Partial-measurement back-action and non-classical weak values in a superconducting circuit

  1. J. P. Groen,
  2. D. Ristè,
  3. L. Tornberg,
  4. J. Cramer,
  5. P. C. de Groot,
  6. T. Picot,
  7. G. Johansson,
  8. and L. DiCarlo
We realize indirect partial measurement of a transmon qubit in circuit quantum electrodynamics by interaction with an ancilla qubit and projective ancilla measurement with a dedicated readout resonator. Accurate control of the interaction and ancilla measurement basis allows tailoring the measurement strength and operator. The tradeoff between measurement strength and qubit back-action is characterized through the distortion of a qubit Rabi oscillation imposed by ancilla measurement in different bases. Combining partial and projective qubit measurements, we provide the solid-state demonstration of the correspondence between a non-classical weak value and the violation of a Leggett-Garg inequality.
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