Eric Sembrat's Test Bonanza

Congratulations to Senior Research Scientist Dr. Constantine Yannouleas, who has been awarded as a 2012 APS Outstanding Referee. 

A research scientist with the School of Physics and the Center for Computational Materials Science at Georgia Tech since 1992, he will be attending the  recognition ceremony at the 2012 APS March meeting in Boston, MA.

The U.S. Air Force Office of Scientific Research (AFOSR) has awarded $8.5 million to a consortium of seven U.S. universities that will work together to determine the best approach for generating quantum memories based on interaction between light and matter.  

The team will consider three different approaches for creating entangled quantum memories that could facilitate the long-distance transmission of secure information. The five-year Multidisciplinary University Research Initiative (MURI) will be led by the Georgia Institute of Technology and include scientists from Columbia University, Harvard University, the Massachusetts Institute of Technology, the University of Michigan, Stanford University and the University of Wisconsin.

“We want to develop a set of novel and powerful approaches to quantum networking,” said Alex Kuzmich, a professor in Georgia Tech’s School of Physics and the MURI’s principal investigator.  “The three basic capabilities will be (1) storing quantum information for longer periods of time, on the order of seconds, (2) converting the information to light, and (3) transmitting the information over long distances. We aim to create large-scale systems that use entanglement for quantum communication and potentially also quantum computing.”

For the full article, please visit: http://www.gatech.edu/newsroom/release.html?nid=109721

The U.S. Air Force Office of Scientific Research (AFOSR) has awarded $8.5 million to a consortium of seven U.S. universities that will work together to determine the best approach for generating quantum memories based on interaction between light and matter.  

The team will consider three different approaches for creating entangled quantum memories that could facilitate the long-distance transmission of secure information. The five-year Multidisciplinary University Research Initiative (MURI) will be led by the Georgia Institute of Technology and include scientists from Columbia University, Harvard University, the Massachusetts Institute of Technology, the University of Michigan, Stanford University and the University of Wisconsin.

“We want to develop a set of novel and powerful approaches to quantum networking,” said Alex Kuzmich, a professor in Georgia Tech’s School of Physics and the MURI’s principal investigator.  “The three basic capabilities will be (1) storing quantum information for longer periods of time, on the order of seconds, (2) converting the information to light, and (3) transmitting the information over long distances. We aim to create large-scale systems that use entanglement for quantum communication and potentially also quantum computing.”

The MURI scientists will study three different physical platforms for designing the matter-light interaction used to generate the entangled photons.  These include neutral atom memories with electronically-excited Rydberg-level interactions, nitrogen-vacancy (NV) defect centers in diamonds, and charged quantum dots.

“A large body of work has been initiated in this area over the past 15 years by our team members and their research groups,” Kuzmich noted. “The physical approaches are different, but the goals are closely related, so there are significant opportunities for synergistic activities. Through this MURI, we will be able to interact more closely, communicate more quickly and provide new opportunities for our students and postdoctoral fellows.”

Overall, the MURI has four major goals:

• To implement efficient light-matter interfaces using three different approaches to entanglement;
• To realize entanglement lifetimes of more than one second in both the nitrogen-vacancy centers and atomic quantum memories;
• To implement two-qubit quantum states within memory nodes;
• To integrate different components and physical implementations into small units capable of significant quantum processing tasks.

Quantum memories generated from the interaction of neutral atoms and light now have maximum lifetimes of approximately 200 milliseconds.  But improvements beyond memory lifetime will be needed before practical systems can be created.

“We aim to be able to combine systems, so that instead of just one memory entangled with one photon, perhaps we could have four of them,” Kuzmich added.  “This may look like a straightforward thing to do, but this is not easy in the laboratory.  The improvements must be made at every level, so the difficulty is significant.”

Among the challenges ahead are maintaining separation between the different memory systems, and minimizing loss of light as signals propagate through the optical fiber systems that would be used to transmit entangled photons.  

“Light is easily lost, and there’s not much that can be done about that from a fundamental physics standpoint,” said Kuzmich.  “The rates of these protocols go down rapidly as you try to scale up the systems.”

Kuzmich and his Georgia Tech research team have been developing quantum memory based on the interaction of light with neutral atoms such as rubidium.  They have made substantial progress over the past decade, but he says it’s not clear which approach will ultimately be used to create large-scale quantum communication system.

The most immediate applications for the quantum memory are in secure communications, in which the entanglement of photons with matter would provide a new form of encryption.

