Circuit Cavity QED with Macroscopic Solid-State Spin Ensembles

136 Pages·2017·10.923 MB·English

by  Stefan Putz (auth.)

Springer Theses
Recognizing Outstanding Ph.D. Research
Stefan Putz

Circuit Cavity QED
with Macroscopic
Solid-State Spin
Ensembles
Springer Theses
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Stefan Putz
Circuit Cavity QED
with Macroscopic Solid-State
Spin Ensembles
Doctoral Thesis accepted by
TU Wien, Vienna, Austria
123
Author Supervisor
Dr. StefanPutz Dr. JohannesMajer
Department ofPhysics TU Wien,Atominstitut
Princeton University Vienna
Princeton, NJ Austria
USA
ISSN 2190-5053 ISSN 2190-5061 (electronic)
SpringerTheses
ISBN978-3-319-66446-0 ISBN978-3-319-66447-7 (eBook)
DOI 10.1007/978-3-319-66447-7
LibraryofCongressControlNumber:2017950034
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To Stephanie
’
Supervisor s Foreword
Hybrid quantum systems have gained a lot of interest as future quantum tech-
nologies.Thehopeisthattwodifferentquantumsystemscanbecombinedandthat
the resulting system profits from advantages of the individual systems. Therewith
one intends to pool the strength of different technologies and realize improved
quantum devices. The thesis presented by Stefan Putz aims at exploring hybrid
quantum devices using superconducting circuits and spin systems, in particular
nitrogen-vacancy color centers in diamond. He tried to combine the advantages of
superconducting devices, like low losses and exibility with the benefits of the
nitrogen-vacancy center, such as the long coherence times and confinement in a
host crystal.
In the first two sections, Stefan Putz lays out the theoretical foundations for the
thesis. Therein he summarizes the relevant literature and illustrates the relevant
physics with analogies like the mass on a spring system or the LC circuit. One
of the major results of the thesis is the experimental demonstration of the cavity
protection effect. Stefan Putz studied the dynamics of a superconducting cavity
strongly coupled to an ensemble of nitrogen-vacancy centers in diamond. He
experimentally observed how decoherence induced by inhomogeneous broadening
canbesuppressedinthestrong-couplingregime,aphenomenonthatisnowknown
as“cavityprotection”.Continuingonthisproject,StefanPutzdevelopedascheme
to engineer long-lived coherent states in a hybrid system. This scheme was suc-
cessfully implemented and improved the coherence times by orders of magnitude.
Remarkably, this strongly coupled system performs better than the two individual
subsystems. Therefore, this experiment is the first one to live up to the promise of
hybrid quantum systems and marks a milestone in the field.
In Chap. 7 Stefan Putz demonstrates that hybrid systems can also be used to
study nonlinear phenomena. In particular, the hybrid system shows amplitude
bistabilityandallowsobservingthetimedynamicsconveniently.Hedemonstratesa
vii
viii Supervisor’sForeword
critical slowing down of the cavity population on the order of several tens of
thousandsofseconds—atimescalemuchlongerthanobservedsofarforthiseffect.
ThethesisofStefanPutzpresentsseveralimportantadvancesinthefieldofhybrid
quantum systems. Therefore, I am convinced that it will be an important reference
for future experiments and novel quantum devices.
Vienna, Austria Johannes Majer
July 2017
Abstract
Hybrid quantum systems are one of the most promising implementations offuture
quantumcomputation,communication,andsimulationdevices.Thesetechnologies
willhaveamajorimpactonsocietyandindustryandheraldthestartofanewage.
However, in the early stages of this development, crucial technological limitations
have to be addressed and solved. As one part of this giant puzzle, this thesis
examines the basic phenomena occurring when interfacing macroscopic spin
ensembleswithasingle-mode cavity.Understandingtheseunderlyingprinciplesis
keyinthepossibleimplementationofquantummemoriesbasedonsolid-statespin
ensembles.
The hybrid solid-state quantum system studied in this thesis consists of a
superconducting microwave cavity strongly coupled to an ensemble of electron
spinshostedbynitrogen-vacancycentersindiamond.Oneofthemainresultsofthe
experimentscarriedoutdemonstrateshowthetotaldecoherenceratescalesinthese
systems. As is shown the collective enhanced coupling strength allows the sup-
pressionofspindephasinginducedbyinhomogeneousspinbroadening.Thiseffect
isknownas“cavityprotectioneffect”andthetotaldecoherenceratescaleswiththe
collective cavity spin interaction strength.
The hybridization acts beneficially on the system coherence time. However,
thesetimescanbedrasticallyimprovedbyspectralholeburning,beyondthenatural
limitattainablebythe“cavityprotectioneffect”.Theobservedlong-livedcoherence
trulylivesuptothepromiseofhybridsystemstoperformbetterthanitsindividual
subcomponents. This demonstrates that dark states can be used to coherently
exchange energy between the cavity and spin ensemble. These engineered dark
states are used to induce coherent Rabi oscillations and a first step is made toward
the implementation of a solid-state microwave frequency comb.
Additionally, this system is a versatile tool for studying strong nonlinear
dynamics.Suchaneffectisamplitudebistability,whichhasnotbeenobservedina
ix
x Abstract
microwave solid-state spin ensemble coupled to a single-mode cavity so far. This
engineered hybrid system approach opens up the possibility for a new route to
cavity QED experiments beyond the standard Dicke and Tavis-Cummings model,
no only also for truly long-lived quantum memories, solid-state microwave fre-
quency combs and optical-to-microwave quantum transducers.