Science and techno world topic: Electronics
Image: The new amplifier consists of a superconducting
material (niobium titanium nitride) coiled into a double spiral 16 millimeters
in diameter.
Researchers at the California Institute of Technology
(Caltech) and NASA's Jet Propulsion Laboratory (JPL) have developed a new type
of amplifier for boosting electrical signals. The device can be used for
everything from studying stars, galaxies, and black holes to exploring the
quantum world and developing quantum computers.
"This amplifier will redefine what it is possible to
measure," says Jonas Zmuidzinas, Caltech's Merle Kingsley Professor of
Physics, the chief technologist at JPL, and a member of the research team.
An amplifier is a device that increases the strength of a
weak signal. "Amplifiers play a basic role in a wide range of scientific
measurements and in electronics in general," says Peter Day, a visiting
associate in physics at Caltech and a principal scientist at JPL. "For
many tasks, current amplifiers are good enough. But for the most demanding
applications, the shortcomings of the available technologies limit us."
Conventional transistor amplifiers—like the ones that
power your car speakers—work for a large span of frequencies. They can also
boost signals ranging from the faint to the strong, and this so-called dynamic
range enables your speakers to play both the quiet and loud parts of a song.
But when an extremely sensitive amplifier is needed—for example, to boost the
faint, high-frequency radio waves from distant galaxies—transistor amplifiers
tend to introduce too much noise, resulting in a signal that is more powerful
but less clear.
One type of highly sensitive amplifier is a parametric
amplifier, which boosts a weak input signal by using a strong signal called the
pump signal. As both signals travel through the instrument, the pump signal
injects energy into the weak signal, therefore amplifying it.
About 50 years ago, Amnon Yariv, Caltech's Martin and
Eileen Summerfield Professor of Applied Physics and Electrical Engineering,
showed that this type of amplifier produces as little noise as possible: the
only noise it must produce is the unavoidable noise caused by the jiggling of
atoms and waves according to the laws of quantum mechanics. The problem with
many parametric amplifiers and sensitive devices like it, however, is that they
can only amplify a narrow frequency range and often have a poor dynamic range.
But the Caltech and JPL researchers say their new
amplifier, which is a type of parametric amplifier, combines only the best
features of other amplifiers. It operates over a frequency range more than ten
times wider than other comparably sensitive amplifiers, can amplify strong
signals without distortion, and introduces nearly the lowest amount of
unavoidable noise. In principle, the researchers say, design improvements
should be able to reduce that noise to the absolute minimum. Versions of the
amplifier can be designed to work at frequencies ranging from a few gigahertz
to a terahertz (1,000 GHz). For comparison, a gigahertz is about 10 times
greater than commercial FM radio signals in the U.S., which range from about 88
to 108 megahertz (1 GHz is 1,000 MHz).
"Our new amplifier has it all," Zmuidzinas
says. "You get to have your cake and eat it too."
The team recently described the new instrument in the
journal Nature Physics.
One of the key features of the new parametric amplifier
is that it incorporates superconductors—materials that allow an electric
current to flow with zero resistance when lowered to certain temperatures. For
their amplifier, the researchers are using titanium nitride (TiN) and niobium
titanium nitride (NbTiN), which have just the right properties to allow the
pump signal to amplify the weak signal.
Although the amplifier has a host of potential
applications, the reason the researchers built the device was to help them
study the universe. The team built the instrument to boost microwave signals,
but the new design can be used to build amplifiers that help astronomers
observe in a wide range of wavelengths, from radio waves to X-rays.
For instance, the team says, the instrument can directly
amplify radio signals from faint sources like distant galaxies, black holes, or
other exotic cosmic objects. Boosting signals in millimeter to submillimeter
wavelengths (between radio and infrared) will allow astronomers to study the
cosmic microwave background—the afterglow of the big bang—and to peer behind
the dusty clouds of galaxies to study the births of stars, or probe primeval
galaxies. The team has already begun working to produce such devices for
Caltech's Owens Valley Radio Observatory (OVRO) near Bishop, California, about
250 miles north of Los Angeles.
These amplifiers, Zmuidzinas says, could be incorporated
into telescope arrays like the Combined Array for Research in Millimeter-wave
Astronomy at OVRO, of which Caltech is a consortium member, and the Atacama
Large Millimeter/submillimeter Array in Chile.
Instead of directly amplifying an astronomical signal,
the instrument can be used to boost the electronic signal from a light detector
in an optical, ultraviolet, or even X-ray telescope, making it easier for
astronomers to tease out faint objects.
Because the instrument is so sensitive and introduces
minimal noise, it can also be used to explore the quantum world. For example,
Keith Schwab, a professor of applied physics at Caltech, is planning to use the
amplifier to measure the behavior of tiny mechanical devices that operate at
the boundary between classical physics and the strange world of quantum
mechanics. The amplifier could also be used in the development quantum computers—which
are still beyond our technological reach but should be able to solve some of
science's hardest problems much more quickly than any regular computer.
"It's hard to predict what all of the applications
are going to end up being, but a nearly perfect amplifier is a pretty handy
thing to have in your bag of tricks," Zmuidzinas says. And by creating
their new device, the researchers have shown that it is indeed possible to
build an essentially perfect amplifier. "Our instrument still has a few rough
edges that need polishing before we would call it perfect, but we think our
results so far show that we can get there."
More information: The title of the Nature Physics paper
is "A wideband, low-noise superconducting amplifier with high dynamic range."
Journal reference: Nature Physics
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