Fig. 1: Device and basic operation.
From: Bell inequality violation in gate-defined quantum dots
a Scanning electron micrograph of a device nominally identical to that used in this work. Active gate electrodes and the microwave antenna are highlighted with colours. An external d.c. magnetic field B0 and the antenna-generated a.c. magnetic field B1 are indicated with arrows. The system operates at T = 0.1 K, unless otherwise specified. b Transmission electron micrograph of the “active” region with schematics indicating the quantum dot and electron spin qubit formation at the Si/SiOx interface including exchange control. c Charge stability diagram in isolated mode as a function of P1, P2 voltage detuning ΔVG = −ΔVP1 = ΔVP2 and the J gate voltage VJ, showing six loaded electrons across the double-dot system. The d.c. plunger gate voltages are VP1 = 1.22 V and VP2 = 1.404 V. The operation points for readout (RO), single-qubit operation (Joff) and two-qubit operation (Jon) are labelled as star (⋆), square (■), and triangle (▴), respectively. d, e Probability of detecting a blockaded state, Pblockade, after a microwave burst of fixed power and duration at different J gate voltages VJ when preparing a mixed odd state \(\frac{1}{\sqrt{2}}(\left\vert \! \downarrow \uparrow \right\rangle+\left\vert \! \uparrow \downarrow \right\rangle )\) (d) and a pure state \(\left\vert \! \downarrow \downarrow \right\rangle\) (e). The power and duration of the microwave burst are roughly calibrated to a single-qubit π-rotation. The following experiments are conducted with \(\left\vert \! \downarrow \downarrow \right\rangle\) initialization, unless otherwise specified. f, g Q1 and Q2 single-qubit Rabi oscillations at VJ = 0.71 V as a function of pulse time tESR, respectively. h Decoupled controlled phase (DCZ) oscillations as a function of exchange time texchange and VJ at fixed ΔVG = −40 mV. i DCZ exchange oscillation fingerprint for fixed exchange time texchange = 5 μs as a function of ΔVG and VJ. The two-qubit operation point (Jon) labelled as a triangle (▴) is picked due to largest resilience against detuning noise. Readout probability is unscaled in all data. Error bars represent the 95% confidence level.
