From The University of California-Santa Barbara: “Keeping the Energy in The Room” 

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From The University of California-Santa Barbara

July 1, 2022

Harrison Tasoff
(805) 893-7220
harrisontasoff@ucsb.edu

Professor Ben Mazin talks superconductors, exoplanets and dance clubs as he explains advances in sensor technology.

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The sensor mounted for use in an MKID Exoplanet Camera. Photo Credit: Ben Mazin.

It may seem like technology advances year after year, as if by magic. But behind every incremental improvement and breakthrough revolution is a team of scientists and engineers hard at work.

UC Santa Barbara Professor Ben Mazin is developing precision optical sensors for telescopes and observatories. In a paper published in Physical Review Letters, he and his team improved the spectra resolution of their superconducting sensor, a major step in their ultimate goal: analyzing the composition of exoplanets.

“We were able to roughly double the spectral resolving power of our detectors,” said first author Nicholas Zobrist, a doctoral student in the Mazin Lab.

“This is the largest energy resolution increase we’ve ever seen,” added Mazin. “It opens up a whole new pathway to science goals that we couldn’t achieve before.”

The Mazin lab works with a type of sensor called an MKID. Most light detectors — like the CMOS sensor in a phone camera — are semiconductors based on silicon. These operate via the photo-electric effect: a photon strikes the sensor knocking off an electron that can then be detected as a signal suitable for processing by a microprocessor.

An MKID uses a superconductor in which electricity can flow with no resistance. In addition to zero resistance, these materials have other useful properties. For instance, semiconductors have a gap energy that needs to be overcome to knock the electron out. The related gap energy in a superconductor is about 10,000 times less, so it can detect even faint signals.

What’s more, a single photon can knock many electrons off of a superconductor, as opposed to only one in a semiconductor. By measuring the number of mobile electrons, an MKID can actually determine the energy (or wavelength) of the incoming light. “And the energy of the photon, or its spectra, tells us a lot about the physics of what emitted that photon,” Mazin said.

Leaking energy

The researchers had hit a limit as to how sensitive they could make these MKIDs. After much scrutiny, they discovered that energy was leaking from the superconductor into the sapphire crystal wafer that the device is made on. As a result, the signal appeared weaker than it truly was.

In typical electronics, current is carried by mobile electrons. But these have a tendency to interact with their surroundings, scattering and losing energy in what’s known as resistance. In a superconductor two electrons will pair up — one spin up and one spin down — and this Cooper pair, as it’s called, is able to move about without resistance.

“It’s like a couple at a club,” Mazin explained. “You’ve got two people who pair up, and then they can move together through the crowd without any resistance. Whereas a single person stops to talk to everybody along the way, slowing them down.”

In a superconductor, all the electrons are paired up. “They’re all dancing together, moving around without interacting with other couples very much because they’re all gazing deeply into each other’s eyes.

“A photon hitting the sensor is like someone coming in and spilling a drink on one of the partners,” he continued. “This breaks the couple up, causing one partner to stumble into other couples and create a disturbance.” This is the cascade of mobile electrons that the MKID measures.

But sometimes this happens at the edge of the dancefloor. The offended party stumbles out of the club without knocking into anyone else. Great for the rest of the dancers, but not for the scientists. If this happens in the MKID, then the light signal will seem weaker than it actually was.

Fencing them in

Mazin, Zobrist and their co-authors discovered that a thin layer of the metal indium — placed between the superconducting sensor and the substrate — drastically reduced the energy leaking out of the sensor. The indium essentially acted like a fence around the dancefloor, keeping the jostled dancers in the room and interacting with the rest of the crowd.

They chose indium because it is also a superconductor at the temperatures at which the MKID will operate, and adjacent superconductors tend to cooperate if they are thin. The metal did present a challenge to the team, though. Indium is softer than lead, so it has a tendency to clump up. That’s not great for making the thin, uniform layer the researchers needed.

