Research Highlights

The Perkins group is helping to develop DNA as a force standard for the nano world. Polymers of DNA act like springs, and DNA's elasticity may one day provide a force standard from 0.1–10 piconewtons (pN). One pN is the force exerted when 1 mW of light reflects off a mirror or the approximate weight of one hundred E. coli cells. DNA is an excellent candidate for a force standard because its double helix is reproduced with exquisite fidelity, which allows researchers (or cells) to build it with atomic precision.

In Ray Bradbury’s book Something Wicked This Way Comes, people get older or younger depending on which direction they ride on a carnival carousel. Something similar may happen to black holes, except that they become gargantuan or just a smidgeon larger depending on how fast they spin while they’re sucking in matter. The slower they spin, the faster they expand, says Visiting Fellow Andrew King of the University of Leicester. And, how fast they spin is influenced by the direction and orientation of clouds of gas being pulled into them. For the clouds, it’s a lot like jumping onto a carousel.

An excellent way to watch proteins fold is to probe the inside of a microfluidics device with light. This tiny device contains micron-sized three-dimensional (3D) transparent channels that carry small amounts of liquid. Inside the channels, the fluid flow is laminar, i.e., there is no turbulence. Consequently, fluid flow through them is predictable and easily modeled. Microfluidics devices have been used to study chemical reaction kinetics and control chemical and biological reactions.

A solid understanding of the structure and behavior of atoms is important for understanding the physical world, from the basic building blocks of nature to the inner workings of modern technology. However, education researchers have expressed different opinions regarding the best way to teach students the ins and outs of atoms. In particular, some have even recommended doing away with teaching the older and simpler Bohr model, asserting that it inhibits students’ ability to understand the quantum nature of electrons in atoms.

Fellows Ralph Jimenez and Henry Kapteyn and their groups recently helped develop optical technology that will make femtosecond laser experiments much simpler to perform, opening the door to using such lasers in many more laboratories. The technology, which employs reflection grisms as laser pulse compressors, has been patented and is now available commercially. A reflection grism consists of metal reflection grating mounted on one face of a prism.

In Fellow Steve Cundiff’s lab, echoes of light are illuminating the quantum world. Former Graduate Student Gina Lorenz used a technique known as echo peak shift spectroscopy to probe the interactions of potassium atoms in a dense vapor. Research Associate Sam Carter then used the same method to investigate the interactions of excitons confined in two-dimensional semiconductor quantum wells.

In JILA Fellow Dick McCray’s view, the way students learn astronomy is nearly the reverse of the way early astronomers learned astronomy. For instance, students might first learn Newton’s law of gravity and Kepler’s laws of planetary motion and then complete exercises in which they calculate what scientists have observed. But that’s not how Kepler did it. He fit observations of planetary motion with a controversial mathematical model that was much later confirmed to be correct by Newton’s theory of gravity.

X-rays are notorious for damaging molecules, including those in our bodies. High in the upper atmosphere, X-rays from the Sun break apart simple molecules like nitrogen (N₂) and drive chemical reactions affecting the Earth. For these reasons, it’s important to understand exactly how radiation interacts with, damages, or destroys specific chemicals.

In the quantum world inside Fellow Eric Cornell’s lab, communication occurs across a two-dimensional lattice array of Bose-Einstein condensates (BECs) when atoms tunnel out of superatoms (made from about 7000 garden-variety rubidium (Rb) atoms) into neighboring BECs. This communication keeps the array coherent, i.e., the phases of all condensates remain locked to each other. But something interesting happens when the tiny superatoms stop communicating among themselves. Vortices form. And how many appear depends on temperature.

It’s easy to make X-rays. Physicians and dentists make them routinely in their offices with a Roentgen X-ray tube, which emits X-rays every which way — just like a light bulb, which is nothing like a laser.

Two egg-shaped necklaces of magnificent stars orbit the enormous black hole known as Sagittarius A* (Sgr A*) at the center of the Milky Way Galaxy. Sgr A* (shown right) has long been thought to be well past promoting new star formation; until the necklaces were discovered, the black hole was considered to be just an aging, depleted relic of its glory days of organizing the Galaxy.

There’s a new aspect to research on gamma-ray bursts: their use to discern features of the environment around the star that produced them during its core’s collapse into a black hole. This type of analysis is possible because the spectrum of a gamma-ray burst afterglow is a straight-line continuum without features. 

A second wave has appeared on the horizon of ultracold atom research. Known as the p-wave, it is opening the door to probing rich new physics, including unexplored quantum phase transitions. The first wave of ultracold atom research focused on s-wave pairing between atoms, where the “s” meant the resultant molecules are not rotating. In contrast, p-waves involve higher-order pairing where the atoms do rotate around each other.

Researchers from the Ye, Bohn, and Greene groups are busy exploring a cold new world crawling with polar hydroxyl radical (OH) molecules. The JILA experimentalists have already discovered how to cool OH to “lukewarm” temperatures of 30 mK. They’ve precisely measured four OH transition frequencies that will help physicists determine whether the fine structure constant has changed in the past 10 billion years.

Small changes in the quantum fluctuations of free space are responsible for a variety of curious phenomena: a gecko’s ability to walk across ceilings, the evaporation of black holes via Hawking radiation, and the fact that warmer surfaces can be stickier than cold ones in micro- and nanoscale electromechanical systems (MEMS and NEMS). The tendency of tiny parts to stick together is a consequence of the Casimir force.

A Fermi sea forms at ultracold temperatures when fermions in a dilute gas stack up in the lowest possible energy states, with two fermions in each state, one spin up and one spin down. New analytic techniques for diving headfirst into the fundamental physics of this exotic form of matter were recently developed by graduate students Seth Rittenhouse and Javier von Stecher, Fellow Chris Greene, and former postdoc Mike Cavagnero, now at the University of Kentucky.

JILA Fellow Dana Z. Anderson, JILA visiting scientist Alex Zozulya, and a colleague from the Worcester Polytechnic Institute postulate that the ultracold coherent atoms in a Bose-Einstein Condensate (BEC) could be configured to act like electrons in a transistor. An “atom transistor” would exhibit absolute and differential gain, as well as allow for the movement of single atoms to be resolved in a precision scientific measurement.

A key challenge in developing new nanotechnologies is figuring out a fast, low-noise technique for translating small mechanical motions into reasonable electronic signals. Solving this problem will one day make it possible to build electronic signal processing devices that are much more compact than their purely electronic counterparts. Much sooner, it will enable the design of advanced scanning tunneling microscopes that operate hundreds to thousands of times faster than current models.

When astronomers observe a star surrounded by an accretion disk in visible light, they typically see radiation from the star at the center of the disk. When they observe the disk in the infrared, they typically see emission at a continuous range of wavelengths, ranging from short to long.

Researchers are investigating a new kind of microelectronics called spintronics. These devices will rely on the spindependent behavior of electrons in addition to (or even instead of) conventional charge-based circuitry. Researchers in physics and engineering anticipate that these devices will process data faster, use less power than today's conventional semiconductor devices, and work well in nanotechnologies, where quantum effects predominate. Spin-FETs (field effect transistors), spin-LEDs (light-emitting diodes), spin-RTDs (resonant tunneling devices), terahertz optical switches, and quantum computers are some of the multifunctional spintronic devices being envisioned.