Atomic quantum metrology with narrowband entangled and squeezed states of light

The use of light, especially of laser light, is in many cases the most sensitive way to perform measurements. However, the highest sensitivity that can be achieved with laser light as probe is bounded by the standard quantum limit (SQL). As many instruments are approaching this fundamental limit, it becomes crucial to explore ways to overcome the SQL. Quantum metrology offers the possibilities to increase the sensitivities of the most accurate measurements beyond the SQL by using photonic quantum states of light as a tool. Two well-known classes of quantum states that provide a metrological advantage and break the SQL are squeezed states and a certain class of entangled states, called NOON states. While it is of special interest to apply these quantum states to atomic systems, such as atomic vapors, this requires quantum states of the highest quality in terms of purity, fidelity, brightness, and indistinguishability. Most importantly, for the probing of atomic systems, the quantum states need to be extremely narrowband to match the atomic linewidths. As NOON states are usually generated in a broadband spontaneous parametric down-conversion (SPDC) process, they are not compatible with narrowband atomic resonances. The goal of this thesis was the generation of suitable narrowband entangled and squeezed quantum states of light and their application to atomic systems. To increase the rate of atom-resonant SPDC photons by orders of magnitude, we used a cavity-enhanced setup. Polarization-squeezed states and polarization-entangled NOON states were created. The spectral brightness of the generated NOON states is one of the highest of pairs of indistinguishable photons reported so far. The photon pairs were carefully characterized by full quantum state tomography showing high fidelities with a perfect NOON state. After filtering the photon source output by a novel filter based on the “interaction-free measurement” scheme, a cross-correlation measurement demonstrated its potential as a narrowband heralded single-photon source, needed for example in quantum information. To apply these states in a quantum metrology scheme and to show the metrological advantage, we chose an atomic magnetometer as a model system. The assembled shot-noise-limited magnetometer is based on the Faraday effect in a vapor of hot rubidium atoms. It could be demonstrated that both quantum states perform better in the magnetometer application than any classical state, i.e., they break the SQL. In the case of NOON states, this is the first use of multi-photon coherence in an atomic experiment. In addition to applications in quantum metrology, the presented techniques of quantum-light generation and filtering are also directly applicable to quantum information tasks, especially to the use in quantum memories.El uso de la luz, en particular la luz láser es, en muchos casos, el método que permite realizar mediciones de la manera más sensible. No obstante, la mayor sensibilidad que se puede conseguir gracias a la luz láser como sistema de sondeo queda delimitada por el límite cuántico estándar (SQL). Visto que muchos instrumentos se están acercando a este límite fundamental, es crucial explorar formas de superar el SQL. La metrología cuántica ofrece la posibilidad de incrementar la sensibilidad de las medidas más precisas más allá del SQL empleando los estados cuánticos de luz como herramienta. Dos categorías conocidas de estados cuánticos que brindan una ventaja metrológica y rompen con el SQL son los estados “comprimidos” y ciertas categorías de estados entrelazados llamados estados “NOON”. Aunque es de especial interés aplicar estos estados cuánticos a los sistemas atómicos, como a los vapores atómicos, se requieren estados cuánticos de óptima calidad en términos de pureza, fidelidad, luminosidad e identidad. Lo más importante para los sistemas atómicos de investigación es que los estados cuánticos sean de banda extremadamente estrecha para que coincidan con el ancho de banda de átomos. Puesto que los estados NOON suelen ser generados en un proceso de conversión espontánea paramétrica descendente (SPDC) de banda ancha, no son compatibles con las resonancias atómicas de banda estrecha. El objeto de esta tesis fue la generación de estados cuánticos de luz apropiados de banda estrecha, entrelazados y comprimidos, y su aplicación en los sistemas atómicos. Para incrementar el número de fotones generados por SPDC resonantes con la transición atómica por órdenes de magnitud, se empleó un sistema aumentado por un resonador. Se crearon estados de polarización comprimida y estados NOON de polarización entrelazada. La luminosidad espectral de los estados NOON generada supone una de las más altas que se hayan reportado hasta el momento entre pares de fotones idénticos. Los pares de fotones fueron cuidadosamente caracterizados por medio de una tomografía completa del estado cuántico que muestra la gran fidelidad con un estado NOON perfecto. Después de filtrar la producción de la fuente de fotones por medio de un novedoso filtro basado en el esquema “interaction-free measurement”, una medida de correlación cruzada demostró su potencial como fuente de fotones individuales anunciados de banda estrecha que resulta necesaria, por ejemplo, en la información cuántica. Para aplicar estos estados en un esquema de metrología cuántica y demostrar la ventaja metrológica, elegimos un magnetómetro atómico como sistema modelo. El montaje del magnetómetro delimitado por el límite cuántico estándar se basa en el efecto Faraday en un vapor de átomos de rubidio calientes. Se podía demostrar que el comportamiento de ambos estados cuánticos es superior en la aplicación con el magnetómetro que cualquier estado clásico, es decir, que superan el SQL. En el caso de los estados NOON, este es el primer uso de la coherencia multifotónica en un experimento atómico. Además de las aplicaciones en la metrología cuántica, las técnicas presentadas de generación de luz cuántica y filtración también son directamente aplicables a las tareas de información cuántica, en especial al uso en las memorias cuánticas

