Nuclear hyperpolarization is a known method to enhance the signal in nuclear magnetic resonance (NMR) by orders of magnitude. The present work addresses the ¹³C hyperpolarization in diamond micro- and nanoparticles, using the optically pumped nitrogen-vacancy center (NV) to polarize ¹³C spins at room temperature. Consequences of the small particle size are mitigated by using a combination of surface treatment improving the ¹³C relaxation (T₁) time, as well as that of NV, and applying a technique for NV illumination based on a microphotonic structure. Adjustments to the dynamical nuclear polarization sequence (PulsePol) are performed, as well as slow sample rotation, to improve the NV-¹³C polarization transfer rate. The hyperpolarized ¹³C NMR signal is observed in particles of 2-micrometer and 100-nanometer median sizes, with enhancements over the thermal signal (at 0.29-tesla magnetic field) of 1500 and 940, respectively. The present demonstration of room-temperature hyperpolarization anticipates the development of agents based on nanoparticles for sensitive magnetic resonance applications.

We present an open-source tensor network Python library for quantum many-body simulations. At its core is an abelian-symmetric tensor, implemented as a sparse block structure managed by a logical layer on top of a dense multi-dimensional array backend. This serves as the basis for higher-level tensor network algorithms, operating on matrix product states and projected entangled pair states. An appropriate backend, such as PyTorch, gives direct access to automatic differentiation (AD) for cost-function gradient calculations and execution on GPU and other supported accelerators. We show the library performance in simulations with infinite projected entangled-pair states, such as finding the ground states with AD and simulating thermal states of the Hubbard model via imaginary time evolution. For these challenging examples, we identify and quantify sources of the numerical advantage exploited by the symmetric-tensor implementation.

We propose a state preparation protocol based on sequential measurements of a central spin coupled with a spin ensemble, and investigate the usefulness of the generated multi-spin states for quantum enhanced metrology. Our protocol is shown to generate highly entangled spin states, devoid of the necessity for non-linear spin interactions. The metrological sensitivity of the resulting state surpasses the standard quantum limit, reaching the Heisenberg limit under symmetric coupling strength conditions. We also explore asymmetric coupling strengths, identifying specific preparation windows in time for optimal sensitivity. Our findings introduce a novel method for generating large-scale, non-classical, entangled states, enabling quantum-enhanced metrology within current experimental capabilities.