Rydberg-Stark deceleration and trapping of helium atoms above electrical transmission-lines Patrick Lancuba Supervisor: Dr. StephenD.Hogan Co-supervisor: Prof. PeterBarker Department of Physics and Astronomy University College London March 2016 A THESIS SUBMITTED TO UNIVERSITY COLLEGE LONDON FOR THE DEGREE OF DoctorofPhilosophy 2 Declaration I,PatrickLancubaconfirmthattheworkpresentedinthisthesisismyown. Whereinformationhas beenderivedfromothersources,Iconfirmthatthishasbeenindicatedinthethesis. Date: ...................... Signature: ...................... 3 Abstract The experimental realisation of a set of surface-based devices for controlling the positions and ve- locitiesofRydbergatomsinitiallytravellinginpulsedsupersonicbeamsisdescribed. Theuniqueas- pectofthesedevicesisthattheyarebasedonthegeometryoftwo-dimensionalelectricaltransmission- linesandarethereforesuitedtointegrationwithchip-basedmicrowavecircuitstorealiseacomplete Rydberglaboratoryonachip. Suchachip-basedlaboratorycouldbeexploitedinhybridapproaches to quantum information processing, and for studies of collisions and decay processes of highly ex- cited atoms and molecules. The devices operate through the generation of inhomogeneous electric fieldsandtakeadvantageofthelargeelectricdipolemomentsassociatedwithhighRydbergstatesto exertforcesontheatoms. Intheexperiments, heliumatomsinRydberg-Starkstateswithprincipal quantumnumbersrangingfrom48to52andelectricdipolemomentsof 10000Dareemployed. ⇠ The devices developed include electrostatic guides which permitted control over the transverse motionofbeamsofatoms. Thesewereusedtotransportsamples,initiallytravellingat 1950m/s ⇠ and deflect them away from their initial axis of propagation. The guided atoms were detected by pulsedelectricfieldionisation. Tocontrolthelongitudinalmotionofthesamples,thetransmission- lines were modified to permit the generation of sets of continuously moving electric traps. The resulting transmission-line decelerators were then employed to guide, accelerate and decelerate atomstrappedinthree-dimensions. Accelerationsupto 2.3x107 m/s2 wereappliedtodecelerate � samples from 2000 m/s to zero-velocity in the laboratory-fixed frame of reference, leading to the removal of 80 meV of kinetic energy, the largest achieved in any Stark decelerator to date. The ⇠ decelerated atoms were trapped in stationary electric traps and detected in-situ. The phase-space acceptancesofthedeceleratorswerecalculatedtocharacterisetheeffectsofaccelerationanddecel- erationonthetrappedatoms. Theresultsofthecalculationswereemployedintheinterpretationof theexperimentaldata,andtoidentifyeffectsofcollisionsandblackbodytransitions. 4 Acknowledgments My doctoral work has been an extraordinary experience. During this time, I was surrounded by a positiveenvironmentandpeople. InagreementwithEpictetus,thishasbeenofgreatimportanceto callforthmybest. TothesepeopleIwouldnowliketoexpressmygratitude. Iwouldliketothankmysupervisor,Dr. StephenHogan,forgivingmetheopportunitytocarry out academic research in such a fascinating area of physics and physical chemistry. As I was the firstPhDstudentofhisnewlyestablishedresearchgroupatUniversityCollegeLondon,Iwasinthe rarepositiontoworkonthedesignandconstructionofanewexperimentallaboratory. Thisallowed metodevelopavarietyofprojects, startingfromtheirimaginativeconception, totheexperimental realisation. Iamgratefulforhissupportthroughoutthesethreeyears,asitallowedmetolearnhow to carry out research in an investigative, scientifically critical and cooperative way, and the results areasourceofprideandexcitement. I would like to express my deep gratitude to Prof. Fre´de´ric Merkt, of the ETH Zu¨rich, for his support in helping me to pursue and realise my academic interests. His trust in me and in my abil- ities provided the foundation for me to persevere and to excel. This became the starting point with whichIrealised,asfirstmentionedbyAristotle,thatqualityisindeednotanact,butitisahabit. As this work required strong self-motivation and commitment, I reinstate the importance of moralsupport,withoutwhichallofthiswouldhavenotbeenpossible. Forthisreason,Iwouldlike to sincerely thank my family, particularly my mother Daniela and my sister Manuela, for their un- conditionalsupportthroughoutmystudies. Iwouldliketoexpressmydeepestappreciationandlove tomypartner,Caroline,asshealwayshasbeenonmyside,andhersupportneverwavered. Iwould liketothankmyfriendsandcolleaguesfortheirbrilliantinsightsandwordsofencouragement. My PhD work allowed me not only to learn new skills and knowledge, but also to grow as a person. Ithasgivenmeanexcellentfoundationonwhichtobuildmyfuturecareer. 