Single-Shot Readout of Macroscopic Quantum Superposition State in a   Superconducting Flux Qubit
  Single-shot readout experiments were performed on the two lowest-energy states of a superconducting qubit with three Josephson junctions embedded in a superconducting loop. We measured the qubit state via switching current Isw of a current-biased dc-SQUID, a quantum detector surrounding the qubit loop. The qubit signals were measured in a small Isw regime of the SQUID, typically less than 100 nA, where the Isw distribution is particularly narrow. The obtained single-shot data indicate that the qubit state is readout, through the flux generated by the qubit persistent-current, as energy eigenstates rather than current eigenstates. 
Hirotaka Tanaka (1,3), Shiro Saito (1,3), Hayato Nakano (1,3), Kouichi   Semba (1,3), Masahito Ueda (1,2,3) and Hideaki Taka...