Figure 1

(a) Electron microscope image of the device consisting of an InSb nanowire contacted by source and drain electrodes, lying across a set of fine gates (numbered, 60 nm pitch) as well as a larger bottom gate (labeled BG). (b) Current through the device when applying microwaves with the double dot in spin blockade configuration (a vertical linecut near 0 mT has been subtracted to suppress resonances at constant frequency). When the microwave frequency matches the Larmor frequency (resonance highlighted by the dashed blue box), blockade is lifted and current increases. (c) Schematic illustration of Pauli spin blockade on which readout depends. Only antiparallel states (right) can occupy the same dot, allowing current through the device. A parallel configuration (left) leads to a suppression of the current.Reuse & Permissions

Figure 2

(a) Bias triangle in which spin blockade was observed for a negative bias of $-5\mathrm{mV}$. This is the $(2m+1,2n+1)\to (2m,2n+2)$ transition (transition $A$; see Ref. 21). (b) Sequence used for measuring Rabi oscillations. Pulses are applied to gates 2 and 4 to move the double dot along the detuning axis between Coulomb blockade (CB) and spin blockade (SB) configurations. In CB a microwave burst is applied via gate BG to rotate the spin. (c) Rabi oscillation obtained at a magnetic field of 31.4 mT, driving frequency of 18.65 GHz, and source power of 11 (bottom) to 17 dBm (top). Dashed lines are fits to $a\cos (f_R{\tau }_{\mathrm{burst}}+\varphi ){\tau }_{\mathrm{burst}}^{-d}+b$, giving Rabi frequencies $f_R$ of $54\pm 1$, $67\pm 1$, $84\pm 1$, and $104\pm 1\mathrm{MHz}$. Linear slopes, attributed to photon-assisted tunneling, of 0.5, 0.6, 0.4, and $0.6\mathrm{fA}/\mathrm{ns}$ (top to bottom) were subtracted. $d=0.5$ for the bottom trace and 0.4 for the others. Curves are offset by 0.5 pA for clarity. Inset: Rabi frequencies set out against driving amplitudes, including a linear fit through 0.Reuse & Permissions

Figure 3

(a) Ramsey experiment; an initial $\pi /2$ pulse rotates the spin to the $xy$ plane. After some delay a $3\pi /2$ pulse is applied, restoring spin blockade or (partially) lifting it, depending on the phase of the pulse. (b) Decay of the Ramsey fringe contrast with increasing delay time $\tau$ for different driving frequencies. The solid line is a fit to $\exp [-(\tau /T_2^{*}{)}^2]$ at a driving frequency of 18.65 GHz, giving $T_2^{*}=8\pm 1\mathrm{ns}$. (c) A Hahn echo sequence (top) extends the decay of the fringe contrast, to 30 ns in this case. (d) Decay of the fringe contrast in the Hahn echo sequence for different microwave frequencies. The solid line is a fit to $\exp [-(\tau /T_{\mathrm{echo}}{)}^3]$ for driving frequency 18.65 GHz, yielding $T_{\mathrm{echo}}=34\pm 2\mathrm{ns}$.Reuse & Permissions

Figure 4

Main panel: Two well separated EDSR peaks for the spin-orbit qubit in each of the two dots. The microwave driving frequency is 20.9 GHz. Insets: Rabi oscillations for the corresponding EDSR peaks. Linear slopes (attributed to photon-assisted tunneling) of 0.6 and $0.9\mathrm{fA}/\mathrm{ns}$, respectively, are subtracted to flatten the average. The Rabi data on the left were obtained at 31.2 mT $B$ field and 20.9 GHz driving frequency. From the fit (as in Fig. 2) a Rabi frequency of $96\pm 2\mathrm{MHz}$ is obtained. On the right, the field was 41.2 mT and driving frequency 21 GHz. The Rabi frequency obtained from the fit is $47\pm 3\mathrm{MHz}$.Reuse & Permissions