Monday, September 10, 2018

quantum mechanics - Proof that energy states of a harmonic oscillator given by ladder operator include all states


In quantum mechanics, while studying the harmonic oscillator, I learnt about ladder operators. And I realised that if you are able to find or determine any energy state of the quantum harmonic oscillator then, using the ladder operators, you can determine the other energy states as well. However in none of the texts I read I found the following fact:




The energy states determined by the above procedure, that is, using the ladder operator are the only possible energy states of the harmonic oscillator. There exists no energy state that is not given by the ladder operator.



So this is my question:



Are the energy states determined by the ladder operator in case of a harmonic oscillator, the only possible energy states? Is any other energy state possible? And what is the proof?



It is well known that the above-mentioned states are the only possible energy states but I want a rigorous proof that no other state is possible. However the analytical procedure mentioned in different books show an approximate solution of the Schrodinger equation which can be considered to be rigorous in the sense that it solves the equation to derive the solutions although it considers certain approximations.


I have searched for this answer in books related to quantum mechanics written by DJ Griffiths, Gasiorowicz, Dirac and online resources like OCW, University of Columbia's courses, caltech.edu, but I couldn't find a proper answer.




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