Quantum dot thermometry at ultra-low temperature in a dilution refrigerator with a $^4$He immersion cell

TL;DR

This paper demonstrates a method to achieve electron temperatures as low as 6.7 mK in a dilution refrigerator using a helium immersion cell, advanced wiring, and optimized measurement techniques.

Contribution

It introduces a novel helium immersion cell and wiring technology to improve thermalization and measurement accuracy at ultra-low temperatures.

Findings

Achieved electron temperature of 6.7 mK in a dilution refrigerator.

Developed a helium immersion cell tight against superleaks.

Implemented optimized transport measurement procedures.

Abstract

Experiments performed at a temperature of a few millikelvin require effective thermalization schemes, low-pass filtering of the measurement lines and low-noise electronics. Here, we report on the modifications to a commercial dilution refrigerator with a base temperature of 3.5 mK that enable us to lower the electron temperature to 6.7 mK measured from the Coulomb peak width of a quantum dot gate-defined in an [Al]GaAs heteostructure. We present the design and implementation of a liquid $^4$He immersion cell tight against superleaks, implement an innovative wiring technology and develop optimized transport measurement procedures.