Duke PHYSICS
http://www.phy.duke.edu
WHAT’S INSIDE
Department Happenings......... 1
Graduate News....................... 2
Graduate Student
Organization News.................. 5
Undergraduate News.............. 6
New Faculty Profiles................ 7
Faculty Awards....................... 9
Outreach.............................. 11
Alumni Profiles:
Robin Canup......................... 12
Randall Ledford.................... 13
Michael Wittmann................. 14
Faculty Research:
Non Linear Optical Imaging... 15
Slaying Dragon-Kings!............ 16
News:
Graduate Students
Visit Jefferson Lab................ 19
Another Outstanding Fermion
Sign Problem Solved............. 19
Editors: Haiyan Gao, Cristin
Paul, Mary-Russell Roberson and
Christopher Walter
Annual Newsletter 2014
Department Happenings
– by Haiyan Gao
This has been another great year. First,
let me thank all of you for your support, and
encouragement in making my third year as chair
still as exciting and enjoyable as my first year. I
look forward to your continuing support in the next
three years.
There has been an important change in
the departmental leadership. Prof. Shailesh
Chandrasekharan stepped down on July 1, 2014
as the Director for Graduate Studies (DGS) in
Physics and Prof. Gleb Finkelstein took over this
important leadership role. Prof. Chandrasekharan
had been working tirelessly as DGS and had
been extremely effective in leading efforts in
improving our graduate program. We thank Prof.
Chandrasekharan for his service to the department
and look forward to working with Prof. Finkelstein
in his new role.
The commencement weekend has always
been the happiest time for the university. We
graduated twenty-six physics and biophysics
majors – an encouraging upward trend from last
year’s nineteen! And more and more students
are choosing physics and biophysics as their
majors! We also graduated an extremely large
number of Ph.D students (seventeen), and one
Master’s student. You will read more in the section
on undergraduate studies in this newsletter,
contributed by Prof. Henry Greenside and Prof.
Kate Scholberg, and graduate studies by Prof.
Shailesh Chandrasekharan. We hosted the second
group of visiting students from Taishan College
of Shandong University this past academic year,
and the first group of students from Hong Yi Class
at Wuhan University in the fall of 2013. We will
welcome the first group of visiting students from
Kuang Yaming Honors School at Nanjing University
in the fall of 2014. Through our Duke-Shanghai
Jiao Tong University (SJTU) Physics Program,
one student from SJTU joined us last fall as a
transfer student, and three more will be joining our
department in the fall of 2014.
In the last year faculty and students have
published many exciting research results and you
can sample some of them in this newsletter. We
are very proud that several of our students and
faculty have received awards, which are also listed
in this newsletter. Members in our department
have also been very active in outreach activities,
and you can read some of them in this newsletter.
Thanks to the generosity of anonymous donors,
two endowed faculty
positions were
created in theoretical
or experimental
condensed matter
physics, broadly
defined, and they are
the Charles H. Townes
Assistant/Associate
Professor and the William M. Fairbank Assistant/
Associate Professor. Dr. Charles H. Townes, a
Nobel laureate in Physics received his M.A. degree
from Duke Physics in 1937, and Dr. William M.
Fairbank was on the Duke Physics faculty from
1952 to 1959 before he joined the Physics faculty
at Stanford.
Profs. Mark Kruse and Ronen Plesser have
been promoted to the rank of Full Professors.
Prof. Ashutosh Kotwal has been named as the
Fritz London Professor of Physics in May 2014.
Congratulations to them all for these important
milestones. We are most delighted that Dr. Thomas
Barthel as the first Charles H. Townes Assistant
Professor, and Dr. Sara Haravifard as the first
William M. Fairbank Assistant Professor, will join
our faculty in July 2015. You will learn more about
Sara and Thomas, and their research in the new
faculty profile section.
This spring we were very proud to welcome
back physics alumna Robin Canup, a member
of the U.S. National Academy of Sciences, who
explained to us the origins of the moons in a most
memorable Sponer Presidential lecture; later in
the spring, another distinguished Duke physics
alumnus, Caltech physics Professor, Jamie Bock
announced together with his collaborators the
successful measurement of a B-mode polarization
signal in the cosmic microwave background (CMB)
using the BICEP2 telescope at the South Pole.
This discovery is an important confirmation of key
aspects of the theory of cosmic inflation.
I would like to end on a very positive
development. The Board of Trustees has recently
approved funding for the planning and design
of a new Engineering/Physics building. This will
provide the much-needed, high-quality lab space
for tabletop experimental program and also new
space for more active-learning physics teaching.
While the space in this new building will meet our
near- to mid-term need, in the long run we very
much look forward to a new Physics building where
the entire physics community will learn, teach, and
research under one roof.
Graduate News
Graduate News
- by Director of Graduate Studies, Shailesh Chandrasekharan
We have completed another exciting year and as the Director of Graduate Studies (DGS) it gives me great
pleasure to report on the various developments in our graduate program and the accomplishments of our
students over the past year (June 1, 2013 – May 31, 2014).
Degrees Awarded
Sixteen students passed their PhD examinations during the past year and one student obtained a terminal
Master’s degree. The table below lists the names of all degree recipients along with the names of their advisors.
I congratulate all of them on their accomplishments and wish them success in their future careers in academia and industry.
Student
Advisor
Student
Advisor
Kristine Callan
Prof. Gauthier
Mengyang Sun
Prof. Socolar
Abram Clark
Prof. Behringer
Shangying Wang
Prof. Raghavachari
Chris Coleman-Smith
Prof. Mueller
Taritree Wongjirad
Prof. Scholberg
Ethan Elliott
Prof. Thomas
Di-Lun Yang
Prof. Mueller
Kevin Finelli
Prof. Kruse
Yang Yang
Prof. Brown
Yuan Lin
Prof. Samei
Qiujian Ye
Prof. Gao
Jonathan Mueller
Prof. Weller
Hao Zhang **
Prof. Chang
Joshua Powell
Prof. Mehen
Yunhui Zhu
Prof. Gauthier
Meizhen Shi *
Prof. Gauthier
* Terminal Masters, ** September 2014 Degrees
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Celebrating the PhD recipients at the May 2014 graduation ceremony. Duke PHYSICS
Preliminary Exams
This year ten students took their preliminary exam and I am glad to report that everyone passed. Their names along with their advisors
are listed in the table below. I extend my very best wishes to these students and look forward to an exciting PhD thesis from each of them in
the next few years.
Student
Advisor
Student
Advisor
Jonah Bernhard
Prof. Bass
Zepeng Li
Prof. Scholberg
David Bjergaard
Prof. Arce
Catherine Marcoux
Prof. Socolar
Kristen Collar
Prof. Brown
Margaret Shea
Prof. Gauthier
Leo Fang
Prof. Baranger
Xuefei Yan
Prof. Gao
Forrest Friesen
Prof. Howell
Weizheng Zhou
Prof. Wu
Fellowships, Awards and Accomplishments
Over the past year students have obtained many new exciting research results and have continued to help the department in its teaching mission. Many students received fellowships and awards for their work. Graduate student Taritree Wongjirad, who
graduated in May 2014, received the prestigious Pappalardo Fellowship for postdoctoral work at MIT. This is a very
competitive fellowship given to very few exceptional students each year. Taritree will be one of three new fellows for the
coming year. For his PhD thesis, Taritree worked with Profs. Scholberg and Walter in the field of experimental neutrino
physics. Congratulations to Taritree for his accomplishments.
Two students were recognized by the National Science Foundation
(NSF) this year. Second year graduate student Anne Watson, who is working with Prof. Finkelstein in the field of experimental Nanophysics, received
the Graduate Research Fellowship (GRF) from the National Science Foundation (NSF) in May 2014. The fellowship will fund her research over the next
Taritree Wongjirad
three years. Another second year student Emilie Huffman, who is working
with me in theoretical and computational quantum many body physics, received an honorable
mention by the NSF based on her application for the GRF. Emilie has already published an interesting paper earlier this year where she solved a thirty year old problem in the field of strongly correAnne Watson
Emilie Huffman
lated electronic system. She has been invited to spend two semesters at Bern University by Prof.
Uwe-Jens Wiese to collaborate with him on a project related to her research work. The Duke Graduate School is supporting her visit and has
given her a travel fellowship for a trip during Fall 2014. Emilie also received a summer research fellowship this year from the Graduate School.
Congratulations to both Anne and Emilie for their achievements.
Every year exceptional graduate students within the department are
considered for three different endowed fellowships. The Walter Gordy
Graduate Fellowship recognizes excellence in research by a physics graduate student in the area of microwave spectroscopy and microwave physics
or closely related topics. This year’s award went to Georgios Laskaris for
his recent work on spin exchange optical pumping and photodisintegration of Helium-3 using polarized high-intensity gamma source (HI\gamma
S). Georgios is a sixth year student working with Prof. Gao. This year the
Fritz London Graduate Fellowship recipient was Abe Clark, a sixth year
Abe Clark
Jun Yan
Georgios Laskaris
student who worked with Prof. Behringer and graduated in May. The London
fellowship is given to excellent students working in the field of condensed matter physics. Abe’s work concerning impacts on granular materials using photo-elastic particles, which led to a better understanding of granular flow, earned him the fellowship. Lastly, Jun Yan, a third year
student working with Prof. Ying Wu, was the recipient of the Henry W. Newson Fellowship, which recognizes excellent research in experimental
nuclear physics. Jun received the fellowship for his contributions to developing two-color lasing at the HI\gamma S. Congratulations to all these
students for receiving these prestigious awards.
