Gated conditional displacement readout of superconducting qubits

  1. S. Touzard,
  2. A. Kou,
  3. N. E. Frattini,
  4. V. V. Sivak,
  5. S. Puri,
  6. A. Grimm,
  7. L. Frunzio,
  8. S. Shankar,
  9. and M.H. Devoret
We have realized a new interaction between superconducting qubits and a readout cavity that results in the displacement of a coherent state in the cavity, conditioned on the state of the qubit. This conditional state, when it reaches the cavity-following, phase-sensitive amplifier, matches its measured observable, namely the in-phase quadrature. In a setup where several qubits are coupled to the same readout resonator, we show it is possible to measure the state of a target qubit with minimal dephasing of the other qubits. Our results suggest novel directions for faster readout of superconducting qubits and implementations of bosonic quantum error-correcting codes.
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