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The quantum harmonic oscillator on a circle -- fragmentation of the algebraic method
Daniel Burgarth, Paolo Facchi·March 24, 2026
Quantum Physics
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Abstract
A quantum particle on a circle in a quadratic potential exhibits a spectrum that is not harmonic, despite having all algebraic properties of the quantum harmonic oscillator. This raises the question where the usual algebraic argument -- implying integer gaps -- fails. The answer is illuminating and covers a surprisingly rich range of physical phenomena for such a simple model.