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Very rubin observatory, Credit: Rubin Obs/NSF/AURA

At Xanadu did Chen and Liu a Quantum Cup receive

Two Perimeter students were part of the winning team at a national quantum coding contest.

Two Perimeter PhD students were part of the winning team at the 2023 Canadian Quantum Cup, a quantum programming competition sponsored by Toronto-based company Xanadu. Yushao Chen and Shuwei Liu, along with teammates Nan Song and Chuan Liu from the University of Waterloo, outperformed 14 other teams from across the country, in a packed, three-day, multi-challenge race.

Each challenge required teams to code using Xanadu’s quantum programming library, PennyLane, to solve a problem. Though the six challenges were worded to sound like fun – “Design an experiment to make a zombie cat” or “Create a circuit that determines whether quantum states have as many mountains as we think they do” – pulling out a win took everything the team had. 


“The first day, we were pretty confident,” said Liu. “We were the first team to complete all three challenges.” 

With half the teams eliminated for day two, the challenges grew much more difficult. 

“The second day’s problems were the hardest,” said Chen. “We almost gave up.”

The team had to create a quantum simulation of a classical “subtractor,” capable of accurately performing arithmetic subtractions. This challenge illustrates the capability differences between quantum and classical computers. Quantum computers can do some jobs in a fraction of a second that would take classical computers thousands of years. But something as simple as coding a quantum computer to subtract five from seven created huge headaches.

“We spent maybe 10 hours on the problem. We had to use quantum gates to simulate a traditional circuit board,” said Chen. “It was pretty interesting, seeing if it was possible for quantum computers to mimic these classical structures.”

Xanadu provided teams with prep challenges in advance of the contest, but every problem required competitors to develop a completely original approach. 

“At Xanadu, we want to help upskill the quantum workforce of the future. The Canadian Quantum Cup motivated students to learn about quantum programming in a fun way,” said Catalina Albornoz, Quantum Community Manager at Xanadu.

“Most of the effort comes in figuring out how to solve the problem. I would say coding the solution was pretty fun once we thought of the correct way to attack the program,” said Chen. 

While teams’ coding solutions had to work efficiently to be accepted, the Cup was primarily a race to see who could complete the challenges fastest. At the end of three days, the Perimeter-Waterloo team had the best times, thanks in part to their combined expertise in theoretical physics and computer science.

Participating in such a competition is primarily its own reward, but Xanadu also paid for the winning team to visit their offices in January 2024 to meet with the company’s employees from different teams, tour their cutting-edge facilities, and receive the Quantum Cup trophy.

“The visit to Xanadu gave a unique opportunity to the winning students from Perimeter and the University of Waterloo to meet experts in the field and learn from them,” said Albornoz.

About PI

Perimeter Institute is the world’s largest research hub devoted to theoretical physics. The independent Institute was founded in 1999 to foster breakthroughs in the fundamental understanding of our universe, from the smallest particles to the entire cosmos. Research at Perimeter is motivated by the understanding that fundamental science advances human knowledge and catalyzes innovation, and that today’s theoretical physics is tomorrow’s technology. Located in the Region of Waterloo, the not-for-profit Institute is a unique public-private endeavour, including the Governments of Ontario and Canada, that enables cutting-edge research, trains the next generation of scientific pioneers, and shares the power of physics through award-winning educational outreach and public engagement. 

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