Scientist talks nanodevices

Researchers at the Yale School of Engineering & Applied Science have made a key discovery in the field of quantum optomechanics, the study of the relationship between light and matter. Led by electrical engineering social research scientist Xiankai Sun, the team designed photonic nanodevices capable of storing large amounts of energy as light. Sun and his co-authors -— engineering and physics professor Hong Tang, electrical engineering postdoctoral scholar Carsten Schuck and Xufeng Zhang GRD ’16 — published a paper on their research in the March 13 issue of the journal “Scientific Reports.” Sun, who is the paper’s lead author, fielded a few questions about the team’s research methods and the importance of the findings Sunday afternoon.

Q: What led your research group to this set of experiments?

A: Our group studies optomechanics — the interaction between light and mechanical vibrations. We designed optomechanical devices to study the relationship between light and mechanical vibration in a tiny region. We reduced the device geometry in this case to have a more localized region. Generally, the free carriers in silicon vibrate, generating heat. The vibration excites electrons, which causes light to lose its intensity. We wanted to design a method that reduces this loss of light intensity.

Q: What did you do to maintain and improve the intensity of light?

A: We immersed the device in superfluid helium, which has low viscosity and density. It has a gas-like refractive index and will not reduce vibration. The thermal conductivity of this helium is the highest of any substance ever known in the world. Below two Kelvin, the free carriers are “frozen” and do not reduce light intensity. This hence allows you to increase interaction between light and mechanics, but at the same time not kill mechanical properties. We also found that the cavity photon number is 40,000 — an order of magnitude above the previous finding for this number.

Q: What are the implications and applications of your findings?

A: Silicon nanocavities are used in telecommunications, laser systems, biochemical sensors and in quantum electrodynamics. All these devices need a strong interaction between light and matter. We want to be able to have enough intensity with even a small amount of light. We did this experiment to improve the Optical Quality Factor. The final goal is not just to enhance OQF, but also to increase the optical intensity in devices to get a stronger interaction between light and subjects.

Q: What organizations helped you in preparing and researching for this project?

A: We had been motivated by the relationship between light and mechanics and wanted to reduce the size of the region under investigation. We received funding from the Defense Advanced Research Projects Agency for this purpose. Yale’s School of Engineering and Applied Science has a clean room that provides the environment to produce the devices involved in the research. Since the devices are toxic, the clean room helps to keep you healthy while in contact with these substances. In terms of fabrication [of devices], Yale is one of the best in the world.