Kang-Hun Ahn

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We investigate the interplay between the quantum coherence and statistics in electrically driven nanostructures. We obtain an expression for the admittance and the current noise for a driven nanocapacitor in terms of the Floquet scattering matrix and derive a nonequilibrium fluctuation-dissipation relation. As an interplay between the quantum phase(More)
In the ear, hair cells transform mechanical stimuli into neuronal signals with great sensitivity, relying on certain active processes. Individual hair cell bundles of non-mammals such as frogs and turtles are known to show spontaneous oscillation. However, hair bundles in vivo must be quiet in the absence of stimuli, otherwise the signal is drowned in(More)
Dissipation of micro- and nanoscale mechanical structures is dominated by quantum-mechanical tunneling of two-level defects intrinsically present in the system. We find that at high frequencies-usually, for smaller, micron-scale structures-a novel mechanism of phonon pumping of two-level defects gives rise to weakly temperature-dependent internal friction,(More)
Inspired by auditory hair cells of lower vertebrates, we design and fabricate an opto-electro-mechanical sensor at the border of its spontaneous activity, called Hopf bifurcation critical point. As proposed for biological hair cells, we observe that, as the system approaches the critical point, the frequency selectivity and the force sensitivity are(More)
We investigate the transport and the dynamical properties of tunnel-coupled double charge shuttles. The oscillation frequencies of two shuttles are mode locked to integer multiples of the applied voltage frequency omega. We show that left-right-symmetric double shuttles may generate direct net current due to bistable motions caused by parametric(More)
We investigate the ground and excited states of interacting electrons in a quantum point contact using an exact diagonalization method. We find that strongly localized states in the point contact appear when a new transverse conductance channel opens and longitudinal resonant level is formed due to momentum mismatch. These localized states form magnetic(More)
We propose a nanostructure control method which uses slowly ramping parameters. We demonstrate the dynamics of this method in both a nonlinear classical system and a quantum system. When a quantum mechanical two-level atom (quantum dot) is irradiated by an electric field with a slowly increasing frequency, there exists a sudden transition from ground(More)