Figure 1

Scanning electron micrograph of a device similar to the measured device, consisting of a double quantum dot with quantum point contact charge sensors formed by gates 8/9 (13/14) adjacent to the left (right) dot. Series conductance $g_{\mathrm{dd}}$ through the double dot was measured simultaneously with conductances $g_{\mathrm{ls}}$ and $g_{\mathrm{rs}}$ through the left and right sensors.Reuse & Permissions

Figure 2

(a) Double dot conductance $g_{\mathrm{dd}}$ as a function of gate voltages $V_2$ and $V_{10}$. White lines indicate the honeycomb pattern. Within each honeycomb cell, the electron number on each dot is well defined, with $M$ ($N$) referring to the electron number in the left (right) dot. (b),(c) Simultaneously measured sensing signals from left (b) and right (c) QPCs. $\delta g_{\mathrm{ls}}$ ($\delta g_{\mathrm{rs}}$) are QPC conductances after subtracting a best-fit plane. See text for details. The horizontal pattern in (b) and vertical pattern in (c) demonstrate that each sensor is predominantly sensitive to the charge on the dot it borders.Reuse & Permissions

Figure 3

(a) Double dot conductance $g_{\mathrm{dd}}$ as a function of gate voltages $V_2$ and $V_{10}$ in the vicinity of a triple point. Same color scale as in Fig. 2a. The detuning diagonal (red line) indicates the fixed-charge transition between $(M+1,N)$ and $(M,N+1)$. (b) Left and right QPC conductance with no background subtraction (blue points), along the detuning diagonal, with fits to the two-level model, Eq. (2) (black curves). See text for fit details. (c) Excess charge (in units of $e$) in the left and right dot, at $T=30\mathrm{mK}$ (blue), 200 mK (green), and 315 mK (red). Corresponding values of $T_e$ extracted from the fits (solid curves) are 102, 196, and 315 mK.Reuse & Permissions

Figure 4

Excess charge on the left dot, extracted from left QPC conductance data, along a detuning diagonal (crossing different triple points from those in Fig. 3) at base temperature and several settings of the coupling gate 11. The temperature-broadened curve (red) widens as $V_{11}$ is made less negative, increasing the tunnel coupling $t$. See text for details of fits (solid curves). Top right inset: comparison of $t$ values extracted from sensing (circles) and transport (triangles) measurements, as a function of $V_{11}$. Colored circles correspond to the transitions shown in the main graph. Lower left inset: Schematic energy diagram of the two-level system model, showing ground and excited states as a function of detuning $ϵ$, with splitting (anticrossing) of $2t$ at $ϵ=0$.Reuse & Permissions