Figure 1

(a) Scanning electron micrograph of the double-dot device, and equivalent circuit at 2 MHz of the noise detection system measuring the power spectral densities and cross-spectral density of fluctuations in currents $I_t$ and $I_b$. (b) Differential conductances $g_t$ (yellow) and $g_b$ (magenta) as a function of $V_{tc}$ and $V_{bc}$ over a few Coulomb blockade peaks in each dot, at $V_t=V_b=0$. Black regions correspond to well-defined charge states in the double-dot system. Superimposed white lines indicate the honeycomb structure resulting from the finite interdot capacitive coupling. (c) Zero-bias (thermal) noise $S_b$ (black dots, right axis), conductance $g_b$ (magenta curve, left axis), and calculated $4k_B{T}_e{g}_b$ (magenta curve, right axis) as a function of gate voltage $V_{bc}$, with $V_{tc}=-852.2\mathrm{mV}$.Reuse & Permissions

Figure 2

Measured (a) and simulated (b) cross-spectral density $S_{tb}$ near a honeycomb vertex, with applied bias $V_t=V_b=-100\mu \mathrm{V}$ ($e|V_{t(b)}|\approx 4k_B{T}_e\approx E_C/6$). Blue regions (lower-left and upper-right) indicate negative $S_{tb}$, whereas red regions indicate positive $S_{tb}$.Reuse & Permissions

Figure 3

Energy level diagrams in the vicinity of a honeycomb vertex, with biases $V_{t(b)}=-100\mu \mathrm{V}$. (The various energies are shown roughly to scale.) The solid horizontal line in the top (bottom) dot represents the energy $E_{t(b)}$ required to add electron $M+1$ ($N+1$) when the bottom (top) dot has $N$ ($M$) electrons. The dashed horizontal line, higher than the solid line by $U$, represents $E_{t(b)}$ when the bottom (top) dot has $N+1$ ($M+1$) electrons. In each dot, the rate of either tunneling in from the left or tunneling out to the right is significantly affected by this difference in the energy level, taking on either a slow value (red arrow) or a fast value (green arrow) depending on the electron number in the other dot. In (a) and (d), where the occurrence of each $U$-sensitive process enhances the rate of the other, we find positive cross correlation. In (b) and (c), where the occurrence of each $U$-sensitive process suppresses the rate of the other, we find negative cross correlation.Reuse & Permissions

Figure 4

(a) Measured $S_{tb}$ near a honeycomb vertex, with opposite biases $V_t=-V_b=-100\mu \mathrm{V}$. Note that the pattern is reversed from Fig. 2a: negative cross correlation (blue) is now found in the upper-left and lower-right regions, while positive cross correlation (red) is now found in the lower-left and upper-right. (b) Measured $S_{tb}$ near a honeycomb vertex, with $V_t=V_b=0$. Cross correlation vanishes at zero bias, though the noise in each dot is finite.Reuse & Permissions