Some graduate students work in interdisciplinary
fields of research and the best students may receive
fellowships offered by the respective programs in order
to support them for short durations. Last year, Nicholas
Haynes, a first year graduate student working with Prof.
Gauthier, received a fellowship from the Wireless Intelligent Sensor Networks Integrative Graduate Education
and Research Training (WISeNet IGERT) program. Due to
his excellent work the fellowship has been renewed for
Nicholas Haynes
Ming-Tso Wei
Gu Zhang
Jiani Huang
a second year. Three students received fellowship from
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Graduate News
continued from page 3
the Graduate Program in Nanoscience, (GPNano) which is yet another interdisciplinary graduate certificate program at Duke. Among the three
are, Gu Zhang and Jiani Huang, two second year students working with Prof. Baranger and Prof. Mikkelsen respectively, and Ming-Tso Wei a
first year student working with Prof. Finkelstein. The GPNano fellowship supports a student registered for the nano-certificate program for one
semester. Congratulations to all these students for their hard work and accomplishments.
Graduate students also play an important role in the teaching mission of the department and
the department recognizes the best teaching assistants through two types of teaching fellowships,
one is sponsored by the American Association of Physics Teachers (AAPT) and the other is the Mary
Creason Memorial award for outstanding undergraduate teaching in physics. This year, two first year
students, Nurul Taimur Islam and Ming-Tso Wei, were nominated as Outstanding Teaching Assistants
for 2014 through the AAPT, while first year student Ron Malone and second year student Emilie Huffman received the Mary Creason Memorial Award. These awards will be distributed during the annual
departmental picnic, scheduled on August 23, 2014. I thank these students for contributing to the
success of our teaching mission and congratulate them for their achievements.
Nurul Taimur Islam
Ron Malone
In addition to the above awards many graduate students have published important research
articles in various journals, have given research presentations at various conferences and have
become recognized in the world through their research work at Duke. We refer the reader to the web site for detailed information about these
other graduate student accomplishments. Congratulations to all graduate students on their accomplishments over the past year.
Graduate Curriculum
This year the Graduate Curriculum Committee (GCC) reviewed the graduate curriculum that was first implemented in 2010. One aspect of
the review was to survey the faculty and students about deficiencies they have experienced. Two concerns emerged from the survey: (1) weak
students did not have a clear path for self-improvement and (2) the preliminary exam experience was not uniform among many students. Based
on this and other findings the GCC has submitted a report to the faculty for discussion in late April. Further discussions on the proposed changes
will occur in early Fall and it is likely that a subset of the proposed changes will be adopted for the next academic year. I thank the members of the
GCC and all the faculty and students for their help during the review process and hope that the effort will make our program stronger.
Graduate Admissions
This year the Graduate School authorized the department to matriculate 15 students for the Fall 2014 class. This number varies every
year based on departmental needs and available funding from the Graduate School. The Graduate Admissions Committee (GAC) reviewed 249
applications during the winter break and made 49 offers to students all over the world. The department held an open house on March 20th and
21st for the accepted applicants, so that they could get a better perspective of our graduate program. I thank Bonnie Schmittberger, a fourth
year student and the president of the Graduate Student Organization (GSO), for her help in organizing the event. I also thank all the students
and faculty who helped during the open house and throughout the recruitment period. Thanks to all their efforts we were successful in recruiting 18 students this year. The incoming class contains students from China (8), India (2), Kazakhstan (1), and the US (7). There are 17 male
and 1 female student in the incoming class. We expect the new class to arrive during mid August and have planned a variety of orientation activities for the incoming class including a departmental picnic on August 23, 2014. One of the incoming students, Andrew Seredinski, received
the James B. Duke fellowship, which is offered to very few outstanding and promising scholars among the Graduate School applicants. Two
other students, Matthew Epland and Douglas Davis, were awarded the Goshaw Family Fellowship, due to their scholarship and past research
experience in the field of experimental high-energy physics. This fellowship will allow them to continue their research during their first year
along with regular coursework.
Memorial: Adamos Kafkarkou
In the midst of all the excitement, we also experienced profound sadness due to the passing away of Adamos
Kafkarkou, one of our bright and talented third year students from Cyprus. Adamos was working with Prof. Weller in
experimental nuclear physics. I personally remember him fondly from my class as an intelligent and soft-spoken student
who always wanted to understand things deeply. We all convey our deepest condolences to his family members for their
great loss. We all miss him very much.
Changes to the Administration
On July 1, 2013 the department appointed Ms. Nancy Morgans as the new assistant to the DGS. Nancy was the
replacement for Mrs. Donna Ruger who retired from Duke after 28 years of service. Nancy has been a part of Duke
for many years and has served in a similar position at the Nicholas School of Environment from 2000-2007. I welcome
Nancy to the department and look forward to working with her for many years to come.
After three years as the DGS, on July 1st 2014, I will step down from this position and will be replaced by Prof. Gleb
Finkelstein. I have promised to help him through the transition if necessary and I wish him all the success in his new position. Graduate education continues to be one of my passions and I have loved my job as the DGS. However, a DGS has
many responsibilities and I look forward to serving the department in a less demanding position for a few years so that I
can find more time for my own research.
Adamos Kafkarkou
Nancy Morgans
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Graduate Student Organization News
– by Meg Shea, GSO President
Annual Picnic
The class of 2012 did a great job organizing the annual picnic last
September. We were all welcomed to the start of the year with
excellent food, fun, and weather. Cate Marcoux and Reggie Bain
were given awards for their excellent work as TAs in the 2012-2013
academic year. The GSO was also proud to announce the creation of
a new award for Excellence in Graduate Teaching. This award, given
to a teacher of a graduate core course, was given to Professor Ying
Wu for his wonderful work teaching electrodynamics.
Colloquium Lunches
This year, the graduate students continued the tradition of taking colloquium speakers out to lunch. Forrest Friesen and Scott Moreland,
assisted by Cate Marcoux, organized the majority of these lunches,
which allowed students an excellent opportunity to meet with the
speaker and ask questions about his or her research and career path.
There were 14 colloquia this year, an unusually high number, due to
the department’s candidate search. The graduate students were
happy to be able to meet with all of the colloquia speakers.
Grads-Chair and Grads-DGS Meetings
We held 2 Grads-Chair meetings this year, during which students were
able to meet with Chair Gao. These meetings allowed students to
ask questions and voice opinions about various departmental issues.
We are very grateful to Chair Gao for her time and consideration in
meeting with us in this way. In addition to Grads-Chair meetings, we
also held two Grads-DGS meetings with Professor Chandrasekharan.
These meetings were more focused around curriculum issues and
were very useful. Students appreciated the chance to discuss proposed curriculum changes with the DGS as well as learn more about
how curriculum decisions are implemented within in the department.
We are grateful to Professor Chandrasekharan for his time and consideration in holding these meetings.
Open House
This year we welcomed 11 prospective students to campus for the
departmental open house in March. GSO vice president Bonnie
Schmittberger spearheaded the organization of the graduate student
led events for the two days. The prospective students attended a
panel on graduate student life at Duke, a poster session of graduate
student research, a tour of campus, and two dinners in downtown
Durham. It was a good event and hopefully we will see many of the
recruits in the fall!
Jefferson Lab Trip
This year the graduate students traveled to the Thomas Jefferson
National Accelerator Facility (Jefferson Lab) during the fall break.
Jefferson Lab, located in Newport News, VA, is an important laboratory facility for medium energy physics and has close ties with
Professor Haiyan Gao’s lab. Students were able to tour the electron
beam accelerator facility as well as the superconducting radiofrequency instrument development facility. It was a very successful trip and
we thank Professor Gao and graduate student Anne Watson for their
leadership in getting it off the ground.
Department Tea
Tea time has continued this year with a slight change of structure.
Tea time was hosted every other week and many of the tea times
were sponsored by individual professors and their groups. Graduate
student Kristen Collar and Professor Ronen Plesser both worked hard
to make this new structure work, and we thank them. We gratefully
acknowledge Professors Meyer, Gauthier, Gao, Arce, and Goshaw for
supporting tea time. We also thank graduate student Jonah Bernhard
for donating his prize money of $1000 of Dunkin’ Donuts gift cards.
These generous donations have allowed tea time to continue to operate, providing an informal atmosphere for student/faculty interaction.
Graduate Student Seminar
This year, Chung-Ting Ke and Venkitesh Ayyar have organized thirteen
graduate student seminars for the graduate student community.
These seminars remain a great way for students to practice speaking
and learn about each other’s fields of research. Students have seminars to practice conference, prelim, and defense talks.
Ch-Ch-Ch-Changes
There was a large shift in the role of the Graduate Student
Organization this year when the GSO was given the added responsibility of maintaining and administering a budget for graduate student
activity. Following discussions among the GSO executive committee, Chair Haiyan Gao, DGS Shailesh Chandrasekharan, DGSA Nancy
Morgans, and Administrative Manager Randy Best, a budget for the
fiscal year of 2014 was determined. The budget covered graduate
student seminars, colloquium lunches, tea time, grads-Chair and
grads-DGS meetings, and graduate student mentor-mentee events.
