Former graduate student Erik Lucero and others take quantum computing to a new level

A group of UCSB faculty, researchers, postdocs and graduate students including  Erik Lucero, Rami Barends, Yu Chen, Matteo Mariantoni, Y. Yin, Julian Kelly, Anthony Megrant, Peter O'Malley, Daniel Sank, Amit Vainsencher, Jim Wenner, Ted White, Andrew Cleland and John Martinis has designed and fabricated a quantum processor capable of factoring a composite number –– in this case the number 15 –– into its constituent prime factors, 3 and 5.

Although what seems on the surface to be a modest achievement, this represents a milestone on the road map to building a quantum computer capable of factoring much larger numbers, with significant implications for cryptography and cybersecurity. The results are published in the advance online issue of the journal Nature Physics.

To conduct the research, Lucero and his colleagues designed and fabricated a quantum processor to map the problem of factoring the number 15 onto a purpose-built superconducting quantum circuit. "We chose the number 15 because it is the smallest composite number that satisfies the conditions appropriate to test Shor's algorithm –– it is a product of two prime numbers, and it's not even," he explained.

The next step, according to Lucero, is to increase the quantum coherence times and go from nine quantum elements to hundreds, then thousands, and on to millions. "Now that we know 15=3x5, we can start thinking about how to factor larger –– dare I say –– more practical numbers," he said.

Erik Lucero