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1. Quantum interference in atom-exchange reactions

   https://doi.org/10.1126/science.adl6570  

   Liu, Yi-Xiang; Zhu, Lingbang; Luke, Jeshurun; Houwman, J_J Arfor; Babin, Mark C; Hu, Ming-Guang; Ni, Kang-Kuen (June 2024, Science)

   Chemical reactions, in which bonds break and form, are highly dynamic quantum processes. A fundamental question is whether coherence can be preserved in chemical reactions and then harnessed to generate entangled products. Here we investigated this question by studying the 2KRb $\to$ ${\text{K}}_2$+ Rb₂reaction at 500 nanokelvins, focusing on the nuclear spin degrees of freedom. We prepared the initial nuclear spins in KRb (potassium-rubidium) in an entangled state by lowering the magnetic field to where the spin-spin interaction dominates and characterized the preserved coherence in nuclear spin wave function after the reaction. We observed an interference pattern that is consistent with full coherence at the end of the reaction, suggesting that entanglement prepared within the reactants could be redistributed through the atom-exchange process. 

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2. Decoupling dipolar interactions in dense spin ensembles

   https://doi.org/10.1103/PhysRevResearch.7.023171  

   Joseph, Linta; Alford, Wynter; Ramanathan, Chandrasekhar (May 2025, Physical Review Research)

   Dense spin ensembles in solids present a natural platform for studying quantum many-body dynamics. Multiple-pulse coherent control can be used to manipulate the magnetic dipolar interaction between the spins to engineer their dynamics. Here, we investigate the performance of a series of well-known pulse sequences that aim to suppress interspin dipolar couplings. We use a combination of numerical simulations and solid-state nuclear magnetic resonance experiments on adamantane to evaluate and compare sequence performance. We study the role of sequence parameters like interpulse delays and resonance offsets. Disagreements between experiments and theory are typically explained by the presence of control errors and experimental nonidealities. The simulations allow us to explore the influence of factors such as finite pulse widths, rotation errors, and phase transient errors. We also investigate the role of local disorder and establish that it is, perhaps unsurprisingly, a distinguishing factor in the decoupling efficiency of spectroscopic sequences (that preserve Hamiltonian terms proportional to $S_z$) and time-suspension sequences (which refocus all terms in the internal Hamiltonian). We discuss our findings in the context of previously known analytical results from average Hamiltonian theory. Finally, we explore the ability of time-suspension sequences to protect multispin correlations in the system. Published by the American Physical Society2025 

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3. Measurements of polarization and spin correlation and observation of entanglement in top quark pairs using $\mathrm{lepton}+\text{jets}$ events from proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$

   https://doi.org/10.1103/PhysRevD.110.112016  

   Hayrapetyan, A; Tumasyan, A; Adam, W; Andrejkovic, J W; Benato, L; Bergauer, T; Chatterjee, S; Damanakis, K; Dragicevic, M; Hussain, P S; et al (December 2024, Physical Review D)

   Measurements of the polarization and spin correlation in top quark pairs ( $t\overline{t}$) are presented using events with a single electron or muon and jets in the final state. The measurements are based on proton-proton collision data from the LHC at $\sqrt{s}=13\mathrm{TeV}$collected by the CMS experiment, corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$. All coefficients of the polarization vectors and the spin correlation matrix are extracted simultaneously by performing a binned likelihood fit to the data. The measurement is performed inclusively and in bins of additional observables, such as the mass of the $t\overline{t}$system and the top quark scattering angle in the $t\overline{t}$rest frame. The measured polarization and spin correlation are in agreement with the standard model. From the measured spin correlation, conclusions on the $t\overline{t}$spin entanglement are drawn by applying the Peres-Horodecki criterion. The standard model predicts entangled spins for $t\overline{t}$states at the production threshold and at high masses of the $t\overline{t}$system. Entanglement is observed for the first time in events at high $t\overline{t}$mass, where a large fraction of the $t\overline{t}$decays are spacelike separated, with an expected and observed significance of above 5 standard deviations. © 2024 CERN, for the CMS Collaboration2024CERN 

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4. Universal coarse geometry of spin systems

   https://doi.org/10.1007/s11005-025-01949-6  

   Elokl, Ali; Jones, Corey (June 2025, Letters in Mathematical Physics)

   Abstract The prospect of realizing highly entangled states on quantum processors with fundamentally different hardware geometries raises the question: to what extent does a state of a quantum spin system have an intrinsic geometry? In this paper, we propose that both states and dynamics of a spin system have a canonically associatedcoarse geometry, in the sense of Roe, on the set of sites in the thermodynamic limit. For a state$$\phi $$ $\varphi$on an (abstract) spin system with an infinite collection of sitesX, we define a universal coarse structure$$\mathcal {E}_{\phi }$$ $E_{\varphi }$on the setXwith the property that a state has decay of correlations with respect to a coarse structure$$\mathcal {E}$$ $E$onXif and only if$$\mathcal {E}_{\phi }\subseteq \mathcal {E}$$ $E_{\varphi }\subseteq E$. We show that under mild assumptions, the coarsely connected completion$$(\mathcal {E}_{\phi })_{con}$$ ${\left(E_{\varphi }\right)}_{\mathrm{con}}$is stable under quasi-local perturbations of the state$$\phi $$ $\varphi$. We also develop in parallel a dynamical coarse structure for arbitrary quantum channels, and prove a similar stability result. We show that several order parameters of a state only depend on the coarse structure of an underlying spatial metric, and we establish a basic compatibility between the dynamical coarse structure associated with a quantum circuit$$\alpha $$ $\alpha$and the coarse structure of the state$$\psi \circ \alpha $$ $\psi \circ \alpha$where$$\psi $$ $\psi$is any product state. 

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5. Thermodynamic Evidence of Fermionic Behavior in the Vicinity of One-Ninth Plateau in a Kagome Antiferromagnet

   https://doi.org/10.1103/PhysRevX.15.021076  

   Zheng, Guoxin; Zhang, Dechen; Zhu, Yuan; Chen, Kuan-Wen; Chan, Aaron; Jenkins, Kaila; Kang, Byungmin; Zeng, Zhenyuan; Xu, Aini; Ratkovski, D; et al (May 2025, Physical Review X)

   The spin- $1/2$kagome Heisenberg antiferromagnets are believed to host exotic quantum entangled states. Recently, the reports of $1/9$magnetization plateau and magnetic oscillations in a kagome antiferromagnet ${\mathrm{YCu}}_3{\left(\mathrm{OH}\right)}_6{\mathrm{Br}}_2\left[{\text{Br}}_x{\left(\mathrm{OH}\right)}_{1-x}\right]$(YCOB) have made this material a promising candidate for experimentally realizing quantum spin liquid states. Here, we present measurements of the specific heat $C_p$in YCOB in high magnetic fields (up to 41.5 T) down to 0.46 K, and the $1/9$plateau feature has been confirmed. Moreover, the temperature dependence of $C_p/T$in the vicinity of $1/9$plateau region can be fitted by a linear in $T$term which indicates the presence of a Dirac spectrum, together with a constant term, which indicates a finite density of states contributed by other spinon Fermi surfaces. Surprisingly, the constant term is highly anisotropic in the direction of the magnetic field. Additionally, we observe a double-peak feature near 30 T above the $1/9$plateau which is another hallmark of fermionic excitations in the specific heat. This combination of gapless behavior and the double-peak structure strongly suggests that the $1/9$plateau in YCOB is nontrivial and hosts fermionic quasiparticles. 

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