News & 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!

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.

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.

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 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.

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 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.

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.

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.

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 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.

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.

JILA physicists are investigating complex and interesting materials, circuits, and devices based on ultracold atoms instead of electrons. Collectively known as atomtronics, they have important theoretical advantages over conventional electronics, including (1) superfluidity and superconductivity, (2) minimal thermal noise and instability, and (3) coherent flow. With such characteristics, atomtronics could play a key role in quantum computing, nanoscale amplifiers, and precision sensors.

Does the electron have an electric dipole moment (eEDM)? If it does, the standard model of elementary particle physics says this dipole moment is many orders of magnitude below what can be measured experimentally. As Fellow John Bohn quips, "It's a darn small one."

When illuminated by X-ray and infrared light beams in tandem, electrons can tap dance off a platinum surface because they've actually grabbed a photon from both beams simultaneously. As you might have guessed, there is more going on here than the ordinary photoelectric effect, which Albert Einstein explained more than a century ago. In the photoelectric effect, electrons escape from a solid after absorbing a single photon or bundle of light energy. 

What do fermions in atomic nuclei, neutron stars, and ultracold trapped gases have in common? They have the same fundamental behavior. The exciting news is that there's now hard evidence that this is true, thanks to graduate students Jayson Stewart and John Gaebler, Cindy Regal who received her Ph.D. in physics in November, and Fellow Debbie Jin.

"Chemistry is a highly improbable science," says Graduate Student Mike Deskevich, who adds "It's good for life on Earth that things are so unreactive." For instance, if chemical reactions happened easily and often, oxygen in the air would cause clothing and other flammable materials to burst into flame. In addition to making life difficult, high probability chemistry would render theoretical chemical physics much less interesting. As it is, theorists spend months determining the particular molecular shapes, vibrations, and energy states that make the simplest chemical reactions possible.

The breakdown of chlorofluorocarbons (CFCs) in the stratosphere has been implicated in the destruction of Earth's protective ozone layer. Consequently, scientists have undertaken studies to better understand the structure and behavior of highly reactive, but short-lived, free radicals produced during the breakdown process. The molecules, which contain either fluorine or chlorine, are an important source of atmospheric halogen atoms. Elucidating their 3D structure and dynamical behavior will help scientists better understand atmospheric chemistry as well as their fundamental molecular properties.