Дисертації з теми "Dipole trapping"

Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 99-103).
Bad-cavity lasers using a gain medium with a narrower linewidth than the laser cavity have the potential to achieve very narrow linewidths and extremely long coherence times. Such lasers could serve as active frequency standards or enable very-long-baseline interferometric telescopes at optical frequencies. The 6s6p³P₀ to 6s²¹S₀ ground state transition in ¹⁷¹Yb is a promising candidate for the gain medium of a bad-cavity laser due to its 44 mHz linewidth. For ytterbium to be used efficiently as a gain medium, its inhomogeneous broadening must be suppressed to a level lower than the linewidth of its gain transition. In this thesis, I design, implement, and characterize an optical lattice trap for ytterbium atoms. The trap consists of a diode laser which is frequency stabilized to an adjustable-length cavity where the ytterbium atoms are trapped. The length of this cavity is then locked by comparison of the laser frequency to a stable reference cavity. The resulting standing wave has high enough intensity that the recoil energy of the gain transition is smaller than the energy spacing between motional modes of the trapped atoms. This situation is known as the Lamb-Dicke regime and means that there is an absence of recoil broadening. The large spacing between motional modes of the trap also enables sideband resolved cooling of the atoms, which allows cooling to temperatures of 3 [mu]K, near the ground state of the trapping potential. Additionally, if the wavelength of the optical lattice is chosen to be at the magic wavelength for ytterbium, where the relative AC Stark shift for the two levels of the gain transition is zero to first order, there is no broadening due to varying intensity in the trap. Since the Doppler effect, recoil broadening and the AC Stark shift are the main sources of inhomogeneous broadening, this trapping scheme is expected to suppress inhomogeneous broadening to a level of 1 Hz.
by David Levonian.
M. Eng.

This thesis provides a summary of the laser system constructed in the Quantum Degenerate Gases Laboratory for laser cooling and trapping of 85/87Rband 6Li as well as of experiments that have been pursued in our lab to date. The first chapter provides an overview of the experimental focus of the QDG lab. The second and third chapters provide the fundamental theory behind laser cooling and trapping. The fourth chapter provides details of the laser system. The fifth chapter describes an experiment performed on the subject of dual-injection, performed in collaboration with Dr. James Booth of the British Columbia Institute of Technology (BCIT) involving the dual-injection of a single slave amplifier. The last chapter describes the progress made on the experimental setup needed for the study of Feshbach resonances between 85/87Rb and 6Li and the photoassociative formation of molecules.

Three-dimensional linear ray theory is used to investigate internal waves interacting with a Lamb-Chaplygin pancake vortex dipole. These interactions involve waves propagating in the same (co-propagating) and opposite (counter-propagating) horizontal directions as the dipole translation. Co-propagating internal waves in the vertical symmetry plane between the vortices of the dipole can approach critical levels where the wave energy is absorbed by the dipole or where the waves are overturned and possibly break. As wave breaking cannot be simulated with this linear model, changes in wave steepness are calculated to aid in estimating the onset of breaking. Counter-propagating internal waves in the vertical symmetry plane can experience horizontal and vertical reflections, including turning points similar to waves in two-dimensional steady shear. Wave capture is also a possible effect of either type of interaction, depending on initial wave properties and positioning relative to the vortex dipole. Away from the vertical symmetry plane, a spanwise converging (focusing) and diverging (defocusing) of wave energy is observed in co- and counter-propagating interactions as symmetric off-center rays interact with the dipole's individual vortices. Some off-center rays experience multiple horizontal refractions similar to wave trapping.

The observation of a permanent electric dipole moment (EDM) in a non-degenerate system would indicate the violation of discrete symmetries of Time reversal (T) or combined application of Charge (C) and Parity (P) symmetry violation through the CPT theorem. The diamagnetic 225Ra atom with nuclear spin I=1/2 is a favorable candidate for an EDM search. Experimental sensitivity to its EDM is enhanced due to its high atomic mass and the increased Schiff moment of its octupole deformed nucleus. An experimental setup is developed where laser cooled neutral radium atoms are collected in a magneto-optical trap (MOT). The collected atoms are transported 1 meter with a far off-resonant optical dipole trap (ODT) and then the atoms are transferred to a second standing-wave ODT in an experimental chamber. The atoms are then optically polarized and allowed to Larmor precess in parallel and antiparallel electric and magnetic fields. The difference between the Larmor precession frequency for parallel and antiparallel fields is experimentally determined to measure the EDM. This thesis is about the first measurement of the EDM of the 225Ra atom where an upper limit of |d(225Ra)|<5.0*10-22 e cm (95\% confidence) is reached.

