Quantum Frequency Conversion between Infrared and Ultraviolet

In hybrid atomic-optical systems for quantum information processing, there is an unfortunate mismatch: The electronic transitions in an atomic two-level system correspond to ultraviolet photons, while the ``light pipes'' for such photons transmit in the infrared range. To address this, the authors demonstrate quantum optical frequency conversion spanning more than 2.4 eV, and thus joining these spectral regions. This is a milestone on the path to integrating atomic-qubit manipulation with low-loss quantum information transfer over optical fibers.