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.

Fast and high-yield fabrication of axially symmetric ion-trap needle electrodes via two step electrochemical etching.

Despite the progress in building sophisticated microfabricated ion traps, Paul traps employing needle electrodes retain their significance due to the simplicity of fabrication while producing high-quality systems suitable for quantum information processing, atomic clocks, etc. For low noise operations such as minimizing "excess micromotion," needles should be geometrically straight and aligned precisely with respect to each other. Self-terminated electrochemical etching, previously employed for fabricating ion-trap needle electrodes, employs a sensitive and time-consuming technique, resulting in a low success rate of usable electrodes. Here, we demonstrate an etching technique for the quick fabrication of straight and symmetric needles with a high success rate and a simple apparatus with reduced sensitivity to alignment imperfections. The novelty of our technique comes from using a two-step approach employing turbulent etching for fast shaping and slow etching/polishing for subsequent surface finish and tip cleaning. Using this technique, needle electrodes for an ion trap can be fabricated within a day, significantly reducing the setup time for a new apparatus. The needles fabricated via this technique have been used in our ion trap to achieve trapping lifetimes of several months.