000221295 001__ 221295
000221295 005__ 20190509132559.0
000221295 0247_ $$2doi$$a10.5075/epfl-thesis-7202
000221295 02470 $$2urn$$aurn:nbn:ch:bel-epfl-thesis7202-7
000221295 02471 $$2nebis$$a10711746
000221295 037__ $$aTHESIS
000221295 041__ $$aeng
000221295 088__ $$a7202
000221295 245__ $$aQuantum limits on measurement and control of a mechanical oscillator
000221295 269__ $$a2016
000221295 260__ $$bEPFL$$c2016$$aLausanne
000221295 300__ $$a183
000221295 336__ $$aTheses
000221295 502__ $$aProf. Yves Bellouard (président) ; Prof. Tobias Kippenberg (directeur de thèse) ; Prof. Theo Lasser, Prof. Antoine Heidmann, Prof. Florian Marquardt (rapporteurs)
000221295 520__ $$aThe precision measurement of position has a long-standing tradition in physics.  Cavendish's verification of the universal law of gravitation using a torsion pendulum,  Perrin's confirmation of the atomic hypothesis via the precise measurement of the Brownian motion,  and, the verification of the mechanical effect of electromagnetic radiation,  all belong to this classical heritage. Quantum mechanics posits that the measurement of position  results in an uncertain momentum; an idea developed to full maturity within the context of interferometric searches for gravity waves. Over the past decade, standing at the confluence of quantum optics and nanomechanics, cavity optomechanics has emerged as a powerful platform to study the quantum limits of position measurements.  The subject of this thesis is the precision measurement of the position of a nano-mechanical oscillator,  the fundamental limits of such measurements, and its relevance to measurement-based feedback control. The nano-mechanical oscillator is coupled to light confined in an optical micro-cavity via radiation pressure.  The fluctuations in the position of the oscillator are transduced onto the phase of the light, while quantum fluctuations in the amplitude of the light leads to a disturbance in the momentum of the oscillator. We perform an interferometric position measurement with a sensitivity that is 10^5 times below what is required to resolve the zero-point motion of the oscillator, constituting the most precise measurement of thermal motion yet. The resulting disturbance -- measurement back-action -- is observed to be  commensurate with the uncertainty principle, leading to a 10% contribution to the total motion of the oscillator.   The continuous record of the measurement (performed in a 4 K cryogenic environment) furnishes the ability to resolve the zero-point motion of the oscillator within its decoherence rate - the necessary condition for  measurement-based feedback control of the state of the oscillator. Using the measurement record as error signal, the oscillator is cooled towards its ground state, resulting in a factor 10^4 suppression of  its total (thermal and back-action) motion, to a final occupation of 5 phonons on average.  Measurements generally proceed by establishing correlations between the system being measured and the  measuring device. For the class of quantum measurements employed here - continuous linear measurements - these correlations arise due to measurement back-action. These back-action-induced correlations appear  as correlations between the degrees of freedom of the measuring device. For interferometric position measurements, quantum correlations are established between the phase and amplitude of the light.  In a homodyne measurement, they lead to optical squeezing, while in a heterodyne measurement, they appear as an asymmetry in the sidebands carrying information about the oscillator position.  Feedback is used to enhance sideband asymmetry, a first proof-of-principle demonstration of the ability  to control quantum correlations using feedback. In the regime where  amplified vacuum noise dominates the feedback signal, the disappearance of sideband asymmetry visualises  a fundamental limit of linear feedback control. Using a homodyne detector, we also characterise these quantum correlations manifested as optical squeezing at the 1% level.
000221295 6531_ $$aquantum measurement
000221295 6531_ $$aquantum control
000221295 6531_ $$acavity optomechanics
000221295 6531_ $$aquantum optics
000221295 6531_ $$aquantum correlations
000221295 700__ $$0245939$$g201058$$aSudhir, Vivishek
000221295 720_2 $$aKippenberg, Tobias$$edir.$$g182444$$0244694
000221295 8564_ $$uhttps://infoscience.epfl.ch/record/221295/files/EPFL_TH7202.pdf$$zn/a$$s28357671$$yn/a
000221295 909C0 $$0252348$$pLPQM
000221295 909CO $$pSTI$$pthesis$$pthesis-bn2018$$pDOI$$pSB$$ooai:infoscience.tind.io:221295$$qDOI2$$qGLOBAL_SET
000221295 917Z8 $$x108898
000221295 917Z8 $$x108898
000221295 918__ $$dEDPO$$aSB
000221295 919__ $$aLPQM1
000221295 920__ $$b2016$$a2016-9-16
000221295 970__ $$a7202/THESES
000221295 973__ $$sPUBLISHED$$aEPFL
000221295 980__ $$aTHESIS