Dissertations / Theses on the topic 'Optical squeezing'

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2001.
Includes bibliographical references (p. 113-122).
by Charles Xiao Yu.
Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2008.
Includes bibliographical references (p. 55-57).
This project aims to reduce measurement uncertainty in atomic clocks by squeezing the collective spin of atoms. Spin-squeezing reduces noise below the standard quantum limit where precision scales as 1/ [square root of] N, allowing us to instead approach the Heisenberg limit where it scales as 1/N. We report spin-squeezing of the (F = 2, mR = 0) --> (F = 1, mF = 0) hyperfine transition of the 5S1/2 level of ⁸⁷Rb. We also demonstrate a viable setup for the spin-squeezing of the magnetically trappable (F = 2, mF = 1) --> (F = 1, mF = -1) transition, which could potentially be used as a compact frequency standard. This thesis provides a brief theoretical background of spin-squeezing and a summary of the project in its current state.
by Adele Ann Schwab.
S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2011.
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 (p. 128-133).
This thesis describes two methods of overcoming the standard quantum limit of signal-to-noise ratio in atomic precision measurements. In both methods, the interaction between an ultracold atomic ensemble and an optical resonator serves to entangle the atoms and deform the uncertainty distribution of the collective hyperfine spin so that it is narrower in some coordinate than would be possible if the atoms were uncorrelated. The first method uses the dispersive shift of the optical resonator's frequency by the atomic index of refraction to perform a quantum non-demolition measurement of the collective spin, projecting it into a squeezed state conditioned on the measurement outcome. The second method exploits the collective coupling of the atoms to the light field in the resonator to generate an effective interaction that entangles the atoms deterministically. Both methods are demonstrated experimentally, achieving metrologically relevant squeezing of 1.5(5) dB and 4.6(6) dB respectively, and simple analytical models, including the effects of scattering into free space, show that much greater squeezing is realistically achievable. To demonstrate the potential usefulness of such squeezing, a proof-of-principle atomic clock whose Allan variance decreases 2.8(3) three times faster than the standard quantum limit is also presented, together with a discussion of the conditions under which squeezing improves its performance.
by Ian Daniel Leroux.
Ph.D.

Le bruit quantique est une des limitations principales des détecteurs interférométriques d'ondes gravitationnelles, comme Virgo et LIGO. Réduire le bruit quantique a un impact direct sur la portée scientifique des futurs détecteurs d'ondes gravitationnelles (Advanced Virgo +, Advanced LIGO+, Einstein Telescope, Cosmic Explorer). L'origine du bruit quantique réside dans la nature quantique de la lumière, et en particulier dans les fluctuations du vide qui entrent par la sortie de l'interféromètre. Actuellement, l'injection d'états de vide comprimé (squeezing indépendant de la fréquence) dans Virgo et LIGO permet de réduire le bruit quantique dans la bande spectrale de détection correspondante à une des deux composantes de ce bruit, le bruit de photons, ou shot noise, pour des fréquences supérieures à environ 100 Hz. La pression de radiation, l'autre composante, se manifeste quant à elle à de plus basses fréquences. Le shot noise émane de l'incertitude sur la phase tandis que la pression de radiation, de l'incertitude sur l'amplitude. Le principe d'incertitude d'Heisenberg impose que la réduction du shot noise grâce à l'injection d'états du vide comprimé sur la phase, se traduise nécessairement par une augmentation de la pression de radiation. Cet état comprimé peut être représenté par une ellipse, illustrant l'état comprimé du vide dans l'espace phase-amplitude, où les incertitudes sur la phase et l'amplitude sont inégales. Cependant, cet effet a commencé à dégrader la sensibilité des interféromètres Virgo et LIGO, durant la prise de données appelée O3. Afin de réduire le bruit quantique sur toute la bande spectrale de détection (et donc aussi à basse fréquence), il est nécessaire d'introduire dans l'interféromètre un squeezing dépendant de la fréquence, c'est-à-dire un état du vide comprimé, tantôt sur l'amplitude et tantôt sur la phase, permettant de réduire à la fois la pression de radiation et le shot noise. Pour Advanced Virgo+ et Advanced LIGO+ (les projets d'améliorations en cours, pour les détecteurs actuels, appelés Advanced Virgo et Advanced LIGO), l'ajout d'une cavité de filtrage quantique suspendue de 300 mètres et avec une très grande finesse, permettra de réaliser ce squeezing dépendant de la fréquence. Ma thèse porte sur le développement de techniques de squeezing pour la réduction du bruit quantique dans les futurs détecteurs d'ondes gravitationnelles. J'ai d'abord contribué à un travail expérimental sur l'automatisation et l'amélioration d'une source de squeezing indépendant de la fréquence et situé sur le site de Virgo, à Pise. Ce travail préparatoire a été réalisé pour la conception d'un banc de démonstration pour l'étude d'une technique de squeezing dépendant de la fréquence, alternative à celle proposée ci-dessus et basée sur l'intrication quantique (de type Einstein-Podolsky-Rosen). Les fondements théoriques de ce squeezing EPR ayant été proposés en 2017, cette technique présente des avantages pour les futurs détecteurs d'ondes gravitationnelles, notamment liés à l'absence de cavité de filtrage. Dans ce cadre, j'ai participé au design optique complet de cette expérience, qui pourra être implémentée sur le détecteur Virgo. J'ai conçu, réalisé et testé dans le laboratoire optique de l'APC, une cavité Fabry-Perot monolithique (de type étalon) nécessaire pour la séparation et la détection de deux faisceaux intriqués. Plus précisément, j'ai effectué des mesures de caractérisation optique et sur la stabilisation thermique de cette cavité, permettant de conclure sur les performances de cet étalon
Quantum noise is one of the main limitations for interferometric gravitational-wave (GW) detectors as Virgo and LIGO. Reducing quantum noise has a direct impact on the science reach of future GW detectors (Advanced Virgo +, Advanced LIGO+, Einstein Telescope, Cosmic Explorer). Quantum noise originates from the quantum nature of light, especially from the vacuum fluctuations entering by the interferometer detection stage. The current injection of vacuum squeezed states (frequency-independent squeezing) into Virgo and LIGO leads to the quantum noise reduction in the spectral detection region corresponding to one of the two components of quantum noise. This so-called quantum shot noise is present at frequencies higher than 100 Hz. The other quantum noise component, the so-called quantum radiation pressure noise, manifests itself at lower frequencies. Shot noise arises from the uncertainty on the phase, while the latter arises from the uncertainty on the amplitude. Heisenberg's uncertainty principles induce that the shot noise reduction, thanks to the injection of vacuum squeezed states, results in a radiation pressure noise increase. This squeezed state of light can be depicted with an ellipse, representing the squeezed states in a phase-amplitude space, with inequal uncertainties for the phase and the amplitude. Nonetheless, during the data-taking period called O3, this subsequent noise increase started to degrade the Virgo and LIGO interferometers' sensitivities. To achieve a broadband reduction of quantum noise, it is necessary to inject a frequency-dependent squeezing inside the interferometer, i.e., injecting vacuum squeezed states in a frequency-dependent way, which will have a smaller uncertainty accordingly to the concerned quantum noise component. For the next upgrade of the current detectors Advanced Virgo and Advanced LIGO, called Advanced Virgo+ and Advanced LIGO+, frequency-dependent squeezing is obtained by adding a suspended 300-meter filter cavity, with very high finesse. My thesis engages in the development of squeezing techniques for quantum noise reduction in future GW detectors. First, I contributed to an experimental work based on the automation and the improvement of a frequency-independent squeezed vacuum source located on the Virgo site, at Pisa. This was a preparatory work for the conception of a table-top experiment to study a frequency-dependent squeezing technique, alternative compared to the one proposed previously and based on Einstein-Podolsky-Rosen entanglement. The theory being brought forward in 2017, this technique offers significant advantages for future GW detectors, due to the absence of an external cost-intensive filter cavity. In this framework, I participated to the realization of a complete optical design for this experimental demonstrator, that can be implemented into the detector Virgo. I designed, realized, and tested a monolithic Fabry-Perot cavity (a solid etalon), at the optical laboratory of APC, necessary for the separation and detection of two entangled beams. More precisely, this cavity was optically characterized and its thermal stabilization was evaluated, which allowed to check its performances

