  Schr\"{o}dinger field theory with an attractive self-interaction possess
non-topological extended solutions with a finite energy in both finite and
infinite-volume cases, namely, bright solitons. The analytical form of the
solution itself is well-known, though analytical investigation of the quantum
fluctuations in this background still requires more thorough investigation, for
instance, analytical computation of quantum corrections to this background
within the saddle-point approximation. In the present work this gap is filled.
Both 2-point Green's function and quantum corrections to the background are
analytically computed and properly renormalized by means of momentum cut-off
procedure. It is deduced that quantum corrections are indeed small provided
that particle number is large. Also, we see that perturbation modes of
continuum spectrum at bright soliton background generate a gap in the energy
spectrum. Moreover, it turns out that the whole spectrum is continuous modulo
zero-modes, which is similar to Sine-Gordon solitons.
