A recent news item headlined “LIGO surpasses the quantum limit ” caught my attention. I know next to nothing about quantum mechanics, but I have a general idea that, among many other things, it describes ultimate limits for physical behavior on a microscopic level. So, surpassing a quantum limit struck me as a strange statement. In some ways, the article reads like science-fiction, for example, “In 2015, the Laser Interferometer Gravitational-Wave Observatory (LIGO) made history when it made the first direct detection of gravitational waves, or ripples in space and time, produced by a pair of colliding black holes.” Ripples in space and time — what does that mean? Or how about: “At the heart of LIGO’s success is its ability to measure the stretching and squeezing of the fabric of space-time on scales 10 thousand trillion times smaller than a human hair.”
The article goes on to describe how the precision of LIGO’s measurements has until now been limited by the tiny amounts of quantum noise that fills empty space. A team led by Lisa Barsotti, a senior research scientist at MIT, has developed a technique called quantum squeezing, which allows them to bypass that limitation. The project is based upon research first done at MIT by scientists in the departments of physics and astrophysics and now includes dozens of scientists and engineers based at MIT, Caltech, and the twin LIGO observatories in Hanford, Washington, and Livingston, Louisiana.
Which brings me to my down-to-earth interest in how innovation happens. In previous blogs I wrote about how innovation comes from people in different areas of expertise working together. And also, how tensions between different kinds of workers, for example, engineers and technicians or theoreticians and experimentalists can produce creative energy.
Scientists are driven by their curiosity — these particular scientists wanted to know more about gravitational waves so they needed a method that would transcend the limits imposed by nature. “We can’t control nature, but we can control our detectors,” said Barsotti.
Transcending those limits required the scientists to come up with theories of how it could be done, and engineers had to figure out practical ways to make it happen. “A project of this scale requires multiple people, from facilities to engineering and optics,” Barsotti said.
A Little History
The existence of gravitational waves was a prediction in Einstein’s general theory of relativity in 1916. A method for detecting them wasn’t theoretically conceived until the 1960s when scientists developed the idea of laser interferometry. That was followed by years of experiments and theoretical revisions. Finally, a small-scale prototype of what was to become LIGO was built in 1980.
However, building a full-scale system required a huge investment of money, resources, and time. The initial funding finally came from the Federal Government’s National Science Foundation, which approved the construction proposal in 1990, although the work didn’t get started until four years later.
But the original LIGO did not find any gravitational waves. It was then redesigned and modified over a span of four years to increase its sensitivity by 10 times and, finally in 2015, the first gravitational wave was detected.
An article on the Caltech LIGO website gives an idea of the scale of engineering that went into the project. “It consists of two L-shaped detectors with 4-km-long vacuum chambers built 3,000 kilometers apart and operating in unison to measure a motion 10,000 times smaller than an atomic nucleus (the smallest measurement ever attempted by science) caused by the most violent and cataclysmic events in the Universe occurring millions or billions of light years away.”
“Now that we have surpassed this quantum limit, we can do a lot more astronomy,” said Lee McCuller, assistant professor of physics at Caltech and one of the leaders of the new study. “LIGO uses lasers and large mirrors to make its observations, but we are working at a level of sensitivity that means the device is affected by the quantum realm.”
The results also have ramifications for future quantum technologies such as quantum computers and other microelectronics as well as for fundamental physics experiments. “We can take what we have learned from LIGO and apply it to problems that require measuring subatomic-scale distances with incredible accuracy,” McCuller said.
“When NSF first invested in building the twin LIGO detectors in the late 1990s, we were enthusiastic about the potential to observe gravitational waves,” said NSF Director Sethuraman Panchanathan. “Not only did these detectors make possible groundbreaking discoveries, but they also unleashed the design and development of novel technologies. This is the true DNA of NSF — curiosity-driven explorations coupled with use-inspired innovations."
Scientists and Engineers
To my mind this is one of the most amazing stories of the interaction of science and engineering. Albert Einstein theoretically predicted the existence of gravitational waves in 2016 and it took a century of work by scientists and engineers to actually observe one.
Scientists and engineers are intimate partners. Scientists’ curiosity drives engineers to expand the horizons of what had seemed possible. And that in turn enables scientists to imagine new things to be curious about and…