Emergent pair localization in a many-body quantum spin system

Understanding how closed quantum systems dynamically approach thermal equilibrium presents a major unresolved problem in statistical physics. Generically, non-integrable quantum systems are expected to thermalize as they comply with the Eigenstate Thermalization Hypothesis. However, in the presence of strong disorder, the dynamics can possibly slow down to a degree that systems fail to thermalize on experimentally accessible timescales, as in spin glasses or many-body localized systems. In general, particularly in long-range interacting quantum systems, the specific nature of the disorder necessary for the emergence of a prethermal, metastable state--distinctly separating the timescales of initial relaxation and subsequent slow thermalization--remains an open question. We study an ensemble of Heisenberg spins with a tunable distribution of random coupling strengths realized by a Rydberg quantum simulator. We observe a drastic change in the late-time magnetization when increasing disorder strength. The data is well described by models based on pairs of strongly interacting spins, which are treated as thermal for weak disorder and isolated for strong disorder. Our results indicate a crossover into a pair-localized prethermal regime in a closed quantum system of thousands of spins in the critical case where the exponent of the power law interaction matches the spatial dimension

Quantum Feature Maps for Graph Machine Learning on a Neutral Atom Quantum Processor

Using a quantum processor to embed and process classical data enables the generation of correlations between variables that are inefficient to represent through classical computation. A fundamental question is whether these correlations could be harnessed to enhance learning performances on real datasets. Here, we report the use of a neutral atom quantum processor comprising up to $32$ qubits to implement machine learning tasks on graph-structured data. To that end, we introduce a quantum feature map to encode the information about graphs in the parameters of a tunable Hamiltonian acting on an array of qubits. Using this tool, we first show that interactions in the quantum system can be used to distinguish non-isomorphic graphs that are locally equivalent. We then realize a toxicity screening experiment, consisting of a binary classification protocol on a biochemistry dataset comprising $286$ molecules of sizes ranging from $2$ to $32$ nodes, and obtain results which are comparable to those using the best classical kernels. Using techniques to compare the geometry of the feature spaces associated with kernel methods, we then show evidence that the quantum feature map perceives data in an original way, which is hard to replicate using classical kernels

Financial Risk Management on a Neutral Atom Quantum Processor

Machine Learning models capable of handling the large datasets collected in the financial world can often become black boxes expensive to run. The quantum computing paradigm suggests new optimization techniques, that combined with classical algorithms, may deliver competitive, faster and more interpretable models. In this work we propose a quantum-enhanced machine learning solution for the prediction of credit rating downgrades, also known as fallen-angels forecasting in the financial risk management field. We implement this solution on a neutral atom Quantum Processing Unit with up to 60 qubits on a real-life dataset. We report competitive performances against the state-of-the-art Random Forest benchmark whilst our model achieves better interpretability and comparable training times. We examine how to improve performance in the near-term validating our ideas with Tensor Networks-based numerical simulations.Comment: 17 pages, 11 figures, 2 tables, revised versio

Microwave engineering of programmable X X Z Hamiltonians in arrays of Rydberg atoms

We use the resonant dipole-dipole interaction between Rydberg atoms and a periodic external microwave field to engineer XXZ spin Hamiltonians with tunable anisotropies. The atoms are placed in one-dimensional (1D) and two-dimensional (2D) arrays of optical tweezers. As illustrations, we apply this engineering to two iconic situations in spin physics: the Heisenberg model in square arrays and spin transport in 1D. We first benchmark the Hamiltonian engineering for two atoms and then demonstrate the freezing of the magnetization on an initially magnetized 2D array. Finally, we explore the dynamics of 1D domain-wall systems with both periodic and open boundary conditions. We systematically compare our data with numerical simulations and assess the residual limitations of the technique as well as routes for improvement. The geometrical versatility of the platform, combined with the flexibility of the simulated Hamiltonians, opens up exciting prospects in the fields of quantum simulation, quantum information processing, and quantum sensing.This work is supported by the European Union (EU) Horizon 2020 research and innovation program “Programmable Atomic Large-Scale Quantum Simulation” (PASQuanS) under Grant Agreement No. 817482, the Agence National de la Recherche (ANR, project RYBOTIN), the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy EXC2181/1-390900948 (the Heidelberg STRUCTURES Excellence Cluster), within the Collaborative Research Center SFB1225 (ISOQUANT), the DFG Priority Program 1929 “GiRyd” (DFG WE2661/12-1), and by the Heidelberg Center for Quantum Dynamics. C.H. acknowledges funding from the Alexander von Humboldt foundation, T.F. from a graduate scholarship of the Heidelberg University (LGFG), and D.B. from the Ramón y Cajal program (RYC2018-025348-I). F.W. is partially supported by the Erasmus+ program of the EU. We also acknowledge support by the state of Baden-Württemberg through Baden-Württemberg high performance computing (bwHPC) and the DFG through Grant No. INST 40/575-1 FUGG (JUSTUS 2 cluster).Peer reviewe

