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Physics Alumnus Wins 2012 Sigma Xi Best Thesis Award

Wednesday, March 14, 2012

School of Physics PhD alumnus and current postdoc Chen Li is a recipient of the 2012 Sigma-Xi Best PhD thesis Award.

Li defended his thesis, "Biological, Robotic, and Physics Studies to Discover Principles of Legged Locomotion on Granular Media", in November and graduated in December (advisor: Daniel Goldman). In July, he will join Prof. Robert Full's Poly-PEDAL Lab at UC Berkeley as a Miller Fellow.

Congratulations!

Summary: 

School of Physics PhD alumnus and current postdoc Chen Li is a recipient of the 2012 Sigma-Xi Best PhD thesis Award

Intro: 

School of Physics PhD alumnus and current postdoc Chen Li is a recipient of the 2012 Sigma-Xi Best PhD thesis Award

Alumni: 

Scientists Score Another Victory Over Uncertainty in Quantum Physics Measurements

Sunday, February 26, 2012

Most people attempt to reduce the little uncertainties of life by carrying umbrellas on cloudy days, purchasing automobile insurance or hiring inspectors to evaluate homes they might consider purchasing. For scientists, reducing uncertainty is a no less important goal, though in the weird realm of quantum physics, the term has a more specific meaning.

For scientists working in quantum physics, the Heisenberg Uncertainty Principle says that measurements of properties such as the momentum of an object and its exact position cannot be simultaneously specified with arbitrary accuracy. As a result, there must be some uncertainty in either the exact position of the object, or its exact momentum. The amount of uncertainty can be determined, and is often represented graphically by a circle showing the area within which the measurement actually lies.

Over the past few decades, scientists have learned to cheat a bit on the Uncertainty Principle through a process called “squeezing,” which has the effect of changing how the uncertainty is shown graphically. Changing the circle to an ellipse and ultimately to almost a line allows one component of the complementary measurements – the momentum or the position, in the case of an object – to be specified more precisely than would otherwise be possible. The actual area of uncertainty remains unchanged, but is represented by a different shape that serves to improve accuracy in measuring one property.

This squeezing has been done in measuring properties of photons and atoms, and can be important to certain high-precision measurements needed by atomic clocks and the magnetometers used to create magnetic resonance imaging views of structures deep inside the body. For the military, squeezing more accuracy could improve the detection of enemy submarines attempting to hide underwater or improve the accuracy of atom-based inertial guidance instruments.

Now physicists at the Georgia Institute of Technology have added another measurement to the list of those that can be squeezed. In a paper appearing online February 26 in the journal Nature Physics, they report squeezing a property called the nematic tensor, which is used to describe the rubidium atoms in Bose-Einstein Condensates, a unique form of matter in which all atoms have the same quantum state. The research was sponsored by the National Science Foundation (NSF).

“What is new about our work is that we have probably achieved the highest level of atom squeezing reported so far, and the more squeezing you get, the better,” said Michael Chapman, a professor in Georgia Tech’s School of Physics. “We are also squeezing something other than what people have squeezed before.”

Scientists have been squeezing the spin states of atoms for 15 years, but only for atoms that have just two relevant quantum states – known as spin ½ systems. In collections of those atoms, the spin states of the individual atoms can be added together to get a collective angular momentum that describes the entire system of atoms.

In the Bose-Einstein condensate atoms being studied by Chapman’s group, the atoms have three quantum states, and their collective spin totals zero – not very helpful for describing systems. So Chapman and graduate students Chris Hamley, Corey Gerving, Thai Hoang and Eva Bookjans learned to squeeze a more complex measure that describes their system of spin 1 atoms: nematic tensor, also known as quadrupole.

Nematicity is a measure of alignment that is important in describing liquid crystals, exotic magnetic materials and some high temperature superconductors.

“We don’t have a spin vector pointing in a particular direction, but there is still some residual information in where this collection of atoms is pointing,” Chapman explained. “That next higher-order description is the quadrupole, or nematic tensor. Squeezing this actually works quite well, and we get a large degree of improvement, so we think it is relatively promising.”

Experimentally, the squeezing is created by entangling some of the atoms, which takes away their independence. Chapman’s group accomplishes this by colliding atoms in their ensemble of some 40,000 rubidium atoms.

“After they collide, the state of one atom is connected to that of the other atom, so they have been entangled in that way,” he said. “This entanglement creates the squeezing.”

Reducing uncertainty in measuring atoms could have important implications for precise magnetic measurements. The next step will be to determine experimentally if the technique can improve the measurement of magnetic field, which could have important applications.

