Featured Research

from universities, journals, and other organizations

Quantum physics first: Physicists measure without distorting

Date:
June 3, 2011
Source:
University of Toronto
Summary:
Quantum mechanics is famous for saying that a tree falling in a forest when there's no one there doesn't make a sound. Quantum mechanics also says that if anyone is listening, it interferes with and changes the tree. And so the famous paradox: how can we know reality if we cannot measure it without distorting it? An international team of researchers has found a way to do just that by applying a modern measurement technique to the historic two-slit interferometer experiment in which a beam of light shone through two slits results in an interference pattern on a screen behind.

In a new experiment, researchers have succeeded for the first time in experimentally reconstructing full trajectories which provide a description of how light particles move through the two slits and form an interference pattern.
Credit: iStockphoto/Karl Dolenc

Quantum mechanics is famous for saying that a tree falling in a forest when there's no one there doesn't make a sound. Quantum mechanics also says that if anyone is listening, it interferes with and changes the tree. And so the famous paradox: how can we know reality if we cannot measure it without distorting it?

An international team of researchers, led by University of Toronto physicist Aephraim Steinberg of the Centre for Quantum Information and Quantum Control, has found a way to do just that by applying a modern measurement technique to the historic two-slit interferometer experiment in which a beam of light shone through two slits results in an interference pattern on a screen behind.

That famous experiment, and the 1927 Neils Bohr and Albert Einstein debates, seemed to establish that you could not watch a particle go through one of two slits without destroying the interference effect: you had to choose which phenomenon to look for.

"Quantum measurement has been the philosophical elephant in the room of quantum mechanics for the past century," says Steinberg, who is lead author of Observing the Average Trajectories of Single Photons in a Two-Slit Interferometer, to be published in Science on June 2. "However, in the past 10 to 15 years, technology has reached the point where detailed experiments on individual quantum systems really can be done, with potential applications such as quantum cryptography and computation."

With this new experiment, the researchers have succeeded for the first time in experimentally reconstructing full trajectories which provide a description of how light particles move through the two slits and form an interference pattern. Their technique builds on a new theory of weak measurement that was developed by Yakir Aharonov's group at Tel Aviv University. Howard Wiseman of Griffith University proposed that it might be possible to measure the direction a photon (particle of light) was moving, conditioned upon where the photon is found. By combining information about the photon's direction at many different points, one could construct its entire flow pattern ie. the trajectories it takes to a screen.

"In our experiment, a new single-photon source developed at the National Institute for Standards and Technology in Colorado was used to send photons one by one into an interferometer constructed at Toronto. We then used a quartz calcite, which has an effect on light that depends on the direction the light is propagating, to measure the direction as a function of position. Our measured trajectories are consistent, as Wiseman had predicted, with the realistic but unconventional interpretation of quantum mechanics of such influential thinkers as David Bohm and Louis de Broglie," said Steinberg.

The original double-slit experiment played a central role in the early development of quantum mechanics, leading directly to Bohr's formulation of the principle of complementarity. Complementarity states that observing particle-like or wave-like behaviour in the double-slit experiment depends on the type of measurement made: the system cannot behave as both a particle and wave simultaneously. Steinberg's recent experiment suggests this doesn't have to be the case: the system can behave as both.

"By applying a modern measurement technique to the historic double-slit experiment, we were able to observe the average particle trajectories undergoing wave-like interference, which is the first observation of its kind. This result should contribute to the ongoing debate over the various interpretations of quantum theory," said Steinberg. "It shows that long-neglected questions about the different types of measurement possible in quantum mechanics can finally be addressed in the lab, and weak measurements such as the sort we use in this work may prove crucial in studying all sorts of new phenomena.

"But mostly, we are all just thrilled to be able to see, in some sense, what a photon does as it goes through an interferometer, something all of our textbooks and professors had always told us was impossible."

Research partners include the University of Toronto's Centre for Quantum Information and Quantum Control, Department of Physics and Institute for Optical Sciences, the National Institute of Standards and Technology in Boulder, Colorado, the Institute for Quantum Computing at the University of Waterloo, Griffith University, Australia, and the Laboratoire Charles Fabry in Orsay, France. Research was funded by the Natural Sciences and Engineering Research Council of Canada, the Canadian Institute for Advanced Research, and Quantum Works.


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. Sacha Kocsis, Boris Braverman, Sylvain Ravets, Martin J. Stevens, Richard P. Mirin, L. Krister Shalm, Aephraim M. Steinberg. Observing the Average Trajectories of Single Photons in a Two-Slit Interferometer. Science, 2011; 332 (6034): 1170-1173 DOI: 10.1126/science.1202218

Cite This Page:

University of Toronto. "Quantum physics first: Physicists measure without distorting." ScienceDaily. ScienceDaily, 3 June 2011. <www.sciencedaily.com/releases/2011/06/110602143159.htm>.
University of Toronto. (2011, June 3). Quantum physics first: Physicists measure without distorting. ScienceDaily. Retrieved July 30, 2014 from www.sciencedaily.com/releases/2011/06/110602143159.htm
University of Toronto. "Quantum physics first: Physicists measure without distorting." ScienceDaily. www.sciencedaily.com/releases/2011/06/110602143159.htm (accessed July 30, 2014).

Share This




More Matter & Energy News

Wednesday, July 30, 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
China's Drone King Says the Revolution Depends on Regulators

China's Drone King Says the Revolution Depends on Regulators

Reuters - Business Video Online (July 30, 2014) — Comparing his current crop of drones to early personal computers, DJI founder Frank Wang says the industry is poised for a growth surge - assuming regulators in more markets clear it for takeoff. Jon Gordon reports. Video provided by Reuters
Powered by NewsLook.com
Climate Change Could Cost Billions, According To White House

Climate Change Could Cost Billions, According To White House

Newsy (July 29, 2014) — A report from the White House warns not curbing greenhouse gas emissions could cost the U.S. billions. Video provided by Newsy
Powered by NewsLook.com
Stranded Whale Watching Boat Returns to Boston

Stranded Whale Watching Boat Returns to Boston

Reuters - US Online Video (July 29, 2014) — Passengers stuck overnight on a whale watching boat return safely to Boston. Linda So 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