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arXiv:cond-mat/0204186 · Journal of the Physical Society of Japan

Probe-Configuration-Dependent Decoherence in an Aharonov–Bohm Ring

Kensuke Kobayashi, Hisashi Aikawa, Shingo Katsumoto, Y. Iye

Published Sep 15, 2002• 42 citations
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Abstract

We have measured transport through mesoscopic Aharonov-Bohm (AB) rings with two different four-terminal configurations. While the amplitude and the phase of the AB oscillations are well explained within the framework of the Landaur-Büttiker formalism, it is found that the probe configuration strongly affects the coherence time of the electrons, i.e., the decoherence is much reduced in the configuration of so-called nonlocal resistance. This result should provide an important clue in clarifying the mechanism of quantum decoherence in solids.

DOI
10.1143/jpsj.71.2094

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We have measured transport through mesoscopic Aharonov-Bohm (AB) rings with two different four-terminal configurations. While the amplitude and the phase of the AB oscillations are well explained within the framework of the Landaur-Büttiker formalism, it is found that the probe configuration strongly affects the coherence time of the electrons, i.e., the decoherence is much reduced in the configuration of so-called nonlocal resistance. This result should provide an important clue in clarifying the mechanism of quantum decoherence in solids.
Abstract Decoherence is an undesirable, but ubiquitous phenomenon in quantum systems. Here, we study the effect of partial decoherence, induced via a Büttiker probe, on two-terminal electronic transport across one-dimensional quantum wires and rings, in both the linear and non-linear regimes. We find that dephasing causes backscattering when introduced locally in a ballistic channel. Further, we find that decoherence results in rectification when inversion is broken in the two-terminal transport set-up by a combination of a local dephasing centre and a static impurity. Interestingly, the rectification strength and even its direction varies strongly with the relative distance between the probe and the scatterer. We further analyze how decoherence affects characteristic quantum effects in electronic transport, such as, Fabry-Pérot oscillations in double-barrier setups, and Aharonov–Bohm interference in one-dimensional rings, and find that the amplitude of oscillations in conductance is reduced by decoherence.
We investigate the dephasing rates in quasiballistic Aharonov-Bohm (AB) rings with local- and nonlocal-probe configurations by tuning the transmission through one arm of the ring. The dephasing rates are independent of the probe configuration while the transmissions through the ring paths are equal. In contrast, as AB interferometers are tuned to be strongly asymmetric, the dephasing rate of the local configuration becomes larger than that of the nonlocal configuration. We find that our observations can be qualitatively explained by voltage fluctuations from the measurement circuit, as proposed by G. Seelig, S. Pilgram, A. N. Jordan, and M. B\"uttiker [Phys. Rev. B 68, 161310(R) (2003)].
We investigate the dependence of decoherence on the mode number M in a multiple-mode Aharonov-Bohm (AB) interferometer. The design of the AB interferometer allows us to precisely determine M by the additivity rule of ballistic conductors; meanwhile, the decoherence rate is simultaneously deduced by the variance of the AB oscillation amplitude. The AB amplitude decreases and fluctuates with depopulating M. Moreover, the normalized amplitude exhibits a maximum at a specific M (∼9). Data analysis reveals that the charge-fluctuation-induced dephasing, which depends on the geometry and the charge relaxation resistance of the system, could play an essential role in the decoherence process. Our results suggest that the phase coherence, in principle, can be optimized using a deliberated design and pave one of the ways toward the engineering of quantum coherence.
We report measurements of Aharonov-Bohm oscillations in normal metal rings in the presence of high-frequency electromagnetic fields. The power dependence of the decoherence time scale ${\ensuremath{\tau}}_{\ensuremath{\phi}}(P)$ agrees well with the anticipated power law ${\ensuremath{\tau}}_{\ensuremath{\phi}}\ensuremath{\propto}{P}^{\ensuremath{-}1∕5}$ when the field-induced decoherence rate ${\ensuremath{\tau}}_{\mathit{ac}}^{\ensuremath{-}1}$ is large compared to the intrinsic decoherence rate ${\ensuremath{\tau}}_{o}^{\ensuremath{-}1}$, measured in the absence of external fields. As theoretically expected, we observe a decline in field-induced decoherence when ${\ensuremath{\tau}}_{\mathit{ac}}^{\ensuremath{-}1}\ensuremath{\leqslant}{\ensuremath{\tau}}_{o}^{\ensuremath{-}1}$. The frequency dependence of ${\ensuremath{\tau}}_{\ensuremath{\phi}}$ shows a minimum in the oscillation amplitude at a characteristic frequency ${\ensuremath{\omega}}_{\mathit{ac}}\ensuremath{\simeq}1∕{\ensuremath{\tau}}_{o}$, where ${\ensuremath{\tau}}_{o}$ is evaluated from the oscillation amplitude using the standard mesoscopic theory. Both the suppression in the oscillation amplitude and the concomitant change in conductivity allow a direct measurement of the intrinsic decoherence time scale.