Nonadiabatic Electron Pumping: Maximal Current with Minimal Noise

The noise properties of pump currents through an open double-quantum-dot setup with nonadiabatic ac driving are investigated. Driving frequencies close to the internal resonances of the double-dot system mark the optimal working points at which the pump current assumes a maximum while its noise power possesses a remarkably low minimum. A rotating-wave approximation provides analytical expressions for the current and its noise power and allows to optimize the noise characteristics. The analytical results are compared to numerical results from a Floquet transport theory.

Figure 1

Level structure of the asymmetric double quantum dot in a pump configuration. The solid lines mark the relevant levels $|1⟩$ and $|2⟩$ with the energies $\pm {ϵ}_0/2$. The arrows indicate the dominating scattering process.

Figure 2

(a) Pump current $I$ (dashed line) and its noise power $S$ (solid line) at $k_{B}T=0$ as a function of the driving frequency for coupling strength $\Gamma =0.3\Delta$, driving amplitude $A=3.7\Delta$, and internal bias ${ϵ}_0=5\Delta$. The dotted lines mark the analytical results (11, 12). Inset: Enlargement of the lower-left corner demonstrating that $I\propto {\Omega }^2$. (b) Corresponding Fano factor.

Figure 3

Fano factor $F$ at the first resonance for various coupling strengths $\Gamma$. The exact Floquet calculation (solid lines) is compared with the RWA for $\delta =0$ (dashed line). The inset depicts the minimal Fano factor in dependence of $\Gamma$ for ${ϵ}_0=5\Delta$ at the resonance $\Omega =\sqrt{{\Delta }^2+{ϵ}_0^2}/\hslash$. The dotted lines mark the optimal Fano factor $F_{\mathrm{opt}}=7/32$.