Trapped-ion quantum simulation of excitation transport: disordered, noisy, and long-range connected quantum networks

The transport of excitations governs fundamental properties of matter. Particularly rich physics emerges in the interplay between disorder and environmental noise, even in small systems such as photosynthetic biomolecules. Counterintuitively, noise can enhance coherent quantum transport, which has been proposed as a mechanism behind the high transport efficiencies observed in photosynthetic complexes. This effect has been called "environmental-assisted quantum transport" (ENAQT). Here, we propose a quantum simulation of the excitation transport in an open quantum network, taking advantage of the high controllability of current trapped-ion experiments. Our scheme allows for the controlled study of various different aspects of the excitation transfer, ranging from the influence of static disorder and interaction range, over the effect of Markovian and non-Markovian dephasing, to the impact of a continuous insertion of excitations. Our proposal discusses experimental error sources and realistic parameters, showing that it can be implemented in state-of-the-art ion-chain experiments.Comment: 14 pages, 11 figure

Dynamics, dephasing and clustering of impurity atoms in Bose-Einstein condensates

We investigate the influence of a Bose-Einstein condensate (BEC) on the properties of immersed impurity atoms, which are trapped in an optical lattice. Assuming a weak coupling of the impurity atoms to the BEC, we derive a quantum master equation for the lattice system. In the special case of fixed impurities with two internal states the atoms represent a quantum register and the quantum master equation reproduces the exact evolution of the qubits. We characterise the qubit dephasing which is caused by the interspecies coupling and show that the effect of sub- and superdecoherence is observable for realistic experimental parameters. Furthermore, the BEC phonons mediate an attractive interaction between the impurities, which has an important impact on their spatial distribution. If the lattice atoms are allowed to move, there occurs a sharp transition with the impurities aggregating in a macroscopic cluster at experimentally achievable temperatures. We also investigate the impact of the BEC on the transport properties of the impurity atoms and show that a crossover from coherent to diffusive behaviour occurs with increasing interaction strength.Comment: 22 pages, 8 figures, some typos correcte

Single-Atom Resolved Imaging and Manipulation in an Atomic Mott Insulator

This thesis reports on new experimental techniques for the study of strongly correlated states of ultracold atoms in optical lattices. We used a high numerical aperture imaging system to probe 87Rb atoms in a two-dimensional lattice with single-site resolution. Fluorescence imaging allows to detect single atoms with a large signal to noise ratio and to reconstruct the atom distribution on the lattice. We applied this new technique to a two-dimensional Mott insulator and directly observed number squeezing and the emerging shell structure. A comparison of the radial density and variance distributions to theory provides a precise in situ temperature and entropy measurement from single images. We find entropies around the critical value for quantum magnetism. In a second series of experiments, we demonstrated two-dimensional single-site spin control in the optical lattice. The differential light shift of a tightly focused laser beam shifts selected atoms into resonance with a microwave field driving a spin flip. In this way, we reach sub-diffraction limited spatial resolution well below the lattice spacing. Starting from a Mott insulator with unity filling we were able to create arbitrary spin patterns. We used this ability to prepare atom distributions to study one-dimensional single-particle tunneling dynamics in a lattice. By discriminating the dynamics of the ground state and of the first excited band, we find that our addressing scheme leaves most atoms in the vibrational ground state. Moreover, we studied coherent light scattering from the atoms in the optical lattice and found diffraction maxima in the far-field. We showed that an antiferromagnetic order leads to additional diffraction peaks which can be used to detect this order also when single-site resolution is not available. The new techniques described in this thesis open the path to a wide range of novel applications from quantum dynamics of spin impurities, entropy transport, implementation of novel cooling schemes, and engineering of quantum many-body phases to quantum information processing.In dieser Arbeit werden neue experimentelle Techniken für die Untersuchung von stark korrelierten Zuständen von ultrakalten Atomen in optischen Gittern vorgestellt. Wir untersuchen 87Rb Atome in einem zwei-dimensionalen Gitter und erreichen dabei eine Auflösung der einzelnen Gitterplätze mit Hilfe eines hochauflösenden Abbildungssystems. Fluoreszenzabbildung erlaubt es, einzelne Atome mit großem Signal-zu-Rausch-Verhältnis zu detektieren und die Verteilung der Atome auf dem Gitter zu rekonstruieren. Wir wenden diese neue Technik auf einen zwei-dimensionalen Mott-Isolator an and beobachten direkt das number squeezing und die Schalenstrukur. Ein Vergleich der radialen Dichte- und Varianzverteilung mit der Theorie ermöglicht eine präzise Temperatur- und Entropiemessung an einzelnen Bildern und wir finden Entropien um den kritischen Wert für Quantenmagnetismus. In einer zweiten Reihe von Experimenten zeigen wir, dass wir gezielt einzelne atomare Spinzustände im Gitter manipulieren können ohne die benachbarten Atome zu beeinflussen. Wir benutzen den differentiellen light shift eines stark fokussierten Laserstrahls, um einzelne Atome in Resonanz mit einem Mikrowellenfeld zu bringen, das den Spin umklappt. Auf diese Weise erreichen wir eine Ortsauflösung unter der Beugungsgrenze. Wir beginnen mit einem Mott-Isolator mit einem Atom pro Gitterplatz und können darin beliebige Spinmuster erzeugen. Diese neuen Möglichkeiten zur Präparation atomarer Verteilungen nutzen wir, um die eindimensionale Einteilchen-Tunneldynamik in einem Gitter zu untersuchen. Wir unterscheiden die Dynamik von Atomen im Grundzustand und im ersten angeregten Band und zeigen so, dass unser Adressierschema die meisten Atome im Grundzustand lässt. Darüber hinaus untersuchen wir kohärente Lichtstreuung an den Atomen im Gitter und finden Beugungsmaxima im Fernfeld. Wir zeigen, dass eine antiferromagnetische Ordnung der Atome zu zusätzlichen Beugungsmaxima führt, die man auch ohne unsere hohe Auflösung zum Nachweis dieser Ordnung nutzen könnte. Die neuen Techniken, die in dieser Arbeit vorgestellt werden, öffnen den Weg für viele neue Anwendungen von der Quantendynamik von Spin-Defekten, Entropietransport, der Umsetzung neuer Kühlschemata sowie der Realisierung von Quanten-Vielteilchenphasen bis hin zur Quanteninformationsverarbeitung

