Fig. 1: Diamond NV center in a P1 bath.
From: Decoherence of nitrogen-vacancy spin ensembles in a nitrogen electron-nuclear spin bath in diamond
Schematic of a nitrogen-vacancy (NV) electron spin (green arrow) surrounded by substitutional nitrogen impurities (P1 centers). The direction of the NV center is parallel to the external magnetic field \({{{\mathrm{B}}}}_0\), which points in the [111] direction. The NV center spin interacts with the P1 spins (red arrow), which includes both an electron spin (S = 1/2) and nuclear spin (I = 1) via a magnetic dipole-dipole interaction. A P1 center can have one of four different Jahn–Teller axes denoted as JT(A), JT(B), JT(C), and JT(D), which are represented by a blue bar for each P1 center.
