Decoherence-free radio-frequency-dressed subspaces

We study the spectral signatures and coherence properties of radio-frequency-dressed hyperfine Zeeman sublevels of $^{87}\mathrm{Rb}$. Experimentally, we engineer combinations of static and RF magnetic fields to modify the response of the atomic spin states to environmental magnetic field noise. We demonstrate analytically and experimentally the existence of ``magic'' dressing conditions where decoherence due to electromagnetic field noise is strongly suppressed. Building on this result, we propose a bichromatic dressing configuration that reduces the global sensitivity of the atomic ground states to low-frequency noise, and enables the simultaneous protection of multiple transitions between the two ground hyperfine manifolds of atomic alkali species. Our methods produce protected transitions between any pair of hyperfine sublevels at arbitrary (low) DC-magnetic fields.