# All-optical cryogenic thermometry based on NV centers in nanodiamonds

## TL;DR

This paper introduces an all-optical, microwave-free thermometry method using NV centers in nanodiamonds, enabling sensitive temperature measurements at cryogenic temperatures without the limitations of traditional techniques.

## Contribution

It presents a novel all-optical thermometry technique that works effectively at cryogenic temperatures, expanding NV center applications beyond room temperature sensing.

## Key findings

- Effective temperature sensing at liquid nitrogen temperatures.
- Demonstrated temperature gradient measurement in a ferromagnetic substrate.
- Platform compatible with various materials without microwave control.

## Abstract

The nitrogen-vacancy (NV) center in diamond has been recognized as a high-sensitivity nanometer-scale metrology platform. Thermometry has been a recent focus, with attention largely confined to room temperature applications. Thermometry has been a recent focus, with attention largely confined to room temperature applications. Temperature sensing at low temperatures, however, remains challenging as the sensitivity decreases for many commonly used techniques which rely on a temperature dependent frequency shift of the NV centers spin resonance and its control with microwaves. Here we use an alternative approach that does not require microwaves, ratiometric all-optical thermometry, and demonstrate that it may be utilized to liquid nitrogen temperatures without deterioration of the sensitivity. The use of an array of nanodiamonds embedded within a portably polydimethylsiloxane (PDMS) sheet provides a versatile temperature sensing platform that can probe a wide variety of systems without the configurational restrictions needed for applying microwaves. With this device, we observe a temperature gradient over tens of microns in a ferromagnetic-insulator substrate (YIG) under local heating by a resistive heater. This thermometry technique provides a cryogenically compatible, microwave-free, minimally invasive approach capable of probing local temperatures with few restrictions on the substrate materials.

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Source: https://tomesphere.com/paper/1903.01605