Diamond Quantum Sensing Achieves 240 GPa, Enabling Studies of Hydrogen-Rich Superconductors and Earth’s Core

Diamond-based quantum sensing now offers unprecedented opportunities to investigate materials under extreme pressure, and a team led by Qingtao Hao, Ze-Xu He, and Na Zuo are pushing the boundaries of this technology. They demonstrate a significant advance in the field by achieving stable quantum measurements at pressures exceeding 240 GPa, a level previously unattainable. The researchers fabricated improved diamond sensors containing nitrogen-vacancy centres, which exhibit increased sensitivity and resilience under immense compression. This breakthrough enables the observation of the Meissner effect in titanium at 180 GPa, confirming the sensor’s capabilities and opening new avenues for exploring the behaviour of materials under conditions similar to those found deep within the Earth, and potentially revealing insights into high-temperature superconductivity.

High Pressure Magnetometry with NV Centers

This research details significant advancements in using nitrogen-vacancy (NV) centers in diamond for quantum sensing under extreme high-pressure conditions. Scientists successfully demonstrated stable and reliable operation of NV center-based magnetometry up to 130 GPa, significantly extending the pressure range compared to previous studies. This breakthrough opens doors to studying materials and phenomena under conditions relevant to Earth’s interior and other extreme environments. The team also provided evidence for superconductivity in titanium at high pressures, demonstrating robust superconductivity at megabar levels.

Researchers refined the process of creating shallow NV centers within diamond, enhancing their sensitivity and performance under high pressure. The method involves fabricating NV centers, atomic-scale defects within diamond, which act as sensitive magnetic field detectors. Scientists employ high-pressure, high-temperature (HPHT) treatment to create these centers, optimizing the process to achieve high-quality, shallow NV centers. They then probe the NV centers’ magnetic properties using optically detected magnetic resonance (ODMR), allowing for sensitive detection of magnetic fields. Raman spectroscopy is used for accurate pressure calibration and material characterization, while electrical transport measurements confirm the superconducting properties of materials under pressure.

Results demonstrate that NV centers maintain coherence and sensitivity even at extreme pressures, enabling reliable measurements. Scientists observed a clear superconducting transition in titanium at high pressure, confirming previous findings and providing further insights into its superconducting behavior. The improved NV center fabrication and experimental setup resulted in enhanced sensitivity for detecting magnetic fields under pressure. This technique provides a powerful tool for studying the behavior of materials under extreme conditions, potentially leading to the discovery of new materials with novel properties.

Understanding the behavior of materials at high pressure is crucial for modeling Earth’s interior and understanding phenomena like the formation of the core and mantle. This work demonstrates the potential of NV centers as versatile quantum sensors for a wide range of applications, including materials science, geophysics, and fundamental physics. The ability to probe superconductivity at high pressure opens new avenues for exploring unconventional superconducting mechanisms and discovering new high-temperature superconductors.

Shallow NV Centers for High-Pressure Magnetometry

Scientists pioneered a novel approach to high-pressure magnetometry by fabricating shallow nitrogen-vacancy (NV) centers within diamond, significantly extending the capabilities of this quantum sensing technology. The team employed ion implantation techniques followed by high-pressure and high-temperature (HPHT) annealing to create these NV centers, resulting in increased density, improved coherence, and reduced internal stresses within the diamond lattice, critical factors for maintaining sensor performance under extreme compression. This innovative fabrication process overcomes limitations encountered at multi-megabar pressures, where conventional sensors struggle with weak signals. The study harnesses the unique properties of NV centers, atomic-scale defects within diamond, which act as sensitive magnetic field detectors.

Each NV center possesses a spin state that responds to external magnetic fields, and scientists read out these changes using optically detected magnetic resonance (ODMR), enabling highly sensitive measurements. Initial demonstrations in 2014 of NV sensing at pressures up to 60 GPa laid the groundwork for this work, which successfully pushed operational limits into the megabar range. To achieve record-high pressures, the team optimized hydrostatic environments and utilized micron-sized diamond particles, further enhancing the stability and performance of the NV centers. This methodology enabled breakthrough pressure capabilities exceeding 240 GPa, constrained only by the structural integrity of the 50μm diamond anvils employed in the experiments. As a benchmark, scientists detected the Meissner effect and trapped flux in elemental titanium at 180 GPa, establishing a solid foundation for exploring complex phenomena at previously unreachable pressures. This approach promises to unlock new insights into high-temperature superconductivity, the evolution of Earth’s core, and the behavior of materials under extreme conditions.

High-Pressure Magnetometry Beyond 240 GPa Demonstrated

Scientists have achieved a breakthrough in high-pressure magnetometry using nitrogen-vacancy (NV) centers in diamond, extending pressure capabilities beyond 240 GPa. This advancement, currently limited by the structural integrity of the 50μm diamond anvils used, opens new avenues for research into materials under extreme conditions, particularly hydrogen-rich superconductors and the behavior of minerals deep within Earth’s core. The team fabricated shallow NV centers through ion implantation and high-pressure, high-temperature annealing, resulting in increased density, improved coherence, and reduced internal stresses, all crucial for maintaining NV center performance under immense compression. Experiments reveal exceptionally narrow linewidths at zero field and 77 G, enhancing the stability and sensitivity of the NV centers.

Detailed analysis of pressure gradients across the diamond culet, using both Raman spectroscopy and ODMR measurements, demonstrates a consistent pressure distribution and provides valuable insights for accurate high-pressure experiments. The team confirmed the effectiveness of NV centers as a means of pressure calibration, observing a linear increase in zero-field splitting. Rabi oscillation measurements demonstrate robust quantum coherence of the NV centers even under extreme pressure, highlighting their potential for quantum sensing in challenging environments. To establish a benchmark for high-pressure magnetometry, scientists investigated the superconducting properties of titanium (Ti).

Resistance measurements revealed a maximum superconducting transition temperature (Tc) at 142. 4 GPa, consistent with previous findings. Further characterization of Ti showed an upper critical field fitting well with the Ginzburg-Landau model. Crucially, NV-based quantum sensors detected the Meissner effect in Ti, observing full magnetic shielding at low temperatures. ODMR measurements revealed a clear transition from diamagnetic shielding to magnetic flux penetration, aligning with the Tc value determined from resistance measurements. These results demonstrate the power of NV centers to probe magnetic phenomena at previously unreachable pressures, paving the way for groundbreaking discoveries in materials science and geophysics.

High-Pressure Magnetometry Exceeds 240 GPa

This research demonstrates a significant advance in the capabilities of nitrogen-vacancy (NV) centers in diamond as tools for high-pressure magnetometry, exceeding 240 GPa. This advancement opens new avenues for research into materials under extreme conditions, particularly hydrogen-rich superconductors and the behavior of minerals deep within Earth’s core. The team fabricated shallow NV centers through ion implantation and high-pressure, high-temperature annealing, resulting in increased density, improved coherence, and reduced internal stresses, all crucial for maintaining NV center performance under immense compression.