But their time and effort paid off. The technique cut down the wavelength measurement uncertainty from 10% to 5%, the study reports. For example, photons with a wavelength of 1,000 nanometers can now be measured to a precision of 50 nm with this system. “This has real implications for the science we can do,” Mazin said, “because we can better resolve the spectra of the objects that we’re looking at.”

Different phenomena emit photons with specific spectra (or wavelengths), and different molecules absorb photons of different wavelengths. Using this light, scientists can use spectroscopy to identify the composition of objects both nearby and across the entire visible universe.

Mazin is particularly interested in applying these detectors to exoplanet science. Right now scientists can only do spectroscopy for a tiny subset of exoplanets. The planet needs to pass between its star and Earth, and it must have a thick atmosphere so that enough light passes through it for researchers to work with. Still, the signal to noise ratio is abysmal, especially for rocky planets, Mazin said.

With better MKIDs scientists can use light reflected off the surface of a planet rather than transmitted through its narrow atmosphere alone. This will soon be possible with the capabilities of the next generation of 30-meter telescopes.

The Mazin group is also experimenting with a completely different approach to the energy-loss issue. Although the results from this paper are impressive, Mazin said he believes the indium technique could be obsolete if his team is successful with this new endeavor. Either way, he added, the scientists are rapidly closing in on their goals.

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The University of California-Santa Barbara is a public land-grant research university in Santa Barbara, California, and one of the ten campuses of the University of California system. Tracing its roots back to 1891 as an independent teachers’ college, The University of California-Santa Barbara joined the University of California system in 1944, and is the third-oldest undergraduate campus in the system.

The university is a comprehensive doctoral university and is organized into five colleges and schools offering 87 undergraduate degrees and 55 graduate degrees. It is classified among “R1: Doctoral Universities – Very high research activity”. According to the National Science Foundation, The University of California-Santa Barbara spent $235 million on research and development in fiscal year 2018, ranking it 100th in the nation. In his 2001 book The Public Ivies: America’s Flagship Public Universities, author Howard Greene labeled The University of California-Santa Barbara a “Public Ivy”.

The University of California-Santa Barbara is a research university with 10 national research centers, including the Kavli Institute for Theoretical Physics and the Center for Control, Dynamical-Systems and Computation. Current University of California-Santa Barbara faculty includes six Nobel Prize laureates; one Fields Medalist; 39 members of the National Academy of Sciences; 27 members of the National Academy of Engineering; and 34 members of the American Academy of Arts and Sciences. The University of California-Santa Barbara was the No. 3 host on the ARPANET and was elected to the Association of American Universities in 1995. The faculty also includes two Academy and Emmy Award winners and recipients of a Millennium Technology Prize; an IEEE Medal of Honor; a National Medal of Technology and Innovation; and a Breakthrough Prize in Fundamental Physics.
The University of California-Santa Barbara Gauchos compete in the Big West Conference of the NCAA Division I. The Gauchos have won NCAA national championships in men’s soccer and men’s water polo.

History

The University of California-Santa Barbara traces its origins back to the Anna Blake School, which was founded in 1891, and offered training in home economics and industrial arts. The Anna Blake School was taken over by the state in 1909 and became the Santa Barbara State Normal School which then became the Santa Barbara State College in 1921.

In 1944, intense lobbying by an interest group in the City of Santa Barbara led by Thomas Storke and Pearl Chase persuaded the State Legislature, Gov. Earl Warren, and the Regents of the University of California to move the State College over to the more research-oriented University of California system. The State College system sued to stop the takeover but the governor did not support the suit. A state constitutional amendment was passed in 1946 to stop subsequent conversions of State Colleges to University of California campuses.

From 1944 to 1958, the school was known as Santa Barbara College of the University of California, before taking on its current name. When the vacated Marine Corps training station in Goleta was purchased for the rapidly growing college Santa Barbara City College moved into the vacated State College buildings.

