TY - BOOK

T1 - Characterisation and integration of an optomechanical system for an all-optical CQNC experiment

AU - Schulte, Bernd Wolfgang

PY - 2023

Y1 - 2023

N2 - This thesis presents the development and characterisation of an optomechanical system (OMS) with the aim to be part of an all-optical coherent quantum noise cancellation scheme (CQNC), as proposed by Tsang & Caves in 2010. The goal of such a CQNC experiment is to enhance the sensitivity of conventional optomechanical displacement and force detectors. Their sensitivity limit is described by a trade-off between shot noise and quantum backaction noise, forming the standard quantum limit of interferometry. This thesis explores the fundamental principles of CQNC and investigates the potential benefits of modifying the mechanical oscillator’s dynamics in the OMS through dynamical backaction using a second beam. The findings suggest that such modifications may be advantageous in the resolved sideband regime. Further investigations are needed due to the vast parameter space involved. However, as shown in previous studies and recapitulated within this thesis, even without a cooling beam quantum backaction noise suppression within an all-optical CQNC experiment is feasible. The experimental setup for an all-optical CQNC involves a shot noise limited probe beam. To achieve this condition, a filter cavity is used to suppress laser amplitude noise. The results indicate that the amplitude noise in transmission is shot noise limited above frequencies of 1 MHz at a power of 1 mW, making this stabilisation scheme suitable for a CQNC experiment. The main focus of this thesis is the development and characterisation of the optomechanical system, one subsystem of the CQNC experiment. The work focused on achieving and measuring a high optomechanical coupling strength (g) between light and a silicon nitride membrane representing the mechanical oscillator. Thus, experimental investigations are conducted to determine the optimal position within the optomechanical system where the coupling strength is highest. However, measurements at cryogenic temperatures, necessary for quantum backaction noise limitation, could not be performed due to technical challenges. The operation of the optomechanical oscillator in a cryogenic environment remains a pending task. Nevertheless, two experiments of the optomechanical system are successfully performed at room temperature and low pressure (10−7 mbar). Both experiments, an optomechanically induced transparency (OMIT) experiment and a dynamical backaction (DBA) experiment provide relevant values. The measurements reveal that the membrane used in the experiments is unsuitable for all-optical CQNC due to its quality factors and coupling strength, which do not meet the quantum backaction cooperativity requirement. To improve precision in extracting quality factors and achieve higher sensitivity, a ring-down measurement is recommended for future investigations. Also, once measurements at cryogenic temperature are feasible, techniques like displacement calibration and quantum noise thermometry for accurate temperature measurements have to be established. In conclusion, the developed optomechanical system holds promise for realising all-optical CQNC once optomechanical oscillators with higher quality factors are used, and cryogenic temperature operation becomes feasible. The thesis also touches upon strategies to surpass the standard quantum limit (SQL) and cancel quantum backaction noise using an all-optical CQNC scheme with an effective negative mass oscillator. Further characterisation and investigation of the positive mass oscillator are conducted to advance the implementation of all-optical CQNC.

AB - This thesis presents the development and characterisation of an optomechanical system (OMS) with the aim to be part of an all-optical coherent quantum noise cancellation scheme (CQNC), as proposed by Tsang & Caves in 2010. The goal of such a CQNC experiment is to enhance the sensitivity of conventional optomechanical displacement and force detectors. Their sensitivity limit is described by a trade-off between shot noise and quantum backaction noise, forming the standard quantum limit of interferometry. This thesis explores the fundamental principles of CQNC and investigates the potential benefits of modifying the mechanical oscillator’s dynamics in the OMS through dynamical backaction using a second beam. The findings suggest that such modifications may be advantageous in the resolved sideband regime. Further investigations are needed due to the vast parameter space involved. However, as shown in previous studies and recapitulated within this thesis, even without a cooling beam quantum backaction noise suppression within an all-optical CQNC experiment is feasible. The experimental setup for an all-optical CQNC involves a shot noise limited probe beam. To achieve this condition, a filter cavity is used to suppress laser amplitude noise. The results indicate that the amplitude noise in transmission is shot noise limited above frequencies of 1 MHz at a power of 1 mW, making this stabilisation scheme suitable for a CQNC experiment. The main focus of this thesis is the development and characterisation of the optomechanical system, one subsystem of the CQNC experiment. The work focused on achieving and measuring a high optomechanical coupling strength (g) between light and a silicon nitride membrane representing the mechanical oscillator. Thus, experimental investigations are conducted to determine the optimal position within the optomechanical system where the coupling strength is highest. However, measurements at cryogenic temperatures, necessary for quantum backaction noise limitation, could not be performed due to technical challenges. The operation of the optomechanical oscillator in a cryogenic environment remains a pending task. Nevertheless, two experiments of the optomechanical system are successfully performed at room temperature and low pressure (10−7 mbar). Both experiments, an optomechanically induced transparency (OMIT) experiment and a dynamical backaction (DBA) experiment provide relevant values. The measurements reveal that the membrane used in the experiments is unsuitable for all-optical CQNC due to its quality factors and coupling strength, which do not meet the quantum backaction cooperativity requirement. To improve precision in extracting quality factors and achieve higher sensitivity, a ring-down measurement is recommended for future investigations. Also, once measurements at cryogenic temperature are feasible, techniques like displacement calibration and quantum noise thermometry for accurate temperature measurements have to be established. In conclusion, the developed optomechanical system holds promise for realising all-optical CQNC once optomechanical oscillators with higher quality factors are used, and cryogenic temperature operation becomes feasible. The thesis also touches upon strategies to surpass the standard quantum limit (SQL) and cancel quantum backaction noise using an all-optical CQNC scheme with an effective negative mass oscillator. Further characterisation and investigation of the positive mass oscillator are conducted to advance the implementation of all-optical CQNC.

KW - kohärente Quantenrauschunterdrückung (CQNC)

KW - StandardQuantenlimit (SQL)

KW - optomechanisch induzierte Transparenz (OMIT)

KW - dynamische Rückwirkung (DBA)

KW - Quantenrückwirkungkooperativität

KW - coherent quantum-noise cancellation

KW - standard quantum limit

KW - optomechanical induced transparency

KW - dynamical backaction

KW - quantum backaction cooperativity

U2 - 10.15488/15472

DO - 10.15488/15472

M3 - Doctoral thesis

CY - Hannover

ER -