Observation of Dynamic Nuclear Polarization Echoes

TL;DR

This paper demonstrates the observation of DNP echoes by reversing the electron-nuclear polarization transfer process on a microsecond timescale, which could enhance future NMR and quantum sensing techniques.

Contribution

It introduces the concept of DNP echoes and shows how they can be generated using pulse trains with different effective Hamiltonians.

Findings

DNP echoes can be observed in pulsed DNP experiments.

The process can be reversed on a microsecond timescale.

Potential applications in NMR sensitivity and quantum sensing.

Abstract

It is demonstrated that the time evolution of the electron-nuclear polarization transfer process during pulsed dynamic nuclear polarization (DNP) can be reversed on a microsecond timescale, leading to the observation of DNP echoes. The DNP echoes are induced by consecutive application of two pulse trains that produce effective Hamiltonians that differ only in the sign of the effective hyperfine coupling. The experiments have been performed on a frozen solution of trityl radicals in water/glycerol on a home-built X-band EPR/DNP spectrometer at 80 K. We envisage that DNP echoes will play an important role in future development of pulsed DNP for sensitivity-enhanced NMR, hyperfine spectroscopy, and quantum sensing.