Coherent State Evolution in a Superconducting Qubit from Partial-Collapse Measurement

TLDR

Measurement is a fundamental building block of quantum‑information processing, and partial measurement—where the wavefunction does not fully collapse—provides a detailed test of the measurement process. The authors aim to introduce quantum‑state tomography on a superconducting qubit that enables high‑fidelity single‑shot measurement. They perform quantum‑state tomography on the qubit to analyze partial‑collapse measurement outcomes. They observe that partial measurement yields either a full collapse or a coherent, nonunitary evolution of the state, confirming modern quantum‑measurement theory and suggesting implications for error‑correction algorithms.

Abstract

Measurement is one of the fundamental building blocks of quantum-information processing systems. Partial measurement, where full wavefunction collapse is not the only outcome, provides a detailed test of the measurement process. We introduce quantum-state tomography in a superconducting qubit that exhibits high-fidelity single-shot measurement. For the two probabilistic outcomes of partial measurement, we find either a full collapse or a coherent yet nonunitary evolution of the state. This latter behavior explicitly confirms modern quantum-measurement theory and may prove important for error-correction algorithms in quantum computation.