GTQI People - College of Sciences, School of Chemistry

Ken Brown
Assistant Professor

Quantum information is an exciting new field that employs quantum mechanical systems to solve problems in computation and communication. The Brown Group uses the experimental and theoretical techniques of quantum information to address challenges in physical chemistry. The basis of our experimental work is a collection of laser cooled ions trapped in a quadrupole ion trap. The theoretical work focuses on understanding the boundary between classical and quantum algorithms for calculating material properties.

Quantum Simulations of Molecules and Materials:
Many materials exhibit magnetic frustration and have low temperature phase diagrams that are often dominated by quantum effects. The Brown Group will examine these quantum effects by building a quantum simulator composed of trapped atomic ions. A quantum simulator will be exponentially more efficient than a classical simulation, making it possible to rapidly calculate the quantum mechanical properties of magnetic materials, superconductors, and molecules.

Cold Molecular Ions:
The reaction dynamics of molecules at millikelvin temperatures exhibit interesting quantum mechanical effects that are typically hidden by thermal averaging. However, preparing molecules at millikelvin temperatures and then accurately measuring reaction products has been a long-standing challenge for physical chemists. The Brown Group is developing a technique that uses atomic ions to cool and measure molecular ions. This technique will allow for the detection of weak molecular transitions by atomic fluorescence which will be useful for fundamental studies of chemical reactions.
Rob Dickson

Dr. Dickson's group is developing novel single molecule methods for the study of intermolecular interactions in biological and materials systems. By directly imaging anisotropic dipolar single molecule emission and modeling expected emission patterns, we have developed the world's only methods for determining true 3-D single molecule orientations. Since each molecule interacts differently with its surroundings, great diversity is observed in molecular behaviors. For example, single molecules in polymeric matrices exhibit surprising rotational mobilities that are indicative of nanoscale polymer dynamics. Such molecular orientational studies directly probe both biological and materials systems to provide greatly enhanced understandings of their dynamics.

Single Molecule Biophysics
Having observed orientation-dependent interactions of fluorescently labeled, single proteins, precise studies of biological mechanisms are performed. Unfortunately, standard fluorescent labels are often unsuitable for long-time single molecule imaging, especially in living systems. Thus, in order to make single molecule methods more accessible, we are developing Au and Ag nanoclusters as a new class of fluorescent labels in biology. These high brightness, robust nanomaterials should enable direct labeling of proteins to image live cells, study protein-protein interactions, and potentially watch individual proteins as they fold to their native conformations. Au and Ag nanoclusters exhibit discrete excitation and emission due to being composed of only a few atoms. Consequently, with size-tunable optical properties and absoprtion comparable to semiconductor quantum dots, but with improved photostability, these nanoclusters offer new opportunities in biological labeling. For example, the extremely small size will be less invasive; noble metals are not toxic; and their discrete energy levels enable energy transfer experiments to be performed—all with weak mercury lamp illumination on the single molecule level. Much brighter and more robust than organic dye molecules, these advanced inorganic nano-materials are being utilized both as optical memory elements and as photo-activated biological labels.

Molecules in Polymeric Environments
Single molecules in polymeric matrices exhibit surprising rotational mobility and spectral dynamics. Since each molecule interacts slightly differently with its surroundings, great diversity is observed in molecular behaviors. Photophysical properties of individual dyes are used to probe both random and enclosed structures to provide a better understanding of polymeric systems.

Single Molecule Electroluminescence
We have created the first electroluminescent single molecules/nanoclusters at room temperature. The discrete energy levels of these 2-20 atom nanoclusters yield molecular emission with color being indicative of nanocluter size. Employing negative differential resistance-like behavior in the EL, we have created single molecule LEDs, single nanocluster logic gates, and even a full adder constructed from only two nanoclusters. We are currently studying the charge injection into different nanoclusters to characterize the interfaces crucial to all nanoscale/molecular electronics and optoelectonics devices.