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

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 injectionâ€”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.


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

  1. 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?

  2. 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.

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

    Please forgive the oxymoron !

  4. 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 the light beam experiences along with the distance the light beam will travel….
    Anything used to measure distance (physical length, or time it takes to travel) will be affected by the gravity wave.
    So how do you make a ruler that is not affected by the physics of space and time?

    I still have not read an article that can explain this to me. Will it work or is it a waste of money?

  5. 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 of the light beam (traversing a constant distance at a constant speed) … it has to traverse the effect and as the effect alters space/time, it equally affects the light beam as it passes through the ripple…

    Putting these thoughts down in words is VERY difficult!

  6. 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 trying to find if it squeezes and expands earth and therefore two points in its surface that will be too much of an assumption.

    I wonder why the mirror on moon that reflects the laser beam from earth has not been used? Using software filtering we could have removed all known natural distortions and at least figured out if there is any indication of earth and moon getting temporarily separated during a gravity wave event. We can even dedicate a geo-stationery satellite for this purpose

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

  8. 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.

  9. 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?

  10. 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?

  11. I agree with Alp.

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

  12. 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.

  13. 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.

  14. 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!

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

    Seriously dude, read up a bit on astronomy. 😛

  16. 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, see my web site at

  17. > 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 wonâ€™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 is unlikely), it would have indeed revolutionary consequences. Then of course, understanding gravitation and space time warping is the first aspect needed for actively using those aspects. And since we do not really understand it yet, we can only speculate whether it is possible or not.

  18. 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).

  19. 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 we never dreamed of.

    In short – the future is never futuristic. Where were the Ipods and 3G mobile phones in the 50es pulp fiction? We suck at predicting what good research will be, but in the long run there will always be something good coming out of even the most fundamental research.

  20. 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 of the orbit (circular? elongated?), where the black holes are in our sky, and how far they are from earth.

    Black holes will be an energy source that will be batlled over in the galactic future. Cities will be created on girder-work rings, giant superconducting coils that will thread a magnetic field through through the hole’s horizon and will hold it on the hole, despite its tendency to pop off. As the horizon spins, it drags the nearby space into a tornado-like swirl which in turn interacts with the threading magnetic field to form a gigantic power generator. The magnetic field lines become transmission for the power.. Electric current is driven out the hole’s equator (in the form of electrons flowing inward) and up the magnetic field lines to the ring world. There the current deposts its power. Then it flows out of the ring world on another set of magnetic field lines and down into the hole’s north and south poles (in the form of positrons flowing inward). By adjusting the strength of the magnetic field, the world’s inhabitants can adjust the power output: weak field and low power in the world’s early years; strong field and high power in later years. Gradually the power is extracted, the hole will slow its spin, but it will take billions of years to exhaust the hole’s enormous store of spin energy..

    3.) Gravitational waves also will contain a partial map of the inspiraling holes’ spacetime curvature. It will test general relativity with more accuracy than any other experiments have. Will the map agree with Kerr’s solution of the Einstein field equation? Does space swirl near the spinning hole?To what degree? Does the swirl change as one approaches the horizon agree with Kerr’s prediction?

    4.)As the two event horizons merged they are predicted to produce a nonlinearity. (A quantitiy if linear if its total size is the sum of its parts). Strong curvature will produce more curvature, which in turn produce still more curvature-much like the growth of an avalanche. Nonlinearity is understood in a quiescent black hole; there it is responsible for holding the hole together. What is not understood is what the nonlinearity does, how it behaves, what its effects are, when the strong curvature is violently dynamical. Scientists will be readjusting their supercomputers for their simulations.”

    From me…How do we apply it to the present? What are the immediate benefits that might be realized?

    First, the topology of space will be understood at a greater level. Topology dictates what shapes existing shapes can truncate or stellate into..the limits of what shapes they can change into.

    Now molecules can form with other molecules into compounds but shape always plays a major role in each change. There is likely a topological geometric signature that describes how a virus enters into a cell and spreads or how a vaccine enters a body and interfaces with all the necessary cells to produce antibodies.

    Today microbiologists are doing way too many experiments to realize cures for diseases. In the future a topologist will generate a software program that will indicate which experiments are heading in the wrong direction and might poison patients needing help. Animals will no longer necessarily be the guinea pigs they are for science today and cures for diseases may come very quickly.

    On board the Columbia moss and sunflowers were sent up to see how microcurvature of spacetime affects them. Moss has been know to react to gravitational fields by growing up walls and onto inner roof tops of caves. Sunflowers, on the other hand, have spiral patterns in their florets called Fibonacci sequences that disappeared onboard the Columbia while moss turned into a beautiful spiral patterned flower like the sunflower does at earth’s surface. This gives us a direct connection of spacetime curvature to the life sciences and tells us that some distant earth-like planet with a greatly differing gravitational field will escort evolution through an entirely different path.

