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Einstein's Cosmic Symphony

Image of the Universe

Einstein's Cosmic Symphony

Squeezing Light

Blocking the Clangs and Bangs

NINJA: Stealth Invaders

 

Squeezing Light

Physicist aims to challenge the fundamental nature of light

Feb 29, 2012 | Article by: Judy Holmes

Ballmer works on laser table

Physics professor Stefan Ballmer (at left) and graduate student James Lough examine some of the equipment that Ballmer is using to construct a mini-LIGO in the Physics Building.


Before arriving at Syracuse University last fall, physics professor Stefan Ballmer worked at LIGO’s Hanford Observatory where he listened for Einstein’s heavenly symphony. He heard a cacophony of sounds: the electrical equivalent of whoops, clangs, and bangs emanating from noises as varied as water flowing over dams hundreds of miles away and trains vibrating their tracks to broken electronic circuits. But, the barely audible “hiss” he was listening for—a sound from the early universe akin to the “yopp” from the tiniest Who in Whoville—eluded him. “We got very good at distinguishing one vibration from another,” Ballmer says. “You learned to hear things that went wrong with the gravitational-wave detector simply by noting a change in the vibrational noise.”

Advanced LIGO, which will be installed in the two observatories over the next three years, is designed to overcome the limitations of the first-generation LIGO instrument. Advanced LIGO will filter out environmental noises, including minute noises generated by the detector itself, all of which can muffle the music of distant objects in the universe. It is as sensitive of an instrument as can be created with known technology. Ballmer, however, aims to explore the unknown. He is building a mini-LIGO in the basement of the Physics Building, which he will use to challenge the fundamental nature of light, and manipulate it to reduce its intrinsic vibrational noise. The knowledge will help scientists further improve LIGO’s sensitivity.

The traditional model of light is represented as an electromagnetic wave traveling across space and time. However, at the fundamental or quantum level, light is composed of tiny particles—individual photons that exhibit both wave-like and particle-like behavior. Laser light exploits the particle-like properties of light. Inside the LIGO interferometer, light is quantized, creating individual photons of light that bombard the mirrors and the photodetector like tiny pieces of hail pelting a window. The photons push the mirrors back a tiny bit (phase noise) and create a blip sound (shot noise) when they return to the photodetector, Ballmer says. These noises limit LIGO’s ability to detect gravitational waves in ways that current technologies have not resolved. “It turns out this is not a fundamental problem,” Ballmer says. “The trick is to produce a non-classical state of light in the interferometer. One way to do that is to squeeze the light so that the phase noise and the shot noise cancel each other out.”

The mini-LIGO will be used to prove that a squeezed state of light can be produced and controlled. Ballmer will also explore ways to manipulate the tiny force that light exerts to automatically re-align the mirrors in the interferometer. The mirrors are currently kept in position through a system of sensors, tiny magnets, and electromagnetic fields. 

The work has just begun. Ballmer estimates it will take up to three years just to build the scale LIGO. There are laser systems to be stabilized, mirror suspension systems to be designed and tested, sensors and circuit boards to be created, and software to be written. “We know the technology that exists,” says Ballmer, who helped build the first LIGO instrument as a doctoral candidate at MIT. “We plan to go beyond that technology and help develop super Advanced LIGO.”



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Contact Information

Judy Holmes
jlholmes@syr.edu

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