Progress in nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) is conventionally associated with working at higher and higher magnetic fields. Although such fields certainly have their virtues, those virtues come with a price, literally and figuratively. A typical high-field setup costs on the order of $1 million, requires constant cryogenic maintenance, is immobile, and can’t be used on samples with metallic inclusions or implanted devices. MRI, for example, has long been off-limits to patients with pacemakers, which can malfunction under strong magnetic fields. Also, larger magnets often require extensive magnetic field shimming to produce the spatially uniform fields needed to obtain high-resolution spectra.
Starting with the pioneering work of Alexander Pines and coworkers in the 1980s,1 however, a somewhat unexpected trend has developed toward using ultralow, submicrotesla fields—or even no external field at all. That trend has been enabled by new techniques and technologies that have...
