Design and construction of a Bose Einstein condensate machine

A dilute gas Bose Einstein condensate (BEC) is a state of matter that occurs when a cloud of atoms in a potential are made cold and dense enough that they all occupy the potential\u27s ground state. The onset of this phenomenon occurs when their de Broglie wavelength, $\Lambda = \sqrt{2 \pi \hbar^2/mk_BT}$, becomes comparable in size to the inter-particle spacing. A BEC is a macroscopic quantum object, since all atoms in the BEC are described by a single quantum wavefunction and, as such, is a fundamental quantum many-body system. The first experimental demonstration of a dilute gas BEC was performed by Eric Cornell and Carl Wieman in 1995 and since then, several dozen groups around the world have achieved and study BECs. This thesis documents design and construction work performed in support of the Bose Einstein Condensate (BEC) experiment at the Los Alamos National Laboratory. The objective of the work performed was to upgrade the existing BEC machine in most of its significant subsystems to attain better experimental cycle times and BECs with a larger atom number than what was previously attainable, as well as improve the optical quality of the imaging and laser manipulation beams at the location of the BEC. These objectives were achieved through the construction of a new laser system with greater power and larger magneto-optical trap (MOT) beam diameters, a new quadrupole magnetic trap with better optical access and higher magnetic field gradients than the Ioffe-Pritchard coil configuration it replaced, and a cuvette-style quartz cell with a much higher optical quality than the hand-blown cell used previously. In addition to these improvements the feasibility of using phase-contrast imaging of the BECs created in this machine for future experimental goals was evaluated and found to be feasible

Quantum Gate Optimization for Rydberg Architectures in the Weak-Coupling Limit

We demonstrate machine learning assisted design of a two-qubit gate in a Rydberg tweezer system. Two low-energy hyperfine states in each of the atoms represent the logical qubit and a Rydberg state acts as an auxiliary state to induce qubit interaction. Utilizing a hybrid quantum-classical optimizer, we generate optimal pulse sequences that implement a CNOT gate with high fidelity, for experimentally realistic parameters and protocols, as well as realistic limitations. We show that local control of single qubit operations is sufficient for performing quantum computation on a large array of atoms. We generate optimized strategies that are robust for both the strong-coupling, blockade regime of the Rydberg states, but also for the weak-coupling limit. Thus, we show that Rydberg-based quantum information processing in the weak-coupling limit is a desirable approach, being robust and optimal, with current technology.Comment: 11 pages, 5 figure

