Microwave device investigations Semiannual progress report, 1 Oct. 1969 - 1 Apr. 1970

Beam-plasma interactions, cyclotron harmonic instability study, and millimeter and submillimeter wave detection by paramagnetic material

Two-mode squeezing over deployed fiber coexisting with conventional communications

Squeezed light is a crucial resource for continuous-variable (CV) quantum information science. Distributed multi-mode squeezing is critical for enabling CV quantum networks and distributed quantum sensing. To date, multi-mode squeezing measured by homodyne detection has been limited to single-room experiments without coexisting classical signals, i.e., on ``dark'' fiber. Here, after distribution through separate fiber spools (5~km), $-0.9\pm0.1$-dB coexistent two-mode squeezing is measured. Moreover, after distribution through separate deployed campus fibers (about 250~m and 1.2~km), $-0.5\pm0.1$-dB coexistent two-mode squeezing is measured. Prior to distribution, the squeezed modes are each frequency multiplexed with several classical signals -- including the local oscillator and conventional network signals -- demonstrating that the squeezed modes do not need dedicated dark fiber. After distribution, joint two-mode squeezing is measured and recorded for post-processing using triggered homodyne detection in separate locations. This demonstration enables future applications in quantum networks and quantum sensing that rely on distributed multi-mode squeezing.Comment: 23 pages, 13 figures, 2 table

Space Shuttle/TDRSS communication and tracking systems analysis

In order to evaluate the technical and operational problem areas and provide a recommendation, the enhancements to the Tracking and Data Delay Satellite System (TDRSS) and Shuttle must be evaluated through simulation and analysis. These enhancement techniques must first be characterized, then modeled mathematically, and finally updated into LinCsim (analytical simulation package). The LinCsim package can then be used as an evaluation tool. Three areas of potential enhancements were identified: shuttle payload accommodations, TDRSS SSA and KSA services, and shuttle tracking system and navigation sensors. Recommendations for each area were discussed

MERITXELL: the Multifrequency Experimental Radiometer with Interference Tracking for Experiments over Land and Littoral—instrument description, calibration and performance

MERITXELL is a ground-based multisensor instrument that includes a multiband dual-polarization radiometer, a GNSS reflectometer, and several optical sensors. Its main goals are twofold: to test data fusion techniques, and to develop Radio-Frequency Interference (RFI) detection, localization and mitigation techniques. The former is necessary to retrieve complementary data useful to develop geophysical models with improved accuracy, whereas the latter aims at solving one of the most important problems of microwave radiometry. This paper describes the hardware design, the instrument control architecture, the calibration of the radiometer, and several captures of RFI signals taken with MERITXELL in urban environment. The multiband radiometer has a dual linear polarization total-power radiometer topology, and it covers the L-, S-, C-, X-, K-, Ka-, and W-band. Its back-end stage is based on a spectrum analyzer structure which allows to perform real-time signal processing, while the rest of the sensors are controlled by a host computer where the off-line processing takes place. The calibration of the radiometer is performed using the hot-cold load procedure, together with the tipping curves technique in the case of the five upper frequency bands. Finally, some captures of RFI signals are shown for most of the radiometric bands under analysis, which evidence the problem of RFI in microwave radiometry, and the limitations they impose in external calibration.Peer ReviewedPostprint (published version

Rubidium resonant squeezed light from a diode-pumped optical-parametric oscillator

