Research Highlights

For decades after the invention of the red ruby laser in 1960, bright laser-like beams were confined to the infrared, visible, and ultraviolet region of the spectrum. Today there’s an exciting revolution afoot: new coherent x-ray beams are now practical, including the EUV beams gracing the cover of the May 1, 2015, special issue of Science honoring the International Year of Light. The same issue features an article entitled “Beyond Crystallography: Diffractive Imaging Using Coherent X-ray Light Sources” that celebrates the revolutionary advances in both large- and small-scale coherent x-ray sources that are transforming imaging in the 21st century.

The Ye group has just improved the accuracy of the world’s best optical atomic clock by another factor of three and set a new record for clock stability. The accuracy and stability of the improved strontium lattice optical clocks is now about 2 x 10-18, or the equivalent of not varying from perfect time by more than one second in 15 billion years—more than the age of the Universe. Clocks like the Ye Group optical lattice clocks are now so exquisitely precise that they may have outpaced traditional applications for timekeeping such as navigation (GPS) and communications.

The Ye Group recently investigated what first appeared to be a “bug” in an experiment and made an unexpected discovery about a new way to generate high-harmonic light using molecular gases rather than gases of noble atoms. Graduate student Craig Benko and his colleagues in the Ye group were studying the interaction of light from an extreme ultraviolet (XUV) frequency comb with molecules of nitrous oxide, or laughing gas (N₂O), when they noticed unusual perturbations in the laser spectrum.

One of the great challenges in the semiconductor and electronics industries is that as nanoscale features get smaller and processes get faster, enormous amounts of heat need to be quickly carried away from the nanostructures. The Kapteyn/Murnane group has made the counter-intuitive discovery that it is easier to cool these nanostructures when they are arranged closely together. The researchers also developed a theory to explain this unexpected new behavior.

Supermassive black holes at the center of active galaxies are known as blazars when they are extremely bright and produce powerful jets of matter and radiation visible along the line of sight to the Earth. Blazars can appear up to a thousand times more luminous than ordinary galaxies, and their associated jets are so powerful they can travel millions of light years across the Universe. Blazar jets produce flares of high-energy gamma rays that are detected by ground- and space-based observatories.

The photoelectric effect has been well known since the publication of Albert Einstein’s 1905 paper explaining that quantized particles of light can stimulate the emission of electrons from materials. The nature of this quantum mechanical effect is closely related to the question how much time it might take for an electron to leave a material such as a helium atom.

When the Rey theory group first modeled a quantum system at JILA, it investigated the interactions of strontium atoms in the Ye group’s strontium-lattice clock. The quantum behavior of these collective interactions was relatively simple to model. However, the group has now successfully tackled some more complicated systems, including the ultracold polar KRb molecule experiment run by the Jin and Ye groups.

When the Rey theory group first modeled a quantum system at JILA, it investigated the interactions of strontium atoms in the Ye group’s strontium-lattice clock. The quantum behavior of these collective interactions was relatively simple to model. However, the group has now successfully tackled some more complicated systems, including the ultracold polar KRb molecule experiment run by the Jin and Ye groups. In the process, the group has developed a new theory that will open the door to probing quantum spin behavior in real materials; atomic, molecular and optical gases; and other complex systems. The new theory promises important insights in different areas of physics, quantum information science, and biology.

Because red fluorescent proteins are important tools for cellular imaging, the Jimenez group is working to improve them to further biophysics research. The group’s quest for a better red-fluorescent protein began with a computer simulation of a protein called mCherry that fluoresces red light after laser illumination. The simulation identified a floppy (i.e., less stable) portion of the protein “barrel” enclosing the red-light emitting compound, or chromophore. The thought was that when the barrel flopped open, it would allow oxygen in to degrade the chromophore, thus destroying its ability to fluoresce.

A grand challenge of ultracold physics is figuring out how fermions become bosons. This is an important question because the tiniest quantum particles of matter are all fermions. However, these fermions can form larger chunks of matter, such as atoms and molecules, which can be either fermions or bosons.

