Quantum harmonic oscillator

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The quantum harmonic oscillator is the quantum mechanical analog of the classical harmonic oscillator. Because an arbitrary potential can be approximated as a harmonic potential at the vicinity of a stable equilibrium point, it is one of the most important model systems in quantum mechanics. Furthermore, it is one of the few quantum mechanical systems for which a simple exact solution is known.

Contents

One-dimensional harmonic oscillator

Hamiltonian and energy eigenstates

In the one-dimensional harmonic oscillator problem, a particle of mass m is subject to a potential V(x) given by

where ω is the angular frequency of the oscillator. In classical mechanics, \displaystyle m \omega^2 = k is called the spring stiffness coefficient, force constant or spring constant, and \displaystyle \omega the angular frequency.

The Hamiltonian of the particle is:

where \hat x = x is the position operator, and \hat p is the momentum operator, given by

The first term in the Hamiltonian represents the kinetic energy of the particle, and the second term represents the potential energy in which it resides. In order to find the energy levels and the corresponding energy eigenstates, we must solve the time-independent Schrödinger equation,

We can solve the differential equation in the coordinate basis, using a spectral method. It turns out that there is a family of solutions. In the position basis they are

The functions Hn are the physicists' Hermite polynomials:

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