Homogeneous Microwave Delivery for Quantum Sensing with Nitrogen-Vacancy Centers at High Pressures

TL;DR

This work addresses the challenge of delivering a uniform microwave field to NV centers inside a diamond-anvil cell during high-pressure experiments. By integrating a vertical-slotted Pt microwave line into a BeCu DAC, the authors achieve a nearly uniform $B_1$ field across the culet and demonstrate zero-field and in-field ODMR on NV centers from 1 to 48 GPa. The results show a pressure-dependent ODMR shift well-described by $ u = a + bP + cP^2$ with $a \,\approx\,2896$ MHz, $b \,\approx\,8.5$ MHz GPa$^{-1}$, and $c \,\approx\,-0.052$ MHz GPa$^{-2}$, a field of about $B_0 \approx 5.6$ mT, and $T_2^* \approx 19$ ns; the slotted design yields Rabi frequencies near $3$ MHz, sufficient to address NV centers with $^{15}$N hyperfine ~3.05 MHz, and provides a stable field better suited for spatially resolved measurements under pressure. The approach offers a practical route to enhanced NV-based sensing in high-pressure environments and suggests future enhancements, such as tungsten embedding or multi-strip geometries, to further improve field uniformity and compatibility with transport measurements.

Abstract

Nitrogen vacancy (NV) centers have been demonstrated as a useful tool in high pressure environments. However, the geometry and small working area of the diamond anvil cells (DACs) used to apply pressure present a challenge to effective delivery of microwave (mw) fields. We designed and characterized a novel slotted design for mw transmission to nitrogen-vacancy centers (NVs) in a diamond anvil cell via zero-field and in-field optically detected magnetic resonance (ODMR) measurements across pressures between 1 and 48 GPa. The mw fields experienced by NVs across the diamond culet was calculated from Rabi frequency and found to be higher and more uniform than those generated by an equivalent simple mw line, which will improve performance for wide-field, high-pressure measurements to probe spatial variations across samples under pressure.

Figures (4)

• Figure 1: (a) The modified Diacell SymmDAC 60 BeCu showing the vertical slot, PCB, and slotted mw line. (b) Detailed diagram of the PCB used to connect the mw line to an external mw source. (c) Detailed diagram of the slotted mw line.
• Figure 2: Optically-detected magnetic resonance (ODMR) spectra at various pressures. Plot (a) shows results without an applied static magnetic field, and plot (b) shows results for an applied field of approximately 5.6m T. In both plots, datasets are vertically offset for clarity.
• Figure 3: (a) ODMR frequency versus pressure values measured with applied static magnetic field (yellow points) and without static field (blue points). A quadratic fit $\nu = a + bP + cP^2$ to the data is shown in green, in which $a$ is approximately 2896(5)M Hz, $b$ is 8.5(6)M Hz G Pa, and and $c$ is about -0.052(1)M Hz G Pa . (b) Linewidth versus pressure values calculated via Lorentzian fits to in-field ODMR peaks.
• Figure 4: (a) Picture of diamond culet with Pt mw line highlighted in purple and the gasket hole highlighted in yellow. A red line shows the approximate path of the Rabi measurements that were taken across the slot of the mw line. (b) Microwave field strength measured across the mw line at ambient pressure. Experimental values calculated from Rabi frequency measurements are shown in red, with theoretical results for slotted and non-slotted mw lines in blue and orange respectively. Purple and yellow highlights show the approximate positions of the mw line and gasket hole relative to the measurements taken.