An analysis of the Quality of Charge Qubit Measurement by a Strongly Coupled Single-Electron Transistor

摘要

We derive a Lindblad-form master equation and a corresponding quantum trajectory model for continuous measurement of a charge qubit by a single electron transistor (SET) operating in the sequential-tunneling regime when the SET-qubit coupling is strong compared to the SET tunnelling rates. We present an analysis of the quality of the qubit measurement in this model (sensitivity versus back-action) and show that in one strongly coupled, asymmetric regime, the SET can approach the limit of an ideal detector with an almost pure conditioned state. We also quantify the quality of the SET using generalized definitions of measurement time and decoherence time.