  We study quantum fluctuations of macroscopic parameters of an NLS breathers,
i.e., the second-order soliton solution of the nonlinear Schr\"odinger
equation. Uncertainty relations for the parameters are derived and compared to
similar relations for fundamental solitons. We compare two models for the state
of the quantum field of fluctuations surrounding the classical field of the
Bose-Einstein condensate: a conventionally used, computationally convenient
"white noise", and a correlated noise which assumes that the breather has been
created from a fundamental soliton, by means of the application of the
factor-of-four quench of the nonlinearity strength. Theoretical methods used in
the work are well suited for a large number of particles, $N$. We thus confirm
the possibility of experimental observation of macroscopic quantum
fluctuations, which is suggested by an extrapolation to large $N$ of recently
reported low-$N$ Bethe-ansatz results [Phys. Rev. Lett. 119 220401 (2017)].