Special thanks to all who helped in this process, particularly the GSO
executive committee, Prof. Gao, Prof. Chandrasekharan, Nancy, and
Randy.
Thanks
The GSO would like to thank all GSO and committee members who
helped to make the past year so successful. The GSO executive
committee consisted of Meg Shea (President), Bonnie Schmittberger
(Vice President), and Kristen Collar (Secretary/Treasurer). The
GSO class reps were Kevin Holway (1st year), Reggie Bain (2nd
year), Dave Bjergaard (3rd year), Lei Li (4th year), Kevin Claytor
(5th year), and Georgios Laskaris (6th year). The subcommittees
were covered by Chung-Ting Ke and Venkitesh Ayyar (Graduate
Student Seminars), Forrest Friesen and Scott Moreland (Colloquium
Committee), Chris Pollard and Venkitesh Ayyar (Curriculum
Committee), Anne Watson and Leo Fang (Ombundspersons), David
Rosin (GPSC), David Bjergaard (Technical/Computing Committee and
Election Comissioner), Jonah Bernhard (Web Committee), Bonnie
Schmittberger (News Committee), and Kristen Collar (Social Chair).
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Undergraduate News
Undergraduate News
– by Director of Undergraduate Studies, Kate Scholberg
At this year’s graduation ceremony in May, eleven students with
first majors in physics and five with secondary majors received their
diplomas. In addition, eight students with first majors in biophysics
and two with second majors in biophysics graduated this year. It’s
now the third year that our successful new biophysics program has
graduated students. We now have a total of 23 first majors and two
second majors in biophysics, as well as 45 first majors and 15 second
majors in physics.
The graduation program can be found here.
The members of the 2014 graduating class will be taking many
paths, including pursuit of advanced degrees in physics, biology,
engineering and math, medical school, and careers in high-school
teaching, consulting, and music.
Three physics seniors, Steven Demers, Ryan McGeehan
and Jackson Matteucci, earned their degrees with distinction by
completing and defending research theses with Physics faculty
members. Of these, Jackson Matteucci’s thesis work earned high
distinction. Jack worked with Professor Al Goshaw on analysis of data
from the ATLAS experiment at CERN. He was also the recipient of
the Daphne Chang Memorial award for excellence in undergraduate
research, which comes with a $1000 prize.
Many other students in the department in all years were involved
in research, and presented progress and results at the lively annual
department poster session in April. We had eleven impressive posters
describing projects in many subfields, including high-energy physics,
condensed matter and biophysics.
The poster session program can be found here.
Attendees voted for the best posters. The first prize winner was
Melody Lim; second prize went to Yiqiu Zhao, and Chris Flower and
Jinzi Zhang tied for third place. We are very proud of our students’
achievements.
The poster session also marked the induction of seven physics
majors into the Sigma Pi Sigma, the nationwide physics honor society.
This recognition is given to students who excel academically or who
have made outstanding research or service contributions.
Junior physics major Eugene Rabinovich received two very
prestigious awards: he was named a Goldwater scholar (the only one
from Duke this year). He was furthermore named Faculty Scholar,
which is the highest honor given bestowed by the University on its
undergraduates. Eugene has been working with Professor Ronen
Plesser and has made impressive contributions to string theory
research.
Duke faculty have continued to pursue undergraduate
teaching innovation. After some prior successful experiments with
undergraduate courses by Professors Dan Gauthier and Roxanne
Springer, this year Professors Dan Gauthier, Ying Wu and Rob Brown
for the first time completely changed the format of Physics 141 and
142 (the introductory sequence for life science majors), to replace
6
lectures with student interaction and
problem-solving time. This is the
“flipped classroom” or “active learning”
approach, which has been shown by
much pedagogical research to improve
learning outcomes.
Format restructuring and
content updating is now also underway for the introductory physics
course sequence designed for physics majors. These courses will
now have a separate experimental physics component, 161L and
162L, to be implemented for the first time next fall and spring. The
Undergraduate Curriculum Committee is also working on a revision of
lecture portion of the course, with the aim of integrating more exciting
research-related material and also incorporating more computer
programming into the course. The goal is to provide fresh, relevant
material, and also to teach students essential skills to enable them to
engage more quickly in research in the later years of their degree.
An exciting event planned for next January is the Triangle
Conference for Undergraduate Women in Physics. This national
series of conferences has been underway since 2004 (Duke hosted
it in 2010). The Triangle was selected by the national organizing
committee as one of the sites for the 2015 conference, and we will
hold it at Duke in January next year over Martin Luther King weekend.
Duke undergraduates (some of who attended previous conferences
in the series) have already been active in the organizing committee,
which includes also members from North Carolina Central University,
North Carolina State University, and the University of North Carolina at
Chapel Hill.
Finally, the Society of Physics Students, whose faculty advisor
is Professor Phil Barbeau, has been very active this year. Professor
Barbeau reports: “This has been a banner year for the Society of
Physics Students, the second oldest chapter in the country (circ.
1925). SPS was recognized as an official student group this year as
particpation increased five-fold. The students held a number of ice
cream social events coupled with tours of the Triangle Universities
Nuclear Laboratory, the Free Electron Laser laboratory, or just
experimenting with cloud chambers and other particle detectors.
The group participated in Astronomy night with Professor Ronen
Plesser and in the spring, ten members of SPS attended a Q&A
with Neil deGrasse Tyson at North Carolina State University. SPS
also sponsored four student-led seminars this year, presented by
SPS members Melody Lim (Corn-Starch Physics), Nicole Gagnon
(Wii-mote Magnetometors for LIGO), Anne Talkington (Modeling of
Animal Migrations) and Caroline Steiblin (Physics at CERN). Currently
the group, lead by Melody Lim and Benjamin Suh, is planning events
for next year, including a trip to the local Nuclear Power Reactor at
Shearon Harris.”
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New Faculty Profiles
New Assistant Professor
Thomas Barthel
— by Mary-Russell Roberson
In July 2015, Thomas Barthel will join the Duke faculty as the
Charles H. Townes Assistant Professor of Physics. Barthel studies the
quantum mechanics of many-particle systems using computer simulations and analytical techniques.
“I like to solve problems which either have high technological
interest or are of some fundamental nature,” Barthel said. “I want to
contribute to understanding these very complex problems.” As one example, he cited high-temperature superconductivity, which still lacks
a thorough theoretical explanation though it was first demonstrated
experimentally several decades ago.
A native of Leipzig, Germany, Barthel studied in Heidelberg
and Aachen, and received his doctoral degree from RWTH Aachen
University. He is currently a research associate at the Laboratoire de
Physique Théorique et Modéles Statistiques, jointly run by University
Paris-Sud and CNRS (France’s National Center for Scientific Research).
Barthel develops and employs methods that model the behavior
of many-particle systems on an atomic scale—behavior which is governed by quantum mechanics rather than the familiar laws of classical
mechanics that apply to balls, cars and other everyday objects.
“Quantum theory is essential for understanding fundamental
properties like the stability of matter, surprising effects like the
frictionless flow of Helium-4 below 2 Kelvin, or advanced technological
applications like the lasers and masers that Charles H. Townes worked
on,” Barthel said. Charles H. Townes, a Nobel laureate for whom the
endowed professorship is named, earned a master’s degree in physics at Duke in 1937.
Barthel studies ultra-cold gases and solids. The number of interacting particles in these systems can range from 100 to 1023, adding
complexity to a situation that’s already pretty complex. In the context
of quantum mechanics, the state of the system can be a superposition, or combination, of all of its possible classical states. “As a consequence, the number of degrees of freedom grows exponentially with
the system size instead of linearly as in the corresponding classical
system,” he said.
With such a large number of particles and degrees of freedom,
the systems typically can’t be described exactly. “The key is to try and
find suitable approximations and identify a manageable reduced set of
relevant effective degrees of freedom,” he said. To meet this challenge, Barthel is developing novel numerical techniques to approximate the many-particle systems. “These techniques make it possible
to go far beyond what we can do with pen and paper,” he said.
After years of working on quantum mechanics he says he’s
developing an intuition about how these systems behave. “That’s what
I like,” he said. “Trying to get an intuition for these many-particle systems. I want to get a feeling for this totally different world. The longer
you work on this, the more intuition you will have.”
However, quantum mechanics still offers plenty of surprises.
Barthel quoted Richard Feynman, a famous physicist who once said, “I
think I can safely say that no one understands quantum mechanics.”
The very complexity that makes understanding these systems
difficult also offers the potential for technological advances, such
as quantum computers, which would be able to process much more
information much more quickly and securely than today’s digital computers.
One roadblock to quantum computing is the issue of decoherence, which is the loss of quantum information due to the “coupling”
of a quantum system to its environment. Barthel and a colleague recently demonstrated that many-particle systems can behave differently than systems with fewer particles in terms of how they move toward
decoherence. “One can tune interactions in the quantum system such
that it moves toward decoherence much more slowly,” he said.
