Atom Optics To Predict Gravitational Waves
October 19, 2012

Using Atom Optics To Predict Gravitational Waves

[ Watch the Video: Atomic Interferometer To Predict Gravitational Waves ]

April Flowers for - Your Universe Online

NASA is pursuing a pioneering technology capable of atomic-level precision to detect gravitational waves or ripples in space-time caused by cataclysmic events, including the Big Bang itself.

Researchers at NASA's Goddard Space Flight Center, AOSense, Inc and Stanford University have been awarded funding under NASA's Innovative Advanced Concepts (NIAC) program to advance atom-optics technology. This emerging, highly precise measurement technology, some believe, is a technological panacea for a wide range of applications, including measuring gravitational waves to steering submarines and airplanes.

"I've been following this technology for a decade," said Bernie Seery, a Goddard executive. "The technology has come of age and I'm delighted NASA has chosen this effort for a NIAC award," he said.

The NIAC program is designed to support high-risk, potentially revolutionary technologies and mission concepts that have a chance of advancing NASA's objectives.

"With this funding and other support, we can move ahead more quickly now," Seery said. He added that the U.S. military has invested heavily in the technology to improve navigation. "It opens up a wealth of possibilities."

This new technology offers promise for a variety of space applications, however the research team is focusing their efforts on using the funding to advance sensors that could detect theoretically predicted gravitational waves.

Einstein's theory of general relativity predicted that gravitational waves occur when massive celestial objects move and disrupt the fabric of space-time. When these waves reach Earth, the planet expands and contracts less than an atom in response because of how weak they are, making their detection with ground-based equipment challenging. Environmental noise, such as ocean tides and earthquakes, can easily swamp the faint murmurings of the waves.

No instrument or observatory, including the ground based Laser Interferometer Gravitational-Wave Observatory, has ever directly detected the gravitational waves, despite the fact that astronomical observations have implied their existence.

Confirmation of the existence of gravitational waves would revolutionize astrophysics, giving scientists a new tool for studying everything from inspiralling black holes to the early universe before the formation of atoms. The NASA/AOSense team believes that atom optics, or atom interferometry, holds the key to direct detection.

Optical interferometry is a 200 year old technique still widely used to obtain highly accurate measurements. The measurements are obtained by comparing light that has been split into equal halves by a beamsplitter device. One light beam is reflected off a mirror that is fixed in place into a camera or detector, while the other shines through whatever the scientist wants to measure. This second beam then reflects off a second mirror, back through the beamsplitter and into a camera or detector.

Because the first beam travels a fixed path and the other travels either an extra distance or on a different path, the two beams overlap and interfere with each other when they meet up. This creates an interference pattern that researchers use to obtain highly precise measurements.

Atom interferometry, works in a similar manner, but hinges on quantum mechanics. Waves of light can act like particles called photons, and if they are cooled to near zero temperatures atoms can be cajoled into acting like waves. Scientists achieve these frigid temperatures by firing a laser at the atom which slows its velocity to nearly zero. Then another series of laser pulses are fired at the atoms, putting them into a "superposition of states."

This superposition of states means that the atoms have different momenta, permitting them to separate spatially. They can then be manipulated into flying along different trajectories, eventually crossing paths and recombining at the detector.

"Atoms have a way of being in two places at once, making it analogous to light interferometry," said Mark Kasevich, a Stanford University professor and team member credited with pushing the frontiers of atom optics.

The unprecedented level of precision is the power of atom interferometry. An atom's path varying by even a picometer can be detected by an atom interferometer.

"Gravitational-wave detection is arguably the most compelling scientific application for this technology in space," said physicist Babak Saif, who is leading the effort at Goddard.

So far, the team has designed a powerful, narrowband fiber-optic laser system. Plans are in the works to test the apparatus at one of the world's largest atom interferometers — a 33-foot drop tower in the basement of a Stanford University physics laboratory. The technology would be a foundation for any atom based instrument created to fly in space.

The team will insert a cloud of neutral rubidium atoms inside the 33-foot tower during the test. The laser system will fire pulses of light to cool falling atoms being affected by gravity. Once these atoms are in a wave-like state, they will encounter another round of laser pulses to separate them spatially. Their paths will be manipulated so they will cross at the detector and create the interference pattern.

The team is working on a gravitational-wave mission concept as well, which is similar to the Laser Interferometer Space Antenna (LISA). The new concept calls for three identical spacecraft in a triangular configuration, with one major difference. The new spacecraft would be equipped with atom interferometers and would orbit much closer to each other, between 500 and 5,000 km apart. LISA's spacecraft have a 5 million kilometer separation. The new spacecraft would be able to detect the miniscule movement of a gravitational wave rolling past.

"I believe this technology will eventually work in space," Kasevich said. "But it presents a really complicated systems challenge that goes beyond our expertise. We really want to fly in space, but how do you fit this technology onto a satellite? Having something work in space is different than the measurements we take on Earth."

Saif said, "We [at Goddard] have experience with everything except the atom part," Saif added that AOSense already employs a team of physicists and engineers focused on building compact, ruggedized atom-optics instruments. "We can do the systems design; we can do the laser. We're spacecraft people. What we shouldn't be doing is reinventing the atomic physics. That's our partners' forte."