Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Microwave-assisted cross-polarization of nuclear spin ensembles from
  optically-pumped nitrogen-vacancy centers in diamond   The ability to optically initialize the electronic spin of the
nitrogen-vacancy (NV) center in diamond has long been considered a valuable
resource to enhance the polarization of neighboring nuclei, but efficient
polarization transfer to spin species outside the diamond crystal has proven
challenging. Here we demonstrate variable-magnetic-field, microwave-enabled
cross-polarization from the NV electronic spin to protons in a model viscous
fluid in contact with the diamond surface. Slight changes in the
cross-relaxation rate as a function of the wait time between successive
repetitions of the transfer protocol suggest slower molecular diffusion near
the diamond surface compared to that in bulk, an observation consistent with
present models of the microscopic structure of a fluid close to a solid
interface.

5
The categories of this paper are: gr-qc
33
The categories of this paper are: plasm-ph
25
The categories of this paper are: patt-sol
15
The categories of this paper are: nucl-ex
28
The categories of this paper are: alg-geom
27
The categories of this paper are: comp-gas
34
The categories of this paper are: chem-ph
3
The categories of this paper are: physics
30
The categories of this paper are: q-alg
24
The categories of this paper are: dg-ga
26
The categories of this paper are: bayes-an
10
The categories of this paper are: q-bio
17
The categories of this paper are: q-fin
37
The categories of this paper are: supr-con
19
The categories of this paper are: eess
0
The categories of this paper are: hep-ph