The quantum properties of matter waves, in particular quantum correlations and entanglement are an important frontier in atom optics with applications in quantum metrology and quantum information. In this thesis, we report the first observation of sub-Poissonian fluctuations in the magnetization of a spinor 87Rb condensate. The fluctuations in the magnetization are reduced up to 10 dB below the classical shot noise limit. This relative number squeezing is indicative of the predicted pair-correlations in a spinor condensate and lay the foundation for future experiments involving spin-squeezing and entanglement measurements. We have investigated the limits of the imaging techniques used in our lab, absorption and fluorescence imaging, and have developed the capability to measure atoms numbers with an uncertainly < 10 atoms. Condensates as small as ≈ 10 atoms were imaged and the measured fluctuations agree well with the theoretical predictions. Furthermore, we implement a reliable calibration method of our imaging system based on quantum projection noise measurements. We have resolved the individual lattice sites of a standing-wave potential created by a CO2 laser, which has a lattice spacing of 5.3 µm. Using microwaves, we site-selectively address and manipulate the condensate and therefore demonstrate the ability to perturb the lattice condensate of a local level. Interference between condensates in adjacent lattice sites and lattice sites separated by a lattice site are observed.

Les plasmons polaritons de surface (SPP) et les plasmons localisés de surface (LSP) font l’objet de nombreuses investigations du fait de leur fort potentiel technologique. Récemment, une attention particulière a été portée à des systèmes supportant ces deux types de résonances en déposant des nanoparticules (NPs) métalliques sur des films minces métalliques. Plusieurs études ont mis en évidence le couplage et l’hybridation entre modes localisés et délocalisés. Cependant, une compréhension en profondeur des propriétés optiques et du potentiel de ces interfaces est toujours manquante. Nous avons mené ici une étude de systèmes NPs/film couplés. Nous avons étudié à la fois expérimentalement et théoriquement l’influence d’une couche séparatrice ultra-mince en SiO2 ainsi que l’évolution des différents modes plasmoniques pour différentes épaisseurs. Nous avons ainsi mis en lumière que de tels systèmes couplés offrent des propriétés optiques exaltées et une large accordabilité spectrale. Nous avons aussi cherché à diminuer l’épaisseur de la couche séparatrice vers le cas ultime monoatomique en utilisant le graphène. Du fait du caractère non-diélectrique de celui-ci, nous avons mis en évidence un comportement optique inattendu de la résonance plasmonique. Nous avons expliqué celui-ci par la mise en évidence du dopage du graphène par les NPs, ce qui est un premier pas en direction de dispositifs optoélectroniques à base de graphène. Enfin, après avoir amélioré notre compréhension théorique de ces systèmes, nous avons évalué leur potentiel comme capteurs SERS ou LSP
Surface plasmon polariton (SPP) and Localized surface plasmon (LSP) have attracted numerous researchers due to their high technological potential. Recently, strong attention was paid to the potential of SPP and LSP combinations by investigating metallic nanoparticles (NPs) on top of metallic thin films. Several studies on such systems have shown the coupling and hybridization between localized and delocalized modes. In this work, we propose a full systematic study on coupled NP/film systems with Au NPs and Au films. We investigate both experimentally and theoretically the influence of an ultra-thin SiO2 dielectric spacer layer, as well as the evolution of the plasmonic modes as the spacer thickness increases. We show that coupled systems exhibit enhanced optical properties and larger tunability compared to uncoupled systems. We also compare these results with those measured for coupled interfaces using graphene as a non-dielectric sub-nanometer spacer. Introducing graphene adds complexity to the system. We show that such coupled systems also exhibit enhanced optical properties and larger tunability of their spectral properties compared to uncoupled systems as well as unexpected optical behavior. We explain this behavior by evidencing graphene doping by metallic NPs, which can be a first step towards graphene based optoelectronic devices. After establishing a deep understanding of coupled systems we perform both SERS and RI sensing measurements to validate the high potential of these plasmonic interfaces

This dissertation aims to investigate systems in which several optical and mechanical degrees of freedom are coupled through optomechanical interactions. Multimode optomechanics creates the prospect of integrated functional devices and it allows us to explore new types of optomechanical interactions which account for collective dynamics and optically mediated mechanical interactions. Owing to the development of fabrication techniques for micro- and nano-sized mechanical elements, macroscopic mechanical oscillators can be cooled to the deep quantum regime via optomechanical interaction. Based on the possibility to control the motion of mechanical oscillators at the quantum level, we design several schemes involving mechanical systems of macroscopic length and mass scales and we explore the nonlinear dynamics of mechanical oscillators. The first scheme includes a quantum cantilever coupled to a classical tuning fork via magnetic dipole-dipole interaction and also coupled to a single optical field mode via optomechanical interaction. We investigate the generation of nonclassical squeezed states in the quantum cantilever and their detection by transferring them to the optical field. The second scheme involves a quantum membrane coupled to two optical modes via optomechanical interaction. We explore dynamic stabilization of an unstable position of a quantum mechanical oscillator via modulation of the optical fields. We then develop a general formalism to fully describe cavity mediated mechanical interactions. We explore a rather general configuration in which multiple mechanical oscillators interact with a single cavity field mode. We specifically consider the situation in which the cavity dissipation is the dominant source of damping so that the cavity field follows the dynamics of the mechanical modes. In particular, we study two limiting regimes with specific applications: the weak-coupling regime and single-photon strong-coupling regime. In the weak-coupling regime, we build a protocol for quantum state transfer between mechanical modes. In the single-photon coupling regime, we investigate the nonlinear nature of the mechanical system which generates bistability and bifurcation in the classical analysis and we also explore how these features manifest themselves in interference, entanglement, and correlation in the quantum theory.

