Extended Data Fig. 3: Two-qubit algorithmic initialisation.
From: High-fidelity spin qubit operation and algorithmic initialization above 1 K
a, Full protocol of the algorithmic initialisation of a two-qubit system, based on parity readout. b, Experiments with various stages of the algorithmic initialisation and the corresponding ESR spectra. The data are taken at T = 1 K and B0 = 85 mT, where the thermal energy is 8 times greater than the qubit energies. The table shows the nominal duration for each part of the operation used in this work. Initialisation with only Step 1 corresponds to the conventional ramped initialisation. The first part of the algorithmic initialisation repeats Step 1 to 3 until an even-parity state is detected. The full algorithmic initialisation repeats Step 1 to 6 in order to detect if the state is solely \(\left|\downarrow \downarrow \right\rangle \). With the partial or the full algorithmic initialisation, measured with 20000 shots each, we record the statistics on the numbers of iterations, Niteration, and evaluate the respective average Niteration. c, Average Niteration as a function of B0 at T = 1 K. Taking the duration amounts from b into account, the average time cost for initialisation, tinitialisation, is estimated. d, The quantities in c as a function of temperature at B0 = 0.4 T. e, Rabi oscillations and charge readout histograms with different amounts of readout integration time, tintegration, at B0 = 0.4 T, T = 1 K. With short tintegration, the Rabi amplitude becomes limited by the charge readout instead. This may be improved by more advanced readout techniques, such as a double-island SET78 operating at RF or gate dispersive readout79.