NSE - Nuclear Science & Engineering at MIT


Guoqing Wang : Exploring quantum phenomena through an engineering perspective

Male postdoc, Guoqing Wang, in lab leaning on his right arm; green laser instrumentation set-up in the foreground to the left and wires hanging above, MIT

Guoqing Wang loves to play the erhu, a Chinese stringed musical instrument, remembering lessons he learned from his father as a young boy. He sees similarities between the music from the bowed instrument and the research subject he works on today: quantum systems.

“When playing music, you play different tones. If these tones are harmonic with each other, it sounds very nice, but if there is some noise, it sounds very bad. A song has some harmonic constellations of each tone, and you want to tune it in a beautiful way and eliminate any possible noises.” says Wang, “tuning an instrument is pretty similar to the concept of quantum control. By applying echo to the quantum system, you can achieve better coherence.”

And better coherence is a good thing in quantum applications because it leads to more stable and longer-lived quantum systems for a variety of applications, including computing.

Growing up in China

As a postdoctoral scholar with MIT Physics professor Vladan Vuletić, Wang obtained his doctoral degree from MIT-NSE under the advisement of Professor Paola Cappellaro. It has been a long journey from growing up in the Shanxi province in central China.

Wang remembers tinkering with discarded objects as a boy and even recreating simple physics experiments he learned at school. “I tried verifying the Lorentz force using just a battery and wires at home,” Wang says.

In high school, Wang drew attention by performing well in math and physics competitions. The president of his high school recommended Wang for further studies in Peking University where he cemented his love for physics.

From coursework to research training, the prescribed course of studies was systematic and, for Wang, eye-opening. From his sophomore year on, Wang joined a research lab studying condensed matter physics. And in the summer of his junior year, Wang traveled to the University of California, Berkeley, to conduct research on quantum sensing. “Those experiences gave me the chance to know what’s on the frontiers of physics in the world,” Wang says.

And what he saw on the frontiers of physics led Wang to pursue studies in quantum information science. Quantum mechanics was discovered more than a century ago but the field has been seeing surging interest in recent years, Wang says. Fueled by his fascination with both fundamental physics and cutting-edge applications, Wang decided to pursue quantum information science. “So on the one hand, it can be used to test and study the fundamental principles of quantum mechanics. On the other hand, as deeper understanding is developed, we can engineer more flexible interactions and develop more powerful platforms to really realize transformative applications including computation, simulation, sensing, and communications,” Wang says.

Doctoral and postdoctoral studies

After his undergraduate education, Wang decided he would do his part to change the world with an advanced degree from his dream school, MIT. “It goes without saying that MIT is one of the best universities, especially for quantum information science,” he says. The collaboration and learning opportunities (such as seminars by world experts) at MIT, are inspirational, Wang adds.

Under Cappellaro, Wang focused on solid-state spin defects. His doctoral research aimed to deepen the understanding of the quantum system and to “really push the quantum application and improve their performance,” Wang says.

One of Wang’s research areas focused on advancing control techniques to improve quantum systems’ performance by focusing on parameters such as coherence time. A longer coherence time is necessary to conduct more computations. Unfortunately, coherence is an extremely fragile entity. In quantum sensing, for example, a lot of sensors operating together shortens coherence time. But Wang overcame this problem by developing an “unbalanced echo” technique that refocused variations and noise much like noise-canceling headphones apply an opposite signal to cancel out unwanted noise. The technique helped Wang improve coherence by a factor of 20.

A qubit, or quantum bit, is the elementary building block of quantum computers and other quantum systems. Studying their interactions is key to advancing the understanding of quantum physics and realizing practical quantum applications. Wang also studied the interactions among different types of spins in quantum systems by engineering local and multi-qubit interactions.

In his postdoctoral research under Vuletić, Wang extends his focus to atom arrays, one of the most promising platforms for quantum computation and simulation. Together with his colleagues, Wang is building a new-generation atom array system coupled to an optical cavity — a few mirrors that can trap light in a small volume to bring about strong light-matter interactions. The system enables the remote interaction of atomic qubits and efficient generation of quantum entanglement, a phenomenon where qubits are correlated regardless of the distance between them, a key ingredient that can make many quantum applications possible. Optical cavities can also be used for connecting different quantum modules, which is important for building large-scale quantum processors in the future, Wang says.

Life outside quantum at MIT

In his graduate student dorm, Wang serves as a cultural exchange officer and hall councilor, organizing cultural exchange events such as dinners and movie-watching sessions, which offer students a chance to unwind and relax.

Wang is the vice president of MIT’s Interdisciplinary Quantum Information Science and Engineering (iQuISE) program, in which he organizes seminars in quantum information science and helps build the cross-departmental quantum community. “I hope to use this opportunity to promote communication and collaboration both among the researchers within MIT and also between MIT and other renowned academic scholars in the field around the world,” he says.

Wang would like to continue a career in academia. The many challenges common in scientific research have shaped his life view and Wang is now used to the rollercoaster rhythms of challenges and the joy of problem-solving. “After a lot of these trials, I have started to understand ‘no pain, no gain.’ So if the results are not so satisfactory, you just continue to try,” Wang says, “when you are really enjoying the process, there will usually be unexpected rewards.”

Written by Poornima Apte. Photo by Gretchen Ertl.

February 2024