Observing quantum measurement collapse as a learnability phase transition

TL;DR

This paper experimentally observes a phase transition in quantum measurement processes, showing how measurement strength influences the emergence of classical-like collapse behavior in a quantum system.

Contribution

It provides the first experimental evidence of a measurement-induced phase transition in a trapped-ion quantum processor, linking measurement strength to information gain and uncertainty.

Findings

Observation of a sharp transition in measurement-induced phase behavior

Demonstration of algorithms to detect the transition without post-selection

Insights into measurement effects on quantum information in noisy hardware

Abstract

The mechanism by which an effective macroscopic description of quantum measurement in terms of discrete, probabilistic collapse events emerges from the reversible microscopic dynamics remains an enduring open question. Emerging quantum computers offer a promising platform to explore how measurement processes evolve across a range of system sizes while retaining coherence. Here, we report the experimental observation of evidence for an observable-sharpening measurement-induced phase transition in a chain of trapped ions in Quantinuum H1-1 system model quantum processor. This transition manifests as a sharp, concomitant change in both the quantum uncertainty of an observable and the amount of information an observer can (in principle) learn from the measurement record, upon increasing the strength of measurements. We leverage insights from statistical mechanical models and machine learning to design efficiently-computable algorithms to observe this transition (without non-scalable post-selection on measurement outcomes) and to mitigate the effects on errors in noisy hardware.