Decoupling of Spin Decoherence Paths near Zero Magnetic Field

Abstract

We demonstrate a method to quantify and manipulate nuclear spin decoherence mechanisms that are active in zero to ultralow magnetic fields. These include (i) nonadiabatic switching of spin quantization axis due to residual background fields and (ii) scalar pathways due to through-bond couplings between 1H and heteronuclear spin species, such as 2H used partially as an isotopic substitute for 1H. Under conditions of free evolution, scalar relaxation due to 2H can significantly limit nuclear spin polarization lifetimes and thus the scope of magnetic resonance procedures near zero field. It is shown that robust trains of pulsed dc magnetic fields that apply π flip angles to one or multiple spin species may switch the effective symmetry of the nuclear spin Hamiltonian, imposing decoupled or coupled dynamic regimes on demand. The method should broaden the spectrum of hyperpolarized biomedical contrast-agent compounds and hyperpolarization procedures that are used near zero field.

Metabolic Reactions Studied by Zero- and Low-Field Nuclear Magnetic Resonance

“…Novel methods now enable decoupling of deuterium nuclei, which should help to alleviate this problem by suppressing the polarization exchange. 36,37 Regardless, for in vivo experiments the fumarate would first be purified and then brought into an H2O solution using established methods. 38 The gradiometric detection scheme used in this work is shown schematically in Fig.…”

Meridional composite pulses for low-field magnetic resonance

“…These durations are much shorter than the periods of the spin-spin scalar couplings between common nuclear spin species, and thus should be applicable to heteronuclear quantum control in low-field NMR, in which pulses selectively rotate one or more spins in a multi-species system. The selectivity and error tolerance should be complementary to existing control methods based on equatorial composite pulses 28,43 .…”

“…In this paper we illustrate the above re-utilization concept to derive error-tolerant pulses for magnetic resonance experiments where orientation of total magnetic field is unconstrained in the laboratory frame of reference. The case includes Earth's field nuclear magnetic resonance (NMR) [20][21][22] as well as the emerging area of zero and ultralow-field (ZULF) NMR 23,24 , which presents attractive regimes for nuclear spin hyperpolarization 25,26 , relaxometry 27,28 and precision spectroscopy [29][30][31] in fields ranging from nT to µT.…”

“…Here, standard ac pulses may achieve spin-species and/or transition-selective excitation 32 . Optimal control pulses 33 and direct-current (dc) analogs of ac composite pulses (e.g., 90 x 180 y 90 x ) 28,34,35 can also be used for error compensation.…”

Real-Time Polarimetry of Hyperpolarized 13C Nuclear Spins Using an Atomic Magnetometer

“…The useful feature of XY4 is the dynamical decoupling of the background field from the spin system at the first-order average Hamiltonian level, 29 which allows us to neglect bias fields with strengths |B bias | ≪ 2π/γτ.…”