Experimental realization of an ideal Floquet disordered system

The atomic Quantum Kicked Rotor is an outstanding "quantum simulator" for the exploration of transport in disordered quantum systems. Here we study experimentally the phase-shifted quantum kicked rotor, which we show to display properties close to an ideal disordered quantum system, opening new windows into the study of Anderson physics.Comment: 10 pages, 7 figures, submitted to New Journal of Physics focus issue on Quantum Transport with Ultracold Atom

Controlling symmetry and localization with an artificial gauge field in a disordered quantum system

Anderson localization, the absence of diffusion in disordered media, draws its origins from the destructive interference between multiple scattering paths. The localization properties of disordered systems are expected to be dramatically sensitive to their symmetry characteristics. So far however, this question has been little explored experimentally. Here, we investigate the realization of an artificial gauge field in a synthetic (temporal) dimension of a disordered, periodically-driven (Floquet) quantum system. Tuning the strength of this gauge field allows us to control the time-reversal symmetry properties of the system, which we probe through the experimental observation of three symmetry-sensitive `smoking-gun' signatures of localization. The first two are the coherent backscattering, marker of weak localization, and the coherent forward scattering, genuine interferential signature of Anderson localization, observed here for the first time. The third is the direct measurement of the $\beta(g)$ scaling function in two different symmetry classes, allowing to demonstrate its universality and the one-parameter scaling hypothesis

Experimental observation of time singularity in classical-to-quantum chaos transition

The emergence of chaotic phenomena in a quantum system has long been an elusive subject. Experimental progresses in this subject have become urgently needed in recent years, when considerable theoretical studies have unveiled the vital roles of chaos in a broad range of topics in quantum physics. Here, we report the first experimental observation of time singularity, that signals a classical-to-quantum chaos transition and finds its origin in the {\it sudden change} in system's memory behaviors. The time singularity observed is an analog of the "dynamical quantum phase transition" (DQPT) -- proposed very recently for regular systems -- in chaotic systems, but with totally different physical origin.Comment: 8 pages, 5 figure

Observation of universal relaxation dynamics in disordered quantum spin systems

A major goal toward understanding far-from-equilibrium dynamics of quantum many-body systems consists in finding indications of universality in the sense that the dynamics no longer depends on microscopic details of the system. We realize a large range of many-body spin systems on a Rydberg atom quantum simulator by choosing appropriate Rydberg state combinations. We use this platform to compare the magnetization relaxation dynamics of disordered Heisenberg XX-, XXZ- and Ising Hamiltonians in a scalable fashion. After appropriate rescaling of evolution time, the dynamics collapse onto a single curve. We find that the observed universal behavior is captured by theoretical models that only consider local pairs of spins. Associated to each pair is a local quasi-conserved quantity, allowing us to describe the early time dynamics of the system in terms of an integrable model similar to systems featuring prethermalization. Since the dynamics of pairs are independent of the type of Hamiltonian up to a scaling factor, this integrable model explains the observed universal relaxation dynamics of disordered Heisenberg quantum spin systems

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

Symmetry effect on localization in disordered quantum systems

Dans cette thèse, nous utilisons le Kicked Rotor, paradigme du chaos quantique, pour d’étudier certains aspects nouveaux de de la physique des systèmes désordonnés. Nous apportons ainsi la première observation expérimentale, avec des ondes de matières atomiques, d’un phénomène lié à la localisation faible qui est l’augmentation de la probabilité de retour à l’origine. Nous montrons également que ce phénomène peut être utilisé comme outil précis de diagnostique de la décohérence dans le système. Nous présentons une nouvelle méthode expérimentale, pour contrôler les propriétés de symétries du Kicked Rotor. Cela nous permet de créer un système désordonné dans lesquel il existe un flux Aharonov-Bohm artificiel non trivial dans une dimension synthétique. Cela nous offre l’opportunité de briser la symétrie par renversement du temps et d’étudier la physique de la localisation d’Anderson dans deux classes d’universalités différentes : la classe orthogonale et la classe unitaire. Nous avons investigué l’effet de cette brisure de symétrie sur les propriétés des systèmes désordonnés 1D en regardant deux signatures du transport quantique.Nous observons ainsi pour la première fois expérimentalement, l’effet de Coherent Forward Scattering, récemment prédit, qui constitue un nouveau marqueur interférientiel de la localisation d’Anderson. Nous mettons en évidence ses signatures caractéristiques et nous trouvons qu’elles sont en très bon accord avec les prédictions théoriques. Enfin, nous réalisons les premières mesures expérimentales des fonctions d’échelles (G), dans les deux classes de symétries et nous démontrons leur universalité.In this thesis, we use the Kicked Rotor, paradigm of quantum chaos, to study new physical aspects of disordered systems.We thus present the first experimental observation with atomic matter wave of a phenomenon directly linked to weak localization which is the Enhanced Return to the Origin. We show that this effect can be used as a tool to measure accuratly the decoherence in the system. We present a novel, outstandingly simple, experimental method to control symmetry properties of the Kicked Rotor. This allows us to study a disordered system in presence of a non-trivial artificial Aharonov-Bohm flux in a synthetic dimension. This gives us the opportunity to break the time reversal symmetry and then to study the physics of Anderson localization in two different symmetry classes : the orthogonal class and the unitary class. We have investigated the effect of this symmetry breaking on physical properties of 1D disordered systems by looking two signatures of quantum transport. We observe thus experimentally, for the first time, the Coherent Forward Scattering effect, predicted recently and which represents a novel genuine signature of Anderson localization. We show its distinctive signatures and a good agreement with theoretical predictions. Finally, we realise the first experimental measurements of the (G) scaling function, characteristic of transport in disordered medium, in two symmetry classes and we demonstrate their universality