Until recently, researchers who wanted to understand how magnetic materials work had to reserve time on a large, stadium-sized X-ray machine called a synchrotron. Synchrotrons can produce X-ray beams that can be sculpted very precisely to capture how the spins in magnetic materials work together to give us beautiful and useful magnetic properties – for example to store data in a computer hard drive. But now, thanks to Patrik Grychtol and his colleagues in the Kapteyn/Murnane group, there’s a way to conduct this kind of research in a small university laboratory.

New theory describing the spin behavior of ultracold polar molecules is opening the door to explorations of exciting, new physics in JILA’s cold molecular lab, operated by the Jin and Ye groups. According to the Rey theory group and its collaborators, ultracold dipolar molecules can do even more interesting things than swapping spins.

Dynamical phase transitions in the quantum world are wildly noisy and chaotic. They don’t look anything like the phase transitions we observe in our everyday world. In Colorado, we see phase transitions caused by temperature changes all the time: snow banks melting in the spring, water boiling on the stove, slick spots on the sidewalk after the first freeze. Quantum phase transitions happen, too, but not because of temperature changes. Instead, they occur as a kind of quantum “metamorphosis” when a system at zero temperature shifts between completely distinct forms.

A Be star is a luminous, blue B-type star with distinctive spectral lines that can provide two types of feasts (tasty snacks or full-scale banquets) for a former companion star in a binary system. The feasting begins when the companion star goes supernova and becomes a neutron star or, more rarely, a black hole. Typically, the companion blows up with enough force to kick itself into an eccentric (elliptical) orbit that is misaligned with respect to the Be star’s orbit.

Symmetries described by SU(N) group theory made it possible for physicists in the 1950s to explain how quarks combine to make protons and neutrons and JILA theorists in 2013 to model the behavior of atoms inside a laser. Now, the Ye group has observed a manifestation of SU(N≤10) symmetry in the magnetic behavior of strontium-87 (⁸⁷Sr) atoms trapped in crystals of light created by intersecting laser beams inside a quantum simulator (originally developed as an optical atomic clock).

The Raschke group recently came up with a clever way to detect folds and grain boundaries in graphene. a sheet made of a single layer of carbon atoms.Such defects stop the flow of electrons in graphene and are a big headache for engineers working on touch screens and other electronic devices made of this material.

The spooky quantum property of entanglement is set to become a powerful tool in precision measurement, thanks to researchers in the Thompson group. Entanglement means that the quantum states of something physical—two atoms, two hundred atoms, or two million atoms—interact and retain a connection, even over long distances.

Graduate student Adam Kaufman and his colleagues in the Regal and Rey groups have demonstrated a key first step in assembling quantum matter one atom at a time. Kaufman accomplished this feat by laser-cooling two atoms of rubidium (⁸⁷Rb) trapped in separate laser beam traps called optical tweezers. Then, while maintaining complete control over the atoms to be sure they were identical in every way, he moved the optical tweezers closer and closer until they were about 600 nm apart. At this distance, the trapped atoms were close enough to “tunnel” their way over to the other laser beam trap if they were so inclined.

The Ye group has not only made two invisible rulers of extreme ultraviolet (XUV) light, but also figured out how to observe them with ordinary laboratory electronics. With this setup, the researchers were able to prove that the two rulers had extraordinarily long phase-coherence time. This feat is so profound, it is nearly certain to transform the investigation of matter with extreme ultraviolet light, according to Ye’s colleagues in precision measurement and laser science. This research was reported online in Nature Photonics this week.

Imagine a network of multiple clocks orbiting the Earth, not only reporting down to us, but also collaborating quantum mechanically among themselves to operate precisely in sync as a single global superclock, or world clock. The world clock is delivering the most precise timekeeping in all of human history—to every member nation regardless of politics, alliances, or behavior on the ground. Moreover, the world clock itself is virtually immune to sabotage and can peer under the surface of the Earth to uncover its detailed composition or out into space to reveal a better understanding of fundamental physical principles such as quantum mechanics and gravity.