Falls and ups in development of a cold-electron bolometer
Fig. 1. Falls and Ups in development of a Cold-Electron Bolometer. 1. Hot-electron Bolometer with SIN tunnel junction as thermometer and Andreev mirrors for RF coupling and thermal isolation. M. Nahum and J. M. Martinis (1993). 2. Hot-electron Bolometer with SIN tunnel junction as thermometer and other SIN junctions for RF coupling and thermal isolation. L. Kuzmin (1998). 3. Six-legs Bolometer with SIN tunnel junctions as thermometer, other SIN tunnel junctions as electron cooler, and Andreev mirrors for RF coupling and thermal isolation. L. Kuzmin, I. Devyatov, & D. Golubev (1999). 4. Two-legs Cold-Electron Bolometer (CEB) with SIN tunnel junctions as thermometer, electron cooler, RF capacitive coupling and thermal isolation. L. Kuzmin (2001). ​Illustration: Leonid Kuzmin

Self-cooled bolometer with ultimate sensitivity created for the first time

​Researchers at Chalmers University of Technology have managed to create the first cold-electron bolometer in the world with ultimate sensitivity due to an effective on-chip self-cooling. The results were recently published in the scientific journal Communications Physics of Nature group.​
Photo of Leonid Kuzmin.
Superconducting bolometers are widely used for balloon and space missions and have seen extensive development because of their capacity to test primordial conditions of the Universe. The major improvements consist in lowering the operating temperature to reach higher sensitivities.
“The big difference between our cold-electron bolometer with an effective self-cooling and other types, is that the latter ones require cooling of the entire sample. Our technology can significantly reduce the cost of future space missions because we can avoid dilution refrigerators”, says Leonid Kuzmin (to the right), professor at the Quantum Device Physics Laboratory at the Department of Microtechnology and Nanoscience – MC2, and main author of the paper.

In their study, the researchers show that an array of 192 cold-electron bolometers demonstrates photon-noise-limited operation at the cryostat temperature of 310 millikelvin (mK) due to effective self-cooling of the absorber. 
“This bolometer works at electron temperature less than phonon temperature, thus being a good candidate for future space missions without the use of complicated dilution refrigerators that can’t normally work in space due to absence of gravity”, says Leonid Kuzmin.

He describes the research as a four-step-process which led to the invention of a bolometer that operates at an electron temperature that is less than the phonon temperature. Attempts and failures along the way stimulated the team to even more intensive thinking for better decisions and suggestions.
“As a result, the optimal decision in Step 4 has been found. Instead of a ‘six-legged cuttlefish’, which turned out to be too complicated, the two-legged cold-electron bolometer with only one pair of SIN tunnel junctions was invented”, says Leonid Kuzmin.

The study suggests that such cold-electron bolometers with internal self-cooling are potential candidates for advanced radio astronomy projects that must avoid dilution refrigerators. 
“This can solve the main problem of the COrE space mission that was not accepted by the European Space Agency due to necessity to find a compromise between sensitivity, cryogenics and cost. We can develop arrays of cold-electron bolometers practically for any frequency range achieving ultimate sensitivity at 300 mK without dilution refrigerator”, says Leonid Kuzmin.

The research was a collaboration between Chalmers University of Technology, Nizhny Novgorod State Technical University, Institute for Physics of Microstructures of RAS in Nizhny Novgorod, Russia, and Dipartimento di Fisica, Universita La Sapienza in Rome, Italy.

The paper has already earned wide interest in the science community, with more than 2 000 accesses. 

Text: Michael Nystås
Photo of Leonid Kuzmin: Private
Illustration: Leonid Kuzmin

Leonid Kuzmin, Professor, Quantum Device Physics Laboratory, Department of Microtechnology and Nanoscience – MC2, Chalmers University of Technology, Gothenburg, Sweden, +46 31 772 36 08, leonid.kuzmin@chalmers.se

Two more papers about Cold Electron Bolometers were selected as "featured article of the issue" of Superconductor Science and Technology in 2019 >>>

Published: Wed 22 Jan 2020.