Cavity'Optomechanics:'Controlling' Light'and'Motion'at'the'Quantum' Level'' '

Transcription

1 Cavity'Optomechanics:'Controlling' Light'and'Motion'at'the'Quantum' Level'' ' ALBERT SCHLIESSER SWISS FEDERAL INSTITUTE OF TECHNOLOGY, EPFL, LAUSANNE Max-Planck-Institute of Quantum Optics, Munich, Niels Bohr Institute, Copenhagen

2 Cavity'Optomechanics:'' Controlling'Light'and'Motion'at'the'Quantum'Level' Albert'Schliesser'' Cavity'Optomechanics:'Backaction'and'Quantum'Motion' Oursenseofsightiscentraltoourexperienceoftheworldinevery7daylife.But lighthasalsobeen,forcenturies,theprimarytoolforscientistslooking deeper, trying to understand the inner workings of the universe we live in. Ever more sophisticated measurements with light have enabled us to study the laws that govern the world all the way from atomic to galactic length scales. Today, our mosttrustedphysicaltheories,quantummechanicsandrelativitytheory,are,to alargeextent,abstractionsofobservationsmadewithopticalinstruments.these observationsrelyonthefactthatmostobjects beitabacteriumoracloudof interstellardust interactwithlight,andmodifyitsproperties. Itislesswidelyknownthatwhenlightinteractswiththeseobjects,italso acts back on them. In particular, light exerts forces. Historically, the concept of optical forces has been known for long: Kepler already speculated about their natureinthe17 th century,inspiredbytheobservationthatthetailsofcomets always point away from the sun. Maxwell put this concept on more solid theoretical grounds in the 1860ies. However, still in the beginning of the 20 th century, Heisenberg and Bohr debated the role of optical forces when they strived to understand the process of an optical measurement of a particle s positioninquantummechanicalterms. In the 1970ies, theorists around the world started to revisit the role of opticalforcesinprecisionmeasurements.theycametorealizethattheseforces could beconsidered a particular form of backaction a mechanism inherent to any measurement process obeying the laws of quantum mechanics. And remarkably, while the latter continued to be confirmed by ever more sophisticated experiments with atoms and ions, controversies on their implicationsformeasurementsinvolvinglargerobjectsremainedopenduringall of the 20 th century. The Russian physicist Vladimir B. Braginsky and his

3 coworkers,andtheus7americancarltonm.cavescouldsettlemanyofthose,by workingoutatheoryofbackactionforcesinopticalmeasurements,embeddedin the framework of a comprehensive theory of Quantum/ Measurements using electromagneticwaves 173. Figure 1 shows a rendering of a Gedankenexperiment illustrating some elementary features of backaction forces in optical measurements: an interferometer,consistingoftwomirrors,betweenwhichalaserbeambounces back and forth. The interferometer couples and traps the laser light best if the distancebetweenthemirrorsisanintegermultipleofthelaser swavelength.if thewavelengthisknown,theinstrumentcanthusbeusedtopreciselymeasure the distance between the mirrors. However, optical forces may change this distance illustratedherebyamirrormountedonaspring,readytomovewhen aforceisapplied.unavoidablequantumfluctuationsofthelight sintensitymay set the mirror into random motion, rendering its position, and therefore the distancetobemeasured,ill7(orlesssharply)defined. Figure'1.'A'generic'optomechanical'system:'An'optical'interferometer'consisting'of'two'mirrors,'one' of' which' is' moveable.' Only' if' the' distance' between' the' mirrors' equals' an' integer' multiple' of' the' laser s' wavelength,' laser' light' couples' into' the' interferometer' particularly' well,' and' is' trapped' between'the'mirrors.'thus'the'distance'between'the'mirrors'can'be'measured.'on'the'other'hand,' the'presence'of'the'laser'light'also'exerts'a'force which'may'deflect'the'spring'holding'one'mirror,' thus'changing'this'distance.'

