'Squeezed' Light May Improve Gravitational Wave Detectors

June 5, 2008 By Laura Mgrdichian, Phys.org feature
'Squeezed' Light May Improve Gravitational Wave Detectors
Aerial view of the LIGO interferometer in Hanford, Washington. Photo courtesy LIGO Laboratory.

A research collaboration has taken steps toward improving the sensitivity of gravitational wave detectors, devices designed to measure distance changes as minute as one-thousandth the diameter of a proton. Scientists hope these detectors can one day further verify Einstein's theory of general relativity and even open a new window into the strange workings of the universe.

Gravitational waves, such as those emitted by extremely massive astronomical sources like neutron stars and black holes, can change the distance between two objects—even if that distance change is almost incomprehensibly small—by altering the shape of spacetime. Devices that can sense gravitational waves are among the most sensitive position meters ever built, but, right now, their abilities are inherently limited by quantum mechanics.

'Squeezed' Light May Improve Gravitational Wave Detectors
Part of the light-squeezing experimental setup. Photo taken by research-team member Keisuke Goda.

Laser interferometer gravitational wave detectors use laser light to measure the distances between mirrors. And light, being an electromagnetic (EM) field, is quantum in nature. EM fields contain quantum noise, fluctuations that make the beams less “sharp,” so to speak. Fluctuations mean that the physical parameters describing the beam are not fixed, but instead have built-in uncertainty or fuzziness, which limits the sensitivity of a gravitational wave detector.

The researchers in this study, from several institutions in the U.S. and Australia,* seem to have found a solution to this problem: using “squeezed” light. When light is squeezed, the fluctuations of one parameter, such as the light wave's amplitude, can be reduced at the expense of increased fluctuations of another parameter, such as its phase. The amplitude is a measure of the number of photons in the light beam, while the phase describes its location in time. Quantities corresponding to amplitude and phase are called quadratures, and quantum mechanics allows the uncertainty in one quadrature to be reduced as long as the uncertainty in the complementary quadrature increases.

In this case, the scientists squeezed one quadrature of the light, decreasing its quantum noise. While the noise of the other quadrature is necessarily increased, it is a quadrature they don't need to measure. By injecting the squeezed EM field in their prototype detector, the scientists were able to make it 44 percent more sensitive.

“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,” said Massachusetts Institute of Technology physicist Nergis Mavalvala, the team's leader.

“We are now much better positioned to implement squeezing in the kilometer-scale detectors, and catch that elusive gravitational wave.” she added.

Gravitational wave detectors work, in general, by interfering two laser beams that have traveled very long distances. The beams travel down two arms that form a 90 degree angle. While each arm is up to 4 kilometers in length, mirrors reflect the beams back and forth multiple times, effectively increasing the arm length to a few hundred kilometers. If a gravitational wave from deep space alters the length of each arm, the change to the laser interference pattern will be measurable.

Existing gravitational wave detectors are so sensitive that they have already approached the quantum limit. They include the two LIGO (Laser Interferometry Gravitational Wave Observatory) facilities in Washington and Louisiana, both operated jointly by the Massachusetts Institute of Technology and the California Institute of Technology; and Europe's largest gravitational wave detector, Virgo, located in Italy.

The researchers say that the next generation of gravitational wave detectors, such as Advanced LIGO, the planned upgrade to both LIGO facilities, will boast some impressive improvements, but further advancements will have to rely on quantum techniques such as squeezing.

Citation: K. Goda, O. Miyakawa, E. E. Mikhailov, S. Saraf, R. Adhikari, K. McKenzie, R. Ward, S. Vass, A. J. Weinstein, and N. Mavalvala Nature Physics advance online publication, 30 March 2008 DOI:10.1038/nphys920

*Massachusetts Institute of Technology, Cambridge, Massachusetts; California Institute of Technology, Pasadena, California; The College of William and Mary, Williamsburg, Virginia; Rochester Institute of Technology, Rochester, New York; and The Australian National University, Canberra, Australia

Copyright 2008 PhysOrg.com.
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earls
2.6 / 5 (5) Jun 05, 2008
I think we all know where this comments section is headed...

Quesion - If the gravity wave alters the length of the arm, does it not alter the laser beam as well?

The light is entangled with the matter, what happens to one happens to the other?

So won't the distance between emitter and reflector always be relative to one another?
DogMaEye
2.4 / 5 (7) Jun 05, 2008
This article is poorly written. It implies that gravity waves have been detected. No one has detected any gravity waves - ever!

And they will not ever detect them. They do not exist.
Tesla2
1.7 / 5 (7) Jun 05, 2008
There is no here or there. Time does not exist. You do not exist, except within my imagination. No, you say? Prove it.
Mercury_01
2.5 / 5 (2) Jun 05, 2008
gravity waves may not have been found yet, but we do detect fluctuations in gravity. And no, the lazer beam would not grow and shrink with the arm. The speed of light is constant on earth as it is on jupiter, because gravity flows perpendicular to the EM spectra. Gravity can only effect light by bending the spacetime that the light travels through, not by bending the light.
Gravity originates outside of our own 3d, in what could be considered the time dimention. It propagates paralell to the virtual waves that give rise to matter. I believe a gravity wave can exist, as the article says, but I dont know how plausible it is to find one on earth.
Mercury_01
2 / 5 (2) Jun 05, 2008
I think what tesla is trying to say is that you cant measure space. you need something to relate to. here and there are not points in space, but points in relation to something else. Even in empty space, you need a cartesian grid to measure from point A to B. and If you bring one along, it corresponds to your ruler back home. You can bring a lazer to check your measurements though, since light always travels constant, you can measure the distance between two objects, but not two arbitrary points in space.
Quantum_Conundrum
1.3 / 5 (3) Jun 05, 2008
Is length matter that may entangle light? Mass or number of things might be matter but length is a difference between here and there in space.

