  Point defect qubits in semiconductors have demonstrated their outstanding
high spatial resolution sensing capabilities of broad multidisciplinary
interest. Two-dimensional (2D) semiconductors hosting such sensors have
recently opened up new horizons for sensing in the subnanometer scales in 2D
heterostructures. However, controlled creation of quantum sensor in a single
layer 2D materials with high sensitivity has been elusive so far. Here, we
report on a novel 2D quantum sensor, the VB2 centre in hexagonal boron nitride
(hBN), with superior sensing capabilities. The centre's inherently low symmetry
configuration gives rise to unique electronic and spin properties that
implement a qubit in a 2D material with unprecedented sensitivity. The qubit is
decoupled from its dense spin environment at low magnetic fields that gives
rise to the reduction of the spin resonance linewidth and elongation of the
coherence time. The VB2 centre is also equipped with a classical memory that
can be utilized in storing population information. Using scanning transmission
electron microscopy imaging, we confirm the presence of the point defect
structure in free standing monolayer hBN created by electron beam irradiation.
Our results provide a new material solution towards atomic-scale sensing in low
dimensions.
