Nanotechnology Now

Our NanoNews Digest Sponsors
Heifer International



Home > Press > "Wedding Cake" Images Display Transitions between Exotic Quantum States

The 'wedding cake' structure shows the density profile of a heterogeneous mixture of Mott insulating, superfluid and normal phases of ultracold cesium atoms trapped in an optical lattice. "The different layers of the cake are formed by Mott insulating domains of successively higher particle numbers, and their flatness is a result of their incompressibility," said Dr. Nathan Gemelke, of the University of Chicago.

"The edges as we go from one layer of the cake to the next are superfluid regions, where the density varies continuously," he said. "As the temperature is increased, the cake melts like a multi-tiered ice cream cake, and smears out the edges of the layers."

Credit: Cheng Chin, James Franck Institute, University of Chicago
The 'wedding cake' structure shows the density profile of a heterogeneous mixture of Mott insulating, superfluid and normal phases of ultracold cesium atoms trapped in an optical lattice. "The different layers of the cake are formed by Mott insulating domains of successively higher particle numbers, and their flatness is a result of their incompressibility," said Dr. Nathan Gemelke, of the University of Chicago. "The edges as we go from one layer of the cake to the next are superfluid regions, where the density varies continuously," he said. "As the temperature is increased, the cake melts like a multi-tiered ice cream cake, and smears out the edges of the layers." Credit: Cheng Chin, James Franck Institute, University of Chicago

Abstract:
From superfluid to Mott insulator, density profiles of ultracold atomic gases reveal secrets of quantum phase transitions

"Wedding Cake" Images Display Transitions between Exotic Quantum States

Arlington, VA | Posted on August 20th, 2009

Transitions are exciting. And at temperatures close to absolute zero, studying the transition from one quantum phase to another tantalizes physicists looking for a deeper understanding of the fundamental laws of the universe.

Now a team of scientists at the University of Chicago has created the first direct images of the transition between phases of ultracold cesium gas, as it changes from normal to superfluid to Mott insulator, making it possible to "see" this phenomenon as it happens.

"These are the first direct images of a complete physical system in situ, allowing us to unambiguously observe certain unique features of the Mott insulating state," explained post-doctoral student Nathan Gemelke.

In a paper appearing in the journal Nature, Gemelke and his co-authors describe the most striking visual feature of this phase transition--a many-layered wedding cake structure.

The Mott Insulator Observed

"The Mott insulator phenomenon was first observed in ultracold atomic gases in 2002, by the group of Ted Hänsch, at the Johannes Gutenberg-University in Mainz, Germany, and has been a subject of intense research ever since," said Cheng Chin, Gemelke's co-author and an assistant professor at the University of Chicago.

A Mott insulator is a special phase of matter, usually formed at very low temperatures, in which certain materials that should conduct electricity act as electrical insulators, due to unusual interactions between electrons. The system studied in Chicago is the ultracold atom equivalent of a Mott insulator.

To make the insulator, the Chicago team trapped individual atoms using a cross-section of laser beams to create an "optical lattice," something like marbles trapped in the individual sections of an egg carton.

"In a Mott insulator, there is exactly one atom at every site, or two, or three, but never a mixture of, say, one here, two there, etc.," Chin explained.

Three Co-existing Phases

According to Gemelke, the Mott insulator phase sometimes co-exists with superfluid and normal gas phases. Superfluids are another exotic quantum material phase that forms at temperatures near absolute zero.

"The superfluid and normal phases of the ultracold gas will react to small pressures by changing their volumes, and will react to small forces by flowing freely," explained Gemelke.

"In contrast, the Mott insulator phase has a constant density," he said. "Even when it's trapped, if you squeeze it gently, its volume will not change, which means it is incompressible. And if you apply a small force across it, particles do not flow through it, because it acts as an insulator."

The researchers took advantage of the differences between phases to create visual images of the system by measuring the density of the trapped gas.

"In two dimensions, the normal, superfluid and Mott insulating phases can be identified by spatially resolved in-situ imaging," Gemelke said. These two-dimensional images appear as bullseye targets, with denser material showing up as dark rings. The Mott insulator phase image remains a single color all the way through, because its density does not increase.

"In three dimensional systems, the image integrates the density along the line-of-sight, so the measurements represent the combined properties of several phases," Gemelke said.

The result looks like a colorful, multi-layered wedding cake.

