Quantum trajectories for the realistic measurement of a solid-state charge qubit, Phys

We present a new model for the continuous measurement of a coupled quantum dot charge qubit. We model the effects of a realistic measurement, namely adding noise to, and filtering, the current through the detector. This is achieved by embedding the detector in an equivalent circuit for measurement. Our aim is to describe the evolution of the qubit state conditioned on the macroscopic output of the external circuit. We achieve this by generalizing a recently developed quantum trajectory theory for realistic photodetectors fP. Warszawski, H. M. Wiseman, and H. Mabuchi, Phys. Rev. A 65, 023802 s2002dg to treat solid-state detectors. This yields sto-chastic equations whose snumericald solutions are the “realistic quantum trajectories ” of the conditioned qubit state. We derive our general theory in the context of a low transparency quantum point contact. Areas of application for our theory and its relation to previous work are discussed. DOI: 10.1103/PhysRevB.71.165317 PACS numberssd: 73.23.Hk, 03.67.Lx I