddy effect, then we use a first-order decay model to obtain the time constant of the actual magnetic field by fitting the atom loss. This precisely determines the actual magnetic field according to the time response of the three-body loss. After that, we implement the desired magnetic field to the atoms so that we can analyze the three-body loss across the narrow Feshbach resonance. The measured magnetic-field-dependent rate of three-body loss at an ultralow temperature shows that the three-body recombination is the dominated loss mechanism near the resonance. We expect this practical method of correcting the eddy effect error of the magnetic field can be further applied to future studies of quantum few- and many-body physics near a narrow Feshbach resonance.