A Geometric Quantum Speed Limit: Theoretical Insights and Photonic Implementation

TL;DR

This paper introduces a new geometric quantum speed limit based on the Bloch angle, demonstrating its theoretical properties and experimental measurement in photonic systems, offering a resource-efficient way to assess quantum dynamics.

Contribution

The paper presents a novel Bloch-angle-based quantum speed limit and experimentally measures it using photonic systems, improving resource efficiency and tightness over previous bounds.

Findings

New QSL based on Bloch angle introduced

Feasible measurement via photonic swap test demonstrated

Provides tighter bounds for quantum dynamics

Abstract

Quantum mechanics imposes a lower bound on the time required for a quantum system to reach certain given targets. In this paper, from a geometric perspective, we introduce a new quantum speed limit (QSL) based on the Bloch angle and derive the condition for it to saturate. Experimentally, we demonstrate the feasibility of measuring this QSL using a photonic system through direct Bloch angle measurements via a swap test, bypassing the need for comprehensive quantum state tomography. Compared to the existing Bloch-angle-based QSL mentioned in prior work, our QSL requires fewer computational and experimental resources and provides tighter constraints for specific dynamics. Our work underscores the Bloch angle's effectiveness in providing tighter and experimentally accessible QSLs and advances the understanding of quantum dynamics.