A Rydberg tweezer platform with potassium atoms

Quantum simulation offers the possibility to study quantum mechanical problems which are untraceable on classical computers. This thesis introduces a novel platform for quantum simulation and presents the first experimental realisation of single potassium atoms trapped in optical tweezers. Interactions between individual atoms are induced by strong energy shifts of atoms excited to states with large principal quantum number, so-called Rydberg states. Either direct excitation to Rydberg states or off-resonant dressing can be used to induce these interactions. We argue that potassium is well-suited for the implementation of Rydberg dressing, enabling simultaneous dressing of both ground states to engineer complex interactions. Using techniques to cool and trap cold atoms, single potassium atoms are prepared in arrays of optical tweezers. Raman sideband cooling reduces vibrational excitations and prepares the atoms close to the motional ground state. This cooling technique mitigates severe limitations for Rydberg dressing, arising from thermal broadening and inhomogeneous light shifts in the array of atoms. To directly excite atoms to Rydberg states, a high power laser setup with two cavity-enhanced frequency doubling stages is constructed, generating up to one Watt of ulta-violet light at 286 nm. By exciting atoms to Rydberg states we observe Rabi oscillations with Rabi frequencies of up to 1 MHz, demonstrating coherent control of Rydberg atoms. Finally, we combine these techniques to observe interactions in two ways: First, we create a so-called superatom of up to four individual atoms using direct excitation and Rydberg-blockade and observe coherent oscillations to this collective state. We measure the expected square root scaling of the effective Rabi frequency with the number of individual atoms, confirming the creation of a many-body entangled state. Secondly, we off-resonantly dress the atoms prepared in a one-dimensional chain and measure correlated interaction shifts over multiple sites. In summary, we have developed a platform for quantum simulation with single atoms in optical tweezers. The presented results show coherent control of single atoms and interactions induced by Rydberg states. We have thus demonstrated that the system is well-suited for quantum simulation of many-body systems.Quantensimulationen bieten die Möglichkeit quantenmechanische Probleme zu untersuchen, welche auf klassischen Computern nicht berechenbar sind. Diese Arbeit stellt eine neue Plattform für Quantensimulationen vor und präsentiert die erste experimentelle Realisierung einzelner Kaliumatome in optischen Dipolfallen. Wechselwirkungen zwischen einzelnen neutralen Atomen werden durch die starken Energieverschiebungen von Zuständen mit großer Hauptquantenzahl verursacht, sogenannte Rydberg-Zustände. Wechselwirkungen können dabei entweder durch eine direkte Anregung in Rydberg-Zustände oder eine verstimmte optische Kopplung, so genanntes 'Rydberg dressing', erzeugt werden. Wir begründen, warum insbesondere Kalium für die Implementierung von 'Rydberg dressing' geeignet ist und insbesondere durch das gleichzeitige Koppeln beider Grundzustände das Erzeugen komplexer Wechselwirkungen ermöglicht. Kaliumatome werden mittels Laserkühlung abgebremst, gefangen und anschließend werden einzelne Atome in optischen Dipolfallen geladen. Zudem reduziert Raman Seitenbandkühlung die Schwingungsanregungen in den Fallenpotentialen und kühlt die Atome fast zum Bewegungsgrundzustand. Diese Kühltechnik ermöglicht 'Rydberg dressing', welches ansonsten durch thermische Verbreiterung und inhomogenen Fallenpotentiale limitiert wäre. Um Atome direkt in Rydberg-Zustände anzuregen, wird ein Lasersystem mit zwei resonanten Frequenz Verdopplungsstufen aufgebaut, mit welchem bis zu einem Watt ultravioletten Lichts bei 286 nm erzeugt wird. Durch Anregung von Atomen in Rydberg-Zustände beobachten wir Rabi-Oszillationen mit Rabi-Frequenzen von bis zu 1 MHz, was eine kohärente Kontrolle der Rydberg-Atome demonstriert. Zuletzt kombinieren wir diese Techniken, um Wechselwirkungen auf zwei verschiedene Arten zu beobachten: Erstens erzeugen wir durch direkte Anregung und Rydberg-Blockade ein sogenanntes 'Superatom' aus bis zu vier einzelnen Atomen und beobachten kohärente Oszillationen zu diesem kollektiven Zustand. Wir messen die erwartete Skalierung der effektiven Rabi-Frequenz mit der Wurzel der Anzahl der Atome und bestätigen die Erzeugung eines Quantenverschränkten Zustands. Zweitens induzieren wir Wechselwirkungen zwischen Atomen durch optische Beimischung mittels 'Rydberg dressing', die in einer eindimensionalen Kette optischer Dipolfallen gefangen wurden und messen korrelierte Wechselwirkungen über Distanzen von mehreren Fallenplätzen. Zusammenfassend haben wir eine Plattform für die Quantensimulation mittels einzelner Atome in optischen Dipolfallen entwickelt. Die vorgestellten Ergebnisse zeigen eine kohärente Kontrolle einzelner Atome und Wechselwirkungen, die durch Rydberg-Zustände induziert werden. Wir zeigen damit, dass das System für die Quantensimulation von Vielkörpersystemen gut geeignet ist

Controlling superparamagnetic particles with dynamic magnetic fields generated by a Helmholtz-coil system

Tese de mestrado em Engenharia Física, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2010The aim of this work was the creation of a novel system of magnetic tweezers which is surface free and makes possible the massive parallel measurement of macromolecule characteristics. The system is able to magnetically control superparamagnetic microparticles which control macromolecules, DNA strands or cells attached to them in a surface free environment, i.e. without the use of surfaces to which the objects are bond. This allows the system composed by a pair of beads and macromolecule to oat freely in the solution, allowing parallel and inside cell measurements. The system constructed is composed of two pairs of water cooled Helmholtz coils controlled by an electronic circuit and software. The system is mounted on an inverted fluorescence microscope. The magnetic forces acting on deferent types of particles were calculated and fully simulated. This allowed the optimization of the coils' parameters. In the present document we explain the physical concepts behind the behavior of the magnetic particles, the details of the design, fabrication and specifications of the control system and at the end we show and discuss some qualitative experiments made with the system.O objectivo deste trabalho foi a criação de um novo sistema de pinças magnéticas que funciona livre de superfícies e possibilita a medição paralela (ou massiva) de caracter ísticas de macromoléculas. O sistema é capaz de controlar magneticamente micropart ículas superparamagnéticas que controlam macromoléculas, pequenas sequências de DNA ou células a elas acopladas num ambiente livre de superfícies, o que significa sem o uso de um sistema físico para os fixar. Isto permite ao sistema composto por um par de partículas magnéticas e macromolécula flutuar livremente na solução, permitindo medições paralelas e dentro de células. O sistema é composto por dois pares de bobinas de Helmholtz arrefecidas a água, controladas por um sistema electrónico e um programa especificamente projectados para a função. O sistema está montado num microscópio invertido com capacidade para microscopia de fluorescência. As forças magnéticas que actuam nos diferentes tipos de micropartículas magnéticas foram calculadas e simuladas o que permitiu uma optimiza ção dos parâmetros das bobinas. No presente documento explicamos os conceitos físicos intervenientes no comportamento das partículas magnéticas, os detalhes do desenho, construção e especificações do sistema de controlo e no fim mostramos e discutimos algumas experiências qualitativas