Diese Arbeit untersucht die Photo-Lumineszenz (PL)-Unterbrechung (Blinken) einzelner in Polymer-Nanopartikeln eingebetteter CdSe/CdS Halbleiter-Nanokristalle (Quantenpunkte) im Einfluss elektrischer Gleich- und Wechselfelder mittels Weitfeld-Mikroskopie. Hierbei emittieren die einzelnen Quantenpunkte trotz kontinuierlicher Anregung mit einer zwischen hellen An- und dunklen Aus-Zuständen variierenden PL-Intensität. Die Ergebnisse zeigen, dass die Dynamik dieses Blinkens durch Wechselfelder stark beeinflusst wird und von deren Feldstärke, teilweise auch deren Feldfrequenz abhängt. Für zunehmende Feldstärken lässt sich ein schnellerer Wechsel zwischen An- und Aus-Zuständen (erhöhte Blinkfrequenz) beobachten, der von einer reduzierten Häufigkeit langer An- und Aus-Ereignisse begleitet wird. Der Verlauf der An-Zeit-Verteilungen bei kleinen Zeiten wird zunehmend (monoton) flacher, während die Verteilungen der Aus-Zeiten zunächst ebenfalls einem analogen Trend folgen, ab einer bestimmten und von der Feldfrequenz abhängenden Feldstärke jedoch wieder steiler verlaufen. Ein solcher Monotonie-Wechsel in der Blinkdynamik im Fall einer gleichbleibenden Variation einer äußeren Bedingung wurde bei Halbleiter-Nanokristallen so erstmalig beobachtet. Für Gleichfelder zeigen sich hingegen nahezu keine Auswirkungen. Lediglich die An-Zeit-Verteilungen sowie die Blinkfrequenz im Fall hoher Feldstärken werden modifiziert. Die Ergebnisse werden im Kontext verschiedener aktueller Modelle zur PL-Unterbrechung wie dem trapping-Modell, dem self-trapping-Mechanismus oder dem Modell multipler Rekombinationszentren diskutiert und diese entsprechend erweitert. Dabei stehen die dielektrischen Eigenschaften und die Relaxationsdynamik der lokalen Quantenpunkt-Umgebung im Mittelpunkt, deren Reaktion auf die externen Felder durch eine zeitabhängige Ausrichtung permanenter Dipole beschrieben werden kann.

Neste trabalho, estudamos colisões entre átomos de Rydberg ultrafrios em uma amostra atômica de alta densidade aprisionada em uma armadilha óptica de dipolo (AOD) tipo QUEST (Quasi Electrostatic Trap). Nossos objetivos incluíam testar a manifestação de fenômenos de muitos corpos bem como estudar efeitos de anisotropia nos processos colisionais envolvendo dois corpos. Para isso, escolhemos o processo colisional descrito por 5/2+5/2(+2)3/2+(2)7/2 no intervalo de 37 ≤ ≤47. O processo foi estudado na ausência e presença de campo elétrico estático, originando as ressonâncias Förster. Os resultados mostram que mesmo em alta densidade atômica o processo de dois corpos domina a interação, apesar da clara manifestação do bloqueio dipolar. Após modificações na montagem experimental, estudamos um dos picos da ressonância Förster 375/2+375/2393/2+357/2 em função da direção e amplitude em relação ao eixo longitudinal da AOD. Discutimos os resultados e os desafios futuros do experimento.
In this paper, we study collisions between ultracold Rydberg atoms in a high density atomic sample trapped in an optical dipole trap (ODT), type QUEST (Quasi Electrostatic Trap). Our goals included testing the manifestation of many-body phenomena and to study anisotropy effects in collisional processes involving two Rydberg atoms. In order to do this, we have chosen the collision process described by 5/2+5/2(+2)3/2+(2)7/2 in the range of 37 ≤ ≤47. The process was studied in the presence and absence of a dc static electric field, also known as Förster resonances. The results show that even at high atomic density, two-body interaction dominates de process, despite the clear manifestation of Rydberg blockade. After several improvements in our experimental setup, we have studied also a Förster resonance peak 375/2+375/2393/2+357/2 as a function of the magnitude of the dc static electric field as well as the angle between this field and the longitudinal axis of the ODT. We discuss the results and future challenges of the experiment.

