Controlled Dephasing and Measurement Efficiency via Quantum Dot Detector(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

概要

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We study the charge detection and controlled dephasing of a mesoscopic system via a quantum dot detector (QDD), in which the mesoscopic system and the QDD are capacitively coupled. The QDD is considered to exhibit coherent resonant tunnelling via a single level. It is found that dephasing rate is proportional to the square of the conductance of the QDD for the Breit-Wigner model, showing that dephasing is completely different from the shot noise of the detector. Measurement rate, on the other hand, shows a dip near the resonance of the QDD. Our findings are unique especially for a symmetric detector in the following aspects: The dephasing rate is maximum at the resonance of the QDD in which detector conductance is insensitive to the charge state of the mesoscopic system. As a result, the efficiency of the detector shows a dip and vanishes at the resonance, in contrast to the single-channel symmetric nonresonant detector that always has a maximum efficiency. We find that this difference originates from a very general property of the scattering matrix: An abrupt phase change exists at scattering amplitude in the presence of the symmetry, which is insensitive to detector current but stores information on the quantum state of a mesoscopic system.
社団法人日本物理学会の論文
2006-06-15