Ultralow-power cryogenic thermometry based on optical-transition broadening of a two-level system in diamond

TL;DR

This paper introduces an ultralow power optical thermometry method for cryogenic temperatures using linewidth broadening of a two-level system in diamond, achieving high sensitivity with minimal heating.

Contribution

The paper presents a novel, highly sensitive cryogenic thermometry technique utilizing optical linewidth broadening in germanium vacancy centers, requiring extremely low excitation powers.

Findings

Achieves 20%/K sensitivity at 5 K

Uses only tens of nanowatts of excitation power

Accurately measures local temperature differences

Abstract

Cryogenic temperatures are the prerequisite for many advanced scientific applications and technologies. The accurate determination of temperature in this range and at the submicrometer scale is, however, nontrivial. This is due to the fact that temperature reading in cryogenic conditions can be inaccurate due to optically induced heating. Here, we present an ultralow power, optical thermometry technique that operates at cryogenic temperatures. The technique exploits the temperature dependent linewidth broadening measured by resonant photoluminescence of a two level system, a germanium vacancy color center in a nanodiamond host. The proposed technique achieves a relative sensitivity of 20% 1/K, at 5 K. This is higher than any other all optical nanothermometry method. Additionally, it achieves such sensitivities while employing excitation powers of just a few tens of nanowatts, several orders of magnitude lower than other traditional optical thermometry protocols. To showcase the performance of the method, we demonstrate its ability to accurately read out local differences in temperatures at various target locations of a custom-made microcircuit. Our work is a definite step towards the advancement of nanoscale optical thermometry at cryogenic temperatures.