“In principle, this should be a straightforward experiment, but it turns out that the biggest challenge is that magnetic fields in the laboratory fluctuate due to environmental factors such as the effects of devices such as computer monitors,” Chapman said. “If we had a noiseless laboratory, we could measure the magnetic field both with and without squeezed states to demonstrate the enhanced precision. But in our current lab environment, our measurements would be affected by outside noise, not the limitations of the atomic sensors we are using.”

The new squeezed property could also have application to quantum information systems, which can store information in the spin of atoms and their nematic tensor.

“There are a lot of things you can do with quantum entanglement, and improving the accuracy of measurements is one of them,” Chapman added. “We still have to obey Heisenberg’s Uncertainty Principle, but we do have the ability to manipulate it.”

Research News & Publications Office
Georgia Institute of Technology
75 Fifth Street, N.W., Suite 314
Atlanta, Georgia  30308  USA

Media Relations Contacts: John Toon (404-894-6986)(jtoon@gatech.edu) or Abby Robinson (404-385-3364)(abby@innovate.gatech.edu)

Writer: John Toon

Media Contact: 

John Toon

Research News & Publications Office

404-894-6986

jtoon@gatech.edu

Summary: 

Uncertainty affects the accuracy with which measurements can be made in quantum physics. To reduce this uncertainty, physicists have learned to "squeeze" certain measurements. Researchers are now reporting a new type of measurement that can be squeezed to improve precision.

Intro: 

Uncertainty affects the accuracy with which measurements can be made in quantum physics. To reduce this uncertainty, physicists have learned to "squeeze" certain measurements. Researchers are now reporting a new type of measurement that can be squeezed to improve precision.

Alumni: 

Dr. Constantine Yannouleas awarded as 2012 APS Outstanding Referee

Thursday, February 16, 2012

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.

Summary: 

Dr. Constantine Yannouleas awarded as 2012 APS Outstanding Referee

Intro: 

Dr. Constantine Yannouleas awarded as 2012 APS Outstanding Referee

Alumni: 

$8.5 Million Research Initiative Will Study Best Approaches for Quantum Memories

Thursday, February 16, 2012
$8.5 Million Research Initiative Will Study Best Approaches for Quantum Memories

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

Summary: 

$8.5 Million Research Initiative Will Study Best Approaches for Quantum Memories

Intro: 

$8.5 Million Research Initiative Will Study Best Approaches for Quantum Memories

Alumni: 

$8.5 Million Research Initiative Will Study Best Approaches for Quantum Memories

Wednesday, February 15, 2012

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
75 Fifth Street, N.W., Suite 314
Atlanta, Georgia  30308  USA

Media Relations Contacts: John Toon (404-894-6986)(jtoon@gatech.edu) or Abby Robinson (404-385-3364)(abby@innovate.gatech.edu).

Writer: John Toon

Media Contact: 

John Toon

Research News & Publications Office

404-894-6986

jtoon@gatech.edu

Summary: 

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.

Intro: 

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.

Alumni: 

Town Hall Meeting with GT President Bud Peterson and Provost Rafael Bras

Thursday, January 26, 2012

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...

 
What: Town Hall Meeting with GT President Bud Peterson and Provost Rafael Bras.
When: Monday, January 30 at 4 p.m.
Where: In the Student Center Theater.
Summary: 

Town Hall Meeting with GT President Bud Peterson and Provost Rafael Bras

Intro: 

Town Hall Meeting with GT President Bud Peterson and Provost Rafael Bras

Alumni: 

Squishy Physics: The Physics of Food and Cooking

Thursday, January 19, 2012

 

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.

 

Summary: 

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.

Intro: 

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.

Alumni: 

Provost Appoints New Chair of Library Faculty Advisory Board

Monday, November 14, 2011

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.”

Media Contact: 

Jennifer Herazy
Office of the Provost 

Summary: 

Provost Rafael L. Bras has appointed Andrew Zangwill, professor in the School of Physics, chair of the Library Faculty Advisory Board (LFAB). 

Intro: 

Provost Rafael L. Bras has appointed Andrew Zangwill, professor in the School of Physics, chair of the Library Faculty Advisory Board (LFAB). 

Alumni: 

A Two-Dimensional Electron Liquid Solidifies in a Magnetic Field

Wednesday, November 9, 2011

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.

Source:  http://www.gatech.edu/newsroom/release.html?nid=72404

Summary: 

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.

Intro: 

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.

Alumni: 

A Two-Dimensional Electron Liquid Solidifies in a Magnetic Field

Friday, November 4, 2011

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.

 

Media Contact: 

Jason Maderer

Georgia Tech Media Relations

404-385-2966

maderer@gatech.edu

Summary: 

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.

Intro: 

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.

Alumni: 

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