Figure 1

(a) The DQD is operated by biasing a global top gate at voltage $V_{\mathrm{T}}$ to accumulate carriers in the quantum well (left). Local depletion gates define the DQD confinement potential (center). Charge sensing is performed using rf reflectometry (right). (b) Few electron charge stability diagram visible in the derivative of the reflected rf amplitude $dA/d{V}_{\mathrm{L}}$. ($N_{\mathrm{L}}$, $N_{\mathrm{R}}$) indicate the number of electrons in the left and right dots. (Inset) $P_{(1,0)}$ plotted as a function of detuning, for different values of $V_{\mathrm{N}}$, showing tunable interdot tunnel coupling at the $(1,0)\leftrightarrow (0,1)$ interdot charge transition.Reuse & Permissions

Figure 2

(a) (left) Current $I$ measured as a function of $V_{\mathrm{L}}$ and $V_{\mathrm{R}}$ near the $(1,0)\leftrightarrow (0,1)$ charge transition. A cut through the finite bias triangle (right) indicates the presence of a low-lying excited state. (b) $P_{(1,0)}$ plotted as a function of detuning $\epsilon$ for different excitation frequencies $f$. For $f\gtrsim 15\mathrm{GHz}$, a new PAT peak emerges (gray arrow) corresponding to the $(1,0{)}_{\mathrm{g}}\leftrightarrow (0,1{)}_{\mathrm{e}}$ transition. The appearance of this PAT peak is accompanied by the suppression of the $(1,0{)}_{\mathrm{g}}\leftrightarrow (0,1{)}_{\mathrm{g}}$ PAT peak (black arrow) at positive detuning. (c) Transition frequencies as a function of detuning and (d) energy level diagram extracted from data in (c). The data in (c) are best fit with an interdot tunnel coupling $t_{\mathrm{c}}=1.9\mathrm{GHz}$ and an excited state energy $\Delta =55\mu \mathrm{eV}$.Reuse & Permissions

Figure 3

(a) Pulse sequence used to measure $T_1$ and simulated qubit response. $P_{(1,0)}=0.5$ when resonant microwaves drive transitions between $(0,1{)}_{\mathrm{g}}$ and $(1,0{)}_{\mathrm{g}}$, and approaches 1 on a time scale set by $T_1$ when the microwaves are turned off. (b) $P_{(1,0)}^{*}$ as a function of $\tau$ extracted for different $V_{\mathrm{N}}$ at $f=19.5\mathrm{GHz}$. Fits to the data give $T_1=1.4$, 0.3, and $0.05\mu \mathrm{s}$ for $V_{\mathrm{N}}=225$, 250, and 265 mV. (Inset) Comparison of typical PAT peaks at different $\tau$, with fixed $V_{\mathrm{N}}=225\mathrm{mV}$ and $f=25.9\mathrm{GHz}$. (c) $T_1$ as a function of $V_{\mathrm{N}}$ in Device 1. (d) $T_1$ as a function of $V_{\mathrm{C}}$ in Device 2.Reuse & Permissions

Figure 4

(a) $T_1$ increases weakly with $f$ for the $(0,1{)}_{\mathrm{g}}\to (1,0{)}_{\mathrm{g}}$ transition. (b) $T_1$ for the $(0,1{)}_{\mathrm{g}}\to (1,0{)}_{\mathrm{g}}$ and $(0,1{)}_{\mathrm{e}}\to (1,0{)}_{\mathrm{g}}$ transitions as a function of $f$ with $V_{\mathrm{N}}=250\mathrm{mV}$ (lower). There are two $(0,1{)}_{\mathrm{e}}\to (1,0{)}_{\mathrm{g}}$ relaxation pathways (upper).Reuse & Permissions