Research Highlights

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.

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.

Our Sun and its eight planets were born in a rough neighborhood nearly 5 billion years ago. Since then our star has traveled countless light years through the Milky Way, and our planet Earth has evolved the only intelligent life we know of in the Universe. Now, Earth's progeny are seeking to understand not only their own origins, but those of the Sun and its planets. 

Scientists anticipate that cold molecules will allow them to explore all kinds of exciting new cold-matter physics. For instance, cold molecules should be able to interact with each other over much longer distances than atoms. They often exhibit an uneven distribution of electric charge called a dipole moment. Unfortunately, the complicated structures of ordinary "warm" molecules means it is very difficult to directly cool them to very cold temperatures.

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.

If you want to "see" physical objects whose dimensions are measured in nanometers and simultaneously probe the electronic structure of the atoms, molecules, and surfaces populating this nanoworld, you just might have to invent a new microscope. In fact, that's exactly what Fellow David Nesbitt's group recently accomplished.

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."

There is an enormous black hole at the center of every galaxy, gobbling up matter over eons of time - some for as long as 13 billion years. One of the great questions of modern astronomy is: Where did the seeds for all these black holes come from? Not, as you might think, from the fiery collapse of massive hot stars formed in the early Universe, says Fellow Mitch Begelman. That may well be how new, much smaller black holes are formed, even now. However, despite long-standing theories to the contrary, Begelman believes that ancient supernovae cannot account for the genesis of the black holes as massive as a million suns at the center of galaxies.

Under ordinary circumstances, making new molecules can be simple and straightforward - just a matter of mixing together some highly reactive chemicals and letting nature take its course. However, when the reactants are a few millionths of a degree above absolute zero, the creation of new molecules requires the sophisticated tools of modern experimental physics. Using those tools, graduate student Scott Papp and Fellow Carl Wieman recently created the world's first ultracold diatomic molecules made from two different atoms.

Pancakes of Bose-Einstein condensates (BECs) of polar molecules are repulsive and potentially unstable. However, the physics of these dipolar condensates is delicious, according to research associate Shai Ronen, graduate student Daniele Bortolotti, and Fellow John Bohn. The JILA theorists recently studied BECs with purely dipolar interactions in oblate (pancake) traps.

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. 

In the race to develop the world's best optical atomic clock, accuracy and precision are what count. Accuracy is the degree to which a measurement of time conforms to time's true value. Precision is a gauge of the exactness, or reproducibility, of the measurements. By definition, a high-precision clock must be extremely stable.

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.

For astrophysicists working to discover the origins of stars and planets, a small clue can go a long way. They can't get a close look at distant stars and planets, so they only know the barest details about other planetary systems. One such detail is that some extra-solar planets revolve around their stars in elliptical orbits rather than the nearly circular orbits that are the norm in our solar system. 

Left to their own devices, deuterium atoms would attach themselves to cold specks of soot floating in interstellar gas clouds and remain there for eternity. In fact, deuterium has a great affinity for the buckyballs, bucky onions, bucky tubes, and other forms of carbon, such as polycyclic aromatic hydrocarbons, comprising soot. It readily replaces hydrogen in these molecules. Deuterium atoms bond to interstellar soot so tightly it takes an encounter with a hot star or supernova explosion to pry them loose.

"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.