  One of the earliest proposed phase transitions beyond the
Landau-Ginzburg-Wilson paradigm is the quantum critical point separating an
antiferromagnet and a valence-bond-solid on a square lattice. The low energy
description of this transition is believed to be given by the 2+1 dimensional
CP(1) model -- a theory of bosonic spinons coupled to an abelian gauge field.
Monopole defects of the gauge field play a prominent role in the physics of
this phase transition. In the present paper, we use the state-operator
correspondence of conformal field theory in conjunction with the 1/N expansion
to study monopole operators at the critical fixed point of the CP(N-1) model.
This elegant method reproduces the result for monopole scaling dimension
obtained through a direct calculation by Murthy and Sachdev. The technical
simplicity of our approach makes it the method of choice when dealing with
monopole operators in a conformal field theory.
