Single-Shot Spin-to-Charge Conversion in Si/SiGe Quantum Dots Using Latched Readout and Cryogenic Amplification

Achieving high signal-to-noise readout of multi-electron Si/SiGe spin qubits is critical for the rapid development of this technology for quantum applications. We report on single-shot spin-to-charge readout of a triple dot using an enhanced readout protocol where the spin states are pulsed to the (1,1,1)/(2,0,1) charge boundary and then into the (1,0,1) charge state. In this scheme, spin singlets decay from (1,1,1) -> (2,0,1) -> (1,0,1), whereas spin triplets are prevented from decaying to (2,0,1) by Pauli spin blockade. The resulting singlet-triplet differential signal is between states with differing numbers of electrons rather than just a spatial re-distribution of a fixed number of electrons. Using enhanced readout in conjunction with a low noise cryogenic HEMT amplifier, we achieve a measurement fidelity of <1e-2 in 600 ns of integration time. At these integration times, our measurement noise is dominated by broadband sources including the HEMT and the Johnson noise of our readout circuitry which together limit fidelity to ~1e-6. Decay mechanisms bound fidelity more severely; we arrive at 1e-2 by including triplet to singlet relaxation (T1) during measurement. Errors arising from T1 decrease linearly with integration time, incentivizing faster measurement.