We developed a high speed homodyne detector in the telecommunication wavelength region for a Gaussian-modulated coherent-state quantum key distribution experiment. We are able to achieve a 100 MHz bandwidth, ultra-low electronic noise and pulse-resolved homodyne detector. The bandwidth of this homodyne detector has reached the same order of magnitude of the best homodyne detectors reported. By overcoming photodiode response functions mismatch, choosing proper laser sources, ensuring the homodyne detector linearity and stabilizing the homodyne detection system, we demonstrate that the homodyne detector has a 10 dB shot-noise-to-electronic-noise ratio in the time domain at a local oscillator of 5.4*10^8 photons/pulse at a laser repetition rate of 10 MHz. With this homodyne detector, we expect to ncrease our GMCS QKD experiment speed by 100 times, which will improve the key generation rate by 1-2 orders of magnitude.

We developed a high speed homodyne detector in the telecommunication wavelength region for a Gaussian-modulated coherent-state quantum key distribution experiment. We are able to achieve a 100 MHz bandwidth, ultra-low electronic noise and pulse-resolved homodyne detector. The bandwidth of this homodyne detector has reached the same order of magnitude of the best homodyne detectors reported. By overcoming photodiode response functions mismatch, choosing proper laser sources, ensuring the homodyne detector linearity and stabilizing the homodyne detection system, we demonstrate that the homodyne detector has a 10 dB shot-noise-to-electronic-noise ratio in the time domain at a local oscillator of 5.4*10^8 photons/pulse at a laser repetition rate of 10 MHz. With this homodyne detector, we expect to ncrease our GMCS QKD experiment speed by 100 times, which will improve the key generation rate by 1-2 orders of magnitude.

Quantum correlations play a fundamental role in quantum information science. The variety of their manifestations has become increasingly apparent following the development of novel light sources, protocols and photodetectors. One broad classification identifies two instances of non-classical correlations: particle and mode entanglement. These categories mirror two coexisting descriptions of quantum systems in terms of discrete and continuous variables of the electromagnetic field. The past decades have generated a number of promising results based on schemes which encompass elements from both frameworks, rather than viewing the two descriptions as mutually exclusive. In this context, it is possible to conceive and realise experiments where either the quantum resource or the detection system is 'hybrid'. Optical weak-field homodyne detectors bring together phase sensitivity and photon counting; as such, they represent a detection scheme which works across continuous and discrete variables of the radiation field. In this thesis we present a two-mode weak-field homodyne detection layout with added photon-number resolution and apply it to the study of a split single-photon state and a squeezed vacuum state. As a first test of the capabilities of this system, we investigate the reconstruction of relevant features of a given quantum resource - such as its photon statistics - with our detection scheme. Further, we experimentally demonstrate the observation of an instance of non-classical optical coherence which combines the continuous- and discrete-variable descriptions explicitly. The ability to probe phenomena at the interface of wave and particle regimes opens the way to novel, improved schemes for quantum information processing. From a more fundamental perspective, such hybrid approaches may shed light on the very roots of quantum enhancement.

In this work I have evaluated a measurement method for glucose concentration in aqueous solutions and developed a system that performs the measurement and presents the result on a computer screen. The method is based on the dielectric properties of glucose and the varying phase shift of a microwave resonance cavity. The phase shift is measured using homodyne detection. The measurement system can measure the concentration of glucose in aqueous solutions in real time. I have tested concentrations from 0 to 3000 mg/dl. / I detta arbete har jag undersökt en metod för att mäta glukoskoncentration och med denna metod konstruerat en mätutrustning som visar glukoskoncentrationen för ett prov på en datorskärm. Mätningen baseras på radiovågor och permittiviteten för glukoslösningar. För att mäta permittiviteten används en mikrovågsresonanskavitet och homodyn detektering. Det gör det möjligt att mäta även mycket små prov, och detta utan att vara i direkt kontakt med provet. Mätsystemet kan mäta koncentrationen på vattenlösningar av glukos i realtid. Jag har testat systemet på koncentrationer mellan 0 och 3000 mg/dl.

The diploma work deals with techniques of optical contactless distance and velocity measurement. A basic summary of the methods are involved. The problematic of interferometric methods for vibration measurements is analysed in detail. It contains division of interferometers, description of their function principles and also chapters dealing with elements used in interferometers such as lasers, photodetectors and elements in the ray optical way - polarizers, retarders, optical isolators. The vibration and length measurement methods are described, as well as the conception of homodyne and heterodyne detection. Part of this work focuses on the quadrature signal processing and on the proposal of algorithm for demodulation of velocity/displacement and undergoing simple motioning object deviation. This algorithm is implemented in Labview and the whole software instrument served also for visualisation of measured data of the interferometer model constructed in the laboratory. The way how to build up a model, its setting and two possible configurations suitable for homodyne detection are described. Model of interferometer is built-up on the optical breadboard. Particular components are fixed by the help of mounts. The model and software enable to measure the velocity and the vibration deviation with the light wavelength exactness. Functionality and the exactness of the laboratory model are verified by vibrometer. Effects on the measurement uncertainty are discussed here and ways how to restrain them are proposed.

L'objectif de cette thèse concerne la manipulation à l'échelle quantique du champ électromagnétique dans le cadre de l'information quantique à variables continues. Pour ce faire nous mélangeons les outils de l'optique quantique à variables discrètes, où la lumière est décrite en termes de photons, avec l'approche continue, traitant des quadratures du champ. Cette technique permet de produire des états non-classiques décrits par des fonctions de Wigner prenant des valeurs négatives. Nous avons pu générer des états intriqués à partir d'impulsions lumineuses initialement indépendantes et pouvant être séparées par une longue distance, l'intrication s'effectuant au travers d'un canal acceptant de fortes pertes. Nous avons ensuite démontré et caractérisé expérimentalement un protocole non-déterministe permettant d'amplifier de faibles signaux sans en amplifier le bruit quantique, augmentant ainsi le rapport signal sur bruit. Puis nous avons mis en œuvre et comparé expérimentalement différentes mesures de non-gaussianité d'un état quantique : ce caractère propre à une description continue de la lumière est d'un intérêt capital pour l'information quantique. Enfin nous avons développé et testé deux améliorations pour notre dispositif. La première est un amplificateur femtoseconde pour notre laser impulsionnel, qui permettra d'obtenir de meilleurs états de départ pour nos expériences. La deuxième est un appareil capable de discriminer le nombre de photon, donnant ainsi des résultats plus précis que ceux des détecteurs dont nous disposons actuellement qui sont uniquement capable de détecter la présence de photons. / This thesis aims at handling the electromagnetic field at a quantum scale in the area of quantum information processing. For this purpose we mixed tools of discrete variable quantum optics, where light is described in terms of photons, with the continuous approach, which uses the quadratures of the field. This technique enables the production of non-classical states which should be described by Wigner functions that takes negative values. We have generated entangled states from ultra-short light pulses initially independent and which can be separated by a long distance: the entanglement is indeed performed through a low-transmission channel. Then we have experimentally demonstrated and characterized a protocol that non-deterministically amplifies low signals without amplifying the quantum noise, increasing the signal to noise ratio. Furthermore we experimentally implement and compared several measures of the non-gaussianity of a quantum state: this characteristic, which belongs to continuous description of light, is of essential interest for quantum information processing. Finally we develop and test two improvements for our setup. The first one is a femtosecond amplifier for our pulsed laser. It will enable us to obtain better primitive states for our experiments. The second one is an apparatus that can discriminate the number of photon in a pulse, giving more accurate results than the detectors we used up to now that are only able to detect the presence of photons.