“The immediate focus is on communication, including memories and distributed systems, which is important for sharing and transmitting information,” Kuzmich explained.  “It also has implications for quantum computation because similar techniques are often used.”

In addition to Kuzmich, collaborators in the MURI include:

• Luming Duan, professor of physics in the School of Physics at the University of Michigan, Ann Arbor, Michigan.
• Dirk Englund, assistant professor of electrical engineering and applied physics in the School of Engineering and Applied Science at Columbia University, New York, New York.
• Marko Lonkar, associate professor of electrical engineering in the School of Engineering and Applied Sciences at Harvard University, Cambridge, Massachusetts.
• Brian Kennedy, professor of physics in the School of Physics at the Georgia Institute of Technology, Atlanta, Georgia.
• Mikhail Lukin, professor of physics in the Department of Physics at Harvard University, Cambridge, Massachusetts.
• Mark Saffman, professor of physics in the Department of Physics at the University of Wisconsin, Madison, Wisconsin.
• Jelena Vuckovic, associate professor of electrical engineering in the Department of Electrical Engineering at Stanford University, Stanford, California.
• Vladan Vuletic, the Lester Wolfe Professor of Physics in the School of Physics at Massachusetts Institute of Technology, Cambridge, Massachusetts.
• Thad Walker, professor of physics in the Department of Physics at the University of Wisconsin, Madison, Wisconsin.

“If we are successful with this over the next five years, long-distance quantum communications may become promising for real-world implementation,” Kuzmich added.  “Integrating these advances with existing infrastructure – optical fiber that’s in the ground – will continue to be an important engineering challenge.”

This material is based upon work conducted under contract FA9550-12-1-0025.  Any opinions, findings and conclusions or recommendations expressed are those of the researchers and do not necessarily reflect the views of the Air Force Office of Scientific Research.

Research News & Publications Office
Georgia Institute of Technology
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Media Relations Contacts: John Toon (404-894-6986)(jtoon@gatech.edu) or Abby Robinson (404-385-3364)(abby@innovate.gatech.edu).

Writer: John Toon

In the coming weeks, President Bud Peterson and Provost Rafael Bras will jointly address the GT Academic Faculty during a series of one-hour, "town hall style" conversations.  These events will include brief presentations, followed by an open question-and-answer session with the audience.  Information about the first of these events is as follows...

In this exciting event, three lectures will be presented from world renown Chef Jose Andres and Harvard Physics Professors Michael P. Brenner and David A. Weitz.  Awards will also be presented to the top Dekalb County high school student submissions for the Squishy Physics photography contest in conjunction with the Fernbank Science Center, with all the submissions on display at the event.

Most of what we eat is squishy - behaving as a solid on a plate, or as a liquid when processed in your mouth.  Squishy Physics investigates materials that are soft and easy to deform and, in most cases, are made from mixtures of phases.  The lectures will cover interesting and entertaining physical questions that are critical to cooking and understanding the properties of food.

Free tickets are available online at http://squishyphysics.eventbrite.com

Time/Date:  Saturday, March 10, 2012 from 9:30am to 1:00pm

Location:  Georgia Institute of Technology's G. Wayne Clough Undergraduate Learning Commons

Parking:  Flat-rate parking is available on a first-come, first-served basis at the W02 deck and Area 2 lot adjacent to the Student Center.

Provost Rafael L. Bras has appointed Andrew Zangwill, professor in the School of Physics, chair of the Library Faculty Advisory Board (LFAB). Zangwill will assume the role from Haskell Beckham, professor in the School of Materials Science and Engineering.  

“As chair, Professor Zangwill will help strengthen the relationship among the board, the library and Tech faculty on issues such as scholarly communication, library collections and services,” said Catherine Murray-Rust, dean and director of libraries.”  

The 20-member LFAB was created in 2007 to encourage communication among Institute faculty members and the Library. 

“I am delighted to assume the duties of chair of the Library Faculty Advisory Board,” Zangwill said. “Not everyone realizes that the library plays an even bigger part in student education and in faculty teaching and research than it did in the Dark Ages before the Internet.”

Physicists
from the Georgia Institute of Technology have developed a theory that describes,
in a unified manner, the coexistence of liquid and pinned solid phases of
electrons in two dimensions under the influence of a magnetic field. The theory
also describes the transition between these phases as the field is varied. The
theoretical predictions by Constantine Yannouleas and Uzi Landman, from Georgia
Tech’s School of Physics, aim to explain and provide insights into the origins
of experimental findings published last year by a team of researchers from
Princeton, Florida State and Purdue universities. The research appears in the
October 27 edition of the journal Physical
Review B.