---

It has been proposed that space itself must be quantized.

Space may be "empty", but it is not "nothing".

In reality, space isn't empty, its just very low density of mostly hydrogen and helium "dust".
Mercury_01
2 / 5 (1) Jun 05, 2008
these particles would go into the category of things to relate to if measuring distance. When talking about "space", a physicyst isnt talking about outer space or any region of the universe. by "space", I meant 3d t, or spacetime.
There have been some attempts to quantize spacetime its-self, but this involves knowing what gives rise to constants like the mass of particles and other such mathematical crazyness that I dont understand... Spacetime and matter seem inextricably linked. You just cant have one without the other.
brant
1 / 5 (2) Jun 05, 2008
I would say that they will soon prove with a impressive degree of certainty that gravity waves do not exist....
Suzu
not rated yet Jun 06, 2008
I would say that they will soon prove with a impressive degree of certainty that gravity waves do not exist....


That's why I am pro gene pool control. :)
Noumenon
3 / 5 (2) Jun 06, 2008
Earls,
The gravitational wave, if exists, will effect the light wave (shifted) phase which is then combined with the other beem at 90* in order to look for an interferece pattern.
Noumenon
1.8 / 5 (4) Jun 06, 2008
Space, time, etc,.. In reality, these are not 'things' in themselves. In order for us to form conceptions of reality, our minds must order and relate sense experience, necessarily by use of the above a-priori concepts (mental forms). We cannot have ideas of reality except through these forms, so therefore our model of reality will be necessarily conditioned subjectively,.. it will necessarily involve space and time, cause & effect, because of the way the mind processes sense experience. Reality of itself is subjected to mental conditions, so our resulting concept of reality will never be disentangled from these built in forms of understanding. This is why qm is probabilistic. Our minds have evolved to function in the macroscopic relm, but these methods of ordering sense experience will not apply in the quantum relm. God does not play dice but we must.
Alexa
2.3 / 5 (3) Jun 09, 2008
By AWT the gravitational waves exists, but they're heavily dispersed by vacuum environment, having a longitudinal character. So we cannot detect them at longer distances.
Noumenon
1 / 5 (1) Jun 09, 2008
Maybe with satellites and so much longer distance if earth bound dosn't detect anything,... but I would think they 'worked it out' that if they exist it should be detectable with existing set ups.
hibiscus
3 / 5 (1) Jun 09, 2008
Space, time, etc,.. In reality, these are not 'things' in themselves. In order for us to form conceptions of reality, our minds must order and relate sense experience, necessarily by use of the above a-priori concepts (mental forms). We cannot have ideas of reality except through these forms, so therefore our model of reality will be necessarily conditioned subjectively,.. it will necessarily involve space and time, cause & effect, because of the way the mind processes sense experience. Reality of itself is subjected to mental conditions, so our resulting concept of reality will never be disentangled from these built in forms of understanding. This is why qm is probabilistic. Our minds have evolved to function in the macroscopic relm, but these methods of ordering sense experience will not apply in the quantum relm. God does not play dice but we must.


You really smoke heavy stuff huh?

Damn... that sounds like one of those opium tales.

And how does your theory apply to your own message?
ShadowRam
2 / 5 (1) Jun 09, 2008
Don't they have to find something thats NOT affected by gravity in order to detect gravity waves?

So far I haven't heard of anything thats not affected by gravity...
Noumenon
3 / 5 (2) Jun 09, 2008
Space, time, etc,.. In reality, these are not 'things' in themselves. In order for us to form conceptions of reality, our minds must order and relate sense experience, necessarily by use of the above a-priori concepts (mental forms). We cannot have ideas of reality except through these forms, so therefore our model of reality will be necessarily conditioned subjectively,.. it will necessarily involve space and time, cause & effect, because of the way the mind processes sense experience. Reality of itself is subjected to mental conditions, so our resulting concept of reality will never be disentangled from these built in forms of understanding. This is why qm is probabilistic. Our minds have evolved to function in the macroscopic relm, but these methods of ordering sense experience will not apply in the quantum relm. God does not play dice but we must.


You really smoke heavy stuff huh?

Damn... that sounds like one of those opium tales.

And how does your theory apply to your own message?


Lol, perhaps a little out of context; I was referring to q-cunundrums comment.
earls
not rated yet Jun 10, 2008
Right back to where we started from ShadowRam. ;)
TimESimmons
1 / 5 (1) Jun 17, 2008
Or maybe there's something in the way stopping the gravitational waves

http://www.presto...ndex.htm

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