A recently chosen Fulbright fellow in chemistry at the University of Houston (UH) is hoping to accomplish something no one has done before. Among other things on professor Eric Bittner’s wish list is to prepare a two-dimensional optical analog of a black hole on a laser table and study some of its properties without actually having to go to outer space to find a real one.
Bittner, who is the John and Rebecca Moores Professor of Chemical Physics at UH, was named a 2012-13 Fulbright Scholar and will be collaborating with physics professor Carlos Silva at the Universite de Montreal in Canada from January through April. Bittner says his work is 100 percent theoretical, with a good portion of his time spent writing equations on the blackboard. That’s where the teamwork comes in. Silva will be actively pursuing the experimental realization of their models.
“We are studying a quantum state visible to the naked eye that involves the strong coupling between an applied laser field and organic semiconducting material sandwiched between reflective mirrors,” Bittner said. “Such states, called polaritons, belong to a class of particles called bosons that can exhibit a quantum collective phenomena called Bose-Einstein condensation where the entire system collapses to a single quantum state where everything moves in sync.”
He likens it to a mosh pit at a rock concert. When there are only a few dancers in the pit, everyone can do their own thing and more people can be added to it without much difficulty. If more and more people are added, there is a point where everyone has to do the exact same motion – all in perfect sync – in order to pack in more people. Bittner says that is what a phase transition is like, and it happens when there are so many bosons in a given region that they have to synchronize.
“The properties of a polariton condensate are really unique and can be tuned by manipulating the cavity and the various laser fields used to create the condensate,” he said. “In one limit of the model, the condensate will have all the properties of a two-dimensional black hole. Not a real one, but a ‘pseudo black hole,’ created with photons from a laser on a lab benchtop with many analogous properties of a real black hole.”
Bittner explains that, with polaritons, these collective effects give rise to super-radiant emission that may be useful for optical and electronic devices, such as solid-state lasers, as well as perhaps being used in quantum cryptology, which has applications for computer security.
Typically, Bittner says, these phenomena occur at very low, or cryogenic, temperatures. This research will give them a chance to see these effects occurring at much higher temperatures in non-cryogenic conditions. The goal is for scientists to potentially study something like superconductivity in a much warmer device. In a recent paper, the researchers showed that warming the system leads to a lower critical threshold for condensation that, he explains, seems counterintuitive at first.
Bittner says no one, to date, has observed polariton condensation in an organic thin-film material. His team predicts it should be possible, and Silva will be working to observe this effect. The experiments, he says, are tricky to set up and require careful sample preparation and state-of-the-art laser systems. Silva, an expert in ultrafast laser spectroscopy, will be doing the experimental studies, trying to observe some of the effects Bittner’s group predicts. They say the experimental realization could be any day, and once they see the effect, it should be easier to set up new experiments.
“I’m hoping Silva’s group can create the condensate,” Bittner said. “It will be fun to be on hand to see something predicted by my theory come into being. I’m sure I’ll learn a lot about the experimental side of the work, and they’ll learn a lot of the theory.”
Initially, Silva got Bittner interested in this topic. Silva needed some theoretical guidance to create these systems in his lab and asked Bittner to collaborate. Bittner received a grant from the National Science Foundation for his part of this work two years ago.
“Before that, I had no idea what a polariton was, why they should form a condensate or even why I should spend my time studying them,” Bittner said. “It’s a major change of research direction for me. One of my colleagues, who is a leader in the field of quantum dynamics, said it was extremely brave of me to step off into a totally new field at this stage in my career. I’m happy the risk is paying off.”
Established in 1946, the Fulbright Program awards approximately 8,000 new grants annually in more than 155 countries worldwide. An international educational exchange program sponsored by the U.S. government, it is designed to increase mutual understanding between the people of the United States and other countries.
- Lisa Merkl, UH Communication