4 It may seem that this effect, and the instrument shown in Figure 1, are a constructwithlittlepracticalorscientificimpact.thecontraryisthecase.infact, suchinterferometersareattheheartofsomeofthemostsensitiveexperiments thatscientistshaveeverrealized:gravitationalwaveantennas(figure2a)rely onapairofsuchinterferometerswithsuspendedmirrors,eachwithkilometer7 scalelengthforanewkindofobservationalastronomy 4.Apairofblackholes,for example,spiralingintoeachother,shouldinducemeasurablelengthchangesdue to the general7relativistic distortion of space7time that their motion induces. While astronomers hope to dramatically extend the observable space with this technique, they require sheer stunning sensitivity: At present, scientists can discernlengthdifferencesof meterifaveragingtheirdataforonesecond thatcorrespondsto1/1000ofthediameterofaproton buthighersensitivity isstillrequiredinthehuntfortheblackhole ssignatures. IntheNanosciences,opticalinterferometersareroutinelyusedtomeasure themotionofcantileversknownasprimeforcesensors.indeed,thetechniqueof magnetic resonance force microscopy (Figure 2 b) uses an interferometer in whichonemirrorisformedbysuchaflexiblecantilever.theforceexertedbya single electron spin on a tiny nano7magnet can be measured in this way, representing a many7orders of magnitude boost of sensitivity, for a potentially new approach to magnetic resonance imaging (MRI) of biomolecules 5. Even higher sensitivity will be needed to measure nuclear spins, and again, optical forces could overwhelm the weak forces to be measured. The outlook of such ultra7precisionexperimentsoriginallytriggeredbraginskyandhiscoworkersto re7think the physics of optical measurements, accounting for the fact that light has to be described in quantum mechanical terms, acting back on the object being measured via optical forces. These experiments are becoming a reality today.

5 a b Figure'2'Ultraprecision'scientific'experiments'based'on'optomechanical'interferometers.''(a)'Laser' interferometric'gravitational'wave'antenna 6,'and'(b)'single'spin'sensing'experiment 5.'In'both'cases' interferometers'with'movable'elements such'as'the'one'shown'in'figure'1 are'at'the'heart'of'the' experiment.'in'(a),'the'mirrors'are'suspended'like'swings,'and'they'are'separated'by'kilometers.'in' (b),'one'interferometer'mirror'is'formed'by'light'reflection'from'a'floppy'cantilever. The young research field of Cavity Optomechanics 7711 has assembled researchers aiming to systematically explore this new realm of optical measurements. New micro7 and nanofabrication technologies have brought forwardawidevarietyofplatformsforthesestudies,revealinganarrayofnew insights.amongthem,maybemostremarkably,isthefactthatbackactionforces cannotonlybeobserved,butconstituteapowerfultooltopreciselymanipulate the object being measured in particular, the motion of the interferometer s boundaries (the movable mirror in Figure 1). They thus provide an unprecedentedly elaborate handle on another unexplored area of Quantum Physics: the quantum nature of the motion of mechanical objects of massively superatomic size. Indeed, Cavity Optomechanical systems have been scientists prime tool to probe the quantum properties of nano7 and micro7mechanical oscillators,anactiveresearchfrontierformorethanadecade 12.Muchofmyown workhasbeendoneinthisarea,contributingtothedevelopmentofthefieldof CavityOptomechanicsfieldfromitsbeginnings.Inthefollowing,Iwillreporton thesecontributions. Ultrasensitive'Interferometry'with'Glass'Resonators' The workhorses of much of my research are whispering7gallery7mode resonatorsmadeofglass.inthesedevices(figure3),lightrunsincircularorbits

6 along the rim of a thin glass ring, similar to words whispered in the gallery of London s St Paul cathedral which gave this type of optical resonators their name. Our optical resonators are much smaller, though, with a diameter of the glassringofsome100µmorless;thatisaboutthediameterofahumanhair. InspiredbyearlyresearchinBraginsky slab 13,theseresonators(or cavities ) were developed by Kerry Vahala and coworkers at Caltech, to study optical phenomenaatthemicroscale 14.AttheMax7Planck7InstituteofQuantumOptics, and with a much wider palette of tools at EPFL s Center of MicroNanoTechnology,weoptimizedthedesignandfabricationprocedure,and couldproducethesamplesforourresearchourselves 15,16. Figure' 3' Glass' microring' (Nor' toroid)' cavity' used' for' our' research' in' Cavity' Optomechanics.' (a)' Scanning' electron' beam' micrograph' of' the' device.' The' glass' ring' (top)' shows' in' grey' as' it' is' intransparent'to'electrons.'the'surface'of'the'ring'is'atomically'smooth'and'the'material'very'clean.' Thus'light'can'be'guided'along'the'rim'of'the'structure'with'very'little'losses,'traveling'hundreds'of' meters'in'the'microstructure.'(b)'oscillations'of'the'radius'of'the'structure'measured'optically.'(c)' Rendering'showing'both'an' optical' whispering'gallery'mode '(WGM) essentially' a'circular'light' orbit'along'the'ring s'rim as'well'as'the'a'mechanical' radial'breathing'mode '(RBM),'leading'to'a' radial'oscillation'of'the'cavity'boundary.'(d)'illustrations'of'mechanical'mode'patterns,'including'the' RBM'(number'14),'extracted'from'a'computer'simulation.' Whiletheirgeometryiscertainlydifferentthantheinterferometershown in Figure 1, theserings exhibit the same characteristic functionality: Light can complete a large number of round7trips (yet along a circular, instead of linear trajectory),andlightfromalaseriscoupledinbestatresonance,thatis,ifthe

