QUROPE Quantum Information Processing and Communication in Europe

In a recent publication in Physical Review Letters the TU-Delft group led by SOLID partner Leo DiCarlo demonstrated an indirect partial measurement of a transmon qubit in circuit quantum electrodynamics.  This was don by interaction with an ancilla qubit and projective ancilla measurement with a dedicated readout resonator. Accurate control of the interaction and ancilla measurement basis allowed the group to show how it is possible to tailor the measurement strength and operator. The tradeoff between measurement strength and qubit backaction was shown to be characterized through the distortion of a qubit Rabi oscillation imposed by ancilla measurement in different bases. By combining partial and projective qubit measurements, the group made a solid-state demonstration of the correspondence between a nonclassical weak value and the violation of a Leggett-Garg inequality.