  This chapter covers the development of feedback control of superconducting
qubits using projective measurement and a discrete set of conditional actions,
here referred to as digital feedback. We begin with an overview of the
applications of digital feedback in quantum computing. We then introduce an
implementation of high-fidelity projective measurement of superconducting
qubits. This development lays the ground for closed-loop control based on the
binary measurement result. A first application of digital feedback control is
fast and deterministic qubit reset, allowing the repeated initialization of a
qubit more than an order of magnitude faster than its relaxation rate. A second
application employs feedback in a multi-qubit setting to convert the generation
of entanglement by parity measurement from probabilistic to deterministic,
targeting an entangled state with the desired parity every time.
