Fig. 3: Bell test.
From: Bell inequality violation in gate-defined quantum dots
a Protocol for conducting the Bell test in a gate-defined double-dot electron spin system. After preparation of a maximally entangled Bell state (i–iv), the quantum correlation is measured via (I) a direct parity measurement after rotation of each qubit to obtain the desired combination of projection axes in two bases, rotated by π/4, or (II) quantum state tomography. b Schematic of the two projection basis \((\alpha,{\alpha }^{{\prime} })\) and \((\beta,{\beta }^{{\prime} })\) of the electron spin qubit in quantum dot 1 and 2, respectively. c Histograms of RF-SET readout signal for all four Bell states in all possible combinations of axis projections at T = 0.1 K. The data is fitted with a bimodal Gaussian distribution. The intersect of the two Gaussian curves is indicated by a dashed line defining the threshold for distinguishing odd (unblockaded) and even (blockaded) parity. d Quantum state tomography results for all four Bell states at T = 0.1 K. No corrections have been applied to compensate for initialization and readout errors. Insets indicate the theoretical density matrix of each Bell state. Error bars represent the 95% confidence level.