Ultracold matter offers a unique capability to reach the best high-precision spectroscopy measurements and leads to exciting perspectives in many different areas of science and technology. Molecules, thanks to their complex spectra, couple with a broader range of photons compared to atoms, so they are extremely attractive for fundamental science or to design new quantum technologies. However, to date, only a few molecular species have been brought to temperatures of the order of the microkelvin. This was done by laser cooling, a process that has been demonstrated only for species featuring an unpaired electron that does not participate to the chemical bond. A different approach, which is indifferent to the molecule electronic structure and thus potentially universal, is sympathetic cooling, where neutral molecules are cooled in a bath of ultracold atoms. However, inelastic collisions between molecules and the coolant is a major obstacle that has hindered the advances of this method thus far. Trapping the molecules in their absolute ground state would circumvent this problem or at least greatly simplify it. In this thesis we simulate the feasibility of an experiment in which metastable CO molecules are first slowed down to a few m/s with a microstructured Stark decelerator, then they are stopped by a strong DC electrical barrier and finally they are transferred irreversibly to their absolute ground state and captured in an optical trap. Unfortunately, the results of the simulations indicate that the total number of molecules that can be accumulated in the optical trap is rather low, far behind the observation threshold. Therefore, we concluded that other approaches to produce ultracold molecules must to be searched.

This thesis describes the physics, design, and construction of an experiment to measure the electric dipole moment (EDM) of the electron. In the experiment, laser-cooled Cs atoms will be held in an optical dipole force trap in the presence of applied electric and magnetic fields. The signature of an electron EDM is a first-order electric field shift of the Zeeman resonance frequency of the Cs ground state. We present an analysis of the systematic and statistical errors of this experiment, which shows that the experiment should have a sensitivity of the order of 10⁻²⁹ e-cm. We pay particular attention to potential light-shift induced errors and to magnetic field noise. We also present the design and experimental results for a cold Cs atom source, high voltage field plates, optical trapping field in a resonant build-up cavity, noval titanim ultrahigh vacuum system, and magnetic sheilding system. These results show that a measurement of the electron edm at the level of 10⁻²⁹ e-cm. should be feasible.
text

碩士
國立交通大學
電子研究所
99
In this thesis, we first study the influence of the presence of “intrinsic dipole” on the electrical properties of a SONOS-type nonvolatile memory (NVM) by a capacitor structure. The magnitudes of “intrinsic dipole” were extracted by the VFB shift observed in the C-V curves of the capacitors with adding Al2O3 or HfO2 inside the standard gate stack structure of a SONOS-type NVM, i.e., SiO2/Si3N4/SiO2. We found that VFB shifted toward positive direction when Al2O3 or HfO2 were deposited on top of SiO2 (tunneling layer). In contrast, VFB shifted toward negative direction when Al2O3 or HfO2 was deposited on top of Si3N4 (blocking layer). In addition, the magnitude of VFB shift for Al2O3 was about twice larger than HfO2. Next we also applied this scheme to the HfO2 nanocrystal SONOS-type NVM, and found that the tendency of VFB shift in the HfO2 nanocrystal NVM was the same with the conventional SONOS NVM. However, there was a serious gate injection problem in our device, so the fabricated devices can not be normally erased by FN-tunneling. We would tackle this problem in later chapters. Then, we adopted the high-k material (Al2O3, HfAlOx) to replace the traditional SiO2 as blocking layer for the HfO2 nanocrystal NVM. With high thermal budget processing for device fabrication, the high-k materials sustained pretty well and did not depict visible degradation. We exhibited the HfAlOx as blocking layer having faster programming and erasing speed. However, there were plentiful defects in the HfAlOx layer, and this made our device have “transient phenomenon” during erase operation. For our nanocrystal memory devices, there were advantages of fast programming speed, excellent data retention time at room temperature, and superior endurance after P/E cycles of 104. Finally, we adopted the intrinsic dipole scheme, i.e., depositing additional Al2O3 and HfO2 on top of tunneling oxide and used Al2O3 as blocking layer to make the so called SANOS-type NVM. The presence of dipole reflected on the observed larger device threshold voltage than the conventional one. Here we use both the FN-tunneling and hot carrier injection to study the electrical characteristics of the fabricated devices. We found that FN-tunneling operation has led to better endurance than hot carrier injection operation. Moreover, we also discussed the impact of dipole engineering on the retention and disturbance characteristics of our newly-developed nonvolatile memories.

