Single Electron Spin Qubits in Silicon Quantum Dots · PDF file quantum dots by...
Embed Size (px)
Transcript of Single Electron Spin Qubits in Silicon Quantum Dots · PDF file quantum dots by...
Single Electron Spin Qubits in Silicon
Presented to the Faculty
of Princeton University
in Candidacy for the Degree
of Doctor of Philosophy
Recommended for Acceptance
by the Department of
Adviser: Jason R. Petta
c© Copyright by David Zajac, 2018.
All rights reserved.
Electron spins in quantum dots form ideal two-level systems for implementing
quantum computation in the solid state. While spin states can have extremely long
quantum coherence times, addressing single spins and coupling large arrays of spins
have been formidable experimental challenges. Research over the past several decades
has resulted in a variety of creative approaches to address these problems, yielded new
insights into the physics of spins in semiconductors, and demonstrated many of the
basic criteria for quantum computation.
This thesis presents a systematic study of the physics and quantum control of spins
in few-electron Si/SiGe quantum dots. We present novel designs for quantum dot de-
vices that yield improved control of single electron wavefunctions. We demonstrate
full control of single electron spin states by placing a quantum dot in the vicinity of a
strong magnetic field gradient produced by a micron-scale ferromagnet, and quantify
the control fidelity using randomized benchmarking. Utilizing the exchange interac-
tion between neighboring spins in combination with arbitrary single-spin rotations,
we present one of the first demonstrations of all the criteria for universal quantum
computation (initialization, readout, and a universal set of gates) with electron spins
in a single device. Finally, we take the first steps towards controlling a large array of
quantum dots by deterministically shuttling single electrons through an array of nine
Firstly I would like to thank my advisor Jason Petta for all of the guidance he has
provided over the course of my PhD. Throughout the years working in his lab I’ve
learned an incredibly diverse set of skills including sweating copper pipes, designing
printed circuit boards, fabricating nanoscale electronics, installing dilution refrigera-
tors, manipulating microwave signals, and many more. Above all I’ve learned from
Jason how to approach problems with intense focus and how to avoid getting dis-
tracted from the big picture goal. I’ve learned by example how to give a good, clear
presentation, how to get in the lab and make things happen, and the genius that is
the Sawzall. I’m truly grateful for my experience in working in his lab and have no
doubt that it will serve me well in the future.
Throughout my time in Petta Lab I’ve been privileged to work alongside a great
cohort of peers. Xiao Mi has demonstrated a truly impressive work ethic and an
uncanny ability to plow through tough problems. George Stehlik has the ability to
lift the spirits of those around him with a childish sense of wonder and playfulness,
and I will miss racing him to the coffee machine after lunch each day. Ke Wang
really helped me get started in the lab and passed on indispensable knowledge of
the cleanroom that was key to my success within the group. Peace always impressed
me with his efficiency and ingenuity in the lab. For someone so quiet in lab, I
was amazed by Yinyu’s ability to relentlessly churn out new results. Tom Hazard
always lightened the mood around the lab, and has been great to have as a climbing
partner and friend. Stefan Putz always kept the lunchtime discussions interesting
with intriguing trivia. Felix Borjans and Adam Mills have both impressed me with
their programming skills, and I have no doubt the lab will be in good hands with
them alongside the experimental expertise of Anthony Sigillito.
I also could not have done the work in this thesis without the support of our
collaborators. Jake Taylor and Guido Burkard provided invaluable theory support
while exploring the exchange interaction between neighboring spins. Max Russ and
Michael Gullans have both been extremely patient in explaining new theory concepts
to me. Also, none of this could have been possible without financial support from
agencies that fund our research. The work in this thesis was supported by US Depart-
ment of Defense under contract H98230-15-C0453, the Army Research Office through
Grant No. W911NF-15-1-0149, the Gordon and Betty Moore Foundations EPiQS Ini-
tiative through grant GBMF4535, the National Science Foundation through Grants
No. DMR-1409556 and No. DMR-1420541, and the Spanish Ministry of Economy
and Competiveness through Grant MAT2017-86717-P. Also, the devices these ex-
periments were performed on were fabricated in the Princeton University Quantum
Device Nanofabrication Laboratory.
I’ve also had the support of numerous friends and family members over the span
of my PhD. I wish I could thank you all individually, but know that even if you’re not
mentioned here I appreciate everything that you’ve done for me over this significant
period of my life. Throughout my time at Princeton I could always count on Zach
Sethna to get me out of the lab to play softball, get in a quick game of pool between
study sessions, or host a night of drinks at the Z-bar. As for Josh Hardenbrook, I’ll
always remember our Monday night fantasy league, you forcing me to go to the gym
at unreasonable hours, and your intense drive for life.
Life at Princeton would not have been what it was without KL by my side. You’ve
been so supportive throughout this entire process and have helped me grow as a
person. I’m excited to move to NYC with you and start a new chapter in our lives
which I’m sure will be every bit as special as our time together in Princeton. Robin
and Michelle, you’ve treated me like family and given me a home away from home,
and I can’t say how grateful I am for that. The number of ways you’ve helped me
over the years is immeasurable, but if it could be measured I have a feeling it would
be in six-packs and racks of ribs. Dick and Mo, you’ve also become family to me, and
taught me some of the best jokes I know. Mattia I’ve felt like a brother with you,
sharing apartments over the past few years. Princeton doesn’t feel the same without
you, and I hope you’ll move back to the east coast once you get fed up with the San
Fransisco weather. Leslie, I can always count on you to make me smile. Spending
time with you always reminds me of what’s most important in life.
Of course the people who have most shaped who I am throughout my life is my
family. Tommy, I couldn’t have asked for a better brother in life. Thank you for
supporting me from all the way across the country. Whether it’s airport phone calls,
late night gaming, or family vacations, it’s always great to spend time with you. Aunt
Noreen, you’ve also been a big part of my life for as long as I can remember. As a
kid I remember always being excited to spend the day with Aunt Noreen and that’s
still true to this day.
Lastly, no one has supported me more than my parents. Dad, thanks for inspiring
my passion for building things with my own hands. From constructing skateboard
ramps to pool decks, watching and learning from you has shaped the way I approach
problems and came in handy during my research. Mom, probably no one has impacted
who I am more than you. You’ve always encouraged me to pursue my interests and
supported me in my pursuit. Whether it was driving me to hockey practice or signing
me up for guitar lessons, you’ve always been there for me. Thanks Mom and Dad for
making all of this possible. I couldn’t have done it without you.
The work described in this dissertation has been published in the following articles
and presented at the following conferences:
Appl. Phys. Lett. 106, 223507 (2015).
Phys. Rev. Appl. 6, 054013 (2016).
Science 359, 439 (2018).
Nature 555, 599 (2018).
American Physical Society Meeting, March 2015, San Antonio, Texas.
Silicon Quantum Electronics Workshop, August 2015, Takamatsu, Japan.
MRS Fall Meeting, November 2016, Boston, Massachusetts.
American Physical Society Meeting, March 2017, New Orleans, Louisiana.
Silicon Quantum Electronics Workshop, August 2017, Hillsboro, Oregon.
Spin Qubit 3, November 2017, Sydney, Australia.
American Physical Society Meeting, March 2018, Los Angeles, California.
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi
List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii
1 Introduction 1
1.1 Quantum Computing . . . . . . . . . .