  The algebra of observables of a system of two identical vortices in a
superfluid thin film is described as a generalized deformed oscillator with a
structure function containing a linear (harmonic oscillator) term and a
quadratic term. In contrast to the deformed oscillators occuring in other
physical systems (correlated fermion pairs in a single-$j$ nuclear shell, Morse
oscillator), this oscillator is not amenable to perturbative treatment and
cannot be approximated by quons. From the mathematical viewpoint, this
oscillator provides a novel boson realization of the algebra su(1,1).
