Chirp asymmetry in Zeeman electromagnetically induced transparency

The simplest three-level system exhibiting electromagnetically induced transparency (EIT) exhibits an effective conjugation symmetry as well as a permutation symmetry. Breaking conjugation symmetry leads to a distinct chirp asymmetry; the differential response to a frequency increase versus a frequency decrease. Hanle-Zeeman EIT resonance is an ideal platform for testing the theory of chirp asymmetry because so many parameters of the system can be changed experimentally. We describe the theory and our results from a recent experiment using 87Rb in a buffer gas cell that, in comparison with earlier multi-photon chirp asymmetry work, explores the asymmetry at nearly a billionth the earlier chirp rate. This universal picture of chirp asymmetry has potential metrological consequences for understanding the systematic dependence on modulation/demodulation parameters.