Pulsed polarisation for robust DNP

TL;DR

This paper introduces pulse sequence Hamiltonian engineering for robust, fast dynamical nuclear polarisation using NV centres in diamond, overcoming control error limitations of previous methods and enabling advanced quantum and biomedical applications.

Contribution

The authors develop a systematic pulse sequence design approach for robust and rapid DNP with NV centres, improving efficiency and error resilience over existing techniques.

Findings

Sequences enable efficient polarisation transfer despite control errors

Experimental validation shows robustness and speed improvements

Potential applications in quantum information and biomedical imaging

Abstract

Dynamical nuclear polarisation (DNP) is an important technique that uses polarisation transfer from electron to nuclear spins to achieve nuclear hyperpolarisation. As the electron spin of the nitrogen vacancy (NV) centres in diamond can be optically initialised nearly perfectly even at room temperature and ambient conditions, new opportunities become possible by the combination of efficient DNP with optically polarised NV centres. Among such applications are nanoscale nuclear magnetic resonance spectroscopy of liquids, hyperpolarised nanodiamonds as MRI contrast agents as well as the initialisation of nuclear spin based diamond quantum simulators. Current realisations of DNP perform the polarisation transfer by achieving energetic resonance between electrons and nuclei via carefully tuned microwave fields or by using quasi-adiabatic sweep-based schemes across resonance points. The former limits robustness against control errors while the latter limits polarisation rates, making the realisation of the applications extremely challenging. Here we introduce the concept of Hamiltonian engineering by pulse sequences and use it for the systematic design of polarisation sequences that are simultaneously robust and fast. We derive sequences theoretically and demonstrate experimentally that they are capable of efficient polarisation transfer from an optically polarised nitrogen-vacancy centre in diamond to the surrounding $^{13}$C nuclear spin bath even in the presence of control errors, making it an ideal tool for the realisation of the above NV centre based applications.