In his free time, Barthel enjoys hiking, reading history and philosophy, and playing basketball. He expects to add “watching basketball”
to that list once he gets to Durham. “I’ve heard Duke has one of the
best teams and a big coach who also coaches the Olympic team, so
I’m looking forward to following some games,” he said. “In the United
States, basketball is much more important than in Europe. It will be
interesting to see how the discussion works.”
Barthel is also looking forward to collaborating with students and
other scientists at Duke, not only on condensed matter, but also on
quantum chemistry, which involves smaller systems of electrons in
atoms or molecules.
Potential collaborators include physicists Harold Baranger, Albert
Chang, and Gleb Finkelstein, and mathematician Jianfeng Lu. Barthel
enjoys working not just with other theoreticians, but with experimentalists as well. “I can give them some ideas for interesting experiments,”
he said, “or if they have done a nice experiment, I can help explain the
results.”
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7
New Faculty Profiles
New Assistant Professor Sara Haravifard
— by Mary-Russell Roberson
Sara Haravifard has enjoyed experimenting with magnets and
phase changes her whole life. As a little girl, she loved to watch boiling
water jiggle the lid of a pot. “I was amazed at how water changes to
a different phase and there is energy involved that can move things,”
she said. At school, she was captivated by the slow-motion fall of a
magnet through a copper pipe.
Today, she studies phase changes and magnetic moments of
crystals in an environment of low temperature, high pressure, and a
high magnetic field. In July 2015, she will join the Duke faculty as the
William Fairbank Assistant Professor of Physics.
In her experimental work, Haravifard mainly studies single
crystals whose ions are arranged in a layered lattice. She cools
the sample to extremely low temperatures, then applies pressure
and a magnetic field. “By getting to very low temperatures, you are
eliminating fluctuations due to thermal energy, and you can look
at how atoms are changing their positions and magnetic moments
because of quantum mechanical interactions,” she said.
As an aside, she noted that the work of William Fairbank, for
whom her endowed position was named, makes her own work
possible. “He opened the door to low-temperature physics,” Haravifard
said. “If he had not done the research on liquid helium I would not
be able to get down to these low temperatures and look at quantum
mechanical interactions.” William Fairbank was a professor at Duke
from 1952-1959.
After adjusting the pressure and magnetic field, Haravifard
measures the structural and magnetic properties of the crystal to
see how the ions are reacting and whether the material is in a new
phase, such as superconductivity. ”With the high pressure, I change
the distance between these ions, and as I change that, their magnetic
interactions will start to change and that causes different phases to
emerge,” she said.
To measure the properties of the materials in her experiments,
she probes the crystals with x-rays and neutrons. X-rays can measure
the structure of the crystal very precisely, providing information
about the location of the ions in the lattice. Neutrons, because they
have a magnetic moment themselves, can give information about the
magnetic state of the ions.
“By doing these experiments, we are trying to understand some
of the very fundamental questions we have,” she said. “What causes
a particular phase to be favored over another phase? What causes
superconductivity? What can we do to raise the temperature for
superconductivity? If we could come up with a material that would
8
be a superconductor even at room
temperature, that would be a huge
breakthrough.”
Although these types of
experiments could lead to the
discovery of materials with useful
applications, Haravifard is motivated
more by the fundamental questions. “For me, it is the passion to
solve the mystery,” she said. “There are too many open questions.
Superconductivity was discovered by an accident, and a century later
we still do not understand what is happening.”
In her quest to solve mysteries, Haravifard seeks out theorists for
collaboration. “I’m mainly an experimentalist,” she said. “But it cannot
be done without working with the theorists. We have data we can
share, and they can give us an idea of what is happening. We can learn
more by collaborating with them and putting everything on the table.”
Haravifard is currently a joint assistant physicist at the University
of Chicago and Argonne National Laboratory, which is one of the
facilities worldwide that she uses for her experiments. Another is Oak
Ridge National Laboratory in Tennessee, where she uses instruments
including the Spallation Neutrons and Pressure Diffractometer (SNAP).
Using SNAP, she and her colleagues recently performed the first
successful single-crystal high-pressure neutron experiment in the
United States.
Carrying out experiments is only part of her research. She
also designs and grows new crystals. She typically uses lattices
constructed from layers of oxides such as copper and oxygen, or
metals such as iron, as her building blocks. By substituting different
ions, or rearranging the positions of the ions, she hopes to find
materials with interesting and useful properties. “It’s like cooking. I
have some main ingredients and I start changing the recipe to see
what happens to the dish,” she said.
Once she’s made the crystal, she investigates the physical and
magnetic properties, and makes sure all the ions are sitting in the
intended places. This is work she will do at Duke, before traveling to
other facilities to study the crystals under extreme conditions.
When she’s not experimenting, Haravifard enjoys road trips,
hiking, swimming, and downhill skiing. While in Hamilton, Ontario,
earning her undergraduate and PhD degrees at McMaster University,
she visited lots of Canadian national parks, where she saw moose,
wolves, black bears, and other wildlife. “I love nature,” she said. “When
I have time, I usually go explore.”
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Faculty Awards
Barbeau Receives 2014 Sloan Fellowship
Prof. Phil Barbeau is among the recipients of the 2014 Sloan Research Fellowships. A full list of all 2014
recipients is listed in February 18’s New York Times; see it here.
The Duke Today piece “Five Faculty Science Win Sloan Fellowships” is here.
Behringer is 2013 Beams Award Recipient
Prof. Robert P. Behringer has won the SESAPS Jesse W. Beams award for pioneering the field of granular
media and the development of elegant experimental methods for understanding the fluctuations, dynamics,
force transmission and jamming transition in granular materials. The award was presented to Prof. Behringer
at the 80th Annual SESAPS Meeting in November, 2013. A description of the award and a list of past winners
may be found here. Previous SESAPS Beams award winners from Duke Physics are: Larry Biedenharn (1979),
Edward Bilpuch (1992), Walter Gordy (1974), Horst Meyer (1982), Berndt Mueller (2007) and John Thomas
(2011).
Curtarolo and Scholberg are New APS Fellows
Curtarolo
Profs. Kate Scholberg and Stefano Curtarolo were elected recently as
APS fellows.
Prof. Scholberg’s citation reads: “For work with atmospheric and accelerator neutrinos that established the phenomenon of neutrino oscillation, and for
leadership in the worldwide effort of the supernova neutrino detection.’’
Prof. Curtarolo’s citation reads: “For pioneering automatic high-throughput
computational materials science, and for the creation of on-line materials
development techniques, the ingredients of the Materials Genome Initiative.’’
The election to Fellowship in the APS is limited to no more than one half of
one percent of the membership. Elections to APS Fellowship is a recognition
of the outstanding contributions of Prof. Scholberg’s and Prof. Curtarolo’s to
Physics by their peers.
Scholberg
Kotwal is Among 37 Newly Named Distinguished Professors at
Duke University and Elected Foreign Fellow
Prof. Ashutosh Kotwal has been named as the Fritz London Professor of Physics. Read the DukeToday
news release “Duke Announces 2014 Distinguished Professors” here.
Prof. Kotwal has also been elected as the Foreign Fellow of the Maharashtra Academy of Sciences in
India for his significant contributions to Physical Sciences.
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9
Faculty Awards
Gauthier, Greenside, and Socolar
Recognized for Teaching by Students
in 2012-2013 Academic Year
Gauthier
During the fall semester 2012 in the categories of Quality of Course and/
or Intellectual Stimulation, Prof. Josh Socolar’s PHY 264L: Optics and Modern Physics’ course evaluations were among the top 5% of all undergraduate
Socolar
instructors at Duke for a medium class (29 - 59 students). During the fall semester 2012 in the categories of Quality of Course and/or Intellectual Stimulation,
Prof. Dan Gauthier’s PHY 621L: Advanced Optics’ course evaluations were among the top 5% of all undergraduate instructors at Duke for a small class (less than 20 students). During the 2013 spring semester in the
categories of Quality of Course or Intellectual Stimulation, Prof. Henry Greenside’s PHY 162L: Fundamentals
of Physics II course evaluations were among the top 5% of all undergraduate instructors at Duke for a medium
class. This is great recognition for these professors’ accomplishments and talents as outstanding teachers.
Greenside
Wu is Winner of Inaugural Award for Excellence in Graduate
Teaching in Physics
On August 25th, at the annual Physics Department Picnic, Prof. Ying K. Wu was awarded the first ever
Award for Excellence in Graduate Teaching. The Award for Excellence in Graduate Teaching was created to
recognize outstanding instruction of a core graduate physics course. The recipient of this award is selected by
graduate students, and it honors an instructor who demonstrates exceptional teaching skills in the classroom
as well as an eagerness to help students gain a deeper understanding of the course material outside the classroom. The graduate students were very happy to award this to Prof. Wu, who went out of his way to ensure that
his students got as much out of his Electrodynamics course as possible.