5 Contents 1 ApplicationofRydbergstates 15 1.1 Precisionspectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 1.2 InteractionsofRydbergatomsandmoleculeswithsurfaces . . . . . . . . . . . . . 19 1.3 Hybridapproachestoquantuminformationprocessing . . . . . . . . . . . . . . . 21 1.4 Positroniumandantihydrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 2 Rydberg-Starkdeceleration 26 2.1 Earlyexperimentswithtime-independentfields . . . . . . . . . . . . . . . . . . . 27 2.2 Experimentswithtime-dependentfields . . . . . . . . . . . . . . . . . . . . . . . 28 2.3 Electrostatictrapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 2.4 Chip-baseddeceleratorsandtraps . . . . . . . . . . . . . . . . . . . . . . . . . . 36 3 Theoreticalbackground 44 3.1 Rydbergstatesofthehydrogenatom . . . . . . . . . . . . . . . . . . . . . . . . . 44 3.2 Rydbergstatesofnon-hydrogenicatoms . . . . . . . . . . . . . . . . . . . . . . . 46 3.3 Rydbergstateslifetimes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 3.4 Rydbergatomsinhomogeneouselectricfields . . . . . . . . . . . . . . . . . . . . 49 3.5 Blackbodyradiationeffects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 4 Experimentalmethods 62 4.1 Pulsedsupersonicbeams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 4.2 Generationofabeamofmetastableheliumatoms . . . . . . . . . . . . . . . . . . 67 4.3 Laserphotoexcitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 4.4 PulsedelectricfieldionisationandMCPdetector . . . . . . . . . . . . . . . . . . 71 6 4.5 LabVIEWcontrolanddataacquisitionprogram . . . . . . . . . . . . . . . . . . . 72 5 GuidingRydbergatomsaboveelectricaltransmission-lines 77 5.1 Designofthetransmission-lineguide . . . . . . . . . . . . . . . . . . . . . . . . 78 5.2 Descriptionoftheexperimentalapparatus . . . . . . . . . . . . . . . . . . . . . . 79 5.3 Experimentalresults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 5.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 6 Transmission-linedeceleratorsforatomsinhighRydbergstates 89 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 6.2 Deceleratordesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 6.3 Experimentalapparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 6.4 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 6.5 DiscussionandConclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 7 Rydbergatomtrajectoriesinacurvedtransmission-linedecelerator 110 7.1 Particlegeneration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 7.2 Particledynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 7.3 Boundaryconditionsandparticledetection . . . . . . . . . . . . . . . . . . . . . 115 7.4 Phase-spaceacceptances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 7.5 Time-of-flightdistributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 8 StoppingandtrappingRydbergatombeamsinatransmission-linedecelerator 123 8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 8.2 Deceleratordesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 8.3 In-situRydbergatomdetection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 8.4 Experimentalsetup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 8.5 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 9 Conclusionandoutlook 137 A C++programmeforcalculatingRydbergatomtrajectories 140 Bibliography 164 7 List of Figures 1.1 Millimeter-wave spectra of the 77d[3/2](J = 1) 93p[3/2](J = 1) transition in 0 ! krypton(adaptedfromRef.[18]).. . . . . . . . . . . . . . . . . . . . . . . . . . . 