  We propose an efficient qubit initialization protocol based on a dissipative
environment that can be dynamically adjusted. Here the qubit is coupled to a
thermal bath through a tunable harmonic oscillator. On-demand initialization is
achieved by sweeping the oscillator rapidly into resonance with the qubit. This
resonant coupling with the engineered environment induces fast relaxation to
the ground state of the system, and a consecutive rapid sweep back to off
resonance guarantees weak excess dissipation during quantum computations. We
solve the corresponding quantum dynamics using a Markovian master equation for
the reduced density operator of the qubit-bath system. This allows us to
optimize the parameters and the initialization protocol for the qubit. Our
analytical calculations show that the ground-state occupation of our system is
well protected during the fast sweeps of the environmental coupling and,
consequently, we obtain an estimate for the duration of our protocol by solving
the transition rates between the low-energy eigenstates with the Jacobian
diagonalization method. Our results suggest that the current experimental state
of the art for the initialization speed of superconducting qubits at a given
fidelity can be considerably improved.
