  Feedback control of qubits is a highly demanded technique for advanced
quantum information protocols such as quantum error correction. Here we
demonstrate active reset of a silicon spin qubit using feedback control. The
active reset is based on quantum non-demolition readout of the qubit and
feedback according to the readout results, which is enabled by hardware data
processing and sequencing. We incorporate a cumulative readout technique to the
active reset protocol, enhancing initialization fidelity above a limitation
imposed by accuracy of the single QND measurement fidelity. Based on an
analysis of the reset protocol, we suggest a way to achieve the initialization
fidelity sufficient for the fault-tolerant quantum computation.
