New method measures temperature within 3D objects

four infrared images of the fused silica window used

University of Wisconsin–Madison engineers have made it possible to remotely determine the temperature beneath the surface of certain materials using a new technique they call depth thermography. The method may be useful in applications where traditional temperature probes won’t work, like monitoring semiconductor performance or next-generation nuclear reactors.

Many temperature sensors measure thermal radiation, most of which is in the infrared spectrum, coming off the surface of an object. The hotter the object, the more radiation it emits, which is the basis for gadgets like thermal imaging cameras.

Depth thermography, however, goes beyond the surface and works with a certain class of materials that are partially transparent to infrared radiation.

“We can measure the spectrum of thermal radiation emitted from the object and use a sophisticated algorithm to infer the temperature not just on the surface, but also underneath the surface, tens to hundreds of microns in,” says Mikhail Kats, a UW–Madison professor of electrical and computer engineering. “We’re able to do that precisely and accurately, at least in some instances.”

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four infrared images of the fused silica window used
An infrared image of the fused silica window used to test the depth thermography concept. For the project, the team heated the silica, a type of glass, and analyzed it using a spectrometer. They then measured temperature readings from various depths of the sample. IMAGE COURTESY OF MIKHAIL KATS

Measurement of a superconducting qubit with a microwave photon counter

Data image from the paper. It shows rainbow-colored curve lines.


The superconducting qubit group at WQI introduced an approach to measurement based on a microwave photon counter demonstrating raw single-shot measurement fidelity of 92% [Science, 361, 1239 (2018)]. This scheme provides access to the classical outcome of projective quantum measurement at the millikelvin stage and could form the basis for a scalable quantum-to-classical interface, see this article for broader perspective on this technology.

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Effects of charge noise on a pulse-gated singlet-triplet qubit

schematic of a quantum dot qubit and the available electron paths

We study the dynamics of a pulse-gated semiconductor double quantum dot qubit. In our experiments, the qubit coherence times are relatively long, but the visibility of the quantum oscillations is low. We show that these observations are consistent with a theory that incorporates decoherence arising from charge noise that gives rise to detuning fluctuations of the double dot.


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Quasiparticle poisoning of superconducting microwave resonators

graph of Steady-state QP density as a function of bias e V / ?”

Nonequilibrium quasiparticles represent a significant source of decoherence in superconducting quantum circuits. Here we investigate the mechanism of quasiparticle poisoning in devices subjected to local quasiparticle injection.

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