Table Of ContentSpringer Theses
Recognizing Outstanding Ph.D. Research
Mickey McDonald
High Precision Optical
Spectroscopy and
Quantum State Selected
Photodissociation
of Ultracold 88Sr2
Molecules in an Optical
Lattice
Springer Theses
Recognizing Outstanding Ph.D. Research
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Mickey McDonald
High Precision Optical
Spectroscopy and Quantum
State Selected
Photodissociation of
Ultracold 88Sr2 Molecules
in an Optical Lattice
Doctoral Thesis accepted by Columbia University,
New York, USA
123
MickeyMcDonald
UniversityofChicago
JamesFranckInstitute
Chicago,IL,USA
ISSN2190-5053 ISSN2190-5061 (electronic)
SpringerTheses
ISBN978-3-319-68734-6 ISBN978-3-319-68735-3 (eBook)
https://doi.org/10.1007/978-3-319-68735-3
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ToBartMcGuyer,whotaught mewhatit
meanstobeascientist.
Supervisor’s Foreword
This is an exciting time for physics, and particularly for the field of atomic and
molecular physics. Scientists can exert nearly perfect control over atomic motion
andquantumstatesandusethisexquisiteprecisiontoseekanswerstofundamental
questions. In recent years, there has been a surge in growth of cold and ultracold
molecular science. Molecules are in many ways similar to atoms but offer greatly
expandedpossibilitiesforunderstandingawidearrayofphysicalphenomena.This,
of course, comes with new challenges, since even diatomic molecules have much
morecomplicatedspectrathanatoms.
Mickey McDonald’s thesis work unites studies of basic molecular quantum
physicswiththehigh-precisiontechniquesofultracold-atomopticallatticeclocks.
Hissophisticatedexperimentinvolvesmicrokelvindiatomicstrontiummoleculesin
an optical lattice trap and utilizes optical spectroscopy to study physics near the
atom-moleculethreshold.Mickeyobtaineduniquelatticeclock-stylespectroscopic
measurements that clearly demonstrate the potential of ultracold molecule science
and open the door to table-top tests of fundamental physics, such as molecular
quantumelectrodynamicsandnanometer-scaledeviationsfromNewtoniangravity,
atalevelthatwasnotpossiblebefore.
Mickey’s thesis carefully demonstrates how forbidden transitions in molecules
can be enabled with much weaker magnetic fields than in their constituent atoms,
withimplicationsformetrologyandprecisionmeasurement.Italsodescribeswork
on two-body subradiance, reporting by far the deepest subradiance to date, a 300-
foldsuppressionofradiativeemission.Thisisafundamentaltwo-particlequantum
optics effect, and it turns out that homonuclear diatomic molecules in an optical
latticearetheidealsystemforstudyingitsproperties.
Furthermore, Mickey’s thesis describes pioneering work on ultracold chem-
istry via studies of molecular photodissociation. At extremely low temperatures,
processes that create or break chemical bonds proceed according to quantum
mechanical rules, and several approaches had been tried to observe these non-
classical phenomena. In our lab, we had been detecting weakly bound molecules
by fragmenting them into atoms, which were then imaged with a camera facing
perpendicular tothe lattice trapping axis.Mickey was curious what would happen
vii
viii Supervisor’sForeword
if we aligned a camera on axis with the lattice and looked at the photofragment
angulardistributions.Soheledanefforttobuildthissetupandlearnhowtoprocess
and interpret the images. The textbook-quality images shown in this thesis are
beautiful pictures of diatomic molecules breaking apart in up to eight different
directions, exhibiting coherent quantum mechanical patterns. This nonclassical
behavior challenged intuition that was established before the 1980s. The thesis
demonstrateshowtobreakmolecularbondswhileimpartingonlyaminisculelevel
of excess energy to the fragments and thoroughly explores the cold regime from
100nKtotensofmillikelvin.Theresultsshowmatter-waveinterferenceofreaction
productsaswellasquantummechanicalreactionbarriertunneling.
Measuring ultralow temperatures, down to the nanokelvin level, is in itself an
important outstanding problem, and Mickey’s thesis describes an invention of an
excellent technique that relies purely on spectroscopy, thus yielding very high
precision. It only requires the atoms or molecules to be tightly trapped in a lattice
and to possess a narrow transition. Mickey uses this technique to characterize the
temperature of ultracold strontium molecules and even to cool them down with a
newtechniqueof“carriercooling.”
The pioneering experiments described in this thesis set the stage for optical
precision measurements with simple molecules at a level of quantum control that
was previously impossible. With this new toolkit of controlling and measuring
molecular properties at an unprecedented level, we can be sure to unlock many
additionalmysteriesofmolecularandfundamentalphysics.
NewYork,NY,USA TanyaZelevinsky
July2017
Acknowledgments
Writing a thesis can be a difficult, despair-ridden thing, marked by lonely nights
and waves of self-doubt. And in the midst of this undertaking, it’s easy to lose
perspective. In some ways, the thesis itself seems silly and ill-defined. Is it really
possible to distill 6 years of life experience into 200 pages? Is that even the most
efficient way to transfer knowledge? And who in their right mind would actually
read such a thing? Should the thesis be a survey of the field? An original piece
of unpublished research? A technical manual for the next generation of graduate
students?Anopportunitytowaxpoeticonthemeaningoflifeandhowitallrelates
toultracoldmolecules?