Scrambling and thermalization in a diffusive quantum many-body system

Out-of-time ordered (OTO) correlation functions describe scrambling of information in correlated quantum matter. They are of particular interest in incoherent quantum systems lacking well defined quasi-particles. Thus far, it is largely elusive how OTO correlators spread in incoherent systems with diffusive transport governed by a few globally conserved quantities. Here, we study the dynamical response of such a system using high-performance matrix-product-operator techniques. Specifically, we consider the non-integrable, one-dimensional Bose-Hubbard model in the incoherent high-temperature regime. Our system exhibits diffusive dynamics in time-ordered correlators of globally conserved quantities, whereas OTO correlators display a ballistic, light-cone spreading of quantum information. The slowest process in the global thermalization of the system is thus diffusive, yet information spreading is not inhibited by such slow dynamics. We furthermore develop an experimentally feasible protocol to overcome some challenges faced by existing proposals and to probe time-ordered and OTO correlation functions. Our study opens new avenues for both the theoretical and experimental exploration of thermalization and information scrambling dynamics.Comment: 7+4 pages, 8+3 figures; streamlined versio

Tactical Electronics Simulation Test System: Final Report CDRL A004

Report addresses the preliminary findings of the Tactical Electronics Simulation Test System (TESTS) Phase I effort: Requirements Analysis and Feasibility Assessment, involving requirements for an advanced identification friend or foe (IFF) simulation environment, existing applicable and available facilities and resources for subsequent project phases, technical issues and concerns to minimize risk, and technical approach and conceptual design for an advanced IFF system and environment simulation leading to TESTS

Anyonic interferometry and protected memories in atomic spin lattices

Strongly correlated quantum systems can exhibit exotic behavior called topological order which is characterized by non-local correlations that depend on the system topology. Such systems can exhibit remarkable phenomena such as quasi-particles with anyonic statistics and have been proposed as candidates for naturally fault-tolerant quantum computation. Despite these remarkable properties, anyons have never been observed in nature directly. Here we describe how to unambiguously detect and characterize such states in recently proposed spin lattice realizations using ultra-cold atoms or molecules trapped in an optical lattice. We propose an experimentally feasible technique to access non-local degrees of freedom by performing global operations on trapped spins mediated by an optical cavity mode. We show how to reliably read and write topologically protected quantum memory using an atomic or photonic qubit. Furthermore, our technique can be used to probe statistics and dynamics of anyonic excitations.Comment: 14 pages, 6 figure

Predicting Jamming Systems Frequency Hopping Sequences Using Artificial Neural Networks

This work proposes a neural network architecture that was designed to predict and reverse engineer frequency hopping jamming systems. The neural network was initially optimized for use with a 12th order linear shift feedback register maximum length sequence utilizing a minimal polynomial as the characteristic polynomial. This neural network was then scaled to accommodate 7 different sequences, of orders 6 through 12. The neural network was trained for these sequences using training data that is 10 times the length of the sequence. This information is then used to generate a hopping sequence that reduces the jamming interference to 0 with as few as 4 jammer hopping samples. The model is also capable of determining if the jammer is utilizing a sequence that the model is trained for in as few as 25 jammer hopping samples