Quantum Nondemolition Measurements of a Qubit

Jiang, Wei Wei, Yu +2 more

D. V. Averin

Kohji Takashima, Munehiro Nishida, Shigemasa Matsuo +1 more

Quantum nondemolition (QND) measurements allow us to measure an observable of a quantum system without introducing a back‐action on this observable due to the measurement itself. Here we propose a method for the QND measurement of a superconducting flux qubit by extending the spin QND measurement. Under an adequate condition, qubit and interaction Hamiltonian satisfy QND conditions and then QND measurement of a superconducting flux qubit is possible.

Gerard J Milburn, Daniel F. Walls

Ying-Dan Wang, Xiaobo Zhu, Christoph Bruder

We propose a scheme to realize a quantum nondemolition (QND) measurement of a superconducting flux qubit by a Josephson bifurcation amplifier. Our scheme can implement a perfect QND measurement for a qubit subject to a variable magnetic bias. Measurement back-action-induced qubit relaxation can be suppressed and hence the QND fidelity is expected to be high over a wide range of bias conditions.

Timothy C. Ralph, Stephen D. Bartlett, Jeremy L. O’Brien +2 more

We discuss the characterization and properties of quantum nondemolition (QND) measurements on qubit systems. We introduce figures of merit which can be applied to systems of any Hilbert space dimension, thus providing universal criteria for characterizing QND measurements. The controlled-NOT gate and an optical implementation are examined as examples of QND devices for qubits. We also consider the QND measurement of weak values.