Effets des symétries sur la localisation dans des systèmes quantiques désordonnés

Contrary to the classical case, transport of a quantum particle in a disorderedmedium is strongly affected by interference effects. For exemple, in dimension 1, classicaldiffusion is initialy reduced by weak localization effects and, at long times, lead to the socalled Anderson localization phénomenon. In this thesis, we use the Kicked Rotor, paradigmof quantum chaos, to study new physical aspects of disordered systems. We thus present thefirst experimental observation with atomic matter wave of a phenomenon directly linked toweak localization which is the Enhanced Return to the Origin. We show that this effect canbe used as a tool to measure accuratly the decoherence in the system. We present a novel,outstandingly simple, experimental method to control symmetry properties of the KickedRotor. This allows us to study a disordered system in presence of a non-trivial artificialAharonov-Bohm flux in a synthetic dimension. This gives us the opportunity to break thetime reversal symmetry and then to study the physics of Anderson localization in two differentsymmetry classes : the orthogonal class and the unitary class. We have investigated the effectof this symmetry breaking on physical properties of 1D disordered systems by looking twosignatures of quantum transport. We observe thus experimentally, for the first time, theCoherent Forward Scattering effect, predicted recently and which represents a novel genuinesignature of Anderson localization. We show its distinctive signatures and a good agreementwith theoretical predictions. Finally, we realise the first experimental measurements of theβ(G) scaling function, characteristic of transport in disordered medium, in two symmetryclasses. furthermore, we demonstrate their universality confirming thus the one-parameterscaling hypothesis.Contrairement au cas classique, le transport d’une particule quantique dans unmilieu désordonné est fortement affecté par des effets d’interférences. Par exemple, en dimension1, la diffusion classique est réduite initialement par des effets de localisation faible jusqu’às’annuler totalement aux temps longs, ce qui représente le célèbre phénomène de localisationd’Anderson. Dans cette thèse, nous utilisons le Kicked Rotor, paradigme du chaos quantique,pour étudier certains aspects nouveaux de la physique des systèmes désordonnés. Nous apportonsainsi la première observation expérimentale, avec des ondes de matière atomique, d’unphénomène lié à la localisation faible qui est l’augmentation de la probabilité de retour àl’origine. Nous montrons également que ce phénomène peut être utilisé comme outil précis dediagnostic de la décohérence dans le système. Nous présentons une nouvelle méthode expérimentale,remarquablement simple, pour contrôler les propriétés de symétries du Kicked Rotor.Cela nous permet de créer un système désordonné dans lequel il existe un flux Aharonov-Bohmartificiel non trivial dans une dimension synthétique. Cela nous offre l’opportunité de briserla symétrie par renversement du temps et d’étudier la physique de la localisation d’Andersondans deux classes d’universalité différentes : la classe orthogonale et la classe unitaire. Nousavons exploré l’effet de cette brisure de symétrie sur les propriétés physiques des systèmesdésordonnés 1D en regardant deux signatures du transport quantique.Nous observons ainsipour la première fois expérimentalement, l’effet de Coherent Forward Scattering, récemmentprédit, qui constitue un nouveau marqueur interférentiel de la localisation d’Anderson. Nousmettons en évidence ses signatures caractéristiques et nous trouvons qu’elles sont en très bonaccord avec les prédictions théoriques. Enfin, nous réalisons les premières mesures expérimentalesdes fonctions d’échelle β(G), caractéristiques du transport dans les milieux désordonnés,dans les deux classes de symétrie. Nous démontrons également leur universalité validant ainsil’hypothèse de la loi d’échelle à un paramètre