In this thesis, we report the observations of optical squeezing from second harmonic generation (SHG), optical parametric oscillation (OPO) and optical parametric amplification (OPA). Demonstrations and proposals of applications involving the squeezed light and electro-optic control loops are presented. ¶ In our SHG setup, we report the observation of 2.1 dB of intensity squeezing on the second harmonic (SH) output. Investigations into the system show that the squeezing performance of a SHG system is critically affected by the pump noise and a modular theory of noise propagation is developed to describe and quantify this effect. Our experimental data has also shown that in a low-loss SHG system, intra-cavity nondegenerate OPO modes can simultaneously occur. This competition of nonlinear processes leads to the optical clamping of the SH output power and in general can degrade the SH squeezing. We model this competition and show that it imposes a limit to the observable SH squeezing. Proposals for minimizing the effect of competition are presented. ¶ In our OPO setup, we report the observation of 7.1 dB of vacuum squeezing and more than 4 dB of intensity squeezing when the OPO is operating as a parametric amplifier. We present the design criteria and discuss the limits to the observable squeezing from the OPO.We attribute the large amount of squeezing obtained in our experiment to the high escape efficiency of the OPO. The effect of phase jitter on the squeezing of the vacuum state is modeled. ¶ The quantum noise performance of an electro-optic feedforward control loop is investigated. With classical coherent inputs, we demonstrate that vacuum fluctuations introduced at the beam splitter of the control loop can be completely cancelled by an optimum amount of positive feedforward. The cancellation of vacuum fluctuations leads to the possibility of noiseless signal amplification with the feedforward loop. Comparison shows that the feedforward amplifier is superior or at least comparable in performance with other noiseless amplification schemes. When combined with an injection-locked non-planar ring Nd:YAG laser, we demonstrate that signal and power amplifications can both be noiseless and independently variable. ¶ Using squeezed inputs to the feedforward control loop, we demonstrate that information carrying squeezed states can be made robust to large downstream transmission losses via a noiseless signal amplification. We show that the combination of a squeezed vacuum meter input and a feedforward loop is a quantum nondemolition (QND) device, with the feedforward loop providing an additional improvement on the transfer of signal. In general, the use of a squeezed vacuum meter input and an electro-optic feedforward loop can provide pre- and post- enhancements to many existing QND schemes. ¶ Finally, we proposed that the quantum teleportation of a continuous-wave optical state can be achieved using a pair of phase and amplitude electro-optic feedforward loops with two orthogonal quadrature squeezed inputs. The signal transfer and quantum correlation of the teleported optical state are analysed. We show that a two dimensional diagram, similar to the QND figures of merits, can be used to quantify the performance of a teleporter.

Nesta dissertação, descreveremos as primeiras medidas de ruído quântico em um oscilador paramétrico ótico (OPO) bombeado em 780 nm, construído no nosso laboratório. Esse OPO servirá de fonte de estados não clássicos da luz para interação com átomos de rubídio. Faremos uma revisão da teoria clássica do OPO: o bombeamento de um cristal não linear inserido dentro de uma cavidade ótica, produzindo dois feixes intensos de luz (sinal e complementar) com cores distintas. Calcularemos as expressões para o limiar de oscilação, potências de saída dos feixes convertidos e compararemos as principais diferenças entre OPOs com cristais do tipo I e tipo II. Analisaremos a descrição quântica do OPO, calcularemos os espectros de ruído para as quadraturas do bombeio refletido e para as quadraturas dos feixes gêmeos. Veremos que o OPO gera feixes com correlações quânticas, como o emaranhamento tripartido, entres os três feixes envolvidos no processo não linear. O cristal não linear utilizado no nosso experimento é um PPKTP tipo I. Ajustando a temperatura do cristal, podemos gerar feixes próximos da degenerescência até uma diferença de comprimentos de onda de aproximadamente 350 nm. A compressão de ruído quântico observado na diferença das amplitudes dos feixes sinal e complementar é 44%(-2.5 dB). O próximo passo é a implementação da técnica da rotação da elipse de ruído por cavidades óticas, para medir os ruídos de fase dos três campos . Fazendo a verificação do emaranhamento tripartido e determinando a sua dependência com o ruído de fônons inserido pelo cristal, a caracterização do OPO estará completa. A caracterização deste OPO é um passo importante nos objetivos do LMCAL, que é realizar a troca de informação entre luz e átomos em uma rede quântica.
In this dissertation, we will describe the first measurements of quantum noise in an optical parametric oscillator (OPO) pumped at 780 nm, built at our laboratory. This OPO will be the source of nonclassical states of light to interact with rubidium atoms. We will review the classical OPO theory: the pumping of a nonlinear crystal inside a cavity producing two bright light beams (signal and idler) with different colors. We will calculate the power threshold, output power of the converted beams and compare the main differences between type-I and type-II OPO.We will analyze the quantum description of the OPO, and calculate the noise spectrum of the reflected pump quadratures and for the twin beams quadratures. We will observe that the OPO generates beams with quantum correlations, for example, the tripartite entanglement among the three fields involved in the nonlinear phenomena. The nonlinear crystal used in our experiment is a PPKTP type-I. By adjusting the temperature of the crystal, we can generate beams from close to degenerate regime to a difference between them of 350 nm. The squeezing of quantum noise measured in the amplitude quadratures subtraction for signal and idler is 44%(-2.5 dB). The next step is to implement the method of ellipse noise rotation by an optical cavity, to be able to measure phase quadratures of the three different fields. By verifying the tripartite entanglement and determining the phonon noise due to the crystal, our source characterization will be complete. The characterization of this OPO is an important step in LMCAL goals, which is to realize exchange of information between light and atoms in a quantum network.