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Outreach
Hawbridge Charter School Tours TUNL, FEL and LENA
— by Shanee Cowland and Haiyan Gao
On January 22, 2014 the Department of Physics at Duke
University and the Triangle Universities Nuclear Laboratory (TUNL)
hosted a visit by a group of students, teachers and parents from the
Hawbridge Charter School. Hawbridge Charter School is a rural charter school located in Saxapahaw, NC. The school comprises almost
200 middle and high school students who work in small classes with
a dedicated faculty of about twenty teachers. Its location adjacent
to the Haw River makes the school ideally placed for the environmental theme that runs strongly through the school culture. Hawbridge
also prides itself on interdisciplinary units that provide opportunities
for students and teachers to apply these and projects to their core
curricula. In addition to the interdisciplinary units, there is a strong
outdoor program that provides the students with opportunities to
learn about themselves, develop leadership skills, understand nature
and experience the beautiful outdoors.
The planning of this trip started in the fall of 2013 when
Hawbridge physics teacher Shanee Cowland contacted Profs. Art
Champagne (UNC-CH), Tom Clegg (UNC-CH) and Haiyan Gao (Duke).
Duke staff Cristin Paul coordinated the visit. Students were so
excited about this visit that they arrived on January 22 as planned
despite the fact that their school was closed on that day due to the
inclement weather. Prof. Haiyan Gao, Chair of Physics, welcomed the
students. The Hawbridge students visited the Tandem Lab in TUNL
first with the tour guided by Prof. Tom Clegg, and then the Free
Electron Laser Laboratory under the guidance of Mr. Pat Wallace.
The last laboratory the students visited was the Low-Energy Nuclear
Astrophysics (LENA) lab guided by Prof. Art Champagne. The entire
visited was concluded by a warm pizza lunch, which was highly appreciated and enjoyed by the visitors on such a cold day.
The students who visited thought it was a cool visit and
several shared about their experience. Nathan Forbis’ favorite was
the tandem lab: “There I learned how a radioactive isotope called
Carbon 11 can be injected into a plant (which absorbs the Carbon
11 through photosynthesis) so that the scientists there can study
the nature of a plant’s metabolism and how the environment affects
it.’’ Alex Preston was fascinated by the magnets: “One of the most
interesting things to me was how important magnets were in this
process. It was actually quite fascinating how the magnet guided
the beam so precisely. I was also very surprised by the chemistry
aspect before the particles were accelerated, the whole process of
removing ions and making the elements positive or negative.”
Prof. Tom Clegg (UNC-CH) gives the tour of TUNL’s Tandem Lab.
Prof. Art Champagne (UNC-CH) guides the tour of LENA Lab.
Pat Wallace (Duke) tells students about the
Free Electron Laser Laboratory (FEL).
Photos by Cristin Paul
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11
Alumni Profiles
Planetary Scientist Robin Canup
Models the Origins of Moons
— by Mary-Russell Roberson
Duke physics alum Robin Canup, ‘90, has been thinking about
moons—and their origins—ever since graduate school at the University of Colorado (CU). She was halfway through her PhD thesis on
Saturn’s rings when, she says, “I got this idea that I wanted to start
working on the origin of the moon. My thesis advisor was very supportive, so I changed the topic of my thesis. I’m forever grateful to him
for that.”
In fact, he suggested that she send a grant proposal to NASA,
with the result that she had funding for a postdoc at CU as soon as
she graduated.
Since then, she’s proposed leading theories not just about our
moon, but many other moons as well. “I’m best known for my work
on the Earth-moon system because that’s the one that generates the
most public interest,” she says. “But I’ve worked on the origin of all the
big satellites in the solar system.”
Canup has been a scientist at the Boulder office of the San
Antonio-based Southwest Research Institute (SwRI) since 1998. Today
she’s Associate Vice President, managing all 80 SwRI scientists in the
Boulder office. In 2012, she was elected to the National Academy of
Sciences.
In February, she visited Duke to deliver the fifth Hertha Sponer
Lecture, in which she spoke about her recent modeling of the catastrophic collision that created the Earth-moon system.
The model that had been around for decades proposed a smallish impactor (say the size of Mars) colliding with an Earth the size of
today’s Earth. The problem? The debris field from the collision—the
raw ingredients of the moon—would come mostly from the demolished impactor, which almost surely be compositionally different from
the Earth. But in fact, the moon and the Earth’s mantle are made of
the same stuff.
In Canup’s model, the impactor and the proto-Earth are about
the same size (between 40-50% of the mass of today’s Earth). The
collision destroys the impactor and deforms the Earth, mixing the
materials of the two planets. When the dust settles in her computer
simulation, what’s left is the Earth as we know it, surrounded by an
orbiting disk of detritus similar in composition to the outer layers of
the Earth. (Later, debris in the orbiting disks coalesces to form the
moon.)
The only problem with this model is that it leaves the Earth with
too much angular momentum—the Earth would be rotating at least
twice as fast as it does today, giving us a much shorter day. However,
recent work by Matija Ćuk and Sarah Stewart provides a fix for this
problem by suggesting a resonant interaction between the moon
and sun called evection resonance that would reduce Earth’s angular
momentum enough to give us our 24-hour day.
Canup uses a computer simulation based on hydrodynamical
equations of motion. Each of the colliding planets is divided up into
about a million particles, and the simulation tracks each particle’s
position, velocity, temperature, physical state, and gravitational interactions during the collision.
“It models the time of the impact through about 24 hours typically,” she says. “That’s how long it takes for the system to settle
down into a central planet surrounded by a debris disk. Prior to that,
the impactor might be partially intact and on a re-collision course
with the Earth.” (Read more about Canup’s Hertha Sponer lecture and
see a video of one of her simulations here.) Moon formation around
12
Photo by Horst Meyer
gaseous planets is totally different. As those planets formed, they
captured hydrogen and helium gas that was orbiting the sun for a few
million years in the early days of the solar system. Some of the gas
was added to the planets, but gas with too much angular momentum
formed broad rings or disks around the planets rather than falling into
them. Particles in the disks came together to form solid moons.
Canup says as the moons formed, gas in the disks interacted
gravitationally with them, causing their orbits to spiral in toward the
planets. “One of the things I’ve discovered,” she says, “is that this
process will tend to select for a certain mass of satellites around the
planet. Independent of the total mass of rock and ice that’s delivered
to these disks, you tend to form a satellite system that has 10-4 of the
planet’s mass.” Canup calls it “one of the very odd things in our solar
system” that even though Jupiter, Saturn, Uranus, and Neptune are so
different from one another, all of them have the same mass ratio with
their satellites.
Now that other astronomers are discovering exoplanets and
starting to search for large satellites around them, Canup is interested
to find out whether this same mass ratio will exist in other solar systems as well.
When Canup came to Duke from upstate New York, she planned
to major in biology and become a physician. But her first physics class
changed her mind. Then, in her sophomore year, she took an astrophysics course from John Kolena who also taught at the North Carolina School for Science and Mathematics. “He was one of the—if not
the—best professors I had at Duke,” Canup says. “He was a fantastic
teacher.”
When she went to graduate school, she didn’t have a clear vision
for a career, but she soon realized how much she loved research.
“The switch from solving abstract problems that have been solved
many, many times to, ‘Here’s a problem and nobody knows the
answer—go see what you can figure out,’ was a complete transformation for me,” she says. She also loved living in Boulder, so it was a
happy coincidence that SwRI opened a lab in Boulder about the time
she was looking for her first job.
She and her husband live in the foothills just outside the city
limits on 45 acres, which they enjoy improving. Taking care of their
two young children and working on their property in addition to their
careers doesn’t leave time for much else. “That pretty much fills up
every 30-hour-day, and unfortunately I only have 24 hours a day, so I
get 6 hours behind every day,” she says.
While many professionals might say something similar, Canup is
one of the few who can explain why and how she only has 24 hours a
day.
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Duke PHYSICS
Randall Ledford Uses
Lessons Learned From
Physics in Role as CTO
—by Mary-Russell Roberson
“Students graduating now have got to keep learning, be flexible,
and be open to new opportunities,” says Randall Ledford. “What they
think they are going to do on graduation day is not necessarily what
they are going to do for the rest of their lives.”
Ledford should know. He left Duke Physics in 1976, new PhD
in hand, to work as a researcher at AT&T Bell Laboratories in New
Jersey. Today he is the Chief Technical Officer at Emerson Electric in
St. Louis, and the President of Emerson Ventures, which is an internal subsidiary of Emerson that has its own board. Emerson Electric,
founded in 1890, employs about 135,000 people around the world.
“Being a CTO of a large company was never in my plan,” Ledford
says. “It’s turned out to be a lot more rewarding than I ever anticipated.”
While at Bell Labs, Ledford developed an interest in business
and took courses at the company, essentially earning an MBA from
AT&T. His wife Wanda, who also worked at Bell Labs, noticed an ad
for an engineering manager at Texas Instruments (TI) and suggested
that he apply. He got the position, and he and Wanda headed to
Tennessee, then Maryland, then Texas with TI, raising two daughters
along the way.
He spent 18 years at TI, eventually serving as president of four
different divisions. He was friends with the CEO, and he was looking
forward to spending the rest of his career at TI. Then the CEO died
of a heart attack. “It was one of those moments when you realize
how much your life and career are shaped by things totally out of
your control,” he says. A new CEO came in with a new direction, and
Ledford began to wonder, “Do I really want to make silicon chips for
the rest of my life?”
