Featured Research

from universities, journals, and other organizations

Scientists cast doubt on Heisenberg's uncertainty principle

Date:
September 7, 2012
Source:
University of Toronto
Summary:
Werner Heisenberg's uncertainty principle, formulated by the theoretical physicist in 1927, is one of the cornerstones of quantum mechanics. The principle has bedeviled quantum physicists for nearly a century, until recently, when researchers demonstrated the ability to directly measure the disturbance caused by measuring a property of something, and confirm that Heisenberg was too pessimistic.

Heisenberg's gamma-ray microscope for locating an electron (shown in blue). The incoming gamma ray (shown in green) is scattered by the electron up into the microscope's aperture angle . The scattered gamma-ray is shown in red. Classical optics shows that the electron position can be resolved only up to an uncertainty ”x that depends on and the wavelength of the incoming light.
Credit: By parri (Wikimedia commons) [GFDL or CC-BY-SA-3.0], via Wikimedia Commons

Werner Heisenberg's uncertainty principle, formulated by the theoretical physicist in 1927, is one of the cornerstones of quantum mechanics. In its most familiar form, it says that it is impossible to measure anything without disturbing it. For instance, any attempt to measure a particle's position must randomly change its speed.

The principle has bedeviled quantum physicists for nearly a century, until recently, when researchers at the University of Toronto demonstrated the ability to directly measure the disturbance and confirm that Heisenberg was too pessimistic.

"We designed an apparatus to measure a property -- the polarization -- of a single photon. We then needed to measure how much that apparatus disturbed that photon," says Lee Rozema, a Ph.D. candidate in Professor Aephraim Steinberg's quantum optics research group at U of T, and lead author of a study published this week in Physical Review Letters.

"To do this, we would need to measure the photon before the apparatus but that measurement would also disturb the photon," Rozema says.

In order to overcome this hurdle, Rozema and his colleagues employed a technique known as weak measurement wherein the action of a measuring device is weak enough to have an imperceptible impact on what is being measured. Before each photon was sent to the measurement apparatus, the researchers measured it weakly and then measured it again afterwards, comparing the results. They found that the disturbance induced by the measurement is less than Heisenberg's precision-disturbance relation would require.

"Each shot only gave us a tiny bit of information about the disturbance, but by repeating the experiment many times we were able to get a very good idea about how much the photon was disturbed," says Rozema.

The findings build on recent challenges to Heisenberg's principle by scientists the world over. Nagoya University physicist Masanao Ozawa suggested in 2003 that Heisenberg's uncertainty principle does not apply to measurement, but could only suggest an indirect way to confirm his predictions. A validation of the sort he proposed was carried out last year by Yuji Hasegawa's group at the Vienna University of Technology. In 2010, Griffith University scientists Austin Lund and Howard Wiseman showed that weak measurements could be used to characterize the process of measuring a quantum system. However, there were still hurdles to clear as their idea effectively required a small quantum computer, which is difficult to build.

"In the past, we have worked experimentally both on implementing weak measurements, and using a technique called 'cluster state quantum computing' to simplify building quantum computers. The combination of these two ideas led to the realization that there was a way to implement Lund and Wiseman's ideas in the lab," says Rozema.

It is often assumed that Heisenberg's uncertainty principle applies to both the intrinsic uncertainty that a quantum system must possess, as well as to measurements. These results show that this is not the case and demonstrate the degree of precision that can be achieved with weak-measurement techniques.

"The results force us to adjust our view of exactly what limits quantum mechanics places on measurement," says Rozema. "These limits are important to fundamental quantum mechanics and also central in developing 'quantum cryptography' technology, which relies on the uncertainty principle to guarantee that any eavesdropper would be detected due to the disturbance caused by her measurements."

"The quantum world is still full of uncertainty, but at least our attempts to look at it don't have to add as much uncertainty as we used to think!"

The findings are reported in the paper "Violation of Heisenberg's Measurement-Disturbance Relationship by Weak Measurements." The research is supported by funding from Natural Sciences and Engineering Research Council of Canada and the Canadian Institute for Advanced Research.


Story Source:

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


Journal Reference:

  1. Lee Rozema, Ardavan Darabi, Dylan Mahler, Alex Hayat, Yasaman Soudagar, Aephraim Steinberg. Violation of Heisenberg’s Measurement-Disturbance Relationship by Weak Measurements. Physical Review Letters, 2012; 109 (10) DOI: 10.1103/PhysRevLett.109.100404

Cite This Page:

University of Toronto. "Scientists cast doubt on Heisenberg's uncertainty principle." ScienceDaily. ScienceDaily, 7 September 2012. <www.sciencedaily.com/releases/2012/09/120907125154.htm>.
University of Toronto. (2012, September 7). Scientists cast doubt on Heisenberg's uncertainty principle. ScienceDaily. Retrieved July 31, 2014 from www.sciencedaily.com/releases/2012/09/120907125154.htm
University of Toronto. "Scientists cast doubt on Heisenberg's uncertainty principle." ScienceDaily. www.sciencedaily.com/releases/2012/09/120907125154.htm (accessed July 31, 2014).

Share This




More Matter & Energy News

Thursday, July 31, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Britain Testing Driverless Cars on Roadways

Britain Testing Driverless Cars on Roadways

AP (July 30, 2014) British officials said on Wednesday that driverless cars will be tested on roads in as many as three cities in a trial program set to begin in January. Officials said the tests will last up to three years. (July 30) Video provided by AP
Powered by NewsLook.com
7 Ways to Use Toothpaste: Howdini Hacks

7 Ways to Use Toothpaste: Howdini Hacks

Howdini (July 30, 2014) Fresh breath and clean teeth are great, but have you ever thought, "my toothpaste could be doing more". Well, it can! Lots of things! Howdini has 7 new uses for this household staple. Video provided by Howdini
Powered by NewsLook.com
Amid Drought, UCLA Sees Only Water

Amid Drought, UCLA Sees Only Water

AP (July 30, 2014) A ruptured 93-year-old water main left the UCLA campus awash in 8 million gallons of water in the middle of California's worst drought in decades. (July 30) Video provided by AP
Powered by NewsLook.com
Smartphone Powered Paper Plane Debuts at Airshow

Smartphone Powered Paper Plane Debuts at Airshow

AP (July 30, 2014) Smartphone powered paper airplane that was popular on crowdfunding website KickStarter makes its debut at Wisconsin airshow (July 30) Video provided by AP
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