Assembling Single RbCs Molecules with Optical Tweezers

Optical tweezer arrays are useful tools for manipulating single atoms and molecules. An exciting avenue for research with optical tweezers is using the interactions between polar molecules for quantum computation or quantum simulation. Molecules can be assembled in an optical tweezer array starting from pairs of atoms. The atoms must be initialised in the relative motional ground state of a common trap. This work outlines the design of a Raman sideband cooling protocol which is implemented to prepare an 87-Rubidium atom in the motional ground state of an 817 nm tweezer, and a 133-Caesium atom in the motional ground state of a 938 nm tweezer. The protocol circumvents strong heating and dephasing associated with the trap by operating at lower trap depths and cooling from outside the Lamb-Dicke regime. By analysing several sources of heating, we design and implement a merging sequence that transfers the Rb atom and the Cs atom to a common trap with minimal motional excitation. Subsequently, we perform a detailed characterisation of AC Stark shifts caused by the tweezer light, and identify several situations in which the confinement of the atom pair influences their interactions. Then, we demonstrate the preparation of a molecular bound state after an adiabatic ramp across a magnetic Feshbach resonance. Measurements of molecular loss rates provide evidence that the atoms are in fact associated during the merging sequence, before the magnetic field ramp. By preparing a weakly-bound molecule in an optical tweezer, we carry out important steps towards assembling an array of ultracold RbCs molecules in their rovibrational ground states

Biological Particle Control and Separation using Active Forces in Microfluidic Environments

Exploration of active manipulation of bioparticles has been impacted by the development of micro-/nanofluidic technologies, enabling evident observation of particle responses by means of applied tunable external force field, namely, dielectrophoresis (DEP), magnetophoresis (MAG), acoustophoresis (ACT), thermophoresis (THM), and optical tweezing or trapping (OPT). In this chapter, each mechanism is presented in brief yet concise, for broad range of readers, as strong foundation for amateur as well as brainstorming source for experts. The discussion covers the fundamental mechanism that underlying the phenomenon, presenting the theoretical and schematic description; how the response being tuned; and utmost practical, the understanding by specific implementation into bioparticles manipulation engaging from micron-sized material down to molecular level particles

Black-body radiation induced correlated excitation of Potassium Rydberg atoms in tweezer arrays