  21. First of all, it is a complete waste of money and resources mainly because gravitational radiation does not exist. Einsteinâ€™s view of spacetime is a clever but inaccurate in the sense that the directional arrow of time and the existence of space is not explained by his concept of General Relativity. If he was right then by now we would be using anti-gravity machines to fly around in and produce all our power requirements. It is a complete lack of understanding of spacetime that is holding physics back.
    If Einstein was right then LISA would have detected gravitational radiation from GRB070201 in the relatively nearby Andromeda galaxy which in theory it is sensitive enough to detect, but didnâ€™t.
    Donâ€™t hold your breath, LIGO will never detect gravitational waves, nor will LISA when it is launched. The reason is simple, individual spacetime fields collapse when any object is accelerated so spacetime does not ripple!

  22. Uclock,
    Fields do not collapse and if you wish to take on GR then you must disprove how GPS systems are so accurate. Without GR taken into account, the calculated locations of objects would be miles off.

    You need also to explain why light is bent gravitationally and produuces Einstein crosses in the universe without General Relativity and how GR has calculated the delays in pulse signals from binary neutron stars. Those calculations match observed results.

    Antigravity machines have nothing to do with GR. GR does not allow a mass to unwarp spacetime. That is like asking the tides to stop rising when the moon is overhead. if such a machine was built, the antigravitational forces would have to exceed the electrical forces that hold it together and it would fly apart before the inventor could put it together.

    Spacetime does ripple. Everything ripples because everything can vibrate. All accelerations produce ripples whether it is the acceleration of electrons, protons or boats through water or humans on ground.

    If LIGO or LISA fail to detect any gravitational waves, it is because gravitational waves are very weak since gravity is weaker than electrical forces by 10^37 times and both EM and gravitational waves obey a weakening with distance by the inverse square law. Big events are needed and they are simply too far away.

  23. If they find a way to make detecting gravitational waves easier and easier, hopefully the answer to the question, “Does the sun have a brown dwarf companion or a red dwarf companion that causes life threatening sized asteroids and comets to come dangerously close to the Earth, causing 1 major impact every 100 million years or so?” is yes. Hopefully a red dwarf star, because then we could observe one way closer than Proxima. Maybe even send a probe to get an even better close up. Also if it exists, then both would be a binary star system and we could observe it up close. Right now it’s unpredictable, because although a red dwarf is a star, it would be dim and possibly a trillion miles away. And it’s orbit could be tilted up to 90 degrees compared to the 8 planets. So the range in area in the sky it could be viewed could be the whole sky until we find it if it exists. The hope isn’t dumb because it’s gravity if it exists could send life threatening asteroids to the inner solar system. Whether the answer is yes or no, the major impacts do happen. So a yes won’t make things worst than they already are. And a star means a chance for even more planets to observe, including gas planets. Not to mention, habitable planets.

  24. If there is a brown or red dwarf companion in an orbit tilted 90 degrees to the ecliptic then it would disturb all of the orbits of the solar system including the sun. The sun’s wobble would not be matching patterns that associate it with Jupiter. It would have a different cylce and solar activity would be enormous at perihelion. Now maybe that is possible but you would need to gather some evidence that shows weather patterns on the earth changed very dramitically and very rarely in earth history. There is no such evidence that has been measured.

  25. i should have phrased the first sentence with a proposed dqarf tilted 90 degrees to the zodiac instead of the ecliptic.

    A second point against a dwarf companion is that perihelions of all the planets would be affected dramatically, elongating the orbits much greater than exists right now. When the dwarf is crossing the zodiac it would tug the orbits to one side. When the dwarf is 90 degrees from that point it would warp the orbits closer together and there would be a pattern all the planets would follow year by year and would be observable annually.

  26. OK you got a load of ideas and you don’t even see them as great tests in themselves, like the red shift idea . How about looking for gravity waves from red shifted objects out in space that are in or very near objects that should be producing waves. If you hit a bell the whole thing varies and rings for awhile afterward ,wouldn’t gravity waves create a ringing effect for a short while even after the wave passes by ,thus allowing the detection after the initial undetectable g. wave . How about looking at the gravity lenses that we see in space and see if they are ringing ? This is something you don’t find unless you look for the ringing effect , things are probably ringing all over and we need to look for !
    The gravitation lenses are a fact and its the best spot to look for this effect because it directly effects optically our view of whats behind them , the things we see through them are at varying distances and this variation will probably prove through the differences between the objects observed that there is a gravity wave . The objects that are creating the gravity lenses are probably getting bombarded by objects that get pulled into them regularly causing gravity waves that vary at least a small amount . This should really have a dramatic effect on the lensing effect. There is probably data out there ready to look at and they don’t know gravity waves are the reason for their occasional wobbly observations.

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