7 path7length along the rim is an integer multiple of the laser wavelength. With that,thediameteroftheringcanbeaccuratelymeasured 17. We found that the diameter of the ring is not stable in time, instead it fluctuates by many femtometers (1 fm= m), which our measurement can easily resolve(figure 3b). These fluctuations can be attributed to the fact that the glass ring supports also acoustic modes, similar to a tuning fork, or a wineglass, which can sing a tone if struck mechanically. Figure 3d shows patterns of displacement that the ring undergoes when different acoustic modes eachcorrespondingtoadifferent tone,oroscillationfrequency are excited.somelooklikethewound7upversionsofaguitarstring,butofgreatest interestforourpurposesisthe radialbreathingmode (no.14):ifthismodeis excited, the radius of the ring periodically changesbetween 20 and 100 times permicrosecond( MHz), leaving the clearly observable signature in the measurementoffigure3b.thepresenceofsuchamechanicalmodecompletes theanalogytothesystemoffigure1:insteadofamirrormountedonaspring, the entire structure can be deformed when a force is applied. This naturally includes the optical forces arising from the fact that light trapped in the glass ringexertsradiationpressurepointingradiallyoutwards. Aiming to optically measure the radius of the glass ring with the highest possible sensitivity, we implemented state7of7the art quantum optical measurementtechniquesbasedonthecavities principalsuitabilityasanoptical interferometer. Figure 4 shows the result of these efforts. When probing the radius of one particular device, fluctuations with a characteristic frequency of 40.6MHzcanbeobserved.Thisisevidencedbythesharppeakinthesignalat this frequency, reflecting the oscillations of Figure 3b in a frequency7domain representation. The background, or imprecision of this measurement, is given by the quantumnoiseofthelightusedinthemeasurement:thelightarrivesinenergy packets, or photons, in the detector, where they are converted into electronic signals.acertainnaturalrandomnessofarrivaltimesoftheindividualphotons onthedetectorsurfaceleadstoabackgroundnoise conceptuallysimilartothe oneheardwhenraindropletsimpactonametalroof,andcommonlyreferredto

8 asshotnoise.iftheradiusfluctuationsofthecavityweresmallerthanabout m,thentheshotnoise(bluepoints,measuredindependently)wouldobscure theweakopticalsignaltobemeasuredwithinonesecondaveragingtime. ' Figure'4.'Measurement'of'radius'fluctuations'due'to'the'radial'breathing'mode.'(a)'The'fluctuations' are'very'clearly'discerned'in'the'measurement,'at'a'frequency'around'40.6'mhz'(yellow'circles).'the' background' of' the' measurement' due' to' shot' noise' (blue' circles)' is' much' smaller,' at' about' 10 N18 ' meters' in' 1' second' averaging' time.' (b)' For' the' employed' optical' power,' the' imprecision' of' the' measurement,' due' to' shot' noise,' is' already' lower' than' the' induced' fluctuations' due' to' optical' backaction'forces.'however,'as'these'measurements'were'taken'at'room'temperature,'the'effects'of' backaction'are'masked'by'thermal'noise.' Byusingmorelight,theimprecisioncouldinprinciplebereducedfurther, as the signal strength increases more rapidly than the shot noise. However, according to the theory of Quantum Measurements, backaction fluctuations would at some point limit the sensitivity: shot noise is also present within the cavity,andtherandombouncesofphotonsagainstthecavity swallwouldsetit into random motion, obscuring the measurement of its radius. This backaction effectcouldnotbediscernedinourmeasurements,astheinherentfluctuations of the radius were larger (Figure 4). They are actually caused by the thermal motion of the molecules that constitute the resonator. Viewed from merely a different perspective, this corresponds to an excitation of the radial breathing mode (and all other mechanical modes) to a certain amplitude the very amplitudeobservedinfigure3a.

