Doubled sensitivity could allow gravitational wave detectors to reach deeper into space

Doubled sensitivity could allow gravitational wave detectors to reach deeper into space
A new squeezed vacuum source could make gravitational wave detectors sensitive enough to study neutron stars. Credit: Eric Oelker, Massachusetts Institute of Technology

Researchers from the Massachusetts Institute of Technology (MIT) and Australian National University have developed new technology that aims to make the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) even more sensitive to faint ripples in space-time called gravitational waves.

Scientists at Advanced LIGO announced the first-ever observation of gravitational waves earlier this year, a century after Albert Einstein predicted their existence in his general theory of relativity. Studying gravitational waves can reveal important information about cataclysmic astrophysical events involving black holes and neutron stars.

In The Optical Society's journal for high impact research, Optica, the researchers report on improvements to what is called a squeezed vacuum source. Although not part of the original Advanced LIGO design, injecting the new squeezed vacuum source into the LIGO detector could help double its sensitivity. This would allow detection of gravitational waves that are far weaker or that originate from farther away than is possible now.

A wrinkle in space-time

For millennia, people have used light as a way of viewing the universe. Telescopes magnify what is visible with the naked eye, and newer telescopes use non-visible parts of the electromagnetic spectrum to provide a picture of the universe surrounding us.

"There are many processes in the universe that are inherently dark; they don't give off light of any color," said Nergis Mavalvala, part of the MIT Kavli Institute for Astrophysics and Space Research team and a leader of the research team. "Since many of those processes involve gravity, we want to observe the universe using gravity as a messenger."

Researchers from the California Institute of Technology and MIT conceived, built, and operate identical Advanced LIGO detectors in Livingston, Louisiana and Hanford, Washington. Each observatory uses a 2.5-mile long optical device known as an interferometer to detect gravitational waves coming from distant events, such as the collision of two black holes detected last year.

Laser light traveling back and forth down the interferometer's two arms is used to monitor the distance between mirrors at each arm's end. Gravitational waves will cause a slight, but detectable variation in the distance between the mirrors. Both detectors must detect the variation to confirm that gravitational waves, not seismic activity or other terrestrial effects, caused the distance between mirrors to change.

Studying neutron star collisions

"We want to use the Advanced LIGO detectors to sense the farthest gravitational wave or weakest gravitational wave possible," said Mavalvala. "However, this is limited by the quantum fluctuations of the laser light, which create a certain level of noise. If a gravitational wave is weaker than that level of noise, then we can't detect it. Thus, we have a big impetus to decrease that noise, and we can do that using our squeezed vacuum source."

The researchers are planning to add their new squeezed vacuum source to Advanced LIGO in the next year or so. Once implemented, it will improve the sensitivity of the gravitational detectors, particularly at the higher frequencies important for understanding the composition of neutron stars. These extremely dense stars contain the mass of the sun, which has a radius of 700,000 kilometers, within just a 10-kilometer diameter.

"Nobody knows exactly how the neutrons in these stars behave when you crush them into such a dense package," said Mavalvala. "These neutron stars sometimes collide with each other, and at the moment that they are ripping each other apart, you can study the properties of this nuclear matter by detecting that occur at higher frequencies."

How can a squeezed vacuum state help?

Mavalvala explains that the laser light used in the LIGO detectors can be thought of as a type of ruler. "The that results from the quantum fluctuations of the laser light is like trying to measure the length of a piece of paper while the ruler's tick marks keep wiggling and moving about," she said. "Because this noise causes the tick marks on our meter stick to jitter, we want to reduce that by injecting this special squeezed vacuum state that has smaller fluctuations, or produces less jitter on the tick marks of our ruler."

Creating the squeezed vacuum source involved modifying a vacuum state, which is the quantum state with the lowest possible energy. "We captured part of this electromagnetic vacuum in an optical cavity by first building the experiment with laser beams and then making the squeezed vacuum state by dialing down the laser power until there is no light, and only the vacuum is left," said Mavalvala. "Then, everything we would have done to the light, we can do to the squeezed vacuum state."

The improved squeezed vacuum source builds on work conducted by researchers at Leibniz University of Hannover and the University of Hamburg, both in Germany. The new squeezed vacuum source exhibits about ten times less phase noise than previously reported sources. The researchers accomplished this by decreasing vibrations that can adversely affect the squeezed state and by making improvements to a system that corrects any remaining phase noise.

