Science 339, 1187–1191 (2013)

While studying the electronic spin of a single trapped atomic ion, Yinnon Glickman and co-workers from the Weizmann Institute of Science in Israel discovered a set of spin states that are invariant under photon scattering. States that do not change under coupling to the environment are potentially useful for realizing robust quantum control applications and protecting quantum information. The researchers investigated spin initialization, readout and rotations of a single trapped 88Sr+ ion by applying a combination of optical and radiofrequency pulses. First, they aligned a 422 nm laser beam and a magnetic field along the y and z directions, respectively. They then used a polarization analysis unit to characterize the polarization of the scattered photons. The x-elongated ellipsoid in the Bloch-sphere representation clearly revealed the emergence of a spin measurement basis that is invariant. To demonstrate that this state was a measurement basis, the researchers analysed the polarization of photons scattered by ions with different initial spin states.