Featured Research

from universities, journals, and other organizations

Quantum Computer Solves Problem, Without Running

Date:
February 23, 2006
Source:
University of Illinois at Urbana-Champaign
Summary:
By combining quantum computation and quantum interrogation, scientists at the University of Illinois at Urbana-Champaign have found an exotic way of determining an answer to an algorithm -- without ever running the algorithm. Using an optical-based quantum computer, a research team led by physicist Paul Kwiat has presented the first demonstration of "counterfactual computation," inferring information about an answer, even though the computer did not run.

Paul Kwiat, right, a John Bardeen Professor of Electrical and Computer Enginering and Physics, and graduate student Onur Hosten have found an exotic way of determining an answer to an algorithm €“ without ever running the algorithm.
Credit: Photo by L. Brian Stauffer

By combining quantum computation and quantum interrogation, scientists at the University of Illinois at Urbana-Champaign have found an exotic way of determining an answer to an algorithm -- without ever running the algorithm.

Using an optical-based quantum computer, a research team led by physicist Paul Kwiat has presented the first demonstration of "counterfactual computation," inferring information about an answer, even though the computer did not run. The researchers report their work in the Feb. 23 issue of Nature.

Quantum computers have the potential for solving certain types of problems much faster than classical computers. Speed and efficiency are gained because quantum bits can be placed in superpositions of one and zero, as opposed to classical bits, which are either one or zero. Moreover, the logic behind the coherent nature of quantum information processing often deviates from intuitive reasoning, leading to some surprising effects.

"It seems absolutely bizarre that counterfactual computation -- using information that is counter to what must have actually happened -- could find an answer without running the entire quantum computer," said Kwiat, a John Bardeen Professor of Electrical and Computer Engineering and Physics at Illinois. "But the nature of quantum interrogation makes this amazing feat possible."

Sometimes called interaction-free measurement, quantum interrogation is a technique that makes use of wave-particle duality (in this case, of photons) to search a region of space without actually entering that region of space.

Utilizing two coupled optical interferometers, nested within a third, Kwiat's team succeeded in counterfactually searching a four-element database using Grover's quantum search algorithm. "By placing our photon in a quantum superposition of running and not running the search algorithm, we obtained information about the answer even when the photon did not run the search algorithm," said graduate student Onur Hosten, lead author of the Nature paper. "We also showed theoretically how to obtain the answer without ever running the algorithm, by using a 'chained Zeno' effect."

Through clever use of beam splitters and both constructive and destructive interference, the researchers can put each photon in a superposition of taking two paths. Although a photon can occupy multiple places simultaneously, it can only make an actual appearance at one location. Its presence defines its path, and that can, in a very strange way, negate the need for the search algorithm to run.

"In a sense, it is the possibility that the algorithm could run which prevents the algorithm from running," Kwiat said. "That is at the heart of quantum interrogation schemes, and to my mind, quantum mechanics doesn't get any more mysterious than this."

While the researchers' optical quantum computer cannot be scaled up, using these kinds of interrogation techniques may make it possible to reduce errors in quantum computing, Kwiat said. "Anything you can do to reduce the errors will make it more likely that eventually you'll get a large-scale quantum computer."

###

In addition to Kwiat and Hosten, co-authors of the Nature paper are graduate students Julio Barreiro, Nicholas Peters and Matthew Rakher (now at the University of California at Santa Barbara). The work was funded by the Disruptive Technologies Office and the National Science Foundation.


Story Source:

The above story is based on materials provided by University of Illinois at Urbana-Champaign. Note: Materials may be edited for content and length.


Cite This Page:

University of Illinois at Urbana-Champaign. "Quantum Computer Solves Problem, Without Running." ScienceDaily. ScienceDaily, 23 February 2006. <www.sciencedaily.com/releases/2006/02/060223084147.htm>.
University of Illinois at Urbana-Champaign. (2006, February 23). Quantum Computer Solves Problem, Without Running. ScienceDaily. Retrieved August 22, 2014 from www.sciencedaily.com/releases/2006/02/060223084147.htm
University of Illinois at Urbana-Champaign. "Quantum Computer Solves Problem, Without Running." ScienceDaily. www.sciencedaily.com/releases/2006/02/060223084147.htm (accessed August 22, 2014).

Share This




More Computers & Math News

Friday, August 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Families Can Now Ask Twitter To Remove Photos Of Deceased

Families Can Now Ask Twitter To Remove Photos Of Deceased

Newsy (Aug. 20, 2014) In the wake of a high-profile harassment case, Twitter says family members can ask for photos of dying or dead relatives to be taken down. Video provided by Newsy
Powered by NewsLook.com
Ballmer Leaves Microsoft's Board, Has Advice For Nadella

Ballmer Leaves Microsoft's Board, Has Advice For Nadella

Newsy (Aug. 19, 2014) In a letter to Microsoft CEO Satya Nadella, Ballmer said he's leaving the board of directors and offered tips on how the company can be successful. Video provided by Newsy
Powered by NewsLook.com
What Google Can Gain From Special Accounts For Children

What Google Can Gain From Special Accounts For Children

Newsy (Aug. 19, 2014) Google will reportedly offer official accounts for children younger than 13 years old. Video provided by Newsy
Powered by NewsLook.com
Breakingviews: Ebola's Economic Impact Could Eclipse SARS

Breakingviews: Ebola's Economic Impact Could Eclipse SARS

Reuters - Business Video Online (Aug. 18, 2014) The virus ravaging Africa has yet to spread elsewhere. Yet Asia’s SARS crisis in 2003 showed how changes to behaviour can hurt the economy more than the actual disease, says Breakingviews' Una Galani. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins