Of sensors and science students

Click click.

Once the clasps unfastened, the tubular black case opened like a yard-long mussel. It might have held a bazooka, a collapsible pole tent, or enough shellfish for three plates of paella.

“This,” said Rob Young, for certain types of light, “is the most efficient detector in the world.”

Rob builds quantum dots at Lancaster University. Constructed atom by atom, dots measure a few nanometers across. They sit, Rob explains on one website, like “islands of one material, embedded in a sea of another.” Applications range from computation to lasers to biomedical engineering. As explained on its website, Lancaster is a northern-English city that dates to 2,000 years ago, give or take a few centuries. When I visited Lancaster last November, Rob showed me his toys.


A Lancaster coffee shop that shares its name with one of Britain’s most renowned physicists

The detector, he said, detects 30% of the photons aimed at it. Photons—particles of light—shoot out of quantum dots. Having frequencies of about 1.5 μm (carrying less energy than visible light), and traveling far from source to detector, these photons escape most sensors. Rob’s sensor consists of superconductors, quantum systems described here. Thanks to superconductivity, the sensor’s efficiency outweighs its anvil of a name, “superconducting nanowire single-photon detector” (SNSPD). By registering photons, Rob’s team learns how quantum dots operate and reads out information that the dots process.

Thirty percent of photons. Using the world’s most efficient photodetector.

If Johnny the outfielder caught just 30% of fly balls, he wouldn’t play varsity that year. If your phone dropped 70% of calls, you might switch providers. (But if Congress enacted 30% of the bills it introduced, its enacted-to-introduced ratio would jump about sixfold.)

Doing and studying science can leave one feeling like a photodetector. Seminars can sound like gobbledegook. Explanations about our work sound like gobbledegook, according to relatives. Theorems shy away from attempts to rederive them. After you’ve searched two books, calculated all afternoon, and run your hand through your hair enough times that the hair stands on end, Mr. Considerate strolls past, glances over your shoulder, and calls your problem “trivial.”

Before braining the fellow with a pole tent—be you student, scientist, or cherished reader in a similar boat—remember: We resemble not just any photodetectors. We resemble the most efficient sensors (for long-distance–traveling 1.5-μm light) in the world. And the best detectors’ efficiency rises like a balloon at a county fair.

Today’s detectors, Rob said, stand head and shoulders above the detectors that topped records five years ago.

Not that sensors evolved of their own accord. Despite clichés, balloons do not rise effortlessly. They push air molecules aside, performing—in physics jargon—work. Work might consist of applying superconductors to photodetection, of shrinking sensors’ nanowires, of testing sensor designs and materials. Work, to a theoretical physicist, involves cordoning off ideas to model, finding math to model them, not understanding the math, reading about the math, interpreting the math, and using it till you understand.

Doing and studying science can make one feel like a photodetector. But after enough work, once in a while, the latches click, and the black case of the world swings open. Once in a while, if you do science, the world is your mussel.

With thanks to Rob Young for a tour of his labs and for explanations; and to Rob and the Lancaster University Department of Physics for their hospitality.

This entry was posted in Experimental highlights, Real science, Reflections and tagged , , , , by Nicole Yunger Halpern. Bookmark the permalink.

About Nicole Yunger Halpern

I’m a theoretical physicist at the Joint Center for Quantum Information and Computer Science in Maryland. My research group re-envisions 19th-century thermodynamics for the 21st century, using the mathematical toolkit of quantum information theory. We then apply quantum thermodynamics as a lens through which to view the rest of science. I call this research “quantum steampunk,” after the steampunk genre of art and literature that juxtaposes Victorian settings (à la thermodynamics) with futuristic technologies (à la quantum information). For more information, check out my upcoming book Quantum Steampunk: The Physics of Yesterday’s Tomorrow. I earned my PhD at Caltech under John Preskill’s auspices; one of my life goals is to be the subject of one of his famous (if not Pullitzer-worthy) poems. Follow me on Twitter @nicoleyh11.

8 thoughts on “Of sensors and science students

  1. It’s our job, not only to increase the efficiency of the photodetector, but also to increase the efficiency of passing around the physics knowledge from person to person as well 🙂

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    • It is well for students to be aware, that as photon-detectors and photon-emitters alike are made more-and-more efficient, they concomitantly modify the vacuum of the apparatus more-and-more strongly.

      In consequence, scalable optical quantum information processing devices and/or BosonSampling experiments are *far* more difficult to design and implement than was commonly appreciated in the early literature.

      Michael Landry’s interview in Ligo Magazine, titled “Realizing Squeezing: An interview with Carlton Caves” (2013), provides a student-friendly introduction to the challenges and opportunities attendant to high-efficiency vacuum-modifying photon-detection technologies.

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