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Graduate Student Solves Quantum Verification Problem


Urmila Mahadev giving a computer science seminar last week at the University of California, Berkeley.

University of California, Berkeley, graduate student Urmila Mahadev has spent years working to answer a very basic regarding quantum computing: If you ask a quantum computer to perform a computation for you, how can you know whether it has really followed your instructions, or done anything quantum at all?

Credit: Jana Aenbrennerov

In the spring of 2017, Urmila Mahadev found herself in what most graduate students would consider a pretty sweet position. She had just solved a major problem in quantum computation, the study of computers that derive their power from the strange laws of quantum physics. Combined with her earlier papers, Mahadev's new result, on what is called blind computation, made it "clear she was a rising star," said Scott Aaronson, a computer scientist at the University of Texas, Austin.

Mahadev, who was 28 at the time, was already in her seventh year of graduate school at the University of California, Berkeley — long past the stage when most students become impatient to graduate. Now, finally, she had the makings of a "very beautiful Ph.D. dissertation," said Umesh Vazirani, her doctoral adviser at Berkeley.

But Mahadev did not graduate that year. She didn't even consider graduating. She wasn't finished.

For more than five years, she'd had a different research problem in her sights, one that Aaronson called "one of the most basic questions you can ask in quantum computation." Namely: If you ask a quantum computer to perform a computation for you, how can you know whether it has really followed your instructions, or even done anything quantum at all?

This question may soon be far from academic. Before too many years have elapsed, researchers hope, quantum computers may be able to offer exponential speedups on a host of problems, from modeling the behavior around a black hole to simulating how a large protein folds up.

 

From Quanta Magazine
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