Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New MIT developments in quantum computing

03.03.2011
New MIT experiment would use quantum effects to perform otherwise intractable calculations

Quantum computers are computers that exploit the weird properties of matter at extremely small scales. Many experts believe that a full-blown quantum computer could perform calculations that would be hopelessly time consuming on classical computers, but so far, quantum computers have proven hard to build.

At the Association for Computing Machinery's 43rd Symposium on Theory of Computing in June, associate professor of computer science Scott Aaronson and his graduate student Alex Arkhipov will present a paper describing an experiment that, if it worked, would offer strong evidence that quantum computers can do things that classical computers can't. Although building the experimental apparatus would be difficult, it shouldn't be as difficult as building a fully functional quantum computer.

Aaronson and Arkhipov's proposal is a variation on an experiment conducted by physicists at the University of Rochester in 1987, which relied on a device called a beam splitter, which takes an incoming beam of light and splits it into two beams traveling in different directions. The Rochester researchers demonstrated that if two identical light particles — photons — reach the beam splitter at exactly the same time, they will both go either right or left; they won't take different paths. It's another quantum behavior of fundamental particles that defies our physical intuitions.

The MIT researchers' experiment would use a larger number of photons, which would pass through a network of beam splitters and eventually strike photon detectors. The number of detectors would be somewhere in the vicinity of the square of the number of photons — about 36 detectors for six photons, 100 detectors for 10 photons.

For any run of the MIT experiment, it would be impossible to predict how many photons would strike any given detector. But over successive runs, statistical patterns would begin to build up. In the six-photon version of the experiment, for instance, it could turn out that there's an 8 percent chance that photons will strike detectors 1, 3, 5, 7, 9 and 11, a 4 percent chance that they'll strike detectors 2, 4, 6, 8, 10 and 12, and so on, for any conceivable combination of detectors.

Calculating that distribution — the likelihood of photons striking a given combination of detectors — is a hard problem. The researchers' experiment doesn't solve it outright, but every successful execution of the experiment does take a sample from the solution set. One of the key findings in Aaronson and Arkhipov's paper is that, not only is calculating the distribution a hard problem, but so is simulating the sampling of it. For an experiment with more than, say, 100 photons, it would probably be beyond the computational capacity of all the computers in the world.

The question, then, is whether the experiment can be successfully executed. The Rochester researchers performed it with two photons, but getting multiple photons to arrive at a whole sequence of beam splitters at exactly the right time is more complicated. Barry Sanders, director of the University of Calgary's Institute for Quantum Information Science, points out that in 1987, when the Rochester researchers performed their initial experiment, they were using lasers mounted on lab tables and getting photons to arrive at the beam splitter simultaneously by sending them down fiber-optic cables of different lengths. But recent years have seen the advent of optical chips, in which all the optical components are etched into a silicon substrate, which makes it much easier to control the photons' trajectories.

The biggest problem, Sanders believes, is generating individual photons at predictable enough intervals to synchronize their arrival at the beam splitters. "People have been working on it for a decade, making great things," Sanders says. "But getting a train of single photons is still a challenge."

Sanders points out that even if the problem of getting single photons onto the chip is solved, photon detectors still have inefficiencies that could make their measurements inexact: in engineering parlance, there would be noise in the system. But Aaronson says that he and Arkhipov explicitly consider the question of whether simulating even a noisy version of their optical experiment would be an intractably hard problem. Although they were unable to prove that it was, Aaronson says that "most of our paper is devoted to giving evidence that the answer to that is yes." He's hopeful that a proof is forthcoming, whether from his research group or others'.

Caroline McCall | EurekAlert!
Further information:
http://www.mit.edu

More articles from Physics and Astronomy:

nachricht Space radiation won't stop NASA's human exploration
18.10.2017 | NASA/Johnson Space Center

nachricht Study shows how water could have flowed on 'cold and icy' ancient Mars
18.10.2017 | Brown University

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Osaka university researchers make the slipperiest surfaces adhesive

18.10.2017 | Materials Sciences

Space radiation won't stop NASA's human exploration

18.10.2017 | Physics and Astronomy

Los Alamos researchers and supercomputers help interpret the latest LIGO findings

18.10.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>