Manufacturing Bits: Jan. 8

Atom interferometry; quantum measurements; climate funding.


Atom interferometry
NASA and AOSense have demonstrated a prototype quantum sensor that uses a measurement technique called atom interferometry.

The technology could one day enable more accurate gravitational measurements, climate-monitoring missions in space and other applications.

Originally developed in the 1980s, atom interferometry is like today’s optical interferometry. Used in science and engineering, optical interferometers are specialized instruments. They measure displacements, refractive index changes, irregularities of surfaces and even gravitational waves.

Interferometers make measurements using two or more sources of electromagnetic waves. The waves are projected in a system and then superimposed. Then, the so-called interference pattern is measured and analyzed.

“Atom interferometry, however, hinges on quantum mechanics, the theory that describes how matter behaves at sub-microscopic scales,” according to NASA. “Atoms, which are highly sensitive to gravitational signals, can also be cajoled into behaving like light waves. Special pulsing lasers can split and manipulate atom waves to travel different paths. The two atom waves will interact with gravity in a way that affects the interference pattern produced once the two waves recombine. Scientists can then analyze this pattern to obtain an extraordinarily accurate measure of the gravitational field.”

For years, researchers have tried to make small and practical quantum sensors based on atom interferometry. This in turn could enable these components to be used in spacecraft and other small form-factor applications.

Recently, NASA and AOSense developed what researchers call an atom-optics gravity gradiometer. This technology is aimed to map Earth’s time-varying gravitational field.

The Goddard-AOSense team built this terrestrial proof-of-concept gravity gradiometer.
(Credits: AOSense, Inc.)

“Our sensor is smaller than competing sensors with similar sensitivity goals,” said Babak Saif, an optical physicist at NASA’s Goddard Space Flight Center. “Previous atom interferometer-based instruments included components that would literally fill a room. Our sensor, in dramatic comparison, is compact and efficient. It could be used on a spacecraft to obtain an extraordinary data set for understanding Earth’s water cycle and its response to climate change. In fact, the sensor is a candidate for future NASA missions across a variety of scientific disciplines.”

“With this new technology, we can measure the changes of Earth’s gravity that come from melting ice caps, droughts, and draining underground water supplies, greatly improving on the pioneering GRACE mission,” added John Mather, a scientist at NASA’s Goddard Space Flight Center. “We can measure the interior structure of planets, moons, asteroids, and comets when we send probes to visit them. The technology is so powerful that it can even extend the Nobel-winning measurements of gravitational waves from distant black holes, observing at a new frequency range.”

Quantum measurements
The U.S. Department of Energy’s Oak Ridge National Laboratory has developed a new and sensitive interferometer that could pave the way towards quantum-enhanced measurements.

Today’s optical interferometers consist of a component called a beam splitter or a parametric amplifier. These components split one beam of light into two. Then, the light is combined. This in turn measures the changes light phases relative to one another.

At times, though, interferometers suffer from optical loss and noise. This impacts the accuracy of the system. In response, Oak Ridge National Lab has developed a nonlinear fiber-based phase-sensitive amplifier. Researchers call this system a nonlinear interferometer (NLI).

The NLI overcomes many of the issues with traditional interferometers. The NLI also brings the industry one step closer to quantum-enhanced measurements. “We want to build the most sensitive instruments allowed by quantum mechanics,” said Nick Peters, a senior R&D staff member at Oak Ridge National Lab. “The real significance of our work is that this interferometer is the first built with this special kind of fiber, which is important for two reasons. One is that it provides potential for a notable sensitivity enhancement, and the other is that this fiber is commercial, which means its use could become widespread, once perfected.”

There are some barriers, however. It is difficult to increase the sensitivity of interferometers to a certain point, sometimes called the standard quantum limit, according to Oak Ridge National Lab.

“The standard quantum limit is defined by the number of available photons,” said Peters. “Using a special kind of light field can help lower the amount of noise in measurements taken by an interferometer, which increases sensitivity and helps measurements inch closer to the Heisenberg limit.”

Climate change funding
The U.S. Department of Energy (DOE) announced a plan to provide $16 million for new research aimed at improving the accuracy of today’s climate and earth system models.

The funds will be made available under two separate initiatives, with $11 million targeted at atmospheric research focused on better understanding the role of clouds and aerosols, and $5 million devoted to the study of terrestrial processes. The atmospheric research is expected to center on data taken by the Atmospheric Radiation Measurement (ARM) User Facility, a major DOE Office of Science facility. ARM has been a leading source for observational data on the interactions of clouds, aerosols, and precipitation.

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