The National Science Foundation has named Rensselaer Polytechnic Institute physicist Esther Wertz the winner of its CAREER award to support her investigation of nanometer-scale metal structures that will control light at the quantum limit. “I’m interested in understanding how quantum states, either single photons or qubits, interact with components of what, in the future, might be a photonic quantum circuit,” Wertz said. “My work is aimed at manipulating quantum states without destroying superposition.” A photon can be held in a device known as an optical cavity, and Wertz is interested in exploring a type of optical cavity that relies on plasmonic nanoparticles or “plasmons,” quasiparticles arising from the collective motion of electrons on the surface of metal. Physicist Esther Wertz. Courtesy of Rensselaer Polytechnic Institute. “Plasmonic nanoparticles can confine light to very small volumes, smaller than the diffraction limit of light,” Wertz said. “Because the plasmons can confine the field to much smaller volumes than other cavities, you can get very strong interactions between light and matter within them.” Inside the plasmonic cavity, Wertz places an emitter made of a material capable of absorbing a single photon. Under calculated conditions the photon can be alternately absorbed and re-emitted. This reversible exchange of energy gives rise to a half-light half-matter particle called a polariton, which is what allows the photon transistor to work. To understand how the structure of the cavity and the position of the emitter influence the efficiency of the emitter’s output, Wertz will use plasmonic optical trapping to create a cavity into which she can place and remove the emitter within the gap. She will then use an imaging technique of single-molecule superresolution combined with fluorescence lifetime imaging to investigate the physics of the emitter and the nanocavity. “Winning a CAREER award is an honor that recognizes both a researcher’s vision and her ability to realize that vision,” said Curt Breneman, dean of the School of Science. “Esther’s work involves a systematic approach to controlling photons that is certain to advance the frontier of photonic quantum transistor research. We congratulate her and are proud to have her as a colleague.”