The
experimental discovery in 1982 of a new Hall conductance step at a fraction
ν=1/m with m=3, that is at  (1/3)e²/h
(with more conductance steps, at other m, found later) – where h is the Planck
constant and e is the electron charge – was made for  two-dimensional electrons at low temperatures
and strong magnetic fields and was greeted with great surprise.  The theoretical explanation of this finding a
year later by Robert Laughlin in terms of a new form of a quantum fluid, earned
him and the experimentalists Horst Störmer and Daniel Tsui the 1998 Nobel Prize
with the citation “for the discovery of a new form of quantum fluid with fractionally
charged excitations.” These discoveries represent conceptual breakthroughs in
the understanding of matter, and the fractional quantum Hall effect (FQHE) liquid
states, originating from the highly correlated nature of the electrons in these
systems, have been termed as new states of matter.

“The
quantum fluid state at the 1/3 primary fraction is the hallmark of the FQHE,
whose theoretical understanding has been formulated around the antithesis
between a new form of quantum fluid and the pinned Wigner crystal,” said Landman,
Regents’ and Institute Professor in the School of
Physics, F.E. Callaway Chair and director of the Center for Computational
Materials Science (CCMS) at Georgia Tech. “Therefore, the
discovery of pinned crystalline signatures in the neighborhood of the 1/3 FQHE fraction,
measured as resonances in the microwave spectrum of the two-dimensional
electron gas and reported in the Physical Review Letters in September 2010 by a
group of researchers headed by Daniel Tsui, was rather surprising,” he added.

Indeed,
formation of a hexagonally ordered two-dimensional electron solid phase, a so
called Wigner crystal (WC) named after the Nobel laureate physicist Eugene
Wigner who predicted its existence in 1934, has been anticipated for smaller
quantum Hall fractional fillings, ν, of the lowest Landau level populated by
the electrons at high magnetic fields, for example ν = 1/9, 1/7 and even 1/5.
However, the electrons in the ν=1/3 fraction were believed to resist
crystallization and remain liquid.

The
Georgia Tech physicists developed a theoretical formalism that, in conjunction
with exact numerical solutions, provides a unified microscopic approach to the
interplay between FQHE liquid and Wigner solid states in the neighborhood of
the 1/3 fractional filling. A major advantage of their approach is the use of a
single class of variational wave functions for description of both the quantum
liquid and solid phases. 

“Liquid
characteristics of the fractional quantum Hall effect states are associated
with symmetry-conserving vibrations and rotations of the strongly interacting
electrons and they coexist with intrinsic correlations that are crystalline in
nature,” Senior Research Scientist Yannouleas and Landman wrote in the opening section of their paper.
“While the electron densities of the fractional quantum Hall effect liquid
state do not exhibit crystalline patterns, the intrinsic crystalline
correlations which they possess are reflected in the emergence of a sequence of
liquid states of enhanced stability, called cusp states, that correspond in the
thermodynamic limit to the fractional quantum Hall effect filling fractions
observed in Hall conductance measurements,” they added.

The
key to their explanation of the recent experimental observations pertaining to
the appearance of solid characteristics for magnetic fields in the neighborhood
of the 1/3 filling fraction is their finding that “away from the exact
fractional fillings, for example near ν=1/3, weak pinning perturbations, due to
weak disorder, may overcome the energy gaps between adjacent good angular
momentum symmetry-conserving states. The coupling between these states
generates broken-symmetry ground states whose densities exhibit spatial
crystalline patterns. At the same time, however, the energy gap between the
ground state at ν=1/3 and adjacent states is found to be sufficiently large to
prevent disorder-induced mixing, thus preserving its quantum fluid nature.” 

Furthermore,
the work shows that the emergence of the crystalline features, via the pinning
perturbations, is a consequence of the aforementioned presence of crystalline
correlations in the symmetry-conserving states. Consequently, mixing rules that
govern the nature of the disorder-pinned crystalline states have been
formulated and tested.  Extrapolation of
the calculated results to the thermodynamic limit shows development of a
hexagonal Wigner crystal with enhanced stability due to quantum correlations.

“In
closing, the nature of electrons in the fractional quantum Hall regime continues
now for close to three decades to be a subject of great fascination, a research
field that raises questions whose investigations can lead to deeper conceptual
understanding of matter and many-body phenomena, and a rich  source of surprise and discovery,” said
Landman.

This work was
supported by the Office of Basic Energy
Sciences of the US Department of Energy.

