New low temperature techniques for electron thermometry and thermal isolation

Chawner, Joshua and Prance, Jonathan and Pashkin, Yuri (2021) New low temperature techniques for electron thermometry and thermal isolation. PhD thesis, Lancaster University.

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Abstract

Measuring electron temperature is an important method to understand the stability and coherence of a quantum circuit, since this variable describes how `quiet' the electronic environment is. In this thesis, the construction, calibration and operation of a quantum dot electron thermometer is demonstrated in two different cryostats. Compared to previous implementations of a quantum dot thermometer, the work presented here is unique in that it only requires a single gate connection to calibrate and operate, which simplifies the application of the device substantially. For the thermometer calibration, a physical model of the quantum-dot reservoir system was developed, which reveals information usually obtained from a stability diagram. Electron thermometry was successfully performed with the calibrated thermometer in a 1.0 K to 3.0 K range. With the fastest mode of operation the quantum dot thermometer was shown to have a sensitivity of 3.7±0.3 mK/√Hz at 1.3 K. This device provides a new versatile, sensitive and effective tool for monitoring electron temperature in nanoelectronic devices at cryogenic temperatures. Also in this thesis, several plastic solid-void structures were demonstrated to offer excellent thermal and structural properties at sub-Kelvin temperatures. Good low temperature insulators are extremely useful for support cryogenic components and sample environments without leaking unwanted heat. A structure fabricated from commercially available ABS LEGO elements was shown to be effective at thermally insulating two bodies at sub-Kelvin temperatures, with a thermal conductivity of κ = (8.7±0.3)×10-5 T1.75±0.02 Wm-1K-1. Similar scale 3D printed ABS and PLA gyroid structures were shown to also be effective as low-temperature insulators, having a thermal conductivity of κ = (3.07±0.05)×10-5T1.72±0.02 Wm-1K-1 and κ = 4.45±0.05)×10-5T1.64±0.02 Wm-1K-1, respectively. These samples demonstrate how low temperature insulation can be improved with readily available, fully customisable and affordable components.