近日，欧洲核子研究中心（CERN）大型强子对撞机（LHC）ATLAS合作组取得一项新进展。经过不懈努力，他们在ATLAS探测器上观测到顶夸克的量子纠缠。相关研究成果已于2024年9月18日在国际权威学术期刊《自然》上发表。

本文报道了在大型强子对撞机（LHC）上产生的顶夸克-反顶夸克对事件中，对纠缠现象进行的最高能量观测。此次观测使用了质子-质子碰撞数据集，其质心能量为√s=13 TeV，积分亮度为140 fb^-1（费米巴恩的倒数），由ATLAS实验记录。通过测量单一可观测量D来检测自旋纠缠，D是根据顶夸克和反顶夸克静止系中带电轻子之间的角度推断出来的。该可观测量是在顶夸克-反顶夸克对产生阈值附近的一个狭窄区间内测量的，在此区间内预计纠缠检测会显著。

该研究中的测量是在一个用稳定粒子定义的基准相空间中进行的，以最大限度地减少蒙特卡洛事件生成器和部分子簇射模型在模拟顶夸克对产生时的局限性所带来的不确定性。在340 GeV＜m_tt＜380 GeV的范围内，测得的纠缠标志为D=0.537±0.002（统计误差）±0.019（系统误差）。观测结果与无纠缠情况相比，偏差超过五个标准差，因此构成了首次在夸克对中观测到纠缠，也是迄今为止能量最高的纠缠观测。

据悉，纠缠是量子力学的一个关键特征，在计量学、密码学、量子信息和量子计算等领域有着广泛的应用。它已在从微观到宏观的广泛系统和长度尺度上被观察到。然而，在可达到的最高能量尺度上，纠缠仍然在很大程度上未被探索。

附：英文原文

Title: Observation of quantum entanglement with top quarks at the ATLAS detector

Author: anonymous

Issue&Volume: 2024-09-18

Abstract: Entanglement is a key feature of quantum mechanics, with applications in fields such as metrology, cryptography, quantum information and quantum computation. It has been observed in a wide variety of systems and length scales, ranging from the microscopic to the macroscopic. However, entanglement remains largely unexplored at the highest accessible energy scales. Here we report the highest-energy observation of entanglement, in top–antitop quark events produced at the Large Hadron Collider, using a proton–proton collision dataset with a centre-of-mass energy of √s=13TeV and an integrated luminosity of 140inverse femtobarns (fb)^-1 recorded with the ATLAS experiment. Spin entanglement is detected from the measurement of a single observable D, inferred from the angle between the charged leptons in their parent top- and antitop-quark rest frames. The observable is measured in a narrow interval around the top–antitop quark production threshold, at which the entanglement detection is expected to be significant. It is reported in a fiducial phase space defined with stable particles to minimize the uncertainties that stem from the limitations of the Monte Carlo event generators and the parton shower model in modelling top-quark pair production. The entanglement marker is measured to be D=0.537±0.002 (stat.)±0.019 (syst.) for 340GeV＜m_tt＜380GeV. The observed result is more than five standard deviations from a scenario without entanglement and hence constitutes the first observation of entanglement in a pair of quarks and the highest-energy observation of entanglement so far.

DOI: 10.1038/s41586-024-07824-z

Source: https://www.nature.com/articles/s41586-024-07824-z