9 The'Backaction'of'Light,'and'How'To'Make'Use'Of'It' ' Nonetheless, backaction forces are present in this resonator. Indeed, the radial force exerted by the light is even enhanced by the number of round7trips that each photon completes (on average) in the glass ring and this number can reach up to millions in this type of resonator. As a result, even when pumped with very modest light powers (much less than that of a laser pointer) the backactionforcescanbecomesignificantenoughtodeformtheresonator. In this case, a particularly intricate effect can set in, referred to as dynamical/backaction 18 :Theforce7induceddeformationofthestructurechanges the optical path length. This may degrade (or improve) the matching of the laser swavelengthtotheopticalpath7lengthalongtherim,sothattheresonator will in turn be able to accommodate less(or more) laserlight decreasing(or increasing) again the optical force. In the right circumstances, any naturally occurring radius fluctuation can thus stimulate a backaction force that exactly counteracts this radius change. This does also apply to the fluctuations associated with the thermal excitation of the radial breathing mode discussed above.thatmeansthat,eventhoughthesampleisatroomtemperaturets~300 K, the thermal fluctuations of this mode get reduced; it thus behaves as if the samplewereheldatalower,effectivetemperatureteff/<ts. Interestingly, this effect can also be understood as an analog to the techniquesknownfor lasercooling themotionofatomsorions,assuggestedin the1970iesbyhänschandschawlow 19,andWinelandandDehmelt 20 :Thelaser beamsenttowardsthecavityis red 7detuned,thatis,thephotonscarryslightly lessenergythannecessarytoexcitethecavity sresonance(figure5).however, inaprocesscalledanti7stokesscattering,theneededextrabitofenergycanbe taken from the motional degree of freedom in our case, the vibration of the radial breathing mode. Thus, a photon with higher energy emerges from the cavity,leavingbehindaslightlycoldermechanicalmode.

10 Figure' 5' Cooling' of' the' radial' breathing' mode' based' on' dynamical' backaction.' (a)' A' laser' beam' whose'frequency'is'lower'by'the'mechanical'frequency'(ω m)'than'the'cavity'resonance'frequency'is' sent'towards'the'cavity.'(b)'light'from'the'cooling'beam'is'upconverted'to'a'higher'frequency'during' a'process'called'antinstokes'scattering.'the'energy'necessary'for'this'upconversion'is'taken'from'the' mechanical'mode which'is'thereby'cooled.' In2006,wewereamongthefirstthreegroupsworldwidetodemonstrate laser cooling of mechanical modes via dynamical backaction 21723, achieving an effectivetemperatureof11k.sincethen,anavalancheofsimilarworkallacross theglobehasbeenlaunched.withtheaimofreducingtheeffectivetemperature Teffclosertoabsolutezero,wehavesincecontinuouslyrefinedboththecooling techniques aswellastheemployedexperimentalplatforms 27,28. Switching'Light'with'Light' During these developments, we found that there exist more analogies between theconceptsofatomicphysicsandoptomechanicalinteractionsthanwhatwas previouslythought.inparticular,optomechanicalsystemscanexhibitabehavior nowreferredtoas OptomechanicallyInducedTransparency 29,9,whichisvery closely related to electromagnetically induced transparency (EIT) known from atomic systems 30,31. While the initial idea was already conceived during my doctoralthesis 29,ithasbeenatEPFLwhereIhave,togetherwithmycolleagues, fullydevelopedthisconcept 32. Itisbasedontheobservationthatsomeatoms,whichusuallyabsorblight of a particular frequency, can be rendered transparent when illuminated by a second laser beam. The simultaneous presence of light of two frequencies prevents the atom from being excited due to interference of excitation pathways. Figure 6 explains how this concept applies, completely analogously, alsotoanoptomechanicalsystem.afirst, probe beam,thatisusuallycoupled intothecavity,andabsorbedthere,cangettransmittedthroughthesystem,ifa