Rozprawa omawia wybrane zastosowania metrologiczne zimnych atomów pułapkowanych optycznie na przykładzie dwóch eksperymentów: pułapki dipolowej dla zimnych atomów rubidu oraz sieci optycznej dla atomów strontu, będącej częścią większego przedsięwzięcia: pierwszego polskiego atomowego zegara optycznego. Optyczna pułapka dipolowa dla atomów rubidu powstała w laboratorium Zimnych Atomów Zakładu Fotoniki Uniwersytetu Jagiellońskiego. Celem budowy nowego stanowiska eksperymentalnego jest możliwości badania nieliniowych efektów magnetooptycznych, jak na przykład efekt Fardaya do celów precyzyjnej magnetometrii. W pierwszym etapie atomy rubidu są chłodzone w dwuwymiarowej pułapce magneto-optycznej (2D-MOT), formując strumień wstępnie schłodzonych atomów dla trójwymiarowej pułapki magnetooptycznej (3D-MOT). Proces przeładowania i formowania wiązki i jest szczegółowo opisany i scharakteryzowany.Następnie zimne atomy są do pułapki optycznej dipolowej (ODT), która przestrzennie przekrywa się z 3D-MOT. Rozprawa opisuje wyniki badania efektu Faradaya w optycznej pułapce dipolowej. Sieć optyczna dla atomów strontu jest częścią budowy Polskiego Optycznego Zegara Atomowego (POZA) w Krajowym Laboratorium Fizyki Atomowej, Molekularnej i Optycznej. Szczegółowo opisana jest aparatura tworząca strontowy standard częstotliwości dla zegara atomowego. Omówione są wyniki badania spektroskopii ultra-wąskiego przejścia zegarowego w próbkach atomów Strontu oraz stabilności stworzonego na jego bazie zegara optycznego.
Two experiments with laser-cooled atoms held in an optical dipole traps are described in the dissertation. First is dedicated to non-linear magneto-optical effects in rubidium atoms, while second is devoted to optical lattice trap for strontium atoms. Selected metrological applications of optically trapped cold atoms in both experiments are discussed and presented. A dipole trap setup has been built at the Department of Photonics in Jagiellonian University. It is aimed at investigations of nonlinear magneto-optical effects like precise magnetometry by Faraday effect. A compact two-dimensional magneto optical (2D-MOT) trap with permanent magnets serves as a source of cold rubidium atoms for further cooling in three-dimensional magneto-optical trap (3D-MOT). The 2D-MOT is described and characterised. The results of the loading an optical dipole trap (ODT) from a the 3D-MOT are then presented. It is followed by the results of a Faraday rotation of a resonant laser beam with atoms confined in the final stage of confinement in ODT. The strontium lattice experiment is a part of a larger project: the construction of the first polish optical atomic clock (project Polish Optical Atomic Clock) at the National Laboratory for Atomic, Molecular and Optical Physics. An introduction to time and frequency metrology with optical clocks is given. We describe strontium atoms confined in the optical lattice as a frequency reference for the optical clock in detail. The results of precision spectroscopy of ultra- narrow clock transition in bosonic Sr-88 and the measurements of the clock stability based on atomic reference are presented and discussed.