Featured Research

from universities, journals, and other organizations

Redefining the kilogram and the ampere

Date:
September 29, 2011
Source:
National Physical Laboratory
Summary:
New research using graphene presents the most precise measurements of the quantum Hall effect ever made, one of the key steps in the process to redefine two Système Internationale d'unités (SI) units. New research is underpinning the biggest change in the SI Units since the system began 50 years ago.

Graphene has the potential to surpass conventional materials in many applications including quantum resistance metrology.
Credit: NPL

Groundbreaking research by the National Physical Laboratory's (NPL) Quantum Detection Group and an international team of collaborators is underpinning the biggest change in the Système Internationale d'unités (SI Units) since the system began 50 years ago.

It has long been the goal of scientists to relate all of the unit definitions to fundamental constants of nature, making them stable and universal, and giving them closer links to each other and the quantities they measure.

Key units to be redefined are the kilogram (mass) and the ampere (electric current). Presently the kilogram is defined by a physical lump of platinum-iridium and the ampere is defined via the force produced between two wires.

The goal is to define the kilogram in terms the Planck constant h and the ampere in terms of the electron charge e.

Making this change relies on the exactness of the relationships that link these constants to measurable quantities.

The quantum Hall effect defines a relationship between these two fundamental physical constants. Experiments are needed to test the quantum Hall effect in different materials in order to prove whether or not it is truly universal.

Until recently the effect was exclusively observed in a few semiconductor materials. A few years ago the quantum Hall effect was also observed by the same team in graphene, a completely different type of material with a very different electronic structure.

This research directly compared the quantum Hall effect in graphene with that observed in a traditional semiconductor material. Graphene is hotly tipped to surpass conventional materials in many important applications, partly due to its extraordinary electrical properties.

The results confirmed that the quantum Hall effect is truly universal with an uncertainty level of 86 parts per trillion, supporting the redefinition of the kilogram and ampere. The quantum Hall effect in graphene is so good that it should be the material of choice for quantum resistance metrology.

The discovery was highlighted in Nature on September 29.

JT Janssen, NPL Science Fellow and the lead author of the research, said: "Many metrology laboratories around the world have been striving to do this experiment and it is a real achievement that the NPL team and its co-workers were the first to get this key result. It turns out that the quantum Hall effect in graphene is very robust and easy to measure -- not bad for a material that was only discovered six years ago."

The research was conducted in collaboration with the Bureau International des Poids et Mesures, Chalmers University of Technology (Sweden), Lancaster University (UK) and Linköping University (Sweden).


Story Source:

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


Journal Reference:

  1. T J B M Janssen, N E Fletcher, R Goebel, J M Williams, A Tzalenchuk, R Yakimova, S Kubatkin, S Lara-Avila, V I Falko. Graphene, universality of the quantum Hall effect and redefinition of the SI system. New Journal of Physics, 2011; 13 (9): 093026 DOI: 10.1088/1367-2630/13/9/093026

Cite This Page:

National Physical Laboratory. "Redefining the kilogram and the ampere." ScienceDaily. ScienceDaily, 29 September 2011. <www.sciencedaily.com/releases/2011/09/110929074207.htm>.
National Physical Laboratory. (2011, September 29). Redefining the kilogram and the ampere. ScienceDaily. Retrieved July 22, 2014 from www.sciencedaily.com/releases/2011/09/110929074207.htm
National Physical Laboratory. "Redefining the kilogram and the ampere." ScienceDaily. www.sciencedaily.com/releases/2011/09/110929074207.htm (accessed July 22, 2014).

Share This




More Matter & Energy News

Tuesday, July 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Government Approves East Coast Oil Exploration

Government Approves East Coast Oil Exploration

AP (July 18, 2014) — The Obama administration approved the use of sonic cannons to discover deposits under the ocean floor by shooting sound waves 100 times louder than a jet engine through waters shared by endangered whales and turtles. (July 18) Video provided by AP
Powered by NewsLook.com
Sunken German U-Boat Clearly Visible For First Time

Sunken German U-Boat Clearly Visible For First Time

Newsy (July 18, 2014) — The wreckage of the German submarine U-166 has become clearly visible for the first time since it was discovered in 2001. Video provided by Newsy
Powered by NewsLook.com
Obama: U.S. Must Have "smartest Airports, Best Power Grid"

Obama: U.S. Must Have "smartest Airports, Best Power Grid"

Reuters - US Online Video (July 17, 2014) — President Barak Obama stopped by at a lunch counter in Delaware before making remarks about boosting the nation's infrastructure. Mana Rabiee reports. Video provided by Reuters
Powered by NewsLook.com
Crude Oil Prices Bounce Back After Falling Below $100 a Barrel

Crude Oil Prices Bounce Back After Falling Below $100 a Barrel

TheStreet (July 16, 2014) — Oil Futures are bouncing back after tumbling below $100 a barrel for the first time since May yesterday. Jeff Grossman is the president of BRG Brokerage and trades at the NYMEX. Grossman tells TheStreet the Middle East is always a concern for oil traders. Oil prices were pushed down in recent weeks on Libya increasing its production. Supply disruptions in Iraq fading also contributed to prices falling. News from China's economic front showing a growth for the second quarter also calmed fears on its slowdown. Jeff Grossman talks to TheStreet's Susannah Lee on this and more on the Energy Department's Energy Information Administration (EIA) report. Video provided by TheStreet
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