L'astronomie gravitationnelle a débuté en septembre 2015 avec la première détection de la fusion de deux trous noirs par LIGO. Depuis lors, plusieurs fusions de trous noirs et une fusion d'étoiles à neutrons ont été observées. Advanced Virgo a rejoint les deux observatoires LIGO dans la prise de données en août 2017, augmentant fortement les capacités de localisation du réseau. Afin d'exploiter pleinement le potentiel scientifique de ce nouveau domaine, un énorme effort expérimental est nécessaire pour améliorer la sensibilité des interféromètres. Cette thèse, développée dans ce contexte, est composée de deux parties. La première concerne Advanced Virgo : nous avons développé un budget de bruit automatique pour le bruit de fréquence du laser et nous avons effectué des mesures de caractérisation optique pour les cavités de bras kilométriques. Des pertes aller-retour aussi faibles que 80 ppm ont été mesurées. Elles sont parmi les plus basses jamais mesurées avec un faisceau de cette taille. La deuxième partie concerne la conception et le développement d'une cavité de filtrage de 300 m, un prototype pour démontrer la production de lumière squeezing dépendante de la fréquence avec les propriétés nécessaires pour une réduction du bruit quantique à large bande dans KAGRA, Advanced Virgo et Advanced LIGO. Nous avons contribué à la fois aux phases de conception et d'intégration du projet. Nous avons d'abord fait le design optique de la cavité, y compris les spécifications pour l'optique de la cavité et une estimation détaillée des sources de dégradation pour le squeezing. Nous avons donc développé un système de contrôle pour les miroirs, assemblé les suspensions et finalement aligné et mis la cavité en résonance avec la lumière laser
Gravitational wave astronomy has started in September 2015 with the first detection of a binary black-hole merger by LIGO. Since then, several black-hole mergers and a binary neutron star merger have been observed. Advanced Virgo joined the two LIGO detector in the observation run, in August 2017, highly increasing the localization capabilities of the network. In order to fully exploit the scientific potential of this new-born field, a huge experimental effort is needed to bring the instruments at their design sensitivity and to further improve them. This thesis, developed in this context, it is composed of two parts. The first is about Advanced Virgo: we have developed an automatic noise budget for the laser frequency noise and we have performed optical characterization measurements for the kilometric arm cavities. Round trip Losses as low as 80 ppm have been measured. They are among the lowest ever measured for beams of these size. The second part is about the design and development of a 300 m filter cavity, a prototype to demonstrate the frequency dependent squeezing production with properties needed for a broadband quantum noise reduction in the future upgrades of KAGRA, Advanced Virgo and Advanced LIGO. We have contributed to the design and integration phases of the project. We have first made the optical design of the cavity, including the the specifications for the main cavity optics and a detailed estimation of the squeezing degradation sources. We have then developed a local control system for the mirrors, assembled the suspensions, and finally aligned and brought the cavity in resonance with the laser light

Free space gradient force traps are hugely versatile experimental systems. Their realisation opens up new avenues for the exploration of various areas of fundamental physics, including both quantum physics and thermodynamics. Their high levels of sensitivity also have attractive implications for force sensing. In this thesis a novel experimental setup will be presented, along with experimental protocols, as a framework upon which such studies can be built. Using a paraboloidal mirror to create a diffraction limited, gradient force optical trap, the motion of nanoparticles ranging from 18 nm to 312 nm in diameter was detected via a single photodiode. Several properties of the levitated particles were measured, including: the mass, radius, oscillation amplitude (via the use of a volts to metre conversion factor) and the damping experienced at various pressures. This was done via two methods. The first, widely established, method required fitting a power spectral density, derived using the kinetic theory of gases, to the motion of the particle. The second, novel method, involved scanning the wavelength of the trapping laser. Using this method, it was possible to determine the mass of a levitated particle without assuming the kinetic model and material density. From the wavelength scan, the sensitivity of the experimental system was measured to be 200 fm/√Hz. Within this optical setup, the ability to control the trap frequencies of all three motional degrees of freedom, through varying the power of the trapping laser, was demonstrated. The ability to independently control and separate the transverse trapping frequencies from one another, as well as from the z axis, was also shown to be possible, using elliptically polarized light. The effect of changing the pressure inside the chamber in which a levitated nanoparticle is trapped is also explored. Trapping of nanoparticles at pressures as low as 10^-5 mbar, without any active feedback, was achieved. A method for measuring the internal temperature of levitated particles was then demonstrated. This was done through measuring and fitting the Planck equation to the emitted thermal spectrum of a levitated silica nanoparticle. It was then shown that the temperature of levitated particles can be controlled via the intensity of the laser light as well as the pressure within the chamber. Over a pressure range of 1000 mbar to 0.04 mbar, an increase of temperature from 388 K to 480 K was measured. In the range of trapping laser intensities between 0.21 TW/m2 and 0.4 TW/m2, the resulting change ofa particle's temperature, from 367 K to 463 K, was observed. To control the centre of mass motion of levitated particles within the optical trap, parametric feedback cooling was implemented via modulation of the trap depth. Using this technique, the effect different feedback parameters have on particle motion was explored. The combination of optimizing the feedback parameters, alongside reducing the pressure, resulted in temperatures of T_z = 14 ±1 mK, T_x = 5 ±1 mK and T_y = 7 ±1 = mK. The observed Q factors on the order of 10⁷ with predicted Q factors on the order of 10¹² hold great promise for the realisation of ultrasensitive force detection. The system presented here has a force sensitivity on the order of 10^-20 N pHz. Theoretical considerations show that, with some improvements to the experimental system, it would be possible to achieve centre of mass temperatures, and thus low phonon numbers, close to the quantum ground state. The second method to control the centre of mass motion of a levitated nanoparticle used squeezing pulses to classically squeeze its mechanical motion. This quadrature squeezing was achieved via non-adiabatic shifts of the nanoparticle's trap frequency and was carried out on a number of particles. The squeezing pulses implemented consisted of a rapid reduction in the trap frequency, followed by a brief period in time where the system was allowed to evolve, before the trapping frequency was rapidly returned to its original value. The effect of using single and multiple pulses to control this was explored and the optimal duration for a squeezing pulse characterized. For a single pulse, the maximum amount of squeezing was found to be λ = 3.2 ± 0.2 dB. To further increase the amount of squeezing applied to the levitated nanoparticle, a multiple pulse scheme was implemented. The effect of varying the time between pulses was investigated and the optimal time was found. The maximum amount of squeezing achieved in the system, occurred after 5 pulses, giving a squeezing factor of λ 9.4 ± 0.1 dB. The multiple pulse scheme was then applied to parametrically feedback cooled nanoparticles. The effect on the phase space, including its decay to a thermal state, after the application of squeezing pulses was characterized. The squeezing on parametricaly cooled particles. after the application of 5 pulses, was measured and the squeezing factor found to be λ = 8.4 ± 0.1 dB.