Physicists have predicted that under the influence of sufficiently high electric fields, liquid droplets of certain materials will undergo solidification, forming crystallites at temperature and pressure conditions that correspond to liquid droplets at field-free conditions. This electric-field-induced phase transformation is termed electrocrystallization. The study, performed by scientists at the Georgia Institute of Technology, appears online and is scheduled as a feature and cover article in the 42^nd issue of Volume 115 of the Journal of Physical Chemistry C.

“We show that with a strong electric field, you can induce a phase transition without altering the thermodynamic parameters,” said Uzi Landman, Regents’ and Institute Professor in the School of Physics, F.E. Callaway Chair and director of the Center for Computational Materials Science (CCMS) at Georgia Tech.

In these simulations, Landman and Senior Research Scientists David Luedtke and Jianping Gao at the CCMS set out first to explore a phenomenon described by Sir Geoffrey Ingram Taylor in 1964 in the course of his study of the effect of lightning on raindrops, expressed as changes in the shape of liquid drops when passing through an electric field.  While liquid drops under field-free conditions are spherical, they alter their shape in response to an applied electric field to become needle-like liquid drops. Instead of the water droplets used in the almost 50-year-old laboratory experiments of Taylor, the Georgia Tech researchers focused their theoretical study on a 10 nanometer (nm) diameter liquid droplet of formamide, which is a material made of small polar molecules each characterized by a dipole moment that is more than twice as large as that of a water molecule.  

With the use of molecular dynamics simulations developed at the CCMS, which allow scientists to track the evolution of materials systems with ultra-high resolution in space and time, the physicists explored the response of the formamide nano-droplet to an applied electric field of variable strength. Influenced by a field of less than 0.5V/nm, the spherical droplet elongated only slightly. However, when the strength of the field was raised to a critical value close to 0.5 V/nm, the simulated droplet was found to undergo a shape transition resulting in a needle-like liquid droplet with its long axis – oriented along the direction of the applied field – measuring about 12 times larger than the perpendicular (cross-sectional) small axis of the needle-like droplet. The value of the critical field found in the simulations agrees well with the prediction obtained almost half a century ago by Taylor from general macroscopic considerations.

Past the shape transition further increase of the applied electric field yielded a slow, gradual increase of the aspect ratio between the long and short axes of the needle-like droplet, with the formamide molecules exhibiting liquid diffusional motions. 

“Here came the Eureka moment,” said Landman. “When the field strength in the simulations was ramped up even further, reaching a value close to 1.5V/nm, the liquid needle underwent a solidification phase transition, exhibited by freezing of the diffusional motion, and culminating in the formation of a formamide single crystal characterized by a structure that differs from that of the x-ray crystallographic one determined years ago under zero-field conditions. Now, who ordered that?” he added. 

Further analysis has shown that the crystallization transition involved arrangement of the molecules into a particular spatial ordered lattice, which optimizes the interactions between the positive and negative ends of the dipoles of neighboring molecules, resulting in minimization of the free energy of the resulting rigid crystalline needle.  When the electric field applied to the droplet was subsequently decreased, the crystalline needle remelted and at zero-field the liquid droplet reverted to a spherical shape. The field reversal process was found to exhibit a hysteresis.

For the full article, please visit: 

http://www.gatech.edu/newsroom/release.html?nid=71054

Physicists
have predicted that under the influence of sufficiently high electric fields,
liquid droplets of certain materials will undergo solidification, forming
crystallites at temperature and pressure conditions that correspond to liquid
droplets at field-free conditions. This electric-field-induced phase
transformation is termed electrocrystallization.
The study, performed by scientists at the Georgia Institute of Technology,
appears online and is scheduled as a feature and cover article in the 42^nd
issue of Volume 115 of the Journal of Physical Chemistry C.

“We
show that with a strong electric field, you can induce a phase transition
without altering the thermodynamic parameters,” said Uzi Landman, Regents’ and
Institute Professor in the School of Physics, F.E. Callaway Chair and director
of the Center for Computational Materials Science (CCMS) at Georgia Tech.

In
these simulations, Landman and Senior Research Scientists David Luedtke and
Jianping Gao at the CCMS set out first to explore a phenomenon described by Sir
Geoffrey Ingram Taylor in 1964 in the course of his study of the effect of
lightning on raindrops, expressed as changes in the shape of liquid drops when
passing through an electric field.  While liquid drops under field-free
conditions are spherical, they alter their shape in response to an applied
electric field to become needle-like liquid drops. Instead of the water
droplets used in the almost 50-year-old laboratory experiments of Taylor, the
Georgia Tech researchers focused their theoretical study on a 10 nanometer (nm)
diameter liquid droplet of formamide, which is a material made of small polar
molecules each characterized by a dipole moment that is more than twice as
large as that of a water molecule.  

