Search Results for « Spontaneous Parametric Down-Conversion »

I investigate the properties of spontaneous parametric down-conversion (SPDC) involving co-linear Gaussian spatial modes for the pump and the photon collection optics. Approximate analytical and numerical results are obtained for the peak spectral density, photon bandwidth, pair collection probability, heralding ratio, and spectral purity, as a function of crystal length and beam focusing parameters. I address the optimization of these properties individually as well as jointly, and find focusing conditions that simultaneously bring the pair collection probability, heralding ratio, and spectral purity to near-optimal values. These properties are also found to be nearly scale invariant, that is, ultimately independent of crystal length. The results obtained here are expected to be useful for designing SPDC sources with high performance in multiple categories for the next generation of SPDC applications.

Spontaneous Parametric Down-Conversion (SPDC) is a cornerstone phenomenon in nonlinear optics, where an incident high-energy photon is transformed into a pair of lower-energy photons. This quantum process serves as a fundamental tool for generating entangled photon pairs, heralded single photons, and squeezed light, making it indispensable in the realms of quantum communication, quantum computing, and precision metrology. In this paper, we present a comprehensive study on the theoretical foundations and practical realization of an SPDC experimental setup, developed for the first time at the Photonics Research Laboratory at Amirkabir University of Technology. Our setup features a self-grown potassium dihydrogen phosphate (KDP) nonlinear crystal, illuminated by a 450 nm blue laser, to achieve parametric down-conversion into infrared photon pairs at 900 nm. By integrating a custom-designed transimpedance amplifier with a BPX65 photodiode, we have successfully amplified and detected the weak SPDC signal, demonstrating the feasibility of achieving high sensitivity with low-cost, widely available components. The experimental results align closely with theoretical predictions, showcasing the effectiveness of the system in detecting photon pairs with minimal resources. This study underscores the accessibility and scalability of SPDC technology, providing a blueprint for constructing versatile quantum optics experiments in resource-limited settings. By bridging the gap between theoretical insight and experimental realization, we aim to inspire further exploration of SPDC's potential in both foundational research and practical applications, laying the groundwork for future innovations in quantum technologies.

Spontaneous Parametric Down-Conversion (SPDC), also known as parametric fluorescence, parametric noise, parametric scattering and all various combinations of the abbreviation SPDC, is a non-linear optical process where a photon spontaneously splits into two other photons of lower energies. One would think that this article is about particle physics and yet it is not, as this process can occur fairly easily on a day to day basis in an optics laboratory. Nowadays, SPDC is at the heart of many quantum optics experiments for applications in quantum cryptography, quantum simulation, quantum metrology but also for testing fundamentals laws of physics in quantum mechanics. In this article, we will focus on the physics of this process and highlight few important properties of SPDC. There will be two parts: a first theoretical one showing the particular quantum nature of SPDC and the second part, more experimental and in particular focusing on applications of parametric down-conversion. This is clearly a non-exhaustive article about parametric down-conversion as there is a tremendous literature on the subject, but it gives the necessary first elements needed for a novice student or researcher to work on SPDC sources of light.

Spontaneous Parametric Down-Conversion (SPDC) is a cornerstone phenomenon in nonlinear optics, where an incident high-energy photon is transformed into a pair of lower-energy photons. This quantum process serves as a fundamental tool for generating entangled photon pairs, heralded single photons, and squeezed light, making it indispensable in the realms of quantum communication, quantum computing, and precision metrology. In this paper, we present a comprehensive study on the theoretical foundations and practical realization of an SPDC experimental setup, developed for the first time at the Photonics Research Laboratory at Amirkabir University of Technology. Our setup features a self-grown potassium dihydrogen phosphate (KDP) nonlinear crystal, illuminated by a 450 nm blue laser, to achieve parametric down-conversion into infrared photon pairs at 900 nm. By integrating a custom-designed transimpedance amplifier with a BPX65 photodiode, we have successfully amplified and detected the weak SPDC signal, demonstrating the feasibility of achieving high sensitivity with low-cost, widely available components. The experimental results align closely with theoretical predictions, showcasing the effectiveness of the system in detecting photon pairs with minimal resources. This study underscores the accessibility and scalability of SPDC technology, providing a blueprint for constructing versatile quantum optics experiments in resource-limited settings. By bridging the gap between theoretical insight and experimental realization, we aim to inspire further exploration of SPDC's potential in both foundational research and practical applications, laying the groundwork for future innovations in quantum technologies.

Surface spontaneous parametric down-conversion is predicted as a consequence of continuity requirements for electric- and magnetic-field amplitudes at a discontinuity of chi2 nonlinearity. A generalization of the usual two-photon spectral amplitude is suggested to describe this effect. Examples of nonlinear layered structures and periodically-poled nonlinear crystals show that surface contributions to spontaneous down-conversion can be important.

A new method for characterization of periodically poled crystals is developed based on spontaneous parametric down-conversion. The method is demonstrated on crystals of Y:LiNbO3, Mg:Y:LiNbO3 with non-uniform periodically poled structures, obtained directly under Czochralski growth procedure and designed for application of OPO in the mid infrared range. Infrared dispersion of refractive index, effective working periods and wavelengths of OPO were determined by special treatment of frequency-angular spectra of spontaneous parametric down-conversion in the visible range. Two-dimensional mapping via spontaneous parametric down-conversion is proposed for characterizing spatial distribution of bulk quasi-phase matching efficiency across the input window of a periodically poled sample.