Quantum control of many body atomic spins is often pursued in the context of an atom-light quantum interface, where a quantized light field acts as a "quantum bus" that can be used to entangle distant atoms. One key challenge is to improve the coherence of the atom-light interface and the amount of atom-light entanglement it can generate, given the constraints of working with multilevel atoms and optical fields in a 3D geometry. We have explored new ways to achieve this, through rigorous optimization of the spatial geometry, and through control of the internal atomic state. Our basic setup consists of a quantized probe beam passing through an atom cloud held in a dipole trap, first generating spin-probe entanglement through the Faraday interaction, and then using backaction from a measurement of the probe polarization to squeeze the collective atomic spin. The relevant figure of merit is the metrologically useful spin squeezing determined by the enhancement in the resolution of rotations of the collective spin, relative to the commonly used spin coherent state. With an optimized free-space geometry, and by using a 2-color probe scheme to suppress tensor light shifts, we achieve 3(2) dB of metrologically useful spin squeezing. We can further increase atom-light coupling by implementing internal state control to prepare spin states with larger initial projection noise relative to the spin coherent state. Under the right conditions this increase in projection noise can lead to stronger measurement backaction and increased atom-atom entanglement. With further internal state control the increased atom-atom entanglement can then be mapped to a basis where it corresponds to improved squeezing of, e.g., the physical spin-angular momentum or the collective atomic clock pseudospin. In practice, controlling the collective spin of N ~ 10⁶ atoms in this fashion is an extraordinarily difficult challenge because errors in the control of individual atoms tend to be highly correlated. By employing precise internal state control, we have prepared and detected projection noise limited "cat" states (which have initial projection noise that is larger by a factor of 2f = 8 for Cs relative to the spin coherent state) and estimate that we can generate up to 6.0(5) dB of metrologically useful spin squeezing, demonstrating the advantage of using the internal atomic structure as a resource for ensemble control.

The primary study of this thesis is spin-nematic squeezing in a spin-1 condensate. The measurement of spin-nematic squeezing builds on the success of previous experiments of spin-mixing together with advances in low noise atom counting. The major contributions of this thesis are linking theoretical models to experimental results and the development of the intuition and tools to address the squeezed subspaces. Understanding how spin-nematic squeezing is generated and how to measure it has required a review of several theoretical models of spin-mixing as well as extending these existing models. This extension reveals that the squeezing is between quadratures of a spin moment and a nematic (quadrapole) moment in abstract subspaces of the SU(3) symmetry group of the spin-1 system. The identification of the subspaces within the SU(3) symmetry allowed the development of techniques using RF and microwave oscillating magnetic fields to manipulate the phase space in order to measure the spin-nematic squeezing. Spin-mixing from a classically meta-stable state, the phase space manipulation, and low noise atom counting form the core of the experiment to measure spin-nematic squeezing. Spin-nematic squeezing is also compared to its quantum optics analogue, two-mode squeezing generated by four-wave mixing. The other experimental study in this thesis is performing spin-dependent photo-association spectroscopy. Spin-mixing is known to depend on the difference of the strengths of the scattering channels of the atoms. Optical Feshbach resonances have been shown to be able to alter these scattering lengths but with prohibitive losses of atoms near the resonance. The possibility of using multiple nearby resonances from different scattering channels has been proposed to overcome this limitation. However there was no spectroscopy in the literature which analyzes for the different scattering channels of atoms for the same initial states. Through analysis of the initial atomic states, this thesis studies how the spin state of the atoms affects what photo-association resonances are available to the colliding atoms based on their scattering channel and how this affects the optical Feshbach resonances. From this analysis a prediction is made for the extent of alteration of spin-mixing achievable as well as the impact on the atom loss rate.

The processing of information based on the generation of common quantum optical states (e.g. coherent states) and the measurement of the quadrature components of the light field (e.g. homodyne detection) is often referred to as continuous-variable quantum information processing. It is a very fertile field of investigation, at a crossroads between quantum optics and information theory, with notable successes such as unconditional continuous-variable quantum teleportation or Gaussian quantum key distribution. In quantum optics, the states of the light field are conveniently characterized using a phase-space representation (e.g. Wigner function), and the common optical components effect simple affine transformations in phase space (e.g. rotations). In quantum information theory, one often needs to determine entropic characteristics of quantum states and operations, since the von Neuman entropy is the quantity at the heart of entanglement measures or channel capacities. Computing entropies of quantum optical states requires instead turning to a state-space representation of the light field, which formally is the Fock space of a bosonic mode.

This interplay between phase-space and state-space representations does not represent a particular problem as long as Gaussian states (e.g. coherent, squeezed, or thermal states) and Gaussian operations (e.g. beam splitters or squeezers) are concerned. Indeed, Gaussian states are fully characterized by the first- and second-order moments of mode operators, while Gaussian operations are defined via their actions on these moments. The so-called symplectic formalism can be used to treat all Gaussian transformations on Gaussian states, including mixed states of an arbitrary number of modes, and the entropies of Gaussian states are directly linked to their symplectic eigenvalues.

This thesis is concerned with the Gaussian transformations applied onto arbitrary states of light, in which case the symplectic formalism is unapplicable and this phase-to-state space interplay becomes highly non trivial. A first motivation to consider arbitrary (non-Gaussian) states of light results from various Gaussian no-go theorems in continuous-variable quantum information theory. For instance, universal quantum computing, quantum entanglement concentration, or quantum error correction are known to be impossible when restricted to the Gaussian realm. A second motivation comes from the fact that several fundamental quantities, such as the entanglement of formation of a Gaussian state or the communication capacity of a Gaussian channel, rely on an optimization over all states, including non-Gaussian states even though the considered state or channel is Gaussian. This thesis is therefore devoted to developing new tools in order to compute state-space properties (e.g. entropies) of transformations defined in phase-space or conversely to computing phase-space properties (e.g. mean-field amplitudes) of transformations defined in state space. Remarkably, even some basic questions such as the entanglement generation of optical squeezers or beam splitters were unsolved, which gave us a nice work-bench to investigate this interplay.

