Power sensitivity of broadband radiofrequency detectors based on quantum diamond spins

TL;DR

This paper analyzes the power sensitivity of NV-centre-based RF detectors, revealing that smaller device structures improve power sensitivity and providing estimates for shot noise-limited performance.

Contribution

It derives scaling laws for power sensitivity in NV RF detectors and highlights the inverse relationship with device size, guiding future optimization.

Findings

Power sensitivity scales inversely with the size of the RF-spin interface.

Photon shot noise limited sensitivities of 10^{-20} W/Hz and 10^{-12} W/Hz^{1/2} are achievable.

Smaller structures yield better power sensitivity, contrary to magnetic field sensitivity trends.

Abstract

Nitrogen-vacancy (NV) centres in diamond can be used to detect radiofrequency (RF) signals through coupling of the RF magnetic field with the NV spins, combined with optical readout of the spin state. The sensitivity of such RF detectors has so far been mainly studied in terms of magnetic field sensitivity, which is relevant when the RF signal is generated by a near-field source. However, for applications where the RF input is delivered externally, a more relevant quantity is the sensitivity in terms of the input RF power. Here we theoretically analyse the power sensitivity of NV-based RF detectors as a function of the RF-spin interface geometry. We derive scaling laws of the power sensitivity for both slope-detection and variance-detection RF sensing protocols, and for various noise regimes. We find that, in most scenarios, the power sensitivity scales inversely with the characteristic physical dimension of the RF-spin interface, for instance the width of a coplanar waveguide or the diameter of a loop antenna. In other words, the smaller the structure and the probed NV volume, the better the power sensitivity, which is contrary to the case of magnetic field sensitivity. Lastly, we numerically estimate that photon shot noise limited sensitivities of 10^{-20} W Hz^{-1} (slope) and 10^{-12} W Hz^{-1/2} (variance) are achievable. This work lays the groundwork for further optimisation of NV-based RF detectors.