Atomic-Scale Nuclear Spin Imaging Using Quantum-Assisted Sensors in Diamond

January 16, 2015
Figure 3: Protocol for quantum-enhanced nuclear spin imaging

Figure 3: Protocol for quantum-enhanced nuclear spin imaging. First the NV measures a 1D NMR spectrum (sense). During this step, polarization is selectively transferred from the NV to a particular nuclear spin in the protein (polarize). Polarization is then allowed to spread (diffusion), driven by the nuclear spin-spin dipolar coupling. The polarization now localized on a different nuclear spin is transferred back to the NV spin and measured optically (reverse-sense). [from A. Ajoy, U. Bissbort, M.D. Lukin, R.L. Walsworth, and P. Cappellaro, "Atomic-Scale Nuclear Spin Imaging Using Quantum-Assisted Sensors in Diamond," Physal Review X 5, 011001 | DOI: http://dx.doi.org/10.1103/PhysRevX.5.011001. Reprinted under the terms of the Creative Commons Attribution 3.0 License.]

Nuclear spin imaging at the atomic level is essential for the understanding of fundamental biological phenomena and for applications such as drug discovery. The advent of novel nanoscale sensors promises to achieve the long-standing goal of single-protein, high spatial-resolution structure determination under ambient conditions. In particular, quantum sensors based on the spin-dependent photoluminescence of nitrogen-vacancy (NV) centers in diamond have recently been used to detect nanoscale ensembles of external nuclear spins. While NV sensitivity is approaching single-spin levels, extracting relevant information from a very complex structure is a further challenge since it requires not only the ability to sense the magnetic field of an isolated nuclear spin but also to achieve atomic-scale spatial resolution.

In a new paper in Physical Review X, physicists from MIT, Singapore University of Technology and Design, and Harvard, including Professors Ronald Walthworth and Mikhail Lukin, propose a method that exploits the coupling of the NV center to an intrinsic quantum memory associated with the nitrogen nuclear spin (see the citation information, above). This method can reach a tenfold improvement in spatial resolution, down to atomic scales. The spatial resolution enhancement is achieved through coherent control of the sensor spin, which creates a dynamic frequency filter selecting only a few nuclear spins at a time. The researchers propose and analyze a protocol that would allow not only sensing individual spins in a complex biomolecule, but also unraveling couplings among them, thus elucidating local characteristics of the molecule structure.

(Also read the MIT News article by David L. Chandler, "Diamonds could help bring proteins into focus" Feb 6, 2015).