17 1.2 Potentialenergydiagramofthehydrogenmolecule(adaptedfromRef.[27]). . . . 18 1.3 VelocitydependenceofhydrogenRydbergatomsonionisationatsurfaces(adapted fromRef.[40]). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 1.4 SchematicrepresentationofahybridcircuitQEDarchitecture(adaptedfromRef.[46]). 22 1.5 Microwave waveguide and Rabi oscillations of helium Rydberg atoms coupled to microwavecircuits(adaptedfromRef.[28]). . . . . . . . . . . . . . . . . . . . . . 23 1.6 Field-free spectrum of Ps Rydberg states, and measured and calculated Rydberg- Starkspectraofn=11Psatomsinanelectricfield(fromRef.[52]). . . . . . . . . 24 1.7 Schematicdiagramoftheantihydrogensynthesis,andimplementationofaRydberg- StarkacceleratorintheAEGISexperiment(fromRef.[53]). . . . . . . . . . . . . 25 2.1 Schematic representation of the experimental apparatus used to deflect beams of kryptonatoms(adaptedfromRef.[59]). . . . . . . . . . . . . . . . . . . . . . . . 27 2.2 Time-of-flight distributions of hydrogen molecules in low-, and high-field-seeking Rydberg-Starkstatesfollowingdecelerationandaccelerationinatime-independent electricfield(fromRef.[61]).. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.3 Schematicrepresentationoftheexperimentalsetupusedtoaccelerateanddecelerate argon Rydberg atoms using time-independent, and time-dependent electric fields (adaptedfromRef.[63]). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 8 2.4 Time-of-flightdistributionsofargonRydbergatoms(n=19)recordedfollowingac- celeration/decelerationintime-independentandtime-dependentelectricfields(adapted fromRef.[63]). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 2.5 Schematic representation of the electrode configuration, and electric field distribu- tionsusedforRydberg-Starkdecelerationand3Delectrostatictrappingofhydrogen Rydbergatoms(fromRef.[67]). . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 2.6 Electrode arrangement and schematic representation of the Rydberg-Stark decel- erator used to decelerate and trap atoms in low-field-seeking Rydberg-Stark states off-axis(adaptedfromRef.[71]). . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 2.7 Measurements of the decay of trapped hydrogen atoms in an off-axis electrostatic trapforblackbodytemperaturesof300K,125Kand11K,andhydrogenmolecules trappedina300Kenvironmentinanon-axiselectrostatictrap(fromRef.[71]). . . 34 2.8 Schematic representation of a chip-based Stark decelerator, with the experimen- tal setup used for loading and decelerating CO metastable polar molecules (from Ref.[74]). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.9 Calculated electric field distributions in chip-based Stark decelerators for selected potentialsusedtodeceleratemetastableCOpolarmolecules(fromRef.[74]). . . . 38 2.10 Measured time-of-flight distributions of metastable CO molecules for selected ac- celerations(fromRef.[74]). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 2.11 SurfaceelectrodeRydberg-StarkdeceleratorforhydrogenRydbergatoms(adapted fromRef.[47]). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 2.12 Experimental,andsimulatedhydrogenatomtime-of-flightdistributionsdemonstrat- ing acceleration and deceleration about surface-electrical Rydberg-Stark decelera- tors(fromRef.[47]). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 2.13 Schematic representation of a surface-electrode device used to trap and deflect hy- drogenmoleculesawayfromtheirinitialaxisofpropagationatanangleof10 (from � Ref.[77]). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 3.1 SchematicdiagramofRydbergstatesofhydrogenandnon-hydrogenicatoms(adapted fromRef.[28]). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 9 3.2 Calculated fluorescence lifetimes of excited np Rydberg states of hydrogen and tripletnpRydbergstatesofhelium. . . . . . . . . . . . . . . . . . . . . . . . . . . 49 3.3 Stark map of the hydrogen atom calculated for Rydberg states with n=51, 52, 53 and m =0. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 | | 3.4 StarkmapsoftripletRydbergstatesofheliuminthevicinityofn=52. . . . . . . 