  Localized spin states in conventional superconductors at low temperatures are
expected to have long decoherence time due to the strong suppression of spin
relaxation channels. We propose a scanning tunneling microscopy (STM)
experiment allowing the direct measurement of the decoherence time of a single
spin in a conventional superconductor. The experimental setup can be readily
applied to general-purpose spin-polarized STM and to local spin relaxation
spectroscopy. A possible extension of the setup to a quantum information
processing scheme is discussed.
