J. Cramer

Entanglement genesis by ancilla-based parity measurement in 2D circuit QED

  1. O.-P. Saira,
  2. J. P. Groen,
  3. J. Cramer,
  4. M. Meretska,
  5. G. de Lange,
  6. and L. DiCarlo
We present an indirect two-qubit parity meter in planar circuit quantum electrodynamics, realized by discrete interaction with an ancilla and a subsequent projective ancilla measurement
with a dedicated, dispersively coupled resonator. Quantum process tomography and successful entanglement by measurement demonstrate that the meter is intrinsically quantum non-demolition. Separate interaction and measurement steps allow commencing subsequent data qubit operations in parallel with ancilla measurement, offering time savings over continuous schemes.
arxiv pdf

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.
arxiv pdf