In the first part of this thesis (Chapter 3), we considered a recently discovered Gaussian probabilistic transformation called the noiseless optical amplifier. More specifically, this is a process enabling the amplification of a quantum state without introducing noise. As it has long been known, when amplifing a quantum signal, the arising of noise is inevitable due to the unitary evolution that governs quantum mechanics. It was recently realized, however, that one can drop the unitarity of the amplification procedure and trade it for a noiseless, albeit probabilistic (heralded) transformation. The fact that the transformation is probabilistic is mathematically reflected in the fact that it is non trace-preserving. This quantum device has gained much interest during the last years because it can be used to compensate losses in a quantum channel, for entanglement distillation, probabilistic quantum cloning, or quantum error correction. Several experimental demonstrations of this device have already been carried out. Our contribution to this topic has been to derive the action of this device on squeezed states and to prove that it acts quite surprisingly as a universal (phase-insensitive) optical squeezer, conserving the signal-to-noise ratio just as a phase-sensitive optical amplifier but for all quadratures at the same time. This also brought into surface a paradoxical effect, namely that such a device could seemingly lead to instantaneous signaling by circumventing the quantum no-cloning theorem. This paradox was discussed and resolved in our work.

In a second step, the action of the noiseless optical amplifier and it dual operation (i.e. heralded noiseless attenuator) on non-Gaussian states has been examined. We have observed that the mean-field amplitude may decrease in the process of noiseless amplification (or may increase in the process of noiseless attenuation), a very counterintuitive effect that Gaussian states cannot exhibit. This work illustrates the above-mentioned phase-to-state space interplay since these devices are defined as simple filtering operations in state space but inferring their action on phase-space quantities such as the mean-field amplitude is not straightforward. It also illustrates the difficulty of dealing with non-Gaussian states in Gaussian transformations (these noiseless devices are probabilistic but Gaussian). Furthermore, we have exhibited an experimental proposal that could be used to test this counterintuitive feature. The proposed set-up is feasible with current technology and robust against usual inefficiencies that occur in optical experiment.

Noiseless amplification and attenuation represent new important tools, which may offer interesting perspectives in quantum optical communications. Therefore, further understanding of these transformations is both of fundamental interest and important for the development and analysis of protocols exploiting these tools. Our work provides a better understanding of these transformations and reveals that the intuition based on ordinary (deterministic phase-insensitive) amplifiers and losses is not always applicable to the noiseless amplifiers and attenuators.

In the last part of this thesis, we have considered the entropic characterization of some of the most fundamental Gaussian transformations in quantum optics, namely a beam splitter and two-mode squeezer. A beam splitter effects a simple rotation in phase space, while a two-mode squeezer produces a Bogoliubov transformation. Thus, there is a well-known phase-space characterization in terms of symplectic transformations, but the difficulty originates from that one must return to state space in order to access quantum entropies or entanglement. This is again a hard problem, linked to the above-mentioned interplay in the reverse direction this time. As soon as non-Gaussian states are concerned, there is no way of calculating the entropy produced by such Gaussian transformations. We have investigated two novel tools in order to treat non-Gaussian states under Gaussian transformations, namely majorization theory and the replica method.

In Chapter 4, we have started by analyzing the entanglement generated by a beam splitter that is fed with a photon-number state, and have shown that the entanglement monotones can be neatly combined with majorization theory in this context. Majorization theory provides a preorder relation between bipartite pure quantum states, and gives a necessary and sufficient condition for the existence of a deterministic LOCC (local operations and classical communication) transformation from one state to another. We have shown that the state resulting from n photons impinging on a beam splitter majorizes the corresponding state with any larger photon number n’ > n, implying that the entanglement monotonically grows with n, as expected. In contrast, we have proven that such a seemingly simple optical component may have a rather surprising behavior when it comes to majorization theory: it does not necessarily lead to states that obey a majorization relation if one varies the transmittance (moving towards a balanced beam splitter). These results are significant for entanglement manipulation, giving rise in particular to a catalysis effect.

Moving forward, in Chapter 5, we took the step of introducing the replica method in quantum optics, with the goal of achieving an entropic characterization of general Gaussian operations on a bosonic quantum field. The replica method, a tool borrowed from statistical physics, can also be used to calculate the von Neumann entropy and is the last line of defense when the usual definition is not practical, which is often the case in quantum optics since the definition involves calculating the eigenvalues of some (infinite-dimensional) density matrix. With this method, the entropy produced by a two-mode squeezer (or parametric optical amplifier) with non-trivial input states has been studied. As an application, we have determined the entropy generated by amplifying a binary superposition of the vacuum and an arbitrary Fock state, which yields a surprisingly simple, yet unknown analytical expression. Finally, we have turned to the replica method in the context of field theory, and have examined the behavior of a bosonic field with finite temperature when the temperature decreases. To this end, information theoretical tools were used, such as the geometric entropy and the mutual information, and interesting connection between phase transitions and informational quantities were found. More specifically, dividing the field in two spatial regions and calculating the mutual information between these two regions, it turns out that the mutual information is non-differentiable exactly at the critical temperature for the formation of the Bose-Einstein condensate.

The replica method provides a new angle of attack to access quantum entropies in fundamental Gaussian bosonic transformations, that is quadratic interactions between bosonic mode operators such as Bogoliubov transformations. The difficulty of accessing entropies produced when transforming non-Gaussian states is also linked to several currently unproven entropic conjectures on Gaussian optimality in the context of bosonic channels. Notably, determining the capacity of a multiple-access or broadcast Gaussian bosonic channel is pending on being able to access entropies. We anticipate that the replica method may become an invaluable tool in order to reach a complete entropic characterization of Gaussian bosonic transformations, or perhaps even solve some of these pending conjectures on Gaussian bosonic channels.

Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

Dans le cadre de l'amélioration du détecteur d'ondes gravitationnelles Advanced Virgo, il est nécessaire de réduire la contribution du bruit quantique au bruit du détecteur afin d'augmenter la sensibilité et donc le volume d'Univers observable. Pour cela une des techniques envisagées afin de dépasser la Limite Quantique Standard est l'utilisation d'états comprimés de la lumière, dit états squeezés, dépendant de la fréquence. L'implémentation de cette technique est testée sur la plateforme expérimentale CALVA au LAL/IJCLab dans le cadre de l'ANR Exsqueez en collaboration avec le LKB, le LMA/IP2I et le LAPP. L'objet de cette thèse est la conception de l'expérience ainsi que l'installation et la caractérisation des premiers systèmes optiques utilisés pour générer et mesurer des états squeezés indépendants de la fréquence
In the context of the improvement of the Advanced Virgo gravitational wave detector, the quantum noise contribution to the detector noise has to be reduced in order to increase its sensitivity and consequently the observable volume of the Universe. One of the idea to go beyond the Standard Quantum Limit is to use frequency dependent squeezed states of light. The implementation of this technique is tested on the CALVA experiment at LAL/IJCLab in the framework of the Exsqueez ANR in collaboration with LKB, LMA/IP2I and LAPP. The aim of this thesis is the design of the experiment followed by the installation and characterization of the first optical systems used to produce and measure frequency independent squeezing

碩士
國立中山大學
光電工程學系研究所
102
Coherent lightwave communications systems are approaching a limit where the error rates and channel capacities are limited by the quantum properties of light. This is often referred to as the shot-noise limit. If ideal laser light is used in the system, there is no way to avoid this limit. However, a novel idea to improve the receiver sensitivity of the coherent detection system is proposed in this master thesis. This novel idea is fulfilled through some numerical simulations. The theoretical study of quantum squeezing is explained, and the simulation method uses two algorithms to compose. The details of these two algorithms, phase rotation and phase sensitive amplification, will be explained. There are two simulations demonstrated in this master thesis, intensity modulation direct detection (IM-DD) and binary phase shift keying (BPSK). The results for these two simulations are demonstrated after the explanations of both simulations.

