By Meng Luo
—
On July 3rd, 2016, I arrived at Haneda International Airport in Tokyo. Although this was already my third time visiting this city, I still could not help myself capturing the beauty of Tokyo Skytree with my camera before landing. This time, I was selected by the University of Tokyo and University of California, Berkeley to participate a six-week summer research program at UTokyo. As a physics major student, I could not describe how excited I was when I was informed that I could work on gravitational wave detector at UTokyo.
With LIGO’s first detection of gravitational wave earlier this year, humans can now explore the universe with not only light but also gravitational wave. Like MIT and Caltech, UTokyo also plays a main role in gravitational wave astronomy. Here at UTokyo, I was fortunate enough to have the opportunity to work on the development of novel gravitational wave detector with Prof. Masaki Ando. In Ando Lab, I was appointed to work on coil-coil actuator, which is a new type of actuator with low magnetic noise when controlling the mirror position in the gravitational wave detector. So how does it work? Currently, gravitational wave is detected by measuring the change of optical path length with a Michelson interferometer. When gravitational wave passes through the interferometer, it distorts the space thus changing the optical path length on the order of 10,000 times smaller than the size of a proton. In order to detect such tiny change in distance, the relative position of the laser-reflecting mirrors must be fixed as much as possible. 
Therefore, actuators are installed on the suspension system of the mirrors to balance the external vibrations like seismic motion, etc. Unfortunately, the coil-magnet actuators that are being used now can cause low-frequency noises in the frequency spectrum because the magnet behaves like a low-frequency dipole, which can couple to the magnetic field in the surrounding.
In order to solve this problem, Ando Lab is developing a new type of actuator, the coil-coil actuator, which can remove the low-frequency noise by driving the coil with a high-frequency current so that it won’t couple to the low-frequency background. My job was mainly testing the prototype of this new actuator with a tabletop experiment setup. Although aligning the mirrors to obtain successful locking of the test mass was very tedious and hard, I have learned so many new experiment skills like CAD design and feedback loop, etc. Additionally, the lab members in Ando Lab are all very friendly and have really made me feel at home. I was deeply moved that they held both welcome and farewell party for me. What’s more, they even invited me to visit KAGRA, the Japanese underground gravitational wave detector located in northern Honshu.
Besides the excellent academic experience, the leisure time in Japan was also very exciting. I went to two firework shows in Tokyo, the Adachi fireworks and Sumida river fireworks. Both of them were amazing and I have truly experienced the traditional summer festivals in Tokyo. Tokyo is also famous for its various kinds of museums. During my stay, I have visited the National Museum of Nature and Science, which is a perfect place to spend a day off when it is rainy. 
Additionally, while visiting the KAGRA experiment site in the northern mountain area of Honshu, I have enjoyed the beautiful scenery of nature there. Taking the Shinkansen bullet train was another unforgettable experience in Japan. All in all, I would like to thank FUTI for giving me such a great opportunity to do research in Japan. And I would definitely come back to Japan in the near future.