55 3.5 CalculatedStarkspectraofRydbergstatesofheliumwithn=52inanelectricfield ~ F =1V/cm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 | | 3.6 StarkspectraoftripletRydbergstatesofheliumwithn=52excitedfromthethe3p state. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 3.7 Potentialenergydistributionresultingfromtheadditionofanelectric~F=(0,0, F) z � toapureCoulombpotential. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 3.8 Dependence of the mean blackbody photon occupation number per mode on fre- quencyforblackbodytemperaturesT =300K,andT =10K. . . . . . . . . . . . 60 4.1 Overview of the apparatus employed in the experiments described in this thesis, includingtheuv-,andir-lasersandthevacuumsystem. . . . . . . . . . . . . . . . 63 4.2 Schematicdiagramofthevacuumchamberusedintheexperimentsdescribedinthis thesis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 4.3 Schematicviewofthegenerationofapulsedsupersonicbeam(afterRef.[94]). . . 65 4.4 Schematic diagram of the discharge source used for the generation of beams of metastableheliumatoms(nottoscale). . . . . . . . . . . . . . . . . . . . . . . . . 67 4.5 Energylevelsofatomichelium. . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 4.6 SchematicrepresentationofTopticaDLProlaserswithsecondharmonicgeneration, andataperedamplifier,asusedintheexperimentsdescribedhere(fromRef.[102]). 70 4.7 SchematicdiagramofaMCPdetectorpairina“chevron”configuration. . . . . . . 72 4.8 LabVIEWblockdiagramdisplayingasimplifiedQueued-State-Machinearchitecture. 74 4.9 Measured He+ time-of-flight signal to the MCP detector following pulsed electric fieldionisationofasampleofRydbergatoms. . . . . . . . . . . . . . . . . . . . . 75 5.1 Geometry of the curved electrical transmission-line, and electric field distribution generatedforguidingatomsinhighRydbergstates. . . . . . . . . . . . . . . . . . 78 10 5.2 Schematic diagram of the experimental apparatus used to demonstrate guiding and deflectionofheliumRydbergatomsaboveasurface-basedelectricaltransmission-line. 80 5.3 Time-of-flightdistributionsofHe+ionsdetectedafterpulsedelectricfieldionisation ofheliumRydbergatomsinitiallyexcitedtostateswithelectricdipolemomentsof 7930Dthatwereguidedusingcurvedtransmissionlineguideswithdisplacements ofDx=2.5mm,andDx=5.0mm. . . . . . . . . . . . . . . . . . . . . . . . . . 82 5.4 Experimentallyrecorded,andcalculatedspectraofthen=52, m =1tripletRydberg- | | Starkstatesofheliumafterguidingthemincurvedtransmission-lineguides. . . . . 84 6.1 Schematicdiagramofatransmission-linedecelerator. Electricfielddistributionsin thexy-plane,andthezy-plane,forV =+120V,andV = V /2. . . . . . . . . . 90 0 u 0 � 6.2 Electricfielddistributionsinthezy-planefortrapslocatedaboveadeceleratorseg- ment, one quarter of the way between two segments, and half-way between two segments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 6.3 Electric field distributions in the zy-plane, and the xy-plane, containing an electric fieldminimumlocatedonequarterofthewaybetweentwodeceleratorsegments. . 96 6.4 Effective depth of the moving decelerator traps for helium atoms in the n,k = | i 52,35 Rydberg-Starkstate,whenV =+120V. . . . . . . . . . . . . . . . . . . 98 0 | i 6.5 Schematic diagram of the experimental apparatus used in deceleration of helium Rydbergatomsinatransmission-linedecelerator. . . . . . . . . . . . . . . . . . . 99 6.6 He+ time-of-flight distributions recorded following pulsed electric field ionisation ofheliumRydbergatomsafterguidingtheminatransmission-linedecelerator. . . 100 6.7 Dependence of the integrated He+ signal on the activation time of the oscillating deceleratorpotentials,foraheliumatomflight-timefromthephotoexcitationregion to the detection region of 82.5 µs, when the decelerator is operated in a guiding modeataconstantspeedof1950m/s. . . . . . . . . . . . . . . . . . . . . . . . . 101 6.8 Time-of-flightdistributionoftheunperturbedbeamofheliumRydbergatomsrecorded withthedeceleratoroffandoperatedtoguideatomsatconstantspeedsrangingfrom 1750m/sto2350m/s. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103