Coherent manipulations of elliptic Rydberg states through quantum Zeno dynamics

Dans ce mémoire, nous décrivons la réalisation d'un nouveau montage expérimental permettant de manipuler, à l'aide d'un champ radiofréquence de polarisation bien définie, l'état interne d'un atome de Rydberg à l'intérieur de la multiplicité Stark. Nous avons utilisé ce dispositif pour transférer, avec une efficacité proche de 1, les atomes depuis un niveau de faible moment angulaire, accessible par excitation optique depuis le fondamental, vers le niveau de Rydberg circulaire, de moment angulaire maximal. Nous avons ensuite cherché à induire des dynamiques quantiques nouvelles de l'état de l'atome et mis en évidence la dynamique Zénon quantique dans un système de grande dimension. En appliquant un champ micro-onde bien choisi, on peut restreindre l'évolution atomique induite par le champ radiofréquence à un sous-ensemble des niveaux Stark de la multiplicité. Cette dynamique confinée est très différente d'une dynamique classique, le système évoluant périodiquement vers un état " chat de Schrödinger ". Nous avons expérimentalement observé cette évolution dans l'espace des phases et mesuré la fonction de Wigner de l'atome au moment de l'apparition du chat, démontrant pour la première fois les aspects non-classiques de la dynamique Zénon quantique dans un espace de Hilbert non-trivial.In this manuscript, we describe the realization of a new experimental setupto manipulate with a well-polarized radiofrequency electric field the internal state of aRydberg atom inside the Stark manifold. We used this setup to transfer with a nearly 1efficiency the atoms from a optically-accessible low-m state to the high angular momentumcircular Rydberg state. We then tried to induce new quantum dynamics of the atomicstate and we showed the quantum Zeno dynamics in a large Hilbert space. By applying awell-choose microwave field, one can restrict the atomic evolution induced by the radiofrequencyfield to a subspace of the Stark manifold. This confined dynamics is very differentfrom a classical dynamics. The system periodically evolves to a « Schrödinger cat state ».We experimentally observed this evolution in the phase space and mesured the atomicWigner function at the cat state . This is the first demonstration of the non-classicalaspect of the quantum Zeno dynamics in a non-trivial Hilbert space

Manipulations cohérentes d'états de Rydberg elliptiques par dynamique Zénon quantique

In this manuscript, we describe the realization of a new experimental setupto manipulate with a well-polarized radiofrequency electric field the internal state of aRydberg atom inside the Stark manifold. We used this setup to transfer with a nearly 1efficiency the atoms from a optically-accessible low-m state to the high angular momentumcircular Rydberg state. We then tried to induce new quantum dynamics of the atomicstate and we showed the quantum Zeno dynamics in a large Hilbert space. By applying awell-choose microwave field, one can restrict the atomic evolution induced by the radiofrequencyfield to a subspace of the Stark manifold. This confined dynamics is very differentfrom a classical dynamics. The system periodically evolves to a « Schrödinger cat state ».We experimentally observed this evolution in the phase space and mesured the atomicWigner function at the cat state . This is the first demonstration of the non-classicalaspect of the quantum Zeno dynamics in a non-trivial Hilbert space.Dans ce mémoire, nous décrivons la réalisation d'un nouveau montage expérimental permettant de manipuler, à l'aide d'un champ radiofréquence de polarisation bien définie, l'état interne d'un atome de Rydberg à l'intérieur de la multiplicité Stark. Nous avons utilisé ce dispositif pour transférer, avec une efficacité proche de 1, les atomes depuis un niveau de faible moment angulaire, accessible par excitation optique depuis le fondamental, vers le niveau de Rydberg circulaire, de moment angulaire maximal. Nous avons ensuite cherché à induire des dynamiques quantiques nouvelles de l'état de l'atome et mis en évidence la dynamique Zénon quantique dans un système de grande dimension. En appliquant un champ micro-onde bien choisi, on peut restreindre l'évolution atomique induite par le champ radiofréquence à un sous-ensemble des niveaux Stark de la multiplicité. Cette dynamique confinée est très différente d'une dynamique classique, le système évoluant périodiquement vers un état " chat de Schrödinger ". Nous avons expérimentalement observé cette évolution dans l'espace des phases et mesuré la fonction de Wigner de l'atome au moment de l'apparition du chat, démontrant pour la première fois les aspects non-classiques de la dynamique Zénon quantique dans un espace de Hilbert non-trivial

Elastic Scattering Time of Matter Waves in Disordered Potentials

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Realisation of relaxed static stability on a commercial transport

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