Creating Strongly Interacting Dipolar Spin Ensembles in Diamond for Quantum Technologies

Diamond is at the forefront of solid-state quantum technologies and spin ensembles in diamond with strong dipolar interactions and controlled dimensionality have become an important platform for quantum sensing and simulation.¹ However, the tantalizing promise of these systems for 1) entanglement-enhanced metrology, leading to sensitivities beyond the standard quantum limit, and 2) simulation of equilibrium phase diagrams and non-equilibrium dynamics of positionally-disordered dipoles has been hampered by outstanding challenges in the controlled synthesis of dense, two-dimensional spin ensembles with non-zero average dipolar interactions and with coherence limited by dipolar interactions amongst the spin ensemble itself. In this work, we demonstrate the synthesis (via plasma-enhanced chemical vapor deposition) and characterization of dense nitrogen and nitrogen-vacancy (NV) center ensembles with control over dimensionality and dipolar interactions.² We pioneer the creation of these 2D, strongly interacting dipolar ensembles in (111)-oriented diamond, which though minimally explored to date, provides unique advantages for quantum technologies that cannot be achieved with 3D ensembles or (001)-oriented diamond.
We find that growth and NV center creation on the (111) plane yields several advantages which motivate the enduring importance of this study. Two-dimensional NV spin ensembles on the (111) plane afford maximally positive dipolar interactions, which otherwise average to zero in 3D ensembles as well as 2D ensembles in the predominantly used (001)-oriented samples. Strong, non-zero dipolar interactions are necessary for entanglement-enhanced sensing and investigating many-body phenomena that will inform directions in quantum simulation. We characterize the dipolar interactions in our samples with a new technique that illustrates the uniquely positive dipolar interactions observed in (111) and highlights the utility of the NV center as a nanoscale probe of its surrounding spin environment. Other features of growth on the (111) plane include significantly higher nitrogen incorporation than (001)-oriented diamond (thus leading to denser and more strongly interacting dipolar spin ensembles), preferential alignment of NV centers along the <111> direction during growth and the control over NV center incorporation via substrate miscut, which results in ensembles with high magnetic field sensitivity.

References
¹ L. B. Hughes, Z. Zhang, C. Jin, S. A. Meynell, B. Ye, W. Wu, Z. Wang, E. J. Davis, T. E. Mates, N. Yao, K. Mukherjee, A. C. B. Jayich, APL Mater. 11, 021101 (2023) https://doi.org/10.1063/5.0133501
² L. B. Hughes, S. A. Meynell, W. Wu, S. Parthasarathy, L. Chen, Z. Zhang, Z. Wang, E. J. Davis, K. Mukherjee, N. Y. Yao, and A. C. Bleszynski Jayich, “A Strongly Interacting, Two-Dimensional, Dipolar Spin Ensemble in (111)-Oriented Diamond,” Submitted. arxiv:2404.10075.