Originally the regents envisioned a small several thousand–student liberal arts college a so-called “Williams College of the West”, at Santa Barbara. Chronologically, The University of California-Santa Barbara is the third general-education campus of the University of California, after The University of California-Berkeley and The University of California-Los Angeles (the only other state campus to have been acquired by the University of California system). The original campus the regents acquired in Santa Barbara was located on only 100 acres (40 ha) of largely unusable land on a seaside mesa. The availability of a 400-acre (160 ha) portion of the land used as Marine Corps Air Station Santa Barbara until 1946 on another seaside mesa in Goleta, which the regents could acquire for free from the federal government, led to that site becoming the Santa Barbara campus in 1949.

Originally only 3000–3500 students were anticipated but the post-WWII baby boom led to the designation of general campus in 1958 along with a name change from “Santa Barbara College” to “University of California-Santa Barbara,” and the discontinuation of the industrial arts program for which the state college was famous. A chancellor- Samuel B. Gould- was appointed in 1959.

In 1959 The University of California-Santa Barbara professor Douwe Stuurman hosted the English writer Aldous Huxley as the university’s first visiting professor. Huxley delivered a lectures series called The Human Situation.

In the late ’60s and early ’70s The University of California-Santa Barbara became nationally known as a hotbed of anti–Vietnam War activity. A bombing at the school’s faculty club in 1969 killed the caretaker Dover Sharp. In the spring of 1970 multiple occasions of arson occurred including a burning of the Bank of America branch building in the student community of Isla Vista during which time one male student Kevin Moran was shot and killed by police. The University of California-Santa Barbara ‘s anti-Vietnam activity impelled then-Gov. Ronald Reagan to impose a curfew and order the National Guard to enforce it. Armed guardsmen were a common sight on campus and in Isla Vista during this time.

In 1995 The University of California-Santa Barbara was elected to the Association of American Universities– an organization of leading research universities with a membership consisting of 59 universities in the United States (both public and private) and two universities in Canada.

On May 23, 2014 a killing spree occurred in Isla Vista, California, a community in close proximity to the campus. All six people killed during the rampage were students at The University of California-Santa Barbara. The murderer was a former Santa Barbara City College student who lived in Isla Vista.

Research activity

According to the National Science Foundation, The University of California-Santa Barbara spent $236.5 million on research and development in fiscal 2013, ranking it 87th in the nation.

From 2005 to 2009 UCSB was ranked fourth in terms of relative citation impact in the U.S. (behind Massachusetts Institute of Technology, California Institute of Technology, and Princeton University) according to Thomson Reuters.

The University of California-Santa Barbara hosts 12 National Research Centers, including The Kavli Institute for Theoretical Physics, the National Center for Ecological Analysis and Synthesis, the Southern California Earthquake Center, the UCSB Center for Spatial Studies, an affiliate of the National Center for Geographic Information and Analysis, and the California Nanosystems Institute. Eight of these centers are supported by The National Science Foundation. UCSB is also home to Microsoft Station Q, a research group working on topological quantum computing where American mathematician and Fields Medalist Michael Freedman is the director.

Research impact rankings

The Times Higher Education World University Rankings ranked The University of California-Santa Barbara 48th worldwide for 2016–17, while the Academic Ranking of World Universities (ARWU) in 2016 ranked https://www.nsf.gov/ 42nd in the world; 28th in the nation; and in 2015 tied for 17th worldwide in engineering.

In the United States National Research Council rankings of graduate programs, 10 University of California-Santa Barbara departments were ranked in the top ten in the country: Materials; Chemical Engineering; Computer Science; Electrical and Computer Engineering; Mechanical Engineering; Physics; Marine Science Institute; Geography; History; and Theater and Dance. Among U.S. university Materials Science and Engineering programs, The University of California-Santa Barbara was ranked first in each measure of a study by the National Research Council of the NAS.

The Centre for Science and Technologies Studies at