"The different layers of the cake are formed by Mott insulating domains of successively higher particle numbers, and their flatness results from their incompressibility," says Gemelke.

"The edges as we go from one layer of the cake to the next are superfluid regions, where the density varies continuously," he said. "As the temperature is increased, the cake melts like a multi-tiered ice cream cake, and smears out the edges of the layers. By measuring its shape, we can infer the temperature-and unlike an ice cream cake, the result is within fifteen parts-per-billion of absolute zero."

Worth more than 1,000 words

The researchers hope to apply the understanding they gain from studying simple quantum gases like this one to the development of a wide range of more subtle and potentially useful new materials, Chin said.

"We are excited to extend this research into basic studies of quantum phase transitions--that is to say, transitions between phases which can occur at zero temperature," he said. "Very fascinating and general phenomena can be observed near these types of transitions, and to have such a simple and readily studied example on the laboratory bench is a great commodity."

"We are surprised by how true the adage is that a picture is worth a thousand words," added Gemlke. "Each image we take of these systems is a high-resolution snapshot into the life of a quantum gas, including all the bumps and wriggles we hope to describe with theory. Every time we think we have extracted all the information we could hope for from an image, we realize there is more to study."

####

About National Science Foundation
The National Science Foundation (NSF) is an independent federal agency that supports fundamental research and education across all fields of science and engineering. In fiscal year (FY) 2009, its budget is $9.5 billion, which includes $3.0 billion provided through the American Recovery and Reinvestment Act. NSF funds reach all 50 states through grants to over 1,900 universities and institutions. Each year, NSF receives about 44,400 competitive requests for funding, and makes over 11,500 new funding awards. NSF also awards over $400 million in professional and service contracts yearly.

For more information, please click here

Contacts:
Media Contacts
Lisa-Joy Zgorski
NSF
(703) 292-8311


Holly Martin
NSF
(703) 292-8070

Copyright © National Science Foundation

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

News and information

Researchers develop artificial building blocks of life March 8th, 2024

How surface roughness influences the adhesion of soft materials: Research team discovers universal mechanism that leads to adhesion hysteresis in soft materials March 8th, 2024

Two-dimensional bimetallic selenium-containing metal-organic frameworks and their calcinated derivatives as electrocatalysts for overall water splitting March 8th, 2024

Curcumin nanoemulsion is tested for treatment of intestinal inflammation: A formulation developed by Brazilian researchers proved effective in tests involving mice March 8th, 2024

Physics

Nanoscale CL thermometry with lanthanide-doped heavy-metal oxide in TEM March 8th, 2024

Optically trapped quantum droplets of light can bind together to form macroscopic complexes March 8th, 2024

Scientists use heat to create transformations between skyrmions and antiskyrmions January 12th, 2024

Focused ion beam technology: A single tool for a wide range of applications January 12th, 2024

Discoveries

What heat can tell us about battery chemistry: using the Peltier effect to study lithium-ion cells March 8th, 2024

Researchers’ approach may protect quantum computers from attacks March 8th, 2024

High-tech 'paint' could spare patients repeated surgeries March 8th, 2024

Nanoscale CL thermometry with lanthanide-doped heavy-metal oxide in TEM March 8th, 2024

Announcements

What heat can tell us about battery chemistry: using the Peltier effect to study lithium-ion cells March 8th, 2024

Curcumin nanoemulsion is tested for treatment of intestinal inflammation: A formulation developed by Brazilian researchers proved effective in tests involving mice March 8th, 2024

The Access to Advanced Health Institute receives up to $12.7 million to develop novel nanoalum adjuvant formulation for better protection against tuberculosis and pandemic influenza March 8th, 2024

Nanoscale CL thermometry with lanthanide-doped heavy-metal oxide in TEM March 8th, 2024

Quantum nanoscience

Optically trapped quantum droplets of light can bind together to form macroscopic complexes March 8th, 2024

Bridging light and electrons January 12th, 2024

'Sudden death' of quantum fluctuations defies current theories of superconductivity: Study challenges the conventional wisdom of superconducting quantum transitions January 12th, 2024

Physicists ‘entangle’ individual molecules for the first time, hastening possibilities for quantum information processing: In work that could lead to more robust quantum computing, Princeton researchers have succeeded in forcing molecules into quantum entanglement December 8th, 2023

NanoNews-Digest
The latest news from around the world, FREE




  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project