With
the use of molecular dynamics simulations developed at the CCMS, which allow
scientists to track the evolution of materials systems with ultra-high
resolution in space and time, the physicists explored the response of the
formamide nano-droplet to an applied electric field of variable strength.
Influenced by a field of less than 0.5V/nm, the spherical droplet elongated
only slightly. However, when the strength of the field was raised to a critical
value close to 0.5 V/nm, the simulated droplet was found to undergo a shape transition
resulting in a needle-like liquid droplet with its long axis – oriented along
the direction of the applied field – measuring about 12 times larger than the
perpendicular (cross-sectional) small axis of the needle-like droplet. The
value of the critical field found in the simulations agrees well with the
prediction obtained almost half a century ago by Taylor from general macroscopic
considerations.

Past
the shape transition further increase of the applied electric field yielded a
slow, gradual increase of the aspect ratio between the long and short axes of
the needle-like droplet, with the formamide molecules exhibiting liquid
diffusional motions. 

“Here
came the Eureka moment,” said Landman. “When the field strength in the
simulations was ramped up even further, reaching a value close to 1.5V/nm, the
liquid needle underwent a solidification phase transition, exhibited by
freezing of the diffusional motion, and culminating in the formation of a
formamide single crystal characterized by a structure that differs from that of
the x-ray crystallographic one determined years ago under zero-field
conditions. Now, who ordered that?” he added. 

Further
analysis has shown that the crystallization transition involved arrangement of
the molecules into a particular spatial ordered lattice, which optimizes the
interactions between the positive and negative ends of the dipoles of
neighboring molecules, resulting in minimization of the free energy of the
resulting rigid crystalline needle.  When the electric field applied to the
droplet was subsequently decreased, the crystalline needle remelted and at
zero-field the liquid droplet reverted to a spherical shape. The field reversal
process was found to exhibit a hysteresis.

Analysis
of the microscopic structural changes that underlie the response of the droplet
to the applied field revealed that accompanying the shape transition at 0.5
V/nm is a sharp increase in the degree of reorientation of the molecular
electric dipoles, which after the transition lie preferentially along the
direction of the applied electric field and coincide with the long axis of the
needle-­­like liquid droplet. The directional dipole reorientation, which is
essentially complete subsequent to the higher field electrocrystallization
transition, breaks the symmetry and transforms the droplet into a field-induced
ferroelectric state where it possesses a large net electric dipole, in contrast
to its unpolarized state at zero–field conditions. 

Along
with the large-scale atomistic computer simulations, researchers formulated and
evaluated an analytical free-energy model, which describes the balance between
the polarization, interfacial tension and dielectric saturation contributions.
This model was shown to yield results in agreement with the computer simulation
experiments, thus providing a theoretical framework for understanding the
response of dielectric droplets to applied fields.

“This
investigation unveiled fascinating properties of a large group of materials
under the influence of applied fields,” Landman said. “Here the field-induced
shape and crystallization transitions occurred because formamide, like water
and many other materials, is characterized by a relatively large electric
dipole moment. The study demonstrated the ability to employ external fields to
direct and control the shape, the aggregation phase (that is, solid or liquid)
and the properties of certain materials.” 

Along
with the fundamental interest in understanding the microscopic origins of
materials behavior, this may lead to development of applications of
field-induced materials control in diverse areas, ranging from targeted drug delivery,
nanoencapsulation, printing of nanostructures and surface patterning, to
aerosol science, electrospray propulsion and environmental science.

This research was supported by a grant from the U.S. Air Force Office of Scientific Research.

School of Physics Assistant Professors Markus Kindermann and Daniel Goldman have been awarded National Science Foundation Faculty Early Career Development (CAREER) Awards.

Dr. Goldman's (pictured at left) award will support his research on the "Discovery and Dissemination of Neuromechanical Principles of Swimming, Walking and Running in Granular Media."

Dr. Kindermann's (pictured at right) award will support his research on "Interactions and Entanglement in Electronic Nanostructures."

The Faculty Early Career Development (CAREER) Program is a Foundation-wide activity that offers the National Science Foundation's most prestigious awards in support of junior faculty who exemplify the role of teacher-scholars through outstanding research, excellent education and the integration of education and research within the context of the mission of their organizations. Such activities should build a firm foundation for a lifetime of leadership in integrating education and research.