Featured Research

from universities, journals, and other organizations

Quantum physicists show a small amount of randomness can be amplified without limit

Date:
May 16, 2012
Source:
ETH Zürich
Summary:
Once again quantum physics gives us philosophical implications: physicists have shown how a small amount of randomness can be amplified without limit.

Once again quantum physics gives us philosophical implications: physicists showed how a small amount of randomness can be amplified without limit.
Credit: © Africa Studio / Fotolia

Once again quantum physics gives us philosophical implications: physicists showed how a small amount of randomness can be amplified without limit.

Classical physics is deterministic: for example, we can determine the position and velocity of a particle at any time in the future. Quantum theory, on the other hand, states that there exist processes which are fundamentally random: for instance, the outcomes of measurements of quantum particles seem to be determined entirely by chance. This is why Einstein argued in a publication in 1935 that the quantum theory is incomplete, and yet another kind of higher theory must exist, but up to the present time there has been no proof either that the world is purely deterministic and all randomness is due solely to a lack of knowledge about certain events, or that everything happens purely by chance. However, ETH Zurich physicists have now succeeded in showing in a thought experiment that randomness can be amplified.

The results, published in the scientific journal Nature Physics, may also have practical applications.

Free choice is decisive for a representative outcome

Experiments in physics always depend on a large number of variables. To obtain a representative result, the choice of the variables -- like the selection of the people questioned in an opinion survey -- must be completely free and random. The entirely free -- random -- choice of variables is also important in information technology, for example, for efficient simulations. It is also extremely important for encoding messages, i.e. in cryptography, and for the random number generators in gambling casinos. If the latter work badly and a fraudster can see through them, he can exploit this to his advantage.

How random is a choice of variables?

In their study, the physicists Roger Colbeck, postdoctoral researcher, and Renato Renner, Professor at the Institute for Theoretical Physics of ETH Zurich, investigated which minimum conditions must be fulfilled in order for a selection of variables to count as absolutely free, and for this selection not to be already practically "pre-programmed" through earlier events. In this study the physicists defined that a variable counts as being chosen freely and at random if it is not correlated with other variables at this or an earlier moment in time.

In 1964 the physicist John Stuart Bell developed what is known as Bell's inequality, which in simple terms states that there are measurements whose results are not pre-determined and are thus random. The experiments proposed by Bell to prove his theorem, which are based on measuring the entanglement of quantum-mechanical particles, did indeed show this, but only subject to the fundamental condition that the measurements performed during the experiment were chosen completely freely and at random. It is like arguing in a circle: the existence of randomness is again presupposed.

Making use of quantum mechanical laws

The scientists now made use of entanglement and locality -- the fact that for example a local event on Earth does not exert any direct influence on another planet -- to show that beyond a certain point "weakly" indeterministic situations can be amplified to such an extent that they are completely random.

This is achievable for example with two entangled quantum particles that are strongly coupled but are then measured independently of one another. The scientists' calculations showed that the quantum correlation between the bits can be so strong that they cannot be correlated with anything existing previously. This means that the results are completely random, whereas only weak randomness is needed for the choice of the measurement.

The two scientists stress that they have not thereby proved that the world is non-deterministic. However, they say there is nothing in between. The existence of weak randomness automatically implies that there must be an unlimited amount of strong randomness. However, Colbeck says it is first of all necessary to achieve a particular "randomness threshold": "Our method allows randomness to be amplified once a certain threshold has been reached. It would now be interesting to know whether this threshold can be made arbitrarily small by using improved methods." This would then mean that an arbitrarily small amount of indetermisism would be sufficient to generate an unlimited amount of randomness.


Story Source:

The above story is based on materials provided by ETH Zürich. Note: Materials may be edited for content and length.


Journal Reference:

  1. Roger Colbeck, Renato Renner. Free randomness can be amplified. Nature Physics, 2012; DOI: 10.1038/NPHYS2300

Cite This Page:

ETH Zürich. "Quantum physicists show a small amount of randomness can be amplified without limit." ScienceDaily. ScienceDaily, 16 May 2012. <www.sciencedaily.com/releases/2012/05/120516093015.htm>.
ETH Zürich. (2012, May 16). Quantum physicists show a small amount of randomness can be amplified without limit. ScienceDaily. Retrieved September 16, 2014 from www.sciencedaily.com/releases/2012/05/120516093015.htm
ETH Zürich. "Quantum physicists show a small amount of randomness can be amplified without limit." ScienceDaily. www.sciencedaily.com/releases/2012/05/120516093015.htm (accessed September 16, 2014).

Share This



More Matter & Energy News

Tuesday, September 16, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Space Race Pits Bezos Vs Musk

Space Race Pits Bezos Vs Musk

Reuters - Business Video Online (Sep. 16, 2014) — Amazon CEO Jeff Bezos' startup will team up with Boeing and Lockheed to develop rocket engines as Elon Musk races to have his rockets certified. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com
MIT's Robot Cheetah Unleashed — Can Now Run, Jump Freely

MIT's Robot Cheetah Unleashed — Can Now Run, Jump Freely

Newsy (Sep. 16, 2014) — MIT developed a robot modeled after a cheetah. It can run up to speeds of 10 mph, though researchers estimate it will eventually reach 30 mph. Video provided by Newsy
Powered by NewsLook.com
Manufacturer Prints 3-D Car In Record Time

Manufacturer Prints 3-D Car In Record Time

Newsy (Sep. 15, 2014) — Automobile manufacturer Local Motors created a drivable electric car using a 3-D printer. Printing the body only took 44 hours. Video provided by Newsy
Powered by NewsLook.com
Refurbished New York Subway Tunnel Unveiled After Sandy Damage

Refurbished New York Subway Tunnel Unveiled After Sandy Damage

Reuters - US Online Video (Sep. 15, 2014) — New York officials unveil subway tunnels that were refurbished after Superstorm Sandy. Nathan Frandino reports. 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