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




Subscribe free to our newsletters via your




















TIME AND SPACE
The sound of quantum vacuum
by Staff Writers
Copenhagen, Denmark (SPX) Jan 03, 2017


A membrane resonator (central white square) is in its 'phononic crystal' shield of cross-shaped holes. Even though the membrane is nearly the size of a flea (0.5mm), its motion follows the laws of quantum mechanics, as Niels Bohr Institute researchers show. Image courtesy Albert Schliesser and NBI. For a larger version of this image please go here.

Quantum mechanics dictates sensitivity limits in the measurements of displacement, velocity and acceleration. A recent experiment at the Niels Bohr Institute probes these limits, analyzing how quantum fluctuations set a sensor membrane into motion in the process of a measurement. The membrane is an accurate model for future ultraprecise quantum sensors, whose complex nature may even hold the key to overcome fundamental quantum limits. The results are published in the prestigious scientific journal, Proceedings of the National Academy of Sciences of the USA.

Vibrating strings and membranes are at the heart of many musical instruments. Plucking a string excites it to vibrations, at a frequency determined by its length and tension. Apart from the fundamental frequency - corresponding to the musical note - the string also vibrates at higher frequencies. These overtones influence how we perceive the 'sound' of the instrument, and allow us to tell a guitar from a violin. Similarly, beating a drumhead excites vibrations at a number of frequencies simultaneously.

These matters are not different when scaling down, from the half-meter bass drum in a classic orchestra to the half-millimeter-sized membrane studied recently at the Niels Bohr Institute. And yet, some things are not the same at all: using sophisticated optical measurement techniques, a team lead by Professor Albert Schliesser could show that the membrane's vibrations, including all its overtones, follow the strange laws of quantum mechanics. In their experiment, these quantum laws implied that the mere attempt to precisely measure the membrane vibrations sets it into motion. As if looking at a drum already made it hum!

A 'drum' with many tones
Although the membrane investigated by the Niels Bohr Institute team can be seen with bare eyes, the researchers used a laser to accurately track the membrane motion. And this indeed reveals a number of vibration resonances, all of which are simultaneously measured.

Their frequencies are in the Megahertz range, about a thousand times higher than the sound waves we hear, essentially because the membrane is much smaller than a musical instrument. But the analogies carry on: just like a violin sounds different depending on where the string is struck (sul tasto vs sul ponticello), the researchers could tell from the spectrum of overtones at which location their membrane was excited by the laser beam.

Yet, observing the subtle quantum effects that the researchers were most interested in, required a few more tricks. Albert Schliesser explains: "For once, there is the problem of vibrational energy loss, leading to what we call quantum decoherence. Think of it this way: in a violin, you provide a resonance body, which picks up the string vibrations and transforms them to sound waves carried away by the air.

"That's what you hear. We had to achieve exactly the opposite: confine the vibrations to the membrane only, so that we can follow its undisturbed quantum motion for as long as possible. For that we had to develop a special 'body' that cannot vibrate at the membrane's frequencies".

This was achieved by a so-called phononic crystal, a regular pattern of holes that exhibits a phononic bandgap, that is, a band of frequencies at which the structure cannot vibrate. Yeghishe Tsaturyan, a PhD student on the team, realized a membrane with such a special body at the Danchip nanofabrication facilities in Lyngby.

A second challenge consists in making sufficiently precise measurements. Using techniques from the field of Optomechanics, which is Schliesser's expertise, the team created a dedicated experiment at the Niels Bohr Institute, based on a laser custom-built to their needs, and a pair of highly reflecting mirrors between which the membrane is arranged. This allowed them to resolve vibrations with amplitudes much smaller than a proton's radius (1 femtometer).

"Making measurements so sensitive is not easy, in particular since pumps and other lab equipment vibrates with much larger amplitudes. So we have to make sure this doesn't show in our measurement record," adds PhD student William Nielsen.

Vacuum beats the drum
Yet it is exactly the range of ultra-precision measurements where it gets interesting. Then, it starts to matter that, according to quantum mechanics, the process of measuring the motion also influences it. In the experiment, this 'quantum measurement backaction' is caused by the inevitable quantum fluctuations of the laser light.

In the framework of quantum optics, these are caused by quantum fluctuations of the electromagnetic field in empty space (vacuum). Odd as it sounds, this effect left clear signatures in the Niels Bohr Institute experiments' data, namely strong correlations between the quantum fluctuations of the light, and the mechanical motion as measured by light.

"Observing and quantifying these quantum fluctuations is important to better understand how they can affect ultraprecision mechanical measurements - that is, measurements of displacement, velocity or acceleration. And here, the multi-mode nature of the membrane comes into play: not only is it a more accurate representation of real-world sensors. It may also contain the key to overcome some of the traditional quantum limits to measurement precision with more sophisticated schemes, exploiting quantum correlations", Albert

Schliesser says and adds, that in the long run, quantum experiments with ever more complex mechanical objects may also provide an answer to the question why we don't ever observe a bass drum in a quantum superposition (or will we?).

Research Report


Comment on this article using your Disqus, Facebook, Google or Twitter login.

Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.

SpaceDaily Contributor
$5 Billed Once


credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly


paypal only

.


Related Links
University of Copenhagen - Niels Bohr Institute
Understanding Time and Space






Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle

Previous Report
TIME AND SPACE
Laser pulses help scientists tease apart complex electron interactions
Upton NY (SPX) Dec 22, 2016
Scientists studying high temperature superconductors-materials that carry electric current with no energy loss when cooled below a certain temperature-have been searching for ways to study in detail the electron interactions thought to drive this promising property. One big challenge is disentangling the many different types of interactions-for example, separating the effects of electrons intera ... read more


TIME AND SPACE
India achieves advances multiple space systems in 2016

Spacewalk for Thomas Pesquet at ISS

NASA's Exo-Brake 'Parachute' to Enable Safe Return for Small Spacecraft

Trump sits down with tech execs, including critics

TIME AND SPACE
Preparing to Plug Into NASA SLS Fuel Tank

New round of wind tunnel tests underway for bigger SLS version

United Launch Alliance launches EchoStar XIX satellite

Ultra-Cold Storage - Liquid Hydrogen may be Fuel of the Future

TIME AND SPACE
Small Troughs Growing on Mars May Become 'Spiders'

All eyes on Trump over Mars

Opportunity performs several drives to ancient gully

Full go-ahead for building ExoMars 2020

TIME AND SPACE
Chinese missile giant seeks 20% of a satellite market

China-made satellites in high demand

Space exploration plans unveiled

China launches 4th data relay satellite

TIME AND SPACE
Airbus DS and Energia eye new medium-class satellite platform

OneWeb announces key funding form SoftBank Group and other investors

Space as a Driver for Socio-Economic Sustainable Development

SoftBank delivers first $1 bn of Trump pledge, to space firm

TIME AND SPACE
Meet a 'Spacecraft Dressmaker'

NASA Satellite Servicing Office Becomes a Projects Division

Ultra-small nanocavity advances technology for secure quantum-based data encryption

Ultra-high-speed optical fiber sensor enables detection of structural damage in real time

TIME AND SPACE
Searching a sea of 'noise' to find exoplanets - using only data as a guide

Microlensing Study Suggests Most Common Outer Planets Likely Neptune-mass

Exciting new creatures discovered on ocean floor

Astronomers discover dark past of planet-eating 'Death Star'

TIME AND SPACE
Juno Captures Jupiter 'Pearl'

Juno Mission Prepares for December 11 Jupiter Flyby

Research Offers Clues About the Timing of Jupiter's Formation

New Perspective on How Pluto's "Icy Heart" Came to Be




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 1995-2017 - 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. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. 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