11 second, control beam is activated. The combined backaction force of the two lasersthenexcitesthemechanicalmode,whichinturnsuppressesthecoupling, andabsorptionoftheprobebeamviaaninterferenceeffect.theprobelaserthus simplygetstransmitted. Figure' 6' Optomechanically' induced' transparency.' (a)' Two' lasers,' a' probe ' and' control ' laser' are' sent' towards' the' cavity,' where' they' can' both' couple' to' the' circular' orbits' (whispering' gallery' modes)'of'the'glass'resonators.'if'the'frequency'difference'between'the'lasers'is'chosen'to'match'the' resonance'frequency'ω m'of'the'vibration'mode'of'the'glass'toroid,'the'combined'backaction'force'of' the' two' fields' resonantly' excites' the' mechanical' mode,' that' is,' the' boundary' of' the' structure' is' oscillating'radially'(blue'arrow).'(b)'in'a'frequency'picture,'this'leads,'in'turn,'to'scattering'of'light' from' the' stronger' control' field,' to' the' frequency' of' the' probe' laser.' The' scattered' light' interferes' with'the'probe'field that'is,'its'electric'field'exactly'cancels'the'probe'laser s'field'in'the'cavity.'the' probe'laser'does'therefore'not'enter'into'the'cavity,'but'gets'transmitted.'(c)'while'the'probe'laser' usually'gets'coupled'into'the'cavity'when'tuned'close'to'resonance,'it'is'not'coupled,'and'therefore' transmitted,'in'a'spectrally'sharp'region'in'the'center exactly'when'the'combined'backaction'force' of'the'lasers'excites'the'mechanical'mode.'' With this technique it is therefore possible to tune on and off the transmission of the probe beam using the control beam. We have first demonstratedthephenomenonofoptomechanicallyinducedtransparency 32 at EPFLin2010.Moreresearchhasbeencarriedoutsince 33,fuelednotlastbythe prospect of applications as light switches and routers in integrated systems. Even more, EIT has been the physical phenomenon underlying theintriguing possibilitytoslowdownanddelaylight,andeventuallyitsstorageinlong7lived atomic states 34. Optomechanical systems, whose key parameters can all be engineered within wide ranges (resonant wavelengths in particular), could provide an extension of these phenomena into the practical realm of telecommunicationsandopticalsignalprocessing.

12 Quantum'Motion'and'Beyond' Astrongfocusofourresearchoverthelastyears,however,hasremainedonthe attempt to cool the mechanical degree of freedom to the lowest possible temperatureteff.thisendeavorhasbeenmotivatedbythefascinatingphysicsof trappedions,whichhasalsobeenhighlightedby2012 sphysicsnobelprize.in this field,researchers have accomplished full control over the motion of single ionsheldinvacuumusingopticalforces.usinglasercoolingtechniques,theycan prepare such ions in the quantum ground state 35, that is, at an effective temperature so low that all but the most fundamental, quantum mechanical, positionfluctuationsarefrozenout.anionatsuchaloweffectivetemperature canthenbepreparedinso7calledschrodingercatstates,inwhichitislocatedat twopositionsatthesametime 36. Such states have, to date, never been observed for a macroscopic object. Whether the reason is fundamental, or merely technical preparation of quantumstatesrequiressuppressionofallthermalfluctuations isnotknown. However, with the new laser cooling techniques that can be applied to optomechanicalsystems,thiscouldbeprobedforthefirsttime.andindeed,we could show that we can prepare the radial breathing mode in the quantum ground state 16 with high probability. To date, this feat has only been achieved withahandfulofoptomechanicalsystems Ifthecoolinglaseristunedtoitshighestpowers(ca.5mW),thecharacter of its effect changes qualitatively. In this regime the optical and mechanical modescouplesostronglyviathelight(figure7)thattheyloosetheirindividual identity,andtheneweigenmodesofthesystemarebothmechanicalandoptical incharacter.suchhybridexcitationshavebeenobservedintheclassicalregime inearlyworkatviennauniversity 40.AtEPFL,wehavepursuedthelong7standing goalofperformingtheseexperimentsinthequantumregime.

