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Title: Quantum Effects in Optomechanical Systems
Authors: Ahmed, Rizwan
Keywords: Physical Sciences
Issue Date: 2019
Publisher: Pakistan Institute of Engineering & Applied Sciences, Islamabad.
Abstract: Quantumoptomechanicsbecameaprofoundrecentinterestthatgivesrisetomanyapplications of quantum mechanics for macroscopic systems. In recent years, quantum optomechanics focuses on the manipulation of mechanical motion under the incident radiation pressure force. The phenomenon of optomechanical interaction can be used toengineerquantumentanglementbetweenopticalmodeandmechanicalmotion. This thesisismainlybasedupondifferentschemesforsteady-stateentanglementbyemployingopticalparametricprocesses. Weareintendedtostudytheoptomechanicalentanglement,weconsiderednon degenerate optical parametric amplifier (NOPA) as a gain medium inside a bimodal cavity, with one movable mirror. The system exploits non-linear effects because of the presence of nonlinear parametric amplifier within the optical cavity. Entanglement quantification has been done by employing logarithmic negativity. The findings of our results is that the entanglement between optical field and mechanical mode can be enhancedandmaderobustbecauseofNOPApresentwithinthesystem. Wehaveshowed thatthereexistsaconsiderableinfluenceofsystemparametersuponentanglemente.g., inputlaserpowers,decayrate,meanphononnumberandtheparametricphase. During this study, We found that an appropriate choice of parametric gain not only enhances the entanglement but also increases the robustness against thermal effects. An importantresultistheinfluenceofparametricphaseonentanglement,whichisrelatedtothe phase matching condition for momentum conservation. This study concludes that, a carefulchoiceofsystemparametersleadtooptimalentanglement. Next,weintroducedanopticalparametricconverter(OPC)insideabimodaloptomechanicalcavity. Ourresultsdemonstratedthekeyfeaturesofentanglementandits dependenceuponvarioussystemparameters. Itisevidentfromtheobtainedresultsthat entanglement can be optimized by a careful selection of system parameters like, parametric phase. We conclude this study that, in general, parametric converter stabilizes themechanicalinstabilitywhichresultsinenhancedentanglementspectrum,bothinred andbluesidebandregimes. Therefore,wecansafelyclaimthatinclusionofparametric converterleadstotheenhancementofentanglementspectrum. xii Laserphasenoise(LPN)isanunavoidablesourceofnoise,evenwiththepresent day technology. We considered a Kerr-down conversion medium inside a single-mode optomechanical cavity under the influence of pump laser phase noise. We studied the effect of different system parameters with non-zero laser phase noise, on the optomechanical entanglement. It is well known that inclusion of LPN greatly affects the amount of achievable entanglement, since LPN acts as a decoherence channel. However,ourresultsshowthatentanglementisstillachievableeveninthepresenceofLPN. Interestingly,wefindthatseveralsystemparameterscontributespositivelytowardsthe enhancementofentanglement, likeinputlaserpower, parametricgainGandnonlinear Kerr non-linearity. In addition, we infer that the inclusion of Kerr down-converter enhances the magnitude of entanglement domain in a two-fold way. Firstly, parametric gain leads to the increased in the photon number inside the cavity and therefore, gives rise to an increased radiation pressure on the movable mirror which results in entanglement enhancement. Secondly, Kerr non-linearity contributes to the stability of the system and therefore, increases the domain of the entanglement spectrum. Our results show that the addition of a Kerr down-converter to the optomechanical cavity can improve the robustness of entanglement even in the presence of LPN.
Gov't Doc #: 20243
Appears in Collections:PhD Thesis of All Public / Private Sector Universities / DAIs.

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