Subscribe free to our newsletters via your
. 24/7 Space News .

Subscribe free to our newsletters via your

More measurement precision in a short time
by Staff Writers
Braunschweig, Germany (SPX) Feb 12, 2016

Noise contributions of the strontium lattice clock as a function of the number of atoms. The predicted total noise at suppressed frequency noise of the interrogation laser (green line) is confirmed by experimental data (green circles). The quantum projection noise (blue line) already dominates with few atoms. Image courtesy PTB. For a larger version of this image please go here.

Researchers from the Physikalisch-Technische Bundesanstalt (PTB) have thoroughly analyzed the noise processes in their optical lattice clock with neutral strontium atoms. This analysis proves that their optical atomic clock has reached the best stability worldwide thanks to a newly developed laser system whose frequency is extremely stable.

This allows high-precision measurements in a short time and considerably facilitates the future reduction of the total measurement uncertainty down to a few parts in 1E18. In the research community, optical clocks have been attracting increasing interest. They could allow the SI base unit of time, the second, to be realized with even greater accuracy in future and thus replace the current definition which is based on the interaction between microwave radiation and cesium atoms.

The most highly precise clocks, however, cover a wide range of applications which range from geodesy (where they allow the direct and more accurate measurement of the gravitational potential of the Earth), to the investigation of the "great questions" of modern physics (such as a unified theory of the fundamental interactions) by searching for possible variations in fundamental constants (e.g. the fine-structure constant) by comparing diverse clocks with each other.

The accuracy and the stability of optical clocks are mainly based on the fact that the frequency of the optical radiation used is higher (by several orders of magnitude) than that of the microwave radiation which is used in cesium atomic clocks, which makes optical clocks much more precise than cesium clocks. In a strontium clock, laser cooling is used to slow an atomic gas down to temperatures near absolute zero.

Then, an extremely narrow transition between long-lived eigenstates of the atoms is excited in order to stabilize the frequency of the excitation laser to that of the atoms. The simultaneous interrogation of numerous atoms leads to a particularly high signal-to-noise ratio and, thus, to high stability.

However, since an atomic cloud must be prepared after each interrogation, interruptions in the observation of the laser frequency occur. The laser itself hence serves as a "flywheel" and is commonly pre-stabilized to an optical resonator which keeps the laser frequency stable over short periods of time. The scientists from PTB have therefore developed a resonator whose frequency is among the most stable worldwide: with a length of 48 cm and ingenious thermal and mechanical isolation from its environment, it reaches a fractional frequency instability of 8 E-17.

The scientists analyzed the individual contributions to noise of the detected excitation probabilities of their clock. Based on their analysis, PTB's strontium clock attains the quantum projection noise limit, which is due to the laws of physics, with as few as 130 atoms. This noise results from the state measurement itself, since after excitation, each atom is first in a superposition of the two eigenstates and is randomly projected into one of the two states only when the measurement is performed.

To analyze the clock's instability, the model derived from this was supplemented by the known influence of the laser frequency noise, and its prediction was experimentally verified by a self-comparison of the clock.

From this, the scientists at PTB derived a fractional instability in normal operation amounting to 1.6 E-16/t1/2 as a function of the averaging time t in seconds. This is the best published value for an atomic clock so far. It is expected to considerably facilitate the further reduction of the total uncertainty of the strontium clock down to a few parts in 1E18.(es/ptb)

A. Al-Masoudi, S. Dorscher, S. Hafner, U. Sterr, Ch. Lisdat: Noise and instability of an optical lattice clock, Physical Review A 92, 063814 (2015)


Related Links
Physikalisch-Technische Bundesanstalt
Understanding Time and Space

Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks DiggDigg RedditReddit GoogleGoogle

Previous Report
Ghost imaging in the time domain could revolutionize disturbance-sensitive signal imaging
Helsinki, Finland (SPX) Feb 10, 2016
Research results recently presented in the distinguished Nature Photonics journal open up new outlooks on ghost imaging in the time domain. The conventional approach to decode information carried by ultrafast optical signals that propagate in optical fibers employs fast detectors that convert the temporal intensity variations of a light beam into an RF electrical signal. This technique is ... read more

Edgar Mitchell, astronaut who walked on Moon, dead at 85

The forgotten moon landing that paved the way for today's space adventures

ASU satellite selected for NASA Space Launch System's first flight

Lunar Flashlight selected to fly as secondary payload on Exploration Mission-1

Opportunity climbing steeper slopes to reach science targets

Opportunity Reaches 12 Years on Mars!

4 people to live in an HERA habitat for 30 days at JSC

Sandy Selfie Sent from NASA Mars Rover

Are private launches changing the rocket equation?

NASA tests solar sail deployment for asteroid-surveying CubeSat NEA Scout

Mars or the Moon

The Orion Crew Module Pressure Vessel Ready For Testing

Last Launch for Long March 2F/G

China aims for the Moon with new rockets

China shoots for first landing on far side of the moon

Chinese Long March 3B to launch Belintersat-1 telco sat for Belarus

Russians spacewalk to retrieve biological samples

Russia to Deliver Three Advanced Spacesuits to ISS in 2016

Russian spacewalk marks end of ESA's exposed space chemistry

New Tool Provides Successful Visual Inspection of ISS Robot Arm

Space Launch System's first flight will launch small Sci-Tech cubesats

Initial launcher assembly clears Ariane 5 for its payload integration process

ILS Proton Successfully Launches Eutelsat 9B for Eutelsat

Pentagon Can't Overcome Its Russian Engines Addiction: McCain

The frigid Flying Saucer

Astronomers discover largest solar system

Lonely Planet Finds a Mum a Trillion Km Away

Follow A Live Planet Hunt

Body temperature triggers newly developed polymer to change shape

Making sense of metallic glass

Twisted X-rays unravel the complexity of helical structures

A deep look into a single molecule

Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News

The content herein, unless otherwise known to be public domain, are Copyright 1995-2016 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.