Soon after, he left TI to become the CTO of Emerson, a position he’s held for 18 years. Emerson produces hundreds of different
products, from toolboxes to computer systems for process control
and automation. As the president of Emerson Ventures, Ledford and
his team of technical, financial and legal experts evaluate and invest
in new ideas generated by startups. He says, “Big companies typically invest in growing the current product line. To get revolutionary
ideas, you need garage shop tinkerers coming up with a new way of
doing things. You place bets on them, and just like bets in real life,
some are winners some are losers.”
Part of his work at Emerson has involved “globalizing” the engineering department. “The sad but true part of that is we couldn’t find
enough qualified engineers in the United States,” he says. He created
an engineering center in India that employs 1,000 engineers.
Ledford says his physics background helps with many of the
seemingly disparate challenges he faces at work. “Physicists have
the ability to solve large complex system problems,” he says. “What I
do on a continual basis is to look at large systems, whether com-
puter or mechanical, and try to visualize from a holistic viewpoint
where these systems are going in the 3-5 years; I augment that with
fresh ideas from venture capital, and help direct the business from a
technical viewpoint into the next generation of products.”
Figuring out the next generation of products is not easy in a
world where hot ticket items from just 5 years ago—like point-andshoot cameras, camcorders, and DVD players—are now passé. And
that’s where Ledford’s advice about learning and staying flexible
comes in. He stays abreast of issues related to sustainability, the
globalization of the economy, and changing demographics—such as
the expansion of the middle class in China and the contraction of the
middle class in the United States. “People (and organizations) need
to be prepared to change as the environment, economy, and government change,” he says.
In October, he gave an Edge seminar to business students at
Duke’s Fuqua School of Business, and he’d like to do more of that
sort of thing when he retires—whenever that may be—to Asheville where he and his wife own a home. Another option would be
teaching in a physics department. “I like the idea of helping the next
generation of physicists, of scientists, of young people as a whole,”
he says. “If I can help them and guide their careers, I would find that
very gratifying to be able to give back like that a little bit.”
He already gives back by sponsoring scholarships for physics
majors at his undergraduate alma mater, Wake Forest University. Ledford’s father died when he was 19 and his mother didn’t have a paid
job; scholarships made it possible for him to attend Wake Forest.
He majored in physics, math, and chemistry, but says, “Physics was my first love.” While at Duke, he did his doctoral research
at TUNL (Triangle Universities Nuclear Laboratory). Lesson learned
there still stick with him today.
“We started our accelerator line from scratch, putting together
the vacuum pipes, the pressure readers, the magnets, making wax
blocks, making lead blocks, getting isotope samples from Oak
Ridge and bringing them in a vacuum container, building high speed
electronics,” he says. “One of the most valuable assets I picked up
from my time at Duke, at TUNL, was being able to synthesize pieces
to see an ultimate solution at the end.”
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13
Alumni Profiles
Michael Wittmann
Specializes in Physics
Education Research
— by Mary-Russell Roberson
Like many physicists, Michael Wittmann (’93) was drawn to the
subject because it’s a way of understanding how the world works. But
Wittmann is also interested in understanding how teaching and learning
work. “I come from a line of teachers and physicists and engineers,” he
says. “So I grew up with dinner table conversation about both of those
topics.”
To satisfy both of his interests, Wittmann specializes in physics
education research (PER) at the University of Maine, where he was
recently promoted to full professor. He is a member of the research
group at the Physics Education Research Laboratory there, as well as
the Center for Research in STEM Education, which he co-founded in
2001. He also co-chairs the biennial Foundations and Frontiers of Physics Education Research conference in Bar Harbor, Maine.
To Wittmann, there’s a little bit of physicist in everyone—or there
ought to be. “It irritates me when I’m at a party and someone says,
‘What do you do?’ and I say, ‘I’m a physicist,’ and their response is,
‘Oooh, that’s hard.’ They are forgetting that they are scientists by
nature—they have questions about the world, and we can answer them.
As a teaching community, we’re missing the boat if people have that
reaction.”
Of course, teaching physics can be tricky because everyday experiences sometimes don’t appear to mesh with the laws of physics. For
example, physicists often think about how things work in the absence
of friction, but friction rules our everyday world, where bricks fall faster
than feathers, and objects in motion tend to slow down and stop. “What
makes teaching physics really interesting is that clash between intuition
and formalism,” Wittmann says.
Wittmann studies physics education at all levels from middle school
to upper level physics. No matter the level, his goal is to understand
what the student is thinking and work from there. Lately, he’s been
studying the use of gesture in teaching and learning physics. Sometimes students don’t have the formal vocabulary to describe what they
are thinking and gestures can help them communicate. “I’m curious to
understand how people are thinking about the physical situation and
gestures help me see more of what people are thinking,” he says.
At UMaine, Wittmann teaches physics to both physics majors and
non-science majors, and he also teaches physics education to future
teachers. He especially enjoys advising physics graduate students who
are focusing on PER. “I think one of the biggest joys I have in my career
is working with graduate students and watching them go from novices
and apprentices to being true colleagues,” he says.
He also enjoys working with middle school and high school teachers on a variety of projects, and helps put on a yearly meeting of high
14 school physics and physical science teachers at the University of Maine.
“I want to influence the teaching of physics so that we spend more time
helping people develop thinking skills and questioning the world around
them,” he says. “There are lots of opportunities to show people interesting ways that physics can be used to understand the world.”
Wittmann himself was inspired by his high-school physics teacher,
David Green at Jordan High School here in Durham. “It’s crazy—I can
still remember half the experiments I ran in his class and it’s been 25
years,” Wittmann says. “There was a strong emphasis on experimental
work so we would draw conclusions from our observations as opposed
to spending time on mathematical analysis. He put a lot of the responsibility of learning in our own hands and worked to give us the tools when
we needed them.”
Wittmann would love to inspire future and current teachers to use
similar techniques to keep students engaged. He points out that young
children are naturally curious about the world, but by high school that
curiosity has often waned, or been stifled. “We have a job to do to help
students keep curiosity alive, and help them realize that curiosity plays
a really big role in how they approach science,” he says.
After graduating from Duke, Wittmann earned his master’s degree
and PhD in physics from the University of Maryland. He moved to
Orono in 2001 to take the position at the University of Maine. He and
his wife—a UNC grad—have two children. Wittmann has dual AustrianAmerican citizenship, and was raised speaking German at home, and
he’s continuing that tradition with his children.
Having grown up in the south, Maine’s long dark winters were a
challenge at first, but now Wittmann says he loves where he lives, and
Durham seems awfully hot when he visits. “You have to get used to
snow,” he says. “You just learn to go cross-country skiing and do as
much outdoors as you can.” Wittmann also plays goalie on an indoor
soccer league and is a DJ at the campus radio station, building on his
undergraduate experience as a DJ at Duke’s WXDU.
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Faculty Research
Nonlinear Optical Imaging and Its Applications:
From Melanoma Diagnosis to Renaissance Paintings
— by Warren S. Warren
The demonstration of the laser in 1960 was published in Nature,
having been rejected by PRL. It was followed quickly by the demonstration of the first laser-induced nonlinear optical effect, second harmonic
generation. This paper was published in PRL (7, 118 (1961)) with that
journal’s most famous typesetting error: the signal (the tiny second harmonic spot on the photographic plate) was assumed by the lithographer
to be a flaw, and airbrushed out of the published image!
Lasers have improved tremendously, and so has nonlinear optical
imaging. Today second harmonic generation (from a near-infrared
pulsed titanium: sapphire laser), or fluorescence after two-photon absorption, is routinely used in “multiphoton microscopes” in biology labs.
But the limitations are rather fundamental. The peak powers we are willing to apply to human skin, or to a priceless painting, are not the same
as what we can use in a physics lab. In round numbers, we deliver
about the same average power as a laser pointer. In that limit, roughly
one photon in a million is typically taken up by nonlinear processes; the
rest are lost to linear absorption, scattering, or transmission. If the nonlinear process creates light of a different color (as it does with second
harmonic generation), that is not a problem, as the weak signal is easily
separated from the strong beam. Unfortunately, most of the molecules
in you don’t fluoresce well (neither do most pigments). So biological
applications of multiphoton microscopy usually are restricted to injected
dyes, or to genetically expressed markers-with obvious limitations for
human work, or for paintings.
If you can see nonlinear effects which do not generate light of a
different color, many other molecular signatures become accessible
(Figure 1). For example, self phase modulation (the nonlinear component of the index of refraction) varies dramatically in different solvents
or varnishes, and stimulated Raman gives molecular content. A more
surprising example is that two color, pump-probe experiments can
reflect extremely subtle molecular dynamics (excited state absorption,
ground state depletion, stimulated emission and other processes)
which have different relaxation rates, and thus give unique molecular
signatures from even very similar appearing compounds. None of these
effects are new; but at these laser powers, the fundamental challenge
is, how do you detect the one-in-a-million photons lost to create your
signal, when the other 999,999 photons are also lost to uninteresting
effects?
Our lab has developed advanced femtosecond pulse shaping and
detection technologies to access these intrinsic nonlinear signatures
that were not previously observable in tissue. These methods permit
high resolution imaging in scattering media, without any requirement
that the imaging target generate fluorescence or other conventional
light signatures. Our principal focus has been to improve biological
imaging; for example, we have uniquely identified a variety of biologi-
cal targets and differentiated between eumelanin and pheomelanin in
pigmented skin lesions to improve melanoma diagnosis (Figure 2). We
have also shown that cross phase modulation, the nonlinear equivalent
of phase contrast imaging, extends detection of transparent species
even in scattering tissue.