Strongly-driven nonlinear optical processes such as spontaneous parametric down-conversion and spontaneous four-wave mixing can produce multiphoton nonclassical beams of light which have applications in quantum information processing and sensing. In contrast to the low-gain regime, new physical effects arise in a high-gain regime due to the interactions between the nonclassical light and the strong pump driving the nonlinear process. Here, we describe and experimentally observe a gain-induced group delay between the multiphoton pulses generated in a high-gain type-II spontaneous parametric down-conversion source. Since the group delay introduces distinguishability between the generated photons, it will be important to compensate for it when designing quantum interference devices in which strong optical nonlinearities are required.

This thesis studies different designs of optical parametric oscillators as sources of atom-resonant quantum light resonant with the rubidium D1 line.We analyze the mode structure and filtering techniques in a conventional OPO based on a crystal inside a ring cavity. We also present a first fully-tunable design of a monolithic doubly-resonant OPO. The first part presents the study of a multimode optical parametric oscillator from the theoretical point of view, calculating a multimode Bogoliubov transformation and a time-domain intensity correlation function. Next, we experimentally observe signatures of multi- and singlemode OPO output in pairwise time-of-arrival correlations of the generated photons, achieved thanks to Faraday anomalous dispersion filtering technique based on optical properties of atomic vapor in magnetic field. The second, more extensive part of the thesis features the study of a new design of the OPO, a monolithic cavity (crystal polished and coated so that it forms a cavity) that allows full tunability even in a multiply resonant configuration. The architecture we propose combines the advantages of a conventional ring cavity based OPO, with robustness, lowmaintenance, compactness and stability characteristic of monolithic systems. The tunability of the doubly-resonant monolithic OPO is realized by maintaining different sections of the crystal at different temperatures and pressing it with a piezoelectric actuator. The tuning method is tested when the system is employed as a second harmonic generator. In addition, we describe a new nonlinear effect that comes into play when the monolithic cavity is pumped with 795 nm light. The phenomenon,that we call a photo-Kerr effect causes the cavity behavior resembling optical bistability due to Kerr nonlinearity, but with the magnitude (Kerr coefficient) dependent on the long-time average of intra-cavity power. The model we propose agrees well with the experimental results. The effect simplifies greatly the cavity stabilization, causing the cavity to maintain itself close to resonance even as the laser wavelength is changed by more than a free spectral range. The thesis concludes by studying the suitability of the monolithic cavity with the photo-Kerr effect for squeezed light generation. We test the monolithic cavity as an OPO and demonstrate 1.6 dB of quadrature squeezing via homodyne detection. Esta tesis estudia diferentes diseños de osciladores paramétricos (OPO, por sus signas en inglés) como fuentes de luz cuántica resonante con la línea D1 de átomos de rubidio. Analizamos la estructura de modos y las técnicas de filtrado en un oscilador paramétrico convencional basado en un cristal no lineal dentro de una cavidad. También presentamos el primer diseño de un OPO monolítico con dos resonancias con frecuencias ajustables. La primera parte de la tesis presenta el estudio de un oscilador paramétrico multimodo desde el punto de vista teórico, calculando una transformación de Bogoliubov multimodo y una función de correlación temporal de intensidad. A continuación, se observan experimentalmente las señales de la emisión de OPO multimodo o de un solo modo en correlaciones de tiempo de llegada de pares de los fotones generados, obtenidos gracias a la técnica de filtración de dispersión anómala de Faraday basada en las propiedades ópticas del vapor atómico en campo magnético. La segunda y más extensa parte de la tesis presenta el estudio de un nuevo diseño del OPO: una cavidad monolítica (cristal pulido y recubierto de tal manera que forma una cavidad) que permite ajustar las frecuencias de resonancia, incluso en una configuración multi-resonante. La arquitectura que proponemos combina las ventajas de una OPO convencional basada en una cavidad afuera de cristal, con robustez, bajo mantenimiento, compacidad y estabilidad característica de los sistemas monolíticos. La ajustibilidad del OPO monolítico con doble resonancia se realiza manteniendo diferentes secciones del cristal a diferentes temperaturas y presionándolo con un element piezoeléctrico. El método de afinación es sometido a prueba cuando el sistema se emplea como generador de segundo armónico. Además, describimos un nuevo efecto no lineal que entra en juego cuando la cavidad monolítica se bombea con luz 795 nm. El fenómeno que denominamos efecto photo-Kerr provoca que el comportamiento de la cavidad se asemeje a la biestabilidad óptica debido a la no linealidad de Kerr, pero con la magnitud (coeficiente de Kerr) dependiente del promedio de tiempo largo de la potencia de la luz dentro de la cavidad. El modelo numérico que proponemos coincide con los resultados experimentales. El efecto simplifica en gran medida la estabilización de la cavidad, hacienda que ésta se mantenga cerca de la resonancia incluso cuando la longitud de onda del láser cambia en más de la distancia entre dos resonancias consecutivas. La tesis concluye estudiando la idoneidad de la cavidad monolítica con el efecto photo-Kerr para la generación de luz comprimida. Se emplea la cavidad monolítica como oscilador paramétrico, obteniando luz comprimida y se demuestra 1.6 dB de squeezing mediante detección homodina.