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Reaching the ultimate energy resolution of a quantum detector

B. Karimi, Fredrik Brange, P. Samuelsson, J. Pekola

Nature Communications, 2020

80 citations

Abstract

Quantum calorimetry, the thermal measurement of quanta, is a method of choice for ultrasensitive radiation detection ranging from microwaves to gamma rays. The fundamental temperature fluctuations of the calorimeter, dictated by the coupling of it to the heat bath, set the ultimate lower bound of its energy resolution. Here we reach this limit of fundamental equilibrium fluctuations of temperature in a nanoscale electron calorimeter, exchanging energy with the phonon bath at very low temperatures. The approach allows noninvasive measurement of energy transport in superconducting quantum circuits in the microwave regime with high efficiency, opening the way, for instance, to observe quantum jumps, detecting their energy to tackle central questions in quantum thermodynamics. Quantum calorimeters can provide time-resolved measurement of single photons by converting them to detectable temperature changes. Here the authors demonstrate a calorimeter that reaches the lower bound of temperature resolution, determined by the coupling to its heat bath and associated fluctuations.

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