Unitary-Feedback-Improved Qubit Initialization in the Dispersive Regime
Luke C. G. Govia, Frank K. Wilhelm · Physical Review Applied · 2015
In quantum information processing one strives for quantum nondemolition (QND) measurements, which are least likely to perturb the subsequent evolution of the system. The authors show, however, that common superconducting-qubit readout schemes are in fact not QND. They identify a mechanism that induces an effective coherent rotation of the qubit, which means that such a scheme is QND only in the limit of infinite measurement time. This affects any protocol where measurement is used during computation, and therefore is of immediate importance to contemporary experiments. Thankfully, the authors also explain how to fix the problem.