Realization of a Λ system with metastable states of a capacitively-shunted fluxonium

  1. Nathan Earnest,
  2. Srivatsan Chakram,
  3. Yao Lu,
  4. Nicholas Irons,
  5. Ravi K. Naik,
  6. Nelson Leung,
  7. Jay Lawrence,
  8. Jens Koch,
  9. and David I. Schuster
We realize a Λ system in a superconducting circuit, with metastable states exhibiting lifetimes up to 7ms. We exponentially suppress the tunneling matrix elements involved in spontaneous
energy relaxation by creating a „heavy“ fluxonium, realized by adding a capacitive shunt to the original circuit design. The device allows for both cavity-assisted and direct fluorescent readout, as well as state preparation schemes akin to optical pumping. Since direct transitions between the metastable states are strongly suppressed, we utilize Raman transitions for coherent manipulation of the states.