Fig. 2: Initialization and readout.
From: High-fidelity spin qubit operation and algorithmic initialization above 1 K
a, Two-qubit algorithmic initialization and the outcomes at B0 = 0.79 T and 35 mT, both at T = 1 K in the (5, 3) charge configuration. Stage I represents the conventional ramped initialization over a duration of 100 μs, and with II and III included, we achieve partial and full algorithmic initialization. The traces are taken at VJ = 1.2 V, in which the exchange is on, with dashed lines indicating the locations of the four state transitions. b, Left, resonantly driven Rabi oscillations of individual qubits for a short tMW and averaged over 500 shots at B0 = 0.79 T and T = 1 K in (5, 3). Pblockade is unscaled in both traces. Right, corresponding charge readout histograms. The signal integration time tintegration is 50 μs. c, The lifetime of PSB, \({T}_{1}^{{\rm{PSB}}}\), for |↓↓⟩ and |↑↑⟩ as a function of temperature from 0.14 K to 1.4 K, at B0 = 0.79 T in (5, 3). d, Measured readout fidelity and estimated T1-limited spin readout fidelity of |↓↓⟩, and charge readout fidelity as a function of temperature from 0.14 K to 1.4 K, at B0 = 0.79 T in (5, 3) with tintegration = 50 μs. e, State reconstruction and state-preparation-and-measurement (SPAM) error analysis using repeated PSB readout at B0 = 0.79 T and T = 1 K in (5, 3). We initialize s0 = |↓↓⟩ using the algorithmic initialization or |↑↓⟩ by π-pulsing on Q1 after the algorithmic |↓↓⟩ initialization. We then perform n PSB readouts, through which the state evolves into sn. Finally, we apply machine learning (ML) on the readout outcomes m1–mn to extract the initialization, readout and spin-flip probabilities and reconstruct the states. The results are shown in the table and the plots. Error bars represent the 95% confidence level.