"The best approach is to try to reduce the amount of intrinsic phase noise, but if you can't do that, you can measure how much it's jittering and then use feedback to correct it," said Eric Oelker, first author of the paper. "We used a variation of a correction scheme that has been employed before, but our version allowed us to increase the bandwidth of the feedback loops, suppressing the phase noise in a completely new way."

The researchers say that the new squeezed vacuum source is almost ready to deploy in Advanced LIGO. In separate research, they have shown that they can also reduce optical losses that can degrade a squeezed vacuum state. "By combining the optical losses that we think we can achieve and this new lower phase noise result, we're aiming for a factor of two in improvements for Advanced LIGO," said Mavalvala. "We hope to achieve greater improvements in gravitational wave sensitivity than was previously thought possible."


Explore further

Closing in on Einstein's window to the universe

More information: Optica, DOI: 10.1364/OPTICA.3.000682
Journal information: Optica

Citation: Doubled sensitivity could allow gravitational wave detectors to reach deeper into space (2016, June 23) retrieved 17 July 2019 from https://phys.org/news/2016-06-sensitivity-gravitational-detectors-deeper-space.html
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Jun 23, 2016
This is misguided, how in the hell do you calibrate if space and time is the thing you're looking to be changing. It's like saying you're moving relative to nothing defined and you don't feel the G force, that is, what G force, all that is misunderstood or something tangible? Either way, I can't seem to calibrate before taking the measurement. So simply put, a measurement is taken and a claim that cannot be supported. Really!? Sounds like instrumentation anomaly for everything feels the same thing even your clock, nothing is defined. This is pseudo science. The only gravity waves are your near field which washes out everything, not to mention your error of assumption, gravity is not a separate force of nature, Einstein was nuts. Speed of light is not a constant. Relative to what? Time to forget 20th century's lack of understanding.

https://drive.goo...4dWFJSDA

Jun 23, 2016
" A Wrinkle in Time" good read as a kid

Jun 23, 2016
At what point will this be exploited in a usable technology?

Jun 23, 2016
At what point will this be exploited in a usable technology?
When they put it in LIGO.

Further downstream, any application for lasers that requires extremely low noise (communications or quantum computing, perhaps?) can make use of principles proven in this experiment.

Good question.

Jun 23, 2016
Einstein claimed that the bending of light passing near the Sun, famously measured by Author Eddington during a solar eclipse, and also the precession of the orbit of Mercury around the Sun were due to space-time deformation as characterized by his general theory of relativity. Of course, if space-time deformation is not the explanation, it remains for us to look for the explanation or explanations, but in any event, whether "space" physically interacts in a gravitational field or not does not address the problem that the non-Euclidean geometry of the general theory of relativity is self-contradicting. Even if Einstein is correct that "space" does interact in a gravitational field or near massive bodies, his statement that "in the presence of a gravitational field the geometry is not Euclidean" cannot be correct if that non-Euclidean geometry is self-contradicting.


Jun 23, 2016
that the non-Euclidean geometry of the general theory of relativity is self-contradicting

How so? What exactly do you find 'contradicting' (with a bit of math to back it up, if you please. Qualitative statements of the kind "ain't so" aren't really useful as a basis for discussion)

Jun 23, 2016
whether "space" physically interacts in a gravitational field
I don't know what this means. For a trivial example, if an object moves it has interacted with spacetime; its position has changed. This can happen whether there is a nonzero gravitational field or not. Also, an interaction requires two participating items; you have only specified one: "space." Finally, relativity, both general and special, show that space and time are a single manifold, called "spacetime." It's incorrect given the existence (and confirmed measurement by experiment) of the Lorentz transform to speak of space alone, particularly when discussing any aspect of relativity.

the non-Euclidean geometry of the general theory of relativity is self-contradicting
You'll need to provide some evidence to support this claim, since GRT has been confirmed in numerous experiments and does not contradict any observation, and does not contradict any theorem of mathematics.

Jun 23, 2016
At what point will this be exploited in a usable technology?

Someday we'll surf these gravitational waves to distant exotic shores.

Jun 23, 2016
Einstein claimed that the bending of light passing near the Sun, famously measured by Author Eddington during a solar eclipse, and also the precession of the orbit of Mercury around the Sun were due to space-time deformation as characterized by his general theory of relativity. Of course, if space-time deformation is not the explanation, it remains for us to look for the explanation or explanations, but in any event, whether "space" physically interacts in a gravitational field or not does not address the problem that the non-Euclidean geometry of the general theory of relativity is self-contradicting. Even if Einstein is correct that "space" does interact in a gravitational field or near massive bodies, his statement that "in the presence of a gravitational field the geometry is not Euclidean" cannot be correct if that non-Euclidean geometry is self-contradicting.


