近日，奥地利科学院量子光学与量子信息研究所的Peter Zoller及其研究小组取得一项新进展。经过不懈努力，他们对量子模拟中的大尺度纠缠进行探索。相关研究成果已于2023年11月29日在国际权威学术期刊《自然》上发表。

本文基于纠缠哈密顿量(EH)作为大型子系统约化密度算子的有效描述，对纠缠进行了实验研究。研究人员在51离子可编程量子模拟器上制备了一维XXZ海森堡链的基态和激发态，并对多达20个晶格格位的子系统进行了采样高效的EH“学习”。该实验为EH的局部结构提供了令人信服的证据。据研究人员所知，这一观测标志着首次证实了Bisognano和Wichmann对量子场论的基本预测，这些预测适用于表示相关量子物质的晶格模型。

约化态采用吉布斯系综形式，空间变化的温度分布作为纠缠标志。研究结果还揭示了冯·诺伊曼纠缠熵从基态到激发态的面积定律到体积定标律的转变。该发现和方法在揭示和理解包括更高空间维度的局部相互作用的，多体问题中的纠缠方面具有广泛适用性，对实现量子优势具有重要意义。

据悉，量子纠缠是量子多体系统中的一个显著特性，在量子模拟实验中，揭示大量粒子之间的纠缠结构是量子信息科学领域所面临的一项基本挑战。

附：英文原文

Title: Exploring large-scale entanglement in quantum simulation

Author: Joshi, Manoj K., Kokail, Christian, van Bijnen, Rick, Kranzl, Florian, Zache, Torsten V., Blatt, Rainer, Roos, Christian F., Zoller, Peter

Issue&Volume: 2023-11-29

Abstract: Entanglement is a distinguishing feature of quantum many-body systems, and uncovering the entanglement structure for large particle numbers in quantum simulation experiments is a fundamental challenge in quantum information science. Here we perform experimental investigations of entanglement on the basis of the entanglement Hamiltonian (EH) as an effective description of the reduced density operator for large subsystems. We prepare ground and excited states of a one-dimensional XXZ Heisenberg chain on a 51-ion programmable quantum simulator and perform sample-efficient ‘learning’ of the EH for subsystems of up to 20 lattice sites. Our experiments provide compelling evidence for a local structure of the EH. To our knowledge, this observation marks the first instance of confirming the fundamental predictions of quantum field theory by Bisognano and Wichmann, adapted to lattice models that represent correlated quantum matter. The reduced state takes the form of a Gibbs ensemble, with a spatially varying temperature profile as a signature of entanglement. Our results also show the transition from area- to volume-law scaling of von Neumann entanglement entropies from ground to excited states. As we venture towards achieving quantum advantage, we anticipate that our findings and methods have wide-ranging applicability to revealing and understanding entanglement in many-body problems with local interactions including higher spatial dimensions.

DOI: 10.1038/s41586-023-06768-0

Source: https://www.nature.com/articles/s41586-023-06768-0