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

Visualization of a massive body generating gravitational waves (UWM)
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


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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!

Comments on this entry are closed.

  • Uclock June 12, 2008, 1:35 PM

    First of all, it is a complete waste of money and resources mainly because gravitational radiation does not exist. Einstein’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 didn’t.
    Don’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!

  • bob June 12, 2008, 4:30 PM

    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.

  • Ricky Diaz June 14, 2008, 4:57 AM

    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.

  • bob June 20, 2008, 4:09 PM

    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.

  • bob June 20, 2008, 4:19 PM

    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.

  • David Gronczniak July 9, 2008, 9:54 PM

    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.

  • Tiq Lee November 20, 2008, 2:25 PM

    Can one control gravity via strong magnetic forces?