Experimental quantum-state tomography of a solid-state qubit

Quantum-state tomography is used to characterize the state of an ensemble based qubit implemented through two hyperfine levels in Pr3+ ions, doped into a Y2SiO5 crystal. We experimentally verify that single-qubit rotation errors due to inhomogeneities of the ensemble can be suppressed using the Roos-Molmer dark-state scheme [Roos and Molmer, Phys. Rev. A 69, 022321 (2004)] Fidelities above > 90%, presumably limited by excited state decoherence, were achieved. Although not explicitly taken care of in the Roos-Molmer scheme, it appears that also decoherence due to inhomogeneous broadening on the hyperfine transition is largely suppressed.