Featured Research

from universities, journals, and other organizations

Physicists Resolve Confounding Paradox Of Quantum Theory

Date:
January 15, 2009
Source:
University of Toronto
Summary:
University of Toronto quantum physicists Jeff Lundeen and Aephraim Steinberg have shown that Hardy's paradox, a proposal that has confounded physicists for over a decade, can be confirmed and ultimately resolved, a task which had seemingly been impossible to perform.

University of Toronto quantum physicists Jeff Lundeen and Aephraim Steinberg have shown that Hardy's paradox, a proposal that has confounded physicists for over a decade, can be confirmed and ultimately resolved, a task which had seemingly been impossible to perform.

"For nearly a century, the widespread interpretation of quantum mechanics suggests that everything is uncertain until it is observed, and that observation inevitably alters reality," says Professor Steinberg. "However, in the 1990s, a technique known as 'interaction-free measurement' seemed to promise the ability to 'see without looking,' as a Scientific American article put it at the time. But when Lucien Hardy proposed that one could never reliably make inferences about past events which hadn't been directly observed, a paradox emerged which suggested that whenever one attempted to reason about the past in this way they would be led into error."

Over the course of nearly two years of work, Steinberg and then-student Jeff Lundeen, now a research associate at the National Research Council of Canada, built a complicated quantum optical experiment and developed new theoretical tools. In essence, they combined Hardy's Paradox with a new theory known as weak measurement proposed by Tel Aviv University physicist Yakir Aharonov, showing that in one sense, one can indeed talk about the past, resolving the paradox. Weak measurement is a tool whereby the presence of a detector is less than the level of uncertainty around what is being measured, so that there is an imperceptible impact on the experiment. "We found that all of the seemingly paradoxical conclusions in Hardy's Paradox can, in fact, be experimentally verified," says Steinberg, "but that the use of weak measurement removes the contradiction."

"Until recently, it seemed impossible to carry out Hardy's proposal in practice, let alone to confirm or resolve the paradox," he says. "We have finally been able to do so, and to apply Aharonov's methods to the problem, showing that there is a way, even in quantum mechanics, in which one can quite consistently discuss past events even after they are over and done. Weak measurement finds what is there without disturbing it."

The research was funded with support from the Natural Sciences and Engineering Research Council of Canada, Quantum Works, the Canadian Institute for Photonic Innovations, 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. J.S. Lundeen and A.M. Steinberg. Experimental Joint Weak Measurement on a Photon Pair as a Probe of Hardy’s Paradox. Physical Review Letters, 2009; 102 (2): 020404 DOI: 10.1103/PhysRevLett.102.020404

Cite This Page:

University of Toronto. "Physicists Resolve Confounding Paradox Of Quantum Theory." ScienceDaily. ScienceDaily, 15 January 2009. <www.sciencedaily.com/releases/2009/01/090114141509.htm>.
University of Toronto. (2009, January 15). Physicists Resolve Confounding Paradox Of Quantum Theory. ScienceDaily. Retrieved August 23, 2014 from www.sciencedaily.com/releases/2009/01/090114141509.htm
University of Toronto. "Physicists Resolve Confounding Paradox Of Quantum Theory." ScienceDaily. www.sciencedaily.com/releases/2009/01/090114141509.htm (accessed August 23, 2014).

Share This




More Matter & Energy News

Saturday, August 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Is It a Plane? No, It's a Hoverbike

Is It a Plane? No, It's a Hoverbike

Reuters - Business Video Online (Aug. 22, 2014) — UK-based Malloy Aeronautics is preparing to test a manned quadcopter capable of out-manouvering a helicopter and presenting a new paradigm for aerial vehicles. A 1/3-sized scale model is already gaining popularity with drone enthusiasts around the world, with the full-sized manned model expected to take flight in the near future. Matthew Stock reports. Video provided by Reuters
Powered by NewsLook.com
Coal Gas Boom in China Holds Climate Risks

Coal Gas Boom in China Holds Climate Risks

AP (Aug. 22, 2014) — China's energy revolution could do more harm than good for the environment, despite the country's commitment to reducing pollution and curbing its carbon emissions. (Aug. 22) Video provided by AP
Powered by NewsLook.com
Former TSA X-Ray Scanners Easily Tricked To Miss Weapons

Former TSA X-Ray Scanners Easily Tricked To Miss Weapons

Newsy (Aug. 21, 2014) — Researchers found the scanners could be duped simply by placing a weapon off to the side of the body or encasing it under a plastic shield. Video provided by Newsy
Powered by NewsLook.com
Flower Power! Dandelions Make Car Tires?

Flower Power! Dandelions Make Car Tires?

Reuters - Business Video Online (Aug. 20, 2014) — Forget rolling on rubber, could car drivers soon be traveling on tires made from dandelions? Teams of scientists are racing to breed a type of the yellow flower whose taproot has a milky fluid with tire-grade rubber particles in it. As Joanna Partridge reports, global tire makers are investing millions in research into a new tire source. 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