Try optics and Maxwell, study a gaussian beam moving through an inhomogeneous media. Choose appropriate order.

Jun 23, 2016
that the non-Euclidean geometry of the general theory of relativity is self-contradicting

How so? What exactly do you find 'contradicting' (with a bit of math to back it up, if you please. Qualitative statements of the kind "ain't so" aren't really useful as a basis for discussion)

With mass as a variable calculate momentum, note that momentum then becomes a function of displacement. Reconcile the math, i.e. dot product, etc. it's all nonsense. Note the discovery of the proton and the electron as in all matter answers Newton, where did the force originate? We must stop being lame.

Jun 23, 2016

With mass as a variable calculate momentum, note that momentum then becomes a function of displacement. Reconcile the math, i.e. dot product, etc. it's all nonsense. Note the discovery of the proton and the electron as in all matter answers Newton, where did the force originate?

Anyone care to translate this from gibberish to english?

Jun 23, 2016
note that momentum then becomes a function of displacement


Okay, so... conservation of momentum only holds when the physical description of a process or particle stays the same when you translate in one direction or another (momentum conserved along the same translation, eg). "Physical description" can be a Lagrangian description, for example. (Noether's theorem)

But, in a curved space, you will find that the Lagrangian changes as you translate. Thus, the expectation of conservation of momentum is invalid. So your complaint that momentum changes as a function of displacement is no complaint at all. It's all a byproduct of different observers measuring lengths and times differently, and thus measuring momentum and energy differently.

What you will find though is that (in units of c=1), m^2 = -E^2 + P^2 will hold true for all local observers. That is to say, as momentum and energy of the particle change from point to point, its mass will be constant.

Jun 23, 2016
note that momentum then becomes a function of displacement


Okay, so... conservation of momentum only holds when the physical description of a process or particle stays the same when you translate in one direction or another (momentum conserved along the same translation, eg). "Physical description" can be a Lagrangian description, for example. (Noether's theorem)

But, in a curved space, you will find that the Lagrangian changes as you translate. Thus, the expectation of conservation of momentum is invalid. So your complaint that momentum changes as a function of displacement is no complaint at all. It's all a byproduct of different observers measuring lengths and times differently, and thus measuring momentum and energy differently.

What you will find though is that (in units of c=1), m^2 = -E^2 + P^2 will hold true for all local observers. That is to say, as momentum and energy of the particle change from point to point, its mass will be constant.

WTF?

Jun 23, 2016
Do the crackpots infesting these comments all come from the same hatchery? Could it be reversed time Zika? Because there's surely a pinhead problem here.

Jun 23, 2016
I came here for the LOLs ; was not disappointed.

Jun 23, 2016
I doubt that HF is human.

Thanks, humans are stupid, ants are smarter and I hear cats know physics.

Jun 24, 2016
Poincaré first came up with the idea of gravity waves in 1905. Einstein's first submission on the issue was in a paper entitled "Do Gravitational Waves Exist?" in which he believed that he disproved their existence. Colleagues pointed out errors in the paper and by the time he corrected them he reversed his position and changed the title to "On Gravitational Waves."

In the meantime, he had promised to give a lecture at Princeton, about the nonexistence of gravitational waves, as claimed in his original proof. He discovered the mistake in this proof the day before this lecture, when he had not yet found the proof of the opposite conclusion. So he gave a lecture about his mistake and ended with these words: "If you ask me whether there are gravitational waves or not, I must answer that I do not know. But it is a highly interesting problem."


Quoted from 'Einstein's Mistakes' by Hans Ohanian, p.322, reference given is D.Kennefick, Physics Today, September 2005, P.43

Jun 24, 2016
Thanks, @Robert! I hadn't heard that anecdote before.

Jun 24, 2016
Thanks, @Robert! I hadn't heard that anecdote before.


Note, Einstein's work was on corpuscular theory without a well defined understanding of atomic and electromagnetic phenomena. His understanding of Planck and Bohr was spotty at best. Although QM was a great tool that defined the wave nature of matter. The centers of the spherical fields was not well defined, i.e. the standard model and the slit experiment. Scientist were at the front of discovery. So let's move on.

Jun 26, 2016
So let's move on.

As if you've had a single intelligible conversation on this site.
No one listens to you.

Jun 27, 2016
So let's move on.

As if you've had a single intelligible conversation on this site.
No one listens to you.

I know; those who cannot hear, do not hear; those who cannot see, do not see; those who cannot think, do not think; those without logic are like a blind squirrel, he might find a nut.

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