13 Figure' 7' Coherent' coupling' in' an' optomechanical' system.' For' very' strong' cooling' laser' fields,' the' light'of'the'cooling'laser'couples'the' optical'mode'(left)'and'mechanical'mode'(right)'so'strongly,' that' they' loos' their' individual' identity,' and' rather' have' to' be' treated' as' a' hybrid' mode' of' both' optical'and'mechanical'nature.' We could eventually observe this photon7phonon hybridization in the quantumregime,bothusingspectroscopic,aswellastime7domaintechniques 16. Inthelatter,weexcitedthecavitywithveryweakopticalpulses,containingless than one photon on average. We could observe that this excitation cyclically transformsitscharacter:intoamechanicalexcitationandback.theanalysisof our experiments revealed that this cyclic transformation occurs on timescales that are faster than the ones of the known mechanisms of quantum decoherence thatis,thelossof quantum information from the system under experimental control to the uncontrolled environment, consisting here of all mechanicaldegreesoffreedominaccessibletoopticalmeasurement. Wehavethereforedemonstratedanoptomechanicalinterfaceacrosswhich quantum information can be coherently transferred. Such interfaces are of interest to quantum physicists 41 in particular for the versatility of mechanical devices:theycanbecoupledtootherquantumsystemssuchasatomicorsolid7 state qubits, or microwave photons, and massive efforts along these lines are now underway. Quantum7coherent links to an optical mode via the mechanics could help interconnect these systems via a simple piece single7 mode optical fiber, thus providing a crucial building block for future heterogeneousquantummachines 42,43. Acknowledgements' IamgratefultotheFondation/Latsis/Internationale/andtheResearchCommission oftheepflfortheirmostgenerousencouragementofyoungresearchers.iam indebted to Prof. T. W. Hänsch and Prof. T. J. Kippenberg for their long7term

14 support and mentorship, and wish to acknowledge all of my co7workers who contributed to this research, in particular O. Arcizet, S.Deléglise,R.Riviere,E. VerhagenandS.Weis. References' ' 1 Braginsky,V.B.&Manukin,A.B.Measurement/of/Weak/Forces/in/Physics/Experiments.(1977). 2 Caves,C.M.Quantum7MechanicalRadiation7PressureFluctuationsinanInterferometer.Phys/Rev/ Lett45,75779(1980). 3 Braginsky,V.B.&Khalili,F.Y.Quantum/Measurement.(1992). 4 Abbott,B.P./et/al.Anupperlimitonthestochasticgravitational7wavebackgroundofcosmological origin.nature460, (2009). 5 D.Rugar,R.Budakian,Mamin,H.J.&Chui,B.W.Singlespindetectionbymagneticresonanceforce microscopy.nature430, (2004). 6 BAbbott/et/al.Observationofakilogram7scaleoscillatornearitsquantumgroundstate.New/ Journal/of/Physics11,073032(2009). 7 Kippenberg,T.J.&Vahala,K.J.CavityOptomechanics:Back7ActionattheMesoscale.Science321, (2008). 8 Favero,I.&Karrai,K.Optomechanicsofdeformableopticalcavities.Nature/Photonics3, (2009). 9 Schliesser,A.&Kippenberg,T.J.inAdvances/in/atomic,/molecular/and/optical/physicsVol.58(edsE. Arimondo,P.Berman,&C.C.L.SchliesserLin) (ElsevierAcademicPress,2010). 10 Aspelmeyer,M.,Gröblacher,S.,Hammerer,K.&Kiesel,N.Quantumoptomechanics:throwinga glance.journal/of/the/optical/society/of/america/b27,a1897a197(2010). 11 Aspelmeyer,M.,Meystre,P.&Schwab,K.C.QuantumOptomechanics.Physics/Today65,29(2012). 12 Schwab,K.C.&Roukes,M.L.PuttingMechanicsintoQuantumMechanics.Physics/Today58,36742 (2005). 13 Gorodetsky,M.L.,Savchenkov,A.A.&Ilchenko,V.S.UltimateQofopticalmicrosphereresonators. Optics/Letters21, (1996). 14 Armani,D.K.,Kippenberg,T.J.,Spillane,S.M.&Vahala,K.J.Ultra7high7Qtoroidmicrocavityona chip.nature421, (2003). 15 Anetsberger,G.,Rivière,R.,Schliesser,A.,Arcizet,O.&Kippenberg,T.J.Ultralow7dissipation optomechanicalresonatorsonachip.nature/photonics2, (2008). 16 Verhagen,E.,Deleglise,S.,Weis,S.,Schliesser,A.&Kippenberg,T.J.Quantum7coherentcouplingof amechanicaloscillatortoanopticalcavitymode.nature482,63767(2012). 17 Schliesser,A.,Anetsberger,G.,Rivière,R.,Arcizet,O.&Kippenberg,T.J.High7sensitivitymonitoring ofmicromechanicalvibrationusingopticalwhisperinggallerymoderesonators.new/journal/of/ Physics10,095015(2008). 18 Braginksy,Braginskii,V.B.&Manukin,A.B.Ponderomotiveeffectsofelectromagneticradiation. Soviet/Physics/JETP/Letters25, (1967). 19 Hänsch,T.W.&Schawlow,A.L.Coolingofgasesbylaserradiation.Optics/Communications13,687 69(1975). 20 Wineland,D.J.&H.Dehmelt.Proposed10^14Dn<nLaserFluorescenceSpectroscopyonTl+Ion Mono7Oscillator.Bulletin/of/the/American/Physical/Society20,637(1975). 21 Arcizet,O.,Cohadon,P.F.,Briant,T.,Pinard,M.&Heidmann,A.Radiation7pressurecoolingand optomechanicalinstabilityofamicromirror.nature444,71774(2006). 22 Gigan,S./et/al.Self7coolingofamicromirrorbyradiationpressure.Nature444,67770(2006). 23 Schliesser,A.,Del'Haye,P.,Nooshi,N.,Vahala,K.J.&Kippenberg,T.RadiationPressureCoolingofa MicromechanicalOscillatorUsingDynamicalBackaction.Phys/Rev/Lett97,243905(2006). 24 Schliesser,A.,Rivière,R.,Anetsberger,G.,Arcizet,O.&Kippenberg,T.J.Resolved7sidebandcooling ofamicromechanicaloscillator.nature/physics4, (2008). 25 Arcizet,O.,Rivière,R.,Schliesser,A.,Anetsberger,G.&Kippenberg,T.J.Cryogenicpropertiesof optomechanicalsilicamicrocavities.physical/review/a80,021803(r)(2009). 26 Rivière,R./et/al.Optomechanicalsidebandcoolingofamicromechanicaloscillatorclosetothe quantumgroundstate.physical/review/a83,063835(2011). 27 Anetsberger,G./et/al.Near7fieldcavityoptomechanicswithnanomechanicaloscillators.Nature/ Physics5, (2009). 28 Hofer,J.,Schliesser,A.&Kippenberg,T.J.Cavityoptomechanicswithultra7highQcrystalline micro7resonators.physical/review/a82,031804(2010). 29 Schliesser,A.Cavity/Optomechanics/and/Optical/Frequency/Comb/Generation/with/Silica/WhisperingO GalleryOMode/Microresonators,Ludwig7Maximilians7UniversitätMünchen,(2009). 30 Harris,S.E.Electromagneticallyinducedtransparency.Physics/Today50,36742(1997). 31 M.Fleischhauer,A.Imamoglu&Marangos,J.P.Electromagneticallyinducedtransparency:Optics incoherentmedia.review/of/modern/physics77, (2005).

