Research Highlights

For a long time, there’s been a mystery concerning how tiny interactions between individual atoms could lead to really big changes in a whole cloud of independent-minded particles. The reason this behavior is mysterious is that the atoms interact weakly, and only when they are very close to each other. Yet, the atoms clear across the cloud seem to know when it’s time to participate in some big-deal quantum behavior such as simultaneously all changing the direction of their spins.

Far-red fluorescent light emitted from proteins could one day illuminate the inner workings of life. But before that happens, scientists like Fellow Ralph Jimenez must figure out how fluorescent proteins’ light-emitting structures work. As part of this effort, Jimenez wants to answer a simple question: How do we design red fluorescent proteins to emit longer-wavelength, or redder, light?

Using frequency comb spectroscopy, the Ye group has directly observed transient intermediate steps in a chemical reaction that plays a key role in combustion, atmospheric chemistry, and chemistry in the interstellar medium. The group was able to make this first-ever measurement because frequency combs generate a wide range of laser wavelengths in ultrafast pulses. These pulses made it possible for the researchers to “see” every step in the chemical reaction of OH + CO → HOCO → CO2 + H.

Exciting new theory from the Rey group reveals the profound effects of electron interactions on the flow of electric currents in metals. Controlling currents of strongly interacting electrons is critical to the development of tomorrow’s advanced microelectronics systems, including spintronics devices that will process data faster, use less power than today’s technology, and operate in conditions where quantum effects predominate.

The Nesbitt group has invented a nifty technique for exploring the physics and chemistry of a gas interacting with molecules on the surface of a liquid. The group originally envisioned the technique because it’s impossible to overestimate the importance of understanding surface chemistry. For instance, ozone depletion in the atmosphere occurs because of chemical reactions of hydrochloric acid on the surface of ice crystals and aerosols in the upper atmosphere. Interstellar chemistry takes place on the surface of tiny grains of dust.

Graduate student Greg Salvesen, JILA Collaborator Jake Simon (Southwest Research Institute), and Fellows Phil Armitage and Mitch Begelman decided they wanted to figure out why swirling disks of gas (accretion disks) around black holes often appear strongly magnetized. They also wanted to figure out the mechanism that allowed this magnetization to persist over time.

Fellow Mitch Begelman’s new theory says it’s possible to form stars while a supermassive black hole consumes massive amounts of stellar debris and other interstellar matter. What’s more, there’s evidence that this is exactly what happened around the black hole at the center of the Milky Way some 4–6 million years ago, according to Associate Fellow Ann-Marie Madigan.

Newly minted Ph.D. Ming-Guang Hu and his colleagues in the Jin and Cornell groups recently investigated immersing an impurity in a quantum bath consisting of a Bose-Einstein condensate, or BEC. The researchers expected the strong impurity-boson interactions to “dress” the impurity, i.e., cause it to get bigger and heavier. In the experiment, dressing the impurity resulted in it becoming a quasi particle called a Bose polaron.

Physics education researchers from the University of Colorado Boulder and the University of Maine recently showed that students troubleshooting a malfunctioning electric circuit successfully tackled the problem by using models of how the circuit ought to work. The researchers confirmed this approach by analyzing videotapes of eight pairs of students talking aloud about their efforts to diagnose and repair a malfunctioning electric circuit. The circuits had not just one, but two problems. Both problems had to be corrected for the circuit to work properly.

Fellow Phil Armitage and group collaborator Jacob Simon of the Southwest Research Institute are leading work to answer a central question about planet formation: How do pea- and pebble-sized objects orbiting within a protoplanetary disk evolve into asteroid-sized objects tens to hundreds of kilometers in size? This is an important question to answer because the eventual formation of planets around a star is mainly governed by the gravitational interactions of these primordial asteroids.

The Raschke group has created an ultrafast optical nanoscope based on a unique way of “nano” focusing the light to image the behavior of electrons on a thin gold film. The nanoscope is 1,000 times more powerful than conventional optical microscopes. It allows the researchers to investigate matter on its natural time and length scales, which are measured in femtoseconds and nanometers, respectively. This new technique may find application to studies of photosynthesis, solar cells, energy conversion and use, and other phenomena based on the transfer of electrons from molecule to molecule.

Bob Peterson and his colleagues in the Lehnert-Regal lab recently set out to try something that had never been done before: use laser cooling to systematically reduce the temperature of a tiny drum made of silicon nitride as low as allowed by the laws of quantum mechanics. Although laser cooling has become commonplace for atoms, researchers have only recently used lasers to cool tiny silicon nitride drums, stretched over a silicon frame, to their quantum ground state. Peterson and his team decided to see just how cold their drum could get via laser cooling.

Fellow Judah Levine recently presented a discussion of our understanding of time from antiquity to the present day in an insightful paper published in the April 2016 issue of the European Physical Journal H.

The Kapteyn/Murnane group has measured how long it takes an electron born into an excited state inside a piece of nickel to escape from its birthplace. The electron’s escape is related to the structure of the metal. The escape is the fastest material process that has been measured before in the laboratory––on a time scale of a few hundred attoseconds, or 10^-18 s. This groundbreaking experiment was reported online in Scienceon June 2, 2016. Also in Science on July 1, 2016, Uwe Bovensiepen and Manuel Ligges offered important insights into the unusual significance of this work. 

The Ye group just solved a major problem for using molecular fingerprinting techniques to identify large, complex molecules: The researchers used an infrared (IR) frequency comb laser to identify four different large or complicated molecules. The IR laser-light absorption technique worked well for the first time with these larger molecules because the group combined it with buffer gas cooling, which precooled their samples to just a few degrees above absolute zero. 

Move over, single-atom laser cooling! The Holland theory group has just come up with a stunning idea for a new kind of laser cooling for use with ensembles of atoms that all “talk” to each other. In other words, the theory looks at laser cooling not from the perspective of cooling a single atom, but rather from the perspective of many atoms working together to rapidly cool themselves to a miniscule fraction of a degree above absolute zero.

The old JILA molecule factory (built in 2002) produced the world’s first ultracold polar molecules [potassium-rubidium (KRb)] in 2008. The old factory has been used since then for ultracold chemistry investigations and studies of the quantum behavior of ultracold molecules and the atoms that form them. The Jin-Ye group, which runs the molecule factory, is now wrapping up operations in the old factory with experiments designed to improve operations in the ultramodern factory, which is close to completion.

The Ye and Rey groups have discovered the strange rules of quantum baseball in which strontium (Sr) atoms are the players, and photons of light are the balls. The balls control the players by not only getting the atoms excited, but also working together. The players coordinate throwing and catching the balls. While this is going on, the balls can change the state of the players! Sometimes the balls even escape the quantum baseball game altogether and land on detectors in the laboratory.

Cong Chen and his colleagues in the Kapteyn/Murnane group have generated one of the most complex coherent light fields ever produced using attosecond (10-18 s) pulses of circularly polarized extreme ultraviolet (EUV) light. (The circularly polarized EUV light is shown as rotating blue sphere on the left of the picture. The complex coherent light field is illustrated with the teal, lilac, and purple structures along the driving laser beam (wide red line).

The Rey and Ye groups are in the midst of an extended collaboration on using the Ye group’s strontium (Sr) lattice clock for studies of spin-orbit coupling in pancake-like layers of cold Sr atoms. Spin-orbit coupling means an atom’s motion is correlated with its spin. It occurs in everyday materials when negatively charged electrons move in response to electromagnetic fields inside a crystal.