La luz comprimida (squeezed light) es uno de los componentes importantes de los experimentos de memorias cuánticas. Un almacenamiento eficientede la luz comprimida en una colectividad de átomos exige que la luz (comprimida) sea resonante a la línea espectral de absorción. El láser de diodopuede acceder a una amplia clase de líneas espectrales dado al amplio rango de longitudes de onda accesibles. Por lo tanto, el uso de fuentes de luz comprimida basadas en láseres de diodo ampliaría el número de los posibles experimentos. Además, los láseres de diodo reúnen muchas buenascaracterísticas como son su construcción robusta y compacta, simplicidad y bajo precio. La única desventaja de los láseres diodo es el ruido de la fase que resulta en un ensanchamiento de sus líneas espectrales.Esta tesis describe estudios experimentales y teóricos de generación de estados de luz omprimida en cuadratura y polarización, adecuados para lainteracción con átomos de rubidio. En ese ocumento damos una atención especial al ruido de fase y sus efectos en el grado de compresión de la luzy los métodos para lograr luz comprimida en presencia de ruido de fase generado en el láser de diodo.La tesis está estructurada de la siguiente manera:El primer capítulo presenta las ideas generales de la conversión paramétrica de frecuencia (parametric downconversion) en un oscilador paramétricoóptico. Aquí derivamos la descripción teórica de la luz comprimida en un oscilador paramétrico óptico operado por debajo del nivel umbral.El segundo capítulo describe el aparato experimental. Primero, damos una descripción detallada del diseño de la cavidad paramétrica óptica yresumimos las propiedades del cristal no lineal. A continuación, pasamos a describir el láser y los sistemas usados para la estabilización del sistemaláser y de la cavidad del oscilador. En el tercero se discute la ganancia de amplificación y la eficiencia de detección. Por último damos una descripcióngeneral del experimento y presentamos los resultados en la compresión cuántica ("squeezing") de la luz.El último capítulo analiza los efectos de ruido de fase en el "squeezing" de cuadratura y describe una técnica para eliminar su efecto. Primero,discutimos el origen del ruido de fase para sistemas de láser de diodo. Segundo, derivamos el grado observable de "squeezing", teniendo en cuentalos efectos de fluctuaciones cuasi-estacionarias de frecuencia. Por último, mostramos cómo los efectos del ruido de fase pueden ser eliminados ycomparamos la predicción teórica con nuestros resultados experimentales.El resultado de este proyecto es una fuente de luz no-clásica resonante con la transición atómica del rubidio. Caracterizamos el "squeezing" del estadode vacío cuántico resultante. El máximo grado de compresión logrado en el experimento fue 2.5dB por debajo del nivel de ruido cuántico. Ademásrealizamos un análisis del efecto que el ruido de fase tiene en el grado de compresión. Los resultados de este análisis mostraron que en presencia deruido de fase se espera que el "squeezing" dependa del retardo relativo entre el haz de luz comprimida y el oscilador local. Comprobamosexperimentalmente esta hipótesis y medimos el grado de compresión como una función del retardo entre la luz comprimida y el oscilador local. Losresultados experimentales obtenidos fueron consistentes con la teoría.Aparte de construir una fuente luz comprimida resonante con rubidio, hemos probado que el láser de diodo es una fuente adecuada para la producciónde luz comprimida. Hemos proporcionado una teoría que trata el efecto de ruido de fase en el grado de compresión de la luz en un osciladorparamétrico óptico. El aparato experimental presentado aquí utiliza técnicas estándar que podrían ser aplicadas a una variedad de otras longitudes de ondas.This thesis describes experimental and theoretical studies of generation of quadrature- and polarization-squeezed light suitable for interaction with rubidium atoms. Special attention is paid to phase noise, its effects on squeezing, and methods to achieve squeezing in the presence of diode laser phase noise.Squeezed light is an important component of quantum memories experiments. Efficient storage of (squeezed) light in atomic ensembles requires thelight to be resonant to the respective atomic transition. Diode lasers can access many atomic transitions as they cover significantly broader wavelengthrange than other classes of lasers. Consequently, employing diode-laser-based squeezed light sources would broaden the range of possible quantummemories experiments. Furthermore, diode lasers posses many attractive features like robustness, simplicity, compactness, and low price. Thedrawback of the diode laser is it's excess phase noise, which results in a relatively large linewidth. This forms an obstacle for detection of phasesensitive quantum states such as quadrature squeezing.The thesis is structured as follows:The first chapter presents the general ideas on parametric downconversion in an optical parametric oscillator. Here we derive the theoretical descriptionof squeezing of the light field in a subthreshold optical parametric oscillator.The second chapter describes the experimental apparatus. First, we give a detailed description of the design of the optical parametric oscillator cavityand summarise the properties of the nonlinear crystal. In continuation, we describe the laser system and the locking systems used for the laser systemand the optical parametric oscillator cavity stabilisations. Third, we discuss the amplification gain and the detection efficiency. Finally, we give a fulloverview of the experiment and we present the squeezing results.The last chapter analyses the effects of phase noise on quadrature squeezing and describes a technique to eliminate its effect. First, we discuss theorigin of the phase noise for diode laser systems. Second, we derive the observable squeezing taking into account the effects of quasi-static frequencyfluctuations. Third, we show how the effects of the phase noise can be eliminated and, last but not least, we compare the theoretical prediction with ourexperimental results.The outcome of this project is a rubidium resonant source of non-classical light. We characterised the output squeezed vacuum state. The maximumsqueezing achieved in the experiment was 2.5dB below shot-noise level. Moreover, we performed an analysis of the effect the phase noise has on thesqueezing. The results of this analysis showed that in presence of phase noise we expected that the squeezing level would depend on the relativedelay between squeezing and local oscillator path. We experimentally tested this statement performing a measurement of squeezing as a function ofthe delay between the squeezed light and the local oscillator. The experimental results were consistent with the theory.Apart form building a source of rubidium resonant squeezed light we have proven that the diode laser is a source suitable for production of squeezedlight. We provided a theory which treats the effect of phase noise on squeezing in optical parametric oscillator.The experimental squeezing apparatus presented here uses standard techniques which could be applied to a variety of other wavelengths