  In 1954, Dicke predicted that a system of quantum emitters confined to a
subwavelength volume would produce a superradiant burst. For such a burst to
occur, the emitters must be in the special Dicke state with zero dipole moment.
We show that a superradiant burst may also arise for non-Dicke initial states
with nonzero dipole moment. Both for Dicke and non-Dicke initial states,
superradiance arises due to a decrease in the dispersion of the quantum phase
of the emitter state. For non-Dicke states, the quantum phase is related to the
phase of long-period envelopes which modulate the oscillations of the dipole
moments. A decrease in dispersion of the quantum phase causes a decrease in the
dispersion of envelope phases that results in constructive interference of the
envelopes and the superradiant burst.