Thefactisthatnoonetellsyouwhatthethesisissupposedtobe.Youjustwrite
it, and hope that someone somewhere will find it useful. Such an open-ended task
can be daunting, and I’ve found myself at times overwhelmed by the immensity
of what lay before me. But as I write these acknowledgements, I’m sitting on a
plane bound from Korea to New York, just getting back from presenting work at
myeighthinternationalconference.Iliterallygetpaidtothinkabouthowtosolve
the mysteries of the universe and interact daily with some of the smartest people
on the planet. Objectively, I am incredibly fortunate. A physicist’s job is difficult,
butatthesametimeitfeelslikeastretchtocalltheprofession“work.”My6years
atColumbiahavebeenmarkedbyaconstantpursuitofanswerstoquestionsabout
howtheuniversebehaves.I’mgratefultohavebeengiventheopportunitytoengage
inthiskindofwork,becauseIknowhowrareitistobeabletogetpaidtodowhat
youlove.
When I first came to Columbia in the fall of 2010, I had the unfortunate com-
binationofabigegoandzeroskills.AtmyfirstmeetingwithTanya Zelevinsky’s
group, Tanya introduced me and asked for Gael Reinaudi and Chris Osborn (the
group’s lead postdoc and first grad student respectively) to try and find something
formetodo.AfteraskingwhetherIhadeverbuiltacircuit(“No...”),possessedany
programming experience (“Matlab 101?”), or knew anything about lasers (“...at
CornellIstudiedparticlephysics?”),Gaelsuggested“Well,perhapsyoucouldrest
yourhandonthisstackofpapersandmakesuretheydon’tblowawayinthewind.”
ix
x Acknowledgments
Despitethisominousbeginning,GaelandChriseventuallytookmeundertheir
wings and showed me how to build lasers, run the experiment, and troubleshoot
thorny problems. My success at Columbia wouldn’t have been possible without
Gael’senthusiasmandChris’spatience.Iwasluckytoinheritanexperimentalready
largelybuiltbythesetwogreatscientistsovertheprevious4years.Withoutthishead
start,ourresultsoverthenextfewyearswouldn’thavebeennearlyasdramatic.
NeartheendofChrisandGael’stimeatZLab,BartMcGuyercametoColumbia
to take over leadership of the strontium experiment. After Chris left I became
the senior grad student working on strontium, meaning that Bart and I would be
collaborating closely. And whereas I had a fragile ego and was driven largely by
passionandobsessioninchoosingwhatquestionstopursue,Bartwaslevelheaded
andcareful,devotedtogettingthedetailsright.Hewasalso(muchtomydismay)
clearlyquiteabitsmarterthanme.
IrememberonceearlyinmytimeatColumbiagettingintosomephysics-related
argumentwithBartandhavinghimclearlyandcalmly(butalsoquitebluntly)telling
me exactly why I was wrong about some finer detail of the analysis of a recent
experiment.Myfragileegowasonceagainsorelybruised,andaftertheconversation
I basically stormed out to clear my head with a coffee and a breath of fresh air.
AndIremembertalkingtoChrislateraboutthis,andcomplainingabouthowBart
was totally unwilling to phrase his criticisms more delicately. To this he replied:
“Mickey, I don’t think you realize how lucky you are to have Bart here as your
postdoc.He’sarealscientist.”Ittookmeanotheryeartofullyappreciatethisfact,
butInowseejusthowprescientChris’swordswere.Thisthesiswouldn’thavebeen
possible without Bart, nor would I be half the scientist I am today without having
hadhimherepushingmetobebetter.AsImoveontomyownpostdoc,IhaveBart’s
exampletofollow,andcanonlyhopethatIcanofferthesamekindofmentorship
to my own future graduate students as Bart did for me. And I hope Bart won’t be
tooembarrassedwhenheseesI’vededicatedthisthesistohim.
I’vehadthegreatpleasureofworkingwithaseriesofoutstandinghighschool,
undergraduate, and master’s students during my time at Columbia, who indulged
my(sometimespoorlythoughtout)curiositiesandinspiredmetothinkmoredeeply
andtotryhardertounderstandwhatIdidn’tyetknowsowell.Highschoolsenior
JenniferHahelpedmefinallyrealizeanoldideaforalecturedemonstrationofthe
wave nature of light, leading to a paper we published in the American Journal of
Physics[1].NoelWanandElijahuBen-Michaelspentcountlesshoursfiddlingwith
prototypes for a crazy idea of mine for a “Laser-light intensity-insensitive passive
polarization-stabilization setup (LLIIPPSS),” which was unfortunately doomed by
subtlypersistentinterferenceeffects(butthanksforthegreatworkguys!).Matthew
Miecnikowskihelpedrealizeanotherideaforanopticsexperimentwithpedagogical
value:iffrequencyshiftsinacousto-opticmodulatorsareduetofirst-orderDoppler
shifts from a diffraction grating moving at the speed of sound, is it possible to
observesecond-ordershifts?(Onceagain,itturnedoutthatunfortunatelytheanswer
was“No”...butwelearnedalot!)
