Symmetries of the quantum damped harmonic oscillator

TL;DR

This paper explores the symmetry structure of the quantum damped harmonic oscillator, revealing a connection to the Bateman dual system and showing that its spectrum is real, continuous, and infinitely degenerate.

Contribution

It introduces a novel algebraic extension that incorporates time evolution as a symmetry, linking the Caldirola-Kanai system to the Bateman dual system in a quantum context.

Findings

The symmetry algebra of the dual system is characterized.

The spectrum of the Bateman Hamiltonian is real and continuous.

A first-order Schrödinger equation for the system is derived.

Abstract

For the non-conservative Caldirola-Kanai system, describing a quantum damped harmonic oscillator, a couple of constant-of-motion operators generating the Heisenberg-Weyl algebra can be found. The inclusion of the standard time evolution generator (which is not a symmetry) as a symmetry in this algebra, in a unitary manner, requires a non-trivial extension of this basic algebra and hence of the physical system itself. Surprisingly, this extension leads directly to the so-called Bateman dual system, which now includes a new particle acting as an energy reservoir. In addition, the Caldirola-Kanai dissipative system can be retrieved by imposing constraints. The algebra of symmetries of the dual system is presented, as well as a quantization that implies, in particular, a first-order Schr\"odinger equation. As opposed to other approaches, where it is claimed that the spectrum of the Bateman Hamiltonian is complex and discrete, we obtain that it is real and continuous, with infinite degeneracy in all regimes.