Liu, Xiaopi = 光格子势中玻色爱因斯坦凝聚体的压缩,纠缠与激发谱 / 刘小披.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2007.
Includes bibliographical references (leaves 97-100).
Abstracts in English and Chinese.
Liu, Xiaopi = Guang ge zi shi zhong bo se ai yin si tan ning ju ti de ya suo, jiu chan yu ji fa pu / Liu Xiaopi.
Chapter 1 --- Introduction --- p.1
Chapter 1.1 --- Review of Superfluidity and B.E. Condensation --- p.1
Chapter 1.2 --- Our Understanding of superfluidity --- p.4
Chapter 1.3 --- Non-classicality in Quantum Mechanics --- p.8
Chapter 2 --- One-Component BECs in optical lattices --- p.16
Chapter 2.1 --- Introduction: The Hamiltonian --- p.16
Chapter 2.2 --- The Hamiltonian in Quasi-momentum space --- p.19
Chapter 2.3 --- Bogoliubov Method and Equation of Motion --- p.21
Chapter 2.3.1 --- Squeezing and Condensation --- p.27
Chapter 2.3.2 --- Two-mode Entanglement and Squeezing --- p.31
Chapter 3 --- Matrix method approach to ground state BECs --- p.39
Chapter 3.1 --- Matrix method --- p.39
Chapter 3.2 --- Ground state and Particle Distribution --- p.42
Chapter 3.3 --- Correlation in Pair Ground State --- p.46
Chapter 4 --- Attractive BECs in optical lattices --- p.50
Chapter 5 --- 2-component BECs in optical lattice --- p.56
Chapter 5.1 --- Model Hamiltonian --- p.56
Chapter 5.2 --- Excitation Spectrum and Critical super-fluid velocity --- p.59
Chapter 5.3 --- Excitation spectrum and Phase Separation Dynamics --- p.63
Chapter 5.4 --- Excitation Spectrum for Asymmetric 2-component BECs --- p.67
Chapter 6 --- Multi-Mode Squeezing of 2-component BECs in optical lattices --- p.69
Chapter 6.1 --- Simultaneous Diagonalization --- p.69
Chapter 6.2 --- Equation of Motion and Variance Matrix --- p.70
Chapter 6.3 --- U(n) Squeezing of Variance Matrix --- p.75
Chapter 6.4 --- Squeezing in the case qA≠ qB and nA≠ nB --- p.82
Chapter 7 --- Entanglement between 2-component BECs in optical lattices --- p.83
Chapter 7.1 --- Variance matrix in block diagonal --- p.83
Chapter 7.2 --- 2-component entangled variance matrix --- p.86
Chapter 7.3 --- Logarithmic negativity --- p.89
Chapter 7.4 --- Beat oscillation mode of logarithmic negativity --- p.91
Chapter 8 --- Conclusion and Outlook --- p.95
Bibliography --- p.97

Quantum control theory is a rapidly evolving research field, which has developed over the last three decades. Quantum optics has practical importance in quantum technology and provides a promising means of implementing quantum information and computing device. In quantum control, it is difficult to acquire information about quantum states without destroying them since microscopic quantum systems have many unique characteristics such as entanglement and coherence which do not occur in classical mechanical system. Therefore, the Lyapunov-based control methodology is used to first construct an artificial closed-loop controller and then an open-loop law is derived by simulation of the artificial closed-loop system. This work considers the stabilization of laser cavity as the main integral part of quantum optical systems through squeezing the output beam of the cavity. As a comprehensive example of this type of system, quantum optomechanical sensors are investigated. To this end, a nonlinear model of quantum optomechanical sensors is first extended incorporating various noises. Then, linear quadratic Gaussian (LQG) control method is used to tackle the problem of mode-squeezing in optomechanical sensors. Coherent feedback quantum control is synthesized by incorporating both shot noise and back-action noise to attenuate the output noise well below the shot noise level (Two waves are said to be coherent if they have a constant relative phase). In the second phase of this work, due to entanglement of the system with critical uncertainties and technical limitations such as laser noise and detector imprecision, robust H [infinity] method is employed for the robust stabilization and robust performance of the system in practice. In H [infinity] methods, a control designer expresses the control problem as a mathematical optimization problem and then finds the controller that solves this. The effectiveness of the proposed control strategy in squeezing the cavity output beam is demonstrated by simulation.

博士
國立交通大學
光電工程系所
93
In this dissertation we study the quantum optical phenomena in photonic crystals. In the part of atom-light interaction, the steady state fluorescence spectra of a two-level atom embedded in a three-dimensional photonic bandgap crystal are predicted to get squeezed in the in-phase quadrature spectra. In the part of nonlinear photonic crystals, we use the back-propagation method to study the quantum fluctuations of optical Bragg solitons propagating in nonlinear fiber Bragg gratings and matter-wave gap solitons in optical lattices. Finally, new schemes for generating continuous-variable entangled states through continuous interaction of two solitons are proposed to produce entangled optical sources for quantum communication and computation.

In this thesis, we report the observations of optical squeezing from second harmonic generation (SHG), optical parametric oscillation (OPO) and optical parametric amplification (OPA). Demonstrations and proposals of applications involving the squeezed light and electro-optic control loops are presented. ¶ ...

Quantum mechanics allows us to use nonclassical states of light to make measurements with a greater precision than comparable classical states. Here an experiment is presented that squeezes the polarization state of three photons. We demonstrate the deep connection that exists between squeezing and entanglement, unifying the squeezed state and multi-photon entangled state approaches to quantum metrology. For the first time we observe the phenomenon of over-squeezing where a system is squeezed to the point that further squeezing leads to a counter-intuitive increase in measurement uncertainty. Quasi-probability distributions on the surface of a Poincaré sphere are the most natural way to represent the topology of our polarization states. Using this representation it is easy to observe the squeezing and over-squeezing behaviour of our photon states. Work is also presented on two different technologies for generating nonclassical states of light. The first is based on the nonlinear process of spontaneous parametric downconversion to produce pairs of photons. With this source up to 200,000 pairs of photons/s have been collected into single-mode fibre, and over 100 double pairs/s have been detected. This downconversion source is suitable for use in a wide variety of multi-qubit quantum information applications. The second source presented is a single-photon source based on semiconductor quantum dots. The single-photon character of the source is verified using a Hanbury Brown-Twiss interferometer.