Im Rahmen dieser Arbeit stellen wir die Realisierung einer neuartigen Plattform zur Quantensimulation mit Kaliumatomen in optischen Pinzetten vor. Wechselwirkungen zwischen den Atomen werden durch die Verwendung von Zuständen mit großen Hauptquantenzahlen, auch bekannt als Rydberg-Zustände, erzeugt. Atome, die zu Rydberg-Zuständen angeregt werden, interagieren durch Dipol-Dipol- oder van-der-Waals-Wechselwirkungen, für die eine große Reichweite charakteristisch ist. Die Wechselwirkung führt zu starken Energieverschiebungen bei typischen Abständen zwischen den gefangenen Atomen. Wir haben das Experiment für die Erzeugung von Wechselwirkungen durch Off-Resonanz-Dressing eines Rydberg-Zustands geplant. Durch verstimmte Dressing-Wechselwirkung bleibt der Langstreckencharakter des gekoppelten Rydberg-Zustands erhalten. Ein Vorteil von Kalium ist seine Grundzustandsaufspaltung, die eine technisch unkomplizierte Beeinflussung beider Grundzustände ermöglicht, so dass Wechselwirkungen erzeugt werden können, die bisher mit Rydberg-Zuständen nicht realisiert wurden. In dieser Arbeit wird eine Methode zur Erzeugung optischer Pinzetten durch eine holographische Technik vorgestellt und wie man sie mit einzelnen Kaliumatomen präpariert. Die besondere Kombination von Kalium mit 1064nm-Licht erforderte die Anwendung spezifischer Techniken für die Präparation und Abbildung einzelner Atome. Die Raman-Seitenband-Kühlung wird eingesetzt, um Einschränkungen aufgrund von Inhomogenitäten der Lichtverschiebung zwischen den Fallen abzumildern. Das deterministische Laden einzelner Atome in die optischen Pinzetten hat sich im Falle von 1064nm-Licht als schwierig erwiesen und erforderte die Verwendung von anderem Fallenlicht. Ein Einzelphotonenschema wird verwendet, um direkt an Rydberg-Zustände bei einer Wellenlänge von 286nm zu koppeln. Dabei wird das UV-Licht dazu verwendet, Atome die in einer eindimensionalen Kette angeordnet sind, durch Rydberg Dressing anzuregen und somit durch die Wechselwirkungsverschiebung Korrelationen zu generieren. Das System ermöglichte die mikroskopische Untersuchung von Avalanche-Verlusten, die experimentell bei der Realisierung des Rydberg-Dressings beobachtet wurden. Die Ursache für diese Verluste wurde auf das Vorhandensein von Verunreinigungen zurückgeführt, in diesem Fall Rydberg-Atome die durch Schwarkörperstrahlung erzeugt wurden und entgegengesetzte Parität zu den durch das UV gekoppelten Atomen besitzen. Solche Verunreinigungen erleichtern die direkte Anregung der Atome aufgrund von Verschiebungen der Dipol-Dipol-Wechselwirkung, wodurch die Lebensdauer des angezogenen Zustands verringert wird. Derselbe Effekt ist in unserem System zu beobachten, wenn die Atome verstimmt an einen Rydberg-Zustand gekoppelt sind. Durch die Möglichkeit Verluste an einzelnen Atomen zu messen, ist es Möglich Paarkorrelationen zu verwenden, um die Erleichterung der Verluste zu bestätigen und die typische Reichweite dazu zu identifizieren. Wir bestätigen die Dipol-Dipol-Skalierung der Erleichterung, die von den durch die Schwarzkörperstrahlung gekoppelten Zuständen erzeugt wird. Wir können auch die Auswirkung der Bewegung der Rydberg-Atome auf diesen Prozess in unserem System identifizieren. Darüber hinaus wird die Signatur des Avalanche-Verlustes bei der Auswertung von Korrelationen höherer Ordnung beobachtet. Zusammenfassend stellt diese Arbeit eine neue Plattform für die Quantensimulation mit Kaliumatomen in optischen Pinzetten vor. Wir identifizieren die Ursache für einen begrenzenden Faktor der Rydberg-Dressing-Technik bei Raumtemperatur. Wir schlagen Ideen vor, um dieses Problem entweder dynamisch zu lösen, indem wir die Bewegung des Atoms aus der Atomebene heraus erzwingen, oder indem wir die Verunreinigungen durch optisches Pumpen entfernen.In the framework of this thesis, we introduce the realization of a novel platform for quantum simulation with Potassium atoms in optical tweezers. Interactions between the atoms are created by using states with large principal quantum numbers, also known as Rydberg states. Atoms excited to Rydberg states interact through dipole-dipole or van-der-Waals interactions, which have a long range character. The interaction produces strong energy shifts at typical distances between the trapped atoms. We planned the experiment for the generation of interactions through off-resonant dressing of a Rydberg state. The off-resonant dressing conserves the long-range character of the coupled Rydberg state. An advantage of Potassium is its ground state splitting that allows for a technically uncomplicated dressing of both ground states with the capability to engineer interactions not realized before with Rydberg states. This thesis presents a method to generate optical tweezers through a holographic technique and how to prepare them with single Potassium atoms. The particular combination of Potassium with 1064nm light required the application of specific techniques for the preparation and imaging of single atoms. Raman sideband cooling is implemented to mitigate limitations from light shifts inhomogeneities between the traps. The deterministic loading of single atoms into the optical tweezers had been proven difficult in the case of 1064nm light and required the use of different trapping light. A single-photon scheme is used to directly couple to Rydberg states at a wavelength of 286nm. The UV light allows us to off-resonantly dress atoms prepared in a one-dimensional chain and the generation of quantum correlations between the atoms thanks to the created interaction shift. The system enabled the microscopic study of avalanche losses that have been experimentally seen during the realization of Rydberg dressing. The cause of such losses was attributed to the presence of impurities, Rydberg atoms with opposite parity to the coupled by UV light, generated by black-body radiation. Such impurities facilitate the direct excitation of atoms due to dipole-dipole interaction shifts, reducing the dressed state lifetime. This same effect can be seen in our system when the atoms are off-resonantly coupled to a Rydberg state. The capacity to identify single atomic losses allows us to use a two-body correlation to confirm the facilitation character of the loss event and to measure the typical facilitation range. We confirm the dipole-dipole scaling of the facilitation generated by the states coupled by black-body radiation. We can also identify the effect of the Rydberg atom motion on the facilitation process in our system. Furthermore, the signature of the avalanche loss is observed with the evaluation of higher-order correlations. In summary, this thesis presents a new platform for quantum simulation with Potassium atoms in optical tweezers. We identify the cause of one limiting factor of the Rydberg dressing technique at room temperature. We propose ideas to solve this problem either dynamically, forcing the movement of the atom out of the atomic plane, or by removing the impurities through optical pumping