Quantum measurement of dynamic qubit information by a double quantum-dot detector

In this paper we propose a novel measurement scheme, based on a double quantum-dot detector, for reading out the qubit information sensed by the detector as a variation of the interdot coupling. By investigating the detector in the static qubit case, we find a sensitive qubit-detector response region determined by the detector geometry. Then we study quantum measurement of the information stored in a dynamic qubit. It is verified that whether the detector can perform well is closely dependent on the ratio of the right dot-lead coupling to interdot coupling in the detector, while the interdot Coulomb interaction only plays a trivial role. Furthermore, it is shown that the dephasing time of the qubit is strongly influenced by the difference between the interdot couplings of the detector corresponding to two qubit states. This work provides some helpful instructions on how to devise an effective qubit detector.