This paper presents an experimental study of microwave single-photon transitions that are magnetic-field-insensitive in degenerate Fermi gases of ${}^{40}\mathrm{K}$. This contrasts with microwave single-photon clock transitions for 0–0 magnetic-field-insensitive states and two-photon clock transitions for non-0–0 magnetic-field-insensitive states in bosonic alkali-metal atoms. We show that there are two sets of special transitions between two different hyperfine ground states ($|F=9/2,m_F=1/2\rangle \iff |7/2,-1/2\rangle$ and $|9/2,-1/2\rangle \iff |7/2,1/2\rangle$), whose microwave single-photon transition frequency is insensitive to low magnetic fields, as the first-order Zeeman shift is almost completely canceled. By using the microwave spectrum and Ramsey interference fringes, we demonstrate the long-time stability of the coherent transition under magnetic field fluctuations. These magnetic-field-insensitive microwave hyperfine transitions in ultracold ${}^{40}\mathrm{K}$ Fermi gases offer promising applications in quantum information and precision measurements.

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• Atomic & molecular collisions
• Atomic, optical & lattice clocks
• Fine & hyperfine structure
• Stark effect
• Zeeman effect
• Atomic gases
• Atoms
• Bose-Einstein condensates
• Fermi gases
• Trapped atoms
• Ultracold gases
• Optical techniques