Phase measurement of photon-assisted tunneling through a quantum dot
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چکیده
– Recent double-slit interference experiments [Schuster et al., Nature 385 (1997) 417 ] have demonstrated the possibility of probing the phase of the complex transmission coefficient of a quantum dot via the Aharonov-Bohm effect. We propose an extension of these experiments: an ac voltage imposed on the side gate with the concomitant photonic sidebands leads to additional structure both in the amplitude and in the phase of the Aharonov-Bohm signal. Observation of these effects would be a definitive proof of coherent absorption and reemission of photons from the ac source. Phase coherence is the hallmark of all mesoscopic transport phenomena. Yet normal transport measurements yield information only about the magnitude of the transmission amplitude, and not its phase. In a groundbreaking set of experiments, Yacoby et al. [1] and Schuster et al. [2] recently demonstrated that a phase measurement is nevertheless possible in a mesoscopic double-slit geometry. Their experimental protocol can be summarized as follows: A magneto-transport measurement is performed on an Aharonov-Bohm ring with a quantum dot fabricated in one of its arms. If the quantum dot supports coherent transport, the transmission amplitudes through the two arms interfere. A magnetic field induces a relative phase change, 2πΦ/Φ0, between the two transmission amplitudes, t0 and tQD, leading to an oscillatory conductance g(B) = (e2/h)T (B), with T (B) = T (0) + 2Re{t0tQDe}+ ..., (1) where Φ is the flux threading the ring, Φ0 = hc/e is the flux quantum, and where the ellipsis represents higher harmonics due to multiple reflections. In the experiments, an oscillatory magnetoconductance of this form was clearly observed thus demonstrating coherent transmission through the dot [1, 2]. Furthermore, controlling the potential on the dot with a Typeset using EURO-LTEX 2 EUROPHYSICS LETTERS
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تاریخ انتشار 1997