NOON states from cavity-enhanced down-conversion: High quality and super-resolution

Indistinguishable photons play a key role in quantum optical information technologies. We characterize the output of an ultra-bright photon-pair source using multi-particle tomography [R. B. A. Adamson et al., Phys. Rev. Lett. 98, 043601 (2007)] and separately identify coherent errors, decoherence, and distinguishability. We demonstrate generation of high-quality indistinguishable pairs and polarization NOON states with 99% fidelity to an ideal NOON state. Using a NOON state we perform a super-resolving angular measurement with 90% visibility.Comment: 4 Pages, 5 figure

Bridging Formal and Informal Roles in Workgroups: Moving Beyond Followership Towards Supportership, A Case Study

Ph.D

The Influence of Community Cultural Wealth and Tauhi Va on the Navigation of Pacific Islanders in Science, Technology, Engineering and Mathematics (STEM)

My research examines the influence of community cultural wealth and tauhi va on the navigation of Pacific Islanders (PIs) in STEM. The disaggregation of data on Asian American and Pacific Islanders (AAPIs) attaining STEM bachelor\u27s degrees revealed that PIs (16%) are represented half as much as Asian Americans (35%) (NCES, 2020). Under the AAPI designation, PIs have been masked, underserved, and underresearched in higher education and STEM. For this reason, this study focuses on the educational trajectories and experiences of PIs in STEM to highlight their strengths and challenges to understand how better to serve and support PIs in STEM. In this phenomenological study, I used an asset-based framework; community cultural wealth and a PI cultural value, tauhi va, to explore how PIs navigate STEM. The research questions for this study are (a) How do community cultural wealth and tauhi va influence the navigation of Pacific Islanders in STEM? and (b) How does tauhi va create va specific to Pacific Islanders to wayfind STEM and develop community cultural wealth? This qualitative study included 31 participants who self-identified as Pacific Islander and were students and recent graduates in STEM. The methods used in this study included a brief demographic survey, an educational trajectory map, and a 60- to 90-minute semistructured artifact elicitation interview using talanoa. The main finding of this study was that the navigation of PIs in STEM was influenced by familial, aspirational, social, navigational, and resistant capital. After facing barriers such as inadequate advising, stereotype threat, and competitive and cutthroat STEM culture from peers, faculty, and staff, PI students maneuvered through the skill of wayfinding. PIs created va (space) to relate, heal, and network with other PIs and individuals who had encountered similar experiences. PIs maintain va through tauhi va, or the caretaking of sociospatial relationships through reciprocity, thus developing Pacific Islander cultural capital to navigate STEM. This qualitative research is based on the successful navigation of PIs in STEM through an asset-based framework and cultural value to highlight the positive impact of PI cultural knowledge, PI identity, and nuances of PIs in STEM

