Research Highlights

There are two competing ideas about the origin of the monster black holes at the center of galaxies. Both include exceptional stars that have never actually been observed: (1) massive population III (Pop III) stars (as big as a thousand Suns) made of pure hydrogen and helium that would have formed less than 100 million years after the Big Bang, and (2) gigantic quasistars whose shining envelopes were powered, not by nuclear fusion, but by energy emitted by the black holes inside them.

Plucking the two electrons out of helium atoms should allow researchers to study how they interact during a double ionization process — at least in theory. Recently, Fellow Andreas Becker explored whether an ultrashort vacuum ultraviolet (VUV) laser pulse could be used to probe the interactions of helium’s electrons during a double ionization in the presence of an intense infrared (IR) laser field.

Of all the fundamental forces, gravity is the most difficult to precisely measure. This difficulty is reflected in how hard it is to accurately measure “Big G,” a fundamental constant that is part of the measurement of the gravitational force. In fact, big G is the least precisely measured fundamental constant in physics. Who would have imagined that the very first fundamental force to be discovered would still be somewhat mysterious more than 300 years later? Or, that a force most of us take for granted in everyday life is actually very hard to precisely measure?

The vision of a tabletop x-ray laser has taken a giant step into reality, thanks to Tenio Popmintchev, Ming-Chang Chen and their colleagues in the Kapteyn/Murnane group. By focusing a femtosecond laser into a gas, Popmintchev and Chen generated many colors of x-rays at once, in a band that stretched from the extreme ultraviolet into the soft x-ray region of the electromagnetic spectrum, spanning wavelengths of ranging from about 6 to 2.5 nm. This broad x-ray band has so many different colors that all the waves can be added together to form the shortest strobe light in existence.

The secret for reducing quantum noise in a precision measurement of spins in a collection of a million atoms is simple: Pre-measure the quantum noise, then subtract it out at the end of the precision measurement. The catch is not to do anything that detects and measures the spins of individual atoms in the ensemble. If states of individual atoms are measured, then those atoms stop being in a superposition and the subsequent precision measurement will be ruined.

Fellow Jun Ye’s group has enhanced the molecular fingerprinting technique with the development of a mid-infrared (mid-IR) frequency comb.  The new rapid-detection technique can now identify traces of a wider variety of molecules found in mixtures of gases. It offers many advantages for chemical analysis of the atmosphere, climate science studies, and the detection of suspicious substances.

Atomic force microscopy (AFM) just got a whole lot more efficient for studying proteins and other biomolecules. Graduate student Allison Churnside, former research associate Gavin King, and Fellow Tom Perkins recently used a laser to detect the position of sparsely distributed biomolecules on a glass cover slip. Since the same laser is also used to locate the AFM tip, it is now possible to align the microscope tip and sample with a precision of 40 nm, before the AFM tip even touches the sample. The researchers say that the new sample detection scheme solves the “needle in a haystack” problem of nanoscale microscopy.

Before there were galaxies with black holes in their centers, there were vast reservoirs of dark matter coupled to ordinary matter, mostly hydrogen gas. These reservoirs were sprinkled with the Universe’s early stars born in pregalactic dark matter halos. But according to Fellow Mitch Begelman, another population of atypical stars formed millions of years later during the creation of galaxies. These stars grew to truly colossal sizes — a million times more massive than the Sun.

The Bohn group has just come up with an exciting, really complicated experiment for someone else to do. This is something theorists like graduate student Ryan Wilson, former research associate Shai Ronen, and Fellow John Bohn get a kick out of. In this case, they’re recommending an experiment to measure how fast a tiny blue laser would have to move through a dipolar Bose-Einstein condensate (BEC) to create ripples.

In 2008, the Deborah Jin Group introduced a new technique, known as atom photoemission spectroscopy, to study a strongly interacting ultracold gas cloud of potassium (40K) atoms at the crossover point between Bose-Einstein condensation and superfl uidity via the pairing of fermionic atoms (See JILA Light & Matter, Summer 2008). Near the crossover point, the physics of superfl uidity in an atom gas system may be connected to that of high-temperature superconductivity.

When former graduate student Mingming Feng started his thesis project, his goal was to build and characterize a mode-locked quantum dot diode laser in Kevin Silverman’s lab at the National Institute of Standards and Technology (NIST).

Senior research associate Brad Hindman of the Toomre group uses helioseismology to understand what’s happening under the surface of the Sun. Helioseismology is a lot like the ultrasound tests used to evaluate medical conditions. However, there’s a big difference: physicians already have a good idea of the basic structures they are probing with sound waves. Helioseismologists don’t. They study sound that travels below the Sun’s surface to learn about the structure and behavior of the Sun’s convection zone, which comprises the outer third of the Sun. However, if they misinterpret the nature of the sounds they analyze, then they are likely to miss the mark in determining what’s happening inside the Sun.

In microscopic studies of single biological molecules or nanoparticles, it’s useful to be able to precisely control the temperature around the sample. Until now, heating has required electric currents that warm up microscope stages, slides, and optics in addition to the specimen under study. Such methods are slow and hard to control, not to mention capable of accidentally altering the chemistry or structure of the sample. Now there is a better solution for keeping samples nice and warm: The nanobathtub.

Solvents don’t just dissolve other chemicals (called solutes) and then sit around with their hands in their pockets. Instead, they get involved in all sorts of different ways when dissolved molecules toss electrons around, i.e., they facilitate charge transfer events. In research, the hard part is fi guring out exactly how and when solvent molecules get involved when an electron hops from one solute molecule to another. For example, in liquids (which do most of the dissolving), solvent molecules move constantly, making it very challenging to see what they’re doing when charge transfer events occur.

A faint star that can easily be seen from Earth with binoculars has a Jupiter-like gas planet orbiting it once in just three days. That means the planet is close enough to its Sun-like star to get scorching hot, which affects both the planet and its atmosphere. The star is called HD209458, and its planet’s moniker is HD209458b.

A while back, Fellow Eric Cornell started thinking about all the waste heat produced by the use of water to cool refi neries and other industrial plants. In a few places, the waste hot water — at ~212°F — is used to heat commercial and apartment buildings. 

If you want to understand how chemical reactions happen, the ability to monitor dynamic positions of atoms in a molecule is critical. There's a well-known laser technique known as coherent Raman spectroscopy that uses a scattering laser pulse to set atoms vibrating and then measures the color shift of reflected light to detect vibration patterns. This technique has been used as a molecular fingerprinting device for simple motions of a molecule.

Fellows Deborah Jin, Jun Ye, and John Bohn are exploring new scientific territory in cold-molecule chemistry. Experimentalists Jin and Ye and their colleagues can now manipulate, observe, and control ultralow-temperature potassium-rubidium (KRb) molecules in their lowest quantum-mechanical state. Theorist Bohn analyzes what the experimentalists see and predicts molecule behaviors under different conditions.

The cold-molecule collaboration has developed a method for directly imaging ultracold ground-state KRb molecules. Their old method required the transfer of ultracold KRb molecules into a Feshbach state, which is sensitive to electric and magnetic fields. Thus researchers had to turn off the electric field and keep the magnetic field at a fixed value during the imaging process.

When Richard Sandberg and his colleagues in the Kapteyn/Murnane group developed a lensless x-ray microscope in 2007 (see JILA Light & Matter, Winter 2008), they were delighted with their ability to obtain a stick-figure image (below) that was comparable in resolution to one from a scanning-electron microscope.