More recently, we have adapted the approach to image historical
artwork, which works for exactly the reasons that pump-probe imaging
works in skin. The face of the Mona Lisa is known to have about 40
layers of paint. daVinci did not do this just because he was obsessive;
he did this because he was replicating the distributed absorption which
is characteristic of actual human skin (light penetrates tens to hundreds
of microns, depending on wavelength). Nonlinear optical imaging suppresses scattering signals and thus allows three-dimensional imaging
ten to thirty times deeper than a conventional microscope. This holds
great promise for understanding technique, detecting retouching or
forgeries, and even for distinguishing between mixtures and layers; today art conservators get this information with a scalpel, taking physical
cross-sections. They are very good at doing this (most paint layers are
cracked anyway, so a slight widening is not noticed) but this is clearly
not desirable. Figure 3 shows one example of our recent work, on the
1330 painting The Crucifixion by Puccio Cappanna, owned by the North
Carolina Museum of Art.
We are currently extending this work to a wide range of other
cultural heritage objects, in work supported by NSF and NIH. We have
Figure 1. Two-photon and sum-frequency absorption, self- and cross-phase modulation,
stimulated Raman, and pump/probe signals are easily observed in a physics laboratorybut seeing them at the low powers needed for safely imaging tissue, or imaging paintings, requires sophisticated laser pulse shaping or pulse train modulation methods,
which have only recently become available.
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examined the melanin in 150 million year old fossils, which looks
remarkably like new melanin (this is important for medical imaging,
because it means we can use tissue from databanks to do retrospective analysis), and we have examined mummy skin. We have built up a
library of Renaissance and modern pigments. We have found that the
iron oxide in pottery produces distinctive pump-probe signatures which
reflect the firing history. We have examined pigments on parchment,
which is usually too fragile to take a cross-section, and often too fragile
to unroll. Overall, this is a nice example of a cultural heritage spinoff of
the massive societal investment made in both laser science and in biomedical imaging (and as a result, has attracted considerable attention
in the popular press).
Figure 2. Above: a standard biopsy specimen from a human
melanoma, “H&E” stained to highlight the contrast. Right:
pump-probe laser image of unstained tissue, in this case the
next slice. Different positions produce different pump-probe
dynamics, reflecting differences in molecular composition that
are currently invisible. From T. E. Matthews, I. R. Piletic, M.
A. Selim, M. J. Simpson, and W. S. Warren, Sci Transl Med. 3,
71ra15 (2011).
Figure 3. (Left) Pump-probe image data taken on a physical
cross-section of The Crucifixion, (right) pump-probe images
taken from the intact painting, in this case from the thick lapis
lazuli in the Virgin Mary’s robe. From Villafana TE, Brown WP,
Delaney JK, Palmer M, Warren WS, Fischer MC. Proc Natl Acad
Sci 111, 1708-13 (2014)
Slaying Dragon-Kings!
— by Daniel Gauthier
We all have some familiarity with extreme events, such as the
extinction of a species, the crash of the stock market, freak ocean
waves that capsize large ships, once-in a century hurricanes, and a
wide range of other natural or human-driven catastrophes. Given the
societal impact of catastrophes, scientists are turning their attention to
the origin of these behaviors and whether they can be forecasted and
suppressed. There has been impressive headway on these problems
undertaken by multidisciplinary teams of researchers with expertise in
statistical physics, network science, nonlinear dynamics and complexity, economics, biology, environmental science among others.
One noteworthy example is predicting the approach of a system
to a “tipping point” - the point of no return associated with a catastrophe [1]. Some systems - such as ecological networks - are believed to
undergo a sudden change in behavior arising from a bifurcation in the
dynamical system. Here, the system switches from one equilibrium
value to another at the bifurcation as a system parameter changes.
(Think of the collapse of the population of a species as the food supply
is decreased slowly or as a chemical is introduced into the environment
that reduces the birth rate.) For some systems, the tipping point can
be anticipated by monitoring how it responds to stochastic perturbations to the system (that is, how it responds to “noise”). For some
16 system, the response of the system to noise is strongly suppressed
and in others it can be greatly enhanced due to a behavior known as
critical slowing down that sometimes occurs when a system is close to
a bifurcation point.
It is rather surprising such simple concepts can apply to complex
systems such as an ecological network, which consists of many interacting individuals who also interact with their surrounding environment.
It is generally known that there exist much more complicated dynamical
behaviors beyond equilibrium states in dynamical systems. Likely, there
is a subset of these behaviors that give rise to catastrophes, but is
there any hope that they can be uncovered given their potential higher
degree of complexity? At least for one specific dynamical system, my
collaborators and I have found that is possible to forecast an impending
extreme event in a network of two coupled chaotic oscillators and, with
this knowledge in hand, suppress the extreme events by applying tiny
control perturbations to the system. In this article, I briefly describe the
science underlying our discovery, but also relate the story how a team
of international researchers came together to address this problem.
The journey to this discovery started in early May 2012 when I
received a digest of nonlinear dynamics papers submitted to the arXiv. I
was very intrigued by a manuscript written by D. Sornette and G. Ouillon
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on “Dragon-kings: mechanisms, statistical methods and empirical evidence,” which was published as a forward to a special journal issue they
edited focused on dragon-kings [2]. Here, I learned that dragon-kings
are extreme behaviors that appear as outliers in the statistical size
distribution characterizing the system - enough of an outlier that they do
not appear to be caused by the same mechanism underlying the other
data. Prof. Didier Sornette (ETH Zurich) uses an analogy to explain this
behavior: the distribution of wealth in a monarchy. The distribution for
everyone except the king (or queen) is believed to be described by a
power-law distribution, where it is less and less likely to find someone
in the society with high wealth. The king, however, has vast resources
and does not appear to be part of this distribution as illustrated in
the cartoon shown in Fig. 1. On a related note, the dragon aspect of
the moniker is that a dragon behaves like no other creature, bringing
extreme behaviors upon unsuspecting communities.
largest desynchronization event and the average event size over a long
data collection session [3], but we never measured the distribution of
the size of these events, so new data needed to be collected to determine whether dragon-kings were present.
Figure 2: Two-dimensional projection of the chaotic attractor for a single circuit. Here, the
vertical axis is the current flowing through the inductor of the circuit and the horizontal
axis is the voltage across one of the capacitors in the circuit. The black solid line shows
the system trajectory, which traces out the dynamical state of the circuit in phase space
as a function of time. The red dot at the origin indicates the location of the unstable
saddle that is responsible for initiating the dragon-king events.
Figure 1: Wealth distribution of a hypothetical monarchy.
After reading Sornette and Ouillon’s article, I realized that an old
experimental device I developed many years ago, together with Dr.
Joshua Bienfang (Duke Physics, B.S., 1994), might display dragon-king
behavior. The device consists of two nearly-identical analog electronic
circuits that display deterministic chaos. Here, each circuit consists of
a so-called negative resistor that acts as a source of current and an inductor-capacitor-resistor circuit coupled to the negative resistor through
a nonlinear element (standard signal diodes). For an appropriate value
of the negative resistance, the trajectory of the system resides on a
strange attractor shown in Fig. 2, displays sensitive dependence on initial conditions (the butterfly effect), and produces a seemingly noise-like
temporal evolution of the two voltages and the current that characterize
the dynamical state of the circuit.
Back in 1994, Dr. Bienfang and I found that the chaotic circuits
can synchronize their behavior when coupled. That is, they both display
chaotic behavior, but they are in lock-step with each other due to the
coupling, astonishing given that they both display sensitive dependence
on initial conditions. Unknown in the literature at the time, we observed
that the circuits would desynchronize for brief periods, that the time of
these events appeared at random, and that the time between events
could be extremely long - thousands or even millions of characteristic
time scales of the circuit. During the study, we measured the size of
Fortunately, the circuits still existed, but had sent them to Dr. Hugo
Cavalcante, a former Duke post-doc who had recently moved to the
Universidade Federal da Paraíba, João Pessoa, Brazil, where he was collaborating with a former Duke sabbatical visitor, Prof. Marcos Oriá. Dr.
Cavalcante was very intrigued by the possibility of observing dragonkings in the circuits and indeed was already starting to study the distribution the desynchronization event sizes in another related system.
Simultaneously, I contacted Prof. Sornette to see if he was interested
in collaboration and started to perform numerical simulations of a
model describing the circuits. These initial contacts were followed by
an incredibly active and engaging international discussion. During this
period of a few months, dragon-kings were observed in both the experiments and the numerical simulations, we discovered how to forecast
and suppress their behavior, and we were searching for connections to
other natural systems that might display similar behaviors such as in
earthquakes and neuronal dynamics. Figure 3 shows the desynchronize
event size distribution observed in the experiments, where the dragonkings are clearly evident.