15 32 Weis,S./et/al.Optomechanicallyinducedtransparency.Science330, (2010). 33 Safavi7Naeini,A.H./et/al.ElectromagneticallyInducedTransparencyandSlowLightwith Optomechanics.Nature472,69773(2011). 34 Lukin,M.D.&A.Imamoglu.Controllingphotonsusingelectromagneticallyinducedtransparency. Nature413, (2001). 35 C.Monroe/et/al.Resolved7sidebandRamanCoolingofaBoundAtomtothe3DZeroPointEnergy. Phys/Rev/Lett75, (1995). 36 Monroe,C.,Meekhof,D.M.,King,B.E.&Wineland,D.J.ASchrödingercatsuperpositionstateofan atom.science272, (1996). 37 O'Connell,A.D./et/al.Quantumgroundstateandsingle7phononcontrolofamechanicalresonator. Nature464, (2010). 38 Chan,J./et/al.Lasercoolingofananomechanicaloscillatorintoitsquantumgroundstate.Nature 478,89792(2011). 39 Teufel,J.D./et/al.Sidebandcoolingofmicromechanicalmotiontothequantumgroundstate. Nature475, (2011). 40 Gröblacher,S.,K.Hammerer,Vanner,M.R.&M.Aspelmeyer.Observationofstrongcoupling betweenamicromechanicalresonatorandanopticalcavityfield.nature460, (2009). 41 Stannigel,K.,Rabl,P.,Sorensen,A.S.,Zoller,P.&Lukin,M.D.OptomechanicalTransducersfor Long7DistanceQuantumCommunication.Phys/Rev/Lett105(2010). 42 Cho,A.FaintestThrumHeraldsQuantumMachines.Science327, (2010). 43 Cho,A.BreakthroughoftheYear:theFirstQuantumMachine.Science330, (2010). '