Tunable Spin Loading andT1of a Silicon Spin Qubit Measured by Single-Shot Readout

We demonstrate single-shot readout of a silicon quantum dot spin qubit, and we measure the spin relaxation time $T_1$. We show that the rate of spin loading can be tuned by an order of magnitude by changing the amplitude of a pulsed-gate voltage, and the fraction of spin-up electrons loaded can also be controlled. This tunability arises because electron spins can be loaded through an orbital excited state. Using a theory that includes excited states of the dot and energy-dependent tunneling, we find that a global fit to the loading rate and spin-up fraction is in good agreement with the data.