Ph.D. candidate Petr Steindl creates complex structures of light using single photons. As a teenager, he wanted to study Czech poetry but decided on quantum physics. "Looking back, I am glad I switched fields," he says. On July 5, he will defend his thesis on quantum optics and quantum dot systems.
"Simply speaking, a quantum dot is a little island of semiconducting material," Steindl says. "Because it is only a few nanometers in size it feels quantum effects, just like an atom." The researcher places this quantum dot in an optical microcavity to manipulate it more efficiently.
"You can imagine this cavity as two mirrors facing each other. Laser light bounces back and forth between them. The quantum dot does not like interacting with light, but the optical cavity makes it more likely because the laser passes the dot many times."
This ingenious device can be used to create single photons, Steindl explains. "The resonant laser excites an electron in the quantum dot from its ground energy state to a higher one. When it falls back to the ground state, the quantum dot emits a single photon. The microcavity conveniently directs this photon toward the rest of our setup. The challenge, however, is to separate this photon from the laser light. It has the same wavelength as the laser but a slightly different polarization. You can exploit that property to isolate the photon. During my Ph.D., I explored and improved this technique."
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