Details
Original language  English 

Qualification  Doctor rerum naturalium 
Awarding Institution  
Supervised by 

Date of Award  17 Feb 2023 
Place of Publication  Hannover 
Publication status  Published  2023 
Abstract
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Hannover, 2023. 119 p.
Research output: Thesis › Doctoral thesis
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TY  BOOK
T1  Quantum backaction evasion and filtering in optomechanical systems
AU  Schweer, Jakob
N1  Doctoral thesis
PY  2023
Y1  2023
N2  The measurement precision of optomechanical sensors reached sensitivity levels such that they have to be described by quantum theory. In quantum mechanics, every measurement will introduce a backaction on the measured system itself. For optomechanical force sensors, a tradeoff between backaction and measurement precision exists through the interplay of quantum shot noise and quantum radiation pressure noise. Finding the optimal power to balance these effects leads to the standard quantum limit (SQL), which bounds the sensitivity of force sensing. To overcome the SQL and reach the fundamental bound of parameter estimation, the quantum CramérRao bound, techniques called quantum smoothing and quantum backaction evasion are required. The first part of this thesis explores quantum smoothing in the context of optomechanical force sensing. Quantum smoothing combines the concepts of prediction and retrodiction to estimate the parameters of a system in the past. To illustrate the intricacies of these estimations in the quantum setting, two filters, the Kalman and Wiener filters, are introduced. Their prediction and retrodiction estimates are given for a simple optomechanical setup, and resulting differences are analyzed concerning the available quantum smoothing theories in the literature. In the second part of this thesis, a backaction evasion technique called coherent quantumnoise cancellation (CQNC) is explored. In CQNC, an effective negativemass oscillator is coupled to an optomechanical sensor to create destructive interference of quantum radiation pressure noise. An alloptical realization of such an effective negativemass oscillator is introduced, and a comprehensive study of its performance in a cascaded CQNC scheme is given. We determine ideal CQNC conditions, analyze nonideal noise cancellation and provide a case study. Under feasible parameters, the case study shows a possible reduction of radiation pressure noise of 20% and that the effective negativemass oscillator as the first subsystem in the cascade is the preferable order.
AB  The measurement precision of optomechanical sensors reached sensitivity levels such that they have to be described by quantum theory. In quantum mechanics, every measurement will introduce a backaction on the measured system itself. For optomechanical force sensors, a tradeoff between backaction and measurement precision exists through the interplay of quantum shot noise and quantum radiation pressure noise. Finding the optimal power to balance these effects leads to the standard quantum limit (SQL), which bounds the sensitivity of force sensing. To overcome the SQL and reach the fundamental bound of parameter estimation, the quantum CramérRao bound, techniques called quantum smoothing and quantum backaction evasion are required. The first part of this thesis explores quantum smoothing in the context of optomechanical force sensing. Quantum smoothing combines the concepts of prediction and retrodiction to estimate the parameters of a system in the past. To illustrate the intricacies of these estimations in the quantum setting, two filters, the Kalman and Wiener filters, are introduced. Their prediction and retrodiction estimates are given for a simple optomechanical setup, and resulting differences are analyzed concerning the available quantum smoothing theories in the literature. In the second part of this thesis, a backaction evasion technique called coherent quantumnoise cancellation (CQNC) is explored. In CQNC, an effective negativemass oscillator is coupled to an optomechanical sensor to create destructive interference of quantum radiation pressure noise. An alloptical realization of such an effective negativemass oscillator is introduced, and a comprehensive study of its performance in a cascaded CQNC scheme is given. We determine ideal CQNC conditions, analyze nonideal noise cancellation and provide a case study. Under feasible parameters, the case study shows a possible reduction of radiation pressure noise of 20% and that the effective negativemass oscillator as the first subsystem in the cascade is the preferable order.
U2  10.15488/13289
DO  10.15488/13289
M3  Doctoral thesis
CY  Hannover
ER 