It may seem that technology advances year after year, like magic. But behind every incremental improvement and revolutionary revolution is a team of hard-working scientists and engineers.
Professor Ben Mazin of UC Santa Barbara is developing precision optical sensors for telescopes and observatories. In an article published in Physical examination lettershe and his team improved the spectral resolution of their superconducting sensor, a major step in their ultimate goal: to analyze the composition of exoplanets.
“We were able to roughly double the spectral resolving power of our detectors,” said first author Nicholas Zobrist, a PhD student at Mazin Lab.
“This is the biggest increase in energy resolution we’ve ever seen,” Mazin added. “It opens up a whole new path to scientific goals that we couldn’t achieve before.”
The Mazin lab works with a type of sensor called MKID. Most light detectors, like the CMOS sensor in a phone camera, are silicon-based semiconductors. These operate by photoelectric effect: a photon strikes the sensor, causing an electron to fall which can then be detected as a signal suitable for processing by a microprocessor.
An MKID uses a superconductor, through which electricity can flow without resistance. In addition to zero resistance, these materials have other useful properties. For example, semiconductors have a gap energy that must be overcome to knock out the electron. The associated deviation energy in a superconductor is about 10,000 times lower, so it can detect even weak signals.
Also, a single photon can knock out many electrons from a superconductor, as opposed to just one in a semiconductor. By measuring the number of mobile electrons, an MKID can actually determine the energy (or wavelength) of 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.
The researchers had reached a limit in the sensitivity of these MKIDs. After careful examination, they discovered that energy was leaking from the superconductor into the slice of sapphire crystal on which the device is made. As a result, the signal appeared weaker than it actually was.
In typical electronics, current is carried by moving electrons. But these tend to interact with their surroundings, scattering and losing energy in what is called resistance. In a superconductor, two electrons will pair up – one spin up and one spin down – and this Cooper pair, as it is called, is able to move without resistance.
“It’s like a couple in a club,” Mazin explained. “You have two people pairing up and then they can move through the crowd together without any resistance. While one person stops to talk to everyone along the way, which slows them down.”
In a superconductor, all the electrons are paired. “They’re all dancing together, moving around without interacting too much with other couples because they’re all looking deep 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. “It breaks up the couple, causing one partner to bump into other couples and create a disturbance.” It is the cascade of mobile electrons that the MKID measures.
But sometimes it happens at the edge of the dance floor. The offended party stumbles out of the club without hitting anyone else. Ideal for the rest of the dancers, but not for the scientists. If this happens in the MKID, the signal light will appear dimmer than it actually was.
Mazin, Zobrist and their co-authors found that a thin layer of metallic indium – placed between the superconducting sensor and the substrate – dramatically reduced the energy leaking from the sensor. The indium essentially acted as a fence around the dance floor, keeping the dancers hustled around 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, however, presented the team with a challenge. Indium is softer than lead, so it tends to clump together. It’s not ideal for creating the thin, even layer the researchers needed.
But their time and effort paid off. The technique reduced wavelength measurement uncertainty from 10% to 5%, the study reports. For example, photons with a wavelength of 1000 nanometers can now be measured with an accuracy of 50 nm with this system. “It has real implications for the science we can do,” Mazin said, “because we can better resolve the spectra of the objects 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 throughout the visible universe.
Mazin is particularly interested in applying these detectors to exoplanet science. Currently, scientists can only perform spectroscopy for a small subset of exoplanets. The planet must pass between its star and Earth, and it must have a thick atmosphere for enough light to pass 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 from a planet’s surface, rather than transmitted only through its narrow atmosphere. This will soon be possible thanks to the capabilities of the next generation of 30-meter telescopes.
The Mazin group is also experimenting with a completely different approach to the issue of energy loss. Although the results of this paper are impressive, Mazin said he thinks the indium technique might be obsolete if his team is successful with this new venture. Either way, he added, scientists are fast approaching their goals.
Spectral resolution of superconducting single-photon detectors more than doubled
Nicholas Zobrist et al, Membraneless phonon trapping and resolution enhancement in kinetic inductance microwave optical detectors, Physical examination letters (2022). DOI: 10.1103/PhysRevLett.129.017701. On Arxiv: arxiv.org/abs/2204.13669
Provided by University of California – Santa Barbara
Quote: Keeping the energy in the room (2022, July 1) retrieved July 2, 2022 from https://phys.org/news/2022-07-energy-room.html
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