  One of the major components for realizing quantum computers is the ability to
initialize the computer to a known fiducial state, also known as state
preparation. We demonstrate a state preparation method via measurement-induced
steering on contemporary, digital quantum computers. By delegating ancilla
qubits and systems qubits, the system state is prepared by repeatedly
performing the following steps: (1) executing a designated system-ancilla
entangling circuit, (2) measuring the ancilla qubits, and (3) re-initializing
ancilla qubits to known states through active reset. While the ancilla qubits
are measured and reinitialized to known states, the system qubits are steered
from arbitrary initial states to desired final states. We show results of the
method by preparing arbitrary qubit states and qutrit (three-level) states. We
also demonstrate that the state convergence can be accelerated by utilizing the
readouts of the ancilla qubits to guide the protocol in an active manner. This
protocol serves as a nontrivial example that incorporates and characterizes
essential operations such as qubit reuse (qubit reset), entangling circuits,
and measurement. These operations are not only vital for near-term noisy
intermediate-scale quantum (NISQ) applications but are also crucial for
realizing future error-correcting codes.