Ultra-Narrow Faraday Rotation Filter at the Rb D1 Line

We present a theoretical and experimental study of the ultra-narrow bandwidth Faraday anomalous dispersion optical filter (FADOF) operating at the rubidium D1 line (795 nm). This atomic line gives better performance than other lines for the main FADOF figures of merit, e.g. simultaneously 71% transmission, 445 MHz bandwidth and 1.2 GHz equivalent noise bandwidth.Comment: 3 pages, 2 figures. Manuscript same as v1. FADOF calculator (ancillary file) now allows for extension to the D2 lin

Entanglement-enhanced probing of a delicate material system

Quantum metrology uses entanglement and other quantum effects to improve the sensitivity of demanding measurements. Probing of delicate systems demands high sensitivity from limited probe energy and has motivated the field's key benchmark-the standard quantum limit. Here we report the first entanglement-enhanced measurement of a delicate material system. We non-destructively probe an atomic spin ensemble by means of near-resonant Faraday rotation, a measurement that is limited by probe-induced scattering in quantum-memory and spin-squeezing applications. We use narrowband, atom-resonant NOON states to beat the standard quantum limit of sensitivity by more than five standard deviations, both on a per-photon and per-damage basis. This demonstrates quantum enhancement with fully realistic loss and noise, including variable-loss effects. The experiment opens the way to ultra-gentle probing of single atoms, single molecules, quantum gases and living cells.Comment: 7 pages, 8 figures; Nature Photonics, advance online publication, 16 December 201

Flexibilisierung des Renteneintritts

Im vorliegenden Artikel wird gezeigt, wie eine Flexibilisierung des Renteneintritts erreicht werden kann, ohne die Versichertengemeinschaft zu schädigen. Die Flexibilisierung wird ermöglicht, indem wie im heutigen Umlageverfahren Zu- und Abschläge von der gesetzlichen Rente ermittelt werden. Im Unterschied zur heutigen Ab- bzw. Zuschlagsberechnung erfolgt die Finanzierung der Flexibilisie-rung jedoch über ein kapitalgedecktes System. Es zeigt sich, dass diese Zu- bzw. Abschläge deutlich höher liegen als die aktuell im Umlagesystem erhobenen. Im Gegensatz zu den heutigen Ab- bzw. Zu-schlägen wird die Versichertengemeinschaft durch die Neuberechnung neutral gestellt und es be-steht keine Möglichkeit mehr, zu Lasten Dritter in den vorzeitigen Ruhestand zu gehen. Zusätzlich können sämtliche weitere Regulierungen, wie die Deckelung des Hinzuverdienstes, entfallen. Im Ergebnis wird ein präferenzgerechter Übergang vom Erwerbsleben in den Ruhestand ermöglicht.Pension reform; Flexibility

Narrowband tunable filter based on velocity-selective optical pumping in an atomic vapor

We demonstrate a tunable, narrow-band filter based on optical-pumping-induced circular dichroism in rubidium vapor. The filter achieves a peak transmission of 14.6%, a linewidth of 80 MHz, and an out-of-band extinction >35 dB. The transmission peak can be tuned within the range of the Doppler linewidth of the D1 line of atomic rubidium at 795 nm. While other atomic filters work at frequencies far from absorption, the presented technique provides light resonant with atomic media, useful for atom-photon interaction experiments. The technique could readily be extended to other alkali atoms.Comment: 3 Pages, 4 figure

Atom-Resonant Heralded Single Photons by Interaction-Free Measurement

We demonstrate the generation of rubidium-resonant heralded single photons for quantum memories. Photon pairs are created by cavity-enhanced down-conversion and narrowed in bandwidth to 7 MHz with a novel atom-based filter operating by "interaction-free measurement" principles. At least 94% of the heralded photons are atom-resonant as demonstrated by a direct absorption measurement with rubidium vapor. A heralded auto-correlation measurement shows $g_c^{(2)}(0)=0.040 \pm 0.012$, i.e., suppression of multi-photon contributions by a factor of 25 relative to a coherent state. The generated heralded photons can readily be used in quantum memories and quantum networks.Comment: 5 pages, 4 figure