Home > Press > UCSB Researchers Demonstrate That 15=3x5 About Half of the Time

The device used to run the first solid state demonstration of Shor's algorithm. It is made up of four phase qubits and five superconducting resonators, for a total of nine engineered quantum elements. The quantum processor measures onequarter inch square. 
Abstract:
Computing prime factors may sound like an elementary math problem, but try it with a large number, say one that contains more than 600 digits, and the task becomes enormously challenging and impossibly timeconsuming. Now, a group of researchers at UC Santa Barbara 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.
UCSB Researchers Demonstrate That 15=3x5 About Half of the Time
Santa Barbara, CA  Posted on August 20th, 2012
Although modest compared to a 600digit number, the achievement 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.
"Fifteen is a small number, but what's important is we've shown that we can run a version of Peter Shor's prime factoring algorithm on a solid state quantum processor. This is really exciting and has never been done before," said Erik Lucero, the paper's lead author. Now a postdoctoral researcher in experimental quantum computing at IBM, Lucero was a doctoral student in physics at UCSB when the research was conducted and the paper was written.
"What is important is that the concepts used in factoring this small number remain the same when factoring much larger numbers," said Andrew Cleland, a professor of physics at UCSB and a collaborator on the experiment. "We just need to scale up the size of this processor to something much larger. This won't be easy, but the path forward is clear."
Practical applications motivated the research, according to Lucero, who explained that factoring very large numbers is at the heart of cybersecurity protocols, such as the most common form of encoding, known as RSA encryption. "Anytime you send a secure transmission  like your credit card information  you are relying on security that is based on the fact that it's really hard to find the prime factors of large numbers," he said. Using a classical computer and the bestknown classical algorithm, factoring something like RSA Laboratory's largest published number  which contains over 600 decimal digits  would take longer than the age of the universe, he continued.
A quantum computer could reduce this wait time to a few tens of minutes. "A quantum computer can solve this problem faster than a classical computer by about 15 orders of magnitude," said Lucero. "This has widespread effect. A quantum computer will be a game changer in a lot of ways, and certainly with respect to computer security."
So, if quantum computing makes RSA encryption no longer secure, what will replace it? The answer, Lucero said, is quantum cryptography. "It's not only harder to break, but it allows you to know if someone has been eavesdropping, or listening in on your transmission. Imagine someone wiretapping your phone, but now, every time that person tries to listen in on your conversation, the audio gets jumbled. With quantum cryptography, if someone tries to extract information, it changes the system, and both the transmitter and the receiver are aware of it."
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 purposebuilt 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 quantum processor was implemented using a quantum circuit composed of four superconducting phase qubits  the quantum equivalents of transistors  and five microwave resonators. The complexity of operating these nine quantum elements required building a control system that allows for precise operation and a significant degree of automation  a prototype that will facilitate scaling up to larger and more complex circuits. The research represents a significant step toward a scalable quantum architecture while meeting a benchmark for quantum computation, as well as having historical relevance for quantum information and cryptography.
"After repeating the experiment 150,000 times, we showed that our quantum processor got the right answer just under half the time" Lucero said. "The best we can expect from Shor's algorithm is to get the right answer exactly 50 percent of the time, so our results were essentially what we'd expect theoretically."
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.
Other UCSB researchers participating in the study include John Martinis, professor of physics; Rami Barends, Yu Chen, Matteo Mariantoni, and Y. Yin, postdoctoral fellows in physics; and physics graduate students Julian Kelly, Anthony Megrant, Peter O'Malley, Daniel Sank, Amit Vainsencher, Jim Wenner, and Ted White.
####
For more information, please click here
Contacts:
Andrea Estrada
(805) 8934620
George Foulsham
(805) 8933071
Copyright © University of California  Santa Barbara
If you have a comment, please
Contact us.
Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.
Bookmark:
Superconductivity
A first glimpse inside a macroscopic quantum state March 28th, 2015
News and information
A first glimpse inside a macroscopic quantum state March 28th, 2015
DFG to Establish One Clinical Research Unit and Five Research Units: New Projects to Investigate Complications in Pregnancy, Particle Physics, Nanoparticles, Implants and Transport Planning / Approximately 13 Million Euros in Funding for an Initial ThreeYear Period March 28th, 2015
Chemists make new siliconbased nanomaterials March 27th, 2015
UT Dallas engineers twist nanofibers to create structures tougher than bulletproof vests March 27th, 2015
Quantum Computing
A first glimpse inside a macroscopic quantum state March 28th, 2015
Quantum compute this  WSU mathematicians build code to take on toughest of cyber attacks: Revamped knapsack code offers online security for the future March 26th, 2015
Building shape inspires new material discovery March 24th, 2015
Quantum cause and effect March 23rd, 2015
Discoveries
A first glimpse inside a macroscopic quantum state March 28th, 2015
UT Dallas engineers twist nanofibers to create structures tougher than bulletproof vests March 27th, 2015
Novel nanoparticle therapy promotes wound healing March 27th, 2015
Designer's toolkit for dynamic DNA nanomachines: Armwaving nanorobot signals new flexibility in DNA origami March 27th, 2015
Announcements
A first glimpse inside a macroscopic quantum state March 28th, 2015
DFG to Establish One Clinical Research Unit and Five Research Units: New Projects to Investigate Complications in Pregnancy, Particle Physics, Nanoparticles, Implants and Transport Planning / Approximately 13 Million Euros in Funding for an Initial ThreeYear Period March 28th, 2015
Designer's toolkit for dynamic DNA nanomachines: Armwaving nanorobot signals new flexibility in DNA origami March 27th, 2015
Using magnetic fields to understand hightemperature superconductivity: Los Alamos explores experimental path to potential 'next theory of superconductivity' March 27th, 2015