Preserving a qubit during state-destroying operations on an adjacent qubit at a few micrometers distance.

Protecting qubits from accidental measurements is essential for controlled quantum operations, especially during state-destroying measurements or resets on adjacent qubits, in protocols like quantum error correction. Current methods to preserve atomic qubits against such disturbances waste coherence time, extra qubits, and introduce additional errors. We demonstrate the feasibility of in-situ state-reset and state-measurement of trapped ions, achieving  >99.9% fidelity in preserving an 'asset' ion-qubit while a neighboring 'process' qubit is reset, and  >99.6% preservation fidelity while applying a detection beam for 11 μs on the same neighbor at a distance of 6 μm. This is achieved through precise wavefront control of addressing optical beams and using a single ion as both a quantum sensor for optical aberrations and an intensity probe with  >50 dB dynamic range. Our demonstrations advance quantum processors, enhancing speed and capabilities for tasks like quantum simulations of dissipation and measurement-driven phases, and implementing error correction.