Gravitational waves are "ripples" in spacetime emitted by massive astrophysical events. Over the past decade, interferometric detectors have been used to measure gravitational waves from the binary mergers of black holes and neutron stars to learn more about such systems; these gravitational waves had frequencies around 100 Hz. Other frequencies of gravitational waves are thought to exist and contain valuable information but are yet to be detected. For example, detecting kilohertz (1–4 kHz) gravitational waves from binary neutron-star mergers could be used to further constrain the neutron-star equation-of-state and better understand exotic states of matter. However, to do so, the sensitivity of current detectors will need to be extended from 100 Hz to the kilohertz regime. The kilohertz sensitivity of current gravitational-wave detectors is limited by quantum noise from the fundamental quantum uncertainties in the state of light inside the detector. This noise can be mitigated by replacing the vacuum fluctuations entering the readout port of the detector with squeezed states. In this thesis, I investigate a new technique to improve kilohertz sensitivity by placing a nondegenerate squeezer inside the detector. This technique, called nondegenerate internal squeezing, improves sensitivity by amplifying the detector's response to the gravitational-wave signal more than it increases the quantum noise. To assess its feasibility, I derive an analytic Hamiltonian model of nondegenerate internal squeezing and calculate its sensitivity and stability as well as analyse its tolerance to the realistic optical losses expected in a future gravitational-wave detector. My model indicates that nondegenerate internal squeezing is stable, robust to detection loss in the readout, and provides a viable alternative to other proposals to improve kilohertz sensitivity. I demonstrate a technique to determine its squeezing threshold and, therefore, the limits of its operation. I find that nondegenerate internal squeezing could feasibly improve the sensitivity of a future detector to 1–4 kHz gravitational waves. I also explore an alternative readout scheme that is promising for broadband 0.1–4 kHz sensitivity.

Squeezed states of light are quantum states that can be used in numerous protocols for quantum computation and quantum communication. Their generation in labora- tories has been investigated before, but they still lack compactness and practicality to easily integrate them into larger experiments. This thesis considers two experiments: one conducted in France, the miniOPO; and one conducted in Australia, the SquOPO. Both are new designs of compact sources of squeezed states of light towards an integrated system. The miniOPO is a linear cavity of 5mm length between the end of a fiber and a curved mirror with a PPKTP crystal of 1mm inside it. The squeezing generated in this cavity is coupled into the fiber to be able to be brought to a measurement device (homodyne) or to a larger experiment. The cavity is resonant for the squeezed light and the pump light, and locked in frequency using self-locking effects due to absorption of the pump in the crystal. The double resonance is achieved by changing the temperature of the crystal. Two different fibers have been tested in this experiment, a standard single-mode fiber and a photonic large core single-mode fiber. The squeezing obtained is still quite low (0.5dB with the standard fiber and 0.9dB for the photonic fiber) but a number of ameliorations are investigated to increase these levels in the future. The SqOPO is a monolithic square cavity made in a Lithium Niobate crystal using four total internal reflections on the four faces of the square to define an optical mode for the squeezed mode and the pump mode. The light is coupled in the resonator using frustrated internal reflection with prisms. The distance between the prisms and the resonator defined the coupling of the light, which allows us to control the finesse of the light in the resonator and by using birefringent prisms it is possible to tune independently the two frequencies in the resonator to achieve an optimal regime. The frequency of the light is locked using absorption of the pump light in the resonator to achieve self-locking, and double resonance is controlled by tuning the temperature of the crystal. We demonstrated 2.6dB of vacuum squeezing with this system. Once again, the amount of squeezing is low, but ameliorations that could be implemented in the future are discussed.

Gravitational waves manifest as a time varying straining of space: they arise from the accelerating motions of large bodies of mass and propagate across the universe at the speed of light as ripples in the fabric of space-time, a fleetingly weak effect so far eluding direct detection. The detection of gravitation waves is expected to yield a rich vein to observational astronomy, complementing existing electromagnetic surveys and revealing a hitherto unexplored range of phenomena. First generation interferometric gravitational wave detectors, notably Enhanced LIGO, achieved strain sensitivities of one part in ten to power twenty-one per square-root-Hertz at 100 Hz with an expected detection rate of 2-3 events per year. Commissioning of a new generation of Advanced LIGO interferometric detectors has concluded recently with a resultant ten-fold sensitivity improvement. Overall their potential event detection space has increased by a factor of 1000. The quantum nature of light within these detectors now limits their sensitivity over most of their frequency range. This quantum noise limit is driven by the vacuum quadrature fluctuations propagated through their open detection ports and represents a fundamental noise floor to their strain sensitivity. This thesis addresses two distinct approaches to quantum noise improvement for future upgrades to advanced detectors. The first addresses the issue of quantum noise by adopting a quantum non-demolition approach to detector readout variables, the so-called `speed-meter’ design. Such a modified instrument samples test mass momentum, a quantity for which time separated measurements commute and are therefore not bound by Heisenberg-like limits. A novel polarisation-folded sloshing cavity type speed-meter is proposed where readout fields are stored and delayed in the orthogonal polarisation of the interferometer’s arms cavities. Here frequency dependence is selected to cancel position like measurements so that only test mass momentum information remains. A quantum noise propagation model is developed and a sensitivity performance is demonstrated that beats the standard quantum limit below 100 Hz over a broad range of frequencies. A second approach to achieve quantum noise enhancement in advanced detectors involves injection of quadrature-squeezed states in the place of vacuum. This dissertation details the development of a prototype squeezed vacuum source suitable to the demanding enhancement requirements for an Advanced LIGO squeezing installation. The construction of a doubly resonant, bow-tie cavity source is presented. This employs a novel monolithic all-glass cavity construction and is vacuum compatible. This design demonstrates the viability of building a cavity using optical contacting as a construction technique for attaching mounting prisms to highly polished fused-silica breadboards. Such a design can be expected to have excellent length noise stability, provide low intrinsic phase noise and would be suitable to mount on seismic isolation stages within the LIGO vacuum envelope. Further, the travelling wave cavity design should provide excellent 50 dB intrinsic backscatter isolation. We demonstrate the first operation of such a complex non-linear device under vacuum, producing 8.6 dB of measured vacuum squeezing down to 10 Hz across the advanced LIGO ‘audio-band’ detection range.