Conductance fluctuations in a quantum dot under almost periodic ac pumping

Abstract

It is shown that the variance of the linear dc-conductance fluctuations in an open quantum dot under a high-frequency ac pumping depends significantly on the spectral content of the ac field. For a sufficiently strong ac field $\ensuremath{\gamma}{\ensuremath{\tau}}_{\ensuremath{\varphi}}\ensuremath{\ll}1,$ where $1/{\ensuremath{\tau}}_{\ensuremath{\varphi}}$ is the dephasing rate induced by ac noise and $\ensuremath{\gamma}$ is the electron escape rate, the dc-conductance fluctuations are much stronger for the harmonic pumping than in the case of the noise ac field of the same intensity. The reduction factor r in a static magnetic field takes the universal value of 2 only for the white-noise pumping. For the strictly harmonic pumping ${A(t)=A}_{0}\mathrm{cos}\ensuremath{\omega}t$ of sufficiently large intensity the variance is almost insensitive to the static magnetic field $r\ensuremath{-}1=2\sqrt{{\ensuremath{\tau}}_{\ensuremath{\varphi}}\ensuremath{\gamma}}\ensuremath{\ll}1.$ For the quasiperiodic ac field of the form ${A(t)=A}_{0}[\mathrm{cos}({\ensuremath{\omega}}_{1}t)+\mathrm{cos}({\ensuremath{\omega}}_{2}t)]$ with ${\ensuremath{\omega}}_{1,2}\ensuremath{\gg}\ensuremath{\gamma}$ and $\ensuremath{\gamma}{\ensuremath{\tau}}_{\ensuremath{\varphi}}\ensuremath{\ll}1$ we predict effect of enchancement of conductance fluctuations at commensurate frequencies ${\ensuremath{\omega}}_{2}/{\ensuremath{\omega}}_{1}=P/Q.$