The underlying concept is that the two electronic circuits want
to synchronize their behavior on average. However, as the oscillator
trajectories move about the strange attractor shown in Fig. 2, there are
local regions of instability where the trajectories can diverge, resulting
in a desynchronization event, and other regions where the synchronized state is highly stable and the trajectories of the two oscillators
coalesce. For these circuits, the most synchronization-unfriendly part of
the attractor is the unstable saddle located at the origin of the attractor
(where the two voltages and the current are zero). The largest desynchronization events - the dragon-kings - occur when the chaotic trajectory happens to make a very close approach to this point. Figure 3b
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shows a three-dimension projection of the six-dimensional phase space
of the two coupled oscillators, where a large event is initiated when the
trajectory approaches the unstable saddle.
With this understanding, forecasting dragon-kings is straightforward: monitor the trajectory of one of the chaotic circuits to see whether it is making a close approach to this “hot spot” on the attractor.
that desynchronization events occur in a wide range of coupled systems, such as that found in simple models of the stock market and in
the large number of coupled cells that make up the kidney, for example.
However, we do not yet know whether the event-size distribution for
these systems displays dragon-kings and whether the underlying “hot
spots” can be identified and exploited as in our initial study. But Prof.
Figure 3: a) Probability distribution of the size of the desynchronization events for two coupled chaotic oscillators without forecasting and control (black line) and with control (red line).
Without control, the dragon-kings are the events that substantially deviate from the approximate power law distribution for the smaller event sizes (blue dashed line). b) Projection
of the six-dimensional phase space of the two coupled oscillators onto a three-dimensional space. The trajectory is in the horizontal plane when the oscillators are synchronized. A
desynchronization event is indicated by a trajectory that has a projection along the vertical axis. Here, a large event - a dragon-king - is shown, where it is initiated near the origin at
the location of the unstable saddle (see the upward pointing arrow), eventually winding its way back to the synchronized state.
Efficient suppression of the dragon-kings is similarly straightforward:
nudge the trajectory away from the hot spot only when the trajectory
is making a close approach. The red line shows the event-size distribution when we use real-time forecasting and apply tiny perturbations to
the system that keeps it away from the hot spot. The dragon-kings are
slayed!
While the results were very compelling, we did not have a simple
analytic model to predict the power-law portion of the event-size distribution that appears for event sizes smaller than the dragon-kings. At a
conference where I was discussing this work, I had an extended conversation with Prof. Edward Ott from the University of Maryland, a long
time collaborator who also worked with me in the 1990’s on the original
synchronization work with Dr. Bienfang. By the end of the conversation,
Prof. Ott already sketched out a simple model to explain our findings
and all of the details fell into place over the ensuing weeks. This was a
fortunate encounter: the referees of our submitted manuscript insisted
that we include this model in the paper and so we added Prof. Ott’s
contribution to the final work.
Buoyed by these results, we are exploring other dynamical systems that might display similar behaviors. It is already well established
18
Sornette is quite hopeful; he has highlighted this work in his recent TED
talk on predicting the next financial crisis [5], which is quite fascinating!
References
[1] M. Scheffer, S. R. Carpenter, T. M. Lenton, J. Bascompte, W. Brock,
V. Dakos, J. van de Koppel, I. A. van de Leemput, S. A. Levin, E. H. van
Nes, M. Pascual, J. Vandermeer, “Anticipating Critical Transitions,” Science 338, 344 (2012).
[2] http://arxiv.org/abs/1205.1002
[3] D.J. Gauthier and J.C. Bienfang, “Intermittent loss of synchronization
in coupled chaotic oscillators: toward a new criterion for high-quality
synchronization,” Phys. Rev. Lett. 77, 1751 (1996). http://www.phy.
duke.edu/~qelectron/pubs/PRL1751.pdf
[4] H. L. D. de S. Cavalcante, M. Oriá, D. Sornette, E. Ott, and D. J.
Gauthier, “Predictability and suppression of extreme events in a chaotic
system,” Phys. Rev. Lett. 111, 198701 (2013). http://www.phy.duke.
edu/~qelectron/pubs/PRL111_198701_2013.pdf
[5] http://www.ted.com/talks/didier_sornette_how_we_can_predict_
the_next_financial_crisis
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Graduate Students Visit Jefferson Lab
— by Anne Watson
Continuing on with the developing tradition of visiting National Laboratories over
Fall Break, last month 8 physics graduate students traveled to Newport News, Virginia,
to explore the Thomas Jefferson National Acceleration Facility (Jefferson Lab). Jefferson Lab is a Department of Energy facility primarily focused on conducting fundamental
research in nuclear physics, with additional programs in accelerator science, cryogenics, and free-electron lasers, to name a few.
The Duke Physics Department already holds important ties with Jefferson Lab, with
Prof. Haiyan Gao’s group in medium energy physics conducting experiments and developing detectors for the lab’s Experimental Halls. Furthering
these connections, graduate students from almost all years attended this trip, from younger students investigating research avenues at a national
lab for the first time, to older students exploring the potential of being employed at one.
In the morning after the essential safety briefing, the students were shown the new Technology and Engineering Development Facility where
superconducting radiofrequency instruments are constructed and tested. Subsequently the students toured some sections of the Continuous
Electron Beam Accelerator Facility (CEBAF). With the electron beam turned off during the construction phase of the 12 GeV upgrade project, the
students were given the unique opportunity to go underground to see part of the ring (where the beam is accelerated) and Experimental Hall A (the
largest of four experimental staging areas). Says Jon Mueller (entered ’09), “I really enjoyed touring the lab, especially seeing the ring and the Hall
A spectrometers” (pictured above). The tour continued with an exploration of a few of the additional scientific programs that Jefferson Lab hosts.
The graduate students saw the High-Performance Computing Center, the Medical Imaging Lab, and the Free-Electron Laser facility.
In addition to the students being exposed to innovative scientific and technological advances made at Jefferson Lab, they also had opportunity to meet with the managing scientists. Director Hugh Montgomery graciously set up an informal pizza lunch with some of his colleagues
and Duke physics alumni to have a round-table discussion about anything the graduate students wished to know. “I was very impressed that the
people at the top took time to talk to us about the organizational workings of JLab,” commented Sean Finch (entered ’09). “I also got to meet
former Duke graduate students who are now staff at JLab. It was very inspiring to hear about their job progression and how specific graduate
school experiences helped them with their job.”
Another Outstanding Fermion Sign Problem Solved
— by Shailesh Chandrasekharan
Second year graduate student Emilie Huffman and Prof. Shailesh
Chandrasekharan have recently solved an outstanding sign problem that
had remained unsolved for almost 30 years.
Sign problems arise when one tries to design Monte Carlo methods
to compute quantum amplitudes in quantum many body physics.
Although Feynman taught us how one can compute such amplitudes
by summing over an exponentially large number of classical paths, to
perform such a sum exactly is almost always impossible in realistic
physical systems. Most analytic calculations involve a “perturbative”
expansion in which one argues that only a few diagrams contribute.
Unfortunately, one needs to sum an incredibly large number of diagrams
before an accurate answer can be found in many interesting strongly
correlated quantum systems.
In thermal equilibrium, the exponential sum can sometimes be
viewed as a classical statistical mechanics problem and Monte Carlo
methods can be used to perform the sum. However, the statistical
Boltzmann weight can be negative or even complex due to quantum
mechanics and in such cases the probability distribution to sample the
classical configurations is unclear. A bad choice can lead to wrong results
since one is sampling a non-representative set of configurations. This is
the so-called sign problem, which has hindered progress in our understanding of many strongly interacting fermionic quantum field theories.
Prof. Chandrasekharan’s research focuses on solving sign problems.
His research has shown that some sign problems are solvable if one is
clever in grouping fermion world lines into what he calls fermion bags. If
the fermions interact with bosons, the solution may also require the use
of world line variables to represent bosons. Both relativistic and non-
relativistic problems are solvable using this
approach. The recent work is an extension of
these ideas to a different class of problems.
The new progress is based on an
interesting compact formula in quantum
many body physics, derived by Huffman. This
formula seems to have remained unappreciated by the quantum Monte Carlo community.
Emilie Huffman
When combined with the fermion bag idea,
the formula solves the sign problem in a class
of lattice field theories involving massless fermions. Since electrons hopping on a honeycomb lattice produce such fermions at low energies, the
progress will help us study quantum critical behavior in graphene inspired
lattice models.
The breakthrough achieved in the current work overcomes another
important barrier. Traditionally, many sign problems are solvable when
there is pairing between an even number of species of fermions. The
recent work of Huffman and Chandrasekharan show that pairing can
occur between particles and holes. This pairing is hidden in traditional
formulations with an odd number of fermion species, but the fermion
bag approach helps to uncover it. Hence we can now solve some models with an odd number of fermion species.
The work was published as a rapid communications in Physical
Review B. More details can be found here. This story was featured on
the Duke Research Blog. Read the story “Grad Student Solves 30-YearOld Physics Problem” here.
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In Bob Behringer’s lab, a laser sheet is used to scan through a packing of transparent soft spheres and produce a 3D reconstruction. This gives the position of each sphere as well as the forces between neighboring spheres. Photo by Nicolas Brodu, Joshua
Dijksman, and Bob Behringer
Cover banner image: A neutrino is shown interacting with the giant Super-Kamiokande detector and making signals recorded by its light detectors. It was
directed 295 kilometers underneath Japan from the JPARC accelerator to Super-Kamiokande as part of the T2K experiment.