Research Highlights

For many years, chemists have explored the differences between liquids and solids. One difference is that liquid surfaces tend to be softer than solid surfaces (from the perspective of molecules crashing onto them). Another difference is that the surface of at least one oily liquid (perfluorinated polyether, or PFPE) actually gets stickier as it gets hotter, according to a new study by graduate student Brad Perkins and Fellow David Nesbitt. This behavior contrasts with solid surfaces, which usually get stickier when they get colder!

Fellow Phil Armitage is excited about the discovery of several new galaxies in which a disk of water masers is orbiting within half a light year of the central massive black hole. Like their counterpart M106 (NGC 4258) discovered in 1995, these hot (600 K) water molecules mase, i.e., emit coherent radio wavelength photons when they return to lower energy states after being excited by collisions inside the gas near the black hole. The water masers orbit black holes much like a planetary system, beaming their steamy songs toward radio telescopes on Earth.

What sort of experiment could detect the effects of quantum gravity, if it exists? Theories that go beyond the Standard Model of physics include a concept that links quantum interactions with gravity. Physicists would very much like to find evidence of this coupling as these two branches of physics are not yet unified in a single theory that explains everything about our world.

By late 2006, Fellow Jun Ye’s clock team had raised the accuracy of its strontium (Sr)-lattice atomic clock to be just shy of that of the nation’s primary time and frequency standard, the NIST-F1 cesium (Cs) fountain clock. Graduate students Marty Boyd and Andrew Ludlow led the effort to improve the clock’s accuracy.

With every breath you take, you breathe out carbon dioxide and roughly 1000 other different molecules. Some of these can signal the early onset of such diseases as asthma, cystic fibrosis, or cancer. Thanks to graduate student Mike Thorpe and his colleagues in Fellow Jun Ye’s group, medical practitioners may one day be able to identify these disease markers with a low-cost, noninvasive breath test. The new laser-based breath test is an offshoot of Thorpe’s research on cavity-enhanced direct optical frequency comb spectroscopy, a molecular fingerprinting technique reported in Science two years ago.

When the Jin and Ye group collaboration wanted to investigate the creation of stable ultracold polar molecules, the researchers initially decided to make ultracold KRb (potassium-rubidium) molecules and then study their collision behavior. Making the molecules required a cloud of incredibly cold K and Rb atoms, the ability to apply a magnetic field of just the right strength to induce a powerful attraction between the different kinds of atoms, and some low-frequency photons.

What did Fellow Jeff Linsky come home with from a 2006 SINS conference? He arrived at JILA with the realization that quasars twinkle for much the same reason stars twinkle: Light from both quasars and stars pass through turbulence that mixes up the light rays, causing the light to vary in intensity, or twinkle. However, the stars we see every night twinkle because of turbulence in the Earth’s dynamic atmosphere, which changes hundreds of times a second.

Neutron stars are born in supernovae, spinning very fast. How fast they spin at birth depends on a variety of factors including the initial rotation of the star that goes supernova and what takes place during the supernova explosion. So, if you want to understand these phenomena, one place to start is by investigating how fast a new neutron star can initially spin.

Benzene has a special ring structure that allows some of its electrons to be shared among all six carbon atoms in the ring. It turns out that chemists like Fellow J. Mathias Weber can adjust the charge density in the ring by exchanging hydrogen (H) atoms in the ring with other atoms or groups of atoms. Such exchanges can change the charge pattern in the ring "seen" by neighboring molecules.

The Kapteyn/Murnane group recently proved that you don’t need an accelerator facility to make the X-Rays for an X-Ray microscope. In fact, you can build the whole device on an optical bench — if you use a femtosecond laser to generate coherent X-Rays. The group makes coherent X-Rays by shining the laser into a glass tube filled with argon gas. The argon atoms absorb many low-energy laser photons and spit out high-energy X-Ray photons when they give up the absorbed energy. The X-Ray beam has all the desirable properties of laser light. For example, it does not spread rapidly and can be used to make holograms.

Fellow Andrew Hamilton recently confirmed a prediction he made 10 years ago of the location of a reverse shock wave slowing the expansion of the debris from a supernova that occurred in 1006 AD. SN1006 was (and still is) the brightest supernova observed in recorded history; it was visible from Earth (without telescopes) for three years.

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 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.

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.

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.