Faculty

In my work as a theoretical astrophysicist, I focus on problems in fluid dynamics near black holes and in protoplanetary disks. My recent work includes studies of the formation and early evolution of extrasolar planetary systems; numerical simulations of turbulence in black hole accretion flows; and investigation of the astrophysical consequences of binary black hole mergers in galactic nuclei.

My research interests center around the behavior of extremely cold atomic gases. Recent developments in laser-cooling techniques have made possible new families of experiments at microKelvin temperatures. My group investigates techniques for manipulating cold atoms and studies interactions between trapped alkali atoms at collision energies below one microKelvin. I am best known for producing a Bose-Einstein condensate in a sample of trapped atoms. Most recently I've begun a project to measure the electric dipole moment of the electron, a project designed to investigate the particle physics concept known as "supersymmetry."

Two recent documents on Solar Cooking: A Solar Fryer and an addendum

 My research interests include quantum coherence in nanoscale electrical circuits (solid-state qubits), dynamics of individual electrons in one-dimensional conductors, and ultrafast quantum-limited charge measurements. Recent advances in nanolithography and cryogenic electronics have made it possible to sense individual electrons as they move through nanometer-sized conductors. My research exploits this ability to detect the quantum superposition of macroscopically distinct states of electrical circuits and to detect the flow of single electrons through molecular wires. My current work addresses the following questions: What are the sources of decoherence in solid-state qubits? How efficiently and how quickly do electrons screen each other in nanoscale circuits? Can a sensor of charge reach quantum-limited sensitivity?

My research focuses on understanding the statistics of precision clocks and frequency standards, developing methods for distributing precise time and frequency information, and applying precision measurement techniques to problems of geophysical interest. My specific projects include developing methods for transmitting time using dial-up telephone lines, the internet, and satellite systems; investigating algorithms for authenticating time signals transmitted via public networks; and designing a statistically optimum method for distributing data from a primary frequency standard without degrading its accuracy. In addition, I continue to work to improve the accuracy and stability of Coordinated Universal Time, the time scale used as a reference by all of the NIST time and frequency services.

My research includes quantum-state-resolved laser spectroscopy and dynamics of van der Waals and hydrogen-bonded clusters, time-resolved kinetics of atmospheric radicals, crossed-beam studies of state-to-state inelastic and reactive dynamics, high-resolution laser spectroscopy of jet-cooled radicals and molecular ions, nonlinear frequency generation of narrowband tunable infrared laser sources, vibrationally mediated photochemistry in size/quantum state-selected clusters, alignment phenomena, collision dynamics of gases with thin films, and development of atomic force/scanning-tunneling methods for near-field-scanning optical microscopy (NSOM) of molecules on surfaces.

The biochemical cycle of mechanoenzymes generates a force and a displacement that can be measured at the single-molecule level. The outstanding question is how motor proteins transduce chemical energy into physical motion. To answer this question, we use optical tweezers, a focused laser beam that can manipulate micron-sized beads in solution, allowing measurement of position and force in the nanometer (nm) and piconewton (pN) ranges, respectively. Our research focuses on developing assays and precision instrumentation to measure the properties of single-DNA-based molecular motors. Typically, enzymatic motion along the DNA is measured by anchoring the enzyme to a surface and monitoring the position of an optically trapped bead attached to the DNA's distal end.

My main research interest is ultracold atoms and molecules loaded in optical lattices, which are periodic trapping potentials created by illuminating the atoms and molecules with laser beams. Atoms in optical lattices are analogous to electrons in solid state crystals. Their big advantage is that these "artificial crystals of light" are perfectly clean and highly controllable. Therefore, they are ideal for exploring a whole range of fundamental phenomena that are extremely difficult — or impossible — to study in traditional condensed matter systems. My goal is to study how to control and manipulate these systems to engineer different quantum phases such as superfluids, insulators, quantum magnets, and topological matter. I plan to use them for understanding the physics of strongly correlated bosonic and fermionic systems and nonequilibrium phenomena. Additionally, I am interested in studying how to generate and manipulate entanglement in quantum systems for use in quantum information processing and precision measurements.

Astrophysical fluid dynamics is my primary research interest, and my work currently centers on theoretical treatments for compressible convection in stars. The nonlinear theory using computational fluid dynamics is complemented by detailed observations of velocity fields on the Sun, from both ground-based and satellite instruments. My interests extend to helioseismology, in which the five-minute oscillations of the Sun are used as probes of velocity and temperature structures within the interior. My group seeks to understand the coupling of global-scale convection with rotation by using a series of experiments flown on the space shuttle. My nonlinear dynamical studies in geophysics include thermohaline convection in the oceans and stratified shear flows.