Shining light on diamond particles makes them MRI-“bright,” opening avenues for room temperature hyperpolarized liquids.

Dynamic Nuclear Polarization (DNP) has enabled enormous gains in magnetic resonance signals and led to vastly accelerated NMR/MRI imaging and spectroscopy. Unlike conventional cw-techniques, DNP methods that exploit the full electron spectrum are appealing since they allow direct participation of all electrons in the hyperpolarization process. Such methods typically entail sweeps of microwave radiation over the broad electron linewidth to excite DNP, but are often inefficient because the sweeps, constrained by adiabaticity requirements, are slow. In this paper we develop a technique to overcome the DNP bottlenecks set by the slow sweeps, employing a swept microwave frequency comb that increases the effective number of polarization transfer events while respecting adiabaticity constraints. This allows a multiplicative gain in DNP enhancement, scaling with the number of comb frequencies and limited only by the hyperfine-mediated electron linewidth. We demonstrate the technique for the optical hyperpolarization of 13 C nuclei in powdered microdiamonds at low fields, increasing the DNP enhancement from 30 to 100 measured with respect to the thermal signal at 7T. For low concentrations of broad linewidth electron radicals, e.g. TEMPO, these multiplicative gains could exceed an order of magnitude.Introduction: -Dynamic nuclear polarization (DNP) -the process of polarizing (cooling) nuclear spins to a spin temperature far lower than the lattice temperature [1, 2] -has emerged as a technological breakthrough that serves as the starting point for a wide-range of applications, including signal enhanced spectroscopy [3,4] and imaging [5] and for state initialization in quantum information processing and metrology [6,7]. Indeed, magnetic resonance (NMR and MRI) signals from hyperpolarized nuclear spins can be enhanced by several orders of magnitude allowing enormous gains, even approaching a million-fold, in experimental averaging time. This has opened up avenues for the sensitive probing of phenomena, species and surfaces [8], whose detection would otherwise have remained intractable.In its simplest manifestation DNP involves the use of electrons whose polarization is transferred to the nuclear spins via microwave irradiation [10], allowing a polarization enhancement ε γ e /γ n , where γ e,n are the gyromagnetic ratios of the electron and nuclear spins respectively. Resonant polarization transfer between electron and nuclear spin is achieved via microwave excitation. Depending on the concentrations of the electron and nuclear spins in the insulating solid, the transfer can be mediated by thermal mixing, the cross effect, the solid effect and even the Overhauser effect. However several common (e.g. nitroxide based) electron polarizing agents have large ganisotropy and severely inhomogeneously broadened electronic linewidths that scale rapidly with field and can be as broad as 0.5GHz at high fields (>3T) [9,[11][12][13]. This broadening limits the number of spins contributing to the resonant energy exchange at a particular mi...

Understanding the origins of spin lifetimes in hybrid quantum systems is a matter of current importance in several areas of quantum information and sensing. Methods that spectrally map spin relaxation processes provide insight into their origin and can motivate methods to mitigate them. In this paper, using a combination of hyperpolarization and precision field cycling over a wide range (1mT-7T), we map frequency dependent relaxation in a prototypical hybrid system of 13 C nuclear spins in diamond coupled to Nitrogen Vacancy centers. Nuclear hyperpolarization through the optically pumped NV electrons allows signal time savings for the measurements exceeding million-fold over conventional methods. We observe that 13 C lifetimes show a dramatic field dependence, growing rapidly with field up to ∼100mT and saturating thereafter. Through a systematic study with increasing substitutional electron (P1 center) concentration as well as 13 C enrichment levels, we identify the operational relaxation channels for the nuclei in different field regimes. In particular, we demonstrate the dominant role played by the 13 C nuclei coupling to the interacting P1 electronic spin bath. These results pave the way for quantum control techniques for dissipation engineering to boost spin lifetimes in diamond, with applications ranging from engineered quantum memories to hyperpolarized 13 C imaging.