Visualization of a massive body generating gravitational waves (UWM)
Visualization of a massive body generating gravitational waves (UWM)

Black Holes, Observatories

Can Light be “Squeezed” to Improve Sensitivity of Gravitational Wave Detectors?

9 Jun , 2008 by

The search is on to detect the first evidence of gravitational waves travelling around the cosmos. How can we do this? The Laser Interferometer Gravitational-Wave Observatory (LIGO) uses a system of laser beams fired over a distance of 4 km (2.5 miles) and reflected back and forth by a system of mirrors. Should a gravitational wave pass through the volume of space-time surrounding the Earth, in theory the laser beam will detect a small change as the passing wave slightly alters the distance between mirrors. It is worth noting that this slight change will be small; so small in fact that LIGO has been designed to detect a distance fluctuation of less than one-thousandth of the width of a proton. This is impressive, but it could be better. Now scientists think they have found a way of increasing the sensitivity of LIGO; use the strange quantum properties of the photon to “squeeze” the laser beam so an increase in sensitivity can be achieved…

LIGO was designed by collaborators from MIT and Caltech to search for observational evidence of theoretical gravitational waves. Gravitational waves are thought to propagate throughout the Universe as massive objects disturb space-time. For example, if two black holes collided and merged (or collided and blasted away from each other), Einstein’s theory of general relativity predicts that a ripple will be sent throughout the fabric of space-time. To prove gravitational waves do exist, a totally different type of observatory needed to be built, not to observe electromagnetic emissions from the source, but to detect the passage of these perturbations travelling through our planet. LIGO is an attempt to measure these waves, and with a gargantuan set-up cost of $365 million, there is huge pressure for the facility to discover the first gravitational wave and its source (for more information on LIGO, see “Listening” for Gravitational Waves to Track Down Black Holes). Alas, after several years of science, none have been found. Is this because there are no gravitational waves out there? Or is LIGO simply not sensitive enough?

The first question is quickly answered by LIGO scientists: more time is needed to collect a longer period of data (there needs to be more “exposure time” before gravitational waves are detected). There is also strong theoretical reasons why gravitational waves should exist. The second question is something scientists from the US and Australia hope to improve; perhaps LIGO needs a boost in sensitivity.

The laser "squeezer" equipment (Keisuke Goda)

To make gravitational wave detectors more sensitive, Nergis Mavalvala leader of this new research and MIT physicist, has focused on the very small to help detect the very big. To understand what the researchers are hoping to achieve, a very brief crash course in quantum “fuzziness” is needed.

Detectors such as LIGO depend on highly accurate laser technology to measure perturbations in space-time. As gravitational waves travel through the Universe, they cause tiny changes in the distance between two positions in space (space is effectively being “warped” by these waves). Although LIGO has the ability to detect a perturbation of less than a thousandth of the width of a proton, it would be great if even more sensitivity is acquired. Although lasers are inherently accurate and very sensitive, laser photons are still governed by quantum dynamics. As the laser photons interact with the interferometer, there is a degree of quantum fuzziness meaning the photon is not a sharp pin-point, but slightly blurred by quantum noise. In an effort to reduce this noise, Mavalvala and her team have been able to “squeeze” laser photons.

Laser photons possess two quantities: phase and amplitude. Phase describes the photons position in time and amplitude describes the number of photons in the laser beam. In this quantum world, if the laser amplitude is reduced (removing some of the noise); quantum uncertainties in laser phase will increase (adding some noise). It is this trade-off that this new squeezing technique is base on. What is important is accuracy in the measurement of amplitude, not the phase, when trying to detect a gravitational wave with lasers.

It is hoped that this new technique can be applied to the multi-million dollar LIGO facility, possibly increasing LIGO’s sensitivity by 44%.

The significance of this work is that it forced us to confront and solve some of the practical challenges of squeezed state injection—and there are many. We are now much better positioned to implement squeezing in the kilometer-scale detectors, and catch that elusive gravitational wave.” – Nergis Mavalvala.

Source: Physorg.com

By  
[Follow me on Twitter (@astroengine)] [Check out my space blog: Astroengine.com] [Check out my radio show: Astroengine Live!] Hello! My name is Ian O'Neill and I've been writing for the Universe Today since December 2007. I am a solar physics doctor, but my space interests are wide-ranging. Since becoming a science writer I have been drawn to the more extreme astrophysics concepts (like black hole dynamics), high energy physics (getting excited about the LHC!) and general space colonization efforts. I am also heavily involved with the Mars Homestead project (run by the Mars Foundation), an international organization to advance our settlement concepts on Mars. I also run my own space physics blog: Astroengine.com, be sure to check it out!


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c-lab
Member
c-lab
June 9, 2008 7:55 PM

Just out of curiosity, what are the practical applications of gravitational waves assuming they exist?

Please don’t think me a naysayer – and, I assume we could use them for something… right?

Mek
Guest
June 9, 2008 8:25 PM

I think there aren’t any applications that would be facilitated by this research, but to be fair a good chunk of scientific research has always been “useless”, in that there aren’t any direct applications that come out of their results.

c-lab
Member
c-lab
June 9, 2008 9:06 PM

Fair enough… just hoping that there was some speculative (yet practical) ideas.

Please forgive the oxymoron !

alp wazungy
Guest
alp wazungy
June 9, 2008 9:41 PM
I read about this gravity wave detecting theory a fews ago. In essence it is based on the “fact” that gravity waves should stretch and compress space/time as it passes through. This means that if you try to use a regular ruler… you will not see any change because the ruler itself will stretch and contract. Not only the ruler, but the space and time it occupies will stretch and contract. Seems to me the “distance” remains constant. It is the material of space and time itself that stretches and contracts as the wave passes through. Would this not also affect the beam of light? The wave would stretch and compress the light beam along with the time… Read more »
alp wazungy
Guest
alp wazungy
June 9, 2008 9:54 PM
I want to add that when I say the distance remains the same and space/time stretches… I mean that 6 inches in a compressed space/time phase of the wave will be indistiguishable from 6 inches in the stretched portion of the wave. The compressed/stretched space takes along any object contained withing it (even the observer). I think even if the wave is able to cause a ripple to pass through a ruler measuring it (rather than a planet sized wave/ripple, maybe a pea sized wave/ripple) a beam of light fired from one end of the ruler to a detector at the other end should detect no difference even when it also passes through this ripple because the properties… Read more »
Essel
Member
Essel
June 9, 2008 10:05 PM
Hi alp, you have a strong point and I hope the LIGO guys have considered it (or not!). One more thing that comes to my mind is the issue of ‘space-time’; Einstein predicted that there will be distortion in space-time, does it mean that even a solid object like Earth will also experience temporary distortion? I doubt if that would be so profound. This will call for transfer of a huge amount of energy to compress and expand earth, which is not a perfect elastic body. As long as we are trying to detect two points in space experincing shrinkage or elongation of distance as a result of gravity wave it may be fine but if we are… Read more »
alp wazungy
Guest
alp wazungy
June 9, 2008 11:51 PM

My understanding is that the wave does not compress matter specificaly. It affects the SPACE the matter (or light beam) resides in.

pantzov
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pantzov
June 10, 2008 1:20 AM

i was prepared to laugh at this idea when i started reading, but now i think it sounds kinda cool and i wish them luck.

GrahamC
Member
GrahamC
June 10, 2008 2:39 AM

Have I missed something? They are measuring small variations in distance by measuring small variations in time. So isn’t phase noise more important than amplitude?

PHWilson
Guest
PHWilson
June 10, 2008 3:47 AM

Just a rogue thought… If Earth’s electromagnetic field protects us from such violence as produced by our Sol, would our EM field also deflect measurable distortions from gravity waves?

Dave Kinsley
Guest
Dave Kinsley
June 10, 2008 4:26 AM

I agree with Alp.

Surely there should be two parrallel detectors so that the two detectors can be compared.

trux
Guest
June 10, 2008 6:11 AM

To Alp: if I remember well the principle of LIGO (it is years I looked at it), there are two identical “rulers” creating an L form – in ideal case then, one arm will be parallel and the other perpendicular to the gravitational wave. By sending a split laser beam to both arms and then interferometrically comparing them on the return (there are mirrors at the end of the arms), you should be able detecting the space warping – only one of the “rulers” will be warped by the gravitational wave, and since the speed of light remains unaffected by the warping, the beam will need a different time to come back than in the other arm.

Sili
Member
Sili
June 10, 2008 7:09 AM

I doubt gravitational waves can ever be harnessed for anything useful.

But I have every confidence that engineers will find something to use the improved laser precision for.

As with the Apollo programme going to the Moon did not in itself mean much, but the whole infrastructure needed to go there gave us microchips, teflon, solarcells and so on and so forth.

Astrofreak
Guest
Astrofreak
June 10, 2008 7:38 AM

Oooh, gravity waves, gravitrons, pretty pictures of an “artist’s concept!” Ain’t science wonderful! What’s next, u guys gonna find “dark matter,” or “dark energy” or “worm holes” or “the God particle” or _________ (fill in the blank). Oh yeah, my favorite, we think the universe is about 13.7B years old but somehow in just the last couple of decades or so we’ve been able to detect that expansion is accelerating. You all would be better off looking for Cleons!

Mek
Guest
June 10, 2008 9:39 AM

Yeah man, what has general relativity ever done for us!?!

Seriously dude, read up a bit on astronomy. razz

Tissa Perera
Guest
June 10, 2008 9:43 AM
I would suggest a different approach to detect gravity waves. Gravity waves will streach and squeeze space as it travels the space. This in turn should streach and squeeze any photons that happen to be there. Problem is, it happens for a fleeting moment. What I am suggesting is light should be red shift modulated by gravity waves. This modulation may be happening randomly all over space if gravity waves are passing all the time. If only we can make a fast detector spectroscope and observe spectral lines oscillating momentrarily when gravity waves flow, that should prove it. I have given the idea, now lets see who can make this experiment. By the way I have other thoughts,… Read more »
trux
Guest
June 10, 2008 11:19 AM
> I doubt gravitational waves can ever be harnessed for anything useful. I do not understand why you doubt it. First of all, confirming or denying their existence will definitely bring us closer to understanding the universe and its laws of physics. Second, if we develop devices sensitive enough, gravitational waves may be used for observing objects and events in the universe otherwise invisible. Gravitation waves unlike EM waves won’t be screened by galaxies, stars, gas, dust, or other material. Theoretically gravitational waves could be used even for communication. And since it is not yet entirely clear whether gravitational waves are limited by the otherwise absolute speed of light, if they turn out to be faster (although it… Read more »
VL Narayanan
Guest
VL Narayanan
June 10, 2008 2:14 PM

I have a simple doubt, hope this wont be stupid….
how could we expect some path difference between two beams of L shaped detectors in LIGO owing to passage of gravitational waves?
Im asking this because when the gravitational waves compress or rarefies the space-time fabric, not only the distance decreases or increases but also the time is expected to behave the same way (since it is space-time). moreover all the objects in space time fabric will be affected including the interferometer as Alps had asked. Am I right (hope LIGO experts might have considered these problems with eqns & tell me that Im wrong).

Sili
Member
Sili
June 11, 2008 3:47 PM
trux, I’m sorry, I didn’t phrase that well. Of course the Scientific results will be pure gold. But I meant ‘useful’ in the engineering sense. We’re not gonna tap into to gravitational waves to power spaceflight (or just lightbulbs for that matter). Splitting the atom gave us nuclear power of course, but splitting the proton isn’t likely to be directly useful in that respect. But CERN still gave us the Internet – and will now likely lead the way in distributed computing. What I was trying to say is that the research may *seem* useless to John Q. Public, but all the infrastructure &c that gets invented, engineered and develop will in all likelihood give us countless benefits… Read more »
bob
Guest
bob
June 11, 2008 4:45 PM
How? The beams are going to bounce off of a mirror and on the return trip of the beam will not lie directly on itself as it does now. Gravitational waves carry a lot of information. This from Kip Thorne’s “Blasck Holes and Time Warps”: “1.)Gravitational waves are the binding energy of two colliding objects, such as black holes. The ripples are produced right near the coalescing holes’ horizons, they are made of the same material (a warpage of the fabric of spacetime) as the holes, they are not distorted at all by propogating through intervening matter like light is. 2.)They tell us just how heavy each of the holes was, how fast they were spinning, the shape… Read more »
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