Quantum physicist Petr Steindl is good at using single photons to create complex light structures, exploring the possibilities of quantum optics and its applications in technology. As a teenager, he wanted to study Czech poetry, but ultimately decided to study quantum physics. Recently, he defended his thesis on quantum optics and quantum dot systems, earning his PhD. "Looking back, I'm glad I switched fields."
"Simply put, a quantum dot is an island of semiconductor material," Steindl explains of the topic of his paper. "Because it's only a few nanometers in size, it can feel quantum effects, just like an atom. The researchers placed the quantum dot in an optical microcavity to manipulate it more efficiently. We can think of the cavity as two opposing mirrors. The laser light bounces back and forth between them. Quantum dots don't like to interact with light, but the optical cavity makes it more likely to interact with light because the laser light passes through the quantum dot multiple times."
Steindl explains that this clever device can be used to create single photons. "The resonant laser excites the electrons in the quantum dot from the ground state to a higher energy state. When the electron returns to the ground state, the quantum dot emits a single photon. The microcavity conveniently directs this photon to the rest of our device. The challenge, however, was how to separate this photon from the laser. It has the same wavelength as the laser, but has a slightly different polarization. You can use this property to separate the photon. I explored and refined this technique during my PhD."
Obtaining single photons is only the first step in research. "When you have high-quality single photons (particles of light), it's a bit like bricks," he said of his work. "With bricks, you can start building a house. My goal is to combine individual photons to build complex light structures. For example, we created a chain of multiple entangled photons. Entangled means that they are so closely connected that you can no longer describe one photon independently of another. We want to better understand these new light states."
single photon physics
Single-photon physics is a relatively new field. In the 1970s, physicists successfully isolated a photon for the first time. However, the efficiency and stability of these single-photon sources are not yet high. Developments in technology, such as the use of quantum dots in optical microcavities, have made it easier to control the generation of single photons. Another benefit of microcavities is that the photons are emitted at a higher speed, ensuring that they maintain their state better. This produces high-quality single photons, ideal for the structures studied by Steindl.
Steindl's vision is to eventually use these new light structures for quantum communications: "We know that single photons are very useful in terms of security and authentication. For example, you can send two identical single photons from different positions in a spectroscope. If the photons arrive in a changed state or at different times, you know there is an eavesdropper. This research may also prove useful in building quantum computers. One basic component is a quantum gate, but it They are very difficult to make. With the structures in this study, there is no need for that. I find it completely amazing that we can understand physics at such a deep level. Although it is fascinating, the potential for quantum applications is probably a big step for me, but it is enough to keep me excited for several years."