Bogolyubov Institute for Theoretical Physics,

14-b Metrologichna Str.,

Kyiv 03143,

UKRAINE

E-mail: aklimyk@bitp.kiev.ua

**Spectra of observables and an analogue of the Fourier
transform for Biedenharn-Macfarlane**
*q*-oscillator

**Abstract:**

The position and momentum operators of the Biedenharn-Macfarlane *q*-oscillator
are symmetric but not self-adjoint if *q*>1. They have one-parameter
families of self-adjoint extensions. These extensions are given explicitly.
Their spectra and eigenfunctions are derived. Spectrum of each extension
is discrete. Spectra of different extensions do not intersect. An
analogue of the Fourier transform is obtained for each extension of the
position operator and each extension of the

momentum operator.

Thus, the creation and annihilation operators of the Biedenharn-Macfarlane
*q*-oscillator at *q*>1 cannot determine a physical system without
further more precise definition. Namely, in order to determine a physical
system we have to choose appropriate self-adjoint extensions of the position
and momentum operators. This means that the Biedenharn-Macfarlane *q*-oscillator
at *q*>1 in fact determines two-parameter family of *q*-